Rad54B serves as a scaffold in the DNA damage response that limits checkpoint strength

Abstract

The strength of the DNA damage checkpoint critically influences cell fate, yet the mechanisms behind the fine tuning of checkpoint strength during the DNA damage response (DDR) are poorly understood. Here we show that Rad54B-a SNF2 helicase-like DNA-repair protein-limits the strength of both the G1/S and G2/M checkpoints. We find that Rad54B functions as a scaffold for p53 degradation via its direct interaction with the MDM2-MDMX ubiquitin-ligase complex. During the early phases of the DDR, Rad54B is upregulated, thereby maintaining low checkpoint strength and facilitating cell cycle progression. Once the p53-mediated checkpoint is established, Rad54B is downregulated, and high checkpoint strength is maintained. Constitutive upregulation of Rad54B activity, which is frequently observed in tumours, promotes genomic instability because of checkpoint override. Thus, the scaffolding function of Rad54B dynamically regulates the maintenance of genome integrity by limiting checkpoint strength.

Mechanistic basis for increased human gene targeting by promoterless vectors—roles of homology arms and Rad54 paralogs

“…Clearly, further work is required to clarify the mechanism of Rad54/Rad54B‐independent gene targeting in human cells, the occurrence of which is demonstrated in our present study. It will also be important to elucidate the exact roles of Rad54B in preserving genome integrity, as this protein has recently been reported to promote genomic instability via the degradation of p53 protein . Interestingly, the combined absence of Rad54B and DNA ligase IV in HCT116 cells is synthetically lethal .…”

The enigmatic oncogene and tumor suppressor‐like properties of RAD54B: Insights into genome instability and cancer

“…Recently, Yasuhara et al identified a novel role for RAD54B in cell cycle checkpoint regulation. More specifically, they showed that following DNA damage induced by Oxaliplatin, RAD54B expression levels increased and were inversely correlated with p53 levels, suggesting RAD54B regulates p53 levels . They further showed that RAD54B acts as a scaffolding protein and physically interacts with the MDM2/MDMX ubiquitin ligase complex.…”

“…Based on the inverse relationship observed between RAD54B and p53, it's not difficult to envision how RAD54B overexpression could lead to abnormal scaffolding of the MDMX/MDM2 ubiquitin ligase complex to induce premature p53 degradation that would adversely impact normal cell cycle regulation and progression. Indeed, RAD54B overexpression effectively suppresses the G1/S checkpoint and promotes checkpoint override (Figure B) to drive oncogenesis . Moreover, high RAD54B expression levels during G2 can result in the bypass of the G2 checkpoint in a process referred to as checkpoint adaptation.…”

“…25 Although MDMX has no intrinsic ubiquitin ligase function, it forms a heterodimer with MDM2 which enhances its ubiquitin ligase activity. 26 Recently, Yasuhara et al 5 identified a novel role for RAD54B in cell cycle checkpoint regulation. More specifically, they showed that following DNA damage induced by Oxaliplatin, RAD54B expression levels increased and were inversely correlated with p53 levels, suggesting RAD54B regulates p53 levels.…”

“…RAD54B generally functions in two distinct aspects of the DDR – it functions in regulating the DNA damage checkpoint response and in the homologous recombination repair (HRR) pathway itself . Thus, the precise regulation of RAD54B expression and function are critical, as both hypermorphic or hypomorphic function contribute to genome instability (detailed below), suggesting RAD54B harbors both oncogene and tumor suppressor‐like properties.…”