The roles of hypoxia inducible factors (HIFs) in regulating steroidogenic enzymes : an in vitro study using the H295R cells

Abstract

Aquatic hypoxia (defined as < 2.8 mg O2 L-1) is a global environmental problem affecting thousands of km2 of marine waters. Recent studies have shown that chronic hypoxia can disrupt steroidogenesis and reproduction in marine vertebrates and invertebrates. In vertebrates, the Hypoxia Inducible Factor-1, -2 and -3 (HIF-1, -2 and -3) transcription factors are known to regulate a variety of genes related to adaptive and survival responses to hypoxia. In this study, the human adrenocortical carcinoma cell line H295R was used as an in vitro model system to test the hypothesis that certain genes involved in steroidogenesis are regulated by the HIF proteins. H295R cells were transfected with individual HIF-1, -2 and -3 expression vectors, and the expression profiles of 10 genes controlling steroidogenic enzymes production were determined using quantitative real-time PCR. Two steroidogenic enzyme genes, StAR and 3-HSD2, were markedly down-regulated in H295R cells over-expressing HIF-1 (p < 0.01). When cells were over-expressed with HIF-3a, expression of CYP17 and CYP19 were significantly suppressed (p < 0.05). In contrast, HMGR and CYP11B1 were upregulated by more than one fold, while StAR, 17b-HSD1, CYP11a1, CYP21, CYP11B2 and 3-HSD2, were up-regulated by more than two folds (p < 0.05). HIF-2 however, did not mediate expression of any steroidogeneic genes studied. For the first time, this study provides evidence that expression of steroidogenic genes can be regulated by the HIF-1 and HIF-3 transcription factors. Our overall results lend support to the hypothesis that the observed disruption of sex hormones by hypoxia is mediated through HIF-1 and HIF-3, and HIF-3 may play a compensatory role in regulating genes responsible for steroidogenesis.