Mutations in the p53 tumor suppressor gene in tree shrew hepatocellular carcinoma associated with hepatitis B virus infection and intake of aflatoxin B1

Aflatoxin B1 and viruses' combined pathogenesis: A mini systematics review of invitro and invivo studies

INTRODUCTION

The combined pathogenesis of Aflatoxin B1 (AFB1) and several viruses such as HBV, EBV and influenza virus have been investigated yet the molecular mechanism of their interaction and possible synergistic effects is not fully understood.

OBJECTIVES

The aim of the current systematic review was to review in-vitro and in-vivo studies investigating the combined pathogenesis of aflatoxins and viruses.

METHODS

This systematic review was performed according to the Preferred Reporting Items for Systematic Reviews and Meta-analyses (PRISMA) guidelines. PECO (Population, Exposure, Comparator, and Outcome) criteria for invitro and invivo studies were used to evaluate the eligibility of the studies for systematic review.

RESULTS

21 studies were eligible for qualitative analysis based on the inclusion criteria. Of all the included studies, 9 (42.9 %) were invivo, 7 (33.3 %) were invitro-invivo and 5(23.8) articles conducted only invitro assay. Furthermore 14 (66.6 %) article explored hepatitis B virus (HBV) combination with AFB1, 4 (19 %) studied influenza A virus (SIV), 2 (9.7 %) were about Epstein-Barr virus (EBV) and only 1 (4.7 %) included hepatitis C virus (HCV).

CONCLUSION

The limited collected evidence suggests that AFB1 enhanced EBV and influenza virus pathogenesis. AFB1 also operated as a cofactor for HBV and EBV-mediated carcinogenesis. On the other hand HBV and HCV also induced AFB-1 carcinogenesis. Due to the limited amount of included studies and the inconsistency of their results further studies especially on HBV and SIV are essential for better understanding of their combined mechanisms.

Highly Similar Tetramerization Domains from the p53 Protein of Different Mammalian Species Possess Varying Biophysical, Functional and Structural Properties

The p53 protein is a transcriptional regulatory factor and many of its functions require that it forms a tetrameric structure. Although the tetramerization domain of mammalian p53 proteins (p53TD) share significant sequence similarities, it was recently shown that the tree shrew p53TD is considerably more thermostable than the human p53TD. To determine whether other mammalian species display differences in this domain, we used biophysical, functional, and structural studies to compare the properties of the p53TDs from six mammalian model organisms (human, tree shrew, guinea pig, Chinese hamster, sheep, and opossum). The results indicate that the p53TD from the opossum and tree shrew are significantly more stable than the human p53TD, and there is a correlation between the thermostability of the p53TDs and their ability to activate transcription. Structural analysis of the tree shrew and opossum p53TDs indicated that amino acid substitutions within two distinct regions of their p53TDs can dramatically alter hydrophobic packing of the tetramer, and in particular substitutions at positions corresponding to F341 and Q354 of the human p53TD. Together, the results suggest that subtle changes in the sequence of the p53TD can dramatically alter the stability, and potentially lead to important changes in the functional activity, of the p53 protein.

Bats, pangolins, minks and other animals - villains or victims of SARS-CoV-2?

Coronavirus disease-19 (COVID-19) is caused by the severe acute Respiratory syndrome coronavirus-2 (SARS-CoV-2), which has become unstoppable, spreading rapidly worldwide and, consequently, reaching a pandemic level. This review aims to provide the information available so far on the likely animal origin of SARS-CoV-2 and its possible hosts/reservoirs as well as all natural animal infections and experimental evidence using animal models. Horseshoe bats from the species Rhinolophus affinis seem to be a natural reservoir and pangolins (Manis javanica) appear to be an intermediate host of SARS-CoV-2. Humans remain the most likely spreading source of SARS-CoV-2 to other humans and also to domestic, zoo and farm animals. Indeed, human-to-animal transmission has been reported in cats, dogs, tigers, lions, a puma and minks. Animal-to-human transmission is not a sustained pathway, although mink-to-human transmission remains to be elucidated. Through experimental infections, other animals seem also to be susceptible hosts for SARS-CoV-2, namely ferrets, some non-human primate species, hamsters and transgenic mice, while dogs, pigs and poultry are resistant. A One Health perspective must be implemented in order to develop epidemiological surveillance and establish disease control mechanisms to limit zoonotic transmission. Moreover, research in this field is important to better understand SARS-CoV-2 and to obtain the long-awaited vaccine and specific treatment.

Susceptibility of tree shrew to SARS-CoV-2 infection

Since severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) became a pandemic event in the world, it has not only caused huge economic losses, but also a serious threat to global public health. Many scientific questions about SARS-CoV-2 and Coronavirus disease (COVID-19) were raised and urgently need to be answered, including the susceptibility of animals to SARS-CoV-2 infection. Here we tested whether tree shrew, an emerging experimental animal domesticated from wild animal, is susceptible to SARS-CoV-2 infection. No clinical signs were observed in SARS-CoV-2 inoculated tree shrews during this experiment except the increasing body temperature particularly in female animals. Low levels of virus shedding and replication in tissues occurred in all three age groups. Notably, young tree shrews (6 months to 12 months) showed virus shedding at the earlier stage of infection than adult (2 years to 4 years) and old (5 years to 7 years) animals that had longer duration of virus shedding comparatively. Histopathological examine revealed that pulmonary abnormalities were the main changes but mild although slight lesions were also observed in other tissues. In summary, tree shrew is less susceptible to SARS-CoV-2 infection compared with the reported animal models and may not be a suitable animal for COVID-19 related researches. However, tree shrew may be a potential intermediate host of SARS-CoV-2 as an asymptomatic carrier.

