Stabilization of snail maintains the sorafenib resistance of hepatocellular carcinoma cells

Abstract

Drug resistance is one of the major challenges for treatment of hepatocellular carcinoma (HCC) with sorafenib. Our present study found that sorafenib resistant (SR) HCC cells showed epithelial-mesenchymal transition (EMT) characteristics with the downregulation of epithelial marker and upregulation of mesenchymal makers. The expression of Snail, a core factor of EMT, was increased in HCC/SR cells, while knockdown of Snail can restore sorafenib sensitivity and EMT potential of HCC/SR cells. Further, the upregulation of protein stability was responsible for the upregulation of Snail in HCC/SR cells. ATM and CSN2, which can stabilize Snail protein, were increased in HCC/SR cells. Knockdown of ATM and CSN2 can suppress the expression of Snail and increase sorafenib sensitivity of HCC/SR cells. It indicated that targeted inhibition of Snail might be helpful to overcome sorafenib resistance of HCC patients.

Introduction

As the sixth most common fatal cancer in the world, hepatocellular carcinoma (HCC) has a poor prognosis with only ~5% of patients surviving more than 5 years [11]. Liver transplantation and hepatic resection can be only used for <20% of HCC patients due to the intra- or extra-hepatic metastasis when diagnosis [15]. Sorafenib, a multi-target tyrosine kinase inhibitor approved by the US Food and Drug Administration for HCC, represents a breakthrough in the management of HCC therapy [6]. As the first systemic therapy approved for patients with advanced-stage HCC, it can suppress cell proliferation and angiogenesis to improve the overall survival of HCC patients [21]. It has been reported that sorafenib can decrease the risk of HCC death in the range of 25–35% and improve the median overall survival from 8 to 11 months [20].

Recent studies indicated that development of drug resistance is the major obstacle contributing to the failure of sorafenib treatment [2]. Studies have revealed several possible mechanisms which are involved in sorafenib resistance of HCC. For example, activation of hypoxia inducible factor-1α (HIF-1α) during sorafenib treatment can induce the expression of vascular endothelial growth factor (VEGF) to confer HCC resistance to sorafenib treatment [40]. In addition, activation of epidermal growth factor receptor (EGFR), AKT, and mTOR can induce cell proliferation under sorafenib treatment [3,36]. Further, sorafenib treatment can increase the expression of stem cells markers CD44 and CD47 and stem cell populations of HCC cells [22]. Collectively, precise molecular mechanisms underlying sorafenib resistance are complicated and remain largely elusive. Further investigations may help to identify new targets to overcome sorafenib resistance.

The epithelial-mesenchymal transition (EMT), a key step for metastatic process of cancer cells, contributes to chemo-resistance of various cancer cells [9]. Transcription factors such as Snail, Slug, Zeb, and Twist are critical for the EMT progression [16,32]. Recent studies indicated that EMT may associate with sorafenib resistance of HCC cells, which was evidenced by results that acquired sorafenib resistant HCC cells showed increased mesenchymal markers N-Cadherin, Vimentin while decreased epithelial marker E-Cadherin [7]. Further, Snail can induce chemoresistance by directly upregulating the ABC transporter ABCB1 in cancer cells [28], while targeting Snail can suppress EMT and chemoresistance of cancer cells [37]. However, the exact roles of EMT and Snail in sorafenib resistance of HCC cells remain to be clarified. Our present study confirmed that sorafenib resistant HCC cells showed EMT characteristics with the upregulation of Snail expression.