HsRec2/Rad51L1, a protein influencing cell cycle progression, has protein kinase activity

A truncating variant of RAD51B associated with primary ovarian insufficiency provides insights into its meiotic and somatic functions

Primary ovarian insufficiency (POI) causes female infertility by abolishing normal ovarian function. Although its genetic etiology has been extensively investigated, most POI cases remain unexplained. Using whole-exome sequencing, we identified a homozygous variant in RAD51B -(c.92delT) in two sisters with POI. In vitro studies revealed that this variant leads to translation reinitiation at methionine 64. Here, we show that this is a pathogenic hypomorphic variant in a mouse model. Rad51bc.92delT/c.92delT mice exhibited meiotic DNA repair defects due to RAD51 and HSF2BP/BMRE1 accumulation in the chromosome axes leading to a reduction in the number of crossovers. Interestingly, the interaction of RAD51B-c.92delT with RAD51C and with its newly identified interactors RAD51 and HELQ was abrogated or diminished. Repair of mitomycin-C-induced chromosomal aberrations was impaired in RAD51B/Rad51b-c.92delT human and mouse somatic cells in vitro and in explanted mouse bone marrow cells. Accordingly, Rad51b-c.92delT variant reduced replication fork progression of patient-derived lymphoblastoid cell lines and pluripotent reprogramming efficiency of primary mouse embryonic fibroblasts. Finally, Rad51bc.92delT/c.92delT mice displayed increased incidence of pituitary gland hyperplasia. These results provide new mechanistic insights into the role of RAD51B not only in meiosis but in the maintenance of somatic genome stability.

Genome expression profiling predicts the molecular mechanism of peripheral myelination

The present study aimed to explore the molecular mechanism of myelination in the peripheral nervous system (PNS) based on genome expression profiles. Microarray data (GSE60345) was acquired from the Gene Expression Omnibus database. Differentially expressed genes (DEGs) were integrated and subsequently subjected to pathway and term enrichment analysis. A protein-protein interaction network was constructed and the top 200 DEGs according to their degree value were further subjected to pathway enrichment analysis. A microRNA (miR)-target gene regulatory network was constructed to explore the role of miRs associated with PNS myelination. A total of 783 upregulated genes and 307 downregulated genes were identified. The upregulated DEGs were significantly enriched in the biological function of complement and coagulation cascades, cytokine-cytokine receptor interactions and cell adhesion molecules. Pathways significantly enriched by the downregulated DEGs included the cell cycle, oocyte meiosis and the p53 signaling pathway. In addition, the upregulated DEGs among the top 200 DEGs were significantly enriched in natural killer (NK) cell mediated cytotoxicity and the B cell receptor (BCR) signaling pathway, in which Fc γ receptor (FCGR), ras-related C3 botulinum toxin substrate 2 (RAC2) and 1-phosphatidylinositol-4,5-bisphosphate phosphodiesterase γ-2 (PLCG2) were involved. miR-339-5p, miR-10a-5p and miR-10b-5p were identified as having a high degree value and may regulate the target genes TOX high mobility group box family member 4 (Tox4), DNA repair protein XRCC2 (Xrcc2) and C5a anaphylatoxin chemotactic receptor C5a2 (C5ar2). NK cell mediated cytotoxicity and the BCR pathway may be involved in peripheral myelination by targeting FCGR, RAC2 and PLCG2. The downregulation of oocyte meiosis, the cell cycle and the cellular tumor antigen p53 signaling pathway suggests decreasing schwann cell proliferation following the initiation of myelination. miR-339-5p, miR-10a-5p and miR-10b-5p may play important roles in PNS myelination by regulating Tox4, Xrcc2 and C5ar2.

A miR-590/Acvr2a/Rad51b axis regulates DNA damage repair during mESC proliferation

Embryonic stem cells (ESCs) enable rapid proliferation that also causes DNA damage. To maintain genomic stabilization during rapid proliferation, ESCs must have an efficient system to repress genotoxic stress. Here, we show that withdrawal of leukemia inhibitory factor (LIF), which maintains the self-renewal capability of mouse ESCs (mESCs), significantly inhibits the cell proliferation and DNA damage of mESCs and upregulates the expression of miR-590. miR-590 promotes single-strand break (SSB) and double-strand break (DSB) damage repair, thus slowing proliferation of mESCs without influencing stemness. miR-590 directly targets Activin receptor type 2a (Acvr2a) to mediate Activin signaling. We identified the homologous recombination-mediated repair (HRR) gene, Rad51b, as a downstream molecule of the miR-590/Acvr2a pathway regulating the SSB and DSB damage repair and cell cycle. Our study shows that a miR-590/Acvr2a/Rad51b signaling axis ensures the stabilization of mESCs by balancing DNA damage repair and rapid proliferation during self-renewal.

