Subcellular localization and partial purification of prelamin A endoprotease: an enzyme which catalyzes the conversion of farnesylated prelamin A to mature lamin A.
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The nuclear lamina protein, lamin A is produced by proteolytic cleavage of a 74 kDa precursor protein, prelamin A. The conversion of this precursor to mature lamin A is mediated by a specific endoprotease, prelamin A endoprotease. Subnuclear fractionation indicates that the prelamin A endoprotease is localized at the nuclear membrane. The enzyme appears to be an integral membrane protein, as it can only be removed from the nuclear envelope with detergent. It is effectively solubilized by the detergent n-octyl-beta-D-glucopyranoside and can be partially-purified (approximately 1200-fold) by size exclusion and cation exchange (Mono S) chromatography. Prelamin A endoprotease from HeLa cells was eluted from Mono S with 0.3 M sodium chloride as a single peak of activity. SDS-PAGE analysis of this prelamin A endoprotease preparation shows that it contains one major polypeptide at 65 kDa and smaller amounts of a second 68 kDa polypeptide. Inhibition of the enzyme activity in this preparation by specific serine protease inhibitors is consistent with the enzyme being a serine protease. (+info)
Heart to heart: from nuclear proteins to Emery-Dreifuss muscular dystrophy.
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Emery-Dreifuss muscular dystrophy has some remarkably specific features, with only cardiac and skeletal tissues being affected. Equally remarkably, the disease is caused by mutations in widely expressed genes for the nuclear membrane/lamina proteins, emerin and lamin A/C. How do mutations in proteins at the heart of the cell lead to stiff joints and sudden heart failure? This and related questions are the subject of this review. (+info)
Dynamics of the nuclear lamina as monitored by GFP-tagged A-type lamins.
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The behavior of chimeric proteins consisting of A-type lamins and green fluorescent protein (GFP) was studied to investigate the localization and dynamics of nuclear lamins in living cells. Cell line CHO-K1 was transfected with cDNA constructs encoding fusion proteins of lamin A-GFP, lamin Adelta10-GFP, or lamin C-GFP. In the interphase nucleus lamin-GFP fluorescence showed a perinuclear localization and incorporation into the lamina for all three constructs. Our findings show for the first time that the newly discovered lamin A 10 protein is localized to the nuclear membrane. The GFP-tagged lamins were processed and behaved similarly to the endogenous lamin molecules, at least in cells that expressed physiological levels of the GFP-lamins. In addition to the typical perinuclear localization, in the majority of transfected cells each individual A-type lamin-GFP revealed an extensive collection of branching intra- and trans-nuclear tubular structures, which showed a clear preference for a vertical orientation. Time-lapse studies of 3-D reconstructed interphase cells showed a remarkable stability in both number and location of these structures over time, while the lamina showed considerable dynamic movements, consisting of folding and indentation of large parts of the lamina. Fluorescence recovery after bleaching studies revealed a low protein turnover of both tubular and lamina-associated lamins. Repetitive bleaching of intranuclear areas revealed the presence of an insoluble intranuclear fraction of A-type lamins. Time-lapse studies of mitotic cells showed that reformation of the lamina and the tubular structures consisting of A-type lamins did not occur until after cytokinesis was completed. (+info)
Decreased and aberrant nuclear lamin expression in gastrointestinal tract neoplasms.
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BACKGROUND: Altered expression of lamins A/C and B1, constituent proteins of the nuclear lamina, may occur during differentiation and has also been reported in primary lung cancer. AIMS: To examine the expression of these proteins in gastrointestinal neoplasms. PATIENTS: Archival human paraffin wax blocks and frozen tissue from patients undergoing surgical resection or endoscopic biopsy. METHODS: Immunohistochemistry and western blotting using polyclonal antisera against A type lamins and lamin B1. RESULTS: The expression of lamin A/C was reduced and was frequently undetectable by immunohistochemistry in all primary colon carcinomas and adenomas, and in 7/8 primary gastric cancers. Lamin B1 expression was reduced in all colon cancers, 16/18 colonic adenomas, and 6/8 gastric cancers. Aberrant, cytoplasmic labelling with both antibodies occurred in some colonic cancers and around one third of colonic adenomas. Cytoplasmic lamin A/C expression was detected in 3/8 gastric cancers. Lamin expression was reduced in gastric dysplasia, but not intestinal metaplasia, atrophy, or chronic gastritis. Lamin expression was low in carcinomas of oesophagus, prostate, breast, and uterus, but not pancreas. CONCLUSIONS: Reduced expression of nuclear lamins, sometimes together with aberrant, cytoplasmic immunoreactivity is common in gastrointestinal neoplasms. Altered lamin expression may be a biomarker of malignancy in the gastrointestinal tract. (+info)
Colocalization of intranuclear lamin foci with RNA splicing factors.
