Hypoxia-mediated up-regulation of MGr1-Ag/37LRP in gastric cancers occurs via hypoxia-inducible-factor 1-dependent mechanism and contributes to drug resistance.
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 hypoxia-induced 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 hypoxia-elicited MGr1-Ag/37LRP expression as a pathway for resistance of gastric cancer to chemotherapeutics.
Liu
Lili
L
State Key Laboratory of Cancer Biology, Institute of Digestive Diseases, Xijing Hospital, Fourth Military Medical University, Xi'an, China.
Sun
Li
L
Zhang
Hongbo
H
Li
Zhichao
Z
Ning
Xiaoxuan
X
Shi
Yongquan
Y
Guo
Changcun
C
Han
Shuang
S
Wu
Kaichun
K
Fan
Daiming
D
D000230:Adenocarcinoma / Q000235:genetics / Q000378:metabolism*; D000818:Animals; D000951:Antigens, Neoplasm / Q000235:genetics / Q000378:metabolism*; D015153:Blotting, Western; D015687:Cell Hypoxia / Q000502:physiology*; D019008:Drug Resistance, Neoplasm / Q000502:physiology*; D024202:Electrophoretic Mobility Shift Assay; D005786:Gene Expression Regulation / Q000502:physiology; D006801:Humans; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000378:metabolism*; D047468:Immunoprecipitation; D051379:Mice; D034741:RNA, Small Interfering; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013274:Stomach Neoplasms / Q000235:genetics / Q000378:metabolism*; D015854:Up-Regulation
D000951:Antigens, Neoplasm; C497442:HIF1A protein, human; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; C470229:MGr1-antigen, human; D034741:RNA, Small Interfering