RAD51 Is Implicated in DNA Damage, Chemoresistance and Immune Dysregulation in Solid Tumors

Abstract

Background: In normal cells, homologous recombination (HR) is tightly regulated and plays an important role in the maintenance of genomic integrity and stability through precise repair of DNA damage. RAD51 is a recombinase that mediates homologous base pairing and strand exchange during DNA repair by HR. Our previous data in multiple myeloma and esophageal adenocarcinoma (EAC) show that dysregulated HR mediates genomic instability. Purpose of this study was to investigate role of HR in genomic instability, chemoresistance and immune dysregulation in solid tumors including colon and breast cancers. Methods: The GEO dataset were used to investigate correlation of RAD51 expression with patient survival and expression of various immune markers in EAC, breast and colorectal cancers. RAD51 was inhibited in cancer cell lines using shRNAs and a small molecule inhibitor. HR activity was evaluated using a plasmid-based assay, DNA breaks assessed by evaluating expression of γ-H2AX (a marker of DNA breaks) and p-RPA32 (a marker of DNA end resection) using Western blotting. Genomic instability was monitored by investigating micronuclei (a marker of genomic instability). Impact of RAD51 inhibitor and/or a DNA-damaging agent was assessed on viability and apoptosis in EAC, breast and colon cancer cell lines in vitro and in a subcutaneous tumor model of EAC. Impact of RAD51 inhibitor on expression profile was monitored by RNA sequencing. Results: Elevated RAD51 expression correlated with poor survival of EAC, breast and colon cancer patients. RAD51 knockdown in cancer cell lines inhibited DNA end resection and strand exchange activity (key steps in the initiation of HR) as well as spontaneous DNA breaks, whereas its overexpression increased DNA breaks and genomic instability. Treatment of EAC, colon and breast cancer cell lines with a small molecule inhibitor of RAD51 inhibited DNA breaking agent-induced DNA breaks and genomic instability. RAD51 inhibitor potentiated cytotoxicity of DNA breaking agent in all cancer cell types tested in vitro as well as in a subcutaneous model of EAC. Evaluation by RNA sequencing demonstrated that DNA repair and cell cycle related pathways were induced by DNA breaking agent whereas their induction either prevented or reversed by RAD51 inhibitor. In addition, immune-related pathways such as PD-1 and Interferon Signaling were also induced by DNA breaking agent whereas their induction prevented by RAD51 inhibitor. Consistent with these observations, elevated RAD51 expression also correlated with that of genes involved in inflammation and other immune surveillance. Conclusions: Elevated expression of RAD51 and associated HR activity is involved in spontaneous and DNA damaging agent-induced DNA breaks and genomic instability thus contributing to chemoresistance, immune dysregulation and poor prognosis in cancer. Therefore, inhibitors of RAD51 have great potential as therapeutic agents for EAC, colon, breast and probably other solid tumors.

Mechanistic study of dual‐function inhibitors targeting topoisomerase II and Rad51‐mediated DNA repair pathway against castration‐resistant prostate cancer

“…Rad51 overexpression is suggested to serve as a negative prognostic marker in several cancers, including colorectal cancer, breast cancer, cervical cancer, and prostate cancer. [37][38][39] It has gathered much attention as both a biomarker and a potential target in antineoplastic therapy and, therefore, several strategies have been raised. Huang and colleagues have developed small molecules to disrupt Rad51 binding to DNA and to inhibit the DNA strand exchange activity of Rad51.…”

“…Rad51 which protects stalled replication forks is the key strand exchange factor in DSBs repair through the homologous recombination pathway. Rad51 overexpression is suggested to serve as a negative prognostic marker in several cancers, including colorectal cancer, breast cancer, cervical cancer, and prostate cancer 37–39 . It has gathered much attention as both a biomarker and a potential target in antineoplastic therapy and, therefore, several strategies have been raised.…”

Importin α accumulates in micronuclei and associates with genomic instability in human cancer cells

“…Increased RAD51 expression promotes recombination events and genome instability in tumor cells (Klein, 2008;Richardson et al, 2004). Importantly, both importin α1 and RAD51 have been implicated in tumorigenesis and patient survival (Christiansen and Dyrskjot, 2013;Han and Wang, 2020;Liao et al, 2022).…”

Rad51 and Systemic Inflammatory Indicators as Novel Prognostic Markers in Esophageal Squamous Cell Carcinoma

“…Elevated levels of RAD51 protein have been observed in numerous cancer cell lines and primary tumors. 10 Previous bioinformatic analyses have provided supporting evidence for the potential clinical significance of RAD51 in cancer management, including cancer diagnosis, prognosis, and therapeutic prediction.…”

“…Previous studies have systematically reviewed the role of some inflammation and nutrition-based indicators in the prognosis of EC. 10 However, no studies have explored the relationship between RAD51, the key mediator of HR and the inflammation status and postoperative outcomes of ESCC patients.…”