Identification and characterization of a novel Rho-specific guanine nucleotide exchange factor

Rho GTPases are implicated in a multitude of cellular processes regulated by membrane receptors, such as cytoskeletal rearrangements, gene transcription and cell growth and motility. Activation of these GTPases is under the direct control of guanine nucleotide exchange factors (GEFs), the Dbl family proteins. By searching protein databases we have identified a novel Rho-GEF, termed p114-Rho-GEF, which similarly to other Rho-GEFs contains a Dbl homology domain followed by a pleckstrin homology domain. p114-Rho-GEF interacted specifically with RhoA, in its nucleotide-free and guanosine 5'-[gamma-thio]triphosphate-bound states, but not with Rac1 and Cdc42, and efficiently catalysed guanine nucleotide exchange of RhoA. Consistent with these results in vitro was our finding that the overexpression of p114-Rho-GEF in J82 and HEK-293 cells induced the formation of actin stress fibres and stimulated serum-response-factor-mediated gene transcription in a Rho-dependent manner. Rho-mediated transcriptional activation induced by M(3) muscarinic acetylcholine and lysophosphatidic acid receptors was enhanced by p114-Rho-GEF, suggesting that the activity of this novel Rho-GEF, which is widely expressed in human tissues, can be controlled by G-protein-coupled receptors.

Rho-specific binding and guanine nucleotide exchange catalysis by KIAA0380, a dbl family member

Several guanine nucleotide exchange factors (GEFs) for Rho-GTPases have been identified, all of them containing a Dbl homology (DH) and pleckstrin homology (PH) domain, but exhibiting different specificities to the Rho family members, Rho, Rac and Cdc42. We report here that KIAA0380, a protein with a tandem DH/PH domain, an amino-terminal PDZ domain and a regulator of G protein signalling (RGS) homology domain, is a specific GEF for RhoA, but not for Rac1 and Cdc42, as determined by GDP release, guanosine 5'-O-(3-thio)triphosphate (GTPgammaS) binding and protein binding assays. When expressed in J82 cells, DH/PH domain-containing forms of KIAA0380 induced actin stress fibers, whereas expression of the RGS homology domain prevented lysophosphatidic acid (LPA)-induced stress fiber formation.