Tyrosine phosphorylation of transcriptional coactivator WW-domain binding protein 2 regulates estrogen receptor α function in breast cancer via the Wnt pathway

WW-binding protein 2 (WBP2) has been demonstrated in different studies to be a tyrosine kinase substrate, to activate estrogen receptor alpha (ER alpha)/progesterone receptor (PR) transcription, and to play a role in breast cancer. However, the role of WBP2 tyrosine phosphorylation in regulating ER alpha function and breast cancer biology is unknown. Here, we established WBP2 as a tyrosine phosphorylation target of estrogen signaling via EGFR crosstalk. Using dominant-negative, constitutively active mutants, RNAi, and pharmacological studies, we demonstrated that phosphorylation of WBP2 at Tyr192 and Tyr231 could be regulated by c-Src and c-Yes kinases. We further showed that abrogating WBP2 phosphorylation impaired >60% of ER alpha reporter activity, putatively by blocking nuclear entry of WBP2 and its interaction with ER alpha. Compared to vector control, overexpression of WBP2 and its phospho-mimic mutant in MCF7 cells resulted in larger tumors in mice, induced loss of cell-cell adhesion, and enhanced cell proliferation, anchorage-independent growth, migration, and invasion in both estrogen-dependent and -independent manners, events of which could be substantially abolished by overexpression of the phosphorylation-defective mutant. Hormone independence of cells expressing WBP2 phospho-mimic mutant was associated with heightened ER alpha and Wnt reporter activities. Wnt/beta-catenin inhibitor FH535 blocked phospho-WBP2-mediated cancer cell growth more pronouncedly than tamoxifen and fulvestrant, in part by reducing the expression of ER alpha. Wnt pathway is likely to be a critical component in WBP2-mediated breast cancer biology.-Lim, S. K., Orhant-Prioux, M., Toy, W., Tan, K. Y., Lim, Y. P. Tyrosine phosphorylation of transcriptional coactivator WW-domain binding protein 2 regulates estrogen receptor alpha function in breast cancer via the Wnt pathway. FASEB J. 25, 3004-3018 (2011). www.fasebj.org