Abstract: Objective Exposure to estrogen is an important independent determinant factor of breast cancer. Many estrogen responsive proteins play an important role in breast cancer occurrence and development. Our study is to investigate the effects of 17β-estradiol(E2) and ICI182,780 (the estrogen receptor antagonist, Faslodex), at different concentrations and different times, on the expression level of the PDZK1(PDZ domain containing 1) protein in ER-MDA-MB-231, MCF-7 cell lines which were ER(+) and MDA-MB-231 cell lines which were ER(-). Methods MDA-MB-231, ER-MDA-MB-231 and MCF-7 cell lines were all incubated for 48 hours in RPMI 1640 medium which was free of phenol red supplemented with 10% charcoal-stripped fetal bovine serum, which aimed to remove the estrogen effects of fetal bovine serum and estrogen-like effects of phenol red in the medium respectively. Western Blot was used to analyse the expression levels of PDZK1 protein in MCF-7 and ER-MDA-MB-231, two ER(+) breast cancer cell lines, at different time points with different doses of 17β-estradiol and ICI182,780. The ER(-) cell line, MDA-MB-231, was used as control. Results Physiological 17β-estradiol could obviously up-regulate PDZK1 protein expression level in ER(+) breast cancer cell lines. The Western Blot analysis showed that after the treatment of 17β-estradiol at the concentration of 10^-8 mol/L for 72 hours, the PDZK1 protein expression level was significantly up-regulated in the two strains of MCF-7 and ER-MDA-MB-231 breast cancer cell lines, which was time and dose dependent. Compared with 17β-estradiol, the effects of ICI182,780 was the exactly opposite: after the treatment with ICI182,780 at the concentration of 10^-6 mol/L for 36 hours, the PDZK1 protein expression level was suppressed in ER-MDA-MB-231 significantly. The ICI182,780 effects were obvious when the concentration was 10^-5 mol/L. In MDA-MB-231 breast cancer cell line which was ER(-), the expression level of PDZK1 did not change as much as the ER(+) breast cancer cell lines, when treated with the same concentration of 17β-estradiol and ICI182,780 at the same time. Conclusion Our study demonstrates that the PDZK1 protein is estrogen responsive. The expression level of PDZK1 protein in ER(+) breast cancer cell lines was mediated through ER signaling transduction pathway. 17β-estradiol and ICI182,780 may affect the cell growth and the drug resistance by regulating the expression level of PDZK1. This finding may provide a new theoretical basis for ER(+) breast cancer endocrinotherapy.

Key words: estrogen, ICI182, breast cancer cells, PDZK1 protein