SMART MODE:

NORMAL GENOMIC

• Mulsant P et al.
• Mutation in bone morphogenetic protein receptor-IB is associated with increased ovulation rate in Booroola Merino ewes.
• Proc Natl Acad Sci U S A. 2001; 98: 5104-9
• Display abstract

• Ewes from the Booroola strain of Australian Merino sheep are characterized by high ovulation rate and litter size. This phenotype is due to the action of the FecB(B) allele of a major gene named FecB, as determined by statistical analysis of phenotypic data. By genetic analysis of 31 informative half-sib families from heterozygous sires, we showed that the FecB locus is situated in the region of ovine chromosome 6 corresponding to the human chromosome 4q22-23 that contains the bone morphogenetic protein receptor IB (BMPR-IB) gene encoding a member of the transforming growth factor-beta (TGF-beta) receptor family. A nonconservative substitution (Q249R) in the BMPR-IB coding sequence was found to be associated fully with the hyperprolificacy phenotype of Booroola ewes. In vitro, ovarian granulosa cells from FecB(B)/FecB(B) ewes were less responsive than granulosa cells from FecB(+)/FecB(+) ewes to the inhibitory effect on steroidogenesis of GDF-5 and BMP-4, natural ligands of BMPR-IB. It is suggested that in FecB(B)/FecB(B) ewes, BMPR-IB would be inactivated partially, leading to an advanced differentiation of granulosa cells and an advanced maturation of ovulatory follicles.

• Bernard DJ, Woodruff TK
• Inhibin binding protein in rats: alternative transcripts and regulation in the pituitary across the estrous cycle.
• Mol Endocrinol. 2001; 15: 654-67
• Display abstract

• Inhibin binding protein (InhBP) and the transforming growth factor-beta (TGF beta) type III receptor, beta glycan, have been identified as putative inhibin coreceptors. Here we cloned the InhBP cDNA in rats and predict that it encodes a large membrane-spanning protein that is part of the Ig superfamily, as has been described for humans. Two abundant InhBP transcripts (4.4 and 1.8 kb) were detected in the adult rat pituitary. The larger transcript encodes the full-length protein while the 1.8-kb transcript (InhBP-short or InhBP-S) corresponds to a splice variant of the receptor. This truncated isoform contains only the N-terminal signal peptide and first two (of 12) Ig-like domains observed in the full-length InhBP (InhBP-long or InhBP-L). InhBP-S does not contain a transmembrane domain and is predicted to be a soluble protein. Beta glycan was also detected in the pituitary; however, it was most abundant within the intermediate lobe. Although we also observed beta glycan immunopositive cells in the anterior pituitary, they rarely colocalized with FSH beta-producing cells. We next examined physiological regulation of the coreceptors across the rat estrous cycle. Like circulating inhibin A and inhibin B levels, pituitary InhBP-L and InhBP-S mRNA levels were dynamically regulated across the cycle and were negatively correlated with serum FSH levels. Expression of both forms of InhBP was also positively correlated with serum inhibin B, but not inhibin A, levels. These data are particularly interesting in light of our in vitro observations that InhBP may function as an inhibin B-specific coreceptor. Pituitary beta glycan mRNA levels did not fluctuate across the cycle nor did they correlate with serum FSH. These observations, coupled with its pattern of expression within the pituitary, indicate that beta glycan likely functions as more than merely an inhibin coreceptor within the pituitary. A direct role for InhBP or beta glycan in regulation of pituitary FSH by inhibin in vivo has yet to be determined, but the demonstration of dynamic regulation of pituitary InhBP and its negative relation to serum FSH across the estrous cycle is an important step in this direction.

• Ehrlich M, Shmuely A, Henis YI
• A single internalization signal from the di-leucine family is critical for constitutive endocytosis of the type II TGF-beta receptor.
• J Cell Sci. 2001; 114: 1777-86
• Display abstract

• Endocytosis has an important contribution to the regulation of the surface expression levels of many receptors. In spite of the central role of the transforming growth factor beta (TGF-beta) receptors in numerous cellular and physiological processes, their endocytosis is largely unexplored. Current information on TGF-beta receptor endocytosis relies exclusively on studies with chimeric constructs containing the extracellular domain of the GM-CSF receptors, following the internalization of the GM-CSF ligand; the conformation and interactions of the chimeric receptors (and therefore their endocytosis) may differ considerably from those of the native TGF-beta receptors. Furthermore, there are no data on the potential endocytosis motif(s) of the TGF-beta receptors or other receptor Ser/Thr kinases. Here, we report the use of type II TGF-beta receptors, myc-tagged at their extracellular terminus, to investigate their endocytosis. Employing fluorescent antibody fragments to label exclusively the cell surface myc-tagged receptors exposed to the external milieu, made it possible to follow the internalization of the receptors, without the complications that render labeling with TGF-beta (which binds to many cellular proteins) unsuitable for such studies. The results demonstrate that the full-length type II TGF-beta receptor undergoes constitutive endocytosis via clathrin-coated pits. Using a series of truncation and deletion mutants of this receptor, we identified a short peptide sequence (I(218)I(219)L(220)), which conforms to the consensus of internalization motifs from the di-leucine family, as the major endocytosis signal of the receptor. The functional importance of this sequence in the full-length receptor was validated by the near complete loss of internalization upon mutation of these three amino acids to alanine.

• Fadok VA, Bratton DL, Rose DM, Pearson A, Ezekewitz RA, Henson PM
• A receptor for phosphatidylserine-specific clearance of apoptotic cells.
• Nature. 2000; 405: 85-90
• Display abstract

• cytosis of cellular corpses. During apoptosis, the asymmetry of plasma membrane phospholipids is lost, which exposes phosphatidylserine externally. The phagocytosis of apoptotic cells can be inhibited stereospecifically by phosphatidylserine and its structural analogues, but not by other anionic phospholipids, suggesting that phosphatidylserine is specifically recognized. Using phage display, we have cloned a gene that appears to recognize phosphatidylserine on apoptotic cells. Here we show that this gene, when transfected into B and T lymphocytes, enables them to recognize and engulf apoptotic cells in a phosphatidylserine-specific manner. Flow cytometric analysis using a monoclonal antibody suggested that the protein is expressed on the surface of macrophages, fibroblasts and epithelial cells; this antibody, like phosphatidylserine liposomes, inhibited the phagocytosis of apoptotic cells and, in macrophages, induced an anti-inflammatory state. This candidate phosphatidylserine receptor is highly homologous to genes of unknown function in Caenorhabditis elegans and Drosophila melanogaster, suggesting that phosphatidylserine recognition on apoptotic cells during their removal by phagocytes is highly conserved throughout phylogeny.

