Hepatitis B virus X protein disrupts the balance of the expression of circadian rhythm genes in hepatocellular carcinoma.

Sheng-Li Yang,Jian-Xin Jiang,Chao Yu,Li-Ping Liu,Chao Wu,Xiefan Fang

doi:10.3892/ol.2014.2570

Abstract

The human circadian rhythm is controlled by at least eight circadian clock genes and disruption of the circadian rhythm is associated with cancer development. The present study aims to elucidate the association between the expression of circadian clock genes and the development of hepatocellular carcinoma (HCC), and also to reveal whether the hepatitis B virus X protein (HBx) is the major regulator that contributes to the disturbance of circadian clock gene expression. The mRNA levels of circadian clock genes in 30 HCC and the paired peritumoral tissues were determined by reverse transcription-quantitative polymerase chain reaction (RT-qPCR). A stable HBx-expressing cell line, Bel-7404-HBx, was established through transfection of HBx plasmids. The mRNA level of circadian clock genes was also detected by RT-qPCR in these cells. Compared with the paired peritumoral tissues, the mRNA levels of the Per1, Per2, Per3 and Cry2 genes in HCC tissue were significantly lower (P<0.05), while no significant difference was observed in the expression levels of CLOCK, BMAL1, Cry1 and casein kinase 1ɛ (CK1ɛ; P>0.05). Compared with Bel-7404 cells, the mRNA levels of the CLOCK, Per1 and Per2 genes in Bel-7404-HBx cells were significantly increased, while the mRNA levels of the BMAL1, Per3, Cry1, Cry2 and CKIɛ genes were decreased (P<0.05). Thus, the present study identified that disturbance of the expression of circadian clock genes is common in HCC. HBx disrupts the expression of circadian clock genes and may, therefore, induce the development of HCC.

Highlights

Hepatocellular carcinoma (HCC) is the fifth most common type of cancer and the third leading cause of cancer‐related mortality worldwide [1,2]
The mRNA levels of circadian clock genes were first determined in 30 HCC and the paired peritumorous tissues using reverse transcription‐quantitative polymerase chain reaction (RT‐qPCR)
It was found that the mRNA levels of Per1, Per2, Per3 and Cry2 in HCC tissues were markedly decreased in comparison with those in the paired peritumoral tissues, while no significant difference was observed in the mRNA levels of CLOCK, BMAL1, Cry1 and casein kinase 1ε (CK1ε) compared with the peritumoral tissues (Fig. 1)

Summary

Introduction

Hepatocellular carcinoma (HCC) is the fifth most common type of cancer and the third leading cause of cancer‐related mortality worldwide [1,2]. The double‐stranded DNA genome of HBV contains four overlapping open‐reading frames that encode the surface protein, the core protein, a polymerase and the HBV X protein (HBx) [4]. HBx is a multifunctional protein that does not bind directly to DNA, but exerts transcriptional activation through its interaction with nuclear transcription factors and the modulation of cytoplasmic signal transduction pathways, including NF‐κB signaling [5]. HBx has been demonstrated to accelerate the progress of HCC in numerous processes, including apoptosis, proliferation, inflammation, angiogenesis, immune responses, multi‐drug resistance, invasion and metastasis [6].

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Results

Conclusion