EMD

Emerin (EMD) is an inner nuclear membrane LEM-domain protein whose function is governed by phosphorylation and whose loss causes X-linked Emery-Dreifuss muscular dystrophy. Genetic epistasis in a family carrying both an EMD deletion and an LMNA mutation established that emerin acts synergistically with lamin A/C, with combined loss most severely depleting both proteins and producing the full dystrophy phenotype (PMID:17536044). EMD function is regulated by phosphorylation in two distinct contexts: virion-associated MAPK/ERK2 phosphorylates emerin in non-dividing cells, an event positioned downstream of the kinase and upstream of nuclear integration of the HIV-1 pre-integration complex (PMID:20463147); and PRKACA-mediated phosphorylation of the LEM domain, induced by C16-ceramide, enables emerin to bind MAP1LC3B and enhance autophagosome formation (PMID:24819607). Loss-of-function EMD mutations cause a predominantly cardiac phenotype — conduction defects, atrial cardiomyopathy, and dilated cardiomyopathy — with variable skeletal muscle involvement (PMID:15967842, PMID:24997722). The molecular basis by which emerin loss produces cardiac and muscle disease has not been dissected in the available corpus.

1. 2005 Low

   Established that EMD loss-of-function can produce a cardiac-predominant disease, decoupling the cardiac phenotype from overt skeletal myopathy.

   Evidence Sequencing of an exon 6 nonsense mutation and cardiologic phenotyping across two EDMD families

   PMID:15967842

   Open questions at the time

   • Genotype-phenotype correlation only; no molecular mechanism linking emerin loss to atrial cardiomyopathy
   • Incomplete penetrance in female carriers unexplained
2. 2007 Medium

   Demonstrated that emerin and lamin A/C interact synergistically, since combined EMD and LMNA mutations were needed for the full dystrophy phenotype and most severely depleted both proteins.

   Evidence Genetic co-segregation and protein expression analysis in patient fibroblasts from a family carrying both EMD delK37 and LMNA R298C

   PMID:17536044

   Open questions at the time

   • Synergy inferred from human genetics and protein levels, not from a reconstituted physical interaction assay
   • Molecular consequence of the emerin–lamin interaction loss not defined
3. 2010 Medium

   Placed emerin phosphorylation in the HIV infection pathway, showing virion-associated MAPK/ERK2 phosphorylates emerin to facilitate pre-integration complex nuclear integration.

   Evidence Kinase inhibitor treatment plus MEK1 kinase-inactive/constitutively-active mutant expression in producer cells, with EMD phosphorylation Western blot and proviral integration assay in primary non-dividing cells

   PMID:20463147

   Open questions at the time

   • Single lab; how phospho-emerin mechanistically promotes integration not defined
   • Phosphorylation site(s) not mapped in this study
4. 2014 Medium

   Identified a regulated, phosphorylation-dependent role for emerin in autophagy, linking LEM-domain phosphorylation to MAP1LC3B binding and autophagosome formation.

   Evidence C16-ceramide treatment of colon cancer cells, phospho-EMD/MAP1LC3B co-IP, PRKACA kinase identification, and autophagosome quantification

   PMID:24819607

   Open questions at the time

   • Single lab, single study; reciprocal validation of the EMD–MAP1LC3B interaction not shown
   • Whether this autophagy role connects to muscle/cardiac pathology unknown
5. 2014 Low

   Broadened the EMD phenotypic spectrum by linking near-complete emerin loss to severe dilated cardiomyopathy with only mild skeletal involvement.

   Evidence Whole exome sequencing, linkage, and protein expression analysis of an exon 1 deletion in a Chinese family

   PMID:24997722

   Open questions at the time

   • No mechanistic dissection of how emerin loss causes cardiomyopathy
   • Modifiers explaining variable skeletal involvement not identified

• How emerin loss mechanistically produces cardiac conduction defects and cardiomyopathy, and how its phosphorylation-dependent roles relate to muscle pathology, remains unresolved.
• No structural or biochemical model of emerin function at the inner nuclear membrane in the corpus
• Phosphorylation sites and their cross-pathway regulation not integrated