• Nagle DL et al.
• The mahogany protein is a receptor involved in suppression of obesity.
• Nature. 1999; 398: 148-52
• Display abstract

• Genetic studies have shown that mutations within the mahogany locus suppress the pleiotropic phenotypes, including obesity, of the agouti-lethal-yellow mutant. Here we identify the mahogany gene and its product; this study, to our knowledge, represents the first positional cloning of a suppressor gene in the mouse. Expression of the mahogany gene is broad; however, in situ hybridization analysis emphasizes the importance of its expression in the ventromedial hypothalamic nucleus, a region that is intimately involved in the regulation of body weight and feeding. We present new genetic studies that indicate that the mahogany locus does not suppress the obese phenotype of the melanocortin-4-receptor null allele or those of the monogenic obese models (Lep(db), tub and Cpe(fat)). However, mahogany can suppress diet-induced obesity, the mechanism of which is likely to have implications for therapeutic intervention in common human obesity. The amino-acid sequence of the mahogany protein suggests that it is a large, single-transmembrane-domain receptor-like molecule, with a short cytoplasmic tail containing a site that is conserved between Caenorhabditis elegans and mammals. We propose two potential, alternative modes of action for mahogany: one draws parallels with the mechanism of action of low-affinity proteoglycan receptors such as fibroblast growth factor and transforming growth factor-beta, and the other suggests that mahogany itself is a signalling receptor.

• Ponce-Castaneda MV, Esparza-Lopez J, Vilchis-Landeros MM, Mendoza V, Lopez-Casillas F
• Murine betaglycan primary structure, expression and glycosaminoglycan attachment sites.
• Biochim Biophys Acta. 1998; 1384: 189-96
• Display abstract

• The primary structure of murine betaglycan, also known as transforming growth factor beta (TGF-beta) type III receptor, was deduced from the nucleotide sequence of a cDNA clone isolated from a heart library. Murine betaglycan is a single spanning membrane polypeptide of 850 amino acids which is highly similar to betaglycan of other species. Transfection of this cDNA into COS1 cells resulted in the expression of a membrane proteoglycan that binds TGF-beta and is recognized by antibodies raised against rat betaglycan. COS1 cells transfected with the double mutant Ser533Ala; Ser544Ala of the murine betaglycan cDNA produced a TGF-beta type III receptor devoid of glycosaminoglycan chains.

• Centrella M, Ji C, Casinghino S, McCarthy TL
• Rapid flux in transforming growth factor-beta receptors on bone cells.
• J Biol Chem. 1996; 271: 18616-22
• Display abstract

• The proportion of transforming growth factor-beta (TGF-beta) binding among conventional membrane receptors on bone cells can vary with hormone or growth factor treatment or with the state of osteoblast-like activity and appears to determine the nature of its biological effects. Therefore, functional TGF-beta receptor stability could be an important aspect of regulation. Suppression of protein synthesis reduced TGF-beta binding to types I and II receptors with t1/2 of 2 h and to betaglycan with t1/2 of 6 h. In contrast, suppression of mRNA transcription reduced TGF-beta binding at least 3-fold more slowly at each receptor site. Preexposure to TGF-beta decreased its binding at all three sites within 4 h in osteoblast-enriched cultures. This effect was transient with lower TGF-beta concentrations, where the receptor profile was nearly fully restored within 24-48 h. In contrast, less differentiated bone cells were less sensitive to ligand-dependent receptor down-regulation. Agents that alter protein kinase and phosphatase activity also modified the TGF-beta binding profile in specific ways. Together, these results indicate that cell surface TGF-beta receptors turn over rapidly by ligand-independent and ligand-dependent mechanisms, demonstrate that the binding capacity of TGF-beta receptors is less stable than their mRNAs, and that functional receptor levels may be determined in part by post-transcriptional events.

• Manning AM, Auchampach JA, Drong RF, Slightom JL
• Cloning of a canine cDNA homologous to the human transforming growth factor-beta 1-encoding gene.
• Gene. 1995; 155: 307-8
• Display abstract

• A 1369-bp cDNA that encodes a homolog of the human transforming growth factor-beta 1 (TGF-beta 1) has been isolated from canine endothelial cells using a combination of PCR and traditional plaque-screening methods. The deduced 390-amino-acid sequence of the canine TGF-beta 1 precursor has 91-94% identity to those deduced from the previously described human and mouse TGF-beta 1 clones.

• Lawrence DA
• Transforming growth factor-beta: an overview.
• Kidney Int Suppl. 1995; 49: 1923-1923

• Chen RH, Miettinen PJ, Maruoka EM, Choy L, Derynck R
• A WD-domain protein that is associated with and phosphorylated by the type II TGF-beta receptor.
• Nature. 1995; 377: 548-52
• Display abstract

• Transforming growth factor-beta (TGF-beta) is the prototype for a family of extracellular polypeptides that affect cell proliferation and differentiation, and tissue morphogenesis. TGF-beta signalling is mediated by two types of serine/threonine kinase receptors, the type I and II receptors, which are able to form a heteromeric complex. No cytoplasmic proteins that associate with these receptors in vivo, or are their kinase targets, have yet been described. We have now identified a WD-domain-containing protein, TRIP-1, which specifically associates with the type II TGF-beta receptor in a kinase-dependent way. TRIP-1 does not interact with the type II activin or type I receptors, but associates with the heteromeric TGF-beta receptor complex. TRIP-1 is phosphorylated on serine and threonine by the receptor kinase, strongly suggesting that it has a role in TGF-beta signalling. This is supported by coexpression of TRIP-1 and type II receptor during development. The existence of TRIP-1 homologues in plant and yeast suggests a conserved function in all eukaryotes.

• Derynck R, Chen RH, Ebner R, Filvaroff EH, Lawler S
• An emerging complexity of receptors for transforming growth factor-beta.
• Princess Takamatsu Symp. 1994; 24: 264-75
• Display abstract

• Transforming growth factor-beta (TGF-beta) is a multifunctional protein that modulates cell proliferation and interaction with the extracellular matrix. Three common TGF-beta receptors are found on the cell surface. The type III receptor is a transmembrane proteoglycan with a short cytoplasmic domain and is thought not to be involved in TGF-beta induced signalling. In contrast, the type II and type I receptors are transmembrane serine/threonine kinases. The type II receptor determines the ligand specificity, whereas the type I receptor interacts with the type II receptor and may not have a ligand binding specificity by itself. Both type II and type I receptors are involved in TGF-beta induced signalling. The type II receptor, likely in conjunction with the type I receptor, is required for the antiproliferative effect of TGF-beta, whereas the type I receptor is the likely mediator of the effects of TGF-beta on the expression of several genes including some extracellular matrix proteins. To address the role of TGF-beta signalling in myoblast differentiation, we transfected a dominant negative mutant of the type II receptor in myoblasts, thus inhibiting type II receptor mediated signalling. These cells not longer had the ability to differentiate in vitro or in vivo, suggesting that TGF-beta signalling through the type II receptor provides competence for myoblastic differentiation. These studies also indicate that there are several signalling pathways involved in myoblastic differentiation, one of which is modulated by the TGF-beta signalling.

• Okano H et al.
• Cloning of a Drosophila melanogaster homologue of the mouse type-I bone morphogenetic proteins-2/-4 receptor: a potential decapentaplegic receptor.
• Gene. 1994; 148: 203-9
• Display abstract

• The Drosophila melanogaster (Dm) decapentaplegic (dpp) gene product plays an essential role during several stages of Dm development. The DPP protein is a member of the transforming growth factor-beta (TGF-beta) superfamily and an orthologue of mammalian bone morphogenetic proteins (BMP-2 and -4). Recently, a cDNA clone encoding the mouse Ser/Thr kinase receptor specific for BMP-2/-4 (mTFR11) was isolated. Here, we describe the deduced primary structure, the cytogenetic position and expression pattern of the Dm homologue of mTFR11 (DTFR), a putative DPP receptor. The cytogenetic position of the Dm dtfr gene was mapped to 25D. DTFR has striking homology to mTFR11, especially in the cytoplasmic domain (approx. 63%), including a Ser + Gly-rich box that is characteristic of type-I receptors for the TGF-beta superfamily. Although the amino acid (aa) sequence of the extracellular domain is less conserved than that of the cytoplasmic domain, the extracellular domains of these two molecules were more homologous (approx. 27%) to each other than any other receptors for the TGF-beta superfamily. The spacing of Cys residues in the extracellular domain, which is considered crucial to ligand specificity, is highly conserved in these two receptors. During Dm embryonic development, its expression pattern changes in a dynamic fashion with high levels of expression in mesoderm and midgut, with some relation to dpp mutant phenotypes.

