Mouse liver tumorigenesis: models, mechanisms, and relevance to human disease

SPG21, a potential oncogene targeted by miR-128-3p, amplifies HBx-induced carcinogenesis and chemoresistance via activation of TRPM7-mediated JNK pathway in hepatocellular carcinoma

PURPOSE

Chronic hepatitis B virus (HBV) infection is the primary risk factor for the malignant progression of hepatocellular carcinoma (HCC). It has been reported that HBV X protein (HBx) possesses oncogenic properties, promoting hepatocarcinogenesis and chemoresistance. However, the detailed molecular mechanisms are not fully understood. Here, we aim to investigate the effects of miR-128-3p/SPG21 axis on HBx-induced hepatocarcinogenesis and chemoresistance.

METHODS

The expression of SPG21 in HCC was determined using bioinformatics analysis, quantitative real-time PCR (qRT-PCR), western blotting, and immunohistochemistry (IHC). The roles of SPG21 in HCC were elucidated through a series of in vitro and in vivo experiments, including real-time cellular analysis (RTCA), matrigel invasion assay, and xenograft mouse model. Pharmacologic treatment and flow cytometry were performed to demonstrate the potential mechanism of SPG21 in HCC.

RESULTS

SPG21 expression was elevated in HCC tissues compared to adjacent non-tumor tissues (NTs). Moreover, higher SPG21 expression correlated with poor overall survival. Functional assays revealed that SPG21 fostered HCC tumorigenesis and invasion. MiR-128-3p, which targeted SPG21, was downregulated in HCC tissues. Subsequent analyses showed that HBx amplified TRPM7-mediated calcium influx via miR-128-3p/SPG21, thereby activating the c-Jun N-terminal kinase (JNK) pathway. Furthermore, HBx inhibited doxorubicin-induced apoptosis by engaging the JNK pathway through miR-128-3p/SPG21.

CONCLUSION

The study suggested that SPG21, targeted by miR-128-3p, might be involved in enhancing HBx-induced carcinogenesis and doxorubicin resistance in HCC via the TRPM7/Ca2+/JNK signaling pathway. This insight suggested that SPG21 could be recognized as a potential oncogene, offering a novel perspective on its role as a prognostic factor and a therapeutic target in the context of HCC.

Network-level analysis of ageing and its relationship with diseases and tissue regeneration in the mouse liver

The liver plays a vital role in maintaining whole-body metabolic homeostasis, compound detoxification and has the unique ability to regenerate itself post-injury. Ageing leads to functional impairment of the liver and predisposes the liver to non-alcoholic fatty liver disease (NAFLD) and hepatocellular carcinoma (HCC). Mapping the molecular changes of the liver with ageing may help to understand the crosstalk of ageing with different liver diseases. A systems-level analysis of the ageing-induced liver changes and its crosstalk with liver-associated conditions is lacking. In the present study, we performed network-level analyses of the ageing liver using mouse transcriptomic data and a protein-protein interaction (PPI) network. A sample-wise analysis using network entropy measure was performed, which showed an increasing trend with ageing and helped to identify ageing genes based on local entropy changes. To gain further insights, we also integrated the differentially expressed genes (DEGs) between young and different age groups with the PPI network and identified core modules and nodes associated with ageing. Finally, we computed the network proximity of the ageing network with different networks of liver diseases and regeneration to quantify the effect of ageing. Our analysis revealed the complex interplay of immune, cancer signalling, and metabolic genes in the ageing liver. We found significant network proximities between ageing and NAFLD, HCC, liver damage conditions, and the early phase of liver regeneration with common nodes including NLRP12, TRP53, GSK3B, CTNNB1, MAT1 and FASN. Overall, our study maps the network-level changes of ageing and their interconnections with the physiology and pathology of the liver.

Effect of Lipopolysaccharides on Liver Tumor Metastasis of twist1a/krasV12 Double Transgenic Zebrafish

The poor prognosis of patients diagnosed with hepatocellular carcinoma (HCC) is directly associated with the multi-step process of tumor metastasis. TWIST1, a basic helix-loop-helix (bHLH) transcription factor, is the most important epithelial-mesenchymal transition (EMT) gene involved in embryonic development, tumor progression, and metastasis. However, the role that TWIST1 gene plays in the process of liver tumor metastasis in vivo is still not well understood. Zebrafish can serve as a powerful model for cancer research. Thus, in this study, we crossed twist1a+ and kras+ transgenic zebrafish, which, respectively, express hepatocyte-specific mCherry and enhanced green fluorescent protein (EGFP); they also drive overexpression of their respective transcription factors. This was found to exacerbate the development of metastatic HCC. Fluorescence of mCherry and EGFP-labeled hepatocytes revealed that approximately 37.5% to 45.5% of the twist1a+/kras+ double transgenic zebrafish exhibited spontaneous tumor metastasis from the liver to the abdomen and tail areas, respectively. We also investigated the inflammatory effects of lipopolysaccharides (LPS) on the hepatocyte-specific co-expression of twist1a+ and kras+ in double transgenic zebrafish. Following LPS exposure, co-expression of twist1a+ and kras+ was found to increase tumor metastasis by 57.8%, likely due to crosstalk with the EMT pathway. Our results confirm that twist1a and kras are important mediators in the development of metastatic HCC. Taken together, our in-vivo model demonstrated that co-expression of twist1a+/kras+ in conjunction with exposure to LPS enhanced metastatic HCC offers a useful platform for the study of tumor initiation and metastasis in liver cancer.

Exacerbation of Liver Tumor Metastasis in twist1a+/xmrk+ Double Transgenic Zebrafish following Lipopolysaccharide or Dextran Sulphate Sodium Exposure

The poor prognosis for patients with hepatocellular carcinoma (HCC) is related directly to metastasis. The Twist1 gene encodes for a transcription factor essential to embryogenesis. It has also been shown to promote epithelial-to-mesenchymal transition (EMT), invasion, and metastasis; however, there is currently no in vivo evidence that Twist1 plays a role in the metastasis of liver tumors. Zebrafish are increasingly being used as an alternative cancer model. In the current study, an adult-stage zebrafish HCC model was used to examine the synergistic effects of twist1a and xmrk, a well characterized oncogene, during HCC metastasis. We also examined the effects of two inflammatory agents, lipopolysaccharides (LPS) and dextran sulfate sodium (DSS), on the hepatocyte-specific expression of transgenic twist1a and xmrk. The conditional overexpression of twist1a and xmrk was shown to promote liver tumor metastasis in zebrafish, resulting in increased apoptosis and cell proliferation as well as tumor maintenance and propagation independent of the inherent EMT-inducing activity of xmrk. Exposing twist1a+/xmrk+ transgenic zebrafish to LPS or DSS was shown to promote metastasis, indicating that the overexpression of twist1a and xmrk led to crosstalk between the signaling pathways involved in EMT. This study provides important evidence pertaining to the largely overlooked effects of signaling crosstalk between twist1a and xmrk in regulating HCC metastasis. Our results also suggest that the co-expression of twist1a/xmrk in conjunction with exposure to LPS or DSS enhances HCC metastasis, and provides a valuable in vivo platform by which to investigate tumor initiation and metastasis in the study of liver cancer.

Role of NF-κB in Ageing and Age-Related Diseases: Lessons from Genetically Modified Mouse Models

Ageing is a complex process, induced by multifaceted interaction of genetic, epigenetic, and environmental factors. It is manifested by a decline in the physiological functions of organisms and associated to the development of age-related chronic diseases and cancer development. It is considered that ageing follows a strictly-regulated program, in which some signaling pathways critically contribute to the establishment and maintenance of the aged state. Chronic inflammation is a major mechanism that promotes the biological ageing process and comorbidity, with the transcription factor NF-κB (nuclear factor kappa-light-chain-enhancer of activated B cells) as a crucial mediator of inflammatory responses. This, together with the finding that the activation or inhibition of NF-κB can induce or reverse respectively the main features of aged organisms, has brought it under consideration as a key transcription factor that acts as a driver of ageing. In this review, we focused on the data obtained entirely through the generation of knockout and transgenic mouse models of either protein involved in the NF-κB signaling pathway that have provided relevant information about the intricate processes or molecular mechanisms that control ageing. We have reviewed the relationship of NF-κB and premature ageing; the development of cancer associated with ageing and the implication of NF-κB activation in the development of age-related diseases, some of which greatly increase the risk of developing cancer.

