Gene Correction of Integrin β4-dependent Pyloric Atresia-Junctional Epidermolysis Bullosa Keratinocytes Establishes a Role for β4 Tyrosines 1422 and 1440 in Hemidesmosome Assembly

Abstract

The cytoplasmic domain of ␤ 4 integrin contains two pairs of fibronectin-like repeats separated by a connecting segment. The connecting segment harbors a putative tyrosine activation motif in which tyrosines 1422 and 1440 are phosphorylated in response to ␣ 6 ␤ 4 binding to laminin-5. Primary ␤ 4 -null keratinocytes, obtained from a newborn suffering from lethal junctional epidermolysis bullosa, were stably transduced with retroviruses carrying a full-length ␤ 4 cDNA or a ␤ 4 cDNA with phenylalanine substitutions at Tyr-1422 and Tyr-1440. Hemidesmosome assembly was evaluated on organotypic skin cultures. ␤ 4 -corrected keratinocytes were indistinguishable from normal cells in terms of ␣ 6 ␤ 4 expression, the localization of hemidesmosome components, and hemidesmosome structure and density, suggesting full genetic and functional correction of ␤ 4 -null keratinocytes. In cultures generated from ␤ 4 Y1422F/Y1440Fkeratinocytes, ␤ 4 mutants as well as ␣ 6 integrin, HD1/ plectin, and BP180 were not concentrated at the dermalepidermal junction. Furthermore, the number of hemidesmosomes was strikingly reduced as compared with ␤ 4 -corrected keratinocytes. The rare hemidesmosomes detected in ␤ 4 Y1422F/Y1440F cells were devoid of subbasal dense plates and of inner cytoplasmic plaques with keratin filament insertion. Collectively, our data demonstrate that the ␤ 4 tyrosine activation motif is not required for the localization of ␣ 6 ␤ 4 at the keratinocyte plasma membrane but is essential for optimal assembly of bona fide hemidesmosomes.Human epidermis consists of a stratified squamous epithelium composed of keratinocytes organized in distinct cellular layers. Keratinocytes forming the basal layer firmly adhere to the basement membrane by means of hemidesmosomes (HDs), 1 multiprotein complexes linking the epithelial intermediate filament network to the dermal anchoring fibrils (see Refs. 1 and 2 for review). HDs are formed by the clustering of several cytoplasmic and trans-membrane proteins (2). The cytoplasmic HD plaque components, which include HD1/plectin (3) and the bullous pemphigoid antigen 1 (BP230) (4), act as linkers for elements of the cytoskeleton at the cytoplasmic surface of plasma membrane. The trans-membrane constituents of HDs, which include the ␣ 6 ␤ 4 integrin (5, 6) and the bullous pemphigoid antigen 2 (BP180) (7), serve as cell receptors connecting the cell interior to extracellular matrix proteins.In particular, the ␣ 6 ␤ 4 integrin is a receptor for the basement membrane component laminin-5, a heterotrimeric protein composed of three distinct polypeptides, ␣3, ␤3, and ␥2, which are encoded by three different genes known as LAMA3, LAMB3, and LAMC2, respectively (see Ref. 8 for review). Laminin-5 binds to the basal keratinocyte cell surface through the ␣ 6 ␤ 4 integrin and tightens the dermal-epidermal junction by binding also to the N-terminal NC-1 domain of type VII collagen (9). The crucial importance of the interaction between laminin-5 and its ␣ 6 ␤ 4 receptor in maintaining the integrity of the i...

Bone marrow transplantation restores epidermal basement membrane protein expression and rescues epidermolysis bullosa model mice

“…Recently, various treatments were reported to restore the deficient proteins. These approaches fall mainly into three strategies: gene therapy (20)(21)(22)(23)(24), protein therapy (21,25,26), and cell therapy. Cell therapies using fibroblasts have been attempted for recessive dystrophic EB (RDEB) model mice and human patients, both of which lack collagen VII.…”

Differential Expression of Pyloric Atresia in Junctional Epidermolysis Bullosa with ITGB4 Mutations Suggests that Pyloric Atresia is due to Factors Other than the Mutations and Not Predictive of a Poor Outcome: Three Novel Mutations and a Review of the Li

“…13-15). This CS harbours a tyrosine activation motif in which residues 1422-1440 are critical for binding to Iam332 and for HD assembly (16,17). The first pair of FNIII repeats and the first 36 amino acids (1320-1355) ofthe CS are crucial for the recruitment of plectin into HD ( 14.…”

Sustainable correction of junctional epidermolysis bullosa via transposon-mediated nonviral gene transfer

“…Prior approaches restored expression of a number of genes to epidermal cells in JEB and other skin diseases in vitro 24,25 and in regenerated tissue in vivo; 2,21-23 however, they relied on amphotropic retroviruses with all their attendant drawbacks. In the plasmid-based approach presented here, functional SB transposase is required for sustained corrective gene delivery because a nonfunctional mutant failed to maintain gene transfer, even in vitro.…”