Characterization of a negative transcriptional element in the BRCA1 promoter.
BACKGROUND
Decreased transcription of the BRCA1 gene has previously been observed to occur in sporadic breast tumours, making elucidation of the mechanisms regulating the expression of this gene important for our understanding of the etiology of the disease.


METHODS
Transcriptional elements involved in the regulation of the BRCA1 promoter were analysed by co-transfection experiments into the human MCF-7 and T-47D breast cancer cell lines.


RESULTS
We have identified a repressor element, referred to as the UP site, within the proximal BRCA1 promoter whose inactivation results in increased promoter activity. An E2F recognition element, previously suggested to mediate repression via E2F-6, is adjacent to the UP site and its inactivation also leads to increased BRCA1 expression. These two elements appear to form a composite repressor element whose combined effect is additive. The UP element is composed of two sequences, one of which binds the ubiquitously expressed ets family transcription factor GABP alpha/beta. This site is distinct from a previously identified GABP alpha/beta site, the RIBS element, though the RIBS site appears to be necessary for derepression of the promoter via mutations in the UP site. Knockdown of GABP alpha using an shRNA vector confirms that this protein is important for the function of both the RIBS and UP sites.


CONCLUSIONS
The identification of a repressor element in the BRCA1 promoter brings a new level of complexity to the regulation of BRCA1 expression. The elements characterized here may play a normal role in the integration of a variety of signals, including two different growth related pathways, and it is possible that loss of the ability to derepress the BRCA1 promoter during critical periods may contribute to breast transformation.
Queen's Cancer Research Institute, Queen's University, Kingston, Ontario, Canada, K7L 3N6.
Gwen
G
MacDonald
Melissa
M
Stramwasser
Christopher R
CR
Mueller
D019313:BRCA1 Protein / Q000235:genetics* / Q000378:metabolism; D015153:Blotting, Western; D001943:Breast Neoplasms / Q000235:genetics* / Q000473:pathology; D047369:Chromatin Immunoprecipitation; D019175:DNA Methylation; D004273:DNA, Neoplasm / Q000235:genetics; D050701:E2F6 Transcription Factor / Q000378:metabolism*; D051268:GA-Binding Protein Transcription Factor / Q000378:metabolism*; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D011401:Promoter Regions, Genetic / Q000235:genetics*; D012045:Regulatory Sequences, Nucleic Acid; D012097:Repressor Proteins / Q000378:metabolism; D014158:Transcription, Genetic; D014162:Transfection; D014407:Tumor Cells, Cultured
D019313:BRCA1 Protein; D004273:DNA, Neoplasm; D050701:E2F6 Transcription Factor; C491744:E2F6 protein, human; D051268:GA-Binding Protein Transcription Factor; D012097:Repressor Proteins