THE SMALL GTP-BINDING PROTEIN RHO POTENTIATES AP-1 TRANSCRIPTION IN T-CELLS

The Rho family of small GTP-binding proteins is invoiced in the regula tion of cytoskeletal structure, gene transcription, specific cell fate development, and transformation. We demonstrate in this report that o verexpression of an activated form of Rho enhances AP-1 activity in Ju rkat T cells in the presence of phorbol myristate acetate (PMA), but a ctivated Rho (V14Rho) has little or no effect on NFAT, Oct-1, and NF-k appa B enhancer element activities under similar conditions. Overexpre ssion of a V14Rho construct incapable of membrane localization (CAAX d eleted) abolishes PMA-induced AP-1 transcriptional activation. The eff ect of Rho on AP-1 is independent of the mitogen-activated protein kin ase pathway, as a dominant-negative MEK and a MEK inhibitor (PD98059) did not affect Rho-induced AP-1 activity. V14Rho binds strongly to pro tein kinase C alpha (PKC alpha) in vivo; however, deletion of the CAAX site on V14Rho severely diminished this association. Evidence for a r ole for PKC alpha as an effector of Rho was obtained by the observatio n that coexpression of the N-terminal domain of PKC alpha blocked the effects of activated Rho plus PMA on AP-1 transcriptional activity. Th ese data suggest that Rho potentiates AP-1 transcription during T-cell activation.