Loss of CDKN2A Cooperates with WWTR1(TAZ)–CAMTA1 Gene Fusion to Promote Tumor Progression in Epithelioid Hemangioendothelioma

Abstract

Purpose: Epithelioid hemangioendothelioma (EHE) is a vascular sarcoma caused by the WWTR1(TAZ)-CAMTA1 (TC) gene fusion. This fusion gene has been observed in almost all reported EHE cases and functions as a constitutively activated TAZ. Sequencing of human tumors has, however, identified additional secondary mutations in approximately 50% of EHE, most commonly the loss of tumor suppressor CDKN2A. In this study, the effect of loss of CDKN2A in EHE tumorigenesis was evaluated. Design: Mice bearing a conditional TC allele were paired with a conditional Cdkn2a knockout allele and an endothelial-specific Cre. Histological characterization and single-cell RNA sequencing of the resultant tumors was performed. EHE cell lines were established through ex vivo culture of tumor cells and evaluated for sensitivity to TEAD inhibition and trametinib. Results: Loss of Cdkn2a within EHE was associated with more aggressive disease, as displayed by earlier tumor-related morbidity/mortality and enhanced tumor cell proliferation. As no previous EHE cell lines exist, we attempted, successfully, to expand EHE tumor cells ex vivo and produced the first EHE cell lines. These cell lines are “addicted” to the TC oncoprotein, replicate the EHE transcriptional profile, and generate EHE tumors when injected into immunodeficient mice. Conclusion: CDKN2A loss enhances the tumorigenicity of EHE in vivo and enabled the generation of. the first cell lines of this disease. These cell line replicate key facets of the human disease phenotype. Therefore, these cell lines and allograft tumors generated after implantation serve as robust model systems for therapeutic testing of compounds either directed at EHE or at other TAZ-driven cancers.

Epithelioid hemangioendothelioma (EHE) with WWTR1::TFE3 gene fusion, a novel fusion variant

“…Previous sequencing studies found secondary mutations in approximately 50% of human EHE, including key secondary variants such as CDKN2A , which can serve as a diagnostic marker for aggressive EHE 26 and is able to drive aggressive tumor behavior in a mouse model of WWTR1::CAMTA1 ‐fused EHE 6 . In our EHE patient, we also observed six secondary somatic variants including DIS3, FANCA, FUBP1, MSH3, ROS1, and SHOC2 , all of which have been linked to poor prognosis in cancer 27–32 .…”

“…Further, in a genetically engineered mouse EHE model, expression of a Wwtr1::Camta1 gene fusion in the endothelial lineage drives EHE tumor formation, recapitulating human WWTR1::CAMTA1 ‐fused EHE 5 . Subsequently, tumor‐derived EHE cell lines and EHE allograft models have been successfully established from this model 6 …”

“…5 Subsequently, tumor-derived EHE cell lines and EHE allograft models have been successfully established from this model. 6 While WWTR1::CAMTA1-fused EHE accounts for approximately 95% of clinical samples of EHE, the more uncommon group of YAP1:: TFE3-fused are associated with unique histology and unique biology. 3,7 Herein, we report the clinicopathologic features of a novel WWTR1::TFE3-fused EHE case, showing combined pathological features of both classical WWTR1::CAMTA1-and variant YAP1::TFE3fused EHEs.…”

The spectrum and significance of secondary (co‐occurring) genetic alterations in sarcomas: the hallmarks of sarcomagenesis

“…On the other hand, in EHE, a recent genomic profiling study demonstrated recurrent alterations in CDKN2A/B , RB1 , APC , and FANCA , which were more common in advanced stage (III/IV) disease [64]. Further, it was shown that CDKN2A loss enhances the tumorigenicity of EHE in a genetically engineered EHE mouse model [65].…”

Mesenchymal tumours of the pleura: review and update

“…Alternative fusions such as WWTR1 :: MAML2 and WWTR1 :: ACTL6A have been reported in rare tumours, with a predominance for cardiac involvement 188 . Genomic changes including CDKN2A loss have been implicated in tumour progression 189 …”