Abstract 2301: E2-induced T47D:A18/PKCα tumor regression is accompanied by translocation of ERα to extranuclear sites in association with caveolin-1

Proceedings: AACR 102nd Annual Meeting 2011‐‐ Apr 2‐6, 2011; Orlando, FL Background: Acquired resistance to tamoxifen (TAM) is a serious clinical problem in the treatment of breast cancer patients. Our laboratory developed and characterized a TAM-resistant and 17 beta-estradiol (E2) independent preclinical model where PKCα was stably transfected into T47D:A18 cells compared with the E2-dependent T47D:A18/neo cells (Chisamore et al, 2001). We and others have shown that PKCα overexpression is associated with TAM resistance in cell lines and in the clinic (Tonetti et al, 2003, Assender et al, 2007). Additionally the T47D:A18/PKCα model exhibits E2-induced tumor regression in vivo or when grown in matrigel (3D matrix) but not on 2D plastic. Recently we have demonstrated that tumor regression involves participation of estrogen receptor alpha (ERα), Fas/FasL and the extracellular matrix (Zhang et al, 2009). Interestingly the membrane impermeable E2-BSA conjugate mediates growth inhibition of T47D:A18/PKCα colonies in matrigel similar to E2 suggesting a potential role of extranuclear ERα. On the basis of our preliminary data we investigated whether extranuclear ERα signaling pathway might play a critical role in E2-induced tumor regression. Materials and methods: Four micrometer thick sections were prepared from paraffin embedded T47D:A18/PKCα tumor tissues from untreated (control) and E2-treated mice and T47D:A18/neo tumors. Fluorescence tagged secondary antibodies were used for immunofluorescence staining. Co-immunoprecipitation (coIP) was done with control and E2 treatment group tumor extracts. Results: Immunofluorescence images of T47D:A18/PKCα tumor sections from untreated control mice showed that the ERα was mainly localized in the nucleus. Interestingly, treatment with E2 resulted in significant translocation of ERα from the nucleus to the cytoplasm and the plasma membrane of tumor cells. However in T47D:A18/neo tumors the majority of ERα was found in the nucleus suggesting the involvement of ERE mediated classical pathway in tumor growth. Confocal microscopy clearly indicates the colocalization of ERα with caveolin-1 in E2-treated T47D:18/PKCα tumor sections. Furthermore coIP performed with T47D:A18/PKCα tumor extracts revealed greater association of ERα with caveolin-1 in E2-treated tumors compared with control tumors. Discussion: We present evidence that E2-induced regression of our clinically relevant PKCα-overexpressing tumor model is accompanied by translocation of ERα to extranuclear sites in association with caveolin. This result suggests that E2-induced tumor regression is likely to be mediated by a membrane-associated signaling pathway. Therapies that stimulate the extranuclear ERα signaling pathway in PKCα overexpressing tumors may be an attractive approach to treat endocrine resistant tumors. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 2301. doi:10.1158/1538-7445.AM2011-2301