Insulin suppresses hepatitis B surface antigen expression in human hepatoma cells

Clear cell hepatocellular carcinoma: origin, metabolic traits and fate of glycogenotic clear and ground glass cells

Clear cell hepatocellular carcinoma (CCHCC) has hitherto been considered an uncommon, highly differentiated variant of hepatocellular carcinoma (HCC) with a relatively favorable prognosis. CCHCC is composed of mixtures of clear and/or acidophilic ground glass hepatocytes with excessive glycogen and/or fat and shares histology, clinical features and etiology with common HCCs. Studies in animal models of chemical, hormonal and viral hepatocarcinogenesis and observations in patients with chronic liver diseases prone to develop HCC have shown that the majority of HCCs are preceded by, or associated with, focal or diffuse excessive storage of glycogen (glycogenosis) which later may be replaced by fat (lipidosis/steatosis). In ground glass cells, the glycogenosis is accompanied by proliferation of the smooth endoplasmic reticulum, which is closely related to glycogen particles and frequently harbors the hepatitis B surface antigen (HBsAg). From the findings in animal models a sequence of changes has been established, commencing with preneoplastic glycogenotic liver lesions, often containing ground glass cells, and progressing to glycogen-poor neoplasms via various intermediate stages, including glycogenotic/lipidotic clear cell foci, clear cell hepatocellular adenomas (CCHCA) rich in glycogen and/or fat, and CCHCC. A similar process seems to take place in humans, with clear cells frequently persisting in CCHCC and steatohepatitic HCC, which presumably represent intermediate stages in the development rather than particular variants of HCC. During the progression of the preneoplastic lesions, the clear and ground glass cells transform into cells characteristic of common HCC. The sequential cellular changes are associated with metabolic aberrations, which start with an activation of the insulin signaling cascade resulting in pre-neoplastic hepatic glycogenosis. The molecular and metabolic changes underlying the glycogenosis/lipidosis are apparently responsible for the dramatic metabolic shift from gluconeogenesis to the pentose phosphate pathway and Warburg-type glycolysis, which provide precursors and energy for an ever increasing cell proliferation during progression.

Envelope proteins derived from naturally integrated hepatitis B virus DNA support assembly and release of infectious hepatitis delta virus particles

A natural subviral agent of human hepatitis B virus (HBV), hepatitis delta virus (HDV), requires only the envelope proteins from HBV in order to maintain persistent infection. HBV surface antigens (HBsAgs) can be produced either by HBV replication or from integrated HBV DNA regardless of replication. The functional properties of the integrant-generated HBsAgs were examined using two human hepatocellular carcinoma-derived cell lines, Hep3B and PLC/PRF/5, that contain HBV integrants but do not produce HBV virions and have no signs of HBV replication. Both cell lines were able to support HDV replication and assembly/egress of HDV virions. Neither of the cell lines was able to produce substantial amounts of the pre-S1-containing HDV particles. HDV virions assembled in PLC/PRF/5 cells were able to infect primary human hepatocytes, while Hep3B-derived HDV appeared to be noninfectious. These results correlate with the findings that the entire open reading frame (ORF) for the large (L) envelope protein that is essential for infectivity is present on HBV RNAs from PLC/PRF/5 cells, while an L protein ORF that was truncated and fused to inverted precore sequences was found using RNAs from Hep3B cells. This study demonstrates for the first time that at least some of the HBV DNA sequence naturally integrated during infection can produce functional small and large envelope proteins capable of the formation of infectious HDV virions. Our data indicate that in vivo chronic HDV infection can persist in the absence of HBV replication (or when HBV replication is profoundly suppressed) if functional envelope proteins are supplied from HBV integrants.

IMPORTANCE

The study addresses the unique mechanism of HDV persistence in the absence of ongoing HBV replication, advances our understanding of HDV-HBV interactions, and supports the implementation of treatments directly targeting HDV for HDV/HBV-infected individuals.

Antiviral efficacy against hepatitis B virus replication of oleuropein isolated from Jasminum officinale L. var. grandiflorum

ETHNOPHARMACOLOGICAL RELEVANCE

Jasminum officinale L. var. grandiflorum (JOG) is a folk medicine used for the treatment of hepatitis in south of China. Phytochemical studies showed that secoiridoid glycosides are the typical constituents of this plant.