Hepatic stellate cells - from past till present: morphology, human markers, human cell lines, behavior in normal and liver pathology

Hepatic stellate cell (HSC), initially analyzed by von Kupffer, in 1876, revealed to be an extraordinary mesenchymal cell, essential for both hepatocellular function and lesions, being the hallmark of hepatic fibrogenesis and carcinogenesis. Apart from their implications in hepatic injury, HSCs play a vital role in liver development and regeneration, xenobiotic response, intermediate metabolism, and regulation of immune response. In this review, we discuss the current state of knowledge regarding HSCs morphology, human HSCs markers and human HSC cell lines. We also summarize the latest findings concerning their roles in normal and liver pathology, focusing on their impact in fibrogenesis, chronic viral hepatitis and liver tumors.

Diethylnitrosamine-induced liver tumorigenesis in mice

Hepatocellular carcinoma (HCC) is the fifth most common cancer worldwide and the third leading cause of cancer related mortality with a 10 year survival rate of merely 22-35%. Tumorigenesis frequently occurs in patients with chronic liver disease where continued liver cell damage, compensatory proliferation and inflammation provide the basis for tumor initiation, promotion and progression. Animal models of HCC are particularly useful to better understand molecular events underlying liver tumorigenesis. To this end, chemical carcinogenesis protocols based on the injection of genotoxic compounds such as diethylnitrosamine (DEN) are widely used to model liver tumorigenesis in rodents. DEN injection into 2 week old mice is sufficient to cause liver tumorigenesis after 8-10 months. When injected into older mice, DEN has to be combined with administration of tumor promoting agents such as phenobarbital or feeding high fat diet. Such protocols allow to dissect the different steps of tumor formation (i.e., tumor initiation and promotion) experimentally and to model liver pathologies in mice which frequently lead to HCC in human patients such as non-alcoholic fatty liver disease. Here, we review several established chemical carcinogenesis protocols based on DEN injection into mice and discuss their advantages as well as potential limitations.

Recent Topics Concerning Combined Hepatocellular Cholangiocarcinoma

Combined hepatocellular-cholangiocarcinoma (CHC) is a relatively rare tumor with an incidence range of 1.0-4.7%. CHC is defined as a tumor containing unequivocal, intimately mixed components of both hepatocellular carcinoma and intrahepatic cholangiocarcinoma. The recent development of biochemical methodologies and cancer stem cell theory have paved the way for a clearer understanding of the histogenesis of CHC. The latest edited WHO classification published in 2010 adopted the concept of stem cell/hepatic progenitor cells in the pathological classification of CHC. Although this classification includes novel and unique concepts of histogenesis and facilitates the recognition of CHC, there are several problems with it in practice. To reduce confusion, an international group of hepatic pathologists, radiologists, surgeons, and clinicians formulated a nomenclature for CHC and issued a consensus article in 2018. In this review article, we discuss the problems with the latest WHO classification and introduce recent topics concerning CHC from pathologic and genetic points of view.

Hepatic Stellate Cells in Liver Tumor

Hepatocellular carcinoma and intrahepatic cholangiocarcinoma are the most common types of primary liver cancers. Moreover, the liver is the second most frequently involved organ in cancer metastasis after lymph nodes. The tumor microenvironment is crucial for the development of both primary and secondary liver cancers. The hepatic microenvironment consists of multiple cell types, including liver sinusoidal endothelial cells, Kupffer cells, natural killer cells, liver-associated lymphocytes, and hepatic stellate cells (HSCs). The microenvironment of a normal liver changes to a tumor microenvironment when tumor cells exist or tumor cells migrate to and multiply in the liver. Interactions between tumor cells and non-transformed cells generate a tumor microenvironment that contributes significantly to tumor progression. HSCs play a central role in the tumor microenvironment crosstalk. As this crosstalk is crucial for liver carcinogenesis and liver-tumor development, elucidating the mechanism underlying the interaction of HSCs with the tumor microenvironment could provide potential therapeutic targets for liver cancer.

Extracellular ATP and Purinergic P2Y2 Receptor Signaling Promote Liver Tumorigenesis in Mice by Exacerbating DNA Damage

Release of ATP to the extracellular compartment and subsequent activation of purinergic receptors is a conserved mechanism mediating inflammatory responses and cell fate decisions in various organs including the liver. Previous findings suggest that extracellular ATP may promote liver tumorigenesis, however, the underlying mechanisms are poorly understood. Therefore, our aim was to dissect the functions of extracellular ATP and P2Y₂ receptors (P2Y₂R) during hepatocarcinogenesis. Liver tumors were induced in wild-type and P2y₂r ^-/- knockout mice by intraperitoneal diethylnitrosamine (DEN) injection. Tumorigenesis was analyzed after 8 to 10 months and molecular analyses were performed at different stages of tumorigenesis in vivo, as well as in primary mouse hepatocytes in vitro. Liver tumor incidence and tumor numbers were strongly reduced in P2y₂r ^-/- mice, whereas tumor size and morphology were comparable to wild-type controls, suggesting that P2Y₂R contributes to tumor initiation. Mechanistically, hepatocyte proliferation in DEN-treated P2y₂r ^-/- mice was reduced, which correlated with reduced c-JUN and CCND1 but increased p21 expression. Moreover, DNA damage as determined by hepatocellular expression of γH2A.X and of genes related to genotoxic stress, as well as STAT3 phosphorylation, was reduced in the absence of P2y₂r. Administration of genotoxic agents to primary hepatocytes in vitro confirmed that DNA damage was indeed exacerbated by extracellular ATP, subsequent P2Y₂R activation, and downstream intracellular calcium-dependent signal transduction. In conclusion, our data reveal that extracellular ATP and subsequent P2Y₂R function stimulate DNA damage responses and hepatocyte proliferation, thereby promoting hepatocarcinogenesis. Targeting this pathway may be an attractive approach for chemoprevention of hepatocellular carcinoma. SIGNIFICANCE: Extracellular ATP and subsequent P2Y₂ receptor function stimulate DNA damage responses and hepatocyte proliferation, thereby promoting hepatocarcinogenesis in mice. Targeting this pathway may be an attractive approach for chemoprevention of hepatocellular carcinoma. GRAPHICAL ABSTRACT: http://cancerres.aacrjournals.org/content/canres/80/4/699/F1.large.jpg.

NADPH Oxidase 1 in Liver Macrophages Promotes Inflammation and Tumor Development in Mice

BACKGROUND & AIMS

Although there are associations among oxidative stress, reduced nicotinamide adenine dinucleotide phosphate oxidase (NOX) activation, and hepatocellular carcinoma (HCC) development, it is not clear how NOX contributes to hepatocarcinogenesis. We studied the functions of different NOX proteins in mice after administration of a liver carcinogen.

METHODS

Fourteen-day-old Nox1^-/- mice, Nox4^-/- mice, Nox1^-/-Nox4^-/- (double-knockout) mice, and wild-type (WT) C57BL/6 mice were given a single intraperitoneal injection of diethylnitrosamine (DEN) and liver tumors were examined at 9 months. We also studied the effects of DEN in mice with disruption of Nox1 specifically in hepatocytes (Nox1^ΔHep), hepatic stellate cells (Nox1^ΔHep), or macrophages (Nox1^ΔMac). Some mice were also given injections of the NOX1-specific inhibitor ML171. To study the acute effects of DEN, 8-12-week-old mice were given a single intraperitoneal injection, and liver and serum were collected at 72 hours. Liver tissues were analyzed by histologic examination, quantitative polymerase chain reaction, and immunoblots. Hepatocytes and macrophages were isolated from WT and knockout mice and analyzed by immunoblots.

