Deficiency of the integrin β4 subunit in junctional epidermolysis bullosa with pyloric atresia: consequences for hemidesmosome formation and adhesion properties

Abstract

Junctional epidermolysis bullosa (JEB) comprises a group of inherited autosomal recessive blistering disorders characterized by dermo-epidermal separation through the lamina lucida of the basement membrane. We identified a patient with JEB associated with pyloric atresia (PA), in whom the integrin beta 4 subunit was completely absent. At the ultrastructural level, the hemidesmosomes were reduced in number, appeared rudimentary and lacked a subbasal dense plate and frequently an inner attachment plaque. However, keratin filaments were still anchored to the cytoplasmic plaque of the hemidesmosome. Immunofluorescence analysis showed that the beta 4 subunit was absent in the skin of the PA-JEB patient, whereas the alpha 6 subunit appeared to be normally distributed along the basement membrane zone, as were the other hemidesmosomal components BP230, BP180 and HD1. Furthermore, the alpha 3 and beta 1 subunits were not only detected at the lateral membranes of basal cells in PA-JEB skin, as in normal skin, but also along the basement membrane zone. The few hemidesmosome-like structures found in cultured keratinocytes from the PA-JEB patient contained the hemidesmosomal components BP230, BP180 and HD1, but not the integrin alpha 6 subunit. Like alpha 3, this subunit was colocalized with vinculin in focal contacts at the ends of actin stress fibers. Immunoprecipitation analysis revealed that alpha 6 was associated with beta 1 on PA-JEB keratinocytes, whereas normal human keratinocytes (NHKs) exclusively express alpha 6 beta 4 on their cell surface. The initial adhesion of PA-JEB and normal keratinocytes to laminin-1 and laminin-5, both ligands for alpha 6 beta 1 and alpha 6 beta 4, was similar. In migration assays, the PA-JEB keratinocytes were more motile on laminin-5 than normal keratinocytes. Our observations indicate that the integrin alpha 6 beta 4 plays a crucial role in the proper assembly of hemidesmosomes and in the stabilization of the dermal-epidermal junction. The fragility of the skin and the blistering in this patient appear to have been due to the deficiency of the integrin beta 4 subunit, which results in the formation of too few and structurally abnormal hemidesmosomes.

Integrins and human intestinal cell functions

“…The alpha6beta4 integrin was first reported as a laminin receptor in intestinal cells working in cooperation with another beta1 integrin, most likely alpha2beta1 (107,111,112). In hemidesmosome-expressing cells such as those at the epidermal-mesenchymal interface, alpha6beta4 plays an essential role in the assembly and for the stability of hemidesmosomes while it mediates anchorage on laminin-5 in cooperation with alpha3beta1 (113)(114)(115). However, as mentioned in a previous section, intestinal cells do not possess true hemidesmosomes but express these receptors.…”

“…Finally, mice lacking the alpha6 subunit develop until birth but die soon after with severe blistering of the skin and other epithelia (122). There is also evidence that alpha6beta4 plays a key role in the modulation of adhesion properties in the human as well (113). Therefore, the suggestion that α6β4 primarily serves as a high affinity receptor for cell adhesion to laminin-1 and laminin-5, and as a regulator for the expression of cyclin-dependent kinase inhibitors, would appear to be in good agreement with the distribution of these molecules along the crypt-villus axis in the intact intestinal epithelium (49,80,81,86,123; Basora et al, submitted).…”

The Nanoscale Geometrical Maturation of Focal Adhesions Controls Stem Cell Differentiation and Mechanotransduction

“…35 Importantly, these adhesions, which are not directly linked to the f-actin cytoskeleton, are not thought to contribute to mechanical tension. Considering the importance of these adhesive structures to keratinocyte spreading, motility, and the maintenance of the epithelial sheet integrity in the interfollicular epidermis, 36 we explored their response to nanoscale restriction (Supporting Information Figure S8). In addition, comparison of the protein recruitment of FA markers to that of proteins involved in the formation of these non-load-bearing adhesions should highlight the role of mechanotransduction mechanisms in nanoscale sensing.…”

Junctional epithelium and hemidesmosomes: Tape and rivets for solving the “percutaneous device dilemma” in dental and other permanent implants

“…Collagen XVII clustering on the basal side of cells in vitro is dependent on integrin α6β4 and plectin, as previously discussed and demonstrated in integrin subunit β4-deficient keratinocytes [ 253 ]. However, collagen XVII clustering is less dependent on integrin α6β4 and plectin in vivo and interacts with BP230 in the absence of plectin [ 254 ]. Regulatory requirements for HD renewal in vivo are unclear but are generally mediated in vitro by interactions between integrin subunit β4 and plectin [ 114 , 255 , 256 ].…”