NOVEL CDC42HS MUTANT INDUCES CELLULAR-TRANSFORMATION

Cdc42Hs is a small GTPase of the Rho-subfamily, which regulates signal ing pathways that influence cell morphology and polarity, cell-cycle p rogression and transcription [1-7]. An essential role for Cdc42Hs in c ell growth regulation has been suggested by the finding that the Dbl o ncoprotein is an upstream activator - a guanine nucleotide exchange fa ctor (GEF) - for Cdc42Hs [8,9], and that activated mutants of the clos ely related GTPases Rac and Rho are transforming [10-13]. As we were u nable to obtain significant over-expression of GTPase-defective Cdc42H s mutants, we have generated a mutant, Cdc42Hs(F28L), which can underg o spontaneous GTP-GDP exchange while maintaining full GTPase activity, and thus should exhibit functional activities normally imparted by Db l. In cultured fibroblasts, Cdc42Hs(F28L) activated the c-Jun kinase ( JNK1) and stimulated filopodia formation. Cells stably expressing Cdc4 2Hs(F28L) also exhibited several hallmarks of transformation - reduced contact inhibition, lower dependence on serum for growth, and anchora ge-independent growth. Our findings indicate that Cdc42Hs plays a role in cell proliferation, and is a likely physiological mediator of Dbl- induced transformation. (C) Current Biology Ltd ISSN 0960-9822.