Abstract 2138: RasGRP3 mediates MAPK pathway activation in GNAQ mutant uveal melanoma

Uveal melanoma (UM) is the most common intraocular malignancy in adults and no effective treatment options are available for metastatic disease. Over 80% of UM show mutations in the Gαq family members GNAQ and GNA11. MAP-kinase pathway activation in part mediated by protein kinase C (PKC) has been shown as one critical contributing factor to GNAQ-mediated oncogenesis. However PKC inhibition alone does not completely suppress MAPK signaling. A more refined understanding of the signaling cascade linking MAPK signaling to mutant GNAQ or GNA11 is required to develop more effective strategies for targeted therapy. Among more than 10 different PKC isoforms, we identified both PKC δ and PKC ε to be required and sufficient to activate MAPK pathway in GNAQ mutant melanomas by using siRNA mediated knock-down and co-transfection of GNAQQ209L and specific PKC isoform cDNAs. Overexpression of GNAQQ209L in 293FT cells increased Ras-GTP level and knock down of three Ras isoforms in GNAQ mutant uveal melanoma cell lines decreased MAPK signaling. Microarray analysis of 5 different GNAQ/11 mutant and 5 NRAS/BRAF-mutant melanoma cells revealed RasGRP3, a Ras-guanyl nucleotide exchange factor (RasGEF), ranks at the top of 487 differentially expressed genes between (cut off : p2 or 100 fold) elevated RasGRP3 levels in GNAQ/11 mutant melanoma cells, while other RasGEFs were not significantly altered. Knock down of RasGRP3 decreased MAPK signaling and proliferation in GNAQ mutant melanoma cells,...
Source: Cancer Research - Category: Cancer & Oncology Authors: Tags: Molecular and Cellular Biology Source Type: research