Protein kinase C epsilon mediates angiotensin II-induced activation of β-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. AII and other growth factors augment h1-integrin-dependent adhesion and spreading by binside-out signalingQ without affecting the total number of integrin receptors. bInside-out signalingQ involves specific signaling pathways, including protein kinase C (PKC), leading to activation of h1-integrins. In the present study we investigated the mechanisms involved in AII-increased adhesion of adult rat cardiac fibroblasts (CFBs), obtained from Sprague–Dawley rats, to collagen I mediated by h1-integrin. Methods and results: Treatment of CFBs with AII induced a concentration-dependent increase in adhesion to collagen I (2.2-fold, pb0.01) within 3–6 h of treatment. This effect was mediated by h1-integrin via the angiotensin AT1 receptor and was significantly reduced by protein kinase C inhibition. AII significantly induced phosphorylation of PKC epsilon (PKCq), which is involved in h1-integrin-dependent adhesion and motility, and phosphorylation of the cytoplasmatic tail of h1-integrin at threonine 788/789, required for adhesion. Phosphorylation of h1integrin and an increase in adhesion was also induced by l-a-phosphatidylinositol-3,4,5-triphosphate (l-a-PIP3), an activator of endogeneous PKCq. AII failed to increase adhesion in myofibroblasts obtained from PKCq (/) mice, but not in cells obtained from control mice. Coimmunoprecipitation and double immunofluorescence demonstrated that AII induced a close association of PKCq with h1-integrin in CFBs. Conclusion: The present study demonstrates that AII increased h1-integrin-dependent adhesion to collagen I in cardiac fibroblasts by insideout signaling via PKCq and phosphorylation of the cytoplasmatic tail of the h1-integrin. D 2005 European Society of Cardiology. Published by Elsevier B.V. All rights reserved.