•

miR-590 promotes DNA damage repair and slows proliferation by targeting Acvr2a

•

miR-590/Acvr2a/Rad51b axis balances SSB and DSB damage repair in mESCs

Inherited genetic susceptibility to breast cancer: the beginning of the end or the end of the beginning?

Genome-wide association studies have identified 72 loci associated with breast cancer susceptibility. Seventeen of these are known to predispose to other cancers. High-penetrance susceptibility loci for breast cancer usually result from coding alterations, principally in genes involved in DNA repair, whereas almost all of the associations identified through genome-wide association studies are found in noncoding regions of the genome and are likely to involve regulation of genes in multiple pathways. However, the genes underlying most associations are not yet known. In this review, we summarize the findings from genome-wide association studies in breast cancer and describe the genes and mechanisms that are likely to be involved in the tumorigenesis process. We also discuss approaches to fine-scale mapping of susceptibility regions used to identify the likely causal variant(s) underlying the associations, a major challenge in genetic epidemiology. Finally, we discuss the potential impact of such findings on personalized medicine and future avenues for screening, prediction, and prevention programs.

A novel PLAG1-RAD51L1 gene fusion resulting from a t(8;14)(q12;q24) in a case of lipoblastoma

Lipoblastomas are rare benign tumors that arise from embryonic adipose tissue and occur predominantly in the pediatric population. Here, we report a case of lipoblastoma in an 8-month-old boy. Surgical excision and subsequent histopathologic examination were consistent with features of lipoblastoma. Chromosome analysis of the tumor revealed a clonal unbalanced t(8;14) translocation. Genomic microarray analysis of the tumor delineated the exact breakpoints at 8q12.1 and 14q24.1, which involved the PLAG1 and RADA51L1 genes, respectively. Furthermore, fluorescence in situ hybridization demonstrated that the translocation fused the PLAG1-RAD51L1 genes. These results suggest that RAD51L1 is an alternative fusion partner gene for the PLAG1 gene in a lipoblastoma with an 8q12 rearrangement.

Gamma-radiation sensitivity and polymorphisms in RAD51L1 modulate glioma risk

BACKGROUND

DNA strand breaks pose the greatest threat to genomic stability. Genetically determined mutagen sensitivity predisposes individuals to a variety of cancers, including glioma. However, polymorphisms in DNA strand break repair genes that may determine mutagen sensitivity are not well studied in cancer risk, especially in gliomas.

METHODS

We correlated genotype data for tag single-nucleotide polymorphisms (tSNPs) of DNA strand break repair genes with a gamma-radiation-induced mutagen sensitivity phenotype [expressed as mean breaks per cell (B/C)] in samples from 426 glioma patients. We also conducted analysis to assess joint and haplotype effects of single-nucleotide polymorphisms (SNPs) on mutagen sensitivity. We further validate our results in an independent external control group totaling 662 subjects.

RESULTS

Of the 392 tSNPs examined, we found that mutagen sensitivity was modified by one tSNP in the EME2 gene and six tSNPs in the RAD51L1 gene (P < 0.01). Among the six RAD51L1 SNPs tested in the validation set, one (RAD51L1 rs2180611) was significantly associated with mutagen sensitivity (P = 0.025). Moreover, we found a significant dose-response relationship between the mutagen sensitivity and the number of adverse tSNP genotypes. Furthermore, haplotype analysis revealed that RAD51L1 haplotypes F-A (zero adverse allele) and F-E (six adverse alleles) exhibited the lowest (0.42) and highest (0.93) mean B/C values, respectively. A similar dose-response relationship also existed between the mutagen sensitivity and the number of adverse haplotypes.

CONCLUSION

These results suggest that polymorphisms in and haplotypes of the RAD51L1 gene, which is involved in the double-strand break repair pathway, modulate gamma-radiation-induced mutagen sensitivity.

