The Breast Cancer Susceptibility Gene BRCA1 Is Required for Subnuclear Assembly of Rad51 and Survival following Treatment with the DNA Cross-linking Agent Cisplatin

Abstract

Germ line mutations in BRCA1 or BRCA2 genes result in a marked increase in the risk of early onset breast and ovarian cancers (5-10). BRCA1 and BRCA2 appear to have multiple functions including roles in transcriptional regulation (11)(12)(13)(14) and cell cycle checkpoint control (15)(16)(17)(18)(19)(20).1 Brca1 and Brca2 both have transcription activation functions (11, 13); Brca1 co-activates transcription with p53 (21,22). Recently it has been demonstrated that Brca1 participates in homologous recombinational repair pathways (2, 3). These observations are consistent with earlier work that demonstrated interaction of Brca1 and Brca2 with the recombinational repair protein Rad51, in addition to studies showing that brca1 and brca2 mutants are phenotypically similar to rad51 mutants (1,4,(23)(24)(25)(26).In addition to contributing to recombinational repair of double strand breaks (DSBs), 2 BRCA1 has also been implicated in other DNA repair pathways. Mutational analysis has shown a role for BRCA1 in transcription-coupled base excision repair of oxidative DNA damage (27,28). Furthermore, a recent study reported biochemical interactions between Brca1 and proteins required for DNA-end joining, nucleotide mismatch repair, DNA replication, and signal transduction in response to damage (29). This study also identified interactions between Brca1 and other proteins thought to be involved in recombinational repair. Although these results raise the possibility that BRCA1 contributes to multiple cellular DNA damage responses, the specific mechanisms through which BRCA1 contributes to these processes remain to be determined.Studies primarily in yeast have indicated that Rad51 promotes homology-dependent repair of DNA DSBs. The strand exchange activity of Rad51 catalyzes the exchange of genetic information between a damaged DNA molecule and an undamaged template copy (30,31). Similarly, studies have shown that the human Rad51 possesses DNA strand-exchange activity (32). Immunostaining analysis of yeast and mammalian cells undergoing DNA repair and recombination have revealed the presence of visible subnuclear assemblies of Rad51 (33,34). The properties of Rad51 foci indicate that they are multimeric nucleoprotein complexes engaged in recombinational repair (33-38). In mammalian cells, rad51 "knock-out" mice have been shown to display embryonic lethality and sensitivity to ionizing radiation indicating a role in mediating genome stability (26).Rad51 plays a central role in mediating homologous recombination events and can promote strand-exchange alone in vitro. However, its strand-exchange activity requires various accessory factors. For example, one category of accessory factor promotes assembly of Rad51 into the helical protein-DNA filaments needed for strand exchange. In yeast, biochemical (39 -42) and cytological (36) observations indicate that RPA, Rad55, Rad57, and Rad52 proteins promote the assembly of Rad51 during yeast meiotic recombination. Thus, one model for Rad51 assembly at sites of damage is that formation of t...

The role of BRCA1 and BRCA2 in prostate cancer

“…Therefore, these tumours show high sensitivity to platinum-based chemotherapy, both in vitro [96][97][98] and in vivo. [99][100][101] Previous studies in ovarian cancer suggested that mutations in both genes were associated with similar responses to platinum-based chemotherapy.…”

A small ubiquitin binding domain inhibits ubiquitin-dependent protein recruitment to DNA repair foci

“…BRCA1 is essential for HR repair and the recruitment of RAD51 to repair foci. 37,38 We therefore measured the efficiency of HR in cells using the DR-GFP reporter assay under conditions where the recruitment of 53BP1 and BRCA1 into IRIF was blocked. 39 U20S cells containing an integrated copy of the DR-GFP reporter were transduced with lentivirus encoding mCherry as a control, or mCherry-tagged RAD18 WT, RAD18 D221A, or RAD18 UBZ domain, and we measured the ability of mCherry-positive cells to express GFP protein following expression of the I-SceI endonuclease.…”

Minding the gap: The underground functions of BRCA1 and BRCA2 at stalled replication forks

“…This led to the proposal that BRCA1 and BRCA2 function in daughter strand gap repair [11,28]. Efficient Rad51 focus formation at DSBs induced by laser scissors or ionizing radiation (IR) is dependent upon BRCA1 and BRCA2, and Rad51 retention on chromatin following HU treatment is impaired in the absence of wild-type BRCA2, suggesting a possible role for BRCA1 and 2 in loading Rad51 onto ssDNA [97][98][99][100]. Lomonosov et al visualized replication structures in rDNA of BRCA2 mutant mouse embryonic fibroblasts (MEF) during HU treatment.…”