The tetramerization domain of the tree shrew p53 protein displays unique thermostability despite sharing high sequence identity with the human p53 protein

The p53 protein plays a number of roles in protecting organisms from different genotoxic stresses and this includes DNA damage induced by acetaldehyde, a metabolite of alcohol. Since the common tree shrew ingests high levels of alcohol as part of its normal diet, this suggests that its p53 protein may possess unique properties. Using a combination of biophysical and modeling studies, we demonstrate that the tetramerization domain of the tree shrew p53 protein is considerably more stable than the corresponding domain from humans despite sharing almost 90% sequence identity. Based on modeling and mutagenesis studies, we determine that a glutamine to methionine substitution at position 354 plays a key role in this difference. Given the link between stability of the p53 tetramerization domain and its transcriptional activity, the results suggest that this enhanced stability could lead to important consequences at p53-regulated genes in the tree shrew.

A novel pancreatic cancer model originated from transformation of acinar cells in adult tree shrew, a primate-like animal

Pancreatic cancer is one of the most lethal common cancers. The cell of origin of pancreatic ductal adenocarcinoma (PDAC) has been controversial, and recent evidence suggested acinar cells as the most probable candidate. However, the genetic alterations driving the transformation of pancreatic acinar cells in fully mature animals remain to be deciphered. In this study, lentivirus was used as a tool to introduce genetic engineering in tree shrew pancreatic acinar cells to explore the driver mutation essential for malignant transformation, establishing a novel tree shrew PDAC model, because we found that lentivirus could selectively infect acinar cells in tree shrew pancreas. Combination of oncogenic KRAS^G12D expression and inactivation of tumor suppressor genes Tp53, Cdkn2a and Cdkn2b could induce pancreatic cancer with full penetrance. Silencing of Cdkn2b is indispensable for Rb1 phosphorylation and tumor induction. Tree shrew PDAC possesses the main histological and molecular features of human PDAC. The gene expression profile of tree shrew PDAC was more similar to human disease than a mouse model. In conclusion, we established a novel pancreatic cancer model in tree shrew and identified driver mutations indispensable for PDAC induction from acinar cells in mature adults, demonstrating the essential roles of Cdkn2b in the induction of PDAC originating from adult acinar cells. Tree shrew could thus provide a better choice than mouse for a PDAC model derived from acinar cells in fully mature animals.

Summary: Our work identified the driver mutations indispensable for PDAC induction from acinar cells in mature adults and established a novel PDAC animal model with increased similarity to human disease.

Tree shrew (Tupaia belangeri) as a novel laboratory disease animal model

The tree shrew (Tupaia belangeri) is a promising laboratory animal that possesses a closer genetic relationship to primates than to rodents. In addition, advantages such as small size, easy breeding, and rapid reproduction make the tree shrew an ideal subject for the study of human disease. Numerous tree shrew disease models have been generated in biological and medical studies in recent years. Here we summarize current tree shrew disease models, including models of infectious diseases, cancers, depressive disorders, drug addiction, myopia, metabolic diseases, and immune-related diseases. With the success of tree shrew transgenic technology, this species will be increasingly used in biological and medical studies in the future.

Hepatocellular carcinoma in two captive golden-headed lion tamarins (Leontopithecus chrysomelas)

Two cases of hepatocellular carcinoma (HCC) in 2 female captive golden-headed lion tamarins (Leontopithecus chrysomelas) are described. HCC was diagnosed in both, with pulmonary metastasis in one of them. Neoplastic cells were positive for hepatocyte-specific antigen (HSA) by immunohistochemistry, confirming the diagnosis.

Factors associated with the high prevalence of oesophageal cancer in Western Kenya: a review

Oesophageal carcinoma (OC) is highly prevalent in Western Kenya especially among the members of the Kalenjin community who reside in the Northern and Southern areas of the Rift Valley. Previous authors have suggested potential association of environmental and genetic risk factors with this high prevalence. The environmental factors that have been suggested include contamination of food by mycotoxins and/or pesticides, consumption of traditional alcohol (locally referred to “Busaa” and “Chan’gaa”), use of fermented milk (“Mursik”), poor diet, tobacco use and genetic predisposition. The aim of this paper is to critically examine the potential contribution of each of the factors that have been postulated to be associated with the high prevalence of the disease in order to establish the most likely cause. We have done this by analyzing the trends, characteristics and behaviours that are specifically unique in the region, and corroborated this with the available literature.

From our findings, the most plausible cause of the high incidence of OC among the Kalenjin community is mycotoxins, particularly fumonisins from the food chain resulting from poor handling of cereals; particularly maize combined with traditional alcohol laced with the toxins interacting synergistically with other high-risk factors such as dietary deficiencies associated alcoholism and viral infections, especially HPV. Urgent mitigating strategies should be developed in order to minimize the levels of mycotoxins in the food chain.

[Study of the Changes on Tree Shrew Bronchial Epithelium Induced by Xuanwei Bituminous Coal Dust]

BACKGROUND AND OBJECTIVE

Lung cancer is the type of cancer with the highest incidence and mortality in numerous countries and regions. Establishing an appropriate animal model that can be used to simulate lung cancer etiology, pathogenesis, and similar processes, is urgent. We explore the feasibility of establishing a lung cancer model induced by Xuanwei bituminous coal dust PM10 (particulate matter with diameters of 10 μm or less), which affects bronchial epithelium of tree shrews.

METHODS

The neck skin of adult tree shrews is dissected, and the thyroid cartilage is fully exposed. Subsequently, the weak part at the top of the thyroid cartilage is treated with intratracheal agents by perfusion via a special infusion needle puncture method. Regular X-ray examination and lung tissue biopsy were performed on the sacrificed animals to observe changes in pulmonary imaging and bronchial epithelial cells after perfusion of Xuanwei bituminous coal dust PM 10.

RESULTS

The tree shrews of the experimental group (exposed to bituminous coal dust) died in a week after perfusion with PM10, whereas no animal died until the end of the experiment in the blank control and the solvent control groups. Sections of lung tissue biopsy of the regularly killed tree shrews were stained with hematoxylin and eosin. The lung tissues of tree shrews in the experimental group showed a serial changes caused by bronchial epithelial hyperplasia, such as squamous metaplasia, dysplasia, and early invasive carcinoma, whereas no significant pathological changes were observed in the blank control and solvent control groups.