Expanded cells in monoclonal TCR-alphabeta+/CD4+/NKa+/CD8-/+dim T-LGL lymphocytosis recognize hCMV antigens

Recent studies suggest the potential involvement of common antigenic stimuli on the ontogeny of monoclonal T-cell receptor (TCR)-alphabeta(+)/CD4(+)/NKa(+)/CD8(-/+dim) T-large granular lymphocyte (LGL) lymphocytosis. Because healthy persons show (oligo)clonal expansions of human cytomegalovirus (hCMV)-specific TCRVbeta(+)/CD4(+)/cytotoxic/memory T cells, we investigate the potential involvement of hCMV in the origin and/or expansion of monoclonal CD4(+) T-LGL. Peripheral blood samples from patients with monoclonal TCR-alphabeta(+)/CD4(+) T-LGL lymphocytosis and other T-chronic lymphoproliferative disorders were evaluated for the specific functional response against hCMV and hEBV whole lysates as well as the "MQLIPDDYSNTHSTRYVTVK" hCMV peptide, which is specifically loaded in HLA-DRB1*0701 molecules. A detailed characterization of those genes that underwent changes in T-LGL cells responding to hCMV was performed by microarray gene expression profile analysis. Patients with TCR-alphabeta(+)/CD4(+) T-LGL displayed a strong and characteristic hCMV-specific functional response, reproduced by the hCMV peptide in a subset of HLA-DRB1*0701(+) patients bearing TCRVbeta13.1(+) clonal T cells. Gene expression profile showed that the hCMV-induced response affects genes involved in inflammatory and immune responses, cell cycle progression, resistance to apoptosis, and genetic instability. This is the first study providing evidence for the involvement of hCMV in the ontogeny of CD4(+) T-LGL, emerging as a model disorder to determine the potential implications of quite a focused CD4(+)/cytotoxic immune response.

ERCC1 expression and RAD51B activity correlate with cell cycle response to platinum drug treatment not DNA repair

BACKGROUND

The H69CIS200 and H69OX400 cell lines are novel models of low-level platinum-drug resistance. Resistance was not associated with increased cellular glutathione or decreased accumulation of platinum, rather the resistant cell lines have a cell cycle alteration allowing them to rapidly proliferate post drug treatment.

RESULTS

A decrease in ERCC1 protein expression and an increase in RAD51B foci activity was observed in association with the platinum induced cell cycle arrest but these changes did not correlate with resistance or altered DNA repair capacity. The H69 cells and resistant cell lines have a p53 mutation and consequently decrease expression of p21 in response to platinum drug treatment, promoting progression of the cell cycle instead of increasing p21 to maintain the arrest.

CONCLUSION

Decreased ERCC1 protein and increased RAD51B foci may in part be mediating the maintenance of the cell cycle arrest in the sensitive cells. Resistance in the H69CIS200 and H69OX400 cells may therefore involve the regulation of ERCC1 and RAD51B independent of their roles in DNA repair. The novel mechanism of platinum resistance in the H69CIS200 and H69OX400 cells demonstrates the multifactorial nature of platinum resistance which can occur independently of alterations in DNA repair capacity and changes in ERCC1.

Cell cycle alterations in biopsied olfactory neuroepithelium in schizophrenia and bipolar I disorder using cell culture and gene expression analyses

We previously demonstrated that olfactory cultures from individuals with schizophrenia had increased cell proliferation compared to cultures from healthy controls. The aims of this study were to (a) replicate this observation in a new group of individuals with schizophrenia, (b) examine the specificity of these findings by including individuals with bipolar I disorder and (c) explore gene expression differences that may underlie cell cycle differences in these diseases. Compared to controls (n = 10), there was significantly more mitosis in schizophrenia patient cultures (n = 8) and significantly more cell death in the bipolar I disorder patient cultures (n = 8). Microarray data showed alterations to the cell cycle and phosphatidylinositol signalling pathways in schizophrenia and bipolar I disorder, respectively. Whilst caution is required in the interpretation of the array results, the study provides evidence indicating that cell proliferation and cell death in olfactory neuroepithelial cultures is differentially altered in schizophrenia and bipolar disorder.

DNA double-strand break repair by homologous recombination

DNA double-strand breaks (DSB) are presumed to be the most deleterious DNA lesions as they disrupt both DNA strands. Homologous recombination (HR), single-strand annealing, and non-homologous end-joining are considered to be the pathways for repairing DSB. In this review, we focus on DSB repair by HR. The proteins involved in this process as well as the interactions among them are summarized and characterized. The main emphasis is on eukaryotic cells, particularly the budding yeast Saccharomyces cerevisiae and mammals. Only the RAD52 epistasis group proteins are included.

