Hepatocellular carcinoma and hepatitis B virus infection: molecular evidence for monoclonal origin and expansion of malignantly transformed hepatocytes

Viral integration drives multifocal HCC during the occult HBV infection

BACKGROUND & AIMS

Although the prognosis of patients with occult hepatitis B virus (HBV) infection (OBI) is usually benign, a small portion may undergo cirrhosis and subsequently hepatocellular carcinoma (HCC). We studied the mechanism of life-long Integration of virus DNA into OBI host's genome, of which may induce hepatocyte transformation.

METHODS

We applied HBV capture sequencing on single cells from an OBI patient who, developed multiple HCC tumors and underwent liver resection in May 2013 at Tongji Hospital in China. Despite with the undetectable virus DNA in serum, we determined the pattern of viral integration in tumor cells and adjacent non-tumor cells and obtained the details of the viral arrangement in host genome, and furthermore the HBV integrated region in cancer genome.

RESULTS

HBV captured sequencing of tissues and individual cells revealed that samples from multiple tumors shared two viral integration sites that could affect three host genes, including CSMD2 on chr1 and MED30/EXT1 on chr8. Whole genome sequencing further indicated one hybrid chromosome formed by HBV integrations between chr1 and chr8 that was shared by multiple tumors. Additional 50 poorly differentiated liver tumors and the paired adjacent non-tumors were evaluated and functional studies suggested up-regulated EXT1 expression promoted HCC growth. We further observed that the most somatic mutations within the tumor cell genome were common among the multiple tumors, suggesting that HBV associated, multifocal HCC is monoclonal in origin.

CONCLUSION

Through analyzing the HBV integration sites in multifocal HCC, our data suggested that the tumor cells were monoclonal in origin and formed in the absence of active viral replication, whereas the affected host genes may subsequently contribute to carcinogenesis.

Searching for human oncoviruses: Histories, challenges, and opportunities

Oncoviruses contribute significantly to cancer burden. A century of tumor virological studies have led to the discovery of seven well-accepted human oncoviruses, cumulatively responsible for approximately 15% of human cancer cases. Virus-caused cancers are largely preventable through vaccination. Identifying additional oncoviruses and virus-caused tumors will advance cancer prevention and precision medicine, benefiting affected individuals, and society as a whole. The historic success of finding human oncoviruses has provided a unique lesson for directing new research efforts in the post-sequencing era. Combing the experiences from these pioneer studies with emerging high-throughput techniques will certainly accelerate new discovery and advance our knowledge of the remaining human oncoviruses.

The Molecular Diagnosis of Hepatitis B Virus-Associated Hepatocellular Carcinoma

Hepatitis B virus (HBV) infection is the major cause of hepatocellular carcinoma (HCC) worldwide. The pathogenesis of HBV-associated HCC has been studied extensively, and molecular changes during malignant transformation have been identified. It has been proposed that the insertion of HBV DNA into the human genome results in chromosomal instability and inactivation of tumor suppressor genes. Transactivation of oncogenes, inactivation of tumor suppressor genes, and alteration of the cell cycle by HBV proteins are also involved in the progression of hepatocellular carcinogenesis. Traditional clinical examinations of HCC, such as biopsy, computer tomography, ultrasonic imaging, and detection of such biomarkers as a-fetoprotein, are currently the "gold standard" in diagnosis. These tests diagnose HCC only in the late stages of disease. This limitation has greatly reduced the chance of survival of HCC patients. To resolve this problem, new biomarkers that can diagnose HCC in earlier stages are necessary. Based on recent molecular studies of the effects of HBV on cellular transformation, differentially expressed biomarkers of HBV infection have been elucidated. With the analyses of the HBV replication profile, the viral load (HBV DNA levels) of patients, and the viral protein expression, the severity of hepatitis in the preneoplastic stages can be assessed. In the future, with the molecular profiles identified by genomic and proteomic approaches, stage-specific biomarkers should be identified to monitor the progression and prognosis of HCC.