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The lamins form a fibrous network underlying the inner nuclear membrane termed the nuclear lamina. In order to gain insights into the role of lamins in nuclear organization, we have characterized a monoclonal antibody (LA-2H10) raised against recombinant rat lamin A that labels nuclei in a speckled pattern in all cells of unsynchronized populations of HeLa and rat F-111 fibroblast cells, unlike the typical nuclear periphery staining by another monoclonal antibody to lamin A, LA-2B3. In immunolocalization studies the lamin A speckles or foci were found to colocalize with the RNA splicing factors SC-35 and U5-116 kD, but not with p80 coilin found in coiled bodies. Lamin B1 was also associated with these foci. These foci dispersed when cells entered mitosis and reformed during anaphase. The differential reactivity of LA-2H10 and LA-2B3 was retained after nuclei were extracted with detergents, nucleases and salt to disrupt interactions of lamins with chromatin and other nuclear proteins. Using deletion fragments of recombinant lamin A, the epitope recognized by LA-2H10 was located between amino acids 171 and 246. Our findings are consistent with a structural role for lamins in supporting nuclear compartments containing proteins involved in RNA splicing. (+info)
Missense mutations in the rod domain of the lamin A/C gene as causes of dilated cardiomyopathy and conduction-system disease.
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BACKGROUND: Inherited mutations cause approximately 35 percent of cases of dilated cardiomyopathy; however, few genes associated with this disease have been identified. Previously, we located a gene defect that was responsible for autosomal dominant dilated cardiomyopathy and conduction-system disease on chromosome 1p1-q21, where nuclear-envelope proteins lamin A and lamin C are encoded by the LMNA (lamin A/C) gene. Mutations in the head or tail domain of this gene cause Emery-Dreifuss muscular dystrophy, a childhood-onset disease characterized by joint contractures and in some cases by abnormalities of cardiac conduction during adulthood. METHODS: We evaluated 11 families with autosomal dominant dilated cardiomyopathy and conduction-system disease. Sequences of the lamin A/C exons were determined in probands from each family, and variants were confirmed by restriction-enzyme digestion. The genotypes of the family members were ascertained. RESULTS: Five novel missense mutations were identified: four in the alpha-helical-rod domain of the lamin A/C gene, and one in the lamin C tail domain. Each mutation caused heritable, progressive conduction-system disease (sinus bradycardia, atrioventricular conduction block, or atrial arrhythmias) and dilated cardiomyopathy. Heart failure and sudden death occurred frequently within these families. No family members with mutations had either joint contractures or skeletal myopathy. Serum creatine kinase levels were normal in family members with mutations of the lamin rod but mildly elevated in some family members with a defect in the tail domain of lamin C. CONCLUSIONS: Genetic defects in distinct domains of the nuclear-envelope proteins lamin A and lamin C selectively cause dilated cardiomyopathy with conduction-system disease or autosomal dominant Emery-Dreifuss muscular dystrophy. Missense mutations in the rod domain of the lamin A/C gene provide a genetic cause for dilated cardiomyopathy and indicate that this intermediate filament protein has an important role in cardiac conduction and contractility. (+info)
Lamin A/C gene mutation associated with dilated cardiomyopathy with variable skeletal muscle involvement.
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BACKGROUND: Dilated cardiomyopathy is a form of heart muscle disease characterized by impaired systolic function and ventricular dilation. Familial transmission of the disease is frequently observed, and genetic heterogeneity is indicated by clinical and morphological variability in the disease phenotype. In the family MDDC1 reported here, the disease phenotype is severe and characterized by an autosomal dominant pattern of transmission. In addition, the majority of affected family members show signs of mild skeletal muscle involvement. METHODS AND RESULTS: On the basis of the clinical observation of both cardiac and skeletal muscle abnormalities in the MDDC1 family, the lamin A/C gene was examined in this kindred. Coding regions were polymerase chain reaction-amplified from genomic DNA and sequenced. A single nucleotide deletion was identified within exon 6, and all affected individuals were found to be heterozygous for this deletion. CONCLUSIONS: Heterozygosity for a single nucleotide deletion in exon 6 of lamin A/C segregates with both the cardiac and skeletal abnormalities observed in the MDDC1 family. (+info)
DNase I hypersensitive sites and transcriptional activation of the lamin A/C gene.
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The lamin A/C gene encodes subtypes of nuclear lamins, which are involved in nuclear envelope formation, and was recently identified as the responsible gene for the autosomal dominant Emery-Dreifuss muscular dystrophy. Expression of the lamin A/C gene is developmentally regulated but little is known about the regulatory mechanism. Previous studies of lamin A/C expression suggested that the chromatin structure is important for the regulation of its expression. To elucidate the regulatory mechanism of the lamin A/C gene expression, we have analysed the functional region of the mouse lamin A/C promoter and the chromatin structure of the gene in terms of nucleosome structure and DNase I hypersensitivity. Our analyses revealed disruption of the nucleosome array at the promoter region and the presence of multiple DNase I hypersensitive sites (HSs) which were specifically associated with expression of the lamin A/C gene. Inclusion of a segment which contained the HSs in a lamin A/C promoter-luciferase reporter plasmid showed no effect on the transfected promoter activity in transient expression assays. On the other hand, substantial enhancement of the promoter activity was detected when the transfected DNA was stably integrated into the genome, suggesting the importance of the HSs in the regulation of lamin A/C expression. (+info)