Alteration of genetic recombination and double-strand break repair in human cells by progerin expression

Hutchinson-Gilford Progeria Syndrome (HGPS) is a rare autosomal, dominant genetic condition characterized by many features of accelerated aging. On average, children with HGPS live to about fourteen years of age. The syndrome is commonly caused by a point mutation in the LMNA gene which normally codes for lamin A and its splice variant lamin C, components of the nuclear lamina. The LMNA mutation alters splicing, leading to production of a truncated, farnesylated form of lamin A referred to as "progerin." Progerin is also expressed at very low levels in healthy individuals and appears to play a role in normal aging. HGPS is associated with an accumulation of genomic DNA double-strand breaks (DSBs), suggesting corruption of DNA repair. In this work, we investigated the influence of progerin expression on DSB repair in the human genome at the nucleotide level. We used a model system that involves a reporter DNA substrate inserted in the genome of cultured human cells. A DSB could be induced within the substrate through exogenous expression of endonuclease I-SceI, and DSB repair events occurring via either homologous recombination (HR) or nonhomologous end-joining (NHEJ) were recoverable. Additionally, spontaneous HR events were recoverable in the absence of artificial DSB induction. We compared DSB repair and spontaneous HR in cells overexpressing progerin versus cells expressing no progerin. We report that overexpression of progerin correlated with an increase in DSB repair via NHEJ relative to HR, as well as an increased fraction of HR events occurring via gene conversion. Progerin also engendered an apparent increase in spontaneous HR events, with a highly significant shift toward gene conversion events, and an increase in DNA amplification events. Such influences of progerin on DNA transactions may impact genome stability and contribute to aging.