Abstract B29: The role of C-Terminal Binding Proteins in BRCA1 silencing and genetic instability of ovarian cancer cells

Abstract

Abstract Objective: Ovarian cancer is the leading cause of mortality from gynecological malignancy in Western countries. High-grade serous ovarian carcinoma (HGSOC) is characterized by genetic instability and frequently harbors defects in genes such as BRCA1 for homologous recombination (HR) pathway. Our group recently demonstrated that the transcriptional co-repressors, C-Terminal Binding Proteins (CtBP1 and CtBP2), are overexpressed in epithelial ovarian carcinoma and CtBP2 overexpression is associated with poor patient survival. We sought to relate the expression of CtBP to genetic instability and chemoresponse in HGSOC cells. Methods: Gene expression profiling was performed for the control and CtBP2-knockdown ovarian cancer cell lines. Chromatin Immunoprecipitation (ChIP)-qPCR assays and a BRCA1 promoter-luciferase reporter assay were performed to compare the binding of CtBP complex to BRCA1 promoter and the activity of BRCA1 promoter in the ovarian cancer cells. Cell cycle status of the cell lines was determined by flow cytometry. DNA double-strand breaks (DSB) were determined by comet assay. esults: Analysis of gene expression profiles revealed potential functions of CtBP2 in silencing the expression of a panel of genes such as BRCA1 and Fanconi anemia complementation group gene FANCD2 that are involved in HR pathway, cell cycle checkpoints, and genetic instability. ChIP analyses and the luciferase assays strongly suggest that the CtBP2 complex binds to the BRCA1 promoter and represses BRCA1 transcription. Ovarian cancer cell lines with knockdown of either CtBP1 or CtBP2 showed increased expression of BRCA1 protein. CtBP2-knockdown ovarian cancer cells showed increased apoptosis and arrest in cell cycle. These cell lines also showed a significant increase in DSB after gamma irradiation than wild-type control cells in a comet assay. Conclusions: CtBP1 and CtBP2 function in the suppression of a panel of target genes such as BRCA1 and FANCD2 that are involved in cell cycle checkpoints and HR pathway. CtBP-mediated BRCA1 silencing may be a significant contributing mechanism for genetic instability and clinicopathologic development of HGSOC. Targeting this epigenetic mechanism may enhance the sensitivity of HGSOC to DNA damaging agents and contribute to improved outcome of ovarian cancer patients. Citation Format: Shubai Liu, Junzheng Yang, Taymaa May, Yuanyuan Hua, Shi Lu, Kevin Elias, Ronny Drapkin, William Welch, Christopher Crum, Ross S. Berkowitz, Shu-Wing Ng. The role of C-Terminal Binding Proteins in BRCA1 silencing and genetic instability of ovarian cancer cells. [abstract]. In: Proceedings of the AACR Special Conference on Advances in Ovarian Cancer Research: From Concept to Clinic; Sep 18-21, 2013; Miami, FL. Philadelphia (PA): AACR; Clin Cancer Res 2013;19(19 Suppl):Abstract nr B29.