Estrogen receptor-α36 is involved in epigallocatechin-3-gallate induced growth inhibition of ER-negative breast cancer stem/progenitor cells

Epigallocatechin-3-gallate (egcg) is a type of catechin extracted from green tea,which is reported to have anticancer effects. egcg is also reported to inhibit the cancer stem/progenitor cells in several estrogen receptor (er)-negative breast cancer cell lines,such as sum-149,sum-190 and mda-mb-231. and all these cancer cells are highly expressed a new variant of er-α,er-α36. the aim of our present study is to determine the role of er-α36 in the growth inhibitory activity of egcg towards er-negative breast cancer mda-mb-231 and mda-mb-436 cells. we found that egcg potently inhibited the growth of cancer stem/progenitor cells in mda-mb-231 and mda-mb-436 cells,and also reduced the expression of er-α36 in these cells. however,in er-α36 knocked-down mda-mb-231 and mda-mb-436 cells,no significant inhibitory effects of egcg on cancer stem/progenitor cells were observed. we also found that down-regulation of er-α36 expression was in accordance with down-regulation of egfr,which further verified a loop between er-α36 and egfr. thus,our study indicated er-α36 is involved in egcg's inhibitory effects on er-negative breast cancer stem/progenitor cells,which supports future preclinical and clinical evaluation of egcg as a therapeutic option for er-α36 positive breast cancer. © 2015 japanese pharmacological society.