Increased solubility of lamins and redistribution of lamin C in X-linked Emery–Dreifuss muscular dystrophy fibroblasts

Changes in the expression and distribution of nuclear lamins were investigated during C2C12 myoblast differentiation. The expression of most lamins was unchanged during myogenesis. By contrast, lamin-B2 expression increased and LAP2α expression decreased twofold. These changes were correlated with reduced solubility and redistribution of A-type lamins. When C2C12 myoblasts were transfected with a lamin-A mutant that causes autosomal dominant Emery-Dreifuss muscular dystrophy (AD-EDMD), the mutant protein accumulated in the nucleoplasm and exerted dominant influences over endogenous lamins. Myoblasts transfected with wild-type lamins differentiated, albeit more slowly, whereas myoblasts transfected with mutant lamins failed to differentiate. Myoblast differentiation requires dephosphorylation of the retinoblastoma protein Rb. During myogenesis, Rb was rapidly and progressively dephosphorylated. Underphosphorylated Rb formed complexes with LAP2α in proliferating myoblasts and postmitotic myoblasts. In myoblasts transfected with the mutant lamins, this complex was disrupted. These data suggest that remodelling of the nucleoskeleton is necessary for skeletal-muscle differentiation and for correct regulation of Rb pathways.

Section: Resultsmentioning

confidence: 99%

Section: Remodelling Of the Nucleoskeleton Accompanies Myogenesismentioning

confidence: 87%

Remodelling of the nuclear lamina and nucleoskeleton is required for skeletal muscle differentiation in vitro

Markiewicz

Ledran

Hutchison

2005

“…This LUMA pool displays extraction properties typical for an integral membrane protein of the INM. For example, LUMA enriches during preparation of nuclei and nuclear envelopes, just like the integral INM protein emerin and lamin A of the nuclear lamina (Riedel and Fasold, 1987;Manilal et al, 1996;Markiewicz et al, 2002). Similar to INM proteins LBR or LAP2␤, which both bind with high affinity to nuclear lamina (Bailer et al, 1991;Foisner and Gerace, 1993), solubilization of LUMA immobilized at the NE requires both high ionic strength and detergent.…”

Section: Discussionmentioning

confidence: 99%

LUMA interacts with emerin and influences its distribution at the inner nuclear membrane

Bengtsson

Otto

2008

105

The nuclear envelope (NE) defines the border of the nucleus: an inner nuclear membrane (INM) and an outer nuclear membrane (ONM) join at the nuclear pores, which harbor the nuclear pore complexes (NPCs) that guard the entry to and exit from the nucleus. Although the ONM is continuous with the rough endoplasmic reticulum (rER), both ONM and INM have specific sets of integral membrane proteins (Schirmer and Foisner, 2007). There are ~80 known INM proteins (Dreger et al., 2001;Schirmer et al., 2003;Schirmer and Foisner, 2007). These enrich at the nucleoplasmic face of the nuclear membrane by binding lamina and chromatin components in the nucleus (Gruenbaum et al., 2005). The nuclear lamina, an extremely stable filament meshwork consisting of intermediate filament proteins, the lamins, supports the INM. Two types of lamins -type A and B -build the lamina. The laminanetwork is thought to act both as tensegrity element (Hutchison, 2002) and as a scaffold, organizing the spatial arrangement of proteins required for cellular functions, such as DNA replication, gene expression, chromosome attachment, signaling and nuclear positioning (Gruenbaum et al., 2005;Schirmer and Foisner, 2007). The best studied INM proteins belong to the family of LEM-domain proteins, which were named for a domain present in LAP2, emerin and MAN1. The LEM-domain is the binding site for the small chromatin protein barrier-to-autointegration factor (BAF) (Margalit et al., 2007) and thus provides a link between the nuclear membrane and chromatin. A similar role is postulated for the lamin B receptor, which binds histones H3 and H4, and heterochromatin protein HP1 (Ye et al., 1997;Polioudaki et al., 2001). Besides BAF, LEM-domain proteins also bind transcriptional co-repressors (e.g. Btf, GCL) (Holaska et al., 2003;Haraguchi et al., 2004;Melcon et al., 2006) and transcription factors (SMADs, E2F) (Bengtsson, 2007). Additionally, some recruit chromatin-modifying complexes (Somech et al., 2005) and some can influence transcription directly (Nili et al., 2001). Thus, INM proteins have active roles in the regulation of gene expression.The importance of the NE in the regulation of cellular processes has been highlighted by the fact that more than 200 mutations in lamins and lamina-associated proteins cause 18 different diseases collectively called laminopathies (Broers et al., 2006;Rankin and Ellard, 2006). Laminopathies range from Emery-Dreifuss muscular dystrophy (EDMD) to Hutchinson-Gilford progeria syndrome (Rankin and Ellard, 2006). Most laminopathies are linked to mutations in A-type lamins, for example the autosomal-dominant EDMD (Bonne et al., 1999). Interestingly, mutations in the laminaassociated LEM-domain protein emerin cause a X-chromosomelinked recessive form of EDMD (Bione et al., 1994). In cells of most patients suffering from any of the EDMD forms, emerin is missing from the NE (Bengtsson and Wilson, 2004). The exact molecular mechanism leading to disease is not yet known. However, cumulating evidence from biochemical and cell biological ...

“…homeodomain proteins, helix-loop-helix or zinc finger transcription factors, nucleolar proteins and tumor suppressors (Marsh et al, 1998;Yang et al, 1999;Fan et al, 2002;Fabbro and Henderson, 2003;Kaiser et al, 2004). In addition, impairment of the NPC components and nuclear lamina has also been associated with the etiology of disease (Markiewicz et al, 2002).…”

Section: Discussionmentioning

confidence: 99%

Impairment of SHOX nuclear localization as a cause for Léri-Weill syndrome

Sabherwal

Schneider

Blaschke

et al. 2004

We report the characterization of the nuclear localization signal (NLS) of the short stature homeobox gene SHOX. Mutations within the SHOX gene cause Léri-Weill dyschondrosteosis (LWD) and Langer mesomelic dysplasia (LD) as well as idiopathic short stature (ISS). Furthermore, haploinsufficiency of SHOX has also been implicated in Turner syndrome. SHOX has been shown to be a cell-type-specific transcriptional activator that localizes to the nucleus. The SHOX protein contains a central homeodomain that together with its transactivation domain regulates the transcription of its target sequences within the nucleus. The sequences for its nuclear localization have not been identified yet. Experimental characterization of SHOX-NLS by deletion mapping identified a non-classic type basic signal, AKCRK, in the recognition helix of the homeodomain. Fusion of this stretch of five amino acids to a cytoplasmic reporter protein resulted in its nuclear translocation. Functional analysis of a missense mutation R173C (C517T) affecting the identified SHOX-NLS in two families with LWS and LD showed that the mutated SHOX protein is unable to enter the nucleus. Conversely, we can demonstrate that insertion of the identified signal adjacent to the mutant site can restore its nuclear translocation. These results establish impairment of nuclear localization as a mechanistic basis for SHOX-related diseases.