RESULTS

Nox4^-/- mice and WT mice developed liver tumors within 9 months after administration of DEN, whereas Nox1^-/- mice developed 80% fewer tumors, which were 50% smaller than those of WT mice. Nox1^ΔHep and Nox1^ΔHSC mice developed liver tumors of the same number and size as WT mice, whereas Nox1^ΔMac developed fewer and smaller tumors, similar to Nox1^-/- mice. After DEN injection, levels of tumor necrosis factor, interleukin 6 (IL6), and phosphorylated signal transducer and activator of transcription 3 were increased in livers from WT, but not Nox1^-/- or Nox1^ΔMac, mice. Conditioned medium from necrotic hepatocytes induced expression of NOX1 in cultured macrophages, followed by expression of tumor necrosis factor, IL6, and other inflammatory cytokines; this medium did not induce expression of IL6 or cytokines in Nox1^ΔMac macrophages. WT mice given DEN followed by ML171 developed fewer and smaller liver tumors than mice given DEN followed by vehicle.

CONCLUSIONS

In mice given injections of a liver carcinogen (DEN), expression of NOX1 by macrophages promotes hepatic tumorigenesis by inducing the production of inflammatory cytokines. We propose that upon liver injury, damage-associated molecular patterns released from dying hepatocytes activate liver macrophages to produce cytokines that promote tumor development. Strategies to block NOX1 or these cytokines might be developed to slow hepatocellular carcinoma progression.

Obesity-Induced TNFα and IL-6 Signaling: The Missing Link between Obesity and Inflammation-Driven Liver and Colorectal Cancers

Obesity promotes the development of numerous cancers, such as liver and colorectal cancers, which is at least partly due to obesity-induced, chronic, low-grade inflammation. In particular, the recruitment and activation of immune cell subsets in the white adipose tissue systemically increase proinflammatory cytokines, such as tumor necrosis factor α (TNFα) and interleukin-6 (IL-6). These proinflammatory cytokines not only impair insulin action in metabolic tissues, but also favor cancer development. Here, we review the current state of knowledge on how obesity affects inflammatory TNFα and IL-6 signaling in hepatocellular carcinoma and colorectal cancers.

Dual role for inositol-requiring enzyme 1α in promoting the development of hepatocellular carcinoma during diet-induced obesity in mice

Obesity is associated with both endoplasmic reticulum (ER) stress and chronic metabolic inflammation. ER stress activates the unfolded protein response (UPR) and has been implicated in a variety of cancers, including hepatocellular carcinoma (HCC). It is unclear whether individual UPR pathways are mechanistically linked to HCC development, however. Here we report a dual role for inositol-requiring enzyme 1α (IRE1α), the ER-localized UPR signal transducer, in obesity-promoted HCC development. We found that genetic ablation of IRE1α in hepatocytes not only markedly reduced the occurrence of diethylnitrosamine (DEN)-induced HCC in liver-specific IRE1α knockout (LKO) mice when fed a normal chow (NC) diet, but also protected against the acceleration of HCC progression during high-fat diet (HFD) feeding. Irrespective of their adiposity states, LKO mice showed decreased hepatocyte proliferation and signal transducer and activator of transcription 3 (STAT3) activation, even in the face of increased hepatic apoptosis. Furthermore, IRE1α abrogation blunted obesity-associated activation of hepatic inhibitor of nuclear factor kappa B kinase subunit beta (IKKβ)-nuclear factor kappa B (NF-κB) pathway, leading to reduced production of the tumor-promoting inflammatory cytokines tumor necrosis factor (TNF) and interleukin 6 (IL-6). Importantly, higher IRE1α expression along with elevated STAT3 phosphorylation was also observed in the tumor tissues from human HCC patients, correlating with their poorer survival rate.

CONCLUSION

IRE1α acts in a feed-forward loop during obesity-induced metabolic inflammation to promote HCC development through STAT3-mediated hepatocyte proliferation. (Hepatology 2018).

Nrf2 Mutagenic Activation Drives Hepatocarcinogenesis

Nrf2, a master regulator of oxidative stress, is considered a prominent target for prevention of hepatocellular carcinoma (HCC), one of the leading causes of cancer-related deaths worldwide. Here we report that Nrf2-deficient mice resisted diethylnitrosamine (DEN)-induced hepatocarcinogenesis without affecting P450-mediated metabolic activation of DEN. Nrf2 expression, nuclear translocation, and transcriptional activity were enhanced in liver tumors. Overactivated Nrf2 was required for hepatoma growth in DEN-induced HCC. Following DEN treatment, Nrf2 genetic disruption reduced expression of pentose phosphate pathway-related enzymes, the depletion of which has been associated with an amelioration of HCC incidence. Conversely, enhanced Nrf2 activity was attributable to alterations in the ability to bind its endogenous inhibitor Keap1. Our findings provide a mechanistic rationale for Nrf2 blockade to prevent and possibly treat liver cancer. Cancer Res; 77(18); 4797-808. ©2017 AACR.

Hesperetin conjugated PEGylated gold nanoparticles exploring the potential role in anti-inflammation and anti-proliferation during diethylnitrosamine-induced hepatocarcinogenesis in rats

Liver cancer is the fifth most common cancer and one of the leading causes of death in the world, and second most common cause of death in men. Natural products emerge as the most enduring approaches in the development of anticancer targeting drug. Hesperetin (HP), one of the abundant flavonoids found naturally in citrus fruits, has received considerable attention in anti-cancer promotion and progression. The present study was conducted to decipher the role of 0.5 ml hesperetin conjugated gold nanoparticles (Au-mPEG_(5000)-S-HP NPs) during diethylnitrosamine (DEN)-induced hepatocarcinogenesis in male Wistar albino rats and shows the better antioxidant that possesses anti-inflammatory, anti-proliferation and anticarcinogenic properties and may modulate signaling pathways. The confirmation of polymer functionalized gold nanoparticles and drug loaded polymer gold nanoparticles were characterized by HR-TEM with EDAX, and DLS with Zeta potential techniques. The drug encapsulation efficiency and release properties were carried out in PBS at pH 7.4 for Au- mPEG_(5000)-S-HP and compared with the control pure hesperetin (HP). Here, we review the role of mast cell counts, tumor necrosis factor alpha (TNF-α), transcription factor nuclear factor-κB (NF-κB), levels of glycoconjugates, proliferating cell nuclear antigen (PCNA) and argyrophilic nucleolar organizing regions, are the master regulator of inflammation and proliferation, in the development of hepatocellular injury, liver fibrosis and HCC. DEN-administered animals showed increased mast cell counts, tumor necrosis factor alpha, transcription factor nuclear factor-κB, glycoconjugates, proliferating cell nuclear antigen, and argyrophilic nucleolar organizing regions. Whereas Au-mPEG_(5000)-S-HP NPs supplementation considerably suppressed all the above abnormalities. These results suggest that the Au-mPEG_(5000)-S-HP NPs exhibited the better potential anticancer activity by inhibiting cell inflammation and proliferation in DEN-induced hepatocellular carcinogenesis.

Dietary restriction protects against diethylnitrosamine-induced hepatocellular tumorigenesis by restoring the disturbed gene expression profile

Hepatocellular carcinoma (HCC) is one of the most lethal and prevalent malignancies, worse still, there are very limited therapeutic measures with poor clinical outcomes. Dietary restriction (DR) has been known to inhibit spontaneous and induced tumors in several species, but the mechanisms are little known. In the current study, by using a diethylnitrosamine (DEN)-induced HCC mice model, we found that DR significantly reduced the hepatic tumor number and size, delayed tumor development, suppressed proliferation and promoted apoptosis. Further transcriptome sequencing of liver tissues from the DEN and the DEN accompanied with DR (DEN+DR) mice showed that DEN induced profound changes in the gene expression profile, especially in cancer-related pathways while DR treatment reversed most of the disturbed gene expression induced by DEN. Finally, transcription factor enrichment analysis uncovered the transcription factor specificity protein 1 (SP1) probably functioned as the main regulator of gene changes, orchestrating the protective effects of DR on DEN induced HCC. Taken together, by the first comprehensive transcriptome analysis, we elucidate that DR protects aginst DEN-induced HCC by restoring the disturbed gene expression profile, which holds the promise to provide effective molecular targets for cancer therapies.

