Single cell RNA-sequencing identifies a paracrine interaction that may drive oncogenic Notch signaling in human adenoid cystic carcinoma

Salivary adenoid cystic carcinoma (ACC) is a rare but biologically unique biphasic tumor, consisting of malignant myoepithelial and luminal epithelial cells. MYB and Notch signaling have been implicated in the pathophysiology of these tumors, but in vivo descriptions of these two programs in human tumors and investigation into their active coordination remain incomplete. We utilized single cell RNA-sequencing to profile human head and neck ACC, including the first comparison of primary ACC with a matched local recurrence. We define expression heterogeneity in these rare tumors, uncovering previously unappreciated diversity in myoepithelial and luminal cell expression. We discover differential expression of Notch ligands DLL1, JAG1, and JAG2 in myoepithelial cells, suggesting a paracrine interaction that may support oncogenic Notch signaling. We further validated this selective expression in three published cohorts of ACC patients. Our data provide a potential explanation for the biphasic nature of low and intermediate grade ACC and may help direct new therapeutic strategies against these tumors. Fresh biopsies of head and neck salivary ACC were collected at the time of surgical resection. Post-operatively, H&E stained sections were reviewed by a dedicated head and neck pathologist and assessed for growth pattern and immunohistochemical staining profile to confirm the pathologic diagnosis of ACC, based upon histomorphologic criteria outlined in the WHO Classification of Head and Neck Tumours. Only cases unequivocally classified as ACC were included in the final dataset. NOTE: RNA-Seq raw data is to be made available through dbGaP (controlled access) due to patient privacy concerns.