Endothelial protein kinase C isoform identity and differential activity of PKCξ in an athero-susceptible region of porcine aorta

Endothelial protein kinase C (PKC) signaling was investigated in different regions of normal porcine aorta. The locations map to differential atherosclerotic susceptibility and correlate with sites of disturbed (DF) or undisturbed (UF) local flow profiles. Endothelial lysates were isolated from the inner curvature of the aortic arch ( DF; athero-susceptible) and a nearby UF region of the descending thoracic aorta ( UF; athero- protected), and in some experiments a distant athero- protected UF site, the common carotid artery. Total endothelial PKC activity in the DF regions was 145% to 240% of that in both UF locations ( P < 0.05), whereas the UF regions were not significantly different from each other. PKC protein isoforms alpha, beta, epsilon, nu, lambda, and zeta were expressed in similar proportions in both aortic regions, suggesting that differences of kinase activity were not directly attributable to expression levels. Inhibition of members of the conventional and novel PKC families had no differential effect on regional kinase activity. However, inhibition of PKC zeta, a member of the atypical PKC family, reduced the DF lysate kinase activity to that of UF levels (NS P = 0.35). Differential phosphorylation of PKC zeta Thr410 and Thr560, along with increased levels of PKC zeta degradation products in UF endothelial lysates, suggested posttranslational modification of PKC zeta as the basis for site-specific differences in vivo. Steady-state regional heterogeneity of an important family of regulatory proteins in intact arterial endothelium in vivo may link localized athero- susceptibility and the associated hemodynamic environment.