Phorbol Esters, but Not Insulin, Promote Depletion of Cytosolic Protein Kinase C in Rat Adipocytes

The tumor-promoting phorbol esters have insulinomimetic effects in several tissues. Employing two different assay systems, we have compared the effects of phorbol ester and insulin on the activity and intracellular distribution of the Ca++ and phospholipid dependent protein kinase (protein kinase C) in isolated rat adipocytes. Phorbol ester leads to a prompt depletion of kinase activity from the cytosolic fraction and appearance of activity in membrane extracts; neither of these effects is mimicked by insulin. These results, taken together with other data, emphasize important divergences between the actions of these agonists and suggest that changes in protein kinase C activity or intracellular distribution are not a necessary concomitant of the cascade of insulin action.