Interferons activate the p42/44 mitogen-activated protein kinase and JAK-STAT (Janus kinase-signal transducer and activator transcription factor) signalling pathways in hepatocytes: differential regulation by acute ethanol via a protein kinase C-dependent mechanism

Acetaldehyde Disrupts Interferon Alpha Signaling in Hepatitis C Virus-Infected Liver Cells by Up-Regulating USP18

BACKGROUND

Alcohol consumption exacerbates the pathogenesis of hepatitis C virus (HCV) infection and worsens disease outcomes. The exact reasons are not clear yet, but they might be partially attributed to the ability of alcohol to further suppress the innate immunity. Innate immunity is known to be already decreased by HCV in liver cells.

METHODS

In this study, we aimed to explore the mechanisms of how alcohol metabolism dysregulates IFNα signaling (STAT1 phosphorylation) in HCV⁺ hepatoma cells. To this end, CYP2E1⁺ Huh7.5 cells were infected with HCV and exposed to the acetaldehyde (Ach) generating system (AGS).

RESULTS

Continuously produced Ach suppressed IFNα-induced STAT1 phosphorylation, but increased the level of a protease, USP18 (both measured by Western blot), which interferes with IFNα signaling. Induction of USP18 by Ach was confirmed in primary human hepatocyte cultures and in livers of ethanol-fed HCV transgenic mice. Silencing of USP18 by specific siRNA attenuated the pSTAT1 suppression by Ach. The mechanism by which Ach down-regulates pSTAT1 is related to an enhanced interaction between IFNαR2 and USP18 that finally dysregulates the cross talk between the IFN receptor on the cell surface and STAT1. Furthermore, Ach decreases ISGylation of STAT1 (protein conjugation of a small ubiquitin-like modifier, ISG15, Western blot), which preserves STAT1 activation. Suppressed ISGylation leads to an increase in STAT1 K48 polyubiquitination which allows pSTAT1 degrading by proteasome.

CONCLUSIONS

We conclude that Ach disrupts IFNα-induced STAT1 phosphorylation by the up-regulation of USP18 to block the innate immunity protection in HCV-infected liver cells, thereby contributing to HCV-alcohol pathogenesis. This, in part, may explain the mechanism of HCV-infection exacerbation/progression in alcohol-abusing patients.

IFNλ Stimulates MxA Production in Human Dermal Fibroblasts via a MAPK-Dependent STAT1-Independent Mechanism

IFNλ is important for epidermal defense against viruses. It is produced by, and acts on, keratinocytes, whereas fibroblasts were previously considered to be unresponsive to this type III IFN. Herein we report findings revealing cell type-specific differences in IFNλ signaling and function in skin resident cells. In dermal fibroblasts, IFNλ induced the expression of myxovirus protein A (MxA), a potent antiviral factor, but not other IFN signature genes as it does in primary keratinocytes. In contrast to its effect on keratinocytes, IFNλ did not phosphorylate signal transducer and activator of transcription 1 in fibroblasts, but instead activated mitogen activated protein kinases (MAPK). Accordingly, inhibition of MAPK activation (p38 and p42/44) blocked the expression of MxA protein in fibroblasts but not in keratinocytes. Functionally, IFNλ inhibited proliferation in keratinocytes but not in fibroblasts. Moreover, IFNλ upregulated the expression of Tumor growth factor beta 1 (TGFβ1)-induced collagens in fibroblasts. Taken together, our findings identify primary human dermal fibroblasts as responder cells to IFNλ. Our study shows cutaneous cell type-specific IFN signaling and suggests that IFNλ, although important for epidermal antiviral competence, may also have a regulatory role in the dermal compartment balancing type I IFN-induced inhibition of tissue repair processes.

