Oncogenic Orphan Nuclear Receptor NR4A3 Interacts and Cooperates with MYB in Acinic Cell Carcinoma

Acinic cell carcinoma (AcCC) is a morphologically distinctive salivary gland malignancy often associated with chromosome rearrangements leading to overexpression of the NR4A3 transcription factor. However, little is known about how NR4A3 contributes to AcCC biology. Detailed RNA-sequencing of 21 archived AcCC samples revealed fusion reads arising from recurrent t(4;9), t(9;12), t(8;9) or t(2;4) chromosomal translocations, which positioned highly active enhancers adjacent to the promoter of theNR4A3gene or the closely relatedNR4A2gene, resulting in their aberrant overexpression. Transcriptome analyses revealed several distinct subgroups of AcCC tumors, including a subgroup that overexpressed bothNR4A3andMSANTD3. A poor survival subset of the tumors with high-grade transformation expressedNR4A3andPOMCas well asMYB, an oncogene that is the major driver in a different type of salivary gland tumor, adenoid cystic carcinoma. The combination ofNR4A3andMYBshowed cooperativity in regulating a distinct set of genes. In addition, the ligand binding domain of NR4A3 directly bound the Myb DNA binding domain. Transformation assays indicated that, while overexpressed NR4A3 was sufficient to generate transformed colonies, the combination of NR4A3 plus Myb was more potent, leading to anchorage-independent growth and increased cellular invasiveness. The results confirm thatNR4A3andNR4A2are the main driver genes of AcCC and suggest that concurrent overexpression ofNR4A3andMYBdefines a subset of AcCC patients with high-grade transformation that display exceptionally poor outcome.