CONCLUSIONS

Endotracheal infusion of Xuanwei bituminous coal dust PM10 induces lung cancer in tree shrews. Thus, the lung cancer model was established.
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Temporal trend of mortality from major cancers in Xuanwei, China

Although a number of studies have examined the etiology of lung cancer in Xuanwei County, China, other types of cancer in this county have not been reported systematically. This study aimed to investigate the temporal trend of eight major cancers in Xuanwei County using data from three mortality surveys (1973-1975, 1990-1992, and 2004-2005). The Chinese population in 1990 was used as a standard population to calculate agestandardized mortality rates. Cancers of lung, liver, breast, brain, esophagus, leukemia, rectum, and stomach were identified as the leading cancers in this county in terms of mortality rate. During the three time periods, lung cancer remained as the most common type of cancer. The mortality rates for all other types of cancer were lower than those of the national average, but an increasing trend was observed for all the cancers, particularly from 1990-1992 to 2004-2005. The temporal trend could be partly explained by changes in risk factors, but it also may be due to the improvement in cancer diagnosis and screening. Further epidemiological studies are warranted to systematically examine the underlying reasons for the temporal trend of the major cancers in Xuanwei County.

PTEN/PIK3CA genes are frequently mutated in spontaneous and medroxyprogesterone acetate-accelerated 7,12-dimethylbenz(a)anthracene-induced mammary tumours of tree shrews

Tree shrew has increasingly become an attractive experimental animal model for human diseases, particularly for breast cancer due to spontaneous breast tumours and their close relationship to primates and by extension to humans. However, neither normal mammary glands nor breast tumours have been well characterised in the Chinese tree shrew (Tupaia belangeri chinensis). In this study, normal mammary glands from four different developmental stages and 18 spontaneous breast tumours were analysed. Haematoxylin and eosin (H&E) staining and immunohistochemistry (IHC) showed that normal mammary gland morphology and structures of tree shrews were quite similar to those found in humans. Spontaneous breast tumours of tree shrews were identified as being intraductal papilloma, papillary carcinoma, and invasive ductal carcinoma with or without lung metastasis. To further analyse breast cancer tumours among tree shrews, 40 3-4 month-old female tree shrews were orally administrated 20 mg 7,12-dimethylbenz(a)anthracene (DMBA) or peanut oil thrice, and then, 15 of these DMBA administrated tree shrews were implanted with medroxyprogesterone acetate (MPA) pellets. DMBA was shown to induce breast tumours (12%) while the addition of MPA increased the tumour incidence (50%). Of these, three induced breast tumours were intraductal papillary carcinomas and one was invasive ductal carcinoma (IDC). The PTEN/PIK3CA (phosphatase and tensin homologue/phosphatidylinositol-4,5-bisphosphate 3-kinase catalytic subunit alpha), but not TP53 and GATA3, genes are frequently mutated in breast tumours, and the PTEN/PIK3CA gene mutation status correlated with the expression of pAKT in tree shrew breast tumours. These results suggest that tree shrews may be a promising animal model for a subset of human breast cancers with PTEN/PIK3CA gene mutations.

The role of NAD(+)-dependent isocitrate dehydrogenase 3 subunit α in AFB1 induced liver lesion

Aflatoxin B1 (AFB1) is a potent hepatocarcinogen that causes carcinogenesis in many animal species. In previous study, we found that isocitrate dehydrogenase 3α subunit (IDH3α) was upregulated in AFB1-induced carcinogenesis process. In this study, the sequences of IDH3α from various species were compared and the protein expression levels in different organs were examined, and the results showed that IDH3α was a widely distributed protein and shared highly conserved sequence in various species. In the same time, IDH3α was demonstrated to accumulate in a dose-dependent manner induced by AFB1 in cells, and was also up-regulated in the process of AFB1-induced liver lesion. Similar results were observed when H2O2 was used to replace AFB1. Over-expression of IDH3α increased the phosphorylation level of Akt (Protein kinase B) and neutralized the cellular toxicity induced by AFB1 or H2O2 and apoptosis induced by AFB1, while the reduced expression of IDH3α by siRNA decreased the phosphorylation, indicating that IDH3α played important roles in oxidative stress-induced PI3K/Akt pathway. Overall, the results suggested that AFB1 treatment could increase the expression of IDH3α, and the activated PI3K/Akt pathway by IDH3α eventually neutralized the apoptosis induced by AFB1.

Bilirubin and related tetrapyrroles inhibit food-borne mutagenesis: a mechanism for antigenotoxic action against a model epoxide

Bilirubin exhibits antioxidant and antimutagenic effects in vitro. Additional tetrapyrroles that are naturally abundant were tested for antigenotoxicity in Salmonella. Un-/conjugated bilirubin (1 and 2), biliverdin (4), bilirubin and biliverdin dimethyl esters (3 and 5), stercobilin (6), urobilin (7), and protoporphyrin (8) were evaluated at physiological concentrations (0.01-2 μmol/plate; 3.5-714 μM) against the metabolically activated food-borne mutagens aflatoxin B1 (9) and 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (10). Compound 8 most effectively inhibited the mutagenic effects of 9 in strain TA102 and 10 in TA98. Compound 7 inhibited 9-induced mutagenesis in strain TA98 most effectively, while 1 and 4 were promutagenic in this strain. This is likely due to their competition with mutagens for phase-II detoxification. Mechanistic investigations into antimutagenesis demonstrate that tetrapyrroles react efficiently with a model epoxide of 9, styrene epoxide (11), to form covalent adducts. This reaction is significantly faster than that of 11 with guanine. Hence, the evaluated tetrapyrroles inhibited genotoxicity induced by poly-/heterocyclic amines found in foods, and novel evidence obtained in the present investigation suggests this may occur via chemical scavenging of genotoxic metabolites of the mutagens investigated. This may have important ramifications for maintaining health, especially with regard to cancer prevention.

