The objectives of this proposal are to determine the distinct roles that protein kinase C (PKC) isoforms (delta and epsilon) play in multistage (initiation, promotion and progression) mouse skin carcinogenesis. Knowledge obtained will contribute to the management of human squamous cell carcinoma (SCC), a predominant nonmelanoma metastatic human skin cancer. PKC, a phospholipid-dependent protein kinase, is a major intracellular receptor for the tumor promoter phorbol ester TPA. PKC represents a family of eleven isozymes (alpha, betaI, betaII, gamma, delta, epsilon, sigma, eta, theta, lambda, and mu), and six of these PKC isoforms (alpha, delta, epsilon, eta, sigma and mu) are expressed in mouse epidermis. To determine the in vivo functional specificity of PKC isoforms in mouse skin carcinogenesis, we have generated transgenic FVB/N mouse lines that overexpress epitope tagged PKCalpha, PKCdelta or PKCepsilon isozyme in epidermis under the control of the human keratin 14 promoter. Since PKC is the key receptor for TPA, the DMBA-TPA protocol was used to induce skin tumors to investigate PKC isoform specificity in these transgenic mice. We found that PKCalpha overexpression had no effect on skin tumor promotion by TPA, PKCS overexpression suppressed the formation of both papilloma and SCC while PKCE overexpression induced metastatic SCC formation independently of prior papilloma development. Based on these observations, we plan to test two hypotheses: 1) PKCdelta and PKCepsilon expression levels determine skin tumor formation susceptibility as the result of modulation of specific steps of mouse skin carcinogenesis (e.g., initiation, promotion and/or progression). 2) Skin tumor suppression in PKCdelta transgenic mice and development of metastatic SCC in PKCepsilon transgenic mice are associated with the altered expression of specific genes and proteins leading to an imbalance within normal cell proliferation, differentiation and apoptosis. We propose the following specific aims to test the hypotheses:
Specific Aim #1. To determine, using several mouse models (transgenic and knockout), whether PKCdelta or PKCepsilon expression level determines susceptibility to skin tumor formation.
Specific Aim #2. To determine, using PKC-inducible transgenic mice, whether tumor suppression in PKCdelta and carcinoma development in PKCepsilon transgenic mice are the results of the effects of transgene overexpression on the initiation, promotion and/or progression stage of carcinogenesis.
Specific Aim #3. To find clues about the mechanisms associated with the opposing effects of PKCdelta and PKCepsilon, on mouse skin carcinogenesis by analysis of gene expression using the cDNA expression array.
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