Abstract 872: Genetic models reveal that the novel VGLL2-NCOA2 fusion oncogene leverages embryonic programs for sarcomagenesis

Abstract

Rhabdomyosarcoma (RMS) is an aggressive pediatric cancer characterized by a misregulation of skeletal muscle developmental pathways. To date, identified oncogenic drivers predominantly include RAS mutations or chromosomal translocations and gene fusions between PAX3 or PAX7 and FOXO1. RNAseq analysis of sarcomas with non-canonical gene fusions has identified new potential genetic drivers of tumorigenesis that have not been rigorously functionally validated for their transformation capacity and biological activity. One new fusion is a chromosomal translocation and inversion between chromosomes 6 and 8, which acts to juxtapose two transcriptional co-activators, VGLL2 and NCOA2. This VGLL2-NCOA2 fusion was identified in congenital rhabdomyosarcoma clinical cohorts by us and others, and characterizes aggressive RMS that express MYOD and MYOG histological markers. However, evidence of VGLL2-NCOA2 transformation capacity has not been verified, hindering insights into its functional contributions to tumorigenesis. Here, we interrogate the function ofVGLL2-NCOA2 using complementary genomic patient data and zebrafish model systems. We utilized the Tol2 transposon system to express mosaic human VGLL2-NCOA2 during early development, and found that VGLL2-NCOA2 is sufficient for tumorigenesis, and results in aggressive tumors with high penetrance by 75 days of age in zebrafish. Further, the histology of zebrafish tumors resembles the human disease, and tumors express markers indicative of RMS such as myog and desma. A cross-species RNAseq of patient and zebrafish VGLL2-NCOA2 RMS tumors highlights a significant enrichment and overlap between gene expression signatures. Finally, mapping the gene expression signatures of VGLL2-NCOA2 zebrafish RMS tumors along the spectrum of zebrafish embryogenesis indicates a clustering with developmental stages corresponding to early somitogenesis, highlighting their arrested developmental nature. Hence, we have generated the first animal model of human VGLL2-NCOA2 tumorigenesis, and have applied this model to understand the biology and identify potential therapeutic targets for this newly identified disease. Citation Format: Genevieve C. Kendall, Sarah Watson, Lin Xu, Collette LaVigne, Whitney Murchison, Dinesh Rakheja, Franck Tirode, Olivier Delattre, James Amatruda. Genetic models reveal that the novel VGLL2-NCOA2 fusion oncogene leverages embryonic programs for sarcomagenesis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 872.

Infantile Rhabdomyosarcomas With VGLL2 Rearrangement Are Not Always an Indolent Disease

“…[30][31][32] It is yet unknown which exact type of adult or embryonic tissue VGLL2-rearranged RMS is most closely related to, but gene expression signatures from a VGLL2-NCOA2 zebrafish tumor model recently pointed toward transcriptomic similarities with early somitogenesis. 14 Overall, our findings expand the current knowledge on VGLL2-rearranged RMS, by demonstrating their propensity for high-grade transformation. Nevertheless, they are limited by the small sample size due to the rarity of these tumors.…”

“…However, the VGLL2-NCOA2 fusion is sufficient for tumorigenesis in a zebrafish model. 14 Of note, some of the above genes are also implicated in fusion events in other types of RMS, albeit with different partners. [15][16][17] Survival data in ssRMS reported before the discovery of VGLL2/NCOA2 rearrangements and MYOD1 mutations are difficult to interpret.…”

“…No morphologic differences seem to exist between ssRMS with those different fusion types2 and it is yet unknown whether they show biological singularities. However, the VGLL2-NCOA2 fusion is sufficient for tumorigenesis in a zebrafish model 14. Of note, some of the above genes are also implicated in fusion events in other types of RMS, albeit with different partners 15–17…”

“…High-grade VGLL2 -rearranged RMS also showed a tendency toward high expression of some factors related to embryonic development, including the transcription factor SOX15 , which is thought to play a role in muscle precursor cell specification and in skeletal muscle regeneration, while inhibiting differentiation of myoblasts to myotubes 30–32. It is yet unknown which exact type of adult or embryonic tissue VGLL2 -rearranged RMS is most closely related to, but gene expression signatures from a VGLL2-NCOA2 zebrafish tumor model recently pointed toward transcriptomic similarities with early somitogenesis 14…”