Investigação do gene p53 de frangos expostos às aflatoxinas

Identificou-se o efeito das aflatoxinas (AFs) sobre o gene p53 de frangos de corte, de linhagem comercial, separados em: grupo experimental, tratado (GT) com ração comercial contendo 2,8ppm de AFs totais durante 21 dias consecutivos, e grupo-controle (GC), sem exposição às AFs. Macroscopicamente, as alterações caracterizaram-se por hepatomegalia e aspecto pálido-amarelado com alguns focos hemorrágicos e, histologicamente, por desarranjo trabecular, pleomorfismo hepatocítico com cariomegalia, degeneração vacuolar intracitoplasmática, necrose com infiltração linfocítica e hiperplasia de ductos biliares. A PCR com os primers GSPT53c-1 com base no gene candidato a p53 (GenBank XM_424937.2) gerou um produto de aproximadamente 350 pares de base. O amplicon sequenciado a partir do DNA dos frangos do GT não apresentou mutação ou deleção, assim como padrão de bandas do PCR-RFLP não foi distinto entre ambos os grupos experimentais e a sequência depositada no banco de genes. Os resultados sugerem que não ocorreu transversão devido à exposição às AFs no fragmento amplificado. Conclui-se que a PCR-RFLP e o sequenciamento do produto da PCR não são ferramentas apropriadas para diagnóstico da exposição de frangos às AFs nas condições experimentais empregadas.

Hepatitis B virus X protein upregulates mTOR signaling through IKKβ to increase cell proliferation and VEGF production in hepatocellular carcinoma

Hepatocellular carcinoma (HCC), a major cause of cancer-related death in Southeast Asia, is frequently associated with hepatitis B virus (HBV) infection. HBV X protein (HBx), encoded by a viral non-structural gene, is a multifunctional regulator in HBV-associated tumor development. We investigated novel signaling pathways underlying HBx-induced liver tumorigenesis and found that the signaling pathway involving IκB kinase β (IKKβ), tuberous sclerosis complex 1 (TSC1), and mammalian target of rapamycin (mTOR) downstream effector S6 kinase (S6K1), was upregulated when HBx was overexpressed in hepatoma cells. HBx-induced S6K1 activation was reversed by IKKβ inhibitor Bay 11-7082 or silencing IKKβ expression using siRNA. HBx upregulated cell proliferation and vascular endothelial growth factor (VEGF) production, and these HBx-upregulated phenotypes were abolished by treatment with IKKβ inhibitor Bay 11-7082 or mTOR inhibitor rapamycin. The association of HBx-modulated IKKβ/mTOR/S6K1 signaling with liver tumorigenesis was verified in a HBx transgenic mouse model in which pIKKβ, pS6K1, and VEGF expression was found to be higher in cancerous than non-cancerous liver tissues. Furthermore, we also found that pIKKβ levels were strongly correlated with pTSC1 and pS6K1 levels in HBV-associated hepatoma tissue specimens taken from 95 patients, and that higher pIKKβ, pTSC1, and pS6K1 levels were correlated with a poor prognosis in these patients. Taken together, our findings demonstrate that HBx deregulates TSC1/mTOR signaling through IKKβ, which is crucially linked to HBV-associated HCC development.

Hepatitis B virus X protein upregulates mTOR signaling through IKKβ to increase cell proliferation and VEGF production in hepatocellular carcinoma

Hepatocellular carcinoma (HCC), a major cause of cancer-related death in Southeast Asia, is frequently associated with hepatitis B virus (HBV) infection. HBV X protein (HBx), encoded by a viral non-structural gene, is a multifunctional regulator in HBV-associated tumor development. We investigated novel signaling pathways underlying HBx-induced liver tumorigenesis and found that the signaling pathway involving IκB kinase β (IKKβ), tuberous sclerosis complex 1 (TSC1), and mammalian target of rapamycin (mTOR) downstream effector S6 kinase (S6K1), was upregulated when HBx was overexpressed in hepatoma cells. HBx-induced S6K1 activation was reversed by IKKβ inhibitor Bay 11-7082 or silencing IKKβ expression using siRNA. HBx upregulated cell proliferation and vascular endothelial growth factor (VEGF) production, and these HBx-upregulated phenotypes were abolished by treatment with IKKβ inhibitor Bay 11-7082 or mTOR inhibitor rapamycin. The association of HBx-modulated IKKβ/mTOR/S6K1 signaling with liver tumorigenesis was verified in a HBx transgenic mouse model in which pIKKβ, pS6K1, and VEGF expression was found to be higher in cancerous than non-cancerous liver tissues. Furthermore, we also found that pIKKβ levels were strongly correlated with pTSC1 and pS6K1 levels in HBV-associated hepatoma tissue specimens taken from 95 patients, and that higher pIKKβ, pTSC1, and pS6K1 levels were correlated with a poor prognosis in these patients. Taken together, our findings demonstrate that HBx deregulates TSC1/mTOR signaling through IKKβ, which is crucially linked to HBV-associated HCC development.

Animal models of liver cancer: progress and prospects

Primary liver cancer remains one of the most lethal malignancies worldwide. As this disease is lethal in most cases, research has to be done to improve our understanding of the disease and to offer insights for possible treatment options. Animal models have been widely used in the research of primary liver cancer. Here, we review the progress and prospects for the development of animal models of primary liver cancer, highlighting the best candidates for future preclinical investigations.

The origins and evolution of the p53 family of genes

A common ancestor to the three p53 family members of human genes p53, p63, and p73 is first detected in the evolution of modern-day sea anemones, in which both structurally and functionally it acts to protect the germ line from genomic instabilities in response to stresses. This p63/p73 common ancestor gene is found in almost all invertebrates and first duplicates to produce a p53 gene and a p63/p73 ancestor in cartilaginous fish. Bony fish contain all three genes, p53, p63, and p73, and the functions of these three transcription factors diversify in the higher vertebrates. Thus, this gene family has preserved its structural features and functional activities for over one billion years of evolution.

