Delayed localization of A-type lamins to the rupture sites in Hutchinson–Gilford progeria syndrome

The nuclear lamina (NL) lines the nuclear envelope (NE) to maintain nuclear structure in metazoan cells. The major NL components, the nuclear lamins contribute to the protection against NE rupture induced by mechanical stress. Lamin A (LA) and a short form of the splicing variant lamin C (LC) are diffused from the nucleoplasm to sites of NE rupture in immortalized mouse embryonic fibroblasts (MEFs). LA localization to the rupture sites is significantly slow and weak compared to LC because of its relatively small pool in the nucleoplasm, but the precise mechanism remains unknown. In this study, we induce NE rupture in wild-type and LA/C-knockout MEFs, and Hutchinson–Gilford Progeria syndrome (HGPS) knock-in MEFs that express progerin, a LA mutant lacking the second proteolytic cleavage site, by laser microirradiation and AFM indentation. The farnesylation at the CaaX motif of unprocessed LA and the inhibition of the second proteolytic cleavage decrease the nucleoplasmic pool and slow the localization to the rupture sites in a long-time window (60-70 min) after the induction of NE rupture. Our data could explain the defective repair of NE rupture in HGPS through the farnesylation at the CaaX motif of unprocessed progerin. In addition, unique segments in LA-specific tail region cooperate with each other to inhibit the rapid accumulation within a short-time window (3 min) that is also observed with LC. Significance Statement Nuclear lamins are the major components of the nuclear lamina (NL) that lies the nuclear envelope (NE). Lamin A (LA) is slowly localized to sites of nuclear envelope (NE) rupture compared to lamin C (LC). This study reveals that the farnesylation at the CaaX motif of unprocessed LA and the inhibition of the second proteolytic cleavage decrease the nucleoplasmic pool and slow the localization to the rupture sites within a long-time window (60-70 min) after the induction of NE rupture, which could explain the defective repair of NE rupture in Hutchinson–Gilford Progeria syndrome (HGPS). Additionally, unique segments in LA-specific tail region are critical for inhibiting the rapid accumulation within a short-time window (3 min). ### Competing Interest Statement The authors have declared no competing interest. * BAF : barrier-to-autointegration factor cGAS : cyclic GMP-AMP synthase DARPin : designed ankyrin repeat protein DCM : dilated cardiomyopathy ESCRT-III : endosomal sorting complex required for transport-III ER : endoplasmic reticulum FAF : fluorescence auto-correlation function FCS : fluorescence correlation spectroscopy FTI : farnesyltransferase inhibitor FPLD : familial partial lipodystrophy HGPS : Hutchinson-Gilford Progeria syndrome Ig-fold : immunoglobulin-like fold INM : inner nuclear membrane KD : knockdown KO : knockout LA : lamin A LACS : LA-characteristic sequence LB1 : lamin B1 LB2 : lamin B2 LC : lamin C LINC : linker of nucleoskeleton and cytoskeleton MEF : mouse embryonic fibroblast MD : muscular dystrophy NE : nuclear envelope NL : nuclear lamina NP : nucleoplasmic pool NPC : nuclear pore complex ONM : outer nuclear membrane PG : progerin REML : restricted maximum likelihood sfGFP : superfolder GFP sfCherry : superfolder Cherry shRNA : short hairpin RNA STING : stimulator of interferon genes WT : wild type