Acetaldehyde accelerates HCV-induced impairment of innate immunity by suppressing methylation reactions in liver cells

Alcohol exposure worsens the course and outcomes of hepatitis C virus (HCV) infection. Activation of protective antiviral genes is induced by IFN-α signaling, which is altered in liver cells by either HCV or ethanol exposure. However, the mechanisms of the combined effects of HCV and ethanol metabolism in IFN-α signaling modulation are not well elucidated. Here, we explored a possibility that ethanol metabolism potentiates HCV-mediated dysregulation of IFN-α signaling in liver cells via impairment of methylation reactions. HCV-infected Huh7.5 CYP2E1(+) cells and human hepatocytes were exposed to acetaldehyde (Ach)-generating system (AGS) and stimulated with IFN-α to activate IFN-sensitive genes (ISG) via the Jak-STAT-1 pathway. We observed significant suppression of signaling events by Ach. Ach exposure decreased STAT-1 methylation via activation of protein phosphatase 2A and increased the protein inhibitor of activated STAT-1 (PIAS-1)-STAT-1 complex formation in both HCV(+) and HCV(-) cells, preventing ISG activation. Treatment with a promethylating agent, betaine, attenuated all examined Ach-induced defects. Ethanol metabolism-induced changes in ISGs are methylation related and confirmed by in vivo studies on HCV(+) transgenic mice. HCV- and Ach-induced impairment of IFN signaling temporarily increased HCV RNA levels followed by apoptosis of heavily infected cells. We concluded that Ach potentiates the suppressive effects of HCV on activation of ISGs attributable to methylation-dependent dysregulation of IFN-α signaling. A temporary increase in HCV RNA sensitizes the liver cells to Ach-induced apoptosis. Betaine reverses the inhibitory effects of Ach on IFN signaling and thus can be used for treatment of HCV(+) alcohol-abusing patients.

Mechanism of Macrophage-Derived Chemokine/CCL22 Production by HaCaT Keratinocytes

Background

CC chemokine ligand 17 (CCL17) and CCL22 are the functional ligands for CCR4. We previously reported that inhibitors of nuclear factor-kappa B and p38 mitogen-activated protein kinase (p38 MAPK), but not of extracellular signal-related kinase (ERK), inhibited tumor necrosis factor (TNF)-α- and interferon (IFN)-γ-induced production of CCL17 by the human keratinocyte cell line, HaCaT. Further, an inhibitor of epidermal growth factor receptor (EGFR) enhanced the CCL17 production by these keratinocytes.

Objective

To identify the mechanism underlying CCL22 production by HaCaT cells.

Methods

We investigated the signal transduction pathways by which TNF-α and IFN-γ stimulate HaCaT cells to produce CCL22 by adding various inhibitors.

Results

TNF-α- and IFN-γ-induced CCL22 production was inhibited by PD98059, PD153035, Bay 11-7085, SB202190, c-Jun N-terminal kinase (JNK) inhibitor II, and Janus kinase (JAK) inhibitor 1.

Conclusion

Our results indicate that CCL22 production in HaCaT cells is dependent on ERK, EGFR, p38 MAPK, JNK, and JAK and is mediated by different signal pathways from those regulating CCL17 production. Altogether, our previous and present results suggest that EGFR activation represses CCL17 but enhances CCL22 production by these cells.

Hepatitis C, innate immunity and alcohol: friends or foes?

Hepatitis C and alcohol are the most widespread causes of liver disease worldwide. Approximately 80% of patients with a history of hepatitis C and alcohol abuse develop chronic liver injury. Alcohol consumption in hepatitis C virus (HCV)-infected patients exacerbates liver disease leading to rapid progression of fibrosis, cirrhosis and even hepatocellular carcinoma. Hepatocytes are the main sites of HCV-infection and ethanol metabolism, both of which generate oxidative stress. Oxidative stress levels affect HCV replication and innate immunity, resulting in a greater susceptibility for HCV-infection and virus spread in the alcoholic patients. In this review paper, we analyze the effects of ethanol metabolism and other factors on HCV replication. In addition, we illustrate the mechanisms of how HCV hijacks innate immunity and how ethanol exposure regulates this process. We also clarify the effects of HCV and ethanol metabolism on interferon signaling-a crucial point for activation of anti-viral genes to protect cells from virus-and the role that HCV- and ethanol-induced impairments play in adaptive immunity which is necessary for recognition of virally-infected hepatocytes. In conclusion, ethanol exposure potentiates the suppressive effects of HCV on innate immunity, which activates viral spread in the liver and finally, leads to impairments in adaptive immunity. The dysregulation of immune response results in impaired elimination of HCV-infected cells, viral persistence, progressive liver damage and establishment of chronic infection that worsens the outcomes of chronic hepatitis C in alcoholic patients.

