Cytoplasmic PELP1 and ERRgamma Protect Human Mammary Epithelial Cells from Tam-Induced Cell Death

Abstract

Tamoxifen (Tam) is the only FDA-approved chemoprevention agent for pre-menopausal women at high risk for developing breast cancer. While Tam reduces a woman's risk of developing estrogen receptor positive (ER+) breast cancer, the molecular mechanisms associated with risk reduction are poorly understood. Prior studies have shown that cytoplasmic proline, glutamic acid and leucine rich protein 1 (PELP1) promotes Tam resistance in breast cancer cell lines. Herein, we tested for PELP1 localization in breast epithelial cells from women at high risk for developing breast cancer and found that PELP1 was localized to the cytoplasm in 36% of samples. In vitro, immortalized HMECs expressing a nuclear localization signal (NLS) mutant of PELP1 (PELP1-cyto) were resistant to Tam-induced death. Furthermore, PELP1-cyto signaling through estrogen-related receptor gamma (ERRγ) promoted cell survival in the presence of Tam. Overexpression of ERRγ in immortalized HMECs protected cells from Tam-induced death, while knockdown of ERRγ sensitized PELP1-cyto expressing HMECs to Tam. Moreover, Tam-induced HMEC cell death was independent of apoptosis and involved accumulation of the autophagy marker LC3-II. Expression of PELP1-cyto and ERRγ reduced Tam-induced LC3-II accumulation, and knockdown of ERRγ increased LC3-II levels in response to Tam. Additionally, PELP1-cyto expression led to the upregulation of MMP-3 and MAOB, known PELP1 and ERRγ target genes, respectively. Our data indicate that cytoplasmic PELP1 induces signaling pathways that converge on ERRγ to promote cell survival in the presence of Tam. These data suggest that PELP1 localization and/or ERRγ activation could be developed as tissue biomarkers for Tam responsiveness.

Cytoplasmic Localization of Proline, Glutamic Acid, Leucine-rich Protein 1 (PELP1) Induces Breast Epithelial Cell Migration through Up-regulation of Inhibitor of κB Kinase ɛ and Inflammatory Cross-talk with Macrophages

“…Formation-We previously demonstrated that altered localization of PELP1 promotes HMEC survival in response to tamoxifen (14). To determine whether cytoplasmic PELP1 (PELP1-cyto) contributes to phenotypes associated with oncogenic signaling and breast cancer initiation, we first developed an additional HMEC model in MCF-10A cells to compare with our previously published HMEC-hTERT cell line model (14).…”

“…To determine whether cytoplasmic PELP1 (PELP1-cyto) contributes to phenotypes associated with oncogenic signaling and breast cancer initiation, we first developed an additional HMEC model in MCF-10A cells to compare with our previously published HMEC-hTERT cell line model (14). These cell lines were chosen as models of spontaneously immortalized and hTERT-immortalized HMECs, respectively, that are susceptible to oncogene-induced transformation.…”

“…Additionally, the MCF-10A model is useful for three-dimensional acini formation assays. As previously published for the HMEC-hTERT model (14), we established stable MCF-10A cell lines that express LXSN control or PELP1-cyto. Cells were selected for stable integration of PELP1 with G418.…”

“…Cytoplasmic PELP1 signaling has primarily been studied in breast cancer cell line models and in vivo mouse models (10,11,13). Recently, however, PELP1 localization was found to be altered in 4 of 11 (36%) atypical breast needle aspirate samples from women at high risk of developing breast cancer (14). These preclinical and preliminary clinical findings suggest that altered PELP1 localization may be an early event in breast cancer initiation.…”

Modifications to glucocorticoid and progesterone receptors alter cell fate in breast cancer

“…Relevant to mechanisms of altered PTMs to SRs in breast cancer, PELP1 is emerging as a driver of altered SR action (including ER, PR, GR, and AR) and endocrine resistance (Daniel et al 2015, Girard et al 2015. In breast cancer studies, PELP1 is restricted to the nucleus of normal MEC but is partially to largely cytoplasmic in a significant number of breast tumors in which its altered localization is associated with tamoxifen resistance (Vadlamudi et al 2005, Kumar et al 2009).…”