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 photoprotection and the proliferation / 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. 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 we have initiated a new project 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, agouti signal protein 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 used differential display to identify a subset of genes involved in modulating pigmentation in response to agouti signal protein and a particularly interesting transcription factor has been identified that regulates pigment genes. Our current research in this area is aimed at further 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 established conditions to purify melanosomes at various stages of development and have begun identifying proteins specifically localized in those fractions. This phase of our study should provide critical information about the biogenesis and function of this organelle, and should hopefully identify new potential melanoma targets. The sum of these studies should improve our understanding of processes important to the malignant transformation of melanocytes and to targeting their specific antigens for immunodetection and/or immunotherapy.
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