title: BRCA1 expression is epigenetically repressed in sporadic ovarian cancer cells by overexpression of C-terminal binding protein 2.
abstract: BACKGROUND
  Ovarian cancer is the leading cause of mortality from gynecological malignancy despite advancements in novel therapeutics. We have recently demonstrated that the transcriptional co-repressor C-terminal binding protein 2 (CtBP2) is overexpressed in epithelial ovarian carcinoma.
  
  
  METHODS
  Reverse-transcribed cDNA from CtBP2 wild-type and knockdown ovarian cancer cell lines was hybridized to Affymetrix Gene 1.0 ST microarrays, and differentially expressed genes were studied. Immunohistochemical analysis of CtBP2 and BRCA1 staining of ovarian tissues was performed. Chromatin immunoprecipitation (ChIP) and luciferase assays were carried out. The effect of the drugs 4-methylthio-2-oxobutyric acid (MTOB) and poly(ADP-ribose) polymerase (PARP) inhibitor Olaparib on CtBP2 wild-type and knockdown cell lines was examined using methylthiazol tetrazolium assays and an xCELLigence System.
  
  
  RESULTS
  Eighty-five genes involved in DNA repair, mitotic checkpoint, nucleosome assembly, and the BRCA1 network were differentially regulated by CtBP2 expression. ChIP and luciferase reporter assays using a BRCA1 promoter-regulated luciferase construct indicated that the CtBP2 complex binds the BRCA1 promoter and represses BRCA1 transcription. Immunohistochemistry illustrated a significant inverse CtBP2 and BRCA1 expression in a panel of malignant ovarian tumor tissues. The CtBP2 inhibitor MTOB suppressed ovarian cancer cell survival in a CtBP2-dependent manner. Ovarian cancer cells with CtBP2 knockdown did not display increased sensitivity to the PARP inhibitor Olaparib.
  
  
  CONCLUSIONS
  CtBP2 is an ovarian cancer oncogene that may play a significant role in epigenetically silencing BRCA1 function in sporadic epithelial ovarian cancer. CtBP2-specific inhibitors, such as MTOB, may be effective adjunct therapies in the management of patients with CtBP2-positive ovarian carcinoma.
authors.affiliation: Department of Obstetrics/Gynecology and Reproductive Biology, Division of Gynecologic Oncology, Brigham and Women's Hospital, Harvard Medical School, Boston, MA, USA.
authors.forename: Taymaa
authors.initials: T
authors.lastname: May
authors.forename: Junzheng
authors.initials: J
authors.lastname: Yang
authors.forename: Melina
authors.initials: M
authors.lastname: Shoni
authors.forename: Shubai
authors.initials: S
authors.lastname: Liu
authors.forename: Housheng
authors.initials: H
authors.lastname: He
authors.forename: Reddy
authors.initials: R
authors.lastname: Gali
authors.forename: Shu-Kay
authors.initials: SK
authors.lastname: Ng
authors.forename: Christopher
authors.initials: C
authors.lastname: Crum
authors.forename: Ross S
authors.initials: RS
authors.lastname: Berkowitz
authors.forename: Shu-Wing
authors.initials: SW
authors.lastname: Ng
mesh_terms: D000429:Alcohol Oxidoreductases / Q000037:antagonists & inhibitors / Q000235:genetics* / Q000378:metabolism; D019313:BRCA1 Protein / Q000235:genetics* / Q000378:metabolism; D000077216:Carcinoma, Ovarian Epithelial; D045744:Cell Line, Tumor; D002470:Cell Survival / Q000187:drug effects; D056970:Co-Repressor Proteins; D044127:Epigenesis, Genetic; D005260:Female; D020869:Gene Expression Profiling; D015972:Gene Expression Regulation, Neoplastic; D055785:Gene Knockdown Techniques; D006801:Humans; D008715:Methionine / Q000031:analogs & derivatives / Q000494:pharmacology; D009375:Neoplasms, Glandular and Epithelial / Q000188:drug therapy / Q000235:genetics* / Q000473:pathology; D009419:Nerve Tissue Proteins / Q000037:antagonists & inhibitors / Q000235:genetics* / Q000378:metabolism; D010051:Ovarian Neoplasms / Q000188:drug therapy / Q000235:genetics* / Q000473:pathology; D010793:Phthalazines / Q000494:pharmacology; D010879:Piperazines / Q000494:pharmacology; D000067856:Poly(ADP-ribose) Polymerase Inhibitors; D011065:Poly(ADP-ribose) Polymerases / Q000378:metabolism; D011401:Promoter Regions, Genetic
chemical_list: D019313:BRCA1 Protein; C492913:BRCA1 protein, human; D056970:Co-Repressor Proteins; D009419:Nerve Tissue Proteins; D010793:Phthalazines; D010879:Piperazines; D000067856:Poly(ADP-ribose) Polymerase Inhibitors; C014632:2-keto-4-methylthiobutyric acid; D008715:Methionine; D000429:Alcohol Oxidoreductases; C421248:CTBP2 protein, human; D011065:Poly(ADP-ribose) Polymerases; C531550:olaparib