AIM OF THE STUDY

The present study was undertaken to evaluate the effect of oleuropein (Ole) derived from the flowers of JOG on hepatitis B virus (HBV) replication in HepG2 2.2.15 cell line in vitro and duck hepatitis B virus (DHBV) replication in ducklings in vivo.

MATERIAL AND METHODS

The extracellular hepatitis B e antigen (HBeAg) and hepatitis B surface antigen (HBsAg) concentrations in cell culture medium were determined by ELISA. DHBV in duck serum was analyzed by dot blot.

RESULTS

Ole blocks effectively HBsAg secretion in HepG2 2.2.15 cells in a dose-dependent manner (IC(50)=23.2 microg/ml). Ole (80 mg/kg, intraperitoneally, twice daily) also reduced viremia in DHBV-infected ducks.

CONCLUSION

Ole therefore warrants further investigation as a potential therapeutic agent for HBV infection.

Regulation of hepatitis B virus replication by the ras-mitogen-activated protein kinase signaling pathway

The replication of hepatitis B virus (HBV) can be regulated by a variety of factors, including hormones, growth factors, and cytokines. However, the molecular mechanisms of these regulations are largely unknown. Ras is a small GTPase that responds to many of these external stimuli. In this study, we investigated the possible effect of Ras on the replication of HBV. Our results indicated that activated Ras could suppress the replication of HBV in both Huh7 and HepG2 cells. This suppression was independent of the X protein and most likely occurred at the transcriptional level. Deletion-mapping analysis of the HBV core promoter and its upstream ENI and ENII enhancers revealed multiple elements responsive to activated Ras. This suppression of HBV replication by activated Ras was apparently mediated by the mitogen-activated protein (MAP) kinase pathway, as it was accompanied by activation of ERK1/2 and abolished by the MEK1/2 inhibitor U0126. Our results thus indicate that external stimuli may suppress HBV replication through the Ras-MAP kinase pathway.

Woodchuck hepatitis virus replication and antigen expression gradually decrease in preneoplastic hepatocellular lineages

BACKGROUND/AIMS

Hepatocellular carcinomas elicited in woodchucks by the woodchuck hepatitis virus (WHV) emerge gradually from parenchymal areas of minimal structural deviation via two predominant preneoplastic hepatocellular lineages, composed of either glycogenotic/basophilic or amphophilic/basophilic cell foci. In this study we analyzed WHV replication during neoplastic development in both lineages.

METHODS

In minimal deviation areas, preneoplastic hepatocellular foci, and hepatocellular neoplasms, developing in 16 WHV-carriers 31-38 months after WHV-inoculation, the proportion of hepatocytes containing WHV replicative intermediates (as detected by in situ hybridization for WHV DNA) and immunoreactive for WHV core and surface antigens was assessed.

RESULTS

Appearance of WHV replicative intermediates and expression of antigens were limited to the cytoplasm of hepatocytes and were strongly correlated (P<0.0001), both showing high levels in minimal deviation areas, but markedly reduced amounts in all types of preneoplastic hepatic focus (P<0.0001), and in hepatocellular adenomas. Most hepatocellular carcinomas were negative for WHV replicative intermediates and antigens.

CONCLUSIONS

In both the glycogenotic-basophilic and the amphophilic-basophilic preneoplastic hepatocellular lineage, WHV replication and antigen expression gradually decrease early during the preneoplastic phase. The close correlation of these changes with metabolic aberrations characterizing preneoplastic hepatocellular lineages suggests that oncogenic effects mimicking insulin/glucagon imbalances may be responsible for the repression of hepadnaviral replication.

Hepadnaviral hepatocarcinogenesis: in situ visualization of viral antigens, cytoplasmic compartmentation, enzymic patterns, and cellular proliferation in preneoplastic hepatocellular lineages in woodchucks

BACKGROUND/AIMS

Hepadnaviral hepatocarcinogenesis induced in woodchucks with and without dietary aflatoxin B1 has been established as an appropriate animal model for studying the pathogenesis of human hepatocellular carcinoma in high-risk areas. Our aim in this study was the elucidation of phenotypic cellular changes in early stages of this process.

METHODS

Woodchucks were inoculated as newborns with woodchuck hepatitis virus (WHV), and partly also exposed to aflatoxin B1. Sequential hepatocellular changes in the expression of viral antigens, ultrastructural organization, cellular proliferation and apoptosis were studied in situ by electron microscopy, enzyme and immunohistochemistry.