Inhibition of tumor growth by U0126 is associated with induction of interferon-γ production

Several MEK1/2 inhibitors have been in clinical trial evaluation for cancer treatment. Interferon-γ (IFN-γ) is a cytokine with multiple biological functions including antitumor activity. Expression of IFN-γ can be induced by liver X receptor (LXR), a ligand-activated transcription factor. However, it remains unknown if the anti-cancer action of MEK1/2 inhibitors is completed, at least in part, by activating IFN-γ expression. In this study, we determined that U0126, a MEK1/2 inhibitor, increased tumor-free and survival rates and decreased growth of inoculated Lewis lung carcinomas in wild type mice. However, the protective effects were substantially attenuated in IFN-γ deficient (IFN-γ-/-) mice. At cellular and molecular levels, MEK1/2 inhibitors increased IFN-γ protein and mRNA expression and activated natural IFN-γ promoter but not the IFN-γ promoters with mutations of the LXR responsive elements (LXREs). MEK1/2 inhibitors also enhanced formation of the LXRE-nuclear protein complexes by inducing LXR expression and nuclear translocation. Similarly, MEK1/2 siRNA inhibited phosphorylation of ERK1/2 by MEK1/2 while activated IFN-γ expression. In contrast, inhibition of LXR expression by siRNA blocked MEK1/2 inhibitors-induced IFN-γ expression. U0126 also inhibited chemicals-induced pulmonary carcinomas, which was associated with increased IFN-γ expression in the lung. Taken together, our study suggests that MEK1/2 inhibitors induce IFN-γ production in an LXR-dependent manner and the induction of IFN-γ expression can partially contribute to the anti-tumorigenic properties of U0126.

Signal transducer and activator of transcription 5b (Stat5b) serine 193 is a novel cytokine-induced phospho-regulatory site that is constitutively activated in primary hematopoietic malignancies

Signal transducer and activator of transcription 5b (Stat5b) is a critical node in the signaling network downstream of external (cytokines or growth factors) or internal (oncogenic tyrosine kinases) stimuli. Maximum transcriptional activation of Stat5b requires both tyrosine and serine phosphorylation. Although the mechanisms governing tyrosine phosphorylation and activation of Stat5b have been extensively studied, the role of serine phosphorylation remains to be fully elucidated. Using mass spectrometry and phospho-specific antibodies, we identified Ser-193 as a novel site of cytokine-induced phosphorylation within human Stat5b. Stat5b Ser(P)-193 was detected in activated primary human peripheral blood mononuclear cells or lymphoid cell lines in response to several γ common (γc) cytokines, including interleukin (IL)-2, IL-7, IL-9, and IL-15. Kinetic and spatial analysis indicated that Stat5b Ser-193 phosphorylation was rapid and transient and occurred in the cytoplasmic compartment of the cell prior to Stat5b translocation to the nucleus. Moreover, inducible Stat5b Ser-193 phosphorylation was sensitive to inhibitors of mammalian target of rapamycin (mTOR), whereas inhibition of protein phosphatase 2A (PP2A) induced phosphorylation of Ser-193. Reconstitution assays in HEK293 cells in conjunction with site-directed mutagenesis, EMSA, and reporter assays indicated that Ser(P)-193 is required for maximal Stat5b transcriptional activity. Indeed, Stat5b Ser-193 was found constitutively phosphorylated in several lymphoid tumor cell lines as well as primary leukemia and lymphoma patient tumor cells. Taken together, IL-2 family cytokines tightly control Stat5b Ser-193 phosphorylation through a rapamycin-sensitive mechanism. Furthermore, constitutive Ser-193 phosphorylation is associated with Stat5b proto-oncogenic activity and therefore may serve as a novel therapeutic target for treating hematopoietic malignancies.

