Silencing of 14-3-3ζ over-expression in hepatocellular carcinoma inhibits tumor growth and enhances chemosensitivity to cis-diammined dichloridoplatium

Abstract

The 14-3-3ζ protein plays a key role in regulation of cellular processes. In the present study, we showed that 14-3-3ζ protein was significantly overexpressed in hepatoma cell lines and human tumorous tissues of hepatocellular carcinoma (HCC) patients. Knockdown with RNA interference in hepatoma cell lines with high 14-3-3ζ expression suppressed tumor cell proliferation via activation of c-Jun N-terminal kinase (JNK) and p38/MAPK. Furthermore, suppression of 14-3-3ζ enhanced the anti-cancer effect of cis-diammined dichloridoplatium (CDDP) in hepatoma cell lines. These results suggest that silencing of 14-3-3ζ may be an attractive target for HCC therapeutic development.

Introduction

Human hepatocellular carcinoma (HCC) is the fifth most common type of cancer and the third leading worldwide cause of cancer death [1]. Despite recent advances in treatment of HCC, options for curing the disease are limited. In cases of advanced HCC, anti-cancer chemotherapeutic drugs, such as cis-diammined dichloridoplatium (cisplatin; CDDP) and 5-fluorouracil (5-FU) have been used; however, data demonstrating their efficacy in patients is limited [2], [3], [4], [5].

The 14-3-3 proteins are a family of highly conserved cellular proteins that play important roles in various cellular processes [6], [7], [8]. Proteins in this family contain a pS/pT-binding motif and regulate cellular processes, including signal transduction, cell cycle, apoptosis, cellular metabolism, stress responses, cytoskeleton organization and malignant transformation [7], [8], [9]. To date, seven mammalian 14-3-3 isoforms (β, γ, ε, σ, η, τ, and ζ) that interact with other key cellular proteins during tumor development and progression have been identified [6], [7]. Recently, 14-3-3ζ expression has been reported in various cancer cells [10], [11], [12], [13]. However, until now, the possible association between 14-3-3ζ expression and hepatocarcinogenesis has not been investigated.

RNA interference (RNAi) represents a natural mechanism by which small interfering RNA (siRNA) molecules can specifically and potently down-regulate expression of target genes [14]. Advances in siRNA technology in recent years have allowed the targeting of oncogenes with high specificity and efficiency in various cancers [15]. In previous study, we identified a 14-3-3ζ gene that is up-regulated in human HCC through genome-wide differential expression analysis and randomly-primed Annealing Control Primer™ (ACP)-based reverse transcription-polymerase chain reaction (RT-PCR) [16], [17]. In this study, we investigated the possible association between 14-3-3ζ expression and HCC, and demonstrated that down-regulation of 14-3-3ζ expression by RNAi not only inhibits tumor cell growth but also enhances the chemotherapeutic effects of CDDP in HCC. This is the first report to demonstrate the co-therapeutic potential of 14-3-3ζ and CDDP in HCC.