Etiology and pathogenesis of uterine leiomyomas: a review

Uterine leiomyomas, or fibroids, represent a major public health problem. It is believed that these tumors develop in the majority of American women and become symptomatic in one-third of these women. They are the most frequent indication for hysterectomy in the United States. Although the initiator or initiators of fibroids are unknown, several predisposing factors have been identified, including age (late reproductive years), African-American ethnicity, nulliparity, and obesity. Nonrandom cytogenetic abnormalities have been found in about 40% of tumors examined. Estrogen and progesterone are recognized as promoters of tumor growth, and the potential role of environmental estrogens has only recently been explored. Growth factors with mitogenic activity, such as transforming growth factor- (subscript)3(/subscript), basic fibroblast growth factor, epidermal growth factor, and insulin-like growth factor-I, are elevated in fibroids and may be the effectors of estrogen and progesterone promotion. These data offer clues to the etiology and pathogenesis of this common condition, which we have analyzed and summarized in this review.

Complex formation by the human RAD51C and XRCC3 recombination repair proteins

In vertebrates, the RAD51 protein is required for genetic recombination, DNA repair, and cellular proliferation. Five paralogs of RAD51, known as RAD51B, RAD51C, RAD51D, XRCC2, and XRCC3, have been identified and also shown to be required for recombination and genome stability. At the present time, however, very little is known about their biochemical properties or precise biological functions. As a first step toward understanding the roles of the RAD51 paralogs in recombination, the human RAD51C and XRCC3 proteins were overexpressed and purified from baculovirus-infected insect cells. The two proteins copurify as a complex, a property that reflects their endogenous association observed in HeLa cells. Purified RAD51C--XRCC3 complex binds single-stranded, but not duplex DNA, to form protein--DNA networks that have been visualized by electron microscopy.

Homologous recombinational repair of DNA ensures mammalian chromosome stability

The process of homologous recombinational repair (HRR) is a major DNA repair pathway that acts on double-strand breaks and interstrand crosslinks, and probably to a lesser extent on other kinds of DNA damage. HRR provides a mechanism for the error-free removal of damage present in DNA that has replicated (S and G2 phases). Thus, HRR acts in a critical way, in coordination with the S and G2 checkpoint machinery, to eliminate chromosomal breaks before the cell division occurs. Many of the human HRR genes, including five Rad51 paralogs, have been identified, and knockout mutants for most of these genes are available in chicken DT40 cells. In the mouse, most of the knockout mutations cause embryonic lethality. The Brca1 and Brca2 breast cancer susceptibility genes appear to be intimately involved in HRR, but the mechanistic basis is unknown. Biochemical studies with purified proteins and cell extracts, combined with cytological studies of nuclear foci, have begun to establish an outline of the steps in mammalian HRR. This pathway is subject to complex regulatory controls from the checkpoint machinery and other processes, and there is increasing evidence that loss of HRR gene function can contribute to tumor development. This review article is meant to be an update of our previous review [Biochimie 81 (1999) 87].

The transition from conjugal development to the first vegetative cell division is dependent on RAD51 expression in the ciliate Tetrahymena thermophila

Rad51p, the eukaryotic homolog of the prokaryotic recA protein, catalyzes strand exchange between single- and double-stranded DNA and is involved in both genetic recombination and double-strand break repair in the ciliate Tetrahymena thermophila. We have previously shown that disruption of the Tetrahymena RAD51 somatic macronuclear locus leads to defective germline micronuclear division and that conjugation of two somatic rad51 null strains results in an early meiotic arrest. We have constructed Tetrahymena strains that are capable of RAD51 expression from their parental macronuclei and are homozygous, rad51 nulls in their germline micronuclei. These rad51 null heterokaryons complete all of the early and middle stages of conjugation, including meiosis, haploid nuclear exchange, zygotic fusion, and the programmed chromosome fragmentations, sequence eliminations, and rDNA amplification that occur during macronuclear development. However, the rad51 null progeny fail to initiate the first vegetative cell division following conjugal development. Coincident with the developmental arrest is a disproportionate amplification of rDNA, despite the maintenance of normal total DNA content in the developing macronuclei. Fusion of arrested rad51 null exconjugants to wild-type cells is sufficient to overcome the arrest. Cells rescued by cytoplasmic fusion continue to divide, eventually recapitulating the micronuclear mitotic defects described previously for rad51 somatic nulls.

