Amphiregulin induces the alternative splicing of p73 into its oncogenic isoform DeltaEx2p73 in human hepatocellular tumors

BACKGROUND & AIMS

Inactivation of the product of the tumor suppressor gene TP73 does not usually occur by mutation but rather through expression of truncated isoforms that have dominant-negative effects on p73 and p53. The truncated oncogenic isoform DeltaEx2p73 is expressed in hepatocellular carcinomas (HCC) and is produced through the alternative splicing of p73 pre-messenger RNA (pre-mRNA); however, the underlying mechanisms regulating this process are unknown.

METHODS

We used human normal and diseased liver tissue samples, as well as human HCC cell lines, to examine the association between activation of epidermal growth factor receptor (EGFR) by its ligand amphiregulin (AR) and the alternative splicing of p73 pre-mRNA into the tumorigenic isoform DeltaEx2p73, via c-Jun N-terminal-kinase-1-mediated signaling.

RESULTS

DeltaEx2p73 was expressed in a subset of premalignant cirrhotic livers and in otherwise healthy livers that harbored a primary tumor, as well as in HCC tissues. DeltaEx2p73 expression was correlated with that of the EGFR ligand AR, which was previously shown to have a role in hepatocarcinogenesis. Autocrine activation of the EGFR by AR triggered c-Jun N-terminal kinase-1 activity and inhibited the expression of the splicing regulator Slu7, leading to the accumulation of DeltaEx2p73 transcripts in HCC cells.

CONCLUSIONS

This study provided a mechanism for the generation of protumorigenic DeltaEx2p73 during liver tumorigenesis, via activation of EGFR signaling by AR and c-Jun N-terminal kinase-1 activity, leading to inhibition of the splicing regulator Slu7.

In vivo depletion of DC impairs the anti-tumor effect of agonistic anti-CD137 mAb

Anti-CD137 mAb are capable of inducing tumor rejection in several syngeneic murine tumor models and are undergoing clinical trials for cancer. The anti-tumor effect involves co-stimulation of tumor-specific CD8(+) T cells. Whether antigen cross-presenting DC are required for the efficacy of anti-CD137 mAb treatment has never been examined. Here we show that the administration of anti-CD137 mAb eradicates EG7-OVA tumors by a strictly CD8beta(+) T-cell-dependent mechanism that correlates with increased CTL activity. Ex vivo analyses to determine the identity of the draining lymph node cell type responsible for tumor antigen cross-presentation revealed that CD11c(+) cells, most likely DC, are the main players in this tumor model. A minute number of tumor cells, revealed by the presence of OVA cDNA, reach tumor-draining lymph nodes. Direct antigen presentation by tumor cells themselves also participates in anti-OVA CTL induction. Using CD11c diphtheria toxin receptor-green fluorescent protein-->C57BL/6 BM chimeric mice, which allow for sustained ablation of DC with diphtheria toxin, we confirmed the involvement of DC in tumor antigen cross-presentation in CTL induction against OVA(257-264) epitope and in the antitumor efficacy induced by anti-CD137 mAb.

The epidermal growth factor receptor: a link between inflammation and liver cancer

Epidemiological studies have established that many tumours occur in association with persistent inflammation. One clear example of inflammation-related cancer is hepatocellular carcinoma (HCC). HCC slowly unfolds on a background of chronic inflammation triggered by exposure to infectious agents (hepatotropic viruses), toxic compounds (ethanol), or metabolic impairment. The molecular links that connect inflammation and cancer are not completely known, but evidence gathered over the past few years is beginning to define the precise mechanisms. A central role for cytokines such as interleukin-6 (IL-6) and IL-1 (alpha and beta) in liver cancer has been established in experimental models. Besides these inflammatory mediators, mounting evidence points to the dysregulation of specific growth and survival-related pathways in HCC development. Among them is the pathway governed by the epidermal growth factor receptor (EGFR), which can be bound and activated by a broad family of ligands. Of special relevance is the fact that the EGFR engages in extensive crosstalk with other signaling pathways, serving as a "signaling hub" for an increasing list of growth factors, cytokines, and inflammatory mediators. In this review, we summarize the most recent evidences supporting a role for the EGFR system in inflammation-related cell signaling, with special emphasis in liver inflammation and HCC. The molecular dissection of the pathways connecting the inflammatory reaction and neoplasia will facilitate the development of novel and more effective antitumor strategies.

