Characterization of TCL, a new GTPase of the Rho family related to TC10 and Cdc42

GTPases of the Rho family control a wide variety of cellular processes such as cell morphology, motility, proliferation, differentiation, and apoptosi s, We report here the characterization of a new Rho member, which shares 85 % and 78% amino acid similarity to TC10 and Cdc42, respectively. This GTPas e, termed as TC10-like (TCL) is encoded by an unexpectedly large locus, mad e of five exons spanning over 85 kilobases on human chromosome 14, TCL mRNA is 2.5 kilobases long and is mainly expressed in heart. In vitro, TCL show s rapid GDP/GTP exchange and displays higher GTP dissociation and hydolysis rates than TC10, Using the yeast two-hybrid system and GST pull-down assay s, we show that GTP-bound but not GDP-bound TCL protein directly interacts with Cdc42/Rac interacting binding domains, such as those found in PAK and WASP. Despite its overall similarity to TC10 and Cdc42, the constitutively active TCL mutant displays distinct morphogenic activity in REF-52 fibrobla sts, producing large and dynamic F-actin-rich ruffles on the dorsal cell me mbrane. Interestingly, TCL morphogenic activity is blocked by dominant nega tive Rad and Cdc42 mutants, suggesting a crosstalk between these three Rho GTPases.