Activation of mitogen-activated protein kinases by 5,6-dimethylxanthenone-4-acetic acid (DMXAA) plays an important role in macrophage stimulation

The small molecule anti-tumor agent, 5,6-dimethylxanthenone-4-acetic acid (DMXAA, now called Vadimezan) is a potent macrophage and dendritic cell activating agent that, in the murine system, results in the release of large amounts of cytokines and chemokines. The mechanisms by which this release is mediated have not been fully elucidated. The mitogen-activated protein kinase (MAPK) pathways play an important role in the regulation of proinflammatory cytokines, such as TNF-α, IL-1β, as well as the responses to extracellular stimuli, such as lipopolysaccharide (LPS). The results of this study demonstrate that DMXAA activates three members of mitogen-activated protein kinase (MAPK) superfamily, namely p38 MAPK, extracellular signal-regulated kinases 1 and 2 (ERK1 and ERK2), and c-Jun N-terminal kinases (JNKs) via a RIP2-independent mechanism in murine macrophages. By using selective inhibitors of MAPKs, this study confirms that both activated p38/MK2 pathways and ERK1/2 MAPK play a significant role in regulation of both TNF-α and IL-6 protein production induced by DMXAA at the post-transcriptional level. Our findings also show that interferon-γ priming can dramatically augment TNF-α protein secretion induced by DMXAA through enhancing activation of multiple MAPK pathways at the post-transcriptional level. This study expands current knowledge on mechanisms of how DMXAA acts as a potent anti-tumor agent in murine system and also provides useful information for further study on the mechanism of action of this potential anti-tumor compound in human macrophages.

Bambusae caulis in Liquamen Suppresses the Expression of Thymus and Activation-Regulated Chemokine and Macrophage-Derived Chemokine in Human Keratinocytes due to Antioxidant Effect

Bambusae caulis in Liquamen (BCL), traditional herbal medicine used in East Asia, is known to have antioxidative and immune-regulating properties. We hypothesized that the potential antioxidant effects of BCL might suppress the production of thymus and activation-regulated chemokine (TARC) and macrophage-derived chemokine (MDC) in human keratinocytes (HaCaT cell). The immune-regulating effect of BCL was demonstrated by antioxidant capacity using DPPH analysis and DCFH-DA analysis. We found that BCL had strong ROS scavenge effect in HaCaT cell. BCL also showed suppression of IFN-γ-induced expression of TARC and MDC, activation of NF-κB, and, moreover, significant block of IFN-γ-induced degradation and phosphorylation of IκB. However, it had no effects on phosphorylation of p38 MAPK. Collectively, these results suggest that BCL may have a therapeutic potential on skin disease such as atopic dermatitis by inhibiting Th2 chemokines which is due, at least in part, to its antioxidant capacities.

Involvement of ERK and JNK pathways in IFN-γ-induced B7-DC expression on tumor cells

PURPOSE

B7-DC on tumor cells was demonstrated to promote tumor immunity; however, the precise mechanism responsible for the aberrant B7-DC expression remains unknown. Interferon gamma (IFN-γ) can induce B7-DC expression on macrophages and has been shown to regulate anti-tumor immunity by various mechanisms. This study was designed to investigate the relationship of IFN-γ and B7-DC on tumor cells and further explored the signal transduction pathways involved.

METHODS

RT-PCR and flow cytometry were used for the analysis of B7-DC expression on various tumor cells. The phosphorylation of p38, ERK1/2, JNK, Akt, and JAK2 was determined by Western blot.

RESULTS

IFN-γ markedly up-regulated B7-DC expression on various tumor cells and resulted in the phosphorylation of JAK2, JNK, ERK, p38, and Akt. Inhibition of ERK or JNK pathway significantly decreased IFN-c-induced B7-DC expression, whereas inhibition of phosphorylation of Akt, p38, and JAK2 had very little effect on IFN-γ-induced B7-DC expression.

CONCLUSIONS

Our findings demonstrate that the pretreatment of tumor cells with IFN-γ enhances B7-DC expression through ERK and JNK pathways.

