DNA repair functional analyses of NBN hypomorphic variants associated with NBN‐related infertility

Abstract

Nijmegen breakage syndrome caused by biallelic pathogenic variants of the DNAdamage response gene NBN, is characterized by severe microcephaly, cancer proneness, infertility, and karyotype abnormalities. We previously reported NBN variants in siblings suffering from fertility defects. Here, we identify a new founder NBN variant (c.442A>G, p.(Thr148Ala)) in Lebanese patients associated with isolated infertility. Functional analyses explored preserved or altered functions correlated with their remarkably mild phenotype. Transcript and protein analyses supported the use of an alternative transcript with in-frame skipping of exons 4-5, leading to p84-NBN protein with a preserved forkhead-associated (FHA) domain. The level of NBN was dramatically reduced and the MRN complex delocalized to the cytoplasm. Interestingly, ataxia-elangiectasia mutated (ATM) also shifted from the nucleus to the cytoplasm, suggesting some interaction between ATM and the MRN complex at a steady state. The ATM pathway activation, attenuated in typical patients with NBS, appeared normal under camptothecin treatment in these new NBN-related infertile patients. Cell cycle checkpoint defect was present in these atypical patients, although to a lesser extent than in typical patients with NBS. In conclusion, we report three new NBN-related infertile patients and we suggest that preserved FHA domain could be responsible for the mild phenotype and intermediate DNA-damage response defects. K E Y W O R D S ATM, cell cycle checkpoint, FHA, infertility, NBN, Nijmegen syndrome, premature ovarian failure *Alice Fiévet and Dorine Bellanger contributed equally to this study.

Impaired p53-Mediated DNA Damage Response Contributes to Microcephaly in Nijmegen Breakage Syndrome Patient-Derived Cerebral Organoids

“…Our results indicate that inhibition of MDM2-p53 interaction by nutlin-3a allows p53 stabilization and the enhanced response to nultin-3a further demonstrates that the levels of DNA damage are higher in NBS organoids. An impaired DDR pathway was observed in the NBS organoids, probably due to the attenuation of the ATM-p53 pathway activation after endogenous DNA damage, in line with previous studies [ 58 , 59 ].…”

Identification of Germline Mutations in Melanoma Patients with Early Onset, Double Primary Tumors, or Family Cancer History by NGS Analysis of 217 Genes

“…The highest prevalence of germline mutations in our melanoma patients was found in the NBN gene (in 7/264 patients; 2.7%), coding for nibrin, a protein contributing to a MRN complex formation, sensing for DNA double strand breaks. We found the most frequent, Slavic founder germ-line hypomorphic variant c.657del5 in five patients [ 48 ]. Two of them also developed ovarian cancer, which was associated with NBN germline mutations in our population [ 49 ].…”

Analysis of clinical and genomic profiles of therapy-related myeloid neoplasm in Korea

“…The RUNX family, including RUNX1, has been implicated in the regulation of DNA damage response [ 54 ], and RUNX1 stimulates the tumor suppressor p53 protein in response to DNA damage [ 55 ]. MRN complex, which is essential for DNA repair, is a sensor of double-strand breaks, and directly functions in the repair process [ 56 ]. NBN is crucial for early MRN recruitment [ 57 ].…”