• Chen RH, Derynck R
• Homomeric interactions between type II transforming growth factor-beta receptors.
• J Biol Chem. 1994; 269: 22868-74
• Display abstract

• Transforming growth factor-beta (TGF-beta) binds with high affinity to three cell-surface receptors. Both type I and II receptors are transmembrane serine/threonine kinases and thought to mediate TGF-beta responses by forming a heteromeric complex in the presence of TGF-beta. We investigated whether the type II receptors form a homomeric complex in the presence or absence of ligand. Double immunoprecipitation analyses were performed using lysates from metabolically labeled cells cotransfected with differentially epitope-tagged type II receptors. We demonstrate that the type II receptors can form a homomeric complex even in the absence of their ligand, TGF-beta. This pre-existing type II receptor complex has the ability to bind TGF-beta. Moreover, in addition to the extracellular and transmembrane domains, the cytoplasmic portions of the receptors are also able to interact with each other, indicating that multiple contact points are involved in the formation of the homomeric type II receptor complex. Our results suggest a novel mechanism of complex formation and receptor activation of the serine/threonine kinase receptor family.

• Ge AZ, Butcher EC
• Cloning and expression of a cDNA encoding mouse endoglin, an endothelial cell TGF-beta ligand.
• Gene. 1994; 138: 201-6
• Display abstract

• The rat monoclonal antibody, MJ7/18, which reacts selectively with the endothelium of blood vessels in mouse was used to screen a cDNA library derived from a transformed mouse brain endothelial cell line. The sequence of a cDNA encoding the cell surface MJ7/18 antigen revealed homology to human endoglin, a homodimeric transforming growth factor-beta (TGF-beta)-binding cell-surface glycoprotein expressed predominantly on vascular endothelial cells. Northern blot analysis shows a 3.4-kb single transcript of the mouse endoglin. The mouse endoglin is a type-I integral membrane protein of 653 amino acids (aa). The human and mouse sequences display 71% aa sequence identity with almost identical transmembrane and cytoplasmic domains. Like its human counterpart, mouse endoglin displays significant sequence homology to the type-III TGF-beta receptor in two extracellular domains, as well as striking similarity in the transmembrane and cytoplasmic regions. One of the extracellular regions of homology with TGF-beta receptor III represents a truncated version of a homology unit defining a novel gene family including uromodulin, the pancreatic granule protein gp2, and zona pellucida receptors for sperm. However, unlike its human counterpart, mouse endoglin does not contain an RGD tripeptide which has been suggested as a ligand of integrins.

• Benzakour O
• [Transforming Growth Factor Beta: structure, biologic effects and mechanism of action]
• Bull Cancer. 1994; 81: 1014-22
• Display abstract

• For more than a decade, Transforming Growth Factor Beta (TGF beta) has been intensively studied. Such studies have led to the identification of many related polypeptides which constitute the TGF beta family. These factors modulate many animal cell processes such as cell cycle progression, differentiation, adhesion, migration, extracellular matrix production, tissue development and repair processes. Recent studies have shown that TGF beta has also a cardioprotective effect and is implicated in inflammatory process. The mechanism by which cytokines of the TGF beta family initiate their many biological effects are not yet fully understood. However, the recent molecular cloning of various TGF beta receptor genes has provided many clues to address these questions. These findings have led to a proposition of an original and specific model for the mechanism of action of TGF beta.

• Lawler S et al.
• The murine type II TGF-beta receptor has a coincident embryonic expression and binding preference for TGF-beta 1.
• Development. 1994; 120: 165-75
• Display abstract

• We have isolated cDNAs of the murine type II TGF-beta receptor and have found a conserved cytoplasmic domain, but a less extensive homology in the extracellular receptor domain between the human and murine homologues. In situ hybridization analysis of the mouse fetus during mid gestation localized the expression of this receptor to various developing tissues, primarily in the mesenchyme and epidermis. This expression pattern correlates well with the expression of TGF-beta in general and especially TGF-beta 1, suggesting that TGF-beta 1 exerts its developmental role through this receptor in an autocrine or paracrine fashion. Type II receptor expression was not detected in the central nervous system and developing cartilage. These tissues lack TGF-beta 1 expression but express TGF-beta 2 and/or TGF-beta 3, suggesting that they may exert their activities through separate receptor isoforms. In addition, the efficient binding of TGF-beta 1, but not TGF-beta 2, to the cloned type II receptor strengthens the likelihood that additional type II receptor isoforms exist which display preferential binding to TGF-beta 2 and have their own defined role in development.

• Damstrup L, Rygaard K, Spang-Thomsen M, Skovgaard Poulsen H
• Expression of transforming growth factor beta (TGF beta) receptors and expression of TGF beta 1, TGF beta 2 and TGF beta 3 in human small cell lung cancer cell lines.
• Br J Cancer. 1993; 67: 1015-21
• Display abstract

• A panel of 21 small cell lung cancer cell (SCLC) lines were examined for the presence of Transforming growth factor beta receptors (TGF beta-r) and the expression of TGF beta mRNAs. By the radioreceptor assay we found high affinity receptors to be expressed in six cell lines. scatchard analysis of the binding data demonstrated that the cells bound between 4.5 and 27.5 fmol mg-1 protein with a KD ranging from 16 to 40 pM. TGF beta 1 binding to the receptors was confirmed by cross-linking TGF beta 1 to the TGF beta-r. Three classes of TGF beta-r were demonstrated, type I and type II receptors with M(r) = 65,000 and 90,000 and the betaglycan (type III) with M(r) = 280,000. Northern blotting showed expression of TGF beta 1 mRNA in ten, TGF beta 2 mRNA in two and TGF beta 3 mRNA in seven cell lines. Our results provide, for the first time, evidence that a large proportion of a broad panel of SCLC cell lines express TGF beta-receptors and also produce TGF beta mRNAs.

• Tsuchida K, Lewis KA, Mathews LS, Vale WW
• Molecular characterization of rat transforming growth factor-beta type II receptor.
• Biochem Biophys Res Commun. 1993; 191: 790-5
• Display abstract

• A cDNA encoding the rat transforming growth factor-beta (TGF-beta) type II receptor was isolated by hybridization from a rat pituitary gland cDNA library. The rat TGF-beta type II receptor comprises 567 amino acid residues with a cysteine-rich extracellular domain, a single transmembrane domain and an intracellular protein kinase domain with predicted serine/threonine specificity. The comparison of the amino acid sequences of the rat and human TGF-beta type II receptors indicated that they are highly conserved particularly in the intracellular kinase domain. RNA blot hybridization and reverse-transcription polymerase chain reaction (RT-PCR) analyses showed that rat TGF-beta type II receptor is widely distributed in various tissues and is expressed abundantly in the ovary and lung.

