Atypical protein kinase C in insulin action and insulin resistance

It now seems clear that all (atypical protein kinase C) isoforms are required for insulin-stimulated glucose transport in muscle and adipocytes. Moreover, there are marked defects in the activation of aPKCs under a variety of insulin-resistant conditions in humans, monkeys and rodents. in humans, defects in aPKC in muscle are seen in Type II diabetes and its precursors, obesity, the obesity-associated polycystic ovary syndrome and impaired glucose tolerance. These defects in muscle all activation are due to both impaired activation of insulin receptor substrate-1-dependent PI3K (phosphoinositide 3-kinase) and the direct activation of all by the lipid product of PI3K, PI-3,4,5-(PO(4))(3). Although it is still uncertain which underlying defect comes first, the resultant defect in all activation in muscle most certainly contributes significantly to the development of skeletal muscle insulin resistance. of further note, unlike the seemingly ubiquitous presence of defective all activation in skeletal muscle in insulin-resistant states, the activation of all is normal or increased in livers of Type II diabetic and obese rodents. The maintenance of aPKC activation in the liver may explain how insulin-dependent lipid synthesis is maintained in these states, as all function mainly in the activation of enzymes important for lipid synthesis. Thus increased activation of liver aPKC in hyperinsulinaemic states may contribute significantly to the development of hyperlipidaemia in insulin-resistant states.