Epidemiology and carcinogenesis of hepatocellular carcinoma

The incidence of hepatocellular carcinoma (HCC) shows marked variation worldwide but the magnitude of this tumor is reflected by the occurrence of at least 1 million new cases annually and the uniformly dismal outlook with median survivals of <25 months after resection and <6 months with symptomatic treatment. The strikingly uneven distribution of this tumor parallels the prevalence of hepatitis B infection with rising incidence in western countries attributed to hepatitis C infection. Chronic hepatitis and cirrhosis constitute the major preneoplastic conditions in the majority of HCCs and may be related to other etiologic agents such as environmental chemical carcinogens including nitrites, hydrocarbons, solvents, organochlorine pesticides, and the chemicals in processed foods, cleaning agents, cosmetics and pharmaceuticals, as well as plant toxins such as anatoxins produced by fungi that cause spoilage of grain and food in the tropics. Genetic diseases such as genetic hematochromatosis, Wilson's disease, alpha-1-antitrypsin deficiency, and the inborn errors of metabolism including hereditary tyrosinemia and hepatic porphyria, are known to be associated with HCC. Numerous genetic alterations and the modulation of DNA methylation are recognized in HCC and it is likely that these genetic and epigenetic changes combine with factors involved in chronic hepatocyte destruction and regeneration to result in neoplastic growth and multiple molecular pathways may be involved in the production of subsets of hepatocellular tumors.

Detection of cellular receptors specific for the hepatitis B virus preS surface protein on cell lines of extrahepatic origin

Hepatitis B virus infection is primarily mediated by the interaction of the preS region of the viral envelope protein with its still unknown cellular receptor. Using recombinantly expressed preS proteins, the distribution of preS-binding receptors on cell lines from extrahepatic origins was determined by immunofluorescence and flow cytometry. In contrast to human liver cell lines, most cell lines from extrahepatic origins did not bind preS proteins. Nevertheless, exceptions were found in the bone marrow-derived cell line, KG-1, and the osteogenic sarcoma cell line SaOS-2, as well as in the previously reported EBV-transformed B-cell line, Wa. To determine the biochemical nature of these receptors, Wa-cells were cell surface biotinylated and the preS-binding receptors were isolated by immunoprecipitation. A specific band with a molecular weight of approximately 30 kDa was identified in a SDS-polyacrylamide gel, which further characterization is expected to provide clues regarding the infection mechanism of HBV in hepatic- and extra-hepatic cells.

Molecular bases for the development of hepatitis B virus (HBV)-related hepatocellular carcinoma (HCC)

Hepatocellular carcinoma (HCC) is the most common histological form of primary liver cancer; the tumor cells having retained features of hepatocytic differentiation. It is important to emphasize the heterogeneity of the histological background on which the tumor develops. Most HCCs complicate the evolution of an active or inactive cirrhosis. However, some tumors occur on livers with minimal histological changes; the prevalence of such cases varies from one geographical region to the other; being much higher in the southern half of Africa (around 40% of HCCs) than in Asia, America and Europe, where at least 90% of HCCs are associated in the cirrhosis. This heterogeneity is probably a reflection of different environmental and genetic factors. A large number of epidemiological and molecular studies have indeed clearly demonstrated the prime importance of environmental factors to the development of primary liver cancers in humans. Chronic hepatitis B (HBV) and C (HCV) infections are major risk factors. This review will mainly analyse the impact of chronic HBV infection but it is important to emphasize the potential synergistic effects between HBV and HCV, as well as between viral infections and other environmental factors, such as alcohol, chemical carcinogens (see review by Dr Wogan) and other, still poorly defined, hormonal factors which may account for the higher incidence of the tumor in man. Finally the review by Dr Buendia highlights the emerging issue of liver-cancer genetics.