• Ross J, Janero DR, Hreniuk D
• Identification and molecular characterization of a high-affinity cardiomyocyte transforming growth factor-beta 2 receptor.
• FEBS Lett. 1993; 320: 229-34
• Display abstract

• Rat neonatal heart muscle cells (cardiomyocytes) were found to express a high-affinity surface receptor for transforming growth factor-beta 2 (TGF-beta 2). Specific binding was rapid, saturable, ligand-selective, and reversible. Equilibrium binding analyses revealed that the cardiomyocyte had one class of specific binding sites with a Kd < or = 26 pM TGF-beta 2, a Bmax of approximately 9 fmol/10(6) cells, and approximately 5,000 binding sites/cardiomyocyte. Binding was selective for TGF-beta 2 in comparison to other TGF-beta isoforms and to unrelated growth factors. Affinity-binding experiments revealed three types of cardiomyocyte TGF-beta 2 binding proteins, the most prominent of which corresponded to the high-molecular mass proteoglycan. These data raise the possibility that the anti-ischemic cardioprotective effects of TGF-beta may reflect receptor-mediated signal transduction at the cardiomyocyte level.

• Glansbeek HL, van der Kraan PM, Vitters EL, van den Berg WB
• Variable TGF-beta receptor expression regulates TGF-beta responses of articular chondrocytes.
• Agents Actions Suppl. 1993; 39: 139-45
• Display abstract

• TGF-beta inhibits the proteoglycan synthesis of freshly isolated articular chondrocytes while TGF-beta stimulates the proteoglycan synthesis of articular chondrocytes cultured for 14 days. To investigate if this differential effect was the result of differences in TGF-beta receptor expression this parameter was studied by affinity labeling in combination with SDS-PAGE. Using this method we demonstrated a difference in size of the TGF-beta type II receptor between freshly isolated and cultured chondrocytes. This difference might explain the differential effect of TGF-beta on the proteoglycan synthesis of chondrocytes cultured for 1 or 14 days.

• Attisano L, Carcamo J, Ventura F, Weis FM, Massague J, Wrana JL
• Identification of human activin and TGF beta type I receptors that form heteromeric kinase complexes with type II receptors.
• Cell. 1993; 75: 671-80
• Display abstract

• Transforming growth factor beta (TGF beta) and activin each bind to pairs of membrane proteins, known as receptor types I and II, that associate to form a signaling complex. We report that TSR-I and ActR-I, two human transmembrane serine/threonine kinases distantly related to TGF beta and activin type II receptors, act as type I receptors for these factors. TSR-I is a type I receptor shared by TGF beta and activin, whereas ActR-I is an activin type I receptor. ActR-I, but not TSR-I, signals a particular transcriptional response in concert with activin type II receptors. The results indicate that type I receptors are transmembrane protein kinases that associate with type II receptors to generate diverse heteromeric serine/threonine kinase complexes of different signaling capacities.

• Franzen P et al.
• Cloning of a TGF beta type I receptor that forms a heteromeric complex with the TGF beta type II receptor.
• Cell. 1993; 75: 681-92
• Display abstract

• A cDNA clone encoding a 53 kd serine/threonine kinase receptor with an overall structure similar to that of the type II receptor for transforming growth factor beta (TGF beta) was obtained. 125I-TGF beta 1 bound to porcine endothelial cells transfected with the cDNA and formed a cross-linked complex of 70 kd, characteristic of a TGF beta type I receptor. Immunoprecipitation of the cross-linked complexes by antibodies against the cloned receptor revealed the 70 kd complex as well as a 94 kd TGF beta type II receptor complex. The immunoprecipitated novel serine/threonine kinase receptor had biochemical properties of the TGF beta type I receptor and was observed in different cell types. Transfection of the cloned cDNA into TGF beta type I receptor-deficient cells restored TGF beta-induced plasminogen activator inhibitor 1 production. These results suggest that signal transduction by TGF beta involves the formation of a heteromeric complex of two different serine/threonine kinase receptors.

• Burmester JK et al.
• Characterization of distinct functional domains of transforming growth factor beta.
• Proc Natl Acad Sci U S A. 1993; 90: 8628-32
• Display abstract

• Three distinct isoforms of transforming growth factor beta (TGF-beta) are expressed in mammalian cells. Although many cells respond equivalently to all three isoforms, certain cells respond selectively. Using chimeric proteins in which selected regions of the different isoforms were interchanged, we have identified two distinct functional domains of TGF-beta involved in determining the biological potencies and functions of the molecule. The first domain is important for determining whether TGF-beta can be sequestered by alpha 2-macroglobulin. By replacing aa 45 and 47 of TGF-beta 2 with the corresponding amino acids of TGF-beta 1, sequestration of the TGF-beta molecule by alpha 2-macroglobulin was markedly reduced. The second domain is functionally different from the alpha 2-macroglobulin sequestration site and is important for determining the potency of TGF-beta to inhibit growth of the LS513 human colorectal cancer cell line. Neither the TGF-beta 2/beta 1-(40-47) replacement construct nor a chimera containing aa 1-39 of TGF-beta 2, aa 40-82 of TGF-beta 1, and aa 83-112 of TGF-beta 2 was equivalent to TGF-beta 1 in inhibiting growth of LS513 cells. This fact suggests that additional amino acids outside of the aa 40-82 region are required to specify TGF-beta 1 activity with these cells.

• Sharma K, Ziyadeh FN
• The transforming growth factor-beta system and the kidney.
• Semin Nephrol. 1993; 13: 116-28

• Inagaki M, Moustakas A, Lin HY, Lodish HF, Carr BI
• Growth inhibition by transforming growth factor beta (TGF-beta) type I is restored in TGF-beta-resistant hepatoma cells after expression of TGF-beta receptor type II cDNA.
• Proc Natl Acad Sci U S A. 1993; 90: 5359-63
• Display abstract

• The growth of human hepatoma Hep 3B cells is potently inhibited by TGF-beta 1 (ID50 = 0.2 ng/ml, 8 pM). A mutant cell line was derived that was not inhibited in growth by TGF-beta 1 at 5 ng/ml (200 pM) and that lacked TGF-beta receptor type II (TGF-beta RII) gene. Transfection of the cloned cDNA for human TGF-beta RII to this mutant cell line restored receptor expression as well as the inhibition in growth by TGF-beta 1. In both wild-type and mutant cells stably transfected with TGF-beta RII cDNA, TGF-beta RII coimmunoprecipitated with TGF-beta receptor type I in the presence of ligand. These experiments provide direct evidence for the role of TGF-beta RII in the inhibitory effect of TGF-beta on growth and suggest that TGF-beta RII acts by means of a heteromeric surface complex with TGF-beta receptor type I.

• Sumitomo S, Saito T, Nohno T
• A new receptor protein kinase from chick embryo related to type II receptor for TGF-beta.
• DNA Seq. 1993; 3: 297-302
• Display abstract

• We have isolated cDNA encoding a new member of protein kinase family from chicken embryo cDNA library. The deduced amino acid sequence comprises a cysteine-rich extracellular domain, a single hydrophobic transmembrane domain, and a cytoplasmic serine/threonine kinase domain. Two short inserts are contained in the kinase domain. The primary structure shows that it belongs to the receptor-type serine/threonine kinase subfamily and is most similar to Daf-1. Conserved cysteine residues in the ectodomain suggest the protein as a receptor for a peptide growth factor of TGF-beta family.

