A Zebrafish Model of Uveal Melanoma

Abstract

Uveal melanoma is the most common primary intraocular tumor in adults, and is often characterized by poor prognosis and few effective therapeutic options. The typical site of metastasis for uveal melanoma is the liver, and over 80% of patients with metastatic disease will die within one year of metastasis diagnosis. The vast majority of human uveal melanomas contain activating somatic mutations in the GPCR alpha subunits GNAQ or GNA11. To directly observe the in vivo effects of GNA11 Q209L (constitutively active) overexpression, I used a zebrafish cancer model in which plasmids can be injected into transgenic fish and melanoma formation can be assessed. Surprisingly, zebrafish injected with a construct overexpressing mitfa:GNA11 Q209L developed a significant incidence of uveal melanomas. A mini-screen of HOX genes using this system revealed a novel role for HOXB7, which also functioned as an inducer of uveal melanomas in our zebrafish model. Other plasmids containing oncogenes do not lead to uveal tumors, suggesting a specificity for GNA11 and HOXB7. Cell lines were derived from GNA11 Q209L-overexpressing zebrafish tumors and uveal melanoma cells were sensitive to PKC inhibition, which has been observed in human uveal melanoma cells as well. Additionally, RNAseq analysis of zebrafish uveal melanoma cell lines revealed high expression of genes such as cyr61 and ctgf, YAP pathway genes that are known to be induced by GNAQ in human uveal melanomas. I found that overexpression of catalytically inactive BAP1, a chromatin factor whose function is frequently lost in metastatic uveal melanomas, led to a significant acceleration of overall melanoma onset but did not induce a uveal melanoma phenotype in our model. Morpholino experiments showed that knockdown of either zebrafish gna11 or bap1 affected the spatial expression of hoxb7a, with a combined knockdown of gna11 and bap1 suggesting that bap1 is epistatic to gna11. My studies demonstrate the first known instance of spontaneous uveal melanoma formation in response to overexpression of a human uveal melanoma oncogene, and that the resulting uveal melanomas share genetic features and drug response tendencies with human uveal melanomas. This model is a useful new tool for the study of uveal melanoma pathogenesis, genetics, and therapeutics.