A model of interaction: aflatoxins and hepatitis viruses in liver cancer aetiology and prevention

Hepatocellular carcinoma (HCC) is one of the most common cancers worldwide and has an extremely poor prognosis. The majority of cases occur in south-east Asia and sub-Saharan Africa where the major risk factors are chronic infection with hepatitis B and C viruses (HBV and HCV) as well as dietary exposure to aflatoxins. Aflatoxin B1, the most commonly occurring and potent of the aflatoxins is associated with a specific AGG to AGT transversion mutation at codon 249 of the p53 gene in human HCC, providing mechanistic support to a causal link between exposure and disease. Prospective epidemiological studies have shown a more than multiplicative interaction between HBV and aflatoxins in terms of HCC risk. However, the biology underlying this statistical interaction is not fully understood. There are a number of potential mechanisms including, among others: the fixation of AFB1-induced mutations in the presence of liver regeneration and hyperplasia induced by chronic HBV infection; the predisposition of HBV-infected hepatocytes to aflatoxin-induced DNA damage; an increase in susceptibility to chronic HBV infection in aflatoxin-exposed individuals; and oxidative stress exacerbated by co-exposure to aflatoxins and chronic hepatitis infection. Priorities for prevention are global HBV vaccination, primary and secondary prevention strategies against aflatoxin and the avoidance of transmission of HCV through good hygiene practices.

Proteome analysis of aflatoxin B1-induced hepatocarcinogenesis in tree shrew (Tupaia belangeri chinensis) and functional identification of candidate protein peroxiredoxin II

In order to explore the proteins responsible for hepatocellular carcinoma (HCC), aflatoxin B(1)-induced hepatocarcinogenesis in tree shrew (Tupaia belangeri chinensis) was analyzed with 2-DE and MS. By comparing HCC samples with their own precancerous biopsies and HCC-surrounding tissues, a group of candidate proteins that differentially expressed in HCC were obtained. Peroxiredoxin (Prx) II, one of the candidates with distinct alteration, was further investigated and validated. Western blot and RT-PCR assays confirmed the overexpression of Prx II in both tree shrew and human HCC tissues. RNA interference for silencing Prx II was employed subsequently to explore the function and underlying mechanism of Prx II on liver cancer cell line Hep3B. Results showed the cell proliferation and clone formation decreased obviously when Prx II expression was inhibited, while the flow cytometer analysis showed the percentage of cell apoptosis enhanced. Inhibition of Prx II expression also obviously increased the generation of ROS and malondialdehyde, both are the products from peroxidation. These results imply the important role of Prx II in hepatocarcinogenesis, possibly through its function in regulating peroxidation and hereby to provide a favorable microenvironment for cancer cell surviving and progressing.

Candidate genes responsible for human hepatocellular carcinoma identified from differentially expressed genes in hepatocarcinogenesis of the tree shrew (Tupaia belangeri chinesis)

AIM

To explore gene expression profiles during hepatocarcinogenesis of the tree shrew, and to find the genes responsible for human hepatocellular carcinoma (HCC).

METHODS

Tree shrews were used as an animal model for HCC induction employing aflatoxin B(1) (AFB(1)) alone or AFB(1) plus hepatitis B virus (HBV) as etiological factors. Gene expression profiles from the tissues of HCC, HCC-surrounding liver tissues (para-HCC) and the corresponding biopsies taken from the same animals before HCC had developed (pre-HCC) were analyzed by cDNA microarray assay to identify differentially expressed genes. Two genes, CuZn-superoxide dismutase (SOD1) and glutathione S-transferase A1 (GSTA1), were further investigated by reverse transcriptase-polymerase chain reaction (RT-PCR) and immunohistochemical (IHC) assays were done on tree shrew and human HCC samples.

RESULTS

RESULTS from the cDNA microarray analysis indicated that the gene expression profiles of HCC between AFB(1)and AFB(1) + HBV treatment groups were markedly different. A total of 11 genes, including SOD1 and GSTA1, were found changing in expression levels in all detected samples from both groups. RESULTS from RT-PCR and IHC assays indicated that mRNA and protein levels of SOD1 and GSTA1 were markedly downregulated in both tree shrew and human HCC, and downregulation of SOD1 and GSTA1 proteins in human HCC samples was closely correlated with the histopathological grading (P < 0.05).

CONCLUSION

The differentially expressed genes found in all HCC cases induced by different etiological factors among different species should be considered as good candidate genes responsible for HCC. Downregulation of SOD1 and GSTA1 might play an important role in hepatocarcinogenesis.

Expression and significance of tumor-related genes in HCC

AIM: To investigate the expression and clinical significance of DEK, cyclin D1, insulin-like growth factor II (IGF-II), glypican 3 (GPC3), ribosomal phosphoprotein 0 (rpP0) mRNA in hepatocellular carcinoma (HCC) and its paraneoplastic tissues.

METHODS: The expression of mRNAs of DEK, cyclin D1, IGF-II, GPC3 and rpP0 mRNA was detected in HCC and its paraneoplastic tissues by multiplex RT-PCR.

