Keratinocytes from Patients Lacking Collagen XVII Display a Migratory Phenotype

Abstract

Acquired or inherited junctional epidermolysis bullosa are skin diseases characterized by a separation between the epidermis and the dermis. In inherited nonlethal junctional epidermolysis bullosa, genetic analysis has identified mutations in the COL17A1 gene coding for the transmembrane collagen XVII whereas patients with acquired diseases have autoantibodies against this protein. This suggests that collagen XVII participates in the adhesion of basal keratinocytes to the extracellular matrix. To test this hypothesis, we studied the behavior of keratinocytes with null mutations in the COL17A1 gene. Initial adhesion of mutant cells to laminin 5 was comparable to controls and similarly dependent on ␣3␤1 integrins. The spreading of mutant cells was, however, enhanced, suggesting a propensity to migrate, which was confirmed by migration assays. In addition, laminin 5 deposited by collagen XVII-deficient keratinocytes was scattered and poorly organized , suggesting that correct integration of laminin 5 within the matrix requires collagen XVII. Collagen XVII (or BPAG2, 180-kd bullous pemphigoid antigen) is expressed by epithelial cells forming hemidesmosomes (HDs), such as basal keratinocytes in skin or mucosa. HDs are multiprotein complexes connecting the intracellular keratin network to anchoring filaments and fibrils located in the basement membrane (BM) and the upper dermis, respectively.1 Collagen XVII is expressed as a transmembrane full-length entity that is in part converted to an extracellular protein by shedding.2-4 Because the full-length protein is anchored in a type II orientation in the plasma membrane, its N-terminus is intracellular and the C-terminus, or ectodomain, is extracellular. The intracellular domain of collagen XVII is located in the cytoplasmic plaque of HDs where it colocalizes and interacts with the intracellular tail of the integrin ␤4 subunit, BPAG1 (230-kd bullous pemphigoid antigen) and HD1/plectin, 5 which in turn acts as a molecular bridge to the keratin-based cytoskeleton.1 A further interaction occurs between extracellular stretches adjacent to the transmembrane domains of collagen XVII and integrin ␣6 subunit.

Context-Dependent Regulation of Collagen XVII Ectodomain Shedding in Skin

“…Previously, we showed that migrating keratinocytes cleave and leave the ectodomain of COL17 in the ECM as seen by the migration track in vitro, which was revealed by Ab HK139, which targets the N-terminal cleavage site at The present study also suggests the presence of binding proteins of cleaved COL17 ectodomain in the ECM, because IIF studies of cleavage-site-specific Abs on 1-M NaCl-split skin showed that the cleaved COL17 ectodomain remains on the epidermal side of artificial blisters. We and another group have reported that the C-terminus of COL17 binds with laminin 332 in vitro 23,29 . Because laminin 332 is always present on the dermal side of 1-M NaCl-split skin 3,30 , the present data indicate that another binding molecule, or molecules, on the epidermal side is present in the ECM, which binds with the shed COL17 ectodomain more strongly than laminin 332 does.…”

Collagenous Transmembrane Proteins: Recent Insights into Biology and Pathology*

“…The overall structure of the ectodomain is that of a flexible rod (13,17). The intracellular ligands of collagen XVII include ␤ 4 -integrin, plectin, and BP230 in the hemidesmosomal plaque (4), and the extracellular ligands ␣ 6 -integrin and laminin 5 in the anchoring filaments (23,24). Further binding partners are likely to exist but still await identification.…”

“…This is supported by the finding that inhibition of collagen XVII processing preserved hemidesmosomal attachment in cultured keratinocytes (32). In the meantime it has become obvious that cell adhesion and motility involve a number of receptors and ligands depending on the spatial and temporal biological context (4) and that these processes are quite complex (24,27,33,34).…”

Alterations in type I hemidesmosome components suggestive of epigenetic control in the salivary glands of patients with Sjögren's syndrome

“…BP180 is suggested to be essential for correct organization of laminin 332 at the BL. This idea is based on the observation that the laminin 332-containing matrix in keratinocytes lacking BP180 is of poor quality (43).…”

“…Type I HDs are formed when BP230 is incorporated into the complex by binding to both ␤4 integrin and BP180. Both BP230 and plectin can bind to cytokeratins via interaction sites present in their respective COOH-termini (43), and ␣6␤4 integrin and BP180 have binding sites to the extracellular matrix (ECM) protein laminin 332. A, Calpain degrades the cytosolic domain of ␤4 integrin, forming 2 proteolytic fragments, which lack the binding sites for BP180 and BP230, thereby producing altered type I HDs.…”