Snail1 induces epithelial-to-mesenchymal transition and tumor initiating stem cell characteristics

Hien Dang,Wei Ding,C Bart Rountree,Dow Emerson

doi:10.1186/1471-2407-11-396

Abstract

BackgroundTumor initiating stem-like cells (TISCs) are a subset of neoplastic cells that possess distinct survival mechanisms and self-renewal characteristics crucial for tumor maintenance and propagation. The induction of epithelial-mesenchymal-transition (EMT) by TGFβ has been recently linked to the acquisition of TISC characteristics in breast cancer. In HCC, a TISC and EMT phenotype correlates with a worse prognosis. In this work, our aim is to elucidate the underlying mechanism by which cells acquire tumor initiating characteristics after EMT.MethodsGene and protein expression assays and Nanog-promoter luciferase reporter were utilized in epithelial and mesenchymal phenotype liver cancer cell lines. EMT was analyzed with migration/invasion assays. TISC characteristics were analyzed with tumor-sphere self-renewal and chemotherapy resistance assays. In vivo tumor assay was performed to investigate the role of Snail1 in tumor initiation.ConclusionTGFβ induced EMT in epithelial cells through the up-regulation of Snail1 in Smad-dependent signaling. Mesenchymal liver cancer post-EMT demonstrates TISC characteristics such as tumor-sphere formation but are not resistant to cytotoxic therapy. The inhibition of Snail1 in mesenchymal cells results in decreased Nanog promoter luciferase activity and loss of self-renewal characteristics in vitro. These changes confirm the direct role of Snail1 in some TISC traits. In vivo, the down-regulation of Snail1 reduced tumor growth but was not sufficient to eliminate tumor initiation. In summary, TGFβ induces EMT and TISC characteristics through Snail1 and Nanog up-regulation. In mesenchymal cells post-EMT, Snail1 directly regulates Nanog expression, and loss of Snail1 regulates tumor growth without affecting tumor initiation.

Highlights

Tumor initiating stem-like cells (TISCs) are a subset of neoplastic cells that possess distinct survival mechanisms and self-renewal characteristics crucial for tumor maintenance and propagation
Tumor initiating stem-like cells (TISCs), defined as cancer stem cells, are a subpopulation of neoplastic cells that possess distinct survival and regeneration mechanisms important for chemotherapy resistance and disease progression [1,2]
We demonstrate that mesenchymal liver cancer cells possess several TISC characteristics compared to epithelial cells

Summary

Introduction

Tumor initiating stem-like cells (TISCs) are a subset of neoplastic cells that possess distinct survival mechanisms and self-renewal characteristics crucial for tumor maintenance and propagation. Tumor initiating stem-like cells (TISCs), defined as cancer stem cells, are a subpopulation of neoplastic cells that possess distinct survival and regeneration mechanisms important for chemotherapy resistance and disease progression [1,2]. TISCs possess stem cell features including resistance to apoptosis and selfrenewal [3,4,5]. After their initial discovery and characterization within hematological malignancies [6,7], TISCs have been described in many different malignancies including hepatocellular carcinoma (HCC) [8,9]. TISCs are hypothesized to be the source of metastatic lesions, as a tumor-initiating cell [15] This hypothesis remains controversial, recent work establishes a connection between epithelialmesenchymal-transition (EMT) and a TISC-phenotype [16,17]. During EMT, epithelial cells lose cell-cell adhesion and apical-polarity, and acquire mesenchymal features, such as motility, invasiveness, and resistance to apoptosis [18]

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