PKCβII modulation of myocyte contractile performance

Significant up-regulation of the protein kinase CβII (PKCβII) develops during heart failure and yet divergent functional outcomes are reported in animal models. The goal here is to investigate PKCβII modulation of contractile function and gain insights into downstream targets in adult cardiac myocytes. Increased PKCβII protein expression and phosphorylation developed after gene transfer into adult myocytes while expression remained undetectable in controls. The PKCβII 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 PKCβII (PKCβDN). Similar decreases were observed in the Ca2+ transient and the Ca2+ decay rate slowed in response to caffeine in PKCβII-expressing myocytes. Parallel phosphorylation studies indicated PKCβII targets phosphatase activity to reduce phospholamban (PLB) phosphorylation at residue Thr17 (pThr17-PLB). The PKCβ inhibitor, LY379196 (LY) restored pThr17-PLB to control levels. In contrast, myofilament protein phosphorylation was enhanced by PKCβII expression, and individually, LY and the phosphatase inhibitor, calyculin A each failed to block this response. Further work showed PKCβII increased Ca2+-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 PKCβII modulates contractile function via intermediate downstream pathway(s) in cardiac myocytes.

► Gene transfer and expression of PKCβII decreases basal contractile function in adult myocytes.
► PKCβII is distributed in a perinuclear pattern under basal conditions.
► Ca2+ cycling and myofilament proteins are end targets in this signaling cascade.
► A complex end target phosphorylation pattern is associated with the diminished function.
► This pattern is associated with increased phosphatase and kinase activity.