• Ebner R et al.
• Cloning of a type I TGF-beta receptor and its effect on TGF-beta binding to the type II receptor.
• Science. 1993; 260: 1344-8
• Display abstract

• Transforming growth factor-beta (TGF-beta) affects cellular proliferation, differentiation, and interaction with the extracellular matrix primarily through interaction with the type I and type II TGF-beta receptors. The type II receptors for TGF-beta and activin contain putative serine-threonine kinase domains. A murine serine-threonine kinase receptor, Tsk 7L, was cloned that shared a conserved extracellular domain with the type II TGF-beta receptor. Overexpression of Tsk 7L alone did not increase cell surface binding of TGF-beta, but coexpression with the type II TGF-beta receptor caused TGF-beta to bind to Tsk 7L, which had the size of the type I TGF-beta receptor. Overexpression of Tsk 7L inhibited binding of TGF-beta to the type II receptor in a dominant negative fashion. Combinatorial interactions and stoichiometric ratios between the type I and II receptors may therefore determine the extent of TGF-beta binding and the resulting biological activities.

• Fox FE, Ford HC, Douglas R, Cherian S, Nowell PC
• Evidence that TGF-beta can inhibit human T-lymphocyte proliferation through paracrine and autocrine mechanisms.
• Cell Immunol. 1993; 150: 45-58
• Display abstract

• Transforming growth factor-beta (TGF-beta) has been documented as having an inhibitory effect on the proliferation and growth of human T-lymphocytes. We examined the relative contribution of both exogenous and endogenous TGF-beta to this inhibitory action. Purified human peripheral blood T-cells were cultured with Con A (0.2 microgram/ml), washed with methyl mannopyranoside, and then cultured in rIL-2 (5 U/ml) with or without TGF-beta (80 pM). Proliferation, as measured by uptake of tritiated thymidine at 72 hr, was inhibited by added active TGF-beta. Addition of neutralizing anti-TGF-beta antibodies at the initiation of culture abrogated the antiproliferative effects of TGF-beta. A mink lung cell bioassay was used to measure endogenous TGF-beta production by the T-cells following transient acidification of the supernatants to activate latent TGF-beta. T-lymphocytes cultured with rIL-2 alone produced low levels of TGF-beta, first detectable at 72 hr. The addition of (active) TGF-beta to these cultures resulted in earlier and higher levels of endogenously produced latent TGF-beta protein. This was reflected at the mRNA level as well. The exogenously added active TGF-beta appeared to be depleted during the culture period, presumably by the activated T-cells, which exhibited elevated levels of types I, II, and III TGF-beta receptors. The increase in TGF-beta protein levels was due to endogenous TGF-beta synthesis and secretion as supported by a capture assay using 35S-labeled culture supernatants. These findings indicate that both paracrine and autocrine mechanisms are involved in the inhibitory effects of TGF-beta on the proliferation of normal human T-lymphocytes and suggest that other TGF-beta-producing cells can augment production of TGF-beta by activated T-lymphocytes.

• Lin HY, Wang XF
• Expression cloning of TGF-beta receptors.
• Mol Reprod Dev. 1992; 32: 105-10
• Display abstract

• Using a powerful expression cloning method in COS cells, we have cloned the TGF-beta types II and III receptors. The type III TGF-beta receptor is a membrane-bound proteoglycan with a core protein of about 110 kDa. Stable expression of the type III receptor in L6 myoblasts leads to an apparent increase in the ability of the type II receptor to bind iodinated TGF-beta 1. The cloned type II receptor has a predicted protein core of about 60 kDa with a cysteine-rich extracellular domain, a single transmembrane domain, and a functional serine/threonine kinase domain that is homologous to the activin receptor and to the C. elegans protein daf-1. These results implicate serine/threonine phosphorylation as an important mechanism of TGF-beta action.

• Moren A, Ichijo H, Miyazono K
• Molecular cloning and characterization of the human and porcine transforming growth factor-beta type III receptors.
• Biochem Biophys Res Commun. 1992; 189: 356-62
• Display abstract

• Full-length cDNAs for the transforming growth factor-beta (TGF-beta) type III receptors were isolated from porcine uterus and human placenta cDNA libraries. The human TGF-beta type III receptor coding region encodes a protein of 849 amino acids with a single transmembrane domain and a short stretch of the intracellular domain. Potential glycosaminoglycan attachment sites were found in the extracellular domain. The overall amino acid sequence identities with those of the porcine and rat TGF-beta type III receptors were 83% and 81%, respectively. A high degree of sequence conservation was observed in the transmembrane and intracellular domains, which also have sequence similarity with human endoglin. In addition, two portions with 29 and 52 amino acids in the extracellular domain were found to be substantially similar with human endoglin.

• Lin HY, Wang XF, Ng-Eaton E, Weinberg RA, Lodish HF
• Expression cloning of the TGF-beta type II receptor, a functional transmembrane serine/threonine kinase.
• Cell. 1992; 68: 775-85
• Display abstract

• A cDNA encoding the TGF-beta type II receptor protein has been isolated by an expression cloning strategy. The cloned cDNA, when transfected into COS cells, leads to overexpression of an approximately 80 kd protein that specifically binds radioiodinated TGF-beta 1. Excess TGF-beta 1 competes for binding of radioiodinated TGF-beta 1 in a dose-dependent manner and is more effective than TGF-beta 2. The predicted receptor structure includes a cysteine-rich extracellular domain, a single hydrophobic transmembrane domain, and a predicted cytoplasmic serine/threonine kinase domain. A chimeric protein containing the intracellular domain of the type II receptor and expressed in E. coli can phosphorylate itself on serine and threonine residues in vitro, indicating that the cytoplasmic domain of the type II receptor is a functional kinase. This result implicates serine/threonine phosphorylation as an important mechanism of TGF-beta receptor-mediated signaling.

• Cheifetz S et al.
• Endoglin is a component of the transforming growth factor-beta receptor system in human endothelial cells.
• J Biol Chem. 1992; 267: 19027-30
• Display abstract

• Endoglin, a dimeric membrane glycoprotein expressed at high levels on human vascular endothelial cells, shares regions of sequence identity with betaglycan, a major binding protein for transforming growth factor-beta (TGF-beta) that co-exists with TGF-beta receptors I and II in a variety of cell lines but is low or absent in endothelial cells. We have examined whether endoglin also binds TGF-beta and demonstrate here that the major TGF-beta 1-binding protein co-existing with TGF-beta receptors I and II on human umbilical vein endothelial cells is endoglin, as determined by specific immunoprecipitation of endoglin affinity-labeled with 125I-TGF-beta. Furthermore, endoglin ectopically expressed in COS cells binds TGF-beta 1. Competition affinity-labeling experiments showed that endoglin binds TGF-beta 1 (KD approximately 50 pM) and TGF-beta 3 with high affinity but fails to bind TGF-beta 2. This difference in affinity of endoglin for the TGF-beta isoforms is in contrast to beta-glycan which recognizes all three isoforms. TGF-beta however is binding with high affinity to only a small fraction of the available endoglin molecules, suggesting that some rate-limiting event is required to sustain TGF-beta binding to endoglin.