Curcumin and Turmeric Modulate the Tumor-Promoting Effects of Iron In Vitro

Free or loosely chelated iron has tumor-promoting properties in vitro. Curcumin, a polyphenol derived from the food spice turmeric (Curcuma longa), is a potent antioxidant that binds iron. The primary aim of this study was to investigate whether curcuminoids prevent tumor-promoting effects of iron in T51B cells, a non-neoplastic rat liver epithelial cell line. Purified curcuminoids (curcumin) or a standardized turmeric extract similarly reduced oxidative stress and cytotoxicity associated with iron overload (IC₅₀ values near 10 μM, P < 0.05). Inhibition of iron-induced tumor promotion (seen upon treatment with 200 μM ferric ammonium citrate ± curcumin/turmeric for 16 wk in culture; subsequently assayed by soft agar colony formation) was nearly complete at 20 μM of total curcuminoids (P < 0.05), a concentration predicted to only partially chelate the added iron. Surprisingly, lower curcumin concentrations (10 μM) increased tumor promotion (P < 0.01). Curcuminoids delivered as a standardized turmeric extract were taken up better by cells, had a longer half-life, and appeared more effective in blocking tumor promotion (P < 0.01), suggesting enhanced curcuminoid delivery to cells in culture. The primary finding that curcuminoids can inhibit tumor promotion caused by iron in T51B cells is tempered by evidence for an underlying increase in neoplastic transformation at lower concentrations.

Phytochemicals of Aristolochia tagala and Curcuma caesia exert anticancer effect by tumor necrosis factor-α-mediated decrease in nuclear factor kappaB binding activity

Rationale:

The active compounds or metabolites of herbal plants exert a definite physiological action on the human body and thus are widely used in human therapy for various diseases including cancer. Previous studies by our group have reported the anticarcinogenic properties of the two herbal plants extracts (HPE) of Aristolochia tagala (AT) Cham. and Curcuma caesia (CC) Roxb. in diethylnitrosamine-induced mouse liver cancer in vivo. The anticarcinogenic properties of these extracts may be due to the active compounds present in them.

Objectives:

Our objective was to analyze the phytochemical constituents present in AT and CC, to assay their antioxidant properties and to determine their role in a possible intervention on tumor progression.

Materials and Methods:

Qualitative and quantitative analysis of constituent with anticancer properties present in the crude methanol extract of the two plants CC and AT was carried out following standard methods. Separation of the phytochemical compounds was done by open column chromatography. The extracts were eluted out with gradients of chloroform-methanol solvents. Ultraviolet-visible spectra of individual fractions were recorded, and the fractions were combined based on their λmax. The free radical scavenging activity of crude extracts and fractions obtained was also determined; the radical scavenging activity was expressed as IC₅₀. High-performance thin layer chromatography (HPTLC) analysis of fractionated compounds was carried out to identify partially the phytochemical compounds. The anti-inflammatory and anticancer activity of AT and CC extracts was studied in DEN induced BALB/c mice by analyzing the tumor necrosis factor-α (TNF-α) levels in serum and the nuclear factor kappaB (NF-κB) binding activity in nuclear extracts of the liver.

Results:

It was observed that both AT and CC contained compounds such as phenolics, tannins, flavonoids, terpenoids, etc., and both extracts exhibited antioxidant capacity. HPTLC analysis revealed the presence of phenolic compounds in CC and indicated the presence of anthocynidin 3-glycosides, 6-hydroxylated flavonols, some flavones and chalcone glycosides in AT and also confirmed the presence of compounds such as terpenes, phenols, steroids, and other organic compounds in CC and presence of flavonoids in AT. In vivo studies carried out in BALB/c mice showed that exposure to DEN caused an increase in TNF-α and NF-κB binding activity. The HPE (CC or AT) was seen to revert this effect.

Conclusions:

The current paper documents the antioxidant, anti-inflammatory, and anticancer activity of the two extracts probably through TNF-α-mediated decrease in NF-κB binding activity. The active components of AT and CC may act as the potential anticancer agents in hepatocellular carcinoma and warrants further investigation.

Inflammatory models drastically alter tumor growth and the immune microenvironment in hepatocellular carcinoma

Initiation and progression of hepatocellular carcinoma (HCC) is intimately associated with a chronically diseased liver tissue. This diseased liver tissue background is a drastically different microenvironment from the healthy liver, especially with regard to immune cell prevalence and presence of mediators of immune function. To better understand the consequences of liver disease on tumor growth and the interplay with its microenvironment, we utilized two standard methods of fibrosis induction and orthotopic implantation of tumors into the inflamed and fibrotic liver to mimic the liver condition in human HCC patients. Compared to non-diseased controls, tumor growth was significantly enhanced under fibrotic conditions. The immune cells that infiltrated the tumors were also drastically different, with decreased numbers of natural killer cells but greatly increased numbers of immune-suppressive CD11b⁺ Gr1^hi myeloid cells in both models of fibrosis. In addition, there were model-specific differences: Increased numbers of CD11b⁺ myeloid cells and CD4⁺ CD25⁺ T cells were found in tumors in the bile duct ligation model but not in the carbon tetrachloride model. Induction of fibrosis altered the cytokine production of implanted tumor cells, which could have farreaching consequences on the immune infiltrate and its functionality. Taken together, this work demonstrates that the combination of fibrosis induction with orthotopic tumor implantation results in a markedly different tumor microenvironment and tumor growth kinetics, emphasizing the necessity for more accurate modeling of HCC progression in mice, which takes into account the drastic changes in the tissue caused by chronic liver disease.

Emerging role of Toll-like receptor 4 in hepatocellular carcinoma

Toll-like receptor (TLR) signaling has been implicated in inflammatory-related cancers. The upregulation of TLR signaling in hepatocellular carcinoma (HCC) suggests that it may play an essential role in the prognosis of chronic and inflammatory diseases that ultimately culminate in HCC. Here, we provide evidence about the involvement of the TLR pathway in the initiation, progression, and metastasis of HCC. The differential expression of TLR in epithelial cells has also been discussed. In particular, we emphasize the physiological role of TLR4 in the development and pathogenesis of HCC and propose novel and promising approaches for HCC therapeutics with the aid of TLR ligands.

Attenuation of steatohepatitis, fibrosis, and carcinogenesis in mice fed a methionine-choline deficient diet by CCAAT/enhancer-binding protein homologous protein deficiency

BACKGROUND AND AIMS

Hepatic steatosis is a metabolic liver disease with the potential to progress to steatohepatitis, cirrhosis, and hepatocellular carcinoma (HCC). The aim of this study was to investigate the impact of CCAAT/enhancer-binding protein homologous protein (CHOP) deficiency in the development of steatosis-associated progression of HCC.

METHODS

Eight-week-old wild-type (WT) and CHOP knockout (CHOP-/-) mice were fed a normal or methionine-choline-deficient (MCD) diet. Mice were sacrificed after 3 weeks, and steatosis, inflammation, apoptosis, and liver damage were assessed. We also evaluated fibrosis after 8 weeks of nutrition intervention. To explore the role of CHOP in liver carcinogenesis, 25 mg/kg of diethylnitrosamine (DEN) was injected intraperitoneally into 2-week-old mice, which were then fed the aforementioned diets from 8 to 24 weeks of age. CHOP expression in HCC patient livers was also evaluated.

