The hexosamine biosynthetic pathway induces gene promoter activity of the cardiac-enriched isoform of acetyl-CoA carboxylase

[摘要] ENGLISH ABSTRACT: The cardiac isoform of acetyl-CoA carboxylase (ACCβ) produces malonyl-CoA, a potent inhibitor of mitochondrial fatty acid (FA) uptake; thus increased ACCβ activity decreases fatty acid utilization thereby potentially leading to intracellular myocardial lipid accumulation and insulin resistance (IR). Previous studies show that greater flux through the hexosamine biosynthetic pathway (HBP) contributes to the development of IR. In light of this, we hypothesize that increased HBP flux induces ACCβ gene expression thereby contributing to the onset of IR. Our initial work focused on ACCβ gene promoter regulation and suggest that the HBP modulates upstream stimulatory factor 2 (USF2) thereby inducing ACCβ gene expression. Here, we further investigated HBP-mediated regulation of ACCβ gene expression by transiently transfecting cardiac-derived H9c2 cells with an expression vector encoding the rate-limiting HBP enzyme (GFAT) ± the full length ACCβ and 4 truncated promoter-luciferase constructs, respectively. GFAT overexpression increased ACCβ gene promoter activity for the full length and 3 larger deletion constructs (p<0.001 vs. controls). However, GFAT-mediated and USF2-mediated ACCβ promoter induction was blunted when co-transfected with the -38/+65 deletion construct suggesting that USF2 binds to the proximal promoter region (near start codon). Further investigation proves that USF2 binds to ACCβ promoter and activates it, but that USF2 is not O-GlcNAc modified even though there is a strong correlation between increased O-GlcNac levels and USF2 activation of ACCβ. This would suggest that there is another O-GlcNac modified factor involved in this regulatory pathway. Our study demonstrates that increased HBP flux induces ACCβ gene promoter activity via HBP modulation of USF2. We propose that ACCβ induction reduces fatty acid oxidation, thereby leading to intracellular lipid accumulation (FA uptake>>FA oxidation) and the onset of cardiac IR.

[发布机构] Stellenbosch University