• Cheifetz S, Massague J
• Isoform-specific transforming growth factor-beta binding proteins with membrane attachments sensitive to phosphatidylinositol-specific phospholipase C.
• J Biol Chem. 1991; 266: 20767-72
• Display abstract

• We report the identification of cell surface glycoproteins that bind transforming growth factor-beta (TGF-beta) in an isoform-specific manner, and are distinct from TGF-beta receptors I and II or the TGF-beta binding proteoglycan beta-glycan. The novel TGF-beta binding proteins have been identified in various cell lines including fetal bovine heart endothelial cells and MG-63 human osteosarcoma cells. They include proteins of 90-100 and 180 kDa that preferentially bind TGF-beta 1 (KD 0.1-0.2 nM) and proteins of 60 and 140 kDa that preferentially bind TGF-beta 2 (KD 0.5-1 nM). The 180-kDa TGF-beta 1 binding protein and the 60- and 140-kDa TGF-beta 2 binding proteins can be released from the cell surface by treatment with phosphatidylinositol-specific phospholipase C, suggesting that these proteins are attached to the plasma membrane through a phosphatidylinositol anchor. The expression of these three proteins as well as their sensitivity to phosphatidylinositol-specific phospholipase C is cell line-dependent. The 90-100-kDa TGF-beta 1 binding proteins are components of a 190-kDa disulfide-linked complex. The structural properties of these proteins and their high affinity and selectivity for different TGF-beta isoforms defines them as a novel class of cell surface TGF-beta binding proteins.

• Mathews LS, Vale WW
• Expression cloning of an activin receptor, a predicted transmembrane serine kinase.
• Cell. 1991; 65: 973-82
• Display abstract

• Activins are involved in the regulation of multiple biological events, ranging from early development to pituitary function. To characterize the cellular mechanisms involved in these processes, cDNAs coding for an activin receptor were cloned from AtT20 mouse corticotropic cells by screening COS cell transfectants for binding of 125I-activin A. The cDNAs code for a protein of 494 amino acids comprising a ligand-binding extracellular domain, a single membrane-spanning domain, and an intracellular kinase domain with predicted serine/threonine specificity. 125I-activin A binds to transfected COS cells with an affinity of 180 pM and can be competed by activin A, activin B, and inhibin A, but not by transforming growth factor beta 1. The kinase domain, but not the extracellular sequence, of the activin receptor is most closely related to the C. elegans daf-1 gene product, a putative transmembrane serine/threonine-specific protein kinase for which the ligand is not known.

• Segarini PR
• A system of transforming growth factor-beta receptors.
• Am J Respir Cell Mol Biol. 1991; 4: 395-6

• Sporn MB, Roberts AB
• Introduction: what is TGF-beta?
• Ciba Found Symp. 1991; 157: 1-6

• Kondo M et al.
• Activin receptor mRNA is expressed early in Xenopus embryogenesis and the level of the expression affects the body axis formation.
• Biochem Biophys Res Commun. 1991; 181: 684-90
• Display abstract

• Activin is a member of the transforming growth factor beta (TGF-beta) and possesses various activities in cellular control phenomena. During Xenopus embryonic development, activin is thought to act as a natural mesoderm-inducing factor. We isolated here the Xenopus activin receptor cDNA from Xenopus tadpole cDNA library and examined the expression of the Xenopus activin receptor gene during the course of early embryonic development. The Xenopus activin receptor has an 87% homology at the level of deduced amino acid sequence with the mouse activin receptor, and using the cDNA obtained, three bands of mRNA with different lengths were detected in Xenopus embryos throughout early embryogenesis. We synthesized activin receptor mRNA in vitro and tested the effect of the injection of the mRNA into Xenopus fertilized eggs on subsequent development. When the synthetic mRNA was injected into uncleaved fertilized eggs, embryos with reduced trunk structure were formed. However, when the mRNA was injected into the ventral blastomeres at the 16-cell stage, embryos with a secondary body axis were formed. These results indicate the importance of the function of activin receptor in the regulatory mechanism for body axis formation.

• MacKay K, Danielpour D
• Novel 150- and 180-kDa glycoproteins that bind transforming growth factor (TGF)-beta 1 but not TGF-beta 2 are present in several cell lines.
• J Biol Chem. 1991; 266: 9907-11
• Display abstract

• We identified transforming growth factor-beta (TGF-beta)-binding proteins which are distinct from previously described TGF-beta receptors or TGF-beta-binding proteins. These TGF-beta-binding proteins migrate as 150- and 180-kDa 125I-TGF-beta 1 affinity-labeled complexes which are consistently co-expressed in A549, Mv1Lu, MG-63, and BS-C-1 cells. They differ from the types I, II, and III TGF-beta receptors in their electrophoretic mobilities, their lack of binding to TGF-beta 2, and their failure to undergo the marked down-regulation seen with types I, II, and III receptors following a 16-h incubation with TGF-beta 1. The 150- and 180-kDa TGF-beta-binding proteins also are distinct from the recently described disulfide-linked TGF-beta 1-binding proteins which are present in rat glomeruli. In contrast to the glomerular TGF-beta 1-binding proteins, the electrophoretic mobilities of the 150- and 180-kDa binding proteins are unchanged following reduction. In addition, the 150- and 180-kDa TGF-beta-binding proteins are present in the detergent-rich phase during Triton X-114 phase separation, whereas the glomerular TGF-beta-binding proteins partition exclusively into the detergent-poor phase.

• Wakefield LM, Kondaiah P, Hollands RS, Winokur TS, Sporn MB
• Addition of a C-terminal extension sequence to transforming growth factor-beta 1 interferes with biosynthetic processing and abolishes biological activity.
• Growth Factors. 1991; 5: 243-53
• Display abstract

• Transforming growth factor-beta 1 (TGF-beta 1) is synthesized and secreted as a biologically latent complex. It has been proposed that one role of the latent complex is to prevent premature interaction of ligand and receptor intracellularly during biosynthesis (Wakefield et al., J. Cell Biol. (1987) 105, 965-975). To test this hypothesis, the endoplasmic reticulum retention sequence Lys-Asp-Glu-Leu (KDEL) was added to the C-terminus of the wildtype TGF-beta 1 coding sequence, and to a construct in which mutagenesis of two cysteine residues in the precursor pro region results in the synthesis and secretion of active, as opposed to latent, TGF-beta. Addition of either SEKDEL, or the control sequence SEKDVS to the TGF-beta 1 protein abolished biological activity. Western blot analysis indicated that the extended gene products are synthesized, but that the extension sequence partially interferes with the normal dimerization of the protein product, and totally inhibits the normal proteolytic processing and glycosylation of the precursor protein. The data suggest that correct folding of the highly conserved C terminus of TGF-beta 1 is critical for subsequent proteolytic cleavage and glycosylation at sites that are quite distant in the primary sequence. Thus molecular strategies for the generation of TGF-beta antagonists or superagonists should avoid extensive modification of this region of the molecule. Since synthesis of the endogenous TGF-beta 1 is unaffected by the presence of the mutated analog, the data further indicate that transfection with the KDEL-extended TGF-beta 1 sequence cannot be used as a dominant negative mutation to prevent secretion of the endogenous TGF-beta protein.