Inflammation and liver cancer: new molecular links

A connection between inflammation and cancer has been long suspected. Epidemiological studies have established that many tumors occur in association with chronic infectious diseases, and it is also known that persistent inflammation in the absence of infections increases the risk and accelerates the development of cancer. One clear example of inflammation-related cancer is hepatocellular carcinoma (HCC). HCC is a type tumor that slowly unfolds on a background of chronic inflammation mainly triggered by exposure to infectious agents (hepatotropic viruses) or to toxic compounds (ethanol). The molecular links that connect inflammation and cancer are not completely known, but evidences gathered over the past few years are beginning to define the precise mechanisms. In this article we review the most compelling evidences on the role of transcription factors such as NF-kappaB and STAT3, cytokines like IL-6 and IL-1alpha, ligands of the EGF receptor and other inflammatory mediators in cancer development, with special emphasis in HCC. The molecular dissection of the pathways connecting the inflammatory reaction and neoplasia will pave the way for better therapies to treat cancers.

Epidermal growth factor receptor ligands in murine models for erythropoietic protoporphyria: potential novel players in the progression of liver injury

Activation of the epidermal growth factor receptor (EGFR) plays an important role in liver regeneration and resistance to acute injury. However its chronic activation participates in the progression of liver disease, including fibrogenesis and malignant transformation. Hepatobiliary disease represents a constant feature in the clinically relevant Fechm1pas/Fechm1pas genetic model of erythropoietic protoporphyria (EPP). Similarly, chronic administration of griseofulvin to mice induces pathological changes similar to those found in patients with EPP-associated liver injury. We investigated the hepatic expression of the EGFR and its seven most relevant ligands in Fechm1pas/Fechm1pas mice bred in three different backgrounds, and in griseofulvin-induced protoporphyria. We observed that the expression of amphiregulin, betacellulin and epiregulin was significantly increased in young EPP mice when compared to aged-matched controls in all genetic backgrounds. The expression of these ligands was also tested in older (11 months) BALB/cJ EPP mice, and it was found to remain induced, while that of the EGFR was downregulated. Griseofulvin feeding also increased the expression of amphiregulin, betacellulin and epiregulin. Interestingly, protoporphyrin accumulation in cultured hepatic AML-12 cells readily elicited the expression of these three EGFR ligands. Our findings suggest that protoporphyrin could directly induce the hepatic expression of EGFR ligands, and that their chronic upregulation might participate in the pathogenesis of EPP-associated liver disease.

Wilms' tumor 1 gene expression in hepatocellular carcinoma promotes cell dedifferentiation and resistance to chemotherapy

The Wilms' tumor 1 gene (WT1) encodes a transcription factor involved in cell growth and development. As we previously reported, WT1 expression is hardly detectable in normal hepatic tissue but is induced in liver cirrhosis. Although WT1 has been found to be overexpressed in a number of malignancies, the role of WT1 in hepatocarcinogenesis has not been clarified. We found that WT1 is expressed in several human hepatocellular carcinoma (HCC) cell lines, including PLC/PRF/5 and HepG2, and in HCC tumor tissue in 42% of patients. WT1 small interfering RNAs did not affect proliferation rate of HCC cells but abrogated their resistance to anoikis. Transcriptome analysis of PLC/PRF/5 cells after WT1 knockdown showed up-regulation of 251 genes and down-regulation of 321. Ninety percent of the former corresponded to metabolic genes, mostly those characterizing the mature hepatocyte phenotype. On the contrary, genes that decreased upon WT1 inhibition were mainly related to defense against apoptosis, cell cycle, and tumor progression. In agreement with these findings, WT1 expression increased the resistance of liver tumor cells to doxorubicin, a compound used to treat HCC. Interestingly, doxorubicin strongly enhanced WT1 expression in both HCC cells and normal human hepatocytes. Among different chemotherapeutics, induction of WT1 transcription was restricted to topoisomerase 2 inhibitors. When WT1 expression was prohibited, doxorubicin caused a marked increase in caspase-3 activation. In conclusion, WT1 is expressed in a substantial proportion of HCC contributing to tumor progression and resistance to chemotherapy, suggesting that WT1 may be an important target for HCC treatment.

