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-ketoacid dehydrogenase
kinase expression in Clone 9 rat cells
2 Department of Genetics and 1 Graduate Program in Nutrition and Health Sciences, Emory University School of Medicine, Atlanta, Georgia 30322
The branched-chain
amino acids (BCAA) are committed to catabolism by the activity
of the branched-chain
-ketoacid dehydrogenase (BCKD) complex. BCKD
activity is regulated through the action of the complex-specific BCKD
kinase that phosphorylates two serine residues in the E1
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.
hormone-controlled gene expression; branched-chain amino acids
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