Conformational Activation of Radixin by G13 Protein α Subunit

G(13) protein, one of the heterotrimeric guanine nucleotide-binding proteins (G proteins), regulates diverse and complex cellular responses by transducing signals from the cell surface presumably involving more than one pathway. Yeast two-hybrid screening of a mouse brain cDNA library identified radixin, a member of the ERM family of three closely related proteins (ezrin, radixin, and moesin), as a protein that interacted with G alpha(13). Interaction between radixin and G alpha(13) was confirmed by in vitro binding assay and by co-immunoprecipitation technique. Activated Ga,, induced conformational activation of radixin, as determined by binding of radixin to polymerized F-actin and by immunofluorescence in intact cells. Finally, two dominant negative mutants of radixin inhibited G alpha(13)-induced focus formation of Rat-1 fibroblasts but did not affect Ras-induced focus formation. Our results identifying a new signaling pathway for G alpha(13) indicate that ERM proteins can be activated by and serve as effecters of heterotrimeric G proteins.