Abstract 5194: Notch regulates squamous differentiation, cell plasticity and tumor heterogeneity in esophageal carcinoma

Abstract

Abstract Introduction: The Notch receptor family regulates cell fates and may act as a tumor suppressor in the squamous epithelia. While squamous differentiation is maintained in esophageal squamous cell carcinoma (ESCC) and its precursor lesions, the roles of Notch in esophageal tumor biology remain elusive. Methods: Transformed human esophageal cells expressing EGFR, p53R175H and cyclin D1 (EPC2-T) and ESCC cell lines were stably transduced with ICN1, an active form of NOTCH1 (N1) in a regulatable manner (Tet-On system). Notch was inhibited by dominant negative mastermind-like1 (DNMAML1), a genetic pan-Notch inhibitor or gamma-secretase inhibitors (GSI). 8xCSL-luciferase reporter was transiently transfected to assess Notch activity. Short hairpin RNA was stably transduced by lentivirus to knockdown ZEB1 and ZEB2. Squamous epithelium was reconstituted in organotypic (3D) culture, a form of tissue engineering. In addition, cell growth was assessed in soft agar and immunodeficient mice. Quantitative RT-PCR, Western blotting, immunohistochemistry (IHC) and flow cytometry were done to determine gene expression. Primary ESCC tissues (n=20) were analyzed by IHC. Results: In primary ESCC, N1 was localized to well-differentiated tumor cell nests expressing involucrin (IVL), a squamous differentiation marker, while downregulated in poorly-differentiated cells lacking IVL within a single tumor tissue, implying N1 in tumor heterogeneity. In cell lines, ICN1 activated Notch-dependent transcription and squamous differentiation in the absence of DNMAML1. In 3D culture, DNMAML1 and GSI not only blocked squamous differentiation but induced massive invasion and epithelial-to-mesenchymal transition (EMT) with Wnt activation as suggested by loss of E-cadherin and nuclear localization of β-catenin. In agreement, DNMAML1 upregulated LEF1, Zinc finger E-box binding proteins ZEB1 and ZEB2, transcription factors all essential in EMT and maintenance of cancer stem cells, facilitating transforming growth factor (TGF)-β1-induced EMT in EPC2-T cells. Moreover, DNMAML1 enriched a unique subset of CD44-bright and CD24-dim cells and augmented colony formation, tumorigenicity as well as chemotherapeutic drug resistance against Cisplatin. Importantly, Cre-mediated removal of chromosomally integrated floxed DNMAML1 reactivated Notch to allow terminal differentiation with IVL induction. Moreover, ZEB knockdown greatly impaired TGF-β-mediated EMT while restoring chemotherapeutic drug sensitivity. Conclusions: These data indicate that Notch activation promotes squamous differentiation whereas Notch inhibition enriches poorly differentiated tumor cells with cancer stem cell potential with drug resistance, which involves ZEB and Wnt activation, thus providing a novel mechanistic insight into how Notch signaling may contribute to tumor heterogeneity in ESCC. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 5194. doi:10.1158/1538-7445.AM2011-5194