The hexosamine pathway regulates the plasminogen activator inhibitor-1 gene promoter and Sp1 transcriptional activation through protein kinase C-βI and -δ

Abstract

Increased flux through the hexosamine biosynthesis pathway (HBP) has been shown to stimulate the expression of a number of genes. We previously demonstrated in glomerular mesangial and endothelial cells that both high glucose concentrations and glucosamine activated the plasminogen activator inhibitor-1 (PAI-1) gene promoter through the transcription factor, Sp1; and that the glutamine:fructose-6-phosphate amidotransferase inhibitor, 6-diazo-5-oxonorleucine, inhibited the effect of high glucose, but not that of glucosamine. Here, we examined the role of protein kinase C (PKC) isoforms in the regulation of the PAI-1 promoter and Sp1 transcriptional activity by the HBP. In transient transfections, exposure to 2 mM glucosamine or 20 mM glucose for 4 days increased the activities of a PAI-1 promoter-luciferase reporter gene as well as the Sp1 transcriptional activation domain fused to the GAL4 DNA-binding domain cotransfected with a GAL4 promoter-luciferase reporter. Cotransfected dominant negative PKC-β1 and -δ completely blocked the induction of PAI-1 promoter transcription by both sugars, whereas only dominant negative PKC-β1 interfered with Sp1-GAL4 activation. Both glucosamine and high glucose stimulated the in vitro kinase activity of immunoprecipitated PKC-βI and -δ. Furthermore, 6-diazo-5-oxonorleucine suppressed high glucose-induced PKC kinase activity and Sp1-GAL4 transcriptional activation. These findings demonstrate a requirement for the PKC-βI and -δ signal transduction pathways in HBP-induced transcription.