RESULTS: By the simplex RT-PCR, the overexpression of mRNAs of DEK, cyclin D1, IGF-II, GPC3, rpP0 mRNA in HCC and its paraneoplastic tissues was 78.1%, 87.5%, 87.5%, 75.0%, 81.3% and 15.6%, 40.6%, 37.5%, 21.9%, 31.3% respectively (P < 0.05). By the multiplex RT-PCR, at least one of the mRNAs was detected in all HCC samples and in 75.0% of paraneoplastic samples (P > 0.05). However, all these five mRNAs were found in 68.8% of HCC samples, but only in 9.4% of paraneoplastic tissues (P < 0.05). The positive expression of mRNAs of DEK, cyclin D1, IGF-II, GPC3, rpP0 in well- and poorly-differentiated HCC was 89.0%, 66.7%, 66.7%, 66.7%, 77.8% and 73.9%, 95.7%, 95.7%, 95.7%, 82.6%, respectively (P > 0.05). The expression of these genes in HCCs with α-feto protein (AFP) negative and positive was 90.0%, 80.0%, 90.0%, 90.0%, 90.0% and 72.7%, 86.3%, 77.3%, 90.9%, 68.2% respectively (P > 0.05).

CONCLUSION: The expression of DEK, cyclin D1, IGF-II, GPC3, rpP0 mRNA in HCC is much higher in HCC than in its paraneoplastic tissues. Multiplex RT-PCR assay is an effective, sensitive, accurate, and cost-effective diagnostic method of HCC.

Scavenger receptor class B type I and hepatitis C virus infection of primary tupaia hepatocytes

Hepatitis C virus (HCV) is a major cause of chronic hepatitis worldwide. The study of early steps during HCV infection has been hampered by the lack of suitable in vitro or in vivo models. Primary Tupaia hepatocytes (PTH) have been shown to be susceptible to HCV infection in vitro and in vivo. Human scavenger receptor class B type I (SR-BI) represents an HCV receptor candidate mediating the cellular binding of E2 glycoprotein to HepG2 hepatoma cells. However, the function of SR-BI for viral infection of hepatocytes is unknown. In this study, we used PTH to assess the functional role of SR-BI as a putative HCV receptor. Sequence analysis of cloned tupaia SR-BI revealed a high homology between tupaia and human SR-BI. Transfection of CHO cells with human or tupaia SR-BI but not mouse SR-BI cDNA resulted in cellular E2 binding, suggesting that E2-binding domains between human and tupaia SR-BI are highly conserved. Preincubation of PTH with anti-SR-BI antibodies resulted in marked inhibition of E2 or HCV-like particle binding. However, anti-SR-BI antibodies were not able to block HCV infection of PTH. In conclusion, our results demonstrate that SR-BI represents an important cell surface molecule for the binding of the HCV envelope to hepatocytes and suggest that other or additional cell surface molecules are required for the initiation of HCV infection. Furthermore, the structural and functional similarities between human and tupaia SR-BI indicate that PTH represent a useful model system to characterize the molecular interaction of the HCV envelope and SR-BI on primary hepatocytes.

Alteration of p53 and p21 during hepatocarcinogenesis in tree shrews

AIM: To investigate p53 mutation and p21 expression in hepatocarcinogenesis induced by hepatitis B virus (HBV) and aflatoxin B₁ (AFB₁) in tree shrews, and to reveal the role of these genes in hepatocarcinogenesis.

METHODS: Tree shrews were divided into four groups: group A, those infected with HBV and fed with AFB₁ (n = 39); group B, those infected with HBV alone (n = 28); group C, those fed with AFB₁ alone (n = 29); and group D, normal controls (n = 20). The tree shrews underwent liver biopsies once every 15 wk. Expression of p53 and p21 proteins and genes in the biopsies and tumor tissues of the experimental tree shrews was detected, respectively, by immunohistochemistry, and by Southern blotting and reverse transcription-polymerase chain reaction and sequencing.

RESULTS: The incidence of hepatocellular carcinomas (HCC) was higher in group A (66.7%) than that in group B (3.57%) and C (30%). The time of HCC occurrence was also earlier in group A than that in group C (120.0 ± 16.6 wk vs 153.3 ± 5.8 wk, respectively, P < 0.01). p53 protein was not detected by immunohistochemistry in all groups before the 75^th wk of the experiment. At the 105^th wk, the positive rates fo p53 were 78.6%, 60% and 71.4% in groups A, B and C, respectively, which were significantly higher than that in group D (10%) (all P < 0.05). An abnormal band of p53 gene was observed in groups A and C. The mutation points of p53 gene in tree shrews with HCC were at codons 275, 78 and 13. The nucleotide sequence and amino acid sequence of tree shrew’s wild-type p53 showed 91.7% and 93.4% homologies with those of human p53, respectively. The immunopositivity for p21 was found before HCC development. The incidence of HCC was significantly higher in tree shrews that were positive for p21 than those negative for p21 (80.0% vs 11.0%, P < 0.001). The incidence of HCC in p21 positive animals in group A was significantly higher than those positive for p21 in group C (P < 0.05).

CONCLUSION: A remarkable synergistic effect on HCC development exists between HBV and AFB₁. p53 mutation promotes the development of HCC. HBV and AFB₁ may synergistically induce p53 gene mutation, and stimulate ras gene expression. ras gene is activated at the earlier stage during hepatocarcinogenesis. p21 protein may be an early marker, and the alterations of p53 may be a late event in the development of HCC.

Re-evaluation and in silico annotation of the Tupaia herpesvirus proteins

Herpesviruses represent an exceptionally suitable model to analyze evolutionary old pathogens, their competency to adapt to existing and changing molecular niches in host species, and the modulation of the gene content and function to comply with the requirements of life. The basis for numerous studies dealing with these questions are reliable statements about the gene content of herpesviral genomes and the functions of viral proteins. The recent determination of the coding strategy of the chimpanzee cytomegalovirus genome and the re-evaluation of the gene content of the human cytomegalovirus genome made it also necessary to restructure the putative transcription map of the Tupaia herpesvirus (THV) genome. Twenty-three THV-specific ORFs formerly predicted to be coding for viral proteins were deleted from the THV transcription map resulting in a gene layout that is now characterized by the presence of conserved genes in the genome center, that probably reflect the genome structure of common herpesviral ancestors, and species-specific genes at the termini. The conserved regions in the THV genome are characterized by high G + C contents between 60% and 80%, a high CpG dinucleotide frequency, and the presence of densely packed putative CpG islands. The genome termini seem to provide the requirements of large scale rearrangements and complements of the gene content to adapt to new environmental demands. With the help of the recently designed method of dictionary-driven, pattern-based protein annotation it was possible to assign putative functions to almost all potential THV proteins, e.g. 123 were found to be putative membrane or secreted proteins, putative signal domains were identified in 69, and 29 proteins were predicted to be glycosylated. The present study adds new aspects to the knowledge about the precise gene composition of herpesvirus genomes and viral protein functions that are of exceptional importance for studies dealing with the phylogeny, the evolution, vaccine vector development, virus-host interactions, pathogenesis and the determination of protein functions of herpesviruses.

