Involvement of hypoxia-inducible factor-1-α in multidrug resistance induced by hypoxia in HepG2 cells

Aim of the study was to explore the influence of hypoxia on multidrug resistance related genes and the potential role of hypoxia-inducible factor-1-alpha (HIF-1 alpha) in formation of multidrug resistance in HepG2 human hepatocellular carcinoma cell line. HepG2 cells were subjected to hypoxia in a cohort of exposed time. A cell model stably expressing HIF-1 alpha was established by liposome-mediated transfection of plasmid pcDNA3/HIF-1 alpha, into HepG2 cells. Apoptosis of HepG2 cells exposed to hypoxia or transfected by plasmid pcDNA3/HIF-1 alpha was detected by Flow Cytometry after administration of chemotherapeutic drug (5-Fu). Real-time fluorescent quantitative PCR and Western-blot technique were used to analyze the expressions of multidrug resistance related genes mdr1, MRP1 and LRP at mRNA and protein level, respectively. Apoptosis Index of HepG2 cells exposed to hypoxia stepped down as exposed time extended after administration of 5-Fu. The expression of mdr1, MRP1 and LRP gene and protein revealed a hypoxic time-dependent induction and was synchronous with the alterations of HIF-1 alpha in HepG2 cells exposed to hypoxia. The expressions of these multidrug resistance related genes were remarkably increased in HIF-1 alpha transfected HepG2 cells as compared to empty vector transfected cells. Apoptosis index of HIF-1 alpha transfected cells was obviously less than that of control cells when they were simultaneously exposed to 5-Fu for 24hrs. In conclusion, ambient hypoxia might be one of the causes for the formation of multidrug resistance in HepG2 human hepatocellular carcinoma cell line. Hypoxia-elicited multidrug resistance related protein expression might be a pathway for resistance of HepG2 cells to chemotherapeutics and HIF-1 alpha might be involved in this process.