Modular architecture and novel protein-protein interactions regulating the RGS-containing Rho guanine nucleotide exchange factors.

The regulator of G-protein signaling (RGS)-containing RhoGEFs, including p115RhoGEF, PDZ-RhoGEF, and LARG, represent a novel family of guanine nucleotide exchange factors for RhoA that are regulated by the Galpha(12/13) family of heterotrimeric G proteins. Experimental evidence indicates that the complex architecture of these RhoGEFs provides the structural basis for novel regulatory mechanisms mediated by protein-protein interactions. These include the direct association of their RGS domain with GTP-bound forms of Galpha(12/13) and the binding of the PDZ domain present in PDZ-RhoGEF and LARG to plexins, which are receptors for semaphorins. The carboxyl-terminal region of these GEFs also exerts regulatory properties, including the ability to form dimers, which is inhibitory to their in vivo GEF activity and, in the case of PDZ-RhoGEF, to associate with PAK4, a downstream target of Cdc42. This carboxyl-terminal region also acts as the target for tyrosine kinases, which have a positive effect on the long-term activity of these GEFs. This article describes the experimental strategies that have been utilized to begin unraveling the molecular mechanisms regulating the functional activity of RGS-containing RhoGEFs.