Insulin increases branched-chain α-ketoacid dehydrogenase kinase expression in Clone 9 rat cells

Abstract

The branched-chain amino acids (BCAA) are committed to catabolism by the activity of the branched-chain α-ketoacid dehydrogenase (BCKD) complex. BCKD activity is regulated through the action of the complex-specific BCKD kinase that phosphorylates two serine residues in the E1α subunit. Greater BCKD kinase expression levels result in a lower activity state of BCKD and thus a decreased rate of BCAA catabolism. Activity state varies among tissues and can be altered by diet, exercise, hormones, and disease state. Within individual tissues, the concentration of BCKD kinase reflects the activity state of the BCKD complex. Here we investigated the effects of insulin, an important regulator of hepatic metabolic enzymes, on BCKD kinase expression in Clone 9 rat cells. Insulin effected a twofold increase in message levels and a twofold increase in BCKD kinase protein levels. The response was completely blocked by treatment with LY-294002 and partially blocked by rapamycin, thus demonstrating a dependence on phosphatidylinositol 3-kinase and mTOR function, respectively. These studies suggest that insulin acts to regulate BCAA catabolism through stimulation of BCKD kinase expression.