Transmembrane Signaling System in Psoriatic Keratinocytes.

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Recent evidence suggests that the breakdown of inositol phospholipids is an important transmembrane signalling system that is composed of two kinds of signals : the diacylglycerol (DAG) -protein kinase C signal, and the inositol trisphosphate - Ca^<++> signal. The system is activated in psoriatic hyperproliferative keratinocytes, which might be associated with the altered function of other transmembrane signaling systems such as the adenylate cyclase. The epidermal adenylate cyclase was shown to be modulated by various protein kinase C activators, which include tumor promoting phorbol esters. The modulation was similar to that of psoriatic involved epidermis. Despite the finding that the classical protein kinase C isozymes are activated by DAG and also by Ca^<++> at higher concentrations, the epidermal adenylate cyclase responses were modulated only by DAG-protein kinase C signal, but not by Ca^<++> signal. Our results indicate that the epidermal adenylate cyclase system is modulated by protein kinase C, which might be the novel Ca^<++>insensitive form of protein kinase C recently described by Kuroki and C -workers.