This project is focused on characterizing the functions and interactions of melanocyte-specific genes, and their encoded products, that regulate mammalian pigmentation and in determining their significance to the proliferation and metastasis of transformed melanocytes (termed malignant melanoma). Our studies have identified, isolated and characterized several different specific melanogenic enzymes and structural melanosomal matrix proteins that regulate the quality and quantity of melanin pigment produced within melanocytes. Many of these normal differentiation proteins serve as immunologic targets for malignant melanoma, including tyrosinase, TRP1, TRP2, silver/gp100 and MART1. These proteins are encoded by genes that are specifically expressed by mammalian melanocytes and mutations in a number of these genes have now been shown to be involved in several different human clinical pigmentary diseases. We have shown that MART1, like tyrosinase and the other melanogenic proteins noted, is localized in melanosomes, specific organelles found only in melanocyte derived tissues, although the physiologic function of MART1 remains unknown. Since these melanocyte differentiation proteins are known to provide highly specific targets for humoral and cellular immune responses against malignant melanoma, our laboratory is continuing to examine approaches to optimize those responses, and to identify novel melanosomal targets. Although expression of these genes is specific to pigment producing tissues, they are independently regulated following stimulation or inhibition of differentiation by various paracrine and autocrine factors, such as ultraviolet light and melanocyte stimulating hormone. The phenotypic and functional properties of the melanins produced by these regulatory catalytic controls differ dramatically, and effects on the functional and photoprotective properties of those melanins are being characterized. We have identified copper as the specific metal ligand critical to the catalytic function of tyrosinase to produce melanin, and have shown that several mutations of the tyrosinase gene disrupt copper binding and thus lead to a type of inherited human hypopigmentation known as oculocutaneous albinism type 1 (OCA1). We are using differential display to identify a subset of genes involved in modulating pigmentation in response to another paracrine factor termed the agouti signal protein and our current research in this area is aimed at characterizing those gene products and the nature of the regulatory mechanisms involved. Individuals with fair skin and red hair have dramatically higher rates of photocarcinogenesis than do individuals with darker phenotypes, and thus such receptor mediated signaling is important, not only to the regulation of skin and hair color, but to the photoprotection of those tissues. We have continued collaborative studies on other melanoma-specific antigens abnormally expressed by transformed melanocytes which play a role in immune responses to tumor growth. Monoclonal antibodies generated in our laboratory to one of those melanocyte membrane antigens, termed B700, specifically cross- react with human melanoma and have proven useful as highly specific probes for malignant melanoma. Intravenous treatment of tumor-bearing hosts with those monoclonal antibodies provides significant protection against metastatic growth, and B700 constitutes the major immunodominant antigen in a vaccine directed against melanoma tumor growth. Current work in this part of the project is targeted at using our recently derived primary sequence data for the cloning of the B700 gene.
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