Anti-inflammatory agents are potent inhibitors of phorbol ester tumor promotion in mouse skin; this ha been interpreted as demonstrating a requirement for inflammation in promotion. We hypothesize that it is the dermal inflammation produced by tumor promoters, and other irritants, via arachidonate release that is responsible for the hyperplasia of the overlying epidermis and that chronic inflammation, regardless of whether it is caused by a chemical or physical agent, is sufficient and necessary to cause both sustained hyperplasia and promotion of tumors in initiated skin. In order to test our hypotheses we wish to do the following: (1) Determine whether arachidonic acid release induced by phorbol esters (TPA) is via protein kinase C (PKC) or represents a PKC-independent signalling mechanism that is common to all promoters, including the nonPKC types. We propose that the principle function of PKC may be signal amplification, allowing TPA to activate phospholipase A2 at lower doses. (2) Demonstrate that inflammation, whether caused by physical or chemical agents, causes hyperplasia of the overlying epidermis and that eicosanoids are the principal mediators of this proces. Both physical (abrasion of the inner ear and injury of underside of skin) and chemical (dinitrofluorobenzene and topical application of arachidonic acid and select irritants) means will be used to achieve inflammation. In order to show that this inflammation is required for hyperplasia, inhibitors of eicosanoid synthesis) will also be used. In vivo treatment for various times coupled with in vitro expression of hyperplasia in organ culture will also be used a measure of the requirement for nonepidermal factors (inflammation) for hyperplasia. (3) Determine whether repeated stimuli of the above agents results in sustained hyperplasia and where this can be demonstrated, whether promotion of tumors in initiated skin will occur. (4) Determine if a paracrine mechanism exists such that the eicosanoids produced by the differentiated epidermal cells have their effect on the basal cells, which synthesize little eicosanoid. Specifically, receptor affinity and number for prostaglandin E2, F2alpha and D2 will be compared between populations of keratinocytes separated on the basis of differentiation. The second messenger or signal transduction pathway to which each of the PG receptors is coupled will also be determined.
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