RESULTS

A characteristic finding in WHV-infected animals (with and without aflatoxin B1) was proliferative areas of minimal structural deviation, which predominated periportally, comprised glycogen-rich, amphophilic, and ground-glass hepatocytes, and expressed the woodchuck hepatitis core and surface antigens. Two main types of proliferative foci emerged from minimal deviation areas, glycogenotic clear cell foci and amphophilic cell foci (being poor in glycogen but rich in mitochondria), giving rise to the glycogenotic-basophilic and the amphophilic preneoplastic hepatocellular lineages. A gradual loss in the expression of viral antigens appeared in both lineages, particularly early in the glycogenotic-basophilic cell lineage. Whereas glycogenosis was associated with an enzymic pattern suggesting an early activation of the insulin-signaling pathway, amphophilic cells showed changes in enzyme activities mimicking a response of the hepatocytes to thyroid hormone, which may also result from early changes in signal transduction.

CONCLUSION

Preneoplastic hepatocellular lineages in hepadnaviral and chemical hepatocarcinognesis show striking phenotypic similarities, indicating concordant and possibly synergistic early changes in signaling.

Phosphatidylinositol 3-kinase is required for the regulation of hepatitis B surface antigen production and mitogen-activated protein kinase activation by insulin but not by TPA

Insulin suppresses hepatitis B surface antigen (HBsAg) gene expression and stimulates cell proliferation in human hepatoma Hep3B cells. 12-O-tetradecanoyl phorbol-13-acetate, TPA, has been demonstrated to mimic insulin actions in these cells. We examined the role of phosphatidylinositol 3-kinase (PI 3-kinase) in the signaling pathways of insulin and TPA towards these two biological phenomena in Hep3B cells. The pre-treatment of 5 microM of wortmannin diminished insulin suppressed HBsAg production and completely abolished insulin stimulated cell proliferation. However, wortmannin had no effect on TPA actions in both HBsAg suppression and cell growth stimulation. We further investigated the effect of wortmannin in mitogen-activated protein kinases (MAPKs) activation induced by insulin or TPA. After the pretreatment of wortmannin, insulin activated MAPKs was completely blocked, but TPA was still capable to activate MAPKs. These results suggest that PI 3-kinase is involved in insulin actions but not in TPA effects, and allow us to dissociate the signaling pathways of insulin and TPA in human hepatoma Hep3B cells.

Characterization of hepatitis B virus integrant that results in chromosomal rearrangement

A hepatitis B virus (HBV) integrant was cloned from the genomic DNA library of human hepatocellular carcinoma cell line, Hep3B. Sequence analysis of the restriction fragment bearing the virus-host junction revealed that its integration pattern was the common type, with the right junction located at the cohesive region. The open reading frame of the major viral surface antigen was intact with rearranged preS1 and core sequences. The X protein, although truncated, maintained the trans-activating activity to simian virus 40 enhancer/promoter. S1 nuclease mapping showed that 4.0-, 2.9-, and 2.2-kb HBV RNAs detected in Hep3B cells were transcribed from this integrant using preS2/S promoter. By somatic-cell hybrid mapping, the left and right cellular flanking sequences were assigned to chromosomes 13 and 4, respectively. The results of this study support the notion that integrated hepatitis B virus, resulting in chromosomal rearrangement as well as the production of the carboxy-terminal truncated X protein with trans-activating activity, is important for viral hepatocarcinogenesis.

Insulin Dominantly Suppresses Hepatitis B Virus Gene Expression in Cultured Human Hepatoma Cells

We have shown previously that insulin suppresses the expression of hepatitis B surface antigen (HBsAg) gene from an endogenous integrated viral genome in cultured human hepatoma Hep3B cells. In this study, we demonstrated that insulin suppresses the viral mRNA transcribed from transiently transfected tandem repeat hepatitis B virus (HBV) dimer DNA or DNA fragment that contains only the major HBsAg gene. Insulin treatment also resulted in a decrease in HBV viral particles produced by the HBV-DNA-transfected cells in a dose-dependent manner. Furthermore, when insulin was simultaneously added with glucocorticoid, which stimulates HBV gene expression, the stimulatory effect of glucocorticoid was completely abolished. Our results suggest that insulin has a dominant negative effect on the HBV gene expression in cultured human liver cells.