• Hirai R
• [The role of transforming growth factors in the growth control of cancer cells]
• Tanpakushitsu Kakusan Koso. 1991; 36: 1357-63

• Segarini PR
• Cell type specificity of TGF-beta binding.
• Ann N Y Acad Sci. 1990; 593: 73-90

• Schwarz LC et al.
• Aberrant TGF-beta production and regulation in metastatic malignancy.
• Growth Factors. 1990; 3: 115-27
• Display abstract

• We have examined the possible role of transforming growth factor-beta (TGF-beta) in metastatic malignancy by analyzing the production and activation of TGF-beta 1 and -beta 2 and the regulation of TGF-beta-responsive genes in oncogene-transformed metastatic fibrosarcomas. All transformed lines derived from either 10T1/2 or NIH 3T3 by either H-ras or protein-kinase encoding oncogenes produced more TGF-beta than parental cells. However, only highly metastatic fibrosarcomas secreted activated TGF-beta at rates that were greater than parental fibroblasts. Immunohistochemical staining for TGF-beta 1 showed widespread intra- and extracellular distribution in metastatic lung nodules and adjacent tissue. Cells isolated from tumors successfully metastasizing to the lung had TGF-beta 1 mRNA levels which were increased 19-fold over in vitro controls. Despite the greatly enhanced rate of secretion of activated TGF-beta, metastatic cells exhibited markedly altered responses of TGF-beta 1 and TGF-beta 2, being unable to either increase collagen secretion or enhance collagen alpha 2(1) or TGF-beta 1 mRNA levels. This lack of response was not due to either altered TGF-beta receptor affinity or numbers. Metastatic progression was, therefore, associated with an increase in the secretion of activated TGF-beta 1 and a loss of the ability to deregulate TGF-beta-responsive genes.

• Cheifetz S, Hernandez H, Laiho M, ten Dijke P, Iwata KK, Massague J
• Distinct transforming growth factor-beta (TGF-beta) receptor subsets as determinants of cellular responsiveness to three TGF-beta isoforms.
• J Biol Chem. 1990; 265: 20533-8
• Display abstract

• Characterization of the three mammalian transforming growth factor-beta (TGF-beta) isoforms, TGF-beta 1, -beta 2, and -beta 3, indicates that TGF-beta 3 is somewhat more potent (ED50 = 0.5 pM versus 2 pM) than TGF-beta 1 and TGF-beta 2 as a growth inhibitor of the Mv1Lu mink lung epithelial cell line. In the fetal bovine heart endothelial (FBHE) cell line, however, TGF-beta 1 and -beta 3 are at least 50-fold more potent than TGF-beta 2 which is a very weak growth inhibitor (ED50 greater than or equal to 0.5 nM). Thus, as growth inhibitors, TGF-beta 1 and -beta 3 resemble each other more than TGF-beta 2. The presence of serum alpha 2-macroglobulin in the FBHE cell assays decreases the biological potency of TGF-beta s, in particular TGF-beta 2. This effect of alpha 2-macroglobulin, however, is not sufficient to explain the low responsiveness of FBHE cells to TGF-beta 2. Evaluation of the role of TGF-beta receptors as determinants of cell-specific responsiveness to TGF-beta isoforms indicates that TGF-beta 1, -beta 2, and -beta 3 have similar affinity for the membrane proteoglycan, betaglycan. They differ, however, in their ability to bind to receptor types I and II which are implicated in TGF-beta signal transduction. TGF-beta 1 is similar, albeit not identical, to TGF-beta 3 and much more potent than TGF-beta 2 as a competitor for binding to the overall population of receptors I and II in all cell lines tested. A subset of receptors I and II has been identified in Mv1Lu cells which has high affinity for TGF-beta 2 (KD approximately 10 pM) and binds this factor at concentrations that are biologically active in Mv1Lu cells. This receptor subset could not be detected in FBHE cells, suggesting that cell-specific differences in the level of high affinity of TGF-beta 2 receptors may lead to cell-specific differences in responsiveness to this isoform. Thus, despite their structural and biological similarities, TGF-beta 1, -beta 2, and -beta 3 diverge in their ability to bind to receptors in a manner that correlates with their potency as growth inhibitors.

• Zhang P
• [Transforming growth factor (TGF)-beta]
• Sheng Li Ke Xue Jin Zhan. 1990; 21: 323-8

• Massague J
• The transforming growth factor-beta family.
• Annu Rev Cell Biol. 1990; 6: 597-641

• Laiho M, Weis MB, Massague J
• Concomitant loss of transforming growth factor (TGF)-beta receptor types I and II in TGF-beta-resistant cell mutants implicates both receptor types in signal transduction.
• J Biol Chem. 1990; 265: 18518-24
• Display abstract

• A panel of 71 chemically mutagenized Mv1Lu mink lung epithelial cell clones were selected based on their resistance to the growth inhibitory action of transforming growth factor beta 1 (TGF-beta 1) and TGF-beta 2. Characterization of TGF-beta receptors in these mutants indicates that the TGF-beta-binding membrane proteoglycan, betaglycan, is apparently normal in all of them. However, 14 of the mutant clones are defective in TGF-beta receptor type I, and 22 clones are simultaneously defective in receptor types I and II. The clones with type I receptor defects fall into two distinct phenotypes, called R and LR. The R phenotype is characterized by the lack of detectable type I receptors, and has been previously described (Boyd, F. T., and Massague, J. (1989) J. Biol. Chem. 264, 2272-2278). LR mutants are characterized by expression of low levels of type I receptor and are, like the R mutants, completely resistant to growth inhibition by TGF-beta 1 or -beta 2. Mutant clones that are simultaneously defective in receptor types I and II fall into three distinct phenotypes. These included DRa mutants which are characterized by lack of detectable receptor types I and II, DRb mutants which are characterized by low expression of both receptor types and an anomalously fast electrophoretic mobility of the type II receptor protein. All mutants that have a low level of type II receptor are also defective in type I receptor. In addition to the loss of growth inhibitory response, the receptor-defective mutants described here have lost all other responses to TGF-beta 1 and -beta 2 known to occur in parental Mv1Lu cells. The defects present in these mutant clones are not encountered in clones isolated from nonmutagenized parental Mv1Lu cells or in mutagenized cells that had not been exposed to selection with TGF-beta. The results implicate TGF-beta receptor types I and II in the mediation of a common set of cellular responses to TGF-beta. Furthermore, the high relative frequency of isolation of DR mutants raises the possibility that receptor types I and II interact as part of a common signaling TGF-beta receptor complex.