RESULTS

CHOP deficiency did not affect steatosis but significantly reduced apoptotic cells, inflammation scores, and serum liver enzymes. It also significantly suppressed total serum bilirubin levels, fibrotic area size, and messenger RNA expression of profibrotic cytokines. DEN-initiated carcinogenesis was promoted by the MCD diet, while CHOP deficiency significantly attenuated the total number and maximum diameter of tumors and the Ki-67 labeling index. In human livers, CHOP expression was enhanced in parallel with non-alcoholic steatohepatitis-to-HCC progression.

CONCLUSIONS

CHOP deficiency attenuated apoptosis, inflammation, fibrosis, and tumorigenesis under fat-loading conditions, indicating that a therapeutic strategy targeting CHOP might be effective for fat-induced liver injury and protecting against promotion of carcinogenesis in patients with liver steatosis.

Immunohistochemical characterization of multicentric hepatocholangiocellular adenoma in a pig

Three spherical opaque-white tumor nodules were found in close proximity to each other in the liver of a breeding sow, postslaughter, at a veterinary food inspection. The tumor nodules were circumscribed and histologically consisted of discrete hepatocellular and cholangiocellular nests, in association with polygonal-to-oval-shaped cells with slight cellular atypia. Immunohistochemically, all cellular components were negative for carcinoembryonic antigen, but positive for p53. Both cholangiocytes and oval-shaped cells were immunoreactive to anti-cytokeratin antibodies AE1/AE3 and MNF116. In addition, cholangiocytes were exclusively immunoreactive to anti-cytokeratin antibody CAM5.2, and hepatocytes were positive for MNF116 and hepatocyte paraffin 1. All neoplastic cells were positive for the hepatic progenitor cell markers, α-1-fetoprotein, sal-like protein 4, and epithelial cell adhesion molecule. From these results, the present case was diagnosed as hepatocholangiocellular adenoma, arising from epithelial cells of the canals of Hering.

p38 MAPK: a dual role in hepatocyte proliferation through reactive oxygen species

p38 MAPKs are important mediators of signal transduction that respond to a wide range of extracellular stressors such as UV radiation, osmotic shock, hypoxia, pro-inflammatory cytokines, and oxidative stress. The most abundant family member is p38α, which helps to couple cell proliferation and growth in response to certain damaging stimuli. In fact, increased proliferation and impaired differentiation are hallmarks of p38α-deficient cells. It has been reported that reactive oxygen species (ROS) play a critical role in cytokine-induced p38α activation. Under physiological conditions, p38α can function as a mediator of ROS signaling and either activate or suppress cell cycle progression depending on the activation stimulus. The interplay between cell proliferation, p38 MAPK activation, and ROS production plays an important role in hepatocytes. In fact, low levels of ROS seem to be needed to activate several signaling pathways in response to hepatectomy and to orchestrate liver regeneration. p38 MAPK works as a sensor of oxidative stress and cells that have developed mechanisms to uncouple p38 MAPK activation from oxidative stress are more likely to become tumorigenic. So far, p38α influences the redox balance, determining cell survival, terminal differentiation, proliferation, and senescence. Further studies would be necessary in order to clarify the precise role of p38 MAPK signaling as a redox therapeutical target.

Clinicopathologic analysis of combined hepatocellular-cholangiocarcinoma according to the latest WHO classification

Combined hepatocellular-cholangiocarcinoma comprises <1% of all liver carcinomas. The histogenesis of combined hepatocellular-cholangiocarcinoma has remained unclear for many years. However, recent advances in hepatic progenitor cell (HPC) investigations have provided new insights. The concept that combined hepatocellular-cholangiocarcinoma originates from HPCs is adopted in the chapter "combined hepatocellular-cholangiocarcinoma" of the latest World Health Organization (WHO) classification. In this study, we conducted clinicopathologic analysis of combined hepatocellular-cholangiocarcinoma according to the latest WHO classification. Fifty-four cases were included in this study. Pathologic diagnosis was made according to the WHO classification. When a tumor contained plural histologic patterns, predominant histologic pattern (≥50%) was defined. Minor histologic patterns were also appended. Immunohistochemical staining with biliary markers (CK7, CK19, and EMA), hepatocyte paraffin (HepPar)-1, HPC markers (CD56, c-kit, CD133, and EpCAM), and vimentin was performed. Forty-five and 50 patients were analyzed for progression-free survival and overall survival, respectively. Ten, 1, 32, and 11 cases were diagnosed as: combined hepatocellular-cholangiocarcinoma, classical type; combined hepatocellular-cholangiocarcinoma, stem cell features, typical subtype; combined hepatocellular-cholangiocarcinoma, stem cell features, intermediate cell subtype; and combined hepatocellular-cholangiocarcinoma, stem cell features, cholangiolocellular type, respectively. Combined hepatocellular-cholangiocarcinomas usually have high expression of biliary markers. CD56, c-kit, and EpCAM were expressed to various degrees in all combined hepatocellular-cholangiocarcinomas apart from the hepatocellular carcinoma component of combined hepatocellular-cholangiocarcinoma, classical type. The expression of CD133 and vimentin was observed only in combined hepatocellular-cholangiocarcinoma, stem cell features of intermediate cell subtype and cholangiolocellular subtype. The expression of CD133, EpCAM, and vimentin was significantly high in combined hepatocellular-cholangiocarcinoma, subtypes with stem cell features, especially cholangiolocellular subtype. Minor histologic patterns were significantly frequent in combined hepatocellular-cholangiocarcinoma, subtypes with stem cell features, compared with combined hepatocellular-cholangiocarcinoma, classical type. There was no significant difference in clinical outcome between each subtype. Combined hepatocellular-cholangiocarcinoma has wide histologic diversity and shows immunophenotypic expression of not only biliary markers but also HPC markers to various degrees, suggesting that the histogenesis of combined hepatocellular-cholangiocarcinoma could be strongly associated with HPCs. Our results pathologically validate the latest WHO classification of combined hepatocellular-cholangiocarcinoma. However, the complex mixture of histologic subtypes has presented a challenge to the classification of combined hepatocellular-cholangiocarcinoma. Further study should be conducted using a large cohort to support this classification.

DNA damage-induced sustained p53 activation contributes to inflammation-associated hepatocarcinogenesis in rats

The tumor suppressor p53 has an important role in inducing cell-intrinsic responses to DNA damage, including cellular senescence or apoptosis, which act to thwart tumor development. It has been shown, however, that senescent or dying cells are capable of eliciting inflammatory responses, which can have pro-tumorigenic effects. Whether DNA damage-induced p53 activity can contribute to senescence- or apoptosis-associated pro-tumorigenic inflammation is unknown. Recently, we generated a p53 knock-out rat via homologous recombination in rat embryonic stem cells. Here we show that in a rat model of inflammation-associated hepatocarcinogenesis, heterozygous deficiency of p53 resulted in attenuated inflammatory responses and ameliorated hepatic cirrhosis and tumorigenesis. Chronic administration of hepatocarcinogenic compound, diethylnitrosamine, led to persistent DNA damage and sustained induction of p53 protein in the wild-type livers, and much less induction in p53 heterozygous livers. Sustained p53 activation subsequent to DNA damage was accompanied by apoptotic rather than senescent hepatic injury, which gave rise to the hepatic inflammatory responses. In contrast, the non-hepatocarcinogenic agent, carbon tetrachloride, failed to induce p53, and caused a similar degree of chronic hepatic inflammation and cirrhosis in wild type and p53 heterozygous rats. These results suggest that although p53 is usually regarded as a tumor suppressor, its constant activation can promote pro-tumorigenic inflammation, especially in livers exposed to agents that inflict lasting mutagenic DNA damage.

