Genomically Complex Human Angiosarcoma and Canine Hemangiosarcoma Establish Convergent Angiogenic Transcriptional Programs Driven by Novel Gene Fusions

Abstract

Sporadic angiosarcomas (ASs) are aggressive vascular sarcomas whose rarity and genomic complexity present significant obstacles in deciphering the pathogenic significance of individual genetic alterations. Numerous fusion genes have been identified across multiple types of cancers, but their existence and significance remain unclear in sporadic ASs. In this study, we leveraged RNA sequencing data from thirteen human ASs and 76 spontaneous canine hemangiosarcomas (HSAs) to identify fusion genes associated with spontaneous vascular malignancies. Ten novel protein-coding fusion genes, including TEX2-PECAM1 and ATP8A2-FLT1, were identified in seven of the thirteen human tumors, with two tumors showing mutations of TP53. HRAS and NRAS mutations were found in ASs without fusions or TP53 mutations. We found fifteen novel protein-coding fusion genes including MYO16-PTK2, GABRA3-FLT1, and AKT3-XPNPEP1 in eleven of the 76 canine HSAs; these fusion genes were seen exclusively in tumors of the angiogenic molecular subtype that contained recurrent mutations in TP53, PIK3CA, PIK3R1, and NRAS. In particular, fusion genes and mutations of TP53 co-occurred in tumors with higher frequency than expected by random chance, and they enriched gene signatures predicting activation of angiogenic pathways. Comparative transcriptomic analysis of human ASs and canine HSAs identified shared molecular signatures associated with activation of PI3K/AKT/mTOR pathways. Our data suggest that genomic instability induced by TP53 mutations might create a predisposition for fusion events that may contribute to tumor progression by promoting selection and/or enhancing fitness through activation of convergent angiogenic pathways in this vascular malignancy.

Hemangiosarcoma Cells Promote Conserved Host-Derived Hematopoietic Expansion

“…We and others showed previously that canine hemangiosarcoma cells could form hemangiosarcomas in NSG mice. 7,21,24,35,36 We also observed that some of the NSG mice inoculated with SB-HSA cells or with another cell line called Emma-brain (EFB), and some BNX mice inoculated with DHSA-1426 canine patient-derived tumor fragments developed what appeared to be round cell tumors. Four mice that received 5 × 10 6 SB-HSA cells intraperitoneally and one of four mice that received 2 × 10 6 EFB cells subcutaneously died acutely two weeks after inoculation.…”

“…Canine hemangiosarcomas can be classified into angiogenic, inflammatory, and adipogenic subtypes based on their transcriptional programs ( Figure S1A ). 4,7 This separation is prognostically significant: of the 43 dogs in this cohort for which we had treatment and outcome data, those with inflammatory hemangiosarcomas accounted for nearly all that showed prolonged survival (>150 days, Figure S1B ). Intriguingly, the subset of dogs whose hemangiosarcomas had a predominant angiogenic phenotype could be further subdivided into a group with a “pure angiogenic” molecular signature and a group with a “mixed angiogenic and inflammatory” molecular signature.…”

“…Consistent with previously reports, 31,32 human angiosarcomas showed highly enriched angiogenic signatures. 7 However, the presence of inflammatory signatures in this tumor has not been thoroughly examined. Using a defined methodology to compare transcriptional signatures in tumors from different species, 33 we identified 588 differentially expressed genes in canine angiogenic and inflammatory hemangiosarcomas and evaluated the expression of their homologs in human angiosarcomas.…”

“…5,6 Furthermore, canine hemangiosarcoma and human angiosarcoma appear to establish convergent molecular programs despite their genomic complexity. 7…”

“…Angiogenesis and inflammation are key molecular features of canine hemangiosarcoma, 8 and convergent transcriptional programs regulating these processes are also observed in human angiosarcoma. 7 These molecular programs are the foundation for a novel subclassification of canine hemangiosarcoma. 4 However, the contribution of the tumor microenvironment to these programs remains incompletely understood.…”