Hypoxia-Induced Down-regulation of BRCA1 Expression by E2Fs

• Published in: Cancer research (Chicago, Ill.) Vol. 65; no. 24; pp. 11597 - 11604
• Main Authors: Bindra, Ranjit S., Gibson, Shannon L., Meng, Alice, Westermark, Ulrica, Jasin, Maria, Pierce, Andrew J., Bristow, Robert G., Classon, Marie K., Glazer, Peter M.
• Format: Journal Article
• Language: English
• Published: Philadelphia, PA American Association for Cancer Research 15.12.2005
• Subjects: Biological and medical sciences; BRCA1 Protein - genetics; BRCA1 Protein - metabolism; Breast Neoplasms - genetics; Breast Neoplasms - metabolism; Cell Hypoxia; Cell physiology; Cell transformation and carcinogenesis. Action of oncogenes and antioncogenes; Chromatin Immunoprecipitation; Colonic Neoplasms - genetics; Colonic Neoplasms - metabolism; DNA Repair; Down-Regulation; E2F Transcription Factors - genetics; E2F Transcription Factors - metabolism; Fundamental and applied biological sciences. Psychology; Gene Expression Regulation, Neoplastic; Gynecology. Andrology. Obstetrics; Humans; Hypoxia-Inducible Factor 1, alpha Subunit - genetics; Hypoxia-Inducible Factor 1, alpha Subunit - metabolism; Luciferases - metabolism; Lung Neoplasms - genetics; Lung Neoplasms - metabolism; Mammary gland diseases; Medical sciences; Molecular and cellular biology; Promoter Regions, Genetic; Recombination, Genetic; Reverse Transcriptase Polymerase Chain Reaction; RNA, Messenger - genetics; RNA, Messenger - metabolism; Transcription, Genetic; Tumor Cells, Cultured; Tumors; Oxygen; Transcription factor E2F; Cell microenvironment; Hypoxia; Malignant tumor; Gene expression; BRCA1 gene; Tumor suppressor gene
• ISSN: 0008-5472; 1538-7445
• DOI: 10.1158/0008-5472.CAN-05-2119

Decreased BRCA1 expression in the absence of genetic mutation is observed frequently in sporadic cancers of the breast and other sites, although little is known regarding the mechanisms by which the expression of this gene can be repressed. Here, we show that activating and repressive E2Fs simultaneously bind the BRCA1 promoter at two adjacent E2F sites in vivo, and that hypoxia induces a dynamic redistribution of promoter occupancy by these factors resulting in the transcriptional repression of BRCA1 expression. Functionally, we show that hypoxia is associated with impaired homologous recombination, whereas the nonhomologous end-joining (NHEJ) repair pathway is unaffected under these conditions. Repression of BRCA1 expression by hypoxia represents an intriguing mechanism of functional BRCA1 inactivation in the absence of genetic mutation. We propose that hypoxia-induced decreases in BRCA1 expression and consequent suppression of homologous recombination may lead to genetic instability by shifting the balance between the high-fidelity homologous recombination pathway and the error-prone NHEJ pathway of DNA repair. Furthermore, these findings provide a novel link between E2Fs and the transcriptional response to hypoxia and provide insight into the mechanisms by which the tumor microenvironment can contribute to genetic instability in cancer. (Cancer Res 2005; 65(24): 11597-604)