Differential expression of genes during aflatoxin B1-induced hepatocarcinogenesis in tree shrews

AIM: Through exploring the regulation of gene expression during hepatocarcinogenesis induced by aflatoxin B₁ (AFB₁), to find out the responsible genes for hepatocellular carcinoma (HCC) and to further understand the underlying molecular mechanism.

METHODS: Tree shrews (Tupaia belangeri chinensis) were treated with or without AFB₁ for about 90 weeks. Liver biopsies were performed regularly during the animal experiment. Eight shares of total RNA were respectively isolated from 2 HCC tissues, 2 HCC-surrounding non-cancerous liver tissues, 2 biopsied tissues at the early stage (30^th week) of the experiment from the same animals as above, 1 mixed sample of three liver tissues biopsied at the beginning (0^th week) of the experiment, and another 1 mixed sample of two liver tissues from the untreated control animals biopsied at the 90^th week of the experiment. The samples were then tested with the method of Atlas^TM cDNA microarray assay. The levels of gene expression in these tissues taken at different time points during hepatocarcinogenesis were compared.

RESULTS: The profiles of differently expressed genes were quite different in different ways of comparison. At the same period of hepatocarcinogenesis, the genes in the same function group usually had the same tendency for up- or down-regulation. Among the checked 588 genes that were known to be related to human cancer, 89 genes (15.1%) were recognized as “important genes” because they showed frequent changes in different ways of comparison. The differentially expressed genes during hepatocarcinogenesis could be classified into four categories: genes up-regulated in HCC tissue, genes with similar expressing levels in both HCC and HCC-surrounding liver tissues which were higher than that in the tissues prior to the development of HCC, genes down-regulated in HCC tissue, and genes up-regulated prior to the development of HCC but down-regulated after the development of HCC.

CONCLUSION: A considerable number of genes could change their expressing levels both in HCC and in HCC-surrounding non-cancerous liver tissues. A few modular genes were up-regulated only in HCC but not in surrounding liver tissues, while some apoptosis-related genes were down-regulated in HCC and up-regulated in surrounding liver tissues. To compare gene-expressing levels among the liver tissues taken at different time points during hepatocarcinogenesis may be helpful to locate the responsible gene (s) and understand the mechanism for AFB₁ induced liver cancer.

Molecular anatomy of Tupaia (tree shrew) adenovirus genome; evolution of viral genes and viral phylogeny

Adenoviruses are globally spread and infect species in all five taxons of vertebrates. Outstanding attention is focused on adenoviruses because of their transformation potential, their possible usability as vectors in gene therapy and their applicability in studies dealing with, e.g. cell cycle control, DNA replication, transcription, splicing, virus-host interactions, apoptosis, and viral evolution. The accumulation of genetic data provides the basis for the increase of our knowledge about adenoviruses. The Tupaia adenovirus (TAV) infects members of the genus Tupaiidae that are frequently used as laboratory animals in behavior research dealing with questions about biological and molecular processes of stress in mammals, in neurobiological and physiological studies, and as model organisms for human hepatitis B and C virus infections. In the present study the TAV genome underwent an extensive analysis including determination of codon usage, CG depletion, gene content, gene arrangement, potential splice sites, and phylogeny. The TAV genome has a length of 33,501 bp with a G+C content of 49.96%. The genome termini show a strong CG depletion that could be due to methylation of these genome regions during the viral replication cycle. The analysis of the coding capacity of the complete TAV genome resulted in the identification of 109 open reading frames (ORFs), of which 38 were predicted to be real viral genes. TAV was classified within the genus Mastadenovirus characterized by typical gene content, arrangement, and homology values of 29 conserved ORFs. Phylogenetic trees show that TAV is part of a separate evolutionary lineage and no mastadenovirus species can be considered as the most related. In contrast to other mastadenoviruses a direct ancestor of TAV captured a DUT gene from its mammalian host, presumably controlling local dUTP levels during replication and enhance viral replication in non-dividing host tissues. Furthermore, TAV possesses a second DNA-binding protein gene, that is likely to play a role in the determination of the host range. In view of these data it is conceivable that TAV underwent evolutionary adaptations to its biological environment resulting in the formation of special genomic components that provided TAV with the ability to expand its host range during viral evolution.

Rising incidence of hepatocellular carcinoma: the role of hepatitis B and C; the impact on transplantation and outcomes

Hepatocellular carcinoma caused by hepatitis B and hepatitis C are global scourges but are likely to peak in incidence in the next 2 decades and then decline. Universal vaccination has been effective in stemming the incidence of chronic hepatitis B and early-onset HCC in regions of high endemicity where implemented, but preventive measures in HCV are not yet available. After the attrition of older affected generations, the incidence of HCC will likely decline rapidly. While no vaccine is currently available for hepatitis C, cases are projected to peak and decline because of a marked reduction in transmission as a result of behavioral modification and safeguarding of blood supplies. Until these epidemiologic projections come to pass, management of hepatocellular carcinoma will continue to become a progressively more frequently encountered clinical challenge. Therapy for chronic hepatitis may ameliorate but will not eliminate the development of tumors. The demand for orthotopic liver transplantation will continue to climb, and palliative therapies for non-resectable cases will require studies aimed at optimization of benefit. LDLT may remain an option for high-risk patients affording tumor-free survival for some otherwise terminal patients.

