Hepatitis B virus X protein suppresses all-trans retinoic acid-induced apoptosis in human hepatocytes by repressing p14 expression via DNA methylation

Abstract

All-trans retinoic acid (ATRA), the most biologically active metabolite of vitamin A, is known to activate p14 expression via promoter hypermethylation to induce p53-dependent apoptosis in human hepatocytes. In this study, we found that the oncogenic hepatitis B virus (HBV) X protein (HBx) of HBV, derived from both overexpression and 1.2-mer replicon systems, suppresses ATRA-induced apoptosis in p53-positive human hepatocytes. For this effect, HBx upregulated both protein and enzyme activity levels of DNA methyltransferase 1, 3a and 3b, in the presence of ATRA and thereby inhibited p14 expression via promoter hypermethylation, resulting in inactivation of the p14-mouse double minute 2 pathway and subsequent downregulation of p53 levels. As a result, HBx was able to impair the potential of ATRA to activate apoptosis-related molecules, including Bax, p53-upregulated modulator of apoptosis, caspase-9, caspase-3 and poly (ADP-ribose) polymerase. In conclusion, the present study provides a new oncogenic action mechanism of HBx, namely by suppressing the anticancer potential of ATRA to induce p53-dependent apoptosis in HBV-infected hepatocytes.

All-trans Retinoic Acid Inhibits Hepatitis B Virus Replication by Downregulating HBx Levels via Siah-1-Mediated Proteasomal Degradation

“…The present study demonstrated that ATRA at pharmacological concentrations (0.01–1 μM), which has already been proven to induce the differentiation of APL cells [ 5 ], inhibits HBV replication in human hepatoma cells ( Figure 1 A,C), suggesting a possible application of ATRA in the development of an anti-viral drug against HBV. According to a previous report, treatment with ATRA for 24 h at 1 μM did not significantly affect the viability of HepG2 cells expressing HBx [ 22 ], which was also confirmed in the present study ( Figure 1 E,F). In addition, the present study demonstrated that the knockdown of Siah-1 using shRNA or the introduction of a dominant negative mutant of Siah-1 significantly attenuated the ability of ATRA to inhibit HBV replication ( Figure 7 B).…”

“…In contrast, ATRA activates the expression of p14, p16, and p21 to induce cell growth arrest, senescence, and apoptosis [ 19 , 20 , 21 ]. It was further demonstrated that HBx and ATRA antagonize each other in the expression of p14, p16, and p21 and subsequent regulation of cell growth [ 22 , 23 ]. In the present study, we evidenced a new round of antagonism between ATRA and HBx in the regulation of HBV replication by demonstrating that HBx stimulates HBV replication ( Figure 3 E,F), as previously demonstrated [ 6 , 13 , 14 ], whereas ATRA inhibits HBV replication by lowering HBx levels in human hepatoma cells ( Figure 1 A,C).…”

“…For example, HBx stimulates cell growth by transcriptionally repressing the expression of p21 and p16 [ 17 , 18 ], whereas ATRA inhibits cell growth by upregulating the levels of p14, p16, and p21 [ 19 , 20 ]. It has been further demonstrated that HBx and ATRA antagonize each other in terms of the expression of p14, p16, and p21 and subsequent regulation of cell growth [ 21 , 22 , 23 ], which may contribute to their roles as positive and negative regulators of HCC progression, respectively. Despite numerous studies concerning antagonism between ATRA and HBx in the regulation of cell growth, the effects of ATRA on HBV replication, which can be considered another aspect of the interaction between HBV and ATRA, are completely unknown.…”

Cordyceps sinensis attenuates HBx‑induced cell apoptosis in�HK‑2 cells through suppressing the PI3K/Akt pathway

“…Once apoptosis is triggered, cellular proteins are cleaved at specific aspartate residues by the effector caspases (38,39). Other studies have reported that HBx overexpression promotes the activation of caspase-3 and -9 (40,41). Thus, activation of caspase-3 and -9 was examined in stable HBx-overexpressing HK -2 cells treated with LY294002 and C. sinensis.…”

Restriction of H1N1 influenza virus infection by selenium nanoparticles loaded with ribavirin via resisting caspase-3 apoptotic pathway

“…20,21 It has been reported that viruses induce apoptosis through caspase-3 activation. [22][23][24] Caspase-3 is the primary executioner of programmed cell death. It is directly or indirectly responsible for the cleavage of many proteins and caspases involved in apoptosis.…”