Study on biosynthesis of laminin-5 and keratinocyte attachment

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Laminin-5 is a component of the anchoring filament in the basement membrane zone of the skin and crucial for keratinocyte attachment. Junctional epidermolysis bullosa (JEB) is an autosomal recessive skin blistering disease with both lethal and non-lethal forms, with most patients shown to have defects in laminin-5. We analyzed the location of mutations, gene expression levels, and protein chain assembly of laminin-5 heterotrimer in six JEB patients to determine how the type of genetic lesion influences the pathophsiology of JEB.Mutations within laminin-5 genes were diversely located, with the most severe forms of JEB correlating best with premature termination codons, rather than mapping to any particular protein domain. In all six JEB patients, the laminin-5 assembly intermediates we observed were as predicuted by our previous work indicating that the alpha3beta2gamma2 heterotrimer assembles intracellularly via a beta2gamma2 heterodimer intermediate. Since assembly procedes secretion, mutations that disrupt protein-protein inteructions needed for assembly are predicuted to limit the secretion of laminin-5, and likely to interfere with function. However, our data indicate that typically the most severe mutations diminish mRNA stabilty, and serve as functional null alleles that block chain assembly by resulting in either a deficiency (in the non-lethal mitis variety) or a complete abscence (in lethal Herlitz-JEB) of one of the chains needed for laminin-5 heterotrimer assembly.