Inflammation- and stress-related signaling pathways in hepatocarcinogenesis

It has been established that cancer can be promoted and exacerbated by inflammation. Hepatocellular carcinoma (HCC) is the fifth most common cancer worldwide, and its long-term prognosis remains poor. Although HCC is a complex and heterogeneous tumor with several genomic mutations, it usually develops in the context of chronic liver damage and inflammation, suggesting that understanding the mechanism(s) of inflammation-mediated hepatocarcinogenesis is essential for the treatment and prevention of HCC. Chronic liver damage induces a persistent cycle of necro-inflammation and hepatocyte regeneration, resulting in genetic mutations in hepatocytes and expansion of initiated cells, eventually leading to HCC development. Recently, several inflammation- and stress-related signaling pathways have been identified as key players in these processes, which include the nuclear factor-κB, signal transducer and activator of transcription, and stress-activated mitogen- activated protein kinase pathways. Although these pathways may suggest potential therapeutic targets, they have a wide range of functions and complex crosstalk occurs among them. This review focuses on recent advances in our understanding of the roles of these signaling pathways in hepatocarcinogenesis.

mTOR inhibitors synergize on regression, reversal of gene expression, and autophagy in hepatocellular carcinoma

Hepatocellular carcinoma (HCC) affects more than half a million people worldwide and is the third most common cause of cancer deaths. Because mammalian target of rapamycin (mTOR) signaling is up-regulated in 50% of HCCs, we compared the effects of the U.S. Food and Drug Administration-approved mTOR-allosteric inhibitor, RAD001, with a new-generation phosphatidylinositol 3-kinase/mTOR adenosine triphosphate-site competitive inhibitor, BEZ235. Unexpectedly, the two drugs acted synergistically in inhibiting the proliferation of cultured HCC cells. The synergistic effect closely paralleled eukaryotic initiation factor 4E-binding protein 1 (4E-BP1) dephosphorylation, which is implicated in the suppression of tumor cell proliferation. In a mouse model approximating human HCC, the drugs in combination, but not singly, induced a marked regression in tumor burden. However, in the tumor, BEZ235 alone was as effective as the combination in inhibiting 4E-BP1 phosphorylation, which suggests that additional target(s) may also be involved. Microarray analyses revealed a large number of genes that reverted to normal liver tissue expression in mice treated with both drugs, but not either drug alone. These analyses also revealed the down-regulation of autophagy genes in tumors compared to normal liver. Moreover, in HCC patients, altered expression of autophagy genes was associated with poor prognosis. Consistent with these findings, the drug combination had a profound effect on UNC51-like kinase 1 (ULK1) dephosphorylation and autophagy in culture, independent of 4E-BP1, and in parallel induced tumor mitophagy, a tumor suppressor process in liver. These observations have led to an investigator-initiated phase 1B-2 dose escalation trial with RAD001 combined with BEZ235 in patients with HCC and other advanced solid tumors.

Chronic activation of mTOR complex 1 is sufficient to cause hepatocellular carcinoma in mice

The mammalian target of rapamycin (mTOR) complex 1 (mTORC1) is a nutrient-sensitive protein kinase that is aberrantly activated in many human cancers. Whether dysregulation of mTORC1 signaling in normal tissues increases the risk for cancer, however, is unknown. We focused on hepatocellular carcinoma, which has been linked to environmental factors that affect mTORC1 activity, including diet. Ablation of the gene encoding TSC1 (tuberous sclerosis complex 1), which as part of the TSC1-TSC2 complex is an upstream inhibitor of mTORC1, results in constitutively increased mTORC1 signaling, an effect on this pathway similar to that of obesity. We found that mice with liver-specific knockout of Tsc1 developed sporadic hepatocellular carcinoma with heterogeneous histological and biochemical features. The spontaneous development of hepatocellular carcinoma in this mouse model was preceded by a series of pathological changes that accompany the primary etiologies of this cancer in humans, including liver damage, inflammation, necrosis, and regeneration. Chronic mTORC1 signaling led to unresolved endoplasmic reticulum stress and defects in autophagy, factors that contributed to hepatocyte damage and hepatocellular carcinoma development. Therefore, we conclude that increased activation of mTORC1 can promote carcinogenesis and may thus represent a key molecular link between cancer risk and environmental factors, such as diet.

FGF19 and cancer

Fibroblast growth factors (FGFs) and their cognate receptors, FGF receptors (FGFRs), play critical roles in a variety of normal developmental and physiological processes. Numerous reports support a role for deregulation of FGF-FGFR signaling, whether it is at the ligand and/or receptor level, in tumor development and progression. The FGF19-FGFR4 signaling axis has been implicated in the pathogenesis of several cancers, including hepatocellular carcinomas in mice and potentially in humans. This chapter focuses on recent progress in the understanding of the molecular mechanisms of FGF19 action and its potential involvement in cancer.

The role of JNK in the development of hepatocellular carcinoma

The cJun NH(2)-terminal kinase (JNK) signal transduction pathway has been implicated in the growth of carcinogen-induced hepatocellular carcinoma. However, the mechanism that accounts for JNK-regulated tumor growth is unclear. Here we demonstrate that compound deficiency of the two ubiquitously expressed JNK isoforms (JNK1 and JNK2) in hepatocytes does not prevent hepatocellular carcinoma development. Indeed, JNK deficiency in hepatocytes increased the tumor burden. In contrast, compound JNK deficiency in hepatocytes and nonparenchymal cells reduced both hepatic inflammation and tumorigenesis. These data indicate that JNK plays a dual role in the development of hepatocellular carcinoma. JNK promotes an inflammatory hepatic environment that supports tumor development, but also functions in hepatocytes to reduce tumor development.

Oleate-mediated activation of phospholipase D and mammalian target of rapamycin (mTOR) regulates proliferation and rapamycin sensitivity of hepatocarcinoma cells

AIMS/HYPOTHESIS

A high-fat diet and obesity are associated with increased risk of liver cancer. Because increased delivery of NEFA to the liver occurs in these conditions, we investigated the involvement of the unsaturated fatty acid oleate in hepatocarcinoma cell proliferation using human-derived hepatocarcinoma cell lines as model systems.

METHODS

Western blotting, FACS analysis and [(3)H]thymidine incorporation were used to study the signalling pathways and the proliferation of cells cultured for up to 72 h with or without a concentration of oleate considered to be relevant to human pathophysiology (50 μmol/l) or a concentration considered elevated (1 mmol/l).

RESULTS

In HepG2 cells, proliferation was increased in the presence of 50 μmol/l oleate, but was decreased at 1 mmol/l. This differential effect was correlated with the activation of the mammalian target of rapamycin complex 1 (mTORC1) and with increased translation of cell cycle regulators. Oleate-mediated mTORC1 activation required phospholipase D activation, which produces phosphatidic acid and is known to render mTORC1 rapamycin resistant. Remarkably, rapamycin resistance was found to affect specifically the mTORC1/eukaryotic initiation factor 4E-binding protein 1 (4E-BP1) branch of the mTORC1 pathway in the presence of 50 μmol/l oleate. Furthermore, inhibition of phosphatidic acid production abolished oleate-induced increases in mTORC1 activity and cyclin A production. Importantly, the same differential effects of oleate on mTORC1 activation, cell cycle regulators and rapamycin resistance were found in SK-Hep1 cells.

CONCLUSIONS/INTERPRETATION

Oleate stimulates mTORC1 activation and rapamycin resistance. We propose that rapamycin-derived mTOR inhibitors are likely to be of limited therapeutic use to restrain hepatic tumour growth, particularly in the context of associated obesity.

Evolution of genomic instability in diethylnitrosamine-induced hepatocarcinogenesis in mice

Diethylnitrosamine (DEN) is a hepatic procarcinogen which is frequently used as an inducer of hepatocellular carcinoma (HCC) in mice. Although mice after DEN exposure are among the most widely used models for liver tumorigenesis, a detailed, mechanistic characterization of the longitudinal changes in the respective tumor genomes has never been performed. Here we established the chronological order of genetic alterations during DEN carcinogenesis by examining mice at different points in time. Tumor samples were isolated by laser microdissection and subjected to array-comparative genomic hybridization (array-CGH) and sequencing analysis. Chromosomal gains and losses were observed in tumors by week 32 and increased significantly by week 56. Loss of distal chromosome 4q, including the tumor suppressors Runx3 and Nr0b2/Shp, was a frequent early event and persisted during all tumor stages. Surprisingly, sequencing revealed that β-catenin mutations occurred late and were clearly preceded by chromosomal instability. Thus, contrary to common belief, β-catenin mutations and activation of the Wnt/β-catenin pathway are not involved in tumor initiation in this model of chemical hepatocarcinogenesis.

