PKCßII modulation of myocyte contractile performance.

Significant up-regulation of the protein kinase Cß(II) (PKCß(II)) develops during heart failure and yet divergent functional outcomes are reported in animal models. The goal here is to investigate PKCß(II) modulation of contractile function and gain insights into downstream targets in adult cardiac myocytes. Increased PKCß(II) protein expression and phosphorylation developed after gene transfer into adult myocytes while expression remained undetectable in controls. The PKCß(II) was distributed in a peri-nuclear pattern and this expression resulted in diminished rates and amplitude of shortening and re-lengthening compared to controls and myocytes expressing dominant negative PKCß(II) (PKCßDN). Similar decreases were observed in the Ca(2+) transient and the Ca(2+) decay rate slowed in response to caffeine in PKCß(II)-expressing myocytes. Parallel phosphorylation studies indicated PKCß(II) targets phosphatase activity to reduce phospholamban (PLB) phosphorylation at residue Thr17 (pThr17-PLB). The PKCß inhibitor, LY379196 (LY) restored pThr17-PLB to control levels. In contrast, myofilament protein phosphorylation was enhanced by PKCß(II) expression, and individually, LY and the phosphatase inhibitor, calyculin A each failed to block this response. Further work showed PKCß(II) increased Ca(2+)-activated, calmodulin-dependent kinase IIδ (CaMKIIδ) expression and enhanced both CaMKIIδ and protein kinase D (PKD) phosphorylation. Phosphorylation of both signaling targets also was resistant to acute inhibition by LY. These later results provide evidence PKCß(II) modulates contractile function via intermediate downstream pathway(s) in cardiac myocytes.