• Boyd FT, Cheifetz S, Andres J, Laiho M, Massague J
• Transforming growth factor-beta receptors and binding proteoglycans.
• J Cell Sci Suppl. 1990; 13: 131-8
• Display abstract

• Transforming growth factors-beta (TGFs-beta) are representative of a superfamily whose members were first identified as regulators of morphogenesis and differentiation, and subsequently found to be structurally related. Other members of the family include the activins and inhibins, BMPs, MIS, the DPP-C gene product and Vg-1. When assayed by affinity-labelling techniques, TGFs-beta bind to three distinct cell surface proteins which are present on most cells. These proteins are all of relatively low abundance but bind TGFs-beta with affinities consistent with the biological potency of the factors. The Type I and Type II binding proteins are glycoproteins with estimated molecular weights of 53 and 73 x 10(3) Mr, respectively. They both bind TGF-beta 1 significantly better than TGF-beta 2. The Type I receptor has been identified as the receptor which mediates many of the responses of TGFs-beta, based on somatic cell genetic studies of epithelial cell mutants unresponsive to TGFs-beta. Betaglycan is the third binding protein present on many, but not all, cell types and is a large proteoglycan (approximately 280 x 10(3) Mr) with 100-120 x 10(3) Mr core proteins. A soluble form of this molecule is present in conditioned media of many cell lines and may be derived from the cell surface-associated molecule by cleavage of a small membrane anchor. Betaglycan binds TGF-beta 1 and TGF-beta 2 with similar affinity and this binding is to the core proteins, not the glycosaminoglycan side chains. This molecule may have a function in the localization and delivery or the clearance of activated TGFs-beta.(ABSTRACT TRUNCATED AT 250 WORDS)

• Cheifetz S, Massague J
• Transforming growth factor-beta (TGF-beta) receptor proteoglycan. Cell surface expression and ligand binding in the absence of glycosaminoglycan chains.
• J Biol Chem. 1989; 264: 12025-8
• Display abstract

• The type III transforming growth factor-beta (TGF-beta) receptor is a cell surface chondroitin/heparan sulfate proteoglycan that binds various forms of TGF-beta with high affinity and specificity. Here, we have used a genetic approach to determine the requirement for glycosaminoglycan (GAG) chains for normal TGF-beta receptor expression and the role that the receptor proteoglycan core and GAG chains play in TGF-beta binding. Chinese hamster ovary (CHO) cells defective in GAG synthesis express on their surface 110-130-kDa type III receptor proteoglycan cores that can bind normal levels of TGF-beta compared to wild type CHO cells. The affinity of the receptor core for TGF-beta 1 and TGF-beta 2 in CHO cell mutants is similar to that of the TGF-beta receptor proteoglycan forms present in wild type CHO cells or in CHO cell mutants that have been allowed to bypass their metabolic defect and express the wild type proteoglycan phenotype. The binding properties of TGF-beta receptor types I and II in CHO cells and the growth-inhibitory response of CHO cell mutants to TGF-beta are not impaired by the absence of GAG chains in the type III receptor. These results show that the GAG chains are dispensable for type III receptor expression on the cell surface, binding of TGF-beta to the receptor core, and growth inhibitory response of the cells to TGF-beta. The evidence also suggests that the type III receptor may act as a multifunctional proteoglycan able to bind TGF-beta via the receptor core while performing another as yet unidentified function(s) via the GAG chains.

• Boyd FT, Massague J
• Transforming growth factor-beta inhibition of epithelial cell proliferation linked to the expression of a 53-kDa membrane receptor.
• J Biol Chem. 1989; 264: 2272-8
• Display abstract

• Cells whose proliferation is blocked by transforming growth factor-beta (TGF-beta) express three distinct surface glycoproteins of 53, 73, and 300 kDa that bind TGF-beta with high affinity, but whose function is unknown. We have isolated two classes of chemically-induced Mv1Lu epithelial cell mutants resistant to growth inhibition by TGF-beta. Class R mutants have selectively lost expression of the 53-kDa (type I) TGF-beta-binding protein. They have also lost the ability to respond to TGF-beta with elevated fibronectin expression and cell flattening. Class S mutants bind normally but do not respond to TGF-beta. TGF-beta-resistant mutants retain a contact inhibited, nontransformed phenotype. The properties of S mutants suggest that they are defective in the TGF-beta signal transduction mechanism, while the results with R mutants identify the type I TGF-beta-binding protein as the receptor involved in mediating TGF-beta actions on cell adhesion and proliferation.

• Segarini PR, Seyedin SM
• The high molecular weight receptor to transforming growth factor-beta contains glycosaminoglycan chains.
• J Biol Chem. 1988; 263: 8366-70
• Display abstract

• Proteoglycans are constituents of the cell surface that may play important roles in the regulation of cell behavior. Here we report that the 250-kDa receptor subunit that binds the multifunctional protein, transforming growth factor-beta 1 (TGF-beta 1), contains chains of heparan sulfate and chondroitin sulfate and thus is a proteoglycan. Digestion of TGF-beta 1-receptor complexes with glycosaminoglycan (GAG)-specific degradative enzymes yield core proteins of 115-140 kDa. Cell monolayers that had been predigested with GAG-specific degradative enzymes were capable of binding high levels of TGF-beta 1, but the size of the binding components was shifted from the high molecular weight species to the lower molecular weight core proteins, indicating that GAG chains are not necessary for TGF-beta 1 binding to the cell. The presence of GAG chains on the receptor subunit indicates that it has the potential for interaction with the extracellular matrix.

• Wakefield LM, Smith DM, Masui T, Harris CC, Sporn MB
• Distribution and modulation of the cellular receptor for transforming growth factor-beta.
• J Cell Biol. 1987; 105: 965-75
• Display abstract

• Scatchard analyses of the binding of transforming growth factor-beta (TGF-beta) to a wide variety of different cell types in culture revealed the universal presence of high affinity (Kd = 1-60 pM) receptors for TGF-beta on every cell type assayed, indicating a wide potential target range for TGF-beta action. There was a strong (r = +0.85) inverse relationship between the receptor affinity and the number of receptors expressed per cell, such that at low TGF-beta concentrations, essentially all cells bound a similar number of TGF-beta molecules per cell. The binding of TGF-beta to various cell types was not altered by many agents that affect the cellular response to TGF-beta, suggesting that modulation of TGF-beta binding to its receptor may not be a primary control mechanism in TGF-beta action. Similarly, in vitro transformation resulted in only relatively small changes in the cellular binding of TGF-beta, and for those cell types that exhibited ligand-induced down-regulation of the receptor, down-regulation was not extensive. Thus the strong conservation of binding observed between cell types is also seen within a given cell type under a variety of conditions, and receptor expression appears to be essentially constitutive. Finally, the biologically inactive form of TGF-beta, which constitutes greater than 98% of autocrine TGF-beta secreted by all of the twelve different cell types assayed, was shown to be unable to bind to the receptor without prior activation in vitro. It is proposed that this may prevent premature interaction of autocrine ligand and receptor in the Golgi apparatus.

• Cheifetz S et al.
• The transforming growth factor-beta system, a complex pattern of cross-reactive ligands and receptors.
• Cell. 1987; 48: 409-15
• Display abstract

• A new homodimer form of transforming growth factor-beta (TGF-beta), TGF-beta 2, has been identified in porcine blood platelets. TGF-beta 2 is homologous to ordinary TGF-beta (TGF-beta 1), which is also present in platelets. TGF-beta 1.2, a heterodimer containing one TGF-beta 1 chain and one TGF-beta 2 chain, has also been isolated. TGF-beta 1 and TGF-beta 2 interact differently with a family of receptors in target cells. A 280 kd receptor displays high affinity for both TGF-beta 1 and TGF-beta 2. Occupancy of this receptor by TGF-beta 1 or TGF-beta 2 correlates with the ability of these TGF-beta s to inhibit cell proliferation. In contrast, 65 kd and 85 kd receptors have high affinity for TGF-beta 1 but lower affinity for TGF-beta 2. The existence of distinct forms of TGF-beta that interact differently with a family of TGF-beta receptors could provide flexibility to the regulation of tissue growth and differentiation by the TGF-beta system.

© 2021 EMBL | Privacy Policy