Regulation of mammalian pyruvate dehydrogenase alpha subunit gene expression by glucose in HepG2 cells

We report the effect of glucose on the expression of the gene encoding the pyruvate dehydrogenase (E1) alpha subunit (E1 alpha) in human hepatoma (Hep G2) cells. Total pyruvate dehydrogenase complex activity as well as the lev els of protein and mRNA of the E1 alpha subunit were significantly increase d in HepG2 cells cultured in medium containing 16.7 mM glucose compared wit h 1.0 mM glucose for a period of 4 weeks. The level of E1 alpha mRNA was el evated approx. 2-fold in HepG2 cells cultured for 24h in medium containing 16.7 mM glucose compared with 1 mM glucose. This effect was specific to glu cose and independent of insulin. Nuclear run-on assays and promoter analysi s indicate that the glucose-induced increases in the levels of E1 alpha mRN A in HepG2 cells are due to increased transcription of the human E1 alpha ( PDHA1) gene. Mutational analysis of the E1 alpha promoter region has identi fied two regions, from -78 to -73 bp (CCCCTG) and from -8 to -3 bp (GCGGTG) , that are responsible for the effect of glucose on promoter activity; the former exhibits a larger effect. These two sequences represent new variatio ns of the carbohydrate-response element that has been identified in other g enes. The stimulation of E1 alpha promoter activity by glucose was abolishe d by okadaic acid at 100 nM but not at 5 nM, suggesting that glucose-mediat ed regulation of pyruvate dehydrogenase complex E1 alpha gene transcription involves a phosphorylation/dephosphorylation mechanism, possibly involving protein phosphatase-1.