cMYC protein interactions and chromatin association in NUT carcinoma

The oncogene c MYC (HGNC:7553) is a critical genomic target of the BRD4-NUT (B4N) protein that defines many of the NUTM1-rearrangement cancer subtypes in NUT carcinoma (NC). B4N interacts with the EP300 lysine acetyltransferase (KAT3B) to create hyperacetylated “megadomains” that activate downstream genes such as cMYC . However, it is less well understood how mis-regulation of cMYC in turn affects its protein interactions and target genes. The goals of this study are to define the protein and genomic interactions of cMYC in NC, and to test whether those change in response to B4N inactivation. We used CRISPR-Cas9 mediated knock-in of a BioTAP affinity tag to analyze cMYC protein expressed from its normal chromosomal context. This allowed us to adapt a crosslinking purification method termed BioTAP-XL to preserve cMYC integrity and chromatin association for genomic and mass spectrometry-based proteomic analyses. We found that cMYC interacts primarily with the NuA4 KAT5 lysine acetyltransferase complex and that the interactions were maintained despite a decrease in cMYC levels after JQ1 treatment. We conclude that a cascade of aberrant acetyltransferase activities, first via EP300 recruitment and then by KAT5 interaction with MYC, drive NC cell proliferation and blockade to differentiation. Simple Summary A longstanding goal in biology is to understand how protein interactions influence and reflect cellular disease states. MYC is a critical regulator of cellular proliferation that is mis-regulated in many cancers, including those with NUTM1-rearrangements featured in this issue. NUT carcinoma cells are dependent on MYC expression, which blocks differentiation. Using a small molecule inhibitor to induce differentiation of a NUTM1-rearranged patient cell line, we sought to understand how MYC protein interactions are affected by cellular status. When cells differentiate, we found MYC levels were globally diminished, yet the identities of its protein partners and genomic binding sites remained constant. During both growth and differentiation, MYC protein interacted with subunits of the NuA4 lysine acetyltransferase complex, similar to its associations in non-NUTM1 cell lines. Taken together, our results suggest that lysine acetyltransferase activities participate in multiple oncogenic steps in NUT carcinoma. ![Figure][1] ### Competing Interest Statement The authors have declared no competing interest. [1]: pending:yes