Roles of the lamin A-specific tail region in the localization to sites of nuclear envelope rupture.

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 with LC, but the underlying mechanism remains unknown. In this study, wild-type (WT), Hutchinson-Gilford Progeria syndrome (HGPS) knock-in MEFs expressing progerin (PG, an LA mutant lacking the second proteolytic cleavage site), and LA/C-knockout MEFs transiently and heterogeneously expressing LA/C WTs and mutants fused to mEmerald are examined before and after NE rupture induced by single-cell compression and laser microirradiation. 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.