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

Abstract

We report the effect of glucose on the expression of the gene encoding the pyruvate dehydrogenase (E1) α subunit (E1α) in human hepatoma (HepG2) cells. Total pyruvate dehydrogenase complex activity as well as the levels of protein and mRNA of the E1α subunit were significantly increased in HepG2 cells cultured in medium containing 16.7 mM glucose compared with 1.0 mM glucose for a period of 4 weeks. The level of E1α mRNA was elevated approx. 2-fold in HepG2 cells cultured for 24 h in medium containing 16.7 mM glucose compared with 1 mM glucose. This effect was specific to glucose and independent of insulin. Nuclear run-on assays and promoter analysis indicate that the glucose-induced increases in the levels of E1α mRNA in HepG2 cells are due to increased transcription of the human E1α (PDHA1) gene. Mutational analysis of the E1α promoter region has identified 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 variations of the carbohydrate-response element that has been identified in other genes. The stimulation of E1α promoter activity by glucose was abolished by okadaic acid at 100 nM but not at 5 nM, suggesting that glucose-mediated regulation of pyruvate dehydrogenase complex E1α gene transcription involves a phosphorylation/dephosphorylation mechanism, possibly involving protein phosphatase-1.