HEMIDESMOSOME ASSEMBLY ASSESSED BY EXPRESSION OF A WILD-TYPE INTEGRIN-BETA-4 CDNA IN JUNCTIONAL EPIDERMOLYSIS-BULLOSA KERATINOCYTES

The cytoplasmic domain of integrin beta 4, which contains four type II I fibronectin-like motifs, seems to be involved in the regulation of t he assembly of hemidesmosomes (HD) and, therefore, in cell adhesion. A n in-frame deletion of 17 amino acids in the second fibronectin type I II repeat of integrin beta 4 (Delta 17-beta 4) has been associated wit h junctional epidermolysis bullosa with pyloric atresia (PA-JEB), a ge netic disease characterized by altered HD and disadhesion of the epide rmis. To determine the effect of deletion Delta 17-beta 4 on HD assemb ly, we have examined the expression and localization of the HD compone nts in the skin and cultured keratinocytes of a patient with PA-JEB, w hich express the mutated integrin beta 4. Our results show that the mu tated beta 4 subunit associates with integrin alpha 6, but the resulti ng heterodimer does not induce nucleation of the bullous pemphigoid an tigens BP180 and BP230, and that of the inner plaque component plectin /HD1, into hemidesmosomal structures. The integrity of the cytoplasmic tail of integrin beta 4 seems to be essential to the targeting and st abilization of plectin/HD1 and BP180 in HD, because transfection of a recombinant wild-type beta 4 cDNA in the Delta 17-beta 4 PA-JEB kerati nocytes restores the synthesis of a functional alpha 6 beta 4 heterodi mer, which promotes the polarization of plectin/HD1 and BP180, to the basal aspect of the cells. Because in the transfected keratinocytes th e distribution of BP230 remains diffuse in the cytoplasm, we suggest t hat the interaction between plectin/HD1 and integrin alpha 6 beta 4, f ollowed by the association with BP180, constitutes the first step in t he nucleation of the HD.