DHODH modulates transcriptional elongation in the neural crest and melanoma

Oncogenes BRAF(V600E) and SETDB1 in melanoma Transgenic zebrafish carrying the human oncogene BRAF(V600E) , the most common mutation in melanoma patients, provide a convenient model for melanoma. Two papers from Leonard Zon and colleagues demonstrate the potential of this system in the study of cancer genetics and in drug development. Ceol et al . screen for genes that cooperate with mutated BRAF , and identify SETDB1 as capable of accelerating melanoma formation in fish. The gene is found in a region that is frequently amplified in human melanomas, and its gene product, SETDB1, is a histone methylating enzyme that is often overexpressed in those melanomas. This work establishes SETDB1 as an important oncogene. White et al . find expression of a gene signature in melanoma-susceptible zebrafish embryos that is indicative of disrupted differentiation of neural crest progenitors. A chemical screen identifies leflunomide, an immunomodulatory drug used to treat rheumatoid arthritis, as an inhibitor of neural crest stem cells. Leflunomide has antimelanoma activity in human melanoma xenografts and might prove useful as an anticancer drug, particularly in combination with BRAF inhibitors. In a zebrafish model of melanoma driven by activated BRAF, this study finds expression of a gene signature indicative of disrupted terminal differentiation of neural crest progenitors. A chemical screen led to the identification of leflunomide as an inhibitor of neural crest stem cells. Leflunomide inhibits dihydroorotate dehydrogenase and thereby transcriptional elongation, including genes involved in neural crest development and melanoma growth. Leflunomide has anti-melanoma activity in the zebrafish model and human melanoma xenografts, and might prove useful as an anticancer drug. Melanoma is a tumour of transformed melanocytes, which are originally derived from the embryonic neural crest. It is unknown to what extent the programs that regulate neural crest development interact with mutations in the BRAF oncogene, which is the most commonly mutated gene in human melanoma 1 . We have used zebrafish embryos to identify the initiating transcriptional events that occur on activation of human BRAF(V600E) (which encodes an amino acid substitution mutant of BRAF) in the neural crest lineage. Zebrafish embryos that are transgenic for mitfa:BRAF(V600E) and lack p53 (also known as tp53 ) have a gene signature that is enriched for markers of multipotent neural crest cells, and neural cre