CONCLUSION

Our study suggests that the majority of the current knowledge about genomic changes in HCC is based on advanced tumor lesions and that systematic analyses of the chronologic order including early lesions may reveal new, unexpected findings.

NF-κB and STAT3 - key players in liver inflammation and cancer

Hepatocellular carcinoma (HCC), the major form of primary liver cancer, is one of the most deadly human cancers. The pathogenesis of HCC is frequently linked with continuous hepatocyte death, inflammatory cell infiltration and compensatory liver regeneration. Understanding the molecular signaling pathways driving or mediating these processes during liver tumorigenesis is important for the identification of novel therapeutic targets for this dreadful disease. The classical IKKβ-dependent NF-κB signaling pathway has been shown to promote hepatocyte survival in both developing and adult livers. In addition, it also plays a crucial role in liver inflammatory responses by controlling the expression of an array of growth factors and cytokines. One of these cytokines is IL-6, which is best known for its role in the liver acute phase response. IL-6 exerts many of its functions via activation of STAT3, a transcription factor found to be important for HCC development. This review will focus on recent studies on the roles of NF-κB and STAT3 in liver cancer. Interactions between the two pathways and their potential as therapeutic targets will also be discussed.

Loss of metallothionein predisposes mice to diethylnitrosamine-induced hepatocarcinogenesis by activating NF-kappaB target genes

Metallothioneins (MT) are potent scavengers of free radicals that are silenced in primary hepatocellular carcinomas (HCC) of human and rodent origin. To examine whether loss of MT promotes hepatocarcinogenesis, male Mt-1 and Mt-2 double knockout (MTKO) and wild-type (WT) mice were exposed to diethylnitrosamine (DEN) and induction of HCC was monitored at 23 and 33 weeks. The size and number of liver tumors, the ratio between liver and body weight, and liver damage were markedly elevated in the MTKO mice at both time points compared with the WT mice. At 23 weeks, MTKO mice developed HCC whereas WT mice developed only preneoplastic nodules suggesting that loss of MT accelerates hepatocarcinogenesis. MTKO tumors also exhibited higher superoxide anion levels. Although NF-κB activity increased in the liver nuclear extracts of both genotypes after DEN exposure, the complex formed in MTKO mice was predominantly p50/65 heterodimer (transcriptional activator) as opposed to p50 homodimer (transcriptional repressor) in WT mice. Phosphorylation of p65 at Ser276 causing its activation was also significantly augmented in DEN-exposed MTKO livers. NF-κB targets that include early growth response genes and proinflammatory cytokines were significantly upregulated in MTKO mice. Concurrently, there was a remarkable increase (∼100-fold) in Pai-1 expression; significant increase in c-Jun, c-Fos, c-Myc, Ets2, and ATF3 expressions; and growth factor signaling that probably contributed to the increased tumor growth in MTKO mice. Taken together, these results demonstrate that MTs protect mice from hepatocarcinogen-induced liver damage and carcinogenesis, underscoring their potential therapeutic application against hepatocellular cancer.

NF-κB, JNK, and TLR Signaling Pathways in Hepatocarcinogenesis

Hepatocellular carcinoma (HCC) is the third largest cause of cancer deaths worldwide. The role of molecular changes in HCC have been used to identify prognostic markers and chemopreventive or therapeutic targets. It seems that toll-like receptors (TLRs) as well as the nuclear factor (NF)-κB, and JNK pathways are critical regulators for the production of the cytokines associated with tumor promotion. The cross-talk between an inflammatory cell and a neoplastic cell, which is instigated by the activation of NF-κB and JNKs, is critical for tumor organization. JNKs also regulate cell proliferation and act as oncogenes, making them the main tumor-promoting protein kinases. TLRs play roles in cytokine and hepatomitogen expression mainly in myeloid cells and may promote liver tumorigenesis. A better understanding of these signaling pathways in the liver will help us understand the mechanism of hepatocarcinogenesis and provide a new therapeutic target for HCC.

Putative association of transforming growth factor-alpha polymorphisms with clearance of hepatitis B virus and occurrence of hepatocellular carcinoma in patients with chronic hepatitis B virus infection

Previous studies showed that several genetic polymorphisms might influence the clinical outcome of chronic hepatitis B virus (HBV) infection, including HBV clearance or development of hepatocellular carcinoma (HCC). The aim of this study was to determine whether polymorphisms of the transforming growth factor-alpha (TGF-alpha) gene are associated with clinical outcome of HBV infection. A total of 1096 Korean subjects having either present or past evidence of HBV infection were prospectively enrolled between January 2001 and August 2003. Among 16 genetic variants in TGFA gene, nine variants were genotyped using TaqMan assay and the genetic association with HBV clearance and HCC occurrence was analysed. Statistical analyses revealed that TGFA+103461T>C, TGFA+106151C>G and TGFA-ht2 were marginally associated with clearance of HBV infection. However, only TGFA-ht2 retained significance after multiple correction (OR = 0.39, P(corr) = 0.007 in recessive model). Although no variants were significant after multiple correction, TGFA+88344G>A and TGFA+103461T>C were weakly associated in recessive model in the analysis of HCC occurrence. In addition, Cox relative hazards model also revealed that TGFA+88344G>A was associated with onset age of HCC occurrence in subjects (RH = 1.46, P(corr) = 0.04). TGF-alpha polymorphisms might be an important factor in immunity, progression of inflammatory process and carcinogenesis, which explains the variable outcome of HBV infection at least in part. Further biological evidence is warranted in the future to support these suggestive associations.

Hepatocyte IKKbeta/NF-kappaB inhibits tumor promotion and progression by preventing oxidative stress-driven STAT3 activation

The NF-kappaB activating kinase IKKbeta suppresses early chemically induced liver tumorigenesis by inhibiting hepatocyte death and compensatory proliferation. To study IKKbeta's role in late tumor promotion and progression, we developed a transplant system that allows initiated mouse hepatocytes to form hepatocellular carcinomas (HCC) in host liver after a long latency. Deletion of IKKbeta long after initiation accelerated HCC development and enhanced proliferation of tumor initiating cells. These effects of IKKbeta/NF-kappaB were cell autonomous and correlated with increased accumulation of reactive oxygen species that led to JNK and STAT3 activation. Hepatocyte-specific STAT3 ablation prevented HCC development. The negative crosstalk between NF-kappaB and STAT3, which is also evident in human HCC, is a critical regulator of liver cancer development and progression.

Hepatocyte IKKbeta/NF-kappaB inhibits tumor promotion and progression by preventing oxidative stress-driven STAT3 activation

The NF-kappaB activating kinase IKKbeta suppresses early chemically induced liver tumorigenesis by inhibiting hepatocyte death and compensatory proliferation. To study IKKbeta's role in late tumor promotion and progression, we developed a transplant system that allows initiated mouse hepatocytes to form hepatocellular carcinomas (HCC) in host liver after a long latency. Deletion of IKKbeta long after initiation accelerated HCC development and enhanced proliferation of tumor initiating cells. These effects of IKKbeta/NF-kappaB were cell autonomous and correlated with increased accumulation of reactive oxygen species that led to JNK and STAT3 activation. Hepatocyte-specific STAT3 ablation prevented HCC development. The negative crosstalk between NF-kappaB and STAT3, which is also evident in human HCC, is a critical regulator of liver cancer development and progression.

