Effect of increased expression of C-terminal binding protein-2 in epithelial ovarian carcinoma on DNA repair pathways and tumor response to histone deacetylase inhibitors.

Abstract

5075 Background: Ovarian cancer continues to be the leading cause of mortality from gynecological malignancy despite advancements in novel therapeutics. Our group recently demonstrated that C-terminal binding protein 2 (CtBP2) is overexpressed in epithelial ovarian carcinoma and alters their response to histone deacetylase (HDAC) inhibitors. We designed a study aimed at examining the differential gene expression between wild-type and CtBP2-knockdown cancer cell lines to identify key pathways regulated by CtBP2. Methods: Gene expression profiling was performed on CtBP2 wild type and knockdown cell lines. RNA was extracted, labeled and hybridized to Affymetrix Gene 1.0 ST Microarray. Differentially expressed genes were identified using D-Chip and SAM, validated using qRT-PCR and integrated into the Ingenuity Protein Analysis system. Key protein interactions were verified by co-immunoprecipitation assays and immunofluorescence microscopy. Protein expression levels were examined using immunohistochemistry (IHC) on 64 ovarian tissues and Western blot on 15 ovarian cancer cell lines. Results: Analyses of gene expression profiling resulted in 89 gene signatures largely involved in DNA repair. A significant number of differentially expressed genes were down-regulated in the knockdown cell lines, which is unexpected when CtBP2 is considered as a co-repressor. The nuclear protein Pinin was found to co-precipitate and co-localize with CtBP2 in the nucleus. IHC and Western blot studies showed significant overexpression of Pinin in carcinoma specimens compared to benign specimens (P<0.001). Conclusions: We propose that CtBP2 is an ovarian cancer oncogene that regulates gene expression by modulating HDAC activity and DNA repair. Specific nuclear interaction between CtBP2 and the co-regulator protein Pinin was discovered suggesting that Pinin may modify the co-repressor function of CtBP2 in ovarian carcinoma. Given that overexpression of CtBP2 decreases sensitivity of ovarian cancer cells to HDAC inhibitors, concurrent CtBP2 targeted therapy may enhance response of epithelial ovarian carcinoma to HDAC inhibitor therapy.