Inhibition of PKC alpha and rhoA translocation in differentiated smooth muscle by a caveolin scaffolding domain peptide

Receptor-coupled contraction of smooth muscle involves recruitment to the p lasma membrane of downstream effector molecules PKC alpha and rhoA but the mechanism of this signal integration is unclear. Caveolins, the principal s tructural proteins of caveolar plasma membrane invaginations, have been imp licated in the organization and regulation of many signal transducing molec ules. Thus, using laser scanning confocal immunofluorescent microscopy, we tested the hypothesis that caveolin is involved in smooth muscle signaling by investigating caveolin isoform expression and localization, together wit h the effect of a peptide inhibitor of caveolin function, in intact differe ntiated smooth muscle cells. All three main caveolin isoforms were identifi ed in uterine, stomach, and ileal smooth muscles and assumed a predominantl y plasma membranous localization in myometrial cells. Cytoplasmic introduct ion of a peptide corresponding to the caveolin-1 scaffolding domain-an esse ntial region for caveolin interaction with signaling molecules-significantl y inhibited agonist-induced translocation of both PKC alpha and rhoA. Trans location was unimpaired by a scrambled peptide and was unaltered in sham-tr eated cells. The membranous localization of caveolins, and direct inhibitio n of receptor-coupled PKC alpha and rhoA translocation by the caveolin-1 sc affolding domain, supports the concept that caveolins can regulate the inte gration of extracellular contractile stimuli and downstream intracellular e ffecters in smooth muscle. (C) 2000 Academic Press.