Dietary and genetic obesity promote liver inflammation and tumorigenesis by enhancing IL-6 and TNF expression

Epidemiological studies indicate that overweight and obesity are associated with increased cancer risk. To study how obesity augments cancer risk and development, we focused on hepatocellular carcinoma (HCC), the common form of liver cancer whose occurrence and progression are the most strongly affected by obesity among all cancers. We now demonstrate that either dietary or genetic obesity is a potent bona fide liver tumor promoter in mice. Obesity-promoted HCC development was dependent on enhanced production of the tumor-promoting cytokines IL-6 and TNF, which cause hepatic inflammation and activation of the oncogenic transcription factor STAT3. The chronic inflammatory response caused by obesity and enhanced production of IL-6 and TNF may also increase the risk of other cancers.

Dietary and genetic obesity promote liver inflammation and tumorigenesis by enhancing IL-6 and TNF expression

Epidemiological studies indicate that overweight and obesity are associated with increased cancer risk. To study how obesity augments cancer risk and development, we focused on hepatocellular carcinoma (HCC), the common form of liver cancer whose occurrence and progression are the most strongly affected by obesity among all cancers. We now demonstrate that either dietary or genetic obesity is a potent bona fide liver tumor promoter in mice. Obesity-promoted HCC development was dependent on enhanced production of the tumor-promoting cytokines IL-6 and TNF, which cause hepatic inflammation and activation of the oncogenic transcription factor STAT3. The chronic inflammatory response caused by obesity and enhanced production of IL-6 and TNF may also increase the risk of other cancers.

Low-level shRNA cytotoxicity can contribute to MYC-induced hepatocellular carcinoma in adult mice

Short hairpin RNAs (shRNAs) have emerged as a novel therapeutic modality, but there is increasing concern over nonspecific effects in vivo. Here, we used viral vectors to express shRNAs against endogenous p53 in livers of conditional MYC-transgenic mice. As expected, the shRNAs silenced hepatic p53 and accelerated liver tumorigenesis when MYC was concurrently expressed. Surprisingly, various irrelevant control shRNAs similarly induced a rapid onset of tumorigenesis, comparable to carbon tetrachloride (CCl4), a potent carcinogen. We found that even marginal shRNA doses can already trigger histologically detectable hepatoxicity and increased hepatocyte apoptosis. Moreover, we noted that shRNA expression globally dysregulated hepatic microRNA (miRNA) expression, and that shRNA levels and activity further increased in the presence of MYC. In MYC-expressing transgenic mice, the marginal shRNA-induced liver injury sufficed to further stimulate hepatocellular division that was in turn associated with markedly increased expression of the mitotic cyclin B1. Hence, even at low doses, shRNAs can cause low-level hepatoxicity that can facilitate the ability of the MYC oncogene to induce liver tumorigenesis. Our data warrant caution regarding the possible carcinogenic potential of shRNAs when used as clinical agent, particularly in circumstances where tissues are genetically predisposed to cellular transformation and proliferation.

FGF19-induced hepatocyte proliferation is mediated through FGFR4 activation

FGF19 and FGF21, unique members of the fibroblast growth factor (FGF) family, are hormones that regulate glucose, lipid, and energy homeostasis. Increased hepatocyte proliferation and liver tumor formation have also been observed in FGF19 transgenic mice. Here, we report that, in contrast to FGF19, FGF21 does not induce hepatocyte proliferation in vivo. To identify the mechanism for FGF19-induced hepatocyte proliferation, we explored similarities and differences in receptor specificity between FGF19 and FGF21. We find that although both are able to activate FGF receptors (FGFRs) 1c, 2c, and 3c, only FGF19 activates FGFR4, the predominant receptor in the liver. Using a C-terminal truncation mutant of FGF19 and a series of FGF19/FGF21 chimeric molecules, we determined that amino acids residues 38-42 of FGF19 are sufficient to confer both FGFR4 activation and increased hepatocyte proliferation in vivo to FGF21. These data suggest that activation of FGFR4 is the mechanism whereby FGF19 can increase hepatocyte proliferation and induce hepatocellular carcinoma formation.

The aryl hydrocarbon receptor functions as a tumor suppressor of liver carcinogenesis

The aryl hydrocarbon receptor (AHR) is a ligand-activated transcription factor that mediates the biological and toxic effects of its xenobiotic ligands. Previous cell culture studies have shown that, in addition to controlling the xenobiotic detoxification response, AHR activation leads to G0-G1 arrest, diminished capacity for DNA replication, and inhibition of cell proliferation. In fact, recent work from our own and from other laboratories suggests that AHR may function as a tumor suppressor gene that becomes silenced during the process of tumor formation. To test this hypothesis and determine whether the mouse Ahr gene acts as a tumor suppressor gene in vivo, we have examined the role of Ahr ablation in liver tumorigenesis induced by the genotoxic chemical diethylnitrosamine (DEN), a hepatic carcinogen that is not an AHR ligand. In mice given a single i.p. injection of DEN, AHR antagonized liver tumor formation and growth by regulating cell proliferation, inflammatory cytokine expression, and DNA damage, parameters which were significantly elevated in the livers of control and, more so, of DEN-exposed Ahr-/- mice. Ahr-/- hepatocytes also showed significantly higher numbers of 4N cells, increased expression of proliferative markers, and repression of tumor suppressor genes. These data support the concept that in its basal state in the absence of a xenobiotic ligand, the Ahr gene functions as a tumor suppressor gene, and that its silencing may be associated with cancer progression.

A review of the molecular mechanisms of chemically induced neoplasia in rat and mouse models in National Toxicology Program bioassays and their relevance to human cancer

Tumor response in the B6C3F1 mouse, F344 rat, and other animal models following exposure to various compounds provides evidence that people exposed to these or similar compounds may be at risk for developing cancer. Although tumors in rodents and humans are often morphologically similar, underlying mechanisms of tumorigenesis are often unknown and may be different between the species. Therefore, the relevance of an animal tumor response to human health would be better determined if the molecular pathogenesis were understood. The underlying molecular mechanisms leading to carcinogenesis are complex and involve multiple genetic and epigenetic events and other factors. To address the molecular pathogenesis of environmental carcinogens, the authors examine rodent tumors (e.g., lung, colon, mammary gland, skin, brain, mesothelioma) for alterations in cancer genes and epigenetic events that are associated with human cancer. National Toxicology Program (NTP) studies have identified several genetic alterations in chemically induced rodent neoplasms that are important in human cancer. Identification of such alterations in rodent models of chemical carcinogenesis caused by exposure to environmental contaminants, occupational chemicals, and other compounds lends further support that they are of potential human health risk. These studies also emphasize the importance of molecular evaluation of chemically induced rodent tumors for providing greater public health significance for NTP evaluated compounds.

Hepatoma-derived growth factor is induced in liver regeneration

AIM

Hepatoma-derived growth factor (HDGF) is a heparin-binding protein, which has been suggested to be involved in the development of kidneys, the cardiovascular system and the liver. We have shown that HDGF is highly expressed in parenchymal hepatocytes in the developing liver and promotes fetal hepatocyte proliferation. In the present study, we asked whether HDGF expression was related to liver regeneration.

METHODS

We examined the mRNA and protein expressions of HDGF in two liver regeneration models. In addition, cellular distribution of HDGF in the regenerating liver was investigated by immunohistochemistry.

RESULTS

In the carbon tetrachloride (CCl(4))-treated liver, HDGF expression was induced and the peak was detected at 24 h after the CCl(4 )injection. HDGF expression was also enhanced in the hepatectomy model and the peak was detected at 12 h after surgery. The increased expression of HDGF protein was also confirmed by western blotting. Expression of the HDGF gene in the regenerating liver was dominantly detected in parenchymal hepatocytes.

CONCLUSION

These findings showed that HDGF expression was induced in parenchymal hepatocytes before the DNA synthesis in the regenerating liver, suggesting the possible involvement of HDGF in liver regeneration as an autocrine factor.