Insulin-like growth factors and insulin stimulate erythropoietin production in primary cultured astrocytes

Erythropoietin (EPO) is established as a major regulator of erythropoiesis. However, we and others have shown that neurons express erythropoietin receptor (EPO-R), that astrocytes produce EPO and that EPO may act as a neurotrophic factor in the CNS. We also found that EPO production is activated by insulin and insulin-like growth factors (IGFs) in astrocytes in a dose-dependent manner and that IGF-I was the most potent activator. The concentrations required for half-maximal activation were 3 nM IGF-I, 10 nM IGF-II and 100 nM insulin. The oxygen concentration regulates EPO production; hypoxia stimulates EPO production in astrocytes. The stimulatory effect of IGFs and insulin on EPO production in astrocytes was not affected by the oxygen concentration of astrocyte culture. Insulin and IGFs did not increase the total protein synthesis of astrocytes but increased EPO mRNA levels, indicating that EPO production is stimulated at the mRNA level. It appeared that the growth factor-induced accumulation of EPO mRNA in astrocytes was caused by activation of the tyrosine kinase-signal transduction pathway, because tyrosine phosphorylation of receptors for IGF-I and insulin was activated when astrocytes were stimulated by these growth factors.

Identification of a protein kinase C (PKC) activator, daphnoretin, that suppresses hepatitis B virus gene expression in human hepatoma cells

We examined the antiviral activity of a crude extract prepared from a Chinese medicinal herb Wikstroemia indica C.A. Mey. One active component, daphnoretin (7-hydroxyl-6-methoxy-3,7'-dicoumarylether), was identified, which showed strong suppressive effects on the expression of the hepatitis B surface antigen (HBsAg) in human hepatoma Hep3B cells. To examine the signaling pathway of daphnoretin on the Hep3B cells, we pretreated Hep3B cells with 12-O-tetradecanoylphorbol-13-O-acetate (200 nM) for 24 hr to down-regulate intracellular protein kinase C (PKC) levels and found that the PKC-down-regulated Hep3B cells did not respond at all to daphnoretin. Furthermore, daphnoretin induced translocation of PKC from the cytosol to the membrane and down-regulated intracellular PKC levels in the Hep3B cells, indicating that it may directly activate PKC. This hypothesis was supported by the observation that daphnoretin directly competed with [3H]phorbol dibutyrate for the binding of PKC in the whole cell and activated purified PKC activity in vitro. Our results demonstrated that daphnoretin, with a structure distinct from phorbol ester, is a PKC activator and has suppressive effects on HBsAg gene expression in human hepatoma cells.

Active compounds from Saussurea lappa Clarks that suppress hepatitis B virus surface antigen gene expression in human hepatoma cells

We have examined the antiviral activity of the crude extract prepared from the root of Saussurea lappa Clarks, a Chinese medicinal herb which is widely used for many illnesses including cancer. Two active components, costunolide and dehydrocostus lactone, were identified which show strong suppressive effect on the expression of the hepatitis B surface antigen (HBsAg) in human hepatoma Hep3B cells, but have little effect on the viability of the cells. Both costunolide and dehydrocostus lactone suppress the HBsAg production by Hep3B cells in a dose-dependent manner with IC50s of 1.0 and 2.0 microM, respectively. Northern blotting analysis shows that the suppression of HBsAg gene expression by both costunolide and dehydrocostus lactone were mainly at the mRNA level. Furthermore, the suppressive effect of costunolide and dehydrocostus lactone on HBsAg and hepatitis B e antigen (HBeAg), a marker for hepatitis B viral genome replication in human liver cells, was also observed in another human hepatoma cell line HepA2 which was derived from HepG2 cells by transfecting a tandemly repeat hepatitis B virus (HBV) DNA. Similarly, the mRNA of HBsAg in HepA2 cells was also suppressed by these two compounds. Our findings suggest that costunolide and dehydrocostus lactone may have potential to develop as specific anti-HBV drugs in the future.

The role of receptor kinase in insulin action and the effects of insulin on human hepatoma cells

Insulin has both short- and long-term effects on cellular metabolism. The short-term effects are known to involve the insulin receptor, a protein kinase capable of phosphorylating itself and other proteins. The role of the receptor was elucidated by studies of a mutant insulin receptor which lacked kinase activity and inhibited several actions of insulin. The long-term effects of insulin could be demonstrated by its growth-promoting effect on hepatoma cells, and by the suppression in transfected hepatoma cells of hepatitis B virus antigen production in a dose-dependent manner. The process whereby insulin appears to regulate gene expression is not clearly understood.