Beta-catenin mutations are frequent in human hepatocellular carcinomas associated with hepatitis C virus infection

Hepatocellular carcinoma (HCC) is one of the most common fatal cancers worldwide. Hepatitis B virus and hepatitis C virus infections, exposure to aflatoxin, and excessive intake of alcohol have been identified as major risk factors. However, the molecular mechanisms underlying their development are still poorly understood. Recently, beta-catenin, one of the key components of the Wnt signaling pathway, has been found to be mutated in about 20% of HCCs, suggesting a role of the Wnt pathway in their development. In this study, we examined beta-catenin and APC mutations in 22 HCCs associated with HCV infection, using single-strand conformation polymorphism (SSCP) followed by direct DNA sequencing. beta-Catenin mutations were found in nine (41%) cases, but no APC mutations were found. beta-Catenin immunohistochemistry revealed nuclear accumulation of beta-catenin protein in all nine tumors with a beta-catenin mutation and two additional tumors without a mutation. These results suggest that activation of the Wnt signaling pathway by beta-catenin mutation contributes significantly to the hepatocellular carcinogenesis associated with HCV infection.

Hepatitis B and C viruses and primary liver cancer

The data presented indicate that viral agents (namely, HBV and HCV) are major environmental aetiological factors for human primary liver cancer. It is important to elucidate the molecular mechanisms further because HCC is one of the few examples of virus-related human cancers. In addition, the available evidence points to the possibility of at least partial prevention of the tumour by large-scale vaccination.

A case of hepatocellular carcinoma consisting of two solitary poorly differentiated polyclonal intrahepatic tumor nodules

Two intrahepatic solitary tumors consisting of poorly differentiated hepatocellular carcinoma (HCC) were identified as polyclonal HCC nodules by analysis of the pattern of integration of hepatitis B viral DNA into nuclear DNA. After the removal of each nodule by partial liver resection, recurrent multiple tumors appeared within 10 months postoperatively. The findings in this case suggest that the effectiveness of reduction surgery for intrahepatic multiple tumors is limited in solitary multicentric HCC that consists of poorly differentiated HCC.

New trends in hepatocellular carcinoma

This review discusses the etiological association of hepatitis C virus with hepatocellular carcinoma and recent progress in the understanding of early histopathological changes that occur in cirrhotic livers leading to hepatocarcinogenesis. In some parts of the world (for example Japan) hepatitis C virus infection is becoming a more important etiological factor in the pathogenesis of hepatocellular carcinoma than infection with hepatitis B virus. Biopsy-proven adenomatous hyperplasia often progresses to hepatocellular carcinoma and adenomatous hyperplasia should be treated as a potentially malignant lesion.

Postresection recurrence of hepatocellular carcinoma treated by arterial embolization: analysis of prognostic factors

Of 270 consecutive patients with hepatocellular carcinoma who underwent surgery, 50 who had recurrence and were subsequently treated with transcatheter arterial embolization were analyzed. The longest interval between surgery and recurrence in the 50 patients who underwent transcatheter arterial embolization was 7 yr. Recurrence was initially found in the remnant liver in all patients but one; extrahepatic metastases were detected in 13 patients (26%) during follow-up. A "multiple" type was the most common (64%) hepatic recurrence pattern on angiography, followed by the "solitary" (16%) and "tumor thrombus" (12%) patterns. Hepatic recurrence was most frequently found in the ipsilateral lobe (48%) relative to the site of the primary hepatocellular carcinoma. Multivariate analysis of the factors affecting survival after transcatheter arterial embolization indicated that recurrence pattern (p = 0.025) and distant metastases (p = 0.011) were significant. Of 13 patients with distant metastases, 11 had the "multiple" pattern of hepatic recurrence. Survival rates for all 50 patients after initial surgery and after transcatheter arterial embolization were 90% and 64%, respectively, at 1 yr; 52% and 24%, respectively, at 3 yr; and 27% and 5%, respectively, at 5 yr. On analysis of survival rates after transcatheter arterial embolization in 37 patients with recurrence only in the liver and of the response of recurrent hepatocellular carcinoma to transcatheter arterial embolization, a significant difference was noted between those with "partial response" and "progressive disease" (p less than 0.05) and between those with "no change" and "progressive disease" (p less than 0.05).

