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Extranuclear ER? is associated with regression of T47D PKC?-overexpressing, tamoxifen-resistant breast cancer.

ABSTRACT:

Background

Prior to the introduction of tamoxifen, high dose estradiol was used to treat breast cancer patients with similar efficacy as tamoxifen, albeit with some undesirable side effects. There is renewed interest to utilize estradiol to treat endocrine resistant breast cancers, especially since findings from several preclinical models and clinical trials indicate that estradiol may be a rational second-line therapy in patients exhibiting resistance to tamoxifen and/or aromatase inhibitors. We and others reported that breast cancer patients bearing protein kinase C alpha (PKC?)- expressing tumors exhibit endocrine resistance and tumor aggressiveness. Our T47D:A18/PKC? preclinical model is tamoxifen-resistant, hormone-independent, yet is inhibited by 17?-estradiol (E2) in vivo. We previously reported that E2-induced T47D:A18/PKC? tumor regression requires extranuclear ER? and interaction with the extracellular matrix.

Methods

T47D:A18/PKC? cells were grown in vitro using two-dimensional (2D) cell culture, three-dimensional (3D) Matrigel and in vivo by establishing xenografts in athymic mice. Immunofluoresence confocal microscopy and co-localization were applied to determine estrogen receptor alpha (ER?) subcellular localization. Co-immunoprecipitation and western blot were used to examine interaction of ER? with caveolin-1.

Results

We report that although T47D:A18/PKC? cells are cross-resistant to raloxifene in cell culture and in Matrigel, raloxifene induces regression of tamoxifen-resistant tumors. ER? rapidly translocates to extranuclear sites during T47D:A18/PKC? tumor regression in response to both raloxifene and E2, whereas ER? is primarily localized in the nucleus in proliferating tumors. E2 treatment induced complete tumor regression whereas cessation of raloxifene treatment resulted in tumor regrowth accompanied by re-localization of ER? to the nucleus. T47D:A18/neo tumors that do not overexpress PKC? maintain ER? in the nucleus during tamoxifen-mediated regression. An association between ER? and caveolin-1 increases in tumors regressing in response to E2.

Conclusions

Extranuclear ER? plays a role in the regression of PKC?-overexpressing tamoxifen-resistant tumors. These studies underline the unique role of extranuclear ER? in E2- and raloxifene-induced tumor regression that may have implications for treatment of endocrine-resistant PKC?-expressing tumors encountered in the clinic.

SUBMITTER: Perez White B

PROVIDER: S-EPMC3661391 | biostudies-literature | 2013 May

REPOSITORIES: biostudies-literature

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Extranuclear ERα is associated with regression of T47D PKCα-overexpressing, tamoxifen-resistant breast cancer.

Perez White Bethany B Molloy Mary Ellen ME Zhao Huiping H Zhang Yiyun Y Tonetti Debra A DA

Molecular cancer 20130501

<h4>Background</h4>Prior to the introduction of tamoxifen, high dose estradiol was used to treat breast cancer patients with similar efficacy as tamoxifen, albeit with some undesirable side effects. There is renewed interest to utilize estradiol to treat endocrine resistant breast cancers, especially since findings from several preclinical models and clinical trials indicate that estradiol may be a rational second-line therapy in patients exhibiting resistance to tamoxifen and/or aromatase inhib ...[more]

PMID: 23634843

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