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Redox-dependent Brca1 transcriptional regulation by an NADH-sensor CtBP1.

Abstract
C-terminal binding protein 1 (CtBP1) is a transcriptional co-repressor and metabolic sensory protein, which often represses tumor suppressor genes. Hence, we sought to determine if CtBP1 affects expression of the tumor suppressor Brca1 in head and neck tissue, as downregulation of Brca1 begins at the early stages of head and neck squamous cell carcinomas (HNSCCs). We found that CtBP1 represses Brca1 transcription by binding to the E2F4 site of the Brca1 promoter. Additionally, the recruitment of CtBP1 to the Brca1 promoter is redox-dependent, that is, increased at high NADH levels in hypoxic conditions. Further, immunostaining using a human HNSCC tissue array revealed that nuclear CtBP1 staining began to accumulate in hyperplasic lesions and HNSCCs, this staining correlated with Brca1 downregulation in these lesions. Pharmacological disruption of CtBP1 binding to Brca1 promoter by the antioxidant Tempol, which reduces NADH levels, relieved CtBP1-mediated repression of Brca1, leading to increased DNA repair in HNSCC cells. As tumor cells are generally hypoxic with increased NADH levels, the dynamic control of Brca1 by a 'metabolic switch' found in this study not only provides an important link between tumor metabolism and tumor suppressor expression but also suggests a potential chemo preventative or therapeutic strategy for HNSCC by blocking NADH-dependent CtBP1 activity at early stages of HNSCC carcinogenesis.
AuthorsY Deng, J Liu, G Han, S-L Lu, S-Y Wang, S Malkoski, A C Tan, C Deng, X-J Wang, Q Zhang
JournalOncogene (Oncogene) Vol. 29 Issue 50 Pg. 6603-8 (Dec 16 2010) ISSN: 1476-5594 [Electronic] England
PMID20818429 (Publication Type: Journal Article, Research Support, N.I.H., Extramural)
Chemical References
  • BRCA1 Protein
  • BRCA1 protein, human
  • Cyclic N-Oxides
  • DNA-Binding Proteins
  • E2F4 Transcription Factor
  • E2F4 protein, human
  • Spin Labels
  • NAD
  • Alcohol Oxidoreductases
  • C-terminal binding protein
  • tempol
Topics
  • Alcohol Oxidoreductases (metabolism)
  • BRCA1 Protein (genetics)
  • Carcinoma, Squamous Cell (genetics)
  • Cyclic N-Oxides (pharmacology)
  • DNA Repair (drug effects)
  • DNA-Binding Proteins (metabolism)
  • Down-Regulation
  • E2F4 Transcription Factor (metabolism)
  • Gene Expression Regulation, Neoplastic
  • Head and Neck Neoplasms (genetics)
  • Humans
  • NAD (metabolism)
  • Oxidation-Reduction
  • Promoter Regions, Genetic (drug effects)
  • Spin Labels
  • Transcription, Genetic

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