Diaphanous-related formins (Drfs) are a family of formin homology (FH) proteins that act as effectors of Rho small GTPases during growth factor-induced cytoskeletal remodelling, stress fibre formation, and cell division [ (PUBMED:10631086) ]. Drf proteins are characterised by a variety of shared domains: an N-terminal GTPase-binding domain (GBD), formin-homology domains FH1, FH2 ( IPR015425 ) and FH3 ( IPR010472 ), and a C-terminal conserved Dia-autoregulatory domain (DAD) that binds the GBD.
This entry represents the GBD, which is a bifunctional autoinhibitory domain that interacts with and is regulated by activated Rho family members. Mammalian Drf3 contains a CRIB-like motif within its GBD for binding to Cdc42, which is required for Cdc42 to activate and guide Drf3 towards the cell cortex where it remodels the actin skeleton [ (PUBMED:12676083) ].
Disruption of the Diaphanous-related formin Drf1 gene encoding mDia1 reveals arole for Drf3 as an effector for Cdc42.
Curr Biol. 2003; 13: 534-45
Display abstract
BACKGROUND: Mammalian Diaphanous-related formins (Drfs) act as Rho small GTPaseeffectors during growth factor-induced cytoskeletal remodeling and cell division.While both p140 mDia1 (herein called Drf1) and p134 mDia2 (Drf3) have been shown to bind in vitro to activated RhoA-C, and Drf3 has also been shown to bind toCdc42, little is known about the cellular function of these GTPase effectorpairs. Thus, we have begun targeting the murine Drf genes to address theirvarious contributions to small GTPase signaling in cytoskeletal remodeling anddevelopment. RESULTS: Drf1 +/+, +/-, and -/- cell lines were derived fromembryonic stem cells. While some Drf1 +/- lines had fewer actin stress fibers,several Drf1 +/- and -/- cells were more motile and had more abundant lamella andfilopodia. Because the apparent "gain-of-function" corresponded with elevatedlevels of Drf3 protein expression, we hypothesized that the effects on the actin cytoskeleton were due to Cdc42 utilization of Drf3 as an effector. In this study,we found that inactive Drf3 variants and microinjected Drf3 antibodies interferedwith Cdc42-induced filopodia. In addition, we observed that Drf3 contains apreviously unidentified CRIB-like motif within its GTPase binding domain (GBD).By fluorescent resonance energy transfer (FRET) analysis, we demonstrate thatthis motif is required for Cdc42 binding and Drf3 recruitment to the leading edgeand, surprisingly, to the microtubule organizing center (MTOC) of migratingfibroblasts. CONCLUSIONS: Our observations extend the role of the mammalian Drfs in cell signaling and demonstrate that Cdc42 not only activates Drf3, but guides the effector to sites at the cell cortex where it remodels the actincytoskeleton.
