Effect of pathogenic mis-sense mutations in lamin A on its interaction with emerin in vivo

Abstract

Mutations in lamin A/C can cause Emery-Dreifuss muscular dystrophy (EDMD)or a related cardiomyopathy (CMD1A). Using transfection of lamin-A/C-deficient fibroblasts, we have studied the effects of nine pathogenic mutations on the ability of lamin A to assemble normally and to localize emerin normally at the nuclear rim.Five mutations in the rod domain (L85R, N195K, E358K, M371K and R386K)affected the assembly of the lamina. With the exception of mutant L85R, all rod domain mutants induced the formation of large nucleoplasmic foci in about 10% of all nuclei. The presence of emerin in these foci suggests that the interaction of lamin A with emerin is not directly affected by the rod domain mutations. Three mutations in the tail region, R453W, W520S and R527P, might directly affect emerin binding by disrupting the structure of the putative emerin-binding site, because mutant lamin A localized normally to the nuclear rim but its ability to trap emerin was impaired. Nucleoplasmic foci rarely formed in these three cases (<2%) but, when they did so, emerin was absent,consistent with a direct effect of the mutations on emerin binding. The lipodystrophy mutation R482Q, which causes a different phenotype and is believed to act through an emerin-independent mechanism, was indistinguishable from wild-type in its localization and its ability to trap emerin at the nuclear rim.The novel hypothesis suggested by the data is that EDMD/CMD1A mutations in the tail domain of lamin A/C work by direct impairment of emerin interaction,whereas mutations in the rod region cause defective lamina assembly that might or might not impair emerin capture at the nuclear rim. Subtle effects on the function of the lamina-emerin complex in EDMD/CMD1A patients might be responsible for the skeletal and/or cardiac muscle phenotype.

Blocking farnesylation of the prelamin A variant in Hutchinson-Gilford progeria syndrome alters the distribution of A-type lamins

“…54 These intranuclear foci are likely to be near the inner nuclear membrane, inducing micro-invaginations of inner nuclear membrane and allowing emerin, a transmembrane protein, to co-localize with them. 54 The localized binding to an A-type lamin likely prevents emerin from redistributing into the endoplasmic reticulum, as it does in cells lacking A-type lamins.…”

“…54 These intranuclear foci are likely to be near the inner nuclear membrane, inducing micro-invaginations of inner nuclear membrane and allowing emerin, a transmembrane protein, to co-localize with them. 54 The localized binding to an A-type lamin likely prevents emerin from redistributing into the endoplasmic reticulum, as it does in cells lacking A-type lamins. 45 Given the observed effects of non-farnesylated progerin on A-type lamin and emerin redistribution, monitoring subjects with HGPS for adverse events involving striated muscle and nerve in clinical trials of protein farnesylation inhibitors would be prudent.…”

Proteins that associate with lamins: Many faces, many functions

“…When expressed, several mutants of emerin (S54F, P183H, P183T, and Del95-99) mislocalized to the cytoplasm [109]. Intriguingly, mutations in lamin A cause the autosomal type of EDMD [110] and similarly, the expression of some of these lamin A mutants (L85R, N195K, E358K, M371K, R386K, R453W, W520S, and R527P) also resulted in mislocalization of emerin [111]. This suggests that functional lamin-emerin complexes are lost by mutations in either protein.…”

Both lamin A and lamin C mutations cause lamina instability as well as loss of internal nuclear lamin organization

“…However, studies on abnormalities in cells from (heterozygous) mutant patient material or cells transfected with mutant lamins yielded partly contradictory results. For instance, while some studies could find no nuclear abnormalities in nuclei of cells transfected with R482W A-type lamin mutants [15,16], others [17] did see clear nuclear abnormalities in fibroblast cells from patients with this mutation.…”

“…The R386K mutation is in the rod domain of lamin A/C, while the other two mutations are localized in its tail domain [22]. While the effects of several of these mutations on lamina organization were already studied previously [15][16][17]23,24], these studies did not examine the effect on internally localized lamins. Moreover, this is the first study that examines the feasibility of FLIP to study organization of lamins at the molecular level.…”