Abstract
The BRCA1 tumor suppressor contributes to the repair of DNA double-strand breaks (DSB) through homologous recombination, but the mechanism is unknown. The rapid accumulation of BRCA1 into nuclear foci in response to induction of DNA breaks suggests that BRCA1 may function in an early step in the repair pathway. We examined the role of BRCA1 in one such early step, the resection of DSBs to generate ssDNA. The appearance of ssDNA in response to ionizing radiation is similar to that of BRCA1 foci formation, suggesting that the two processes are related. Furthermore, BRCA1 colocalizes to ssDNA sites induced by ionizing radiation. Overexpression of BRCA1 causes an increase in cells exhibiting ssDNA induced by ionizing radiation. Mutant BRCA1 that lacks the COOH-terminal BRCT domain also promotes ssDNA but fails to form nuclear foci. Knockdown of BRCA1 expression reduces ssDNA and Rad51 foci formation in response to ionizing radiation. These results indicate that BRCA1 promotes induction of ssDNA in response to ionizing radiation and accumulates at sites of ssDNA.
Highlights
Hereditary predisposition to breast and ovarian cancer has been associated with mutations of BRCA1 [1, 2]
The assay is similar in principle to the flow cytometric assays used to measure cells in S phase, except that the denaturant is omitted. This approach successfully showed that induction of double-strand breaks (DSB) promotes ssDNA formation followed by accumulation of replication protein A (RPA) and Rad51 at ssDNA sites [13]
The appearance of BRCA1 foci exhibits a similar time course as ssDNA, suggesting that BRCA1 is involved in the formation and resolution of the ssDNA intermediate during DSB repair
Summary
Hereditary predisposition to breast and ovarian cancer has been associated with mutations of BRCA1 [1, 2]. The BRCA1 tumor suppressor contributes to the repair of DNA double-strand breaks (DSB) through homologous recombination. Primary cells derived from BRCA1 knockout mice exhibit chromatid breaks and dicentric chromosomes, defects indicative of errors in recombination events [3]. BRCA1-deficient mouse embryonic stem cells exhibit lower rates of DSB repair by homologous recombination [4, 5]. Several activities have been ascribed directly to BRCA1 using in vitro functional assays, including transcriptional activation [6], E3 ubiquitin ligase activity [7, 8], and phosphopeptide-binding activity [9,10,11]. The mechanism by which BRCA1 contributes to homologous recombination is unknown
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
