Effects of insulin on the regulation of branched-chain α-keto acid dehydrogenase E1α subunit gene expression

Abstract

Alterations in dietary intake, especially of protein, may produce changes in the hepatic levels of the branched-chain alpha-keto acid dehydrogenase (BCKAD) complex. The possible role of insulin in the regulation of these observed changes in hepatic capacity for BCKAD expression was therefore examined. Steady-state RNA levels encoding three of the subunits, E1 alpha, E1 beta and E2, increased by 2-4-fold in the livers of mice starved for 3 days, a known hypoinsulinaemic state. In contrast, the levels of E1 beta and E2, but not E1 alpha, RNA were decreased when mice were fed 0% protein diets compared with the levels observed in mice fed standard (23%) or higher protein isocaloric diets. BCKAD subunit protein levels under these conditions changed co-ordinately even though the changes in RNA were not co-ordinate. The effects of hormonal changes that might be associated with these dietary changes were examined, using the rodent hepatoma cell line H4IIEC3. In these cells, the levels of E1 alpha protein and mRNA were significantly depressed in the presence of insulin. In contrast, the levels of E1 beta and E2 RNAs were not decreased by insulin. The half-lives of the E1 alpha and E2 RNAs were determined to be quite long, from 13 to 18 h, with insulin having no dramatic overall effect on the half-lives determined over 24 h. Therefore, it is likely that insulin directly affects the transcription of the E1 alpha gene rather than RNA stability in exerting its negative regulatory effect. This effect is specific to the E1 alpha subunit. The differences in BCKAD subunit RNA levels observed under various nutritional and developmental conditions may therefore be the result of the differential effects of insulin and other hormones on the multiple regulatory mechanisms modulating BCKAD subunit expression.

E1 Enzyme of the Pyruvate Dehydrogenase Complex in Corynebacterium glutamicum : Molecular Analysis of the Gene and Phylogenetic Aspects

“…show significant similarity (28 to 42% identity) to the known heterotetrameric E1 ␣-subunits of the BCOADHC from B. subtilis (69), S. avermitilis (60), P. putida (6), T. thermophilus (36), and M. musculus (10). All these BCOADHC E1 ␣-proteins cluster with the PDHC E1 ␣-proteins of the low-GC-content gram-positive bacteria (Fig.…”

The Immunosuppressant Rapamycin Mimics a Starvation-Like Signal Distinct from Amino Acid and Glucose Deprivation

“…These include well-characterized genes such as BCKAD E1 alpha, UCP2, and SREBP-1 (9,21,35,38). Like caloric restriction of mice, rapamycin affects many genes involved in protein synthesis, folding, and turnover (22).…”

Regulation of adipose branched-chain amino acid catabolism enzyme expression and cross-adipose amino acid flux in human obesity

“…In a murine model of transgenic overexpression of the glucose transporter GLUT-4 in adipocytes, expression of some BCAA catabolism enzymes was found to be reduced (22). Studies by Costeas and Chinsky in rat H4IIEC3 hepatoma cells indicated depression of E1␣ subunit mRNA and protein by insulin treatment (8,10). Whether these contrasting results reflect specific nuances to the chronic GLUT-4 overexpression model or cell-type-specific effects remains to be determined, and the specific associations between insulin and glucose homeostasis and BCAA catabolism remain to be clarified.…”