RHOA-DEPENDENT PHOSPHORYLATION AND RELOCALIZATION OF ERM PROTEINS INTO APICAL MEMBRANE ACTIN PROTRUSIONS IN FIBROBLASTS/

The ERM proteins (ezrin, radixin, and moesin) are a group of band 4.1- related proteins that are proposed to function as membrane/cytoskeleta l linkers. Previous biochemical studies have implicated RhoA in regula ting the association of ERM proteins with their membrane targets. Howe ver, the specific effect and mechanism of action of this regulation is unclear. We show that lysophosphatidic acid stimulation of serum-star ved NIH3T3 cells resulted in relocalization of radixin into apical mem brane/actin protrusions, which was blocked by inactivation of Rho by C 3 transferase. An activated allele of RhoA, but not Pac or CDC42Hs, wa s sufficient to induce apical membrane/actin protrusions and localize radixin or moesin into these structures in both Rat1 and NIH3T3 cells. Lysophosphatidic acid treatment led to phosphorylation of radixin pre ceding its redistribution into apical protrusions. Significantly, cotr ansfection of RhoAV14 or C3 transferase with radixin and moesin reveal ed that RhoA activity is necessary and sufficient for their phosphoryl ation. These findings reveal a novel function of RhoA in reorganizing the apical actin cytoskeleton and suggest that this function may be me diated through phosphorylation of ERM proteins.