The epidermal growth factor receptor ligand amphiregulin participates in the development of mouse liver fibrosis

The hepatic wound-healing response to chronic noxious stimuli may lead to liver fibrosis, a condition characterized by excessive deposition of extracellular matrix. Fibrogenic cells, including hepatic stellate cells and myofibroblasts, are activated in response to a variety of cytokines, growth factors, and inflammatory mediators. The involvement of members of the epidermal growth factor family in this process has been suggested. Amphiregulin (AR) is an epidermal growth factor receptor (EGFR) ligand specifically induced upon liver injury. Here, we have addressed the in vivo role of AR in experimental liver fibrosis. To this end, liver fibrosis was induced in AR+/+ and AR-/- mice by chronic CCl(4) administration. Histological and molecular markers of hepatic fibrogenesis were measured. Additionally, the response of cultured human and mouse liver fibrogenic cells to AR was evaluated. We observed that AR was expressed in isolated Kupffer cells and liver fibrogenic cells in response to inflamatory stimuli and platelet-derived growth factor, respectively. We demonstrate that the expression of alpha-smooth muscle actin and collagen deposition were markedly reduced in AR-/- mice compared to AR+/+ animals. AR-/- mice also showed reduced expression of tissue inhibitor of metalloproteinases-1 and connective tissue growth factor, two genes that responded to AR treatment in cultured fibrogenic cells. AR also stimulated cell proliferation and exerted a potent antiapoptotic effect on isolated fibrogenic cells.

CONCLUSION

These results indicate that among the different EGFR ligands, AR plays a specific role in liver fibrosis. AR may contribute to the expression of fibrogenic mediators, as well as to the growth and survival of fibrogenic cells. Additionally, our data lend further support to the role of the EGFR system in hepatic fibrogenesis.

The epidermal growth factor receptor ligand amphiregulin participates in the development of mouse liver fibrosis

The hepatic wound-healing response to chronic noxious stimuli may lead to liver fibrosis, a condition characterized by excessive deposition of extracellular matrix. Fibrogenic cells, including hepatic stellate cells and myofibroblasts, are activated in response to a variety of cytokines, growth factors, and inflammatory mediators. The involvement of members of the epidermal growth factor family in this process has been suggested. Amphiregulin (AR) is an epidermal growth factor receptor (EGFR) ligand specifically induced upon liver injury. Here, we have addressed the in vivo role of AR in experimental liver fibrosis. To this end, liver fibrosis was induced in AR+/+ and AR-/- mice by chronic CCl(4) administration. Histological and molecular markers of hepatic fibrogenesis were measured. Additionally, the response of cultured human and mouse liver fibrogenic cells to AR was evaluated. We observed that AR was expressed in isolated Kupffer cells and liver fibrogenic cells in response to inflamatory stimuli and platelet-derived growth factor, respectively. We demonstrate that the expression of alpha-smooth muscle actin and collagen deposition were markedly reduced in AR-/- mice compared to AR+/+ animals. AR-/- mice also showed reduced expression of tissue inhibitor of metalloproteinases-1 and connective tissue growth factor, two genes that responded to AR treatment in cultured fibrogenic cells. AR also stimulated cell proliferation and exerted a potent antiapoptotic effect on isolated fibrogenic cells.

CONCLUSION

These results indicate that among the different EGFR ligands, AR plays a specific role in liver fibrosis. AR may contribute to the expression of fibrogenic mediators, as well as to the growth and survival of fibrogenic cells. Additionally, our data lend further support to the role of the EGFR system in hepatic fibrogenesis.

