We have linked Herlitz's junctional epidermolysis bullosa (H-JEB) to the gene (LAMC2) encoding the gamma 2 subunit of nicein/kalinin, an isolaminin (laminin-5) expressed by basal keratinocytes. In four H-JEB kindreds, a maximum two-point lod score of 5.33 at theta = 0 was observed between a microsatellite near LAMC2 at 1q25-31 and the disease. In one family, a homozygous point mutation leading to a premature stop codon (CGA to TGA) was identified in exon 3 of the gene. The segregation of the mutated allele implicates the mutation in the pathology of the disorder and corroborates the linkage results.

Laminin-5 is composed of three distinct polypeptides, alpha3, beta3, and gamma2, which are encoded by three different genes, LAMA3, LAMB3, and LAMC2, respectively. We have isolated epidermal keratinocytes from a patient presenting with a lethal form of junctional epidermolysis bullosa characterized by a homozygous mutation of the LAMB3 gene, which led to complete absence of the beta3 polypeptide. In vitro, beta3-null keratinocytes were unable to synthesize laminin-5 and to assemble hemidesmosomes, maintained the impairment of their adhesive properties, and displayed a decrease of their colony-forming ability. A retroviral construct expressing a human beta3 cDNA was used to transduce primary beta3-null keratinocytes. Clonogenic beta3-null keratinocytes were transduced with an efficiency of 100%. Beta3-transduced keratinocytes were able to synthesize and secrete mature heterotrimeric laminin-5. Gene correction fully restored the keratinocyte adhesion machinery, including the capacity of proper hemidesmosomal assembly, and prevented the loss of the colony-forming ability, suggesting a direct link between adhesion to laminin-5 and keratinocyte proliferative capacity. Clonal analysis demonstrated that holoclones expressed the transgene permanently, suggesting stable correction of epidermal stem cells. Because cultured keratinocytes are used routinely to make autologous grafts for patients suffering from large skin or mucosal defects, the full phenotypic reversion of primary human epidermal stem cells defective for a structural protein opens new perspectives in the long-term treatment of genodermatoses.

We have isolated the basement membrane component nicein and performed rotary-shadow analyses using electron microscopy that showed the presence of two forms (I and 11) of the protein. Molecular cloning of the cDNA that codes for the 100-kDa chain of the protein revealed that the sequence matches those independently identified for the 105 -155-kDa subunit of kalinin, a recently identified basement membrane component. These data demonstrate that nicein and kalinin contain an identical chain. The length of the open reading frame in the cDNA (~5 2 0 0 nucleotides) and amino acid sequences obtained from the N-terminus of the 105-kDa kalinin chain showed the occurrence of a precursor polypeptide. This immature polypeptide is probably related to form I, observed by rotary shadowing, while the mature form is related to form II. It is noteworthy that niceinkalinin subunits share discrete sequence similarities with the B2 chain of human laminin, but with a cleavage occurring within domain 111 that eliminates domains IV and V from the final product. The sequence of this subunit is nearly identical to that of B2t, a recently described polypeptide supposed to be related to a new laminin variant. Since niceinkalinin expression is specifically impaired in the severe genodermatosis Herlitz junctional epidermolysis bullosa, the role and structure of this tissue-restricted laminin variant is crucial for the understanding of epidermal-dermal adhesion.The basement membrane (BM) is a type of extracellular matrix which provides an attachment substrate for overlying cell populations and plays a crucial role in organizing tissue architecture, tissue compartmentalization, differentiation of adjacent cells and filtration of nutrients. Since mechanisms mediating these functions are poorly understood, a considerable amount of research has been devoted to the molecular characterization of BM components and elucidation of their biochemical properties. Some differences exist from one type of BM to another and no less than 14 shared macromolecules have already been found [l].We previously reported the isolation of a novel epidermal BM component, called nicein, which is found in various BM species that we investigated with the monoclonal antibody GB3 [2, 31. This glycosylated protein is composed of three major subunits of 100,125 and 150 kDa, as shown by immunoprecipitation assays performed on keratinocytes in culture [3]. Since nicein is secreted by these cells, we isolated the protein by immunoaffinity chromatography from conditioned

Herlitz junctional epidermolysis bullosa (H-JEB

Herlitz junctional epidermolysis bullosa (H-JEB) providesdeposited into the extracellular matrix. Re-expression of a promising model for somatic gene therapy of heritable laminin-5 induced cell spreading, nucleation of hemidesmechano-bullous disorders. This genodermatosis is mosomal-like structures and enhanced adhesion to the culcaused by the lack of laminin-5 that results in absence of ture substrate. Organotypic cultures performed with the hemidesmosomes (HD) and defective adhesion of squamtransduced keratinocytes, reconstituted epidermis closely ous epithelia. To establish whether re-expression of lamiadhering to the mesenchyme and presenting mature heminin-5 can restore assembly of the dermal-epidermal attachdesmosomes, bridging the cytoplasmic intermediate filament structures lacking in the H-JEB skin, we corrected the ments of the basal cells to the anchoring filaments of the genetic mutation hindering expression of the ␤3 chain of basement membrane. Our results provide the first evilaminin-5 in human H-JEB keratinocytes by transfer of a dence of phenotypic reversion of JEB keratinocytes by laminin ␤3 transgene. The transduced keratinocytes synsomatic gene therapy and demonstrate that genetic treatthesized a recombinant ␤3 polypeptide that assembled ment of the mild forms of skin blistering diseases and other with the endogenous laminin ␣3 and ␥2 chains into a bioinherited extracellular matrix pathologies is a realistic goal. logically active laminin-5 that was secreted, processed and