The hexosamine biosynthetic pathway induces gene promoter activity of acetyl-CoA carboxylase beta.

The cardiac isoform of acetyl-CoA carboxylase (ACCβ) produces malonyl-CoA, a potent inhibitor of mitochondrial fatty acid (FA) uptake. Higher ACCβ activity decreases FA utilization, potentially leading to intracellular myocardial lipid accumulation and insulin resistance (IR). Since increased hexosamine biosynthetic pathway (HBP) flux is linked to IR onset, we hypothesized that HBP activation leads to the induction of ACCβ gene promoter activity. Rat H9c2 cardio-myoblasts were transiently transfected with a 1317bp human ACCβ promoter-luciferase construct (pPIIβ-1317)±an expression construct encoding the HBP rate-limiting step, i.e., glutamine:fructose 6-phosphate amidotransferase (GFAT)±various HBP modulators. The administration of l-glutamine (HBP substrate) dose-dependently increased, while HBP inhibitors attenuated pPIIβ-1317 activity. Co-transfections with dominant-negative GFAT constructs diminished pPIIβ-1317 activity. To explore underlying transcriptional mechanisms, we co-transfected with upstream stimulatory factor (USF) expression constructs and found that USF2 induced pPIIβ-1317 activity vs. controls. Moreover, co-transfection of a GFAT expression construct+USF reporter-promoter construct (with consensus USF binding elements) led to induction of pPIIβ-1317 activity vs. controls. We next performed transfections with GFAT±full length ACCβ and seven truncated promoter-luciferase constructs, respectively. Here GFAT-mediated ACCβ promoter induction was blunted when co-transfected with the pPIIβ-38/+65 deletion construct indicating that USF2 binds to the proximal ACCβ promoter region (near start codon). Our study demonstrates that HBP activation induces ACCβ gene promoter activity in H9c2 cells via USF2. We propose that such ACCβ induction may elicit serious downstream effects, e.g. the inhibition of FA β-oxidation and the onset of IR.

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