High glucose concentrations and protein kinase C isoforms in vascular smooth muscle cells

High extracellular glucose activates protein kinase C (PKC), a family of kinases vital to intracellular signaling. However, which PKC isoforms are involved and where in the cell they operate is unclear. We tested the hypothesis that only those PKC isoforms binding to diacylglycerol (DAG) are activated by high glucose. We also reasoned that the isoforms would translocate to different parts of the cell, where they presumably serve different functions. The PKC isoforms alpha, beta, delta, epsilon, and zeta were studied. Twenty mM glucose caused an increase in total PKC activity at six hours, which was maintained at 24 hours. High glucose decreased the angiotensin II-induced calcium signal. This effect was reversed by preincubating the cells with the PKC inhibitor staurosporine. Glucose induced a translocation of all PKC isoforms except PKC zeta by Western blot. Confocal microscopy showed that PKC alpha, beta, and epsilon were translocated into the nucleus. PKC delta showed strong association with cytoskeletal structures. The effects were sustained at 24 hours for PKC isoform beta and to a lesser extent for PKC delta and epsilon, but not for PKC alpha. Thus, PKC isoforms differ in their propensity to be activated by high glucose. Those isoforms binding to DAG are activated. Both cytoskeletal and nuclear signaling may be involved.