Protein kinase C epsilon mediates angiotensin II-induced activation of beta(1)-integrins in cardiac fibroblasts

Objective: Angiotensin II (AII) promotes cardiac fibrosis by increased extracellular matrix production and enhanced interaction of matrix proteins with their cellular receptors, including integrins. All and other growth factors augment beta(1)-integrin-dependent adhesion and spreading by inside-out signaling without affecting the total number of integrin receptors. Inside-out signaling involves specific signaling pathways, including protein kinase C (PKC), leading to activation of beta(1)-integrins. In the present study we investigated the mechanisms involved in All-increased adhesion of adult rat cardiac fibroblasts (CFBs), obtained from Sprague-Dawley rats, to collagen I mediated by beta(1)-integrin. Methods and results: Treatment of CFBs with All induced a concentration-dependent increase in adhesion to collagen I (2.2-fold, p < 0.01) within 3-6 h of treatment. This effect was mediated by beta 1-integrin via the angiotensin AT(1) receptor and was significantly reduced by protein kinase C inhibition. All significantly induced phosphorylation of PKC epsilon (PKC epsilon), which is involved in beta(1)-integrin-dependent adhesion and motility and phosphorylation of the cytoplasmatic tail of beta(1)-integrin at threonine 788/789, required for adhesion. Phosphorylation of beta(1)-integrin and an increase in adhesion was also induced by L-alpha-phosphatidylinositol-3,4,5-triphosphate (L-alpha-PIP3) an activator of endogeneous PKCe. All failed to increase adhesion in myofibroblasts obtained from PKCe (-/-) mice, but not in cells obtained from control mice. Co-immunoprecipitation and double immunofluorescence demonstrated that All induced a close association of PKC epsilon with beta(1)-integrin in CFBs. Conclusion: The present study demonstrates that All increased beta(1)-integfin-dependent adhesion to collagen I in cardiac fibroblasts by inside-out signaling via PKC epsilon and phosphorylation of the cytoplasmatic tail of the beta(1)-integrin.