Novel pharmacologic strategies to protect the liver from ischemia-reperfusion injury

Ischemia and reperfusion (I/R) injury develops when blood flow is interrupted for a long period of time and then restarted. In the liver, this type of damage occurs in clinical settings such as liver transplantation and hepatic resection. Given the shortage of donor organs it is essential to maximize the use of sub-optimal organs, those previously rejected due to elevated risk of malfunction, and to increase split-liver transplantation interventions. Therefore, the development of strategies that preserve organ viability and promote liver regeneration is urgently needed. As observed for other organs, a brief period of ischemia followed by short reperfusion before the surgical procedure significantly increases liver resistance towards prolonged periods of ischemia. This phenomenon is known as ischemic preconditioning, and is the only protective strategy that has reached clinical practice. Recently, intensive research has improved our understanding of the mechanisms involved in I/R liver injury, and the biologic bases of ischemic preconditioning. This knowledge has generated relevant patented advances in the field, including the targeted inhibition of pro-apoptotic pathways, the interference with neutrophil activation, and the identification of cytoprotective cytokines. Here, we briefly review the mechanisms of hepatic ischemic damage, and present the most promising pharmacologic approaches against I/R injury. This article also includes recent patents on this topic.

Interleukin-15 liver gene transfer increases the number and function of IKDCs and NK cells

The surface phenotype CD3-NK1.1+DX5+CD11c(int)B220+GR1- has been recently ascribed to a novel subset of mouse leukocytes termed interferon (IFN)-producing killer dendritic cells (IKDCs) that shares functions with natural killer (NK) cells and DCs. Interleukin-15 (IL-15) is critical for NK cells but its relationship with IKDC remained unexplored. An expression cassette encoding human IL-15 (hIL-15) has been transferred by hydrodynamic injection into the liver of mice, resulting in transient expression of the cytokine that is detectable during the first 48 h. hIL-15 hydrodynamic gene transfer resulted in an expansion of NK cells and IKDCs. Relative expansions of IKDCs were more dramatic in the IL-15 gene-transferred hepatic tissue than in the spleen. Adoptively transferred DX5+ cells comprising both NK cells and IKDCs proliferated in response to hydrodynamic injection of hIL-15, indicating that quantitative increases are at least in part the result of proliferation from already differentiated cells. Expansion is accompanied by enhanced cytolytic activity and increased expression of TRAIL and CD137 (4-1BB), without augmenting interferon-gamma production. The effects of a single hydrodynamic injection surpassed those of two intraperitoneal doses of the recombinant protein. The novel functional link between circulating IL-15 and IKDCs opens new possibilities to study the biology and applications of this minority cell subset.

Immunotherapy and immunoescape in colorectal cancer

Immunotherapy encompasses a variety of interventions and techniques with the common goal of eliciting tumor cell destructive immune responses. Colorectal carcinoma often presents as metastatic disease that impedes curative surgery. Novel strategies such as active immunization with dendritic cells (DCs), gene transfer of cytokines into tumor cells or administration of immunostimulatory monoclonal antibodies (such as anti-CD137 or anti-CTLA-4) have been assessed in preclinical studies and are at an early clinical development stage. Importantly, there is accumulating evidence that chemotherapy and immunotherapy can be combined in the treatment of some cases with colorectal cancer, with synergistic potentiation as a result of antigens cross-presented by dendritic cells and/or elimination of competitor or suppressive T lymphocyte populations (regulatory T-cells). However, genetic and epigenetic unstable carcinoma cells frequently evolve mechanisms of immunoevasion that are the result of either loss of antigen presentation, or an active expression of immunosuppressive substances. Some of these actively immunosuppressive mechanisms are inducible by cytokines that signify the arrival of an effector immune response. For example, induction of 2, 3 indoleamine dioxygenase (IDO) by IFNγ in colorectal carcinoma cells. Combinational and balanced strategies fostering antigen presentation, T-cell costimulation and interference with immune regulatory mechanisms will probably take the stage in translational research in the treatment of colorectal carcinoma.

Multipotent Adult Progenitor Cells (MAPC) contribute to hepatocarcinoma neovasculature

The use of stem cells as a vehicle of therapeutic genes is an attractive approach for the development of new antitumoral strategies based on gene therapy. The aim of our study was to assess the potential of bone marrow-derived Multipotent Adult Progenitor Cells (rMAPCs) to differentiate in vitro and in vivo into endothelial cells and to be recruited to areas of tumor vasculogenesis. In vitro, rMAPCs obtained from Buffalo rats differentiated into cells expressing endothelial markers and demonstrated functional endothelial capacity. Intravenous injection of undifferentiated rMAPC transduced with a lentivirus expressing GFP in an orthotopic rat model of hepatocellular carcinoma, resulted in tumor recruitment of the injected cells and in vivo differentiation into endothelial cells in the tumor area with contribution to vasculogenesis. In summary, our results suggest that rMAPCs can be efficiently recruited by vascularized tumors and differentiate to endothelium and thus may represent a useful vehicle for delivery of therapeutic genes to sites of active tumor neovascularization.

