High glucose induces transactivation of the α2-HS glycoprotein gene through the ERK1/2 signaling pathway

Abstract

Aim: Alpha2-Heremans Schmid glycoprotein (AHSG), also known as fetuin-A, is secreted from the liver and inhibits tyrosine kinase activity of the insulin receptor. Hyperglycemia in type 2 diabetes is not only a secondary manifestation of insulin resistance, but could also be responsible for directly inducing insulin resistance in target tissues. In this study, we examined the effect of high glucose (HG) on AHSG gene transcription in the human hepatoma cell line HepG2. Methods: AHSG transcriptional activity and protein expression were evaluated using reporter gene assays and Western blot analysis, respectively. Results: D-glucose, but not L-glucose or mannitol, dose-dependently enhanced AHSG promoter activity. HG (25 mM) also increased AHSG protein expression. No protein kinase C inhibitors (bisindolylmaleimide, Ro-31-8220), an inhibitor of hexosamine biosynthesis pathway (6-diazo-5-oxo-L-norleucine), or a superoxide radical scavenger (tempol) affected HG-induced transactivation. MAPK/ERK kinase inhibitors (PD98059, U0126), but not the JNK inhibitor (SP600125) or p38 inhibitor (SB203580), significantly inhibited promoter activation by HG. Conclusion: Our data suggest that HG enhances AHSG transcription through activation of the ERK1/2 signaling pathway. Increased AHSG expression in the liver may be a cause of glucose toxicity in the diabetic state.