Hepatitis B virus infection is one of the most common diseases, with an estimated 350 million chronically infected carriers worldwide. Chronic HBV can lead to cirrhosis, which is considered to be a principal factor pre disposing to the development of HCC [1].

In patients with chronic hepatitis some, but not all, of the infected cells are destroyed due to relatively inefficient T-cell response. This leads to a cycle of liver cell destruc tion and regeneration in the context of continuous intra hepatic inflammation that often terminates in HCC. A model of chronic immune-mediated liver disease using transgenic mice provided evidence that HBV-specific chronic immune-mediated liver cell injury is sufficient to initiate and sustain the process of hepatocarcinogenesis [4]. Hepatitis B virus is a single-stranded DNA virus that becomes integrated into the host genome [1]. The HBV genome consists of four overlapping open reading frames that encode DNA polymerase (P), HBV surface antigen (HBsAg), HBV core protein (HBcAg) and a regulatory X protein (HBx) [5]. The HBV contributes to hepatocarcino genesis via three mechanisms. First, HBV viral DNA can integrate into the host genome and induce chromosomal instability. Integration of HBV DNA into the host genome can induce large inverted duplications, deletions, amplifi-cations, or chromosomal translocations [6]. Second, it may also activate cellular proto-oncogenes or suppress growth-regulating genes in cis [1]. A recent study has shown that integration is located upstream to the promoter of human telomerase reverse transcriptase (hTERT) gene, which codes for the catalytic subunit of telomerase ribonucleo protein, and that HBV enhancer can activate the transcrip tion of the hTERT gene in hepatocarcinoma cell lines [7]. The third mechanism by which HBV contributes to carcinogenesis is through expression of viral proteins, in particular, HBx. Intracellular localization studies have demonstrated that the protein HBx functions as a transcrip tional regulator in both cytoplasm and nucleus [7]. In the nucleus it regulates the promoters of different genes including proto-oncogenes such as v-myc and c-myc [my elocytomatosis viral oncogene homolog (avian)] and c-myb and v-myb [myeloblastosis viral oncogene homolog (avian)] [1], c-jun oncogene [3] and v-fos and c-fos (Finkel-Biskis-Jinkins murine osteogenic sarcoma viral oncogene homolog) [8], tumor suppressor genes including adenomatous polyposis coli (APC), p53, cyclin-dependent kinase inhibitor 1A (p21waf1/cip1), Wilms tumor 1 (WT1) gene [1] and retinoblastoma (Rb) gene [9], and transcriptional factors such as nuclear factor-kappa B (NFêB), activating protein 2 (AP-2) [10] and cAMP response element-binding/activating transcription factor-1 proteins (ATF/CREB) [3]. It increases the expression of the epi dermal growth factor receptor in HCC cell lines and poten tiates transforming growth factor á (TGFá) [8]. On the other hand, HBx protein upregulates the expression of TGFá1 and promotes TGFá1 signaling [9]. Transfection of the human hepatocellular liver carcinoma cell line (HepG2) with an HBx expression vector increased insulin-like growth factor (IGF-II) gene expression which was mediated by protein kinase C (PKC) and p44/p42 mitogen-activated protein MAP kinases (p44/p42MAPK) [11]. The HBx protein exerts its effects on the cell cycle through upregulation of cyclin-dependent kinase 2 (CDK2) and cell division cycle 2 (CDC2), and enhances their active association with cyclin E/cyclin A and cyclin B. It also activates the cyclin A promoter and promotes cycling of growth-arrested cells into a G1 phase of the cell cycle [7]. Transcription of p21waf1/cip1, a key regulatory protein in cell cycle progression, is activated by HBx in the presence of functional p53 [7] and also in a p53-independent manner [3]. The HBx protein can inhibit apoptosis by binding to p53 which leads to inactivation of the sequence specific DNA binding and transcriptional activating properties of p53 [3]. The HBx protein also downregulates TGFâ-induced apoptosis in hepatocytes by stimulating phospho inositide 3-kinase (PI3K) activity [7]. It has been demon strated that HBV achieves protection from apoptotic death through activating the HBx-PI3K-Akt-Bad pathway [Akt is also known as protein kinases B (PKB), Bad: B-cell CLL/lymphoma 2 (BCL-2)-antagonist of cell death] [12].

Cytoplasmic HBx was detected either as punctate granular staining or in dispersed, finely granular patterns. Detailed analysis of cytoplasmic compartmentalization of HBx showed no association with the endoplasmic retic ulum, plasma membrane or lysosomes but a substantial association of HBx with mitochondria [13]. In mitochon dria, HBx may induce mitochondria-dependent cell death via indirect interaction with pro-caspase-9 but it has also been reported to efficiently block caspase 3 (CPP32) activ ity and apoptosis in hepatoma cells [7]. The HBx protein has been demonstrated to activate many signal transduc tion pathways in the cytoplasm such as the Janus kinases (JAKs) and signal transducers and activators of transcrip tion (STATs) pathway, which causes activation of STAT-regulated genes [3]. In HBx stable expressing cells, the tyrosine phosphorylation of STAT3 and STAT5 and in vitro kinase activity of JAK1, are upregulated [7]. Consti tutive activation of JAK/STAT by Hbx protein may con tribute to the development of HCC by stimulating cell growth by cross-talk through v-src sarcoma (Schmidt-Ruppin A-2) viral oncogene homogog (avian) src- and/or the v-ras oncogene homolog ras-associated signal trans duction. HBxAg constitutively activates ras and src kinase. Activated ras leads to activation of MAPK and PI3K sig naling pathways which cooperate with other oncogenes, such as c-myc, in tumorigenesis [9]. Activation of signal ing cascades involving Ras small GTPase (encoded by ras oncogene) raf protooncogene serine-threonine protein kinase (Raf) and MAP kinases (Ras/Raf/MAPK) can acti vate the transcription factors AP-1 and NFêB which con tribute to the deregulation of cell cycle checkpoint controls [3]. The HBx protein interacts with pathway involving wnt and catenin (cadherin-associated protein) â1 oncogenes (Wnt/â-catenin) through association with Wnt protein, through activation of elk-related tyrosine  kinase (ERK) or via hypermethylation of E-cadherin promoter, all of which lead to elevated levels of activated â-catenin [9].