Activation of Grm1 expression by inducible mutated B-RAF in vitro and in vivo

Melanoma is a form of skin cancer that arises from the neoplastic transformation of melanocytes. Constitutive activation of the MAPK pathway due to mutations in the serine-threonine protein kinase B-RAF or N-RAS has been reported to play important roles in melanomagenesis. Previously, our laboratory identified that ectopic expression of metabotropic glutamate receptor 1 (Grm1) in melanocytes was sufficient to induce spontaneous melanoma development in transgenic mouse models (TG-3 and EPv). We also demonstrated that Grm1 expression activates the MAPK pathway. Recently, we detected Grm1 expression by immunohistochemical staining of tumors derived from transgenic mice harboring a B-RAF (V600E) mutation on PTEN null background. Similarly, Grm1 expression was also detected in tumor samples derived from transgenic mice with an N-RAS (Q61R) mutation on INK4a null background. In addition, several stable immortalized mouse melanocytic clones with exogenous mutant B-RAF (V600E) cDNA showed Grm1 expression in vitro. Since normal mouse melanocytes acquire loss of p16INK4a in order to become immortalized, we investigate whether loss of PTEN or INK4a/ARF was required for Grm1 expression by mutated B-RAF (V600E). We made use of a transgenic mouse model (BJB), which has an inducible B-RAF (V600E) genotype only in melanocytes. Here we show that induction of B-RAF (V600E) stimulates skin hyperpigmentation, presumably from increased proliferation of melanocytes. Results showed detectable Grm1 expression in BJB skin samples, suggesting that the induction of mutated B-RAF (V600E) may be sufficient to promote activation of Grm1 expression, and that ablation of PTEN expression/function but not of INK4a may be required.M.S.Includes bibliographical referencesby Jairo L. Sierr