Expression of the Ebola Virus VP24 Protein Compromises the Integrity of the Nuclear Envelope and Induces a Laminopathy-Like Cellular Phenotype.

Ebola virus (EBOV) VP24 protein is a nucleocapsid-associated protein that inhibits interferon (IFN) gene expression and counteracts the IFN-mediated antiviral response, preventing nuclear import of signal transducer and activator of transcription 1 (STAT1). Proteomic studies to identify additional EBOV VP24 partners have pointed to the nuclear membrane component emerin as a potential element of the VP24 cellular interactome. Here, we have further studied this interaction and its impact on cell biology. We demonstrate that VP24 interacts with emerin but also with other components of the inner nuclear membrane, such as lamin A/C and lamin B. We also show that VP24 diminishes the interaction between emerin and lamin A/C and compromises the integrity of the nuclear membrane. This disruption is associated with nuclear morphological abnormalities, activation of a DNA damage response, the phosphorylation of extracellular signal-regulated kinase (ERK), and the induction of interferon-stimulated gene 15 (ISG15). Interestingly, expression of VP24 also promoted the cytoplasmic translocation and downmodulation of barrier-to-autointegration factor (BAF), a common interactor of lamin A/C and emerin, leading to repression of the BAF-regulated CSF1 gene. Importantly, we found that EBOV infection results in the activation of pathways associated with nuclear envelope damage, consistent with our observations in cells expressing VP24. In summary, here we demonstrate that VP24 acts at the nuclear membrane, causing morphological and functional changes in cells that recapitulate several of the hallmarks of laminopathy diseases. IMPORTANCE The Ebola virus (EBOV) VP24 protein is a nucleocapsid-associated protein with multiple functions. Proteomic studies have identified the cellular nuclear membrane component emerin as a potential VP24 interactor. Here, we demonstrate that VP24 not only interacts with emerin but also with lamin A/C and lamin B, prompting nuclear membrane disruption. This disruption is associated with nuclear morphological abnormalities, activation of a DNA damage response, the phosphorylation of extracellular signal-regulated kinase (ERK), and the induction of interferon-stimulated gene 15 (ISG15). Interestingly, VP24 also promotes the cytoplasmic translocation and downmodulation of barrier-to-autointegration factor (BAF), leading to repression of the BAF-regulated CSF1 gene. Finally, we show that EBOV infection also results in the activation of pathways associated with nuclear envelope damage, consistent with our observations in cells expressing VP24. These results reveal novel activities of EBOV VP24 protein, resulting in a cell phenotype similar to that of most laminopathies, with potential impact on EBOV replication.

The lamin protein family.

The lamins are the major architectural proteins of the animal cell nucleus. Lamins line the inside of the nuclear membrane, where they provide a platform for the binding of proteins and chromatin and confer mechanical stability. They have been implicated in a wide range of nuclear functions, including higher-order genome organization, chromatin regulation, transcription, DNA replication and DNA repair. The lamins are members of the intermediate filament (IF) family of proteins, which constitute a major component of the cytoskeleton. Lamins are the only nuclear IFs and are the ancestral founders of the IF protein superfamily. Lamins polymerize into fibers forming a complex protein meshwork in vivo and, like all IF proteins, have a tripartite structure with two globular head and tail domains flanking a central α-helical rod domain, which supports the formation of higher-order polymers. Mutations in lamins cause a large number of diverse human diseases, collectively known as the laminopathies, underscoring their functional importance.

Lamin A/C mutations associated with familial and sporadic cases of dilated cardiomyopathy in Koreans.

Dilated cardiomyopathy (DCM) is characterized by cardiac dilation and systolic dysfunction. So far sixteen genes have been shown to cause autosomal dominant familial dilated cardiomyopathy (FDC). We identified a large Korean family from the Jeju island showing a clear Mendelian inheritance of FDC. A genomewide linkage scan at 9 cM marker density identified a peak multipoint LOD score of 2.82 at D1S195. Haplotyping of the region with 15 additional markers defined a candidate interval that included a known candidate gene encoding the lamin A/C (LMNA). Sequencing of the LMNA exons revealed one missense mutation at C568T (Arg190Trp) in the alpha-helical rod domain of the LMNA gene co-segregating with FDC with conduction-system disease. The same mutation was found in patients of another Korean family with FDC without conduction-system disease. Upon screening 14 sporadic DCM cases, we found three LMNA mutations including a case having a previously described (Glu161Lys) mutation and two having novel mutations (Glu53Val and Glu186Lys). Our results suggest that variable genotypes of laminopathy are implicated in not only familial but also considerable proportion of sporadic DCM.

Lamin A/C mutations associated with familial and sporadic cases of dilated cardiomyopathy in Koreans

Dilated cardiomyopathy (DCM) is characterized by cardiac dilation and systolic dysfunction. So far sixteen genes have been shown to cause autosomal dominant familial dilated cardiomyopathy (FDC). We identified a large Korean family from the Jeju island showing a clear Mendelian inheritance of FDC. A genomewide linkage scan at 9 cM marker density identified a peak multipoint LOD score of 2.82 at D1S195. Haplotyping of the region with 15 additional markers defined a candidate interval that included a known candidate gene encoding the lamin A/C (LMNA). Sequencing of the LMNA exons revealed one missense mutation at C568T (Arg190Trp) in the alpha-helical rod domain of the LMNA gene cosegregating with FDC with conduction-system disease. The same mutation was found in patients of another Korean family with FDC without conduction-system disease. Upon screening 14 sporadic DCM cases, we found three LMNA mutations including a case having a previously described (Glu161Lys) mutation and two having novel mutations (Glu53Val and Glu186Lys). Our results suggest that variable genotypes of laminopathy are implicated in not only familial but also considerable proportion of sporadic DCM.