Hypoxia-mediated up-regulation of MGr1-Ag/37LRP in gastric cancers occurs via hypoxia-inducible-factor 1-dependent mechanism and contributes to drug resistance

Abstract

Our previous study demonstrated hypoxia-inducible factor- 1(HIF-1) could prompt multidrug resistance (MDR) phenotype and MGr1-Ag/37LRP, a novel drug-resistance protein was reported by our labortary, associated with multidrug resistance in gastric cancer. Given this association, we hypothesized that MGr1-Ag/37LRP contributed to HIF-1-dependent hypoxiainduced MDR phenotype. Initial experiments revealed that blocking MGr1-Ag/37LRP expression by siRNA in gastric cancer cells effectively reversed multidrug resistance phenotype induced by hypoxia. Subsequent analysis of MGr1-Ag/37LRP mRNA and protein in gastric cancer cells revealed a time-dependent manner increase with hypoxia. While the up-regulation of MGr1-Ag/ 37LRP was abolished by HIF-1 inhibition with siRNA. Studies using luciferase promoter constructs revealed a significant increase in activity in cells subject to hypoxia and such hypoxia inducibility was lost in cells co-transfected siRNA targeting HIF-1. Analysis of the MGr1-Ag/37LRP promoter revealed several potential binding sites for HIF-1. Electrophoretic mobility shift assay and chromatin immunoprecipitation demonstrated a functional HIF-1 binding site within MGr1-Ag/37LRP gene regulatory sequence located at -16 to -11 relative to the transcriptional initiation point. These observations demonstrate that MGr1-Ag/ 37LRP is actively engaged by hypoxia and represent a novel HIF- 1 target. Such results suggest hypoxiaelicited MGr1-Ag/37LRP expression as a pathway for resistance of gastric cancer to chemo- therapeutics. © 2008 Wiley-Liss, Inc.