Distinct regions specify the nuclear membrane targeting of emerin, the responsible protein for Emery–Dreifuss muscular dystrophy

Abstract

Emery±Dreifuss muscular dystrophy is a neuromuscular disorder that has three characteristics: (a) early contracture of the elbows, Achilles tendons and postcervical muscles; (b) slowly progressive wasting and weakness of skeletal muscle; and (c) cardiomyopathy with severe conduction block. The responsible gene for the X-linked recessive form of this disease encodes an inner nuclear membrane protein named emerin. Although emerin is absent in tissues from patients with this disorder, it remains obscure why the loss of this widely expressed protein affects selectively skeletal muscle, heart and joints. As the first step to address this question, we examined the molecular regions of emerin that are essential for nuclear membrane targeting and stability of the protein. We found that the C-terminal hydrophobic region was necessary, but not sufficient, for nuclear membrane anchoring and stability of the protein. In the absence of this transmembrane domain, the upstream nucleoplasmic domain showed no firm association with the nuclear rim, but showed the tendency to accumulate at the nucleolus-like structures. Furthermore, proper targeting of emerin to the nuclear membrane required the latter half of the nucleoplasmic domain. These characteristics are distinct from those of lamina-associated polypeptide 2. Our findings indicate that emerin has distinct interactions with the inner nuclear membrane components that may be required for the stability and function of rigorously moving nuclei in tissues such as skeletal muscle, heart and joints.

Emery-Dreifuss muscular dystrophy mutations impair TRC40-mediated targeting of emerin to the inner nuclear membrane

“…The two mutants lacking a transmembrane domain, mCherry-FRB-emerin-Trp226* and -Leu225Arg-FS (Fig. 6A,B), localized to the nucleus, in agreement with previous studies, where similar constructs had been used (Östlund et al, 1999;Tsuchiya et al, 1999). Consequently, rapamycin did not induce a relocalization of the GFP reporter protein to the nuclear periphery -instead, this depended on the presence of an FRB-presenting protein at the INM (Fig.…”

“…Thus, our results might suggest that membrane insertion of emerin through the TRC40 pathway and trafficking of the protein to the INM are sequential processes with distinct requirements. However, the major determinants for proper localization of emerin to the INM have been localized to regions outside of the transmembrane domain (Östlund et al, 1999;Tsuchiya et al, 1999). Our observations thus raise the interesting possibility that integration through the TRC40 pathway affects the correct targeting of emerin to its final destination, beyond initial membrane insertion.…”

“…From the ER, it is expected to traffic to the INM via the ONM and the NPC. Emerin as well as several other proteins of the INM contain putative nuclear localization signals (NLSs) and emerin fragments lacking the transmembrane domain were found to accumulate in the nucleus as a result of the NLS activity (Östlund et al, 1999;Tsuchiya et al, 1999). The significance of these NLSs and also of their cognate receptor proteins (e.g.…”

Tyrosine phosphorylation of nuclear-membrane protein emerin by Src, Abl and other kinases

“…Plasmids encoding the following polypeptides were described previously: pET23b human LAP2 residues 1-408 (Gant et al, 1999), pET11c human emerin residues 1-222 , and pEGFP-emerin (human, full-length) (Tsuchiya et al, 1999). pET29b-emerin 1-176 and pGEX-emerin 1-176 were generously provided by J. Ellis (Wheeler et al, 2007).…”

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

“…This interaction involves the globular tail region common to lamins A and C ) and a central region (amino acids 70-164) of the emerin molecule . A similar region of emerin (amino acids 107-175) is required for its localization to the nuclear rim (Tsuchiya et al, 1999;Östlund et al, 1999), suggesting involvement of lamin A/C, and this was confirmed by the location of emerin in the ER in the lamin A/C knockout mouse (Sullivan et al, 1999). However, partial localization of emerin at the nuclear rim was still observed in some knockout mouse tissues, suggesting that factors other than lamin A/C can be involved (Sullivan et al, 1999).…”