Novel interactions between ERα-36 and STAT3 mediate breast cancer cell migration

Background Breast cancer is the leading cause of cancer death in women worldwide which is closely related to metastasis. But the exact molecular mechanism of ER alpha-36 and STAT3 on metastasis is still not fully understood. Methods MCF-7 and MDA-MB-231 human breast cancer cell lines and MCF-10A were overexpressioned or knockdown ER alpha-36 and STAT3 and tested for migration, invasion and proliferation assays. Direct interaction of STAT3 and ER alpha-36 were analyzed by coimmunoprecipitation assays. The effect of STAT3 and ER alpha-36 on MMP2/9 expression was analyzed by qPCR and western blotting. STAT3 phospholyation and acetylation by ER alpha-36 and p300 were observed and quantified by coimmunoprecipitation assays and western blotting. Results Cross-talk between ER alpha-36 and STAT3 was demonstrated to mediate through a direct physical association between the two proteins. Furthermore, the interaction between ER alpha-36 and STAT3 was demonstrated to give rise to functional changes in their signaling events. Both MMP2 and MMP9 expression require the binding of the newly identified protein complex, ER alpha-36-STAT3, to its promoter, the second phase, which is more robust, depends on ER alpha-mediated recruitment of p300 onto the complex and the subsequent acetylation of STAT3. In addition, STAT3 is tyrosine-phosphorylated in a biphasic manner, and the late phase requires ER alpha-36-mediated p300-dependent acetylation. Furthermore, interference with acetylation of STAT3 by overexpression of acetylation null STAT3 mutant led to the loss of MMP2 and MMP9 expression. ChIP analysis and reporter gene assays revealed that ER alpha-36-STAT3 complex binding to the MMP2 and MMP9 promoter led to an enhanceosome formation and facilitated MMP2 and MMP9 expression. Conclusions Our studies demonstrate for the first time that the function of MMP2 and MMP9 in breast cancer cell migration, which is mediated by interactions between ER alpha-36 and STAT3.