Persistence of hepatitis B viral DNA after serological recovery from hepatitis B virus infection

Chronic hepatitis B virus infection is a major medical problem worldwide. Apart from HBsAg carriers, hepatitis B virus has also been identified in some HBsAg-individuals with or without antibodies to viral antigens. The molecular mechanisms underlying hepatitis B virus persistence in HBsAg-individuals are unresolved, however. To identify a possible genetic basis for viral persistence, we cloned the viral genome from the liver of a patient serologically immune to hepatitis B virus infection. DNA sequence analysis of the complete viral genome identified numerous mutations in all viral genes. Analysis of the biological effects of these mutations revealed three major findings: a low level of HBsAg synthesis, absence of HBeAg production and a defect terminating viral replication. These data suggest that mutations accumulating during the natural course of hepatitis B virus infection may be a mechanism underlying viral persistence in HBsAg-individuals, presumably through escape from immune surveillance.

[Hepatology. New research results in its significance for the understanding of liver diseases]

By two exemplary clinical situations--acute viral hepatitis, acute-phase reaction of the liver--the significance of basic research for the understanding of clinical phenomena and for the development of new diagnostic and therapeutic procedures is demonstrated. The very different phenomena following infection with the hepatitis-B-virus can be explained by the variation in the interactions of virus and liver cell, by the immune reaction of the host, and by mutants of the virus. The reaction of the liver to an extrahepatic infection is mediated by interleukin-6, and characterized by an alteration in protein metabolism. The synthesis of acute-phase proteins is increased. The proteins confine the local injury and establish the homeostasis of the organism.

Resection of hepatocellular carcinoma: oligocentric origin of recurrent and multinodular tumours

The structure of integrated hepatitis B virus (HBV) DNA was analysed to determine the origin of recurrent and multinodular hepatocellular carcinoma (HCC). In 5 cases, recurrent tumours were compared with the respective primary tumours, all of which had chromosomally integrated viral DNA. In only one of these cases, an identical HBV DNA integration pattern was found, indicating a monocentric origin of primary and secondary tumour. In all other cases a polycentric origin was deduced. Particular features observed were: (i) the apparent absence of integrated viral DNA in a recurrent tumour; and (ii) an integration pattern identical to that of the primary tumour and a distinct new pattern in two different foci of multinodular recurrent HCC. For multinodular primary HCC one case was analysed and found to be of independent origin.

Chronic hepatitis. The challenge of diagnosis and treatment

Chronic hepatitis can be caused by a variety of viruses or therapeutic agents, but in about 80% of cases, the cause is unknown. Distinguishing between chronic persistent and chronic active hepatitis is of primary importance in diagnosis and treatment. Percutaneous liver biopsy is necessary to make the distinction. In most cases, chronic persistent hepatitis does not necessitate specific therapy. Chronic active hepatitis responds to a wide range of therapeutic options: corticosteroids, immunosuppressants, antivirals, and immunostimulants. Prognosis depends on the risks and advantages of therapy as well as the severity and cause of the disease.

The association of hepatocellular carcinoma in childhood with hepatitis B virus infection

Eleven cases of hepatocellular carcinoma (HCC) in childhood were investigated by immunohistochemistry for association with hepatitis B virus (HBV) infection. Seven of 11 cases (64%) demonstrated positivity for hepatitis B surface antigen (HBsAG), whereas all 11 were negative for hepatitis B core antigen (HBcAG). Cirrhosis was absent in all cases, and other causes for HCC in childhood were not found. All children with HBV-associated HCC died within 6 months of diagnosis. The median survival time of these children was 2 months. Only one child with HCC of trabecular subtype without HBV association is still living after 18 months. However, this child has metastases and a local recurrence. Three other children with HCC of fibrolamellar subtype are free of disease after 2, 5, and 6 years, respectively. The high number of cases of HBV-associated HCC shows the important role of HBV infection as an etiologic factor for the development of childhood HCC in middle Europe.