Amphiregulin: A new growth factor in hepatocarcinogenesis

Amphiregulin (AR) is a member of the epidermal growth factor family and a ligand of the epidermal growth factor receptor (EGFR). As other ligands of the EGFR, AR is synthesized as a precursor that is shed from the plasma membrane by metalloproteases. Hyperactive autocrine loops involving AR production have been described in a variety of tumors, and this growth factor is thought to play a non-redundant role in cancer development. AR expression is not detected in the normal liver, however it is readily induced during acute liver injury and behaves as a potent pro-regenerative and survival factor. Increased AR expression is also detected in human chronic liver injury (liver cirrhosis), which is considered a pre-neoplastic condition. Recent evidences suggest that AR can play a unique role in liver tumorigenesis and in the maintenance of the neoplastic phenotype of hepatocarcinoma cells. In this review, we summarize some aspects of AR patho-biology and the rationale behind its definition as a novel target in hepatocarcinoma therapy.

New molecular targets for hepatocellular carcinoma: the ErbB1 signaling system

Hepatocellular carcinoma (HCC) is a major cause of cancer-related deaths. This malignancy is often diagnosed at an advanced state, when most potentially curative therapies are of limited efficacy. In addition, HCC is a type of tumor highly resistant to available chemotherapeutic agents, which leaves HCC patients with no effective therapeutic options and a poor prognosis. From a molecular perspective, HCC is a heterogeneous type of tumor. However, in most cases, HCC emerges on a background of persistent liver injury, inflammation and hepatocellular proliferation, which is characteristic of chronic hepatitis and cirrhosis. Recent studies have revealed that dysregulation of a limited number of growth and survival-related pathways can play a key role in HCC development. The epidermal growth factor receptor (ErbB1) can be bound and activated by a broad family of ligands, and can also engage in extensive cross talk with other signaling pathways. This system is considered as an important defense mechanism for the liver during acute tissue injury; however, accumulating evidences suggest that its chronic stimulation can participate in the neoplastic conversion of the liver. Agents that target the ErbB1 receptor have shown antineoplastic activity in other types of tumors, but their efficacy either alone or in combination with other compounds has just started to be tested in experimental and human HCC. Here, we review the evidences that support the involvement of the ErbB1 in HCC development and that provide a rationale for ErbB1 targeting in HCC prevention and treatment.

Cardiotrophin-1 defends the liver against ischemia-reperfusion injury and mediates the protective effect of ischemic preconditioning

Ischemia-reperfusion (I/R) liver injury occurs when blood flow is restored after prolonged ischemia. A short interruption of blood flow (ischemic preconditioning [IP]) induces tolerance to subsequent prolonged ischemia through ill-defined mechanisms. Cardiotrophin (CT)-1, a cytokine of the interleukin-6 family, exerts hepatoprotective effects and activates key survival pathways like JAK/STAT3. Here we show that administration of CT-1 to rats or mice protects against I/R liver injury and that CT-1-deficient mice are exceedingly sensitive to this type of damage. IP markedly reduced transaminase levels and abrogated caspase-3 and c-Jun-NH2-terminal kinase activation after I/R in normal mice but not in CT-1-null mice. Moreover, the protective effect afforded by IP was reduced by previous administration of neutralizing anti-CT-1 antibody. Prominent STAT3 phosphorylation in liver tissue was observed after IP plus I/R in normal mice but not in CT-1-null mice. Oxidative stress, a process involved in IP-induced hepatoprotection, was found to stimulate CT-1 release from isolated hepatocytes. Interestingly, brief ischemia followed by short reperfusion caused mild serum transaminase elevation and strong STAT3 activation in normal and IL-6-deficient mice, but failed to activate STAT3 and provoked marked hypertransaminasemia in CT-1-null animals. In conclusion, CT-1 is an essential endogenous defense of the liver against I/R and is a key mediator of the protective effect induced by IP.

