Abstract
Laminins comprise a family of over 20 extracellular glycoproteins that are involved in cell-basement membrane zone (BMZ) adhesion. In skin, laminin isoforms are present in the epidermal BMZ, around blood vessels (BVs), nerves and adnexal structures. Recently, specific antibodies have become available that recognize laminin chains. The antibody 4C7 recognizes the terminal globular domain of the laminin α5 chain in laminins 10 (α5, β1, γ1) and 11 (α5, β2, γ1). Laminin 5 (α3, β3, γ2) is a well-studied hemidesmosome (HD)-associated laminin. We therefore compared the α5 chain expression with laminin 5 in normal and diseased skin. Laminin α3 and α5 chains were linearly expressed in the epidermal BMZ, except beneath melanocytes. The α5 chain but not the α3 chain was expressed around BVs in adult skin. Late anagen hair follicles stained with anti-α3 and α5 chain antibodies showed typical expression patterns described for HD antigens. In cultured RAC-11P bladder cells, that assemble HD-like structures in vitro, both α3 and α5 chains colocalized to discrete focal areas beneath sub-confluent cells presumed to be HDs. Finally, immunogold electron microscopy localized the α5 terminal globular domain to the lower lamina lucida (n=200 gold particles). The majority (75%) of α5 chain labeling was restricted to beneath HDs, similar to laminin 5 (77% labeling restricted to HDs). Laminin α3 and α5 chain expression was assessed in control (n=4) and patients skin suffering from epidermolysis bullosa (EB, n=11). Laminin α5 chain expression was normal in control and all EB subtypes. This was in contrast to the α3 chain that was reduced or absent in JEB subtypes. These data suggest that the α5 chain exhibits an expression pattern restricted to beneath HDs, similar to the α3 chain of laminin 5, however the stable expression of α5 chains is independent of laminin 5. This further supports the hypothesis that several laminin variants may covalently assemble as a multi-molecular complex that together promotes stable epithelial-BMZ attachment.
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