EXTENT OF LAMININ-5 ASSEMBLY AND SECRETION EFFECT JUNCTIONAL EPIDERMOLYSIS-BULLOSA PHENOTYPE

Junctional epidermolysis bullosa (JEB) is an autosomal recessive skin blistering disease with both lethal and nonlethal forms, with most pat ients shown to have defects in laminin-5. We analyzed the location of mutations, gene expression levels, and protein chain assembly of the l aminin-5 heterotrimer in six JEB patients to determine how the type of genetic lesion influences the pathophysiology of JEB. Mutations withi n laminin-5 genes were diversely located, with the most severe forms o f 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 predicted by our previous work indicating that the alpha 3 beta 3 gamma 2 heterotrimer assembles intracellularly via a beta 3 gamma 2 heterodimer intermedia te. Since assembly precedes secretion, mutations that disrupt protein- protein interactions needed for assembly are predicted to limit the se cretion of laminin-5, and likely to interfere with function. However, our data indicate that typically the most severe mutations diminish mR NA stability, and serve as functional null alleles that block chain as sembly by resulting in either a deficiency tin the nonlethal mitis var iety) or a complete absence (in lethal Herlitz-JEB) of one of the chai ns needed for laminin-5 heterotrimer assembly.