Protein kinase C: mediator or inhibitor of insulin action?

The role of protein kinase C in insulin signal transduction is controversial. It has been postulated that protein kinase C is activated by insulin and that the kinase is directly involved in insulin-mediated metabolic processes. In opposition to this view is the hypothesis that protein kinase C is not activated by insulin and, more importantly, may be responsible for attenuation of the insulin signal. The evidence for and against protein kinase C as a mediator of the insulin signal will be put in perspective followed by discussion of the possible role of the kinase in the pathogenesis of insulin resistance in type II diabetes.