EXPRESSION OF PLASMINOGEN-ACTIVATOR ENZYMES IN PSORIATIC EPIDERMIS

The plasminogen activators, tissue type and urokinase type (tPA and uP A, respectively) have been identified in human skin under normal condi tions and in various inflammatory dermatoses, including psoriasis. By Northern blot analyses, mRNA for uPA, but not for tPA, has been previo usly identified in epidermal extracts from normal skin, whereas in pso riasis, mRNA for tPA is readily detected. To further characterize uPA and tPA expression in psoriasis, the localization of uPA and tPA mRNAs was evaluated by in situ hybridization. Studies were conducted using lesional and nonlesional skin of patients with psoriasis as well as no rmal skin. Additionally, in situ zymography using casein gel overlays was utilized to assess enzymatic activity. In psoriatic lesional skin, both uPA and tPA mRNAs were demonstrated by in situ hybridization. Me ssage for tPA was observed throughout the epidermis with areas of acce ntuation in the superficial stratum spinosum. Message for uPA was more focal and was localized primarily in the basal layer. Zymography show ed tPA activity was coordinately increased in psoriatic lesions. Uninv olved skin of psoriatic patients was similar to that of normal skin wi th respect to expression of plasminogen activators. In normal epidermi s, neither tPA nor uPA mRNA could be detected by in situ hybridization . Activity for uPA, but not tPA, was observed by zymography. These stu dies suggest that alterations in plasminogen activators expression may contribute to the pathogenesis of psoriasis.