Abstract 5057: Single-cell RNA-seq analysis of heterogeneous populations within gastroenteropancreatic neuroendocrine tumors: the role of Sox transcription factors
Authors: Lara Haydee , Matysiak-Budnik Tamara , Magness Scott T. 
Published: August 2015

Abstract
Gastroenteropancreatic neuroendocrine tumors (GPNETs) are rare, with 8,000-estimated cases/year in the United States. Several transcriptome analyses have been performed at the population level, but the heterogeneity of these tumors has never been assessed at the single cell level. Moreover, few genetic mutations have been consistently linked to the origin and progression of GPNETs and prognostic biomarkers are greatly lacking. The most commonly reported familial mutations in GPNETS are found in the Multiple Endocrine Neoplasia type 1 gene (MEN1) or Von Hippel-Lindau's gene (VHL). Similar to other neoplasias, we would expect that a combination of mutations drive the malignant transformation in GPNETs. We are interested in assessing the role of Sox factors in GPNET initiation and progression, particularly Sox4 and Sox9. These Sox factors are expressed in stem and progenitor cells in the gastrointestinal tract. Using a Sox9EGFP mouse, we have shown that Sox9 is expressed at differential levels in stem and progenitor cells, demonstrating high expression in a cell population consistent with long-lived secretory progenitor cells with endocrine and stem cell like properties. Other studies from our lab and others point at the role of Sox4 and Sox9 in differentiation of intestinal/pancreatic progenitors and endocrine cells. Based on these observations, we hypothesize that differential levels of Sox factors mark cells with different potential to initiate carcinoids with an underlying secretory signature, consistent with that of GPNET. Using histological analysis, we assessed the expression of Sox 4/9 in samples from 20 GPNETs patients and we found that the majority exhibited heterogeneity within the tumor. We further confirmed that these tumors expressed putative GPNET markers such as CHGA, serotonin and substance P among others. To gain a more global understanding of the genetic heterogeneity present in these tumors, we performed single-cell RNA-seq analysis from a GPNET patient. Consistent with histological analysis, we also observed heterogeneous levels of several Sox Transcription Factors, including Sox4 and Sox9. These data provided insight into the pathways that may be responsible for GPNET initiation and progression. Notable genes highly expressed include markers of stemness, endocrine progenitor cells, endocrine secretion/differentiation, immune subpopulations and cytokine production. These data also elucidated some potential targets for immunotherapies such as IL-10. Through collaborations with 3 different hospitals, we now have access to at least 24 more fixed/fresh GPNET tissues and we are currently focusing our efforts on the confirmation of our findings. Our results suggest the potential use of single-cell RNA-seq analysis to untangle the pathways that drive the cell populations present in the invasive and proliferative front of GPNETs.
Citation Format: Haydee Lara, Tamara Matysiak-Budnik, Scott T. Magness. Single-cell RNA-seq analysis of heterogeneous populations within gastroenteropancreatic neuroendocrine tumors: the role of Sox transcription factors. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 5057. doi:10.1158/1538-7445.AM2015-5057