NORMAL GENOMIC

• Miki K, Eddy EM
• Tumor necrosis factor receptor 1 is an ATPase regulated by silencer of death domain.
• Mol Cell Biol. 2002; 22: 2536-43
• Display abstract

• Self-aggregation of tumor necrosis factor receptor type 1 (TNFR1) induces spontaneous downstream signaling and results in cell death. It has been suggested that silencer of death domain (SODD) binds TNFR1 monomers to prevent self-aggregation. We found that SODD binds through its BAG domain to the ATPase domain of Hsp70. We also determined that SODD binds through its BAG domain to TNFR1. ATP, but not nonhydrolyzable ATP-gamma S, regulates the SODD binding by Hsp70 or TNFR1. ATP binding by TNFR1 was abolished when a point mutation was introduced into a phosphate-binding loop motif characteristic of ATP-binding proteins, suggesting that TNFR1 functions as an ATPase. Furthermore, TNFR1 was present in aggregates in ATP-depleted cells and SODD disassembled aggregates in vitro only in the presence of ATP. These data suggest that SODD functions as a cofactor analogous to the nucleotide exchange factor BAG-1, which modulates the ATPase cycle of Hsp70 proteins. We propose a new model in which a nucleotide-dependent conformational change in TNFR1 has a key role in regulating TNF signaling.

• Antoku K, Maser RS, Scully WJ Jr, Delach SM, Johnson DE
• Isolation of Bcl-2 binding proteins that exhibit homology with BAG-1 and suppressor of death domains protein.
• Biochem Biophys Res Commun. 2001; 286: 1003-10
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• The Bcl-2 oncoprotein is a potent inhibitor of apoptosis and is overexpressed in a variety of different malignancies. Bcl-2 function is regulated through heterodimerization with other members of the Bcl-2 protein family. In addition, several proteins that are not members of the Bcl-2 family can bind to Bcl-2, including BAG-1 protein. In this study, we screened for proteins that bind to Bcl-2, and isolated two additional members of the BAG-1 protein family, BAG-3 and BAG-4. The BAG-4 protein that we cloned also corresponds to the recently isolated suppressor of death domains (SODD) protein, a molecule that binds and inhibits signaling by tumor necrosis factor receptor 1 (TNFR1). Both BAG-3 and BAG-4/SODD were found to physically associate with Bcl-2, and both proteins are well conserved from human to mouse. A region of homology, comprising 68 amino acids, is present in the carboxyl termini of BAG-3 and BAG-4/SODD, and this region corresponds with sequences termed BAG domains that are found in other members of the BAG-1 protein family. In BAG-3 and BAG-4/SODD, the BAG domains appear to constitute the Bcl-2 binding regions of these molecules. BAG-3 and BAG-4/SODD, like BAG-1, were also shown to bind to Hsp70 inside the cell. Moreover, BAG-3 overexpression modestly inhibited apoptosis resulting from cytokine deprivation of IL-3-dependent 32D cells. Together, our findings demonstrate that other members of the BAG-1 protein family, namely BAG-3 and BAG-4/SODD, bind to Bcl-2 and provide a potential link between pathways regulated by Bcl-2 and pathways regulated by Hsp70, as well as TNFR1.