Nijmegen breakage syndrome fibroblasts expressing the C-terminal truncated NBN(p70) protein undergo p38/MK2-dependent premature senescence.

Fibroblasts from the progeroid Nijmegen breakage syndrome that express a truncated version of the nibrin protein (NBN(p70)) undergo premature senescence and have an enlarged morphology with high levels of senescence-associated β-galactosidase, although they do not have F-actin stress fibres. Growth of these fibroblasts in the continuous presence of p38 inhibitors resulted in a large increase in replicative capacity and changed the cellular morphology so that the cells resembled young normal fibroblasts. A similar effect was seen using an inhibitor of the p38 downstream effector kinase MK2. These data suggest that NBN(p70) expressing cells undergo a degree of stress-induced replicative senescence via p38/MK2 activation, potentially due to increased telomere dysfunction, that may play a role in the progeroid features seen in this syndrome.