Fluvastatin inhibits expression of the chemokine MDC/CCL22 induced by interferon-gamma in HaCaT cells, a human keratinocyte cell line

BACKGROUND AND PURPOSE

The macrophage-derived chemokine (MDC/CCL22) is a prototypic Th2-type chemokine intimately involved in Th2-skewed allergic diseases, such as atopic dermatitis and asthma. The statins (3-hydroxy-3-methyl glutaryl coenzyme A reductase inhibitors) have been demonstrated to relieve allergic inflammation. However, the immunological effects and mechanisms of statins against atopic dermatitis remain unknown, at least in vitro. This study aimed to define how different statins affect MDC expression in HaCaT cells, a human keratinocyte cell line.

EXPERIMENTAL APPROACH

To measure the effects of statins on MDC expression in HaCaT cells, we used a cell viability assay, reverse transcription-polymerase chain reaction, enzyme-linked immunosorbent assay and Western blotting analyses.

KEY RESULTS

Fluvastatin, but not atorvastatin or simvastatin, inhibited MDC expression induced by interferon (IFN)-gamma and NF-kappaB activation. A NF-kappaB inhibitor, but not a STAT1 inhibitor, suppressed MDC expression in HaCaT cells. Further, inhibition of p38 mitogen-activated protein kinases (MAPKs) significantly suppressed IFN-gamma-induced MDC expression and NF-kappaB activation. Interestingly, fluvastatin suppressed IFN-gamma-induced NF-kappaB activation in parallel with p38 MAPK phosphorylation.

CONCLUSIONS AND IMPLICATIONS

These results indicate that fluvastatin inhibited expression of the CC chemokine MDC induced by IFN-gamma in HaCaT cells, by inhibiting NF-kappaB activation via the p38 MAPK pathway. This blockade of a Th2 chemokine by fluvastatin may suppress the infiltration of Th2 cells into skin lesions and lessen the skin inflammation seen in atopic dermatitis, suggesting a potential therapeutic use of fluvastatin for this condition.

The adenylyl cyclase-cAMP system suppresses TARC/CCL17 and MDC/CCL22 production through p38 MAPK and NF-kappaB in HaCaT keratinocytes

Patients with atopic dermatitis (AD) have significantly reduced plasma cAMP levels, and the cAMP level is correlated with the immunopathogenesis of AD. The production of thymus and activation-regulated chemokine (TARC/CCL17) and macrophage-derived chemokine (MDC/CCL22) in keratinocytes is significantly enhanced in patients with AD. In the present study, we investigated the in vitro effects of the adenylyl cyclase-cAMP system on IFN-gamma and TNF-alpha-stimulated production of TARC and MDC in human HaCaT keratinocytes. Both forskolin (a direct activator of adenylyl cyclase) and dibutyryl-cAMP (DBcAMP, a permeable analog of cAMP) suppressed production of TARC and MDC in parallel with the activation of NF-kappaB in IFN-gamma and TNF-alpha-stimulated HaCaT cells. Moreover, inhibition of NF-kappaB suppressed TARC and MDC production induced by IFN-gamma plus TNF-alpha. However, dideoxyforskolin, a forskolin derivative that does not activate cAMP, failed to suppress the secretion of these chemokines. An inhibitor of p38 MAPK suppressed the production of TARC and MDC in parallel to the activation of NF-kappaB in HaCaT cells. Of note, the IFN-gamma plus TNF-alpha-stimulated activation of p38 MAPK was suppressed following incubation with forskolin or DBcAMP alone. These results indicate that the adenylyl cyclase-cAMP system has an inhibitory role in IFN-gamma plus TNF-alpha-stimulated production of TARC and MDC in HaCaT keratinocytes by inhibiting NF-kappaB activation through p38 MAPK pathway, implying that the adenylyl cyclase-cAMP system could be a candidate therapeutic target of Th2-skewed skin inflammation such as AD.

