Activation of ClC-3 chloride channel by 17-estradiol relies on the estrogen receptor expression in breast cancer

Although extensively studied, the mechanisms by which estrogen promotes breast cancer growth remain to be fully elucidated. Tamoxifen, an antiestrogen agent to treat ER+ breast cancer, is also a high-affinity blocker of the chloride channels. In this study, we explored the involvement of the chloride channels in the action of estrogen in breast cancer. We found that 17-estradiol (17-E2) concentration-dependently activated the chloride currents in ER+ breast cancer MCF-7 cells. Extracellular hypertonic challenge and chloride channel blockers, NPPB and DIDS inhibited the 17-E2-activated chloride currents. Decreased the ClC-3 protein expression caused the depletion of the 17-E2-activated chloride currents. 17-E2-activated chloride currents which relied on the ER expression were demonstrated by the following evidences. Firstly, 17-E2-activated chloride currents could not be observed in ER- breast cancer MDA-MB-231 cells. Secondly, ER antagonists, tamoxifen and ICI 182,780, and downregulation of ER expression inhibited or abolished the 17-E2-activated chloride currents. Thirdly, ER expression was induced in MDA-MB-231 cells by ESR1 gene transfection, and then 17-E2-activated chloride currents could be observed. In MCF-7 cells, ER and ClC-3 mainly located in nucleus and translocated to cell plasma and membrane with respect to co-localization following treatment of 17-E2. Downregulation of ER expression could decrease the expression of ClC-3 protein. Conversely, downregulation of ClC-3 expression did not influence the ER expression. Taken together, our findings demonstrated that ClC-3 is a potential target of 17-E2 and is modulated by the ER in breast cancer cell. Pharmacological modulation of ClC-3 may provide a deep understanding in antiestrogen treatment of breast cancer patients.