The tree shrews: adjuncts and alternatives to primates as models for biomedical research

The tree shrews are non-rodent, primate-like, small animals. There is increasing interest in using them to establish animal models for medical and biological research. This review focuses on the use of the tree shrews in in vivo studies on viral hepatitis, hepatocellular carcinoma (HCC), myopia, and psychosocial stress. Because of the susceptibility of the tree shrews (Tupaia belangeri) and their hepatocytes to infection with human hepatitis B virus (HBV) in vivo and in vitro, these animals have been used to establish human hepatitis virus-induced hepatitis and human HBV- and aflatoxin B1-associated HCC models. As these animals are phylogenetically close to primates in evolution and have a well-developed visual system and color vision in some species, they have been utilized to establish myopia models. Because dramatic behavioral, physiological, and neuroendocrine changes in subordinate male tree shrews are similar to those observed in depressed human patients, the tree shrews have been successfully employed to experimentally study psychosocial stress. However, the tree shrews holds significant promise as research models and great use could be made of these animals in biomedical research.

Codon 249 mutation in exon 7 of p53 gene in plasma DNA: maybe a new early diagnostic marker of hepatocellular carcinoma in Qidong risk area, China

AIM: One of the characteristics of hepatocellular carcinoma (HCC) in Qidong area is the selective mutation resulting in a serine substitution at codon 249 of the p53 gene (1, 20), and it has been identified as a “hotspot” mutation in heptocellular carcinomas occurring in populations exposed to aflatoxin and with high prevalence of hepatitis B virus carriers (2, 3, 9, 10, 16, 24). We evaluated in this paper whether this “hotspot” mutation could be detected in cell-free DNA circulating in plasma of patients with hepatocellular carcinoma and cirrhosis in Qidong, China, and tried to illustrate the significance of the detection of this molecular biomarker.

METHODS: We collected blood samples from 25 hepatocellular carcinoma patients, 20 cirrhotic patients and 30 healthy controls in Qidong area. DNA was extracted and purified from 200 µl of plasma from each sample. The 249^Ser p53 mutation was detected by restriction digestion analysis and direct sequencing of exon-7 PCR products.

RESULTS: We found in exon 7 of p53 gene G→T transversion at the third base of codon 249 resulting 249^Arg→249^Ser mutation in 10/25 (40%) hepatocellular carcinoma cases, 4/20 (20%) cirrhotics, and 2/30 (7%) healthy controls. The adjusted odds ratio for having the mutation was 22.1 (95%CI, 3.2~91.7) for HCC cases compared to controls.

CONCLUSION: These data show that the 249^Ser p53 mutation in plasma is strongly associated with hepatocellular carcinoma in Qidong patients. We found this mutation was also detected, although it was at a much lower frequency, in plasma DNA of Qidong cirrhotics and healthy controls; We consider that these findings, together with the usual method of HCC diagnosis, will give more information in early diagnosis of HCC, and 249^Ser p53 mutation should be developed to a new early diagnostic marker for HCC.

Primary hepatocytes of Tupaia belangeri as a potential model for hepatitis C virus infection

Hepatitis C virus (HCV) is a major cause of chronic hepatitis worldwide, but the study of HCV infection has been hampered by the lack of an in vitro or in vivo small animal model. The tree shrew Tupaia belangeri is susceptible to infection with a variety of human viruses in vivo, including hepatitis viruses. We show that primary Tupaia hepatocytes can be infected with serum- or plasma-derived HCV from infected humans, as measured by de novo synthesis of HCV RNA, analysis of viral quasispecies evolution, and detection of viral proteins. Production of infectious virus could be demonstrated by passage to naive hepatocytes. To assess whether viral entry in Tupaia hepatocytes was dependent on the recently isolated HCV E2 binding protein CD81, we identified and characterized Tupaia CD81. Sequence analysis of cloned Tupaia cDNA revealed a high degree of homology between Tupaia and human CD81 large extracellular loops (LEL). Cellular binding of E2 and HCV infection could not be inhibited by anti-CD81 antibodies or soluble CD81-LEL, suggesting that viral entry can occur through receptors other than CD81. Thus, primary Tupaia hepatocytes provide a potential model for the study of HCV infection of hepatocytes.

Liver cancer

The prognosis of patients with HCC remains dismal. Even in the subgroups of patients who have the most favorable characteristics and are eligible for surgical resection, the 5-year survival rate is less than 25%. For patients with more advanced disease, the median survival time is less than 1 year. The good news in HCC research is that the disease can be prevented. In Taiwan, the rate of HCC in children aged 6 to 9 years decreased from 5.2 per million population before the neonatal vaccination program began in 1984 to 1.3 per million population in the first vaccinated cohort. Treatment of viral hepatitis with IFN may decrease the rates of long-term development of HCC. Other agents that may prevent second primary tumors following resection of HCC, such as polyprenoic acid and acylic retinoid, are also being investigated.

The chemistry and biology of aflatoxin B(1): from mutational spectrometry to carcinogenesis

Dietary exposure to aflatoxin B(1) (AFB(1)) is associated with an increased incidence of hepatocellular carcinoma (HCC), especially in populations in which exposure to hepatitis B virus (HBV) is a common occurrence. Most HCC samples from people living where HBV is prevalent have one striking mutational hotspot: a GC-->TA transversion at the third position of codon 249 of the p53 gene. In this review, the chemical reaction of an electrophilic derivative of aflatoxin with specific DNA sequences is examined, along with the types of mutations caused by AFB(1) and the sequence context dependence of those mutations. An attempt is made to assign the source of these mutations to specific chemical forms of AFB(1)-DNA damage. In addition, epidemiological and experimental data are examined regarding the synergistic effects of AFB(1) and HBV on HCC formation and the predominance of one hotspot GC-->TA transversion in the p53 gene of affected individuals.