Disease relevance of RAD51

• Structural and mutational results characterize RAD51 interactions with the breast cancer susceptibility protein BRCA2 in higher eukaryotes [1].
• These results define a physiological role for the WRN RecQ helicase protein in RAD51-dependent HR and identify a mechanistic link between defective recombination resolution and limited cell division potential, DNA damage hypersensitivity, and genetic instability in human somatic cells [2].
• RAD51 status did not affect ovarian cancer risk [3].
• Inferring from the function of RAD51 in DNA repair, human pancreatic cancer cells, Capan-1, expressing truncated BRCA2 were shown to be hypersensitive to methyl methanesulfonate (MMS) treatment [4].
• Thus, we postulate that RAD51-dependent facilitation of DSB repair, antiapoptotic activity of Bcl-xL, and delay in progression through the G(2)/M phase work in concert to induce drug resistance in FTK-positive leukemias and lymphomas [5].

Psychiatry related information on RAD51

• Breast cancer risk reduction associated with the RAD51 polymorphism among carriers of the BRCA1 5382insC mutation in Poland [6].
• Here I recap the scientific and personal background of the delineation of the amyloid cascade hypothesis for Alzheimer's disease that I wrote with Gerry Higgins and the events leading to the writing of that influential review [7].

High impact information on RAD51

• We show that PTEN acts on chromatin and regulates expression of Rad51, which reduces the incidence of spontaneous DSBs [8].
• The clustering of between-species variation in the region of the gene encoding the RAD51-interaction domain of BRCA1 suggests the maintenance of genomic integrity as a possible target of selection [9].
• BARD1 and Rad51, two proteins associated with the BRCA1 dots, behaved similarly [10].
• Atm is required for proper assembly of Rad51 onto the chromosomal axial elements during meiosis [11].
• Assembly of Rad51 foci on axial elements remained defective, and gametogenesis proceeded only to pachytene of prophase I [11].

Chemical compound and disease context of RAD51

• XRCC2 mutant irs1 cells exhibit hypersensitivity to hydroxyurea (HU) and are defective in the induction of RAD51 foci after HU treatment [12].
• The carboxyl-terminal of BRCA1 is required for subnuclear assembly of RAD51 after treatment with cisplatin but not ionizing radiation in human breast and ovarian cancer cells [13].
• CONCLUSIONS: Selected DNA-damaging agents (ADR, CPT, and UV) and a reducing agent (SLN) inhibited BRCA1/2, p300, and Rad51 expression in prostate cancer cells, although decreases in mRNA vs. protein did not coincide [14].
• An increase in protein expression of integrin alphav, integrin beta1, MAPK(p42), Rad51, DNA-PK(CS), and ataxia telangiectasia gene (ATM) was detected in HUVEC grown in CC with GFP-U87 cells compared with HUVEC grown in mono-culture [15].
• Chlorambucil induction of HsRad51 in B-cell chronic lymphocytic leukemia [16].

Biological context of RAD51

• Because the paralogs are required for the assembly of DNA damage-induced RAD51 foci, and mutant cell lines are defective in homologous recombination and show genomic instability, their defect is thought to be caused by an inability to promote efficient recombinational repair [17].
• Like BRCA1 and RAD51, BRCA2 relocates to PCNA+ replication sites following exposure of S phase cells to hydroxyurea or UV irradiation [18].
• In addition to being critical for RAD51 focus formation, RAD51C localizes to DNA damage sites [19].
• By controlling the balance between the BLM and the RAD51 pathways, this direct role of p53 could maintain genome stability when replication forks are stalled at regions of DNA damage [20].
• We show that p53 and BLM accumulated after hydroxyurea (HU) treatment, and physically associated and co-localized with each other and with RAD51 at sites of stalled DNA replication forks [21].

Anatomical context of RAD51

• Phylogenetic analyses indicated that the recA/RAD51 family can be divided into three subfamilies: (i) RADalpha, with highly conserved functions; (ii) RADbeta, with relatively divergent functions; and (iii) recA, functioning in eubacteria and eukaryotic organelles [22].
• A rare germ-line missense mutation was identified in RAD54, whereas no sequence variants were found in RAD51 [23].
• Genetic interactions between RAD51 and its paralogues for centrosome fragmentation and ploidy control, independently of the sensitivity to genotoxic stresses [24].
• In eukaryotic cells, RAD52 protein plays a central role in genetic recombination and DNA repair by (i) promoting the annealing of complementary single-stranded DNA and (ii) stimulation of the RAD51 recombinase [25].
• Spontaneous and mitomycin C-induced SCE levels were significantly reduced for chicken DT40 B cells lacking the key HR genes RAD51 and RAD54 but not for nonhomologous DNA end-joining (NHEJ)-defective KU70(-/-) cells [26].

