The Wilms' tumor suppressor WT1 regulates expression of members of the epidermal growth factor receptor (EGFR) and estrogen receptor in acquired tamoxifen resistance.

BACKGROUND In human breast cancer, a growth status switched from estrogen-dependent to growth factor-dependent is a critical step during development of acquired tamoxifen resistance. However, the molecular mechanisms underlying this switch remain poorly understood. The Wilms' tumor suppressor gene, WT1, encodes a zinc-finger protein WT1 that functions as a transcription regulator. High levels of the WT1 expression have been associated with de novo tamoxifen resistance. The goal of this study was to investigate the function of WT1 in acquired tamoxifen resistance. MATERIALS AND METHODS A stable tamoxifen-resistance cell line MCF7(TAM) was established by selecting ER-positive breast cancer MCF7 cells in a medium containing tamoxifen. Western blot, cell growth assay and shRNA method were used to examine the role of WT1 in acquired tamoxifen resistance. RESULTS MCF7(TAM) cells expressed EGFR, HER2 and WT1 at higher levels compared to tamoxifen-sensitive parental MCF7 cells. MCF7(TAM) cells responded weakly to estrogen stimulation, grew rapidly in the absence of estrogen and were insensitive to tamoxifen. We also established stable cell lines from MCF7(TAM) cells to express shRNA specific for WT1, and found expression levels of the epidermal growth factor receptor (EGFR), HER2 and estrogen receptor (ER)-α to be down-regulated in MCF7(TAM) cells with knocked-down levels of WT1 expression. MCF7(TAM) cells with WT1 expression knocked-down by shRNA still retained tamoxifen insensitivity. CONCLUSION Our results indicated that WT1 is involved in expressional regulation of the EGFR family members and ER-α during development of acquired tamoxifen resistance.