Methylthioadenosine reverses brain autoimmune disease

OBJECTIVE

To assess the immunomodulatory activity of methylthioadenosine (MTA) in rodent experimental autoimmune encephalomyelitis (EAE) and in patients with multiple sclerosis.

METHODS

We studied the effect of intraperitoneal MTA in the acute and chronic EAE model by quantifying clinical and histological scores and by performing immunohistochemistry stains of the brain. We studied the immunomodulatory effect of MTA in lymphocytes from EAE animals and in peripheral blood mononuclear cells from healthy control subjects and multiple sclerosis patients by assessing cell proliferation and cytokine gene expression, by real-time polymerase chain reaction, and by nuclear factor-kappaB modulation by Western blot.

RESULTS

We found that MTA prevents acute EAE and, more importantly, reverses chronic-relapsing EAE. MTA treatment markedly inhibited brain inflammation and reduced brain damage. Administration of MTA suppressed T-cell activation in vivo and in vitro, likely through a blockade in T-cell signaling resulting in the prevention of inhibitor of kappa B (IkappaB-alpha) degradation and in the impaired activation transcription factor nuclear factor-kappaB. Indeed, MTA suppressed the production of proinflammatory genes and cytokines (interferon-gamma, tumor necrosis factor-alpha, and inducible nitric oxide synthase) and increased the production of antiinflammatory cytokines (interleukin-10).

INTERPRETATION

MTA has a remarkable immunomodulatory activity and may be beneficial for multiple sclerosis and other autoimmune diseases.

New therapies for hepatocellular carcinoma

Hepatocellular carcinoma (HCC), one of the most common cancers worldwide, is often diagnosed at an advanced stage when most potentially curative therapies such as resection, transplantation or percutaneous and transarterial interventions are of limited efficacy. The fact that HCC is resistant to conventional chemotherapy, and is rarely amenable to radiotherapy, leaves this disease with no effective therapeutic options and a very poor prognosis. Therefore, the development of more effective therapeutic tools and strategies is much needed. HCCs are phenotypically and genetically heterogeneous tumors that commonly emerge on a background of chronic liver disease. However, in spite of this heterogeneity recent insights into the biology of HCC suggest that certain signaling pathways and molecular alterations are likely to play essential roles in HCC development by promoting cell growth and survival. The identification of such mechanisms may open new avenues for the prevention and treatment of HCC through the development of targeted therapies. In this review we will describe the new potential therapeutic targets and clinical developments that have emerged from progress in the knowledge of HCC biology, In addition, recent advances in gene therapy and combined cell and gene therapy, together with new radiotherapy techniques and immunotherapy in patients with HCC will be discussed.

Amphiregulin Contributes to the Transformed Phenotype of Human Hepatocellular Carcinoma Cells

Hepatocellular carcinoma is a major cause of cancer-related deaths. Current treatments are not effective, and the identification of relevant pathways and novel therapeutic targets are much needed. Increasing evidences point to the activation of the epidermal growth factor receptor (EGFR) as an important mechanism in the development of hepatocarcinoma. We previously described that amphiregulin (AR), a ligand of the EGFR, is not expressed in healthy liver but is up-regulated during chronic liver injury, the background on which most liver tumors develop. Now, we have studied the expression and role of AR in human hepatocarcinoma. AR expression and function was studied in human liver tumors and cell lines. AR is expressed in human hepatocellular carcinoma tissues and cell lines and behaves as a mitogenic and antiapoptotic growth factor for hepatocarcinoma cells. We provide several lines of evidence, including AR silencing by small interfering RNAs and inhibition of amphiregulin by neutralizing antibodies, showing the existence of an AR-mediated autocrine loop that contributes to the transformed phenotype. Indeed, interference with endogenous AR production resulted in reduced constitutive EGFR signaling, inhibition of cell proliferation, anchorage-independent growth, and enhanced apoptosis. Moreover, knockdown of AR potentiated transforming growth factor-beta and doxorubicin-induced apoptosis. Conversely, overexpression of AR in SK-Hep1 cells enhanced their proliferation rate, anchorage-independent growth, drug resistance, and in vivo tumorigenic potential. These observations suggest that AR is involved in the acquisition of neoplastic traits in the liver and thus constitutes a novel therapeutic target in human hepatocarcinoma.

