Identification of potential molecular pathways and genes that induced hepatocellular carcinoma by various genotypes of HBx gene in transgenic mouse model

Abstract

Background & Aims: Chronic hepatitis B viral (HBV) infection still raises a high threat for hepatocellular carcinoma (HCC) worldwide, especially in Asia. Different HBV genotypes are associated with varying levels of pathogenicity, while the genetic mechanisms behind this remain unclear. This study attempts to elucidate the mechanisms contributing to tumor progression of K130M/V131I mutant and wild-type variants of HBx genotypes A, B, C and D in vivo. Methods: To compare the potential tumorigenic effects of various HBx genotypes on HCC, the Sleeping Beauty (SB) transposon system was used to deliver different HBx genotypes into the livers of fumarylaccetoacetate hydrolyse (Fah)-deficient mice by hydrodynamic tail vein injection. Short hairpin RNA directed against transformation-related protein (Trp53) was co-injected to determine the combinational effect of Trp53 dysfunction in HBV-associated HCC. Results: The most tumorigenic genotype of HBx gene was genotype D for both wild-type and K130M/V131I mutant variants; while genotype A was the least tumorigenic. Mutant variant of genotype B exerted a stronger tumor burden than its wild-type counterpart; while both wild-type and mutant variants of genotype C induced similar tumorigenic evidence as mutant variant of genotype B. In general, both wild-type and mutant variants of all HBx genotypes played an important role in liver hepatitis by activating the arachidonic acid metabolic pathway. Significant up-regulation of major urinary protein 14 (Mup14) (>100-fold increase) and down-regulation of cytochrome P450, family 4, subfamily f, polypeptide 14 (Cyp4f14) or cytochrome P450, family 4, subfamily f, polypeptide 15 (Cyp4f15) (~3-fold decrease) caused accumulation of pro-inflammatory factors, prostaglandin D2 (PGD2) and leukotriene B4 (LTB4) in liver; at the same time, suppression of anti-inflammatory factors epoxyeicosatrienoic acids (EETs) production by down-regulating cytochrome P450 CYP2 (CYP2) encoding genes was observed in mutant and wild-type variants of all HBx genotypes studied. At the transcriptional level, we identified insulin growth factor 2 (Igf2) was commonly up-regulated in tumors induced by mutant variants of HBx genotypes B, C and D; while p21 (RAC1) activated kinase 6 (Pak6) and Rho GTPase activating protein 27 (Arhgap27) were commonly up-regulated in tumor induced by wild-type variants of HBx genotypes A, C and D. Up-regulation of Igf2 was reported to be associated with phosphatidylinositol 3-kinase (PI3K)/AKT serine/threonine-protein kinase (AKT) and mitogen-activated protein kinase (MAPK) signalling pathways; while Pak6 has been reported to regulate actin cytoskeleton via RAC/PAK signalling pathway. Additionally, at the translational level, HBx genotype B mutant variant induced phosphorylation of AKT and reduction of FOXO1; while genotype C wild-type variant suppressed PPARG and induced accumulation of CTNNB1. Conclusion: HBx-D K130M/V131I mutant demonstrated the strongest tumorigenic effect. HBx-B mutant, HBx-C mutant and wild-type displayed similar tumorigenic effect; while HBx-B wild-type, HBx-A mutant and wild-type were the least tumorigenic. HBx induced inflammation by accumulation of pro-inflammatory factors in the liver via arachidonic acid metabolism. At the transcriptional level, we identified Igf2 as a commonly up-regulated gene in tumor induced by mutant HBx and Pak6 and Arhgap27 as a commonly up-regulated gene in tumor induced by wild-type HBx. Last but not least, we discovered that different genotypes induced tumor development via different signalling pathways predominantly. HBx genotype B induced tumor progression mainly via AKT/FOXO1 signalling cascade; while genotype C induced tumor progression predominantly via PPARG/CTNNB1 signalling cascade.