HER2 and ERβ2 downregulate estrogen-responsive element-mediated transcription activity of ERα-positive cells in response to estrogen stimulation

Although HER2 expression is more common in ER-negative and PR-negative breast cancers, HER2 overexpression is observed in ER-positive cancers and these cancers seem to have intrinsic resistance to endocrine treatment. There are controversial reports about the effect of HER2 on estrogen dependence. ERβ2 has been reported to act as a dominant-negative regulator of ERα in the breast, and ERβ1 and/or…