Increased Cholera Toxin-, and Forskolin-induced Cyclic AMP Accumulations in Psoriatic Involved Versus Uninvolved or Normal Human Epidermis

Psoriatic involved epidermis reveals variously altered receptor-adenylate cyclase responses; among them the most prominent is defective beta-adrenergic adenylate cyclase response, which is normally the major receptor-adenylate cyclase system of human epidermis. It is known that activation of hormone-stimulated adenylate cyclase, a membrane-bound enzyme complex, requires functional coupling of at least 3 distinct subunits: 1) receptor subunit (R), 2) guanine nucleotide binding protein (G), and 3) catalytic subunit (C). The precise nature of the beta-adrenergic defect in the psoriatic epidermis, however, remains to be determined, especially in terms of G and C function. Using the involved and uninvolved skin from psoriatic patients, we investigated effects of cholera toxin (which monitors G-C interaction) and forskolin (which monitors C function) on the adenylate cyclase system of epidermis, which were compared with those of normal human epidermis. Both agents increased cyclic AMP levels of involved, uninvolved, and normal human epidermis. Marked accumulations were observed in the presence of cyclic nucleotide phosphodiesterase inhibitor, isobutyl- methyixanthine (IBMX); without the phosphodiesterase inhibitor, the effect of each agent was minimal. Comparison of the effects of cholera toxin revealed that the psoriatic involved epidermis accumulates much more cyclic AMP than the uninvolved epidermis (involved: 193 ± 65; uninvolved: 117 ± 54 pmoles/mg protein/5 h). Similarly forskolin-induced cyclic AMP accumulations of the involved epidermis were much more than those of uninvolved epidermis (involved: 374 ± 152; uninvolved: 101 ± 41 pmoles/mg protein/2 h). Those of normal human epidermis were not significantly different from those of uninvolved epidermis (cholera toxin: 99 ± 36 pmoles/mg protein/5 h; forskolin: 84 ± 22 pmoles/mg protein/2 h). Our results indicate that G and C function and their interaction is not defective (but rather increased) in the posoriatic involved epidermis. This suggests that the defective beta-adrenergic response of psoriatic involved epidermis reflects defective R or R-G interaction of the epidermal adenylate cyclase system