Associations of RAD51 with chemical compounds

• We show that a radiosensitive cell line, mutant for the RAD51 homolog XRCC2 and defective in homologous recombination repair (HRR), displays significantly diminished caffeine radiosensitization that can be restored by expression of XRCC2 [27].
• We established mutant cell lines complemented with either wild-type or variant cDNAs of three human genes, RAD51, XRCC2, and XRCC3, and assessed their sensitivity to cisplatin and mitomycin C [28].
• Irs1 cells showed increased level of chromatin-bound RAD51 as well as the wild type cells after thymidine treatment [12].
• Here we show that the carboxy-terminal region of BRCA2, which interacts directly with the essential recombination protein RAD51, contains a site (serine 3291; S3291) that is phosphorylated by cyclin-dependent kinases [29].
• The BRC repeats in BRCA2 are critical for RAD51 binding and resistance to methyl methanesulfonate treatment [4].

Physical interactions of RAD51

• A designed P.furiosus RAD51 mutant binds BRC repeats and forms BRCA2-dependent nuclear foci in human cells in response to gamma-irradiation-induced DNA damage, similar to human RAD51 [1].
• In this study, we show that human RAD51 interacts with RAD51C-XRCC3 or RAD51B-C-D-XRCC2 [19].
• Biochemical experiments suggested that BLM resides in a nuclear matrix-bound complex in which association with hRAD51 may be direct [30].
• Both the number of RAD51 foci and the amount of the BLM-p53-RAD51 complex are increased in hMSH2- or hMSH6-deficient cells [31].
• RAD51C interacts with RAD51B and is central to a larger protein complex in vivo exclusive of RAD51 [32].

Enzymatic interactions of RAD51

• Brca1 is hyperphosphorylated in response to DNA damage and co-localizes with Rad51, a protein involved in homologous-recombination, and Nbs1.Mre11.Rad50, a complex required for both homologous-recombination and nonhomologous end joining repair of damaged DNA [33].
• Furthermore, we show that two cancer-related p53 mutant proteins cannot inhibit strand exchange and fork regression catalyzed by human Rad51 [34].
• Chromatin modifications associated with DSBs were monitored after exposure by labeling surface-spread chromatin with antibodies against RAD51 (which recognizes DSBs) and the phosphorylated variant of histone H2AFX (herein designated by its commonly used symbol, H2AX), gammaH2AX (which modifies chromatin associated with DSBs) [35].

Co-localisations of RAD51

• This process correlates with the appearance of XRCC1 nuclear foci that colocalize with Rad51 and may thus function in concert with homologous recombination [36].
• A recent report that BRCA1 and human Rad51 colocalize in S-phase cells suggests a role for BRCA1 in DNA damage repair [37].

Regulatory relationships of RAD51

• Full-length archaeal Rad51 structure and mutants: mechanisms for RAD51 assembly and control by BRCA2 [1].
• hXRCC2 enhances ADP/ATP processing and strand exchange by hRAD51 [38].
• Consistent with these observations, hMSH6 colocalized with BLM and phospho-ser15-p53 in hydroxyurea-induced RAD51 nuclear foci that may correspond to the sites of presumed stalled DNA replication forks and more likely the resultant DNA double-stranded breaks [31].
• Therefore, we suggest that excess Rad52p can inhibit the essential RAD51-dependent pathways of HR most likely to be responsible for gene targeting, while at the same time stimulating the RAD51-independent pathway thought to be responsible for extrachromosomal HR [39].
• By using BRCA1-deficient or -proficient cells, we demonstrated that in response to irofulven, BRCA1 contributes to the control of S and G(2)/M cell cycle arrest and is critical for repairing DNA double-strand breaks and for RAD51-dependent homologous recombination [40].

Other interactions of RAD51

• HU-induced relocalization of BLM to RAD51 foci was p53 independent [21].
• In the RADalpha subfamily, eukaryotic RAD51 and DMC1 genes formed two separate monophyletic groups when archaeal RADA genes were used as an outgroup [22].
• Given the observation that different genes within a common functional pathway may be targeted by mutations in human cancers, we analyzed RAD51, RAD52, and RAD54 for the presence of germ-line mutations in 100 cases with early-onset breast cancer and for somatic mutations in 15 human breast cancer cell lines [23].
• CONCLUSION: Our results suggest that BRCA2 tumors demonstrate more cytoplasmic and less nuclear RAD51 staining, and increased CHEK2 staining [41].
• Functional interaction between the Bloom's syndrome helicase and the RAD51 paralog, RAD51L3 (RAD51D) [42].

Analytical, diagnostic and therapeutic context of RAD51

• The structure reveals how RAD51 proteins assemble into inactive heptameric rings and active DNA-bound filaments matching three-dimensional electron microscopy reconstructions [1].
• RAD51 foci were studied using immunofluorescence [43].
• Western blot analysis revealed that the RAD51 protein was elevated 10-fold above normal levels in group A, C, and G fibroblasts, but was not altered in group D2 fibroblasts [44].
• EXPERIMENTAL DESIGN: We studied the distribution of polymorphisms in RAD51 and XRCC3 in 216 cases of de novo AML, 51 cases of therapy-related AML (t-AML), and 186 control subjects using PCR followed by restriction enzyme digestion [45].
• In alpha particle-irradiated cells and in those cells subsequently cultured in the presence of E, increased BRCA1, BRCA2 and RAD51 expression were detected by immunofluorescence staining and quantified by confocal microscopy [46].

References