Recently, our group has described a murine model of melanoma that is based on ectopic expression of metabotropic glutamate receptor 1 (Grm1). Grm1 is a normally occurring receptor found in the central nervous system of mammals that controls excitatory neural impulses. Ectopic expression of this receptor in melanocytes results in transformation of these cells into a murine form of melanoma indistinguishable from human melanoma. We also found that >60% of human melanoma samples so far tested ectopically express Grm1 while normal skin and melanocytes from the same patients fail to express this protein. Furthermore, stimulation of this receptor in vitro results in downstream upregulation of phosphorylated (activated) ERK demonstrating that this receptor is involved in the regulation of the MAPK pathway, a pathway in the cell important in melanoma formation and growth. Finally, we have now shown that expression of Grm1 in a benign melanocyte cell line results in transformation of this line and inhibition of Grm1 expression in these cells results in reversal of transformation. We have also shown that melanoma cells that express Grm1 undergo G2 cell cycle arrest and subsequent apoptosis upon Grm1 inhibition. The ectopic expression of metabotropic glutamate receptors may thus be important in the pathogenesis of human melanoma and the goal of this proposal is to validate Grm1 as a therapeutic target in humans with melanoma. To accomplish this we will first determine if blocking Grm1 in cell lines alters their invasiveness and ability to migrate and invade tissues, their expression of the proteolytic enzyme uPA, and their ability to form vascular networks in 3D collagen culture (vasculogenic mimicry). Next, we will treat the ectopic Grm1 mouse model of melanoma, a xenograph murine model of melanoma, and a syngeneic murine model of melanoma with commercially available glutamate-blocking agents to determine whether blocking this receptor affects tumor growth in animal models of melanoma. Finally, we will see if a correlation exists between the level of production of Grm1 in primary human melanoma tumors and bad prognostic signs in human melanoma. This series of experiments should yield data that will validate Grm1 as a therapeutic target in patients with melanoma and begin to explain how Grm1 affects pathways that are important in melanoma pathogenesis. Grm receptor blocking agents are already commonly used by Neuroscientists to study and treat common neurologic problems such as epilepsy, chronic pain, and dementia. These receptor-blocking agents could quickly be adapted for use in cancer treatment protocols and the data from this proposal will help us develop clinical trials using Grm1 blocking agents in patients with melanoma. We will be using mice in this study that spontaneous develop melanoma and murine melanoma xenographs. ? ? ?
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