Oncogenic Chromatin Factors Drive Cell Type-Specific Transcription Within Megadomains In Nut Midline Carcinoma

NUT midline carcinoma (NMC), a subtype of squamous cell cancer, is one of the most aggressive human solid malignancies known. NMC is driven by the creation of a translocation oncoprotein, BRD4-NUT, which blocks differentiation and drives growth of NMC cells. BRD4-NUT forms distinctive nuclear foci in patient tumors, which we find correlate with ∼100 unprecedented, hyperacetylated expanses of chromatin that reach up to 2 Mb in size. These ‘megadomains’ appear to be the result of aberrant, feed-forward loops of acetylation and binding of acetylated histones. Megadomains drive transcription of underlying DNA in NMC patient cells and in naive cells induced to express BRD4-NUT. Here we characterize the constituents of BRD4-NUT chromatin complexes using a crosslinking approach, BioTAP-XL. We find many transcriptional activating proteins known to associate with BRD4, along with novel interactors including p300/CBP and a previously uncharacterized BRD4-NUT Megadomain Associated Protein (BMAP1). BMAP1 is expressed in primary NMC tissue and a subset of more common head and neck squamous cell carcinomas (HNSQC). Concurrently, we discovered a patient-derived NMC harboring a novel BMAP1-NUT fusion. BMAP-NUT blocks differentiation, and like BRD4-NUT recruits p300 to form hyperacetylated megadomains, including at the MYC locus. Thus, our proteomic and genetic approaches have converged on a novel mechanism that involves reprogramming very large regulatory regions to drive oncogenic transcription. Citation Format: Mitzi I. Kuroda, Artyom A. Alekseyenko, Erica M. Walsh, Xin Wang, Adlai Grayson, Peter T. Hsi, Peter V. Kharchenko, Christopher A. French. Oncogenic chromatin factors drive cell type-specific transcription within megadomains in NUT midline carcinoma. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 2655.