ARACHIDONIC ACID-INDUCED DOWN-REGULATION OF PROTEIN-KINASE-C-DELTA INBETA-CELLS

We have previously identified expression of multiple protein kinase C( PKC) isoforms in insulinoma-derived beta-cells and whole islets. Both PKC delta and PKC alpha appear to be the more abundantly expressed iso forms. In this report we studied the effects of arachidonic acid (AA) on the subcellular distribution of PKC alpha and PKC delta. AA has bee n reported to activate both PKC alpha and PKC delta and it is thought to be an important second messenger in beta-cells. Here we report that AA interacted with and altered beta-cell pools of PKC delta preferent ially over PKC alpha. AA (100 mu M) over the course of 45 min reduced cytosolic levels of PKC delta (to 40 +/- 15%, compared to time zero co ntrol) leaving membrane and cytoskeleton-associated levels near contro l levels. Analysis of whole cell homogenates showed a slight downregul ation of PKC delta indicating proteolysis. The down-regulation of cyto solic PKC delta appeared to be isoform specific since cytosolic PKC al pha remained at control levels over the time course. The response was dose-dependent and negligible at concentrations below 30 mu M and occu rred, at least partially, in the cytosolic compartment of the cell. In domethacin also down-regulated cytosolic PKC delta preferentially over PKC alpha possibly through accumulation of AA. These findings suggest that cytosolic PKC delta may be a downstream target of this beta-cell second messenger. (C) 1996 Wiley-Liss, Inc.