Evidence for RAD51L1/HMGIC fusion in the pathogenesis of uterine leiomyoma

Chromosome rearrangements involving 12q15 are frequently observed in a variety of human mesenchymal tumors. The high mobility group protein gene HMGIC has been identified as the target involved in these rearrangements. Uterine leiomyomas frequently use chromosome band 14q24 as a translocation partner to HMGIC. Recent studies within the chromosome 14 breakpoint region in cell lines carrying t(12;14)(q15;q23-24) revealed that RAD51L1, a member of the RAD51 recombination gene family, is the HMGIC partner. Using RT-PCR, we screened a panel of 81 uterine leiomyomas removed from 30 women for rearrangement between RAD51L1 and HMGIC. This is the first molecular analysis in which primary tumors have been examined for the RAD51L1/HMGIC transcripts. The chimeric transcripts were identified from two cases in which exon 7 of the RAD51L1 gene is fused in frame to either exon 2 or exon 3 of the HMGIC gene. These transcripts encode fusion proteins containing RAD51L1 nucleotide binding domains and the HMGIC protein lacking the N-terminal AT hook motifs. The detection of the RAD51L1/HMGIC fusion in primary tumors adds to the accumulating evidence implicating this fusion in a proportion of uterine leiomyoma patients.

Human DNA repair genes

DNA repair systems are essential for the maintenance of genome integrity. Consequently, the disregulation of repair genes can be expected to be associated with significant, detrimental health effects, which can include an increased prevalence of birth defects, an enhancement of cancer risk, and an accelerated rate of aging. Although original insights into DNA repair and the genes responsible were largely derived from studies in bacteria and yeast, well over 125 genes directly involved in DNA repair have now been identified in humans, and their cDNA sequence established. These genes function in a diverse set of pathways that involve the recognition and removal of DNA lesions, tolerance to DNA damage, and protection from errors of incorporation made during DNA replication or DNA repair. Additional genes indirectly affect DNA repair, by regulating the cell cycle, ostensibly to provide an opportunity for repair or to direct the cell to apoptosis. For about 70 of the DNA repair genes listed in Table I, both the genomic DNA sequence and the cDNA sequence and chromosomal location have been elucidated. In 45 cases single-nucleotide polymorphisms have been identified and, in some cases, genetic variants have been associated with specific disorders. With the accelerating rate of gene discovery, the number of identified DNA repair genes and sequence variants is quickly rising. This report tabulates the current status of what is known about these genes. The report is limited to genes whose function is directly related to DNA repair.

Evidence for simultaneous protein interactions between human Rad51 paralogs

In yeast, the Rad51-related proteins include Rad55 and Rad57, which form a heterodimer that interacts with Rad51. Five human Rad51 paralogs have been identified (XRCC2, XRCC3, Rad51B/Rad51L1, Rad51C/Rad51L2, and Rad51D/Rad51L3), and each interacts with one or more of the others. Previously we reported that HsRad51 interacts with XRCC3, and Rad51C interacts with XRCC3, Rad51B, and HsRad51. Here we report that in the yeast two-hybrid system, Rad51D interacts with XRCC2 and Rad51C. No other interactions, including self-interactions, were found, indicating that the observed interactions are specific. The yeast Rad51 interacts with human Rad51 and XRCC3, suggesting Rad51 conservation since the human yeast divergence. Data from yeast three-hybrid experiments indicate that a number of the pairs of interactions between human Rad51 paralogs can occur simultaneously. For example, Rad51B expression enhances the binding of Rad51C to XRCC3 and to HsRad51D, and Rad51C expression allows the indirect interaction of Rad51B with Rad51D. Experiments using 6xHis-tagged proteins in the baculovirus system confirm several of our yeast results, including Rad51B interaction with Rad51D only when Rad51C is simultaneously expressed and Rad51C interaction with XRCC2 only when Rad51D is present. These results suggest that these proteins may participate in one complex or multiple smaller ones.

Disruption of muREC2/RAD51L1 in mice results in early embryonic lethality which can Be partially rescued in a p53(-/-) background

muREC2/RAD51L1 is a radiation-inducible gene that regulates cell cycle progression. To elucidate the biological function of muREC2/RAD51L1, the gene was disrupted in embryonic stem cells by homologous recombination. Mice heterozygous for muREC2/RAD51L1 appear normal and fertile; however, no homozygous pups were born after interbreeding of heterozygous mice. Timed pregnancy studies showed that homozygous mutant embryos were severely retarded in growth as early as ca. 5 days gestation (E5.5) and were completely resorbed by E8.5. Mutant blastocyst outgrowth was also severely impaired in a double-knockout embryo, but embryonic development did progress further in a p53-null background. These results suggest that muREC2/RAD51L1 plays a role in cell proliferation and early embryonic development, perhaps through interaction with p53.