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

Abstract

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 ...

Lamin-binding Proteins

“…Emerin directly binds more than ten known partners, suggesting a degree of biochemical complexity at the NE that rivals many cell surface structures. Among these partners are structural proteins (nesprin-1a, nesprin-2b, actin, nuclear myosin 1c, lamins, and tubulin), other INM proteins (MAN1 and LUMA), proteins involved in signaling, transcription, mRNA splicing (b-catenin, GCL, Lmo7, Btf, and YT521-B), and of course, BAF Mislow et al 2002a;Holaska et al 2003;Haraguchi et al 2004;Holaska et al 2004;Mansharamani and Wilson 2005;Markiewicz et al 2006;Wheeler et al 2007;Bengtsson and Otto 2008) (for reviews, see Bengtsson and Wilson 2004;Wagner and Krohne 2007). The biochemical purification of emerin-associated protein complexes from HeLa cell nuclei suggests emerin can form at least six distinct multiprotein complexes (Holaska and Wilson 2007).…”

PP2A regulates BMP signalling by interacting with BMP receptor complexes and by dephosphorylating both the C-terminus and the linker region of Smad1

“…The anti-receptor antibodies were cross-linked to protein-A-Sepharose (SigmaAldrich) with DMS (dimethyl suberimidate dihydrochloride; Pierce, Rockford, IL) before use. For immunoblotting the following antibodies, diluted as indicated in TBST (150 mM NaCl, 50 mM Tris-HCl pH 8.0, 0.1% v/v Tween) were used: anti-PP2A-B (1:1000; Millipore), anti-HA (1:1000; Roche Diagnostics, Mannheim, Germany), anti-FLAG (1:2000; Sigma-Aldrich), anti-β-actin (1:5000-1:10,000; Sigma-Aldrich), anti-MYC [1:1000 (Bengtsson and Otto, 2008)], anti-Smad1 (1:500; Santa Cruz Biotechnology, Santa Cruz, CA or 1:1000; Cell Signalling Technology), anti-MBP (1:1000; Cell Signalling Technology, Danvers, MA), anti-p-Smad1/5/8 (1:1000; Cell Signalling Technology), and anti-MAPK/CDK substrate (1:1000; Cell Signalling Technology). The blots were developed with appropriate HRP-conjugated secondary antibodies followed by ECL reaction.…”

TMEM43 mutations in emery‐dreifuss muscular dystrophy‐related myopathy

“…20 In the meanwhile, the topological and functional characterization of LUMA showed that it contains a large hydrophilic and 4 transmembrane domains, and that the transmembrane spans are necessary for nuclear envelope targeting and homo-oligomerization. 21 In addition, it was demonstrated that LUMA interacts with lamins and emerin and is involved in the structural organization of nuclear membrane. As emerin is postulated to form complexes with different partners at NE to carry out distinct functions, 21,22 and mutation in TMEM43 could cause cardiac conduction defect, a characteristic of EDMD, LUMA can logically be considered to contribute to the pathomechanism of EDMD-related myopathy.…”

“…21 In addition, it was demonstrated that LUMA interacts with lamins and emerin and is involved in the structural organization of nuclear membrane. As emerin is postulated to form complexes with different partners at NE to carry out distinct functions, 21,22 and mutation in TMEM43 could cause cardiac conduction defect, a characteristic of EDMD, LUMA can logically be considered to contribute to the pathomechanism of EDMD-related myopathy.…”