Increased chemoresistance via Snail-Raf kinase inhibitor protein signaling in colorectal cancer in response to a nicotine derivative.

Tsai-Yu Lee,Shin Nieh,Shu-Wen Jao,Chia-Lin Liu,Yun-Ching Chang,Su-Feng Chen,Tsung-Yun Liu,Yaoh-Shiang Lin

doi:10.18632/oncotarget.8049

Abstract

A tobacco-specific component, 4-methylnitrosamino-1-3-pyridyl-1-butanone (NNK), is a major risk factor for many cancers. Recent reports have demonstrated that NNK exposure may be associated with tumor progression and chemoresistance in certain cancers. However, the underlying NNK-induced mechanism contributing to the aggressiveness of colorectal cancer (CRC) has not been thoroughly studied. In this study, we used HT29 cells treated with NNK to simulate the long-term exposure of cigarette smoke. A comparative analysis was performed to evaluate cell proliferation, migration, and invasion as well as epithelial-mesenchymal transition (EMT) markers and drug-resistance genes expression, cancer stem cell (CSC) properties, and anti-apoptotic activity. Signaling pathways related to chemoresistance were also investigated. As a result, NNK exposure dose-dependently stimulates cell proliferation, enhance abilities of migration and invasion, induce EMT phenomenon, and attenuate apoptosis. Furthermore, NNK exposure also promotes the capabilities of sphere formation, upregulation of Snail, and overexpression of CD133, Nanog, OCT4, and the drug-resistant genes. Knockdown of Snail results in upregulation of Raf kinase inhibitor protein (RKIP), increased apoptosis, reversal of EMT phenomenon, and reducation of expression of CSC markers, all of which contribute to a decrease of chemoresistance. Our study demonstrates a number of related mechanisms that mediate the effect of NNK exposure on increasing CRC therapeutic resistance via the Snail signaling pathway. Targeting Snail may provide a feasible strategy for the treatment of CRC.

Highlights

Colorectal cancer (CRC) is a leading cause of cancer-related mortality worldwide [1]
Expression of B-cell lymphoma 2 (Bcl2)-associated X protein (Bax), cleavage caspase-9, cleavage caspase-3, and Raf kinase inhibitor protein (RKIP) was decreased in long-term NNK exposure (LT-NNK)-treated cells compared with parent cells (Figure 1D)
Flow cytometric analysis of representative cancer stem cell (CSC) markers demonstrated significant overexpression of cluster of differentiation 133 (CD133), cluster of differentiation 44 (CD44), and cluster of differentiation 24 (CD24) in LT-NNK-treated cells compared with parent cells (p < 0.05) (Figure 3B)

Summary

Introduction

Colorectal cancer (CRC) is a leading cause of cancer-related mortality worldwide [1]. Despite substantial progress in both the diagnosis and the therapy in recent decades, the rate of local recurrence and distant metastasis remains as high as 15%–20%, and the 5-year overall survival rate remains lower than 10% [4]. The tobacco-related carcinogen nitrosamine, 4-methylnitrosamino-1-3-pyridyl-1-butanone (NNK), is a major component and the most potent carcinogen in cigarette smoke [7]. Ye et al reported that the NNK stimulation of cell proliferation is dependent on 5-lipoxygenase and cyclooxygenase-2 expression in human colon cancer cell line [13]. Despite these studies, there is a lack of experimental evidence regarding the effect of tobacco smoking on CRC pathogenesis

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