Estrogen receptor (ER) beta is predicted to play an important role in prevention of breast cancer development and metastasis. We have shown previously that ERbeta inhibits hypoxia inducible factor (HIF)-1alpha mediated transcription, but the mechanism by which ERbeta works to exert this effect is not understood.

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 ERbeta on HIF-1 function.

In this study, we found that the inhibition of HIF-1 activity by ERbeta expression was correlated with ERbeta's ability to degrade aryl hydrocarbon receptor nuclear translocator (ARNT) via ubiquitination processes leading to the reduction of active HIF-1alpha/ARNT complexes. HIF-1 repression by ERbeta was rescued by overexpression of ARNT as examined by hypoxia-responsive element (HRE) -driven luciferase assays. We show further that ERbeta attenuated the hypoxic induction of VEGF mRNA by directly decreasing HIF-1alpha binding to the VEGF gene promoter.

These results show that ERbeta suppresses HIF-1alpha-mediated transcription via ARNT downregulation, which may account for the tumor suppressive function of ERbeta.

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