Host: The Japan Radiation Research Society
Nijmegen breakage syndrome (NBS) is a rare autosomal recessive genetic disorder characterized by immunodeficiency and cancer predisposition. The NBS cellular phenotype includes chromosomal instability, hyper-sensitivity to radiation and abnormal checkpoints activation. NBS1 protein, product of the NBS gene, forms a complex with MRE11 and RAD50, and the RAD50/MRE11/NBS1 (R/M/N) complex plays a crucial role in DNA double strands break (DSB) repair. The human NBS1 has three functional regions: N-terminus fork head associated (FHA) and BRCA1 C-terminus (BRCT) domains, two serine residues at 278 and 343 that are phosphorylated by the ATM or ATR kinases, and the C-terminus MRE11 binding domain and ATM interacting domain. We have previously reported that the R/M/N complex with functional NBS1 is essential for homologous recombination (HR) repair pathway and that FHA domain is required for regulation of normal HR function. To investigate whether mutation in FHA domain presents a dominant negative effect on cellular HR activity, we analyzed HR efficiency in normal or mutant NBS1 expressing HeLa cells carrying a SCneo reporter construct. It was found that mutation in FHA domain induces significant reduction of HR frequency, suggesting that regulation of nuclear localization of R/M/N complex might be crucial for HR function.
