Abstract B44: The TAZ-CAMTA1 and YAP-TFE3 fusion proteins transform cells by binding to subunits of the histone acetyltransferase Ada2a-containing complex (ATAC)
Authors: Merritt Nicole , Garcia Keith , Rajendran Dushyandi , Lin Zhen-Yuan , Zhang Xiaomeng , Mitchell Katrina , Fullenkamp Colleen , Gingras Anne-Claude , Harvey Kieran , Tanas Munir 
Published: September 2020

Background: Epithelioid hemangioendothelioma (EHE) is a vascular sarcoma characterized by WWTR1(TAZ)-CAMTA1 (85%) and YAP1-TFE3 gene fusions (15%). The fusion proteins contain the N-terminus of TAZ and YAP, including their TEAD binding domains, fused in frame to the C-termini of CAMTA1 and TFE3, respectively. The C-termini of CAMTA1 and TFE3 contain transactivating domains as well as other protein-protein interaction domains. The structure of the fusion proteins led us to hypothesize that the C termini of CAMTA1 and TFE3 interact with novel proteins that potentiate the oncogenic activity of TAZ and YAP.

Methods: NIH 3T3 and SW872 cell lines were transduced with either TAZ-CAMTA1(TC) or YAP-TFE3(YT) and anchorage independent growth was assayed via growth in soft agar and on poly-HEMA. 1x107 NIH 3T3 cells or SW872 cells expressing TC, YT, or containing EV were subcutaneously injected in NOD Scid Gamma mice. TC and YT as well as the controls including TAZ, CAMTA1, YAP, and TFE3 were tagged with the activated BirA biotin ligase. Protein-protein interactions were identified using BioID mass spectrometry and a subsequent shRNA screen was conducted to identify prey proteins crucial to driving anchorage-independent growth.

Results: We showed that TC and YT promote anchorage-independent growth as well as tumorigenesis and metastasis in vivo. Similar to TC, we showed YT requires interaction with TEAD4 to drive its oncogenic transcriptional program. BioID mass spectrometry identified 41 novel interactions with prey proteins (as compared to full-length TAZ and YAP) mediated by the fusion proteins, 26 of which are epigenetic modifying enzymes. Of these 26 proteins, YEATS2 and ZZZ3, both members of the histone acetyltransferase Ada2a-containing complex (ATAC), were identified by the shRNA screen as critical to TC driven anchorage-independent growth. Mass spectrometry showed that an additional subunit of the ATAC complex, KAT14, also interacted with both the TC and YT fusion proteins. ZZZ3 was demonstrated to coimmunoprecipitate with TC, validating the mass spectrometry results. Kaplan-Meier analysis of the TCGA Illumina HiSeq RNA-Seq data set for sarcomas demonstrates that increased expression of YEATS2 or ZZZ3 predicts worse overall survival (p=0.0049 and p=0.0037 respectively) across all sarcomas, independent of histologic type.

Conclusions: Utilizing two serial unbiased assays, we showed that oncogenic properties of TC and YT can be explained in part by their interaction with the ATAC complex, a histone acetyltransferase complex. Future studies will elucidate the mechanisms by which the ATAC complex augments the TAZ and YAP oncogenic transcriptional programs. TAZ and YAP fusion proteins have been identified in other cancers, suggesting that similar epigenetic mechanisms may be at work in these cancers. Furthermore, since the ATAC complex is a histone acetyltransferase complex, and contains a catalytic GCN5 subunit, it represents a potential therapeutic target in EHE and possibly other sarcomas.

Citation Format: Nicole Merritt, Keith Garcia, Dushyandi Rajendran, Zhen-Yuan Lin, Xiaomeng Zhang, Katrina Mitchell, Colleen Fullenkamp, Anne-Claude Gingras, Kieran Harvey, Munir Tanas. The TAZ-CAMTA1 and YAP-TFE3 fusion proteins transform cells by binding to subunits of the histone acetyltransferase Ada2a-containing complex (ATAC) [abstract]. In: Proceedings of the AACR Special Conference on the Hippo Pathway: Signaling, Cancer, and Beyond; 2019 May 8-11; San Diego, CA. Philadelphia (PA): AACR; Mol Cancer Res 2020;18(8_Suppl):Abstract nr B44.