Human RAD51 paralogue RAD51C fosters repair of alkylated DNA by interacting with the ALKBH3 demethylase

The integrity of our DNA is challenged daily by a variety of chemicals that cause DNA base alkylation. DNA alkylation repair is an essential cellular defence mechanism to prevent the cytotoxicity or mutagenesis from DNA alkylating chemicals. Human oxidative demethylase ALKBH3 is a central component of alkylation repair, especially from single-stranded DNA. However, the molecular mechanism of ALKBH3-mediated damage recognition and repair is less understood. We report that ALKBH3 has a direct protein-protein interaction with human RAD51 paralogue RAD51C. We also provide evidence that RAD51C–ALKBH3 interaction stimulates ALKBH3-mediated repair of methyl-adduct located within 3′-tailed DNA, which serves as a substrate for the RAD51 recombinase. We further show that the lack of RAD51C–ALKBH3 interaction affects ALKBH3 function in vitro and in vivo. Our data provide a molecular mechanism underlying upstream events of alkyl adduct recognition and repair by ALKBH3.

Human RAD51 paralogue, SWSAP1, fosters RAD51 filament by regulating the anti-recombinase, FIGNL1 AAA+ ATPase

SummaryRAD51 assembly on single-stranded (ss)DNAs is a crucial step in the homology-dependent repair of DNA damage for genomic stability. The formation of the RAD51 filament is tightly regulated by various RAD51-interacting proteins. The familial breast cancer gene, BRCA2, as well as RAD52 and six RAD51 paralogues (SWSAP1, RAD51B, RAD51C, RAD51D, XRCC2, and XRCC3) promote RAD51 assembly on ssDNAs in humans. However, the mechanisms underlying the differential control of RAD51 filament dynamics by these factors remain largely unknown. Here, we report a role for the human RAD51 paralogue, SWSAP1, as a novel regulator of RAD51 assembly. Swsap1-deficient cells show defects in DNA damage-induced RAD51 assembly during both mitosis and meiosis. Defective RAD51 assembly in SWSAP1-depleted cells is suppressed by the depletion of FIGNL1, an AAA+ ATPase, which binds to RAD51 as well as SWSAP1. Purified FIGNL1 promotes the dissociation of RAD51 from ssDNAs. The in vitro dismantling activity of FIGNL1 does not require its ATPase but depends on RAD51-binding, suggesting a novel mechanism of RAD51 filament remodelling. Purified SWSAP1 inhibits the RAD51-dismantling activity of FIGNL1. Taken together, our data suggest that SWSAP1 protects RAD51 filaments by antagonizing the anti-recombinase, FIGNL1.

RAD-ical New Insights into RAD51 Regulation

The accurate repair of DNA is critical for genome stability and cancer prevention. DNA double-strand breaks are one of the most toxic lesions; however, they can be repaired using homologous recombination. Homologous recombination is a high-fidelity DNA repair pathway that uses a homologous template for repair. One central HR step is RAD51 nucleoprotein filament formation on the single-stranded DNA ends, which is a step required for the homology search and strand invasion steps of HR. RAD51 filament formation is tightly controlled by many positive and negative regulators, which are collectively termed the RAD51 mediators. The RAD51 mediators function to nucleate, elongate, stabilize, and disassemble RAD51 during repair. In model organisms, RAD51 paralogs are RAD51 mediator proteins that structurally resemble RAD51 and promote its HR activity. New functions for the RAD51 paralogs during replication and in RAD51 filament flexibility have recently been uncovered. Mutations in the human RAD51 paralogs (RAD51B, RAD51C, RAD51D, XRCC2, XRCC3, and SWSAP1) are found in a subset of breast and ovarian cancers. Despite their discovery three decades ago, few advances have been made in understanding the function of the human RAD51 paralogs. Here, we discuss the current perspective on the in vivo and in vitro function of the RAD51 paralogs, and their relationship with cancer in vertebrate models.

RAD-ical New Insights into RAD51 Regulation

Accurate repair of DNA is critical for genome stability and cancer prevention. DNA double-strand breaks are one of the most toxic lesions and can be repaired using homologous recombination (HR). HR is a high-fidelity DNA repair pathway that uses a homologous template for repair. One central HR step is RAD51 nucleoprotein filament formation on the single-stranded DNA ends, a step required for the homology search and strand invasion steps of HR. RAD51 filament formation is tightly controlled by many positive and negative regulators, collectively termed the RAD51 mediators. The RAD51 mediators function to nucleate, elongate, stabilize, and disassemble RAD51 during repair. In model organisms, RAD51 paralogs are RAD51 mediator proteins that structurally resemble RAD51 and promote its HR activity. New functions for the RAD51 paralogs during replication and in RAD51 filament flexibility have recently been uncovered. Mutations in the human RAD51 paralogs (RAD51B, RAD51C, RAD51D, XRCC2, XRCC3, and SWSAP1) are found in a subset of breast and ovarian cancers. Despite their discovery three decades ago, few advances have been made in understanding the function of the human RAD51 paralogs. Here we discuss the current perspective on the RAD51 paralogs in vivo and in vitro function and their relationship with cancer in vertebrate models.