Differential regulation of the JNK/AP-1 pathway by S-adenosylmethionine and methylthioadenosine in primary rat hepatocytes versus HuH7 hepatoma cells

S-adenosylmethionine (AdoMet) and 5'-methylthioadenosine (MTA) exert a protective action on apoptosis induced by okadaic acid in primary rat hepatocytes but not in human transformed HuH7 cells. In the present work, we analyzed the role played by the JNK/activator protein (AP)-1 pathway in this differential effect. Okadaic acid induced the phosphorylation of JNK and c-Jun and the binding activity of AP-1 in primary hepatocytes, and pretreatment with either AdoMet or MTA prevented those effects. In HuH7 cells, pretreatment with either AdoMet or MTA did not affect JNK and c-Jun activation or AP-1 binding induced by okadaic acid. In both cell types, p38 was activated by okadaic acid, but neither AdoMet nor MTA presented a significant effect on its activity. Therefore, the differential effect of both AdoMet and MTA on the JNK/AP-1 pathway could explain their antiapoptotic effect on primary hepatocytes and the lack of protection they show against okadaic acid-induced apoptosis in hepatoma cells.

Low surface expression of B7-1 (CD80) is an immunoescape mechanism of colon carcinoma

Artificially enforced expression of CD80 (B7-1) and CD86 (B7-2) on tumor cells renders them more immunogenic by triggering the CD28 receptor on T cells. The enigma is that such B7s interact with much higher affinity with CTLA-4 (CD152), an inhibitory receptor expressed by activated T cells. We show that unmutated CD80 is spontaneously expressed at low levels by mouse colon carcinoma cell lines and other transplantable tumor cell lines of various tissue origins. Silencing of CD80 by interfering RNA led to loss of tumorigenicity of CT26 colon carcinoma in immunocompetent mice, but not in immunodeficient Rag-/- mice. CT26 tumor cells bind CTLA-4Ig, but much more faintly with a similar CD28Ig chimeric protein, thus providing an explanation for the dominant inhibitory effects on tumor immunity displayed by CD80 at that expression level. Interestingly, CD80-negative tumor cell lines such as MC38 colon carcinoma and B16 melanoma express CD80 at dim levels during in vivo growth in syngeneic mice. Therefore, low CD80 surface expression seems to give an advantage to cancer cells against the immune system. Our findings are similar with the inhibitory role described for the dim CD80 expression on immature dendritic cells, providing an explanation for the low levels of CD80 expression described in various human malignancies.

Molecular Profiling of Hepatocellular Carcinoma in Mice with a Chronic Deficiency of HepaticS-Adenosylmethionine: Relevance in Human Liver Diseases

S-adenosylmethionine arises as a central molecule in the preservation of liver homeostasis as a chronic hepatic deficiency results in spontaneous development of steatohepatitis and hepatocellular carcinoma. In the present work, we have attempted a comprehensive analysis of proteins associated with hepatocarcinogenesis in MAT1A knock out mice using a combination of two-dimensional electrophoresis and mass spectrometry, to then apply the resulting information to identify hallmarks of human HCC. Our results suggest the existence of individual-specific factors that might condition the development of preneoplastic lesions. Proteomic analysis allowed the identification of 151 differential proteins in MAT1A-/- mice tumors. Among all differential proteins, 27 changed in at least 50% of the analyzed tumors, and some of these alterations were already detected months before the development of HCC in the KO liver. The expression level of genes coding for 13 of these proteins was markedly decreased in human HCC. Interestingly, seven of these genes were also found to be down-regulated in a pretumoral condition such as cirrhosis, while depletion of only one marker was assessed in less severe liver disorders.

Up-regulation of the anti-inflammatory adipokine adiponectin in acute liver failure in mice

BACKGROUND/AIMS

Recent reports suggest that the adipose tissue and adipokines are potent modulators of inflammation. However, there is only scarce knowledge on the functional role and regulation of endogenous adiponectin in non-fat tissues such as the liver under conditions of acute inflammation.

METHODS

In the present study, we investigated adiponectin expression in healthy murine liver tissue and under inflammatory conditions in vivo.

RESULTS

Adiponectin mRNA was readily detectable in healthy liver tissue and further increased in ConA-mediated acute liver failure. Adiponectin protein expression was mainly found in hepatic endothelial cells. In vitro adiponectin mRNA expression was detectable in several cell types, including primary hepatic sinusoidal endothelial cells, stellate cells, and macrophages. Mice pretreated with adiponectin before ConA administration developed reduced hepatic injury as shown by decreased release of transaminases and reduced hepatocellular apoptotis. Of note, TNF-alpha levels were not affected by adiponectin, whereas IL-10 production was increased. Neutralisation of IL-10 diminished the protective effect of adiponectin.

CONCLUSIONS

Adiponectin expression is up-regulated in ConA-mediated acute liver failure. Therefore, adiponectin might play a role in the control and limitation of inflammation in the liver. Moreover, our data suggest a role for IL-10 in adiponectin-mediated hepatoprotection.

Hepatitis C virus infection of primary tupaia hepatocytes leads to selection of quasispecies variants, induction of interferon-stimulated genes and NF-κB nuclear translocation

Systems for in vitro culture of Hepatitis C virus (HCV) are essential tools to analyse virus–cell interactions and to investigate relevant pathophysiological aspects of HCV infection. Although the HCV replicon methodology has increased our understanding of HCV biology, this system does not reproduce the natural infection. Recently, tupaia (Tupaia belangeri chinensis) hepatocytes have been utilized for in vitro culture of HCV. In the present work, primary tupaia hepatocytes infected in vitro with HCV were used to analyse the evolution of HCV quasispecies in infected cells and the ability of the virus to influence antiviral and proinflammatory responses in cells sustaining virus replication. The results confirmed the potential of tupaia hepatocytes as a model for HCV infection, although this system is limited by rapid loss of differentiated cell phenotype in culture. These findings revealed an extraordinary plasticity of HCV quasispecies, which underwent rapid evolution to tupaia-tropic variants as early as 24 h after infection. It was also shown that HCV could activate interferon-sensitive genes, albeit modestly in comparison with other viruses such as Semliki Forest virus. Importantly, HCV activated NF-κB in primary hepatocytes and upregulated NF-κB-responsive genes including the chemokines MCP-1 and CXCL2 (MIP-2). This effect may play a role in induction of the hepatic inflammatory reaction in vivo. In summary, HCV quasispecies adapt rapidly to the specific biology of the host and HCV stimulates a blunted interferon response while inducing a proinflammatory phenotype in the infected cell.

Influence of impaired liver methionine metabolism on the development of vascular disease and inflammation

Methionine (Met) metabolism involves the sequential formation of S-adenosylmethionine (SAM, the main biological methyl donor), S-adenosylhomocysteine (SAH) and homocysteine (Hcy). Hcy can be remethylated to Met or catabolized through the trans-sulfuration pathway. In mammals, as much as 48% of Met metabolism and up to 85% of all transmethylation reactions occur in the liver. These figures underscore the central role played by this organ in Met metabolism. Maintaining the homeostasis of this metabolic cycle has proved to be essential for the preservation of liver function up to the point of preventing its neoplastic transformation. However, an adequate hepatic metabolism of Met is not only important for the liver parenchymal cell. Evidence has accumulated over the past few years supporting the involvement of Met-derived metabolites in the triggering or attenuation of pathological processes with systemic implications. This is best illustrated by the fact that a deteriorated liver function has emerged as a major factor in the development of hyperhomocysteinemia. Elevated plasma levels of Hcy have been related to several disorders including cardiovascular and cerebrovascular diseases. On the other end, liver damage also leads to deficient SAM synthesis. Among the consequences of impaired SAM synthesis in liver tissue are the enhanced production of pro-inflammatory cytokines and mediators. In this review, we will address the mechanisms and consequences of abnormal Met metabolism in liver injury, the systemic implications of such impairment and finally the potential therapeutic interventions.