Abstract 1076: Single nucleus RNA-sequencing using normal human salivary glands revealed a potential etiologic relationship between each salivary gland cell and salivary gland malignancies
Authors: Nakagawa Takuya , Nasamran Chanond , Hu Jingjing , Sen Prakriti , Guo Theresa , Fisch Kathleen , Califano Joseph 
Published: March 2024

Abstract
Salivary glands are composed of several types of cells, and each cell type is predicted to be involved in the carcinogenesis of different types of cancers including Adenoid cystic carcinoma (ACC), Acinic cell carcinoma (AciCC), salivary duct carcinoma (SDC), myoepithelial carcinoma (MECA) and other histology. In this study, we performed single nucleus RNA-seq on three human salivary gland samples to clarify the gene expression profile of each complex cellular component of the salivary glands and related these expression patterns to expression found in salivary gland cancers (SGC) to infer cell of origin. By single nucleus RNA-seq, total 13,643 salivary gland cells were stratified into four clusters: acinar cells, ductal cells 1, ductal cells 2, and myoepithelial cells/stromal cells, with differentially expressed genes of each group. The localization of each cell group was anatomically validated by IHC of each cluster marker gene, and one group of ductal cells was found to represent intercalated ductal cells labeled with HES1. Gene ontology analysis for this group included “epithelial cell differentiation” confirming the intercalated duct. Furthermore, to elucidate the potential etiologic relationship between normal salivary glands cell type and salivary gland carcinoma histology, we compared the expression of each cluster marker to SGC public RNA-seq data. In comparison between AciCC and ACC, we used normalized RNA-seq data of 54 ACC and 21 AciCC. ACC had significantly less expression of acinar cells markers (STATH, CST2, and LPO) compared to other markers expression(***P = 4 × 10−51), unlike AciCC (P = 0.54), suggesting a possible contribution of acinar cells to the carcinogenesis of AciCC. In another cohort, we compared 16 SDC, and 38 MECA with publicly available RNA-seq data. Remarkably, HES1 and ELF3, each of two different ductal cell markers, were significantly upregulated in SDC consistent with origin of SDC from ductal cells (P=0.001, P=0.0007, respectively). Consistent with bulk RNA-seq results, expression of HES1 in IHC using clinical human SDC and MECA samples was higher in SDC than MECA, suggesting that the expression of the derived cells is involved in salivary gland carcinogenesis. Cell type expressions in specific SGC histology are similar to those found in normal salivary gland populations, indicating a potential etiologic relationship. On the other hand, there was no significant difference in myoepithelial marker ACTA2 expression between SDC and MECA, suggesting that the markers of origin are not always highly expressed, depending on cancer subtypes. Although publicly available SGC RNA-seq data used in this study are limited, the results remarkably reflect the diverse modes of carcinogenesis of SGC. These findings might provide a better understanding of the molecular basis of SGC and treatment strategies for SGC.
Citation Format: Takuya Nakagawa, Chanond Nasamran, Jingjing Hu, Prakriti Sen, Theresa Guo, Kathleen Fisch, Joseph Califano. Single nucleus RNA-sequencing using normal human salivary glands revealed a potential etiologic relationship between each salivary gland cell and salivary gland malignancies [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 1076.