Uveal melanoma is a highly aggressive cancer with a strong propensity for metastasis, yet little is known about the biological mechanisms underlying this metastatic potential.,We recently showed that most metastasizing uveal melanomas, which exhibit a class 2 gene expression profile, contain inactivating mutations in the tumor suppressor BAP1.,The aim of this study was to investigate the role of BAP1 in uveal melanoma progression.,Uveal melanoma cells were studied following RNAi-mediated depletion of BAP1 using proliferation, BrdU incorporation, flow cytometry, migration, invasion, differentiation and clonogenic assays, as well as in vivo tumorigenicity experiments in NOD-SCID-Gamma mice.,Depletion of BAP1 in uveal melanoma cells resulted in a loss of differentiation and gain of stem-like properties, including expression of stem cell markers, increased capacity for self-replication, and enhanced ability to grow in stem cell conditions.,BAP1 depletion did not result in increased proliferation, migration, invasion or tumorigenicity.,BAP1 appears to function in the uveal melanocyte lineage primarily as a regulator of differentiation, with cells deficient for BAP1 exhibiting stem-like qualities.,It will be important to elucidate how this effect of BAP1 loss promotes metastasis and how to reverse this effect therapeutically.
BRAFV600 inhibitors have offered a new gateway for better treatment of metastatic melanoma.,However, the overall efficacy of BRAFV600 inhibitors has been lower than expected in clinical trials, and many patients have shown resistance to the drug’s effect.,We hypothesized that somatic mutations in the Phosphoinositide 3-Kinase (PI3K) pathway, which promotes proliferation and survival, may coincide with BRAFV600 mutations and contribute to chemotherapeutic resistance.,We performed a somatic mutation profiling study using the 454 FLX pyrosequencing platform in order to identify candidate cancer genes within the MAPK and PI3K pathways of melanoma patients.,Somatic mutations of theses candidate cancer genes were then confirmed using Sanger sequencing.,As expected, BRAFV600 mutations were seen in 51% of the melanomas, whereas NRAS mutations were seen in 19% of the melanomas.,However, PI3K pathway mutations, though more heterogeneous, were present in 41% of the melanoma, with PTEN being the highest mutated PI3K gene in melanomas (22%).,Interestingly, several novel PI3K pathway mutations were discovered in MTOR, IRS4, PIK3R1, PIK3R4, PIK3R5, and NFKB1.,PI3K pathway mutations co-occurred with BRAFV600 mutations in 17% of the tumors and co-occurred with 9% of NRAS mutant tumors, implying cooperativity between these pathways in terms of melanoma progression.,These novel PI3K pathway somatic mutations could provide alternative survival and proliferative pathways for metastatic melanoma cells.,They therefore may be potential chemotherapeutic targets for melanoma patients who exhibit resistance to BRAFV600 inhibitors.