ALPHA-3-BETA-1 INTEGRIN IS REQUIRED FOR NORMAL DEVELOPMENT OF THE EPIDERMAL BASEMENT-MEMBRANE

Integrins alpha 3 beta 1 and alpha 6 beta 4 are abundant receptors on keratinocytes for laminin-5, a major component of the basement membran e between the epidermis and the dermis in skin. These integrins are re cruited to distinct adhesion structures within keratinocytes; alpha 6 beta 4 is present in hemidesmosomes, while alpha 3 beta 1 is recruited into focal contacts in cultured cells. To determine whether differenc es in localization reflect distinct functions of these integrins in th e epidermis, we studied skin development in alpha 3 beta 1-deficient m ice. Examination of extracellular matrix by immunofluorescence microsc opy and electron microscopy revealed regions of disorganized basement membrane in alpha 3 beta 1-deficient skin. Disorganized matrix was fir st detected by day 15.5 of embryonic development and became progressiv ely more extensive as development proceeded. In neonatal skin, matrix disorganization was frequently accompanied by blistering at the dermal -epidermal junction. Laminin-5 and other matrix proteins remained asso ciated with both the dermal and epidermal sides of blisters, suggestin g rupture of the basement membrane itself, rather than detachment of t he epidermis from the basement membrane as occurs in some blistering d isorders such as epidermolysis bullosa. Consistent with this notion, p rimary keratinocytes from alpha 3 beta 1-deficient skin adhered to lam inin-5 through alpha 6 integrins. However, alpha 3 beta 1-deficient ke ratinocytes spread poorly compared with wild-type cells on laminin-5, demonstrating a postattachment requirement for alpha 3 beta 1 and indi cating distinct roles for alpha 3 beta 1 and alpha 6 beta 4. Our findi ngs support a novel role for alpha 3 beta 1 in establishment andior ma intenance of basement membrane integrity, while alpha 6 beta 4 is requ ired for stable adhesion of the epidermis to the basement membrane thr ough hemidesmosomes.