The RAD51 recombinase protects mitotic chromatin in human cells

Abstract

The RAD51 recombinase plays critical roles in safeguarding genome integrity, which is fundamentally important for all living cells. While interphase functions of RAD51 in repairing broken DNA and protecting stalled replication forks are well characterised, its role in mitosis remains contentious. In this study, we show that RAD51 protects under-replicated DNA in mitotic human cells and, in this way, promotes mitotic DNA synthesis (MiDAS) and successful chromosome segregation. MiDAS was globally detectable irrespective of DNA damage and was promoted by de novo RAD51 recruitment, RAD51-mediated fork protection, and RAD51 phosphorylation by the key mitotic regulator Polo-like kinase 1. Importantly, acute inhibition of RAD51-promoted MiDAS led to mitotic DNA damage, delayed anaphase onset and induced centromere fragility, revealing a mechanism that prevents the satisfaction of the spindle assembly checkpoint when chromosomal replication remains incomplete. This study hence identifies an unexpected function of RAD51 in promoting the stability of mitotic chromatin.

A conserved PLK1 docking site in TopBP1 maintains genome integrity during mitosis

“…Moreover, treatment of mitotic cells with a PLK1 inhibitor prior to EdU incubation severely reduces MiDAS in both the parental as well as the TopBP1Δ284-301 cell line (Fig. 3D and E) consistent with other studies (Minocherhomji et al, 2015; Wassing et al, 2021).…”

“…Moreover, treatment of mitotic cells with a PLK1 inhibitor prior to EdU incubation severely reduces MiDAS in both the parental as well as the TopBP1Δ284-301 cell line (Fig. 3D and E) consistent with other studies (Minocherhomji et al, 2015;Wassing et al, 2021). This indicates that the identified PLK1 docking site in TopBP1 is important for MiDAS and moreover suggests that the PLK1 TopBP1 interaction via the identified PLK1 docking site is facilitating the involvement of PLK1 in MiDAS.…”

“…PLK1 was shown to promote loading of RAD51 in interphase cells (Moudry et al, 2016) in a process that relies on BRCT7 and BRCT8 of TopBP1 for coordinating the PLK1-mediated phosphorylation of RAD51 (Moudry et al, 2016). Interestingly, PLK1-mediated RAD51-phoshorylation promotes MiDAS (Wassing et al, 2021). Furthermore, PLK1 activity is important for suppressing recruitment of NHEJ factors to camptothecin (CPT)-induced replication problems (Nakamura et al, 2021).…”

The chromatin-binding domain of Ki-67 together with p53 protects human chromosomes from mitotic damage

“…Recent studies have indicated that defects in DNA replication or broken chromosome bridges formed during interphase can result in aberrant DNA synthesis during subsequent mitoses, on a path toward high levels of genome instability (51,52). We did not detect DNA synthesis in Ki-67-depleted mitotic cells (Fig.…”

2-APCAs, the Novel Microtubule Targeting Agents Active against Distinct Cancer Cell Lines

“…Importantly, the physical association of Rad51 with microtubules was revealed in a co-immunoprecipitation assay, thereby indicating that an efficient response to DNA damage involves a cytoplasmic-to-nuclear transport of Rad51 and might be tubulin-dependent [ 51 ]. Lastly, Rad51 recombinase was proposed to be a key factor protecting mitotic chromatin by promoting the mitotic DNA synthesis of the underreplicated DNA [ 52 ], thereby suggesting that cancer cells lacking this DDR protein might be extremely sensitive to mitotic DNA damage when the cells enter mitosis before completion of DNA replication [ 53 ]. Thus, the ability of 2-APCAs to induce apoptosis of cancer cells might be due to the dual mode of action—mitotic arrest due to the enhancement of tubulin polymerization, which in turn substantially reduces Rad51 expression and triggers the cancer cell death due to the unrepairable mitotic DNA damage.…”