Abstract 733: Significance of PELP1/SETDB1 axis in endocrine therapy resistance

Abstract

Abstract BACKGROUND: PELP1 is commonly overexpressed in breast cancer (BCa) and is implicated in endocrine therapy resistance. However, the mechanism by which PELP1 contributes to therapy resistance remains elusive. Our ongoing studies using yeast two hybrid screen identified histone methyltransferase SETDB1 as a novel interactor of PELP1. The objective of this study is to determine the significance of PELP1 interaction with SETDB1 in BCa endocrine therapy resistance. METHODS: We used two ER+ BCa cell lines (MCF7 and ZR75) and three endocrine therapy resistant cell lines (Tamoxifen resistant MCF7-TamR, Fulvestrant resistant MCF7-FR, Tamoxifen resistant MCF7-PELP1-cyto). Additional BCa models with stable overexpression and under expression of SETDB1 and PELP1 (MCF7-SETDB1-PELP1shRNA, ZR75-SETDB1-PELP1shRNA, ZR75-SETDB1, MCF7-SETDB1, MCF7-TamR-SETDB1shRNA, MCF7-FR-SETDB1shRNA) were generated using lentiviral transduction. Functional significance of cross-talk was tested using MTT, soft agar, and colony formation assays. Mechanistic studies were conducted using immunoprecipitation, Western blotting, and RT-qPCR. RESULTS: Analyses of TCGA databases showed that SETDB1 expression is positively correlated with PELP1 expression in ER+ BCa (r=0.30, p<0.0001). Immunoprecipitation assays using multiple ER+ BCa cell lysates confirmed the interaction of SETDB1 with PELP1. Using ER+ BCa models with overexpression of SETDB1 or knockdown, we provided evidence that SETDB1 plays an important role in the proliferation of BCa cells. PELP1 knockdown attenuated SETDB1 mediated BCa cells proliferation. SETDB1 upregulation contributed to tamoxifen resistance, while PELP1 knockdown re-sensitized cells to tamoxifen therapy. Further, endocrine therapy resistant model cells (MCF7-TamR, MCF7-FR, MCF7-PELP1-cyto) showed increased expression of SETDB1, and its knockdown sensitized them to endocrine therapy. Mechanistic studies revealed that PELP1 is needed for SETDB1 mediated Akt phosphorylation and activation of its downstream targets such as S6, and Cyclin D1. CONCLUSIONS: The results of study suggest that the PELP1/SETDB1 interactions contribute to endocrine therapy resistance via aberrant activation of Akt signaling. Targeting PELP1/SETDB1 axis could represent a new therapeutic avenue to mitigate endocrine resistance. Supported by VA grant I01BX004545 (R.K. Vadlamudi) Citation Format: Zexuan Liu, Junhao Liu, Weiwei Tang, Uday P. Pratap, Kristin A. Altwegg, Behnam Ebrahimi, Xiaonan Li, Gangadhara R. Sareddy, Suryavathi Viswanadhapalli, Ratna K. Vadlamudi. Significance of PELP1/SETDB1 axis in endocrine therapy resistance [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 733.