Lymph node architecture collapse and consequent modulation of FOXO3a pathway on memory T- and B-cells during HIV infection

Lymph nodes (LNs) represent the principal site where antigen-specific memory T- and B-cell responses are primed and differentiated into memory and effector cells. During chronic viral infections such as HIV, these lymphoid tissues undergo substantial structural changes. These changes are mostly caused by an imbalanced cytokine milieu, hyper-immune activation and collagen deposition leading to fibrotic LNs. The structural integrity of the LNs is essential to prime and maintain memory responses. Because cellular signalling events both up- and down-stream of FOXO3a are critical to the generation and the maintenance of lymphocyte memory, this review will focus on the interplay between the deregulation of the immune system caused by the virus and its impact on FOXO3a.

Acute alcohol intake induces SOCS1 and SOCS3 and inhibits cytokine-induced STAT1 and STAT3 signaling in human monocytes

BACKGROUND

Acute alcohol consumption is associated with induction of immuno-inhibitory cytokines and down-regulation of pro-inflammatory responses to various pathogens. We previously reported that alcohol activates janus kinase/signal transducer and activator of transcription (JAK/STAT) signaling leading to IL-10 induction. The JAK-STAT pathway also activates its own negative regulators, suppressors of cytokine signaling (SOCS) 1 and SOCS3. SOCS proteins are inducible inhibitors that negatively regulate STAT3/STAT1 signaling pathways induced by cytokines, IL-6 or IFNs. Here we aimed to explore the effect of acute alcohol on induction of SOCS1/SOCS3 and regulation of STAT3/STAT1 pathways induced by IL-6 or IFNs in human monocytes.

METHODS

Blood samples from normal volunteers were collected before and 24 hours after consumption of 2 ml vodka/kg body weight. For in vitro experiments human monocytes were pretreated with ethanol (EtOH) followed by stimulation with cytokines; proteins were analyzed by Western blot, nuclear protein binding to DNA by EMSA, and RNA by real time PCR.

RESULTS

Acute in vivo or in vitro alcohol treatment increased both SOCS1 and SOCS3 RNA expression in monocytes. Alcohol treatment resulted in increased STAT3 and STAT1 DNA binding capacity. Activation of both STAT1 and STAT3 has been shown to induce SOCS1/3. We hypothesized that induction of SOCS proteins by alcohol in turn may lead to modulation of cytokine signaling through STAT1 and STAT3. Indeed, we observed significant down-regulation of IL-6-, IFNalpha- and IFNgamma-induced STAT1 DNA binding as well as inhibition of IL-6- and IFNgamma-induced STAT3 when alcohol was added to monocytes 3 hours prior to the cytokine stimulation. Consistent with inhibition of IL-6-induced STAT3 DNA binding in alcohol-pretreated cells, the levels of IL-6-dependent genes, MCP-1 and ICAM-1, was reduced after IL-6 stimulation. Similar to EtOH alone, combined EtOH+IL-6 simulation resulted in increased expression of both SOCS3 and SOCS1 genes.

CONCLUSION

While acute alcohol treatment alone activates STAT1/3 signaling pathways and induces SOCS3 and SOCS1 levels in monocytes, alcohol also leads to down-regulation of IL-6-, IFNalpha-, and IFNgamma-induced signaling via STAT1/STAT3 pathways, likely through excessive SOCS activation.

Abrogation of the antifibrotic effects of natural killer cells/interferon-gamma contributes to alcohol acceleration of liver fibrosis

BACKGROUND & AIMS

Chronic alcohol drinking accelerates liver fibrosis in patients with viral hepatitis that cannot be fully explained by ethanol-enhanced liver damage. Here, we identified a novel mechanism by which alcohol accelerates liver fibrosis: inhibition of the antifibrotic effects of natural killer (NK) cells and interferon-gamma (IFN-gamma).

METHODS

Alcohol administration was achieved by feeding mice with a liquid diet containing 5% ethanol for 8 weeks. Liver fibrosis was induced by administration of carbon tetrachloride (CCl(4)) for 2 weeks. Hepatic stellate cells (HSCs) were also isolated and cultured for in vitro studies.

RESULTS

CCl(4) treatment induced greater fibrosis and less apoptosis of