Psoriasis is a hyperproliferative cutaneous disease of unknown etiology and etiopathogenesis. Alteration of keratinocyte adhesiveness to basal lamina has been proposed as the initial disturbance leading to poorly controlled proliferation. Keratinocyte adhesion to basal lamina and lateral interactions among basal epidermal cells are mediated, besides other molecules, by integrin receptors that are segregated to discrete membrane domains. In this paper, the expression and function of integrins in psoriatic keratinocytes were examined, both in vivo and in vitro. We found that: (a) in psoriatic keratinocytes the integrin heterodimers alpha-2-beta-1, alpha-3-beta-1, and alpha-6-beta-4 have lost their polarized distribution on the plasma membrane; (b) the role of these integrins in mediating keratinocyte adhesion in vitro is altered; (c) psoriatic keratinocytes form focal contacts containing both beta-1 and beta-4 integrins. In normal adult keratinocytes the alpha-5-beta-1 fibronectin receptor is poorly expressed and diffusely distributed on the basal keratinocyte plasma membrane and is not organized in defined adhesive structures. In contrast, psoriatic keratinocytes show a clear fibronectin receptor staining in vivo, and organize alpha-5-beta-1, in typical focal contacts in vitro without any obvious increase of its expression and synthesis. These multiple alterations of integrins are also present in uninvolved keratinocytes from psoriatic patients, suggesting a key role for altered integrin-mediated adhesion in the pathogenesis of this disease.
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