Role of TRPM1 (Melastatin1) in the Biology of Human Melanocytes

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DESCRIPTION (provided by applicant): The goal of studies proposed here is to understand the functions and regulation of the melanocyte-specific transient receptor potential (TRP) ion channel protein, melastatin. Mammalian TRP channel protein family consists of nearly 30 members. TRPs are critical for functions of wide ranging physiological process, where cellular divalent cations, specifically Ca2+ and Mg2+ play important roles. These processes include photoperception, thermosensation, taste perception, mechanosensation, pain perception, Mg2+ homeostasis in kidney, smooth muscle tone and blood pressure regulation. Melastatin (TRPM1), the founding member of a novel family of TRP channel proteins known as TRPMs, was originally identified as suppressor of mouse melanoma metastasis. Independently, we identified TRPM1 as a gene induced in growth arrested human melanoma cells. Tissue distribution and promoter regulation by microphthalmia transcription factor (MITF) confirmed TRPM1 as a melanocyte-restricted TRP. Functional studies using a partial length human TRPM1 protein in heterologous HEK293 cells suggested that it is a constitutively active Ca2+ channel. Although loss of TRPM1 expression (as assessed by in situ RNA hybridization) is thought to correlate with aggressiveness of cutaneous melanoma, the exact function(s) of TRPM1 and how its expression is regulated in melanocytes are not known. To address these issues, we generated TRPM1 expression (constitutive and tet-inducible) shRNA plasmids and antibody reagents. Preliminary data showed that in primary neonatal human foreskin melanocytes a) knockdown of TRPM1 by shRNA inhibits accumulation of melanin pigment, b) TRPM1 expression is up-regulated by inducers of melanocyte differentiation and down regulated by p53 and c) malignant melanocytes do not tolerate expression of full-lengthTRPM1. These data suggested that TRPM1 is involved in regulation of growth and differentiated functions of epidermal melanocytes. In this proposal we will a) characterize biosynthesis, posttranslational modification, subcellular localization and membrane orientation and establish structure-function relationship of TRPM1, b) investigate the role of TRPM1 in growth of normal and malignant melanocytes and pigmentation using stable shRNA knockdown strategy, and c) investigate mechanism of regulation of TRPM1. These studies on understanding TRPM1 functions are significant in the context of growing interest in functions of TRP channels, association of mutations in TRP genes with genetic disorders and the potential of targeting TRPs for treatment of diseases arising from their malfunction. PUBLIC HEALTH RELEVANCE Melanocytes are the source of skin and hair pigmentation. Genetic defects and environmental factors that alter melanocyte function cause pigmentary disorders including skin cancer melanoma. This proposal investigates the role of a unique calcium transporting protein in maintaining proper functioning of human skin melanocytes. Knowledge gained from these studies could help develop new therapies for pigmentary disorders.