Estrogen receptor beta inhibits transcriptional activity of hypoxia inducible factor-1 through the downregulation of arylhydrocarbon receptor nuclear translocator

Introduction: Estrogen receptor (ER) beta is predicted to play an important role in prevention of breast cancer development and metastasis. We have shown previously that ER beta inhibits hypoxia inducible factor (HIF)-1 alpha mediated transcription, but the mechanism by which ER beta works to exert this effect is not understood. Methods: Vascular endothelial growth factor (VEGF) was measured in conditioned medium by enzyme-linked immunosorbent assays. Reverse transcription polymerase chain reaction (RT-PCR), Western blotting, immunoprecipitation, luciferase assays and chromatin immunoprecipitation (ChIP) assays were used to ascertain the implication of ER beta on HIF-1 function. Results: In this study, we found that the inhibition of HIF-1 activity by ER beta expression was correlated with ER beta's ability to degrade aryl hydrocarbon receptor nuclear translocator (ARNT) via ubiquitination processes leading to the reduction of active HIF-1 alpha/ARNT complexes. HIF-1 repression by ER beta was rescued by overexpression of ARNT as examined by hypoxia-responsive element (HRE)-driven luciferase assays. We show further that ER beta attenuated the hypoxic induction of VEGF mRNA by directly decreasing HIF-1 alpha binding to the VEGF gene promoter. Conclusions: These results show that ER beta suppresses HIF-1 alpha-mediated transcription via ARNT down-regulation, which may account for the tumour suppressive function of ER beta.