Engineering a Genetically Relevant Zebrafish Model of Human Uveal Melanoma

UoM administered thesis: Phd

  • Authors:
  • Mai Abdelmouti

Abstract

Uveal melanoma (UM) is a sight and life-threatening malignancy of the human eye. The potential for progress in translational UM research is, however, hampered by the short supply of clinical samples due to its rarity and also the lack of an informative animal model which would allow experimental intervention to dissect the molecular machinery governing tumor development. Towards this end, we aimed to generate a genetically relevant model of human UM in zebrafish that can be used to study the roles of key genetic determinants in tumor initiation and progression in vivo and also establish a valuable resource for future preclinical studies. Given the pervasive role of Galphaq proteins in driving UM pathogenesis, we engineered transgenic zebrafish to express oncogenic GNAQQ209P in the melanocyte lineage. This resulted in hyperplasia of uveal (choroidal) melanocytes, but with no evidence of malignant progression nor perturbation of RPE or skin melanocytes. However, combining expression of oncogenic GNAQQ209P with tp53 inactivation resulted in an earlier onset and even more extensive hyperplasia of choroidal melanocytes that then progressed to UM. While NRASQ61L and BRAFV600E potently stimulate ERK1/2-MAPK signalling pathway, immunohistochemical analysis revealed only sporadic immunoreactivity to phosphorylated ERK1/2 in hyperplastic choroidal lesions and also uveal tumors driven by oncogenic GNAQQ209P, in contrast to an abundant immunoreactivity in oncogenic HRASG12V-driven cutaneous tumors. Rather, ubiquitous positive staining for nuclear YAP was observed in GNAQQ209P-driven uveal tumor specimens. In keeping with a lesser role of GNAQ in regulating ERK1/2-MAPK signalling in UM, we showed that downregulation of oncogenic GNAQQ209P/L or inhibition of PLC-β in the majority of human UM cells expressing oncogenic GNAQQ209P/L barely affected ERK phosphorylation. In summary, this study demonstrates the insufficiency of oncogenic GNAQQ209P alone in driving UM development which only became evident with a second genetic hit involving tp53 inactivation. Our findings also demonstrate a weak correlation between oncogenic GNAQ mutations and sustained ERK1/2-MAPK activation, implying that ERK1/2 signalling is unlikely to be instrumental in the maintenance of GNAQQ209P-driven uveal tumors.

Details

Original languageEnglish
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Award date31 Dec 2016