Loss of plectin causes epidermolysis bullosa with muscular dystrophy: cDNA cloning and genomic organization.

Abstract

Plectin is a widely expressed high molecular weight protein that is involved in cytoskeleton-membrane attachment in epithelial cells, muscle, and other tissues. The human autosomal recessive disorder epidermolysis bullosa with muscular dystrophy (MD-EBS) shows epidermal blister formation at the level of the hemidesmosome and is associated with a myopathy of unknown etiology. Here, plectin was found to be absent in skin and cultured keratinocytes from an MD-EBS patient by immunofluorescence and immunoprecipitation, suggesting that plectin is a candidate gene/protein system for MD-EBS mutation. The 14800-bp human plectin cDNA was cloned and sequenced. The predicted 518-kD polypeptide has homology to the actin-binding domain of the dystrophin family at the amino terminus, a central rod domain, and homology to the intermediate filament-associated protein desmoplakin at the carboxyl terminus. The corresponding human gene (PLECl), consisting of 33 exons spanning >26 kb of genomic DNA was cloned, sequenced, and mapped to chromosomal band 8q24. Homozygosity by descent was observed in the consanguineous MD-EBS family with intragenic plectin polymorphisms. Direct sequencing of PCR-amplified plectin cDNA from the patient's keratinocytes revealed a homozygous 8-bp deletion in exon 32 causing a frameshift and a premature termination codon 42 bp downstream. The clinically unaffected parents of the proband were found to be heterozygous carriers of the mutation. These results establish the molecular basis of MD-EBS in this family and clearly demonstrate the important structural role for plectin in cytoskeleton-membrane adherence in both skin and muscle.

The N Terminus of the Transmembrane Protein BP180 Interacts with the N-terminal Domain of BP230, Thereby Mediating Keratin Cytoskeleton Anchorage to the Cell Surface at the Site of the Hemidesmosome

“…We speculate that these multiple linkage systems play synergistic roles in maintaining the firm anchorage of keratin bundles to the hemidesmosome plaque. This idea is supported by studies that reveal that ablation of either plectin or BP230 in keratinocytes results in loss of keratin bundle association with the plaque of the hemidesmosome (Guo et al, 1995;Gache et al, 1996;McLean et al, 1996;Smith et al, 1996). These complex interconnections may enhance further the stability of keratin interaction with the cell surface and not only modulate cell-matrix association but also facilitate signal transduction at the site of the hemidesmosome (Giancotti, 1996).…”

Integrin alpha 6 beta 4 forms a complex with the cytoskeletal protein HD1 and induces its redistribution in transfected COS-7 cells.

“…Similar structures were found in cells of the mouse TA3/Ha carcinoma cell line that normally grows in suspension because the large amount of the mucin epiglycanin on their surface prevents attachment of the cells to the substratum (Kemperman 1992), and therefore these molecules may also associate in other cell types to form a complex for anchoring other cytoskeleton components to the plasma membrane. Recent evidence indicates that HD1 and plectin are similar or identical proteins (Gache et al, 1996;McLean et al, 1996;Smith et al, 1996). Plectin is considered to be a general cross-linker of cytoskeletal networks (Foisner and Wiche, 1991), and in COS-7 cells plectin has been shown to associate with the vimentin and keratin networks (Wiche et al, 1993).…”

“…The structure of HD1 has not yet been determined but its apparent molecular mass and tissue distribution are similar to fhose of plectin (Gache et al, 1996). In addition, mutations in the plectin gene correlate with a loss of immunoreactivity not only of plectin but also of HD1 (McLean et al, 1996;Smith et al 1996). Together, these data suggest that HD1 and plectin are identical or related molecules.…”

Diseases of epidermal keratins and their linker proteins

“…Initial examination of biochemical and synthetic properties of cultured keratinocytes from patients with EB-MD using antibodies against plectin showed that this protein was completely absent in the cells of several patients with EB-MD, and subsequently, mutations in the plectin gene (PLEC1) could be demonstrated in a number of families [46][47][48][49]. While EB-MD is a rare autosomal recessive disorder, most of the mutations reported thus far result in premature termination codons on both alleles of plectin, either by nonsense, insertion/deletion or splicing mutations, and the phenotype in these patients is remarkably consistent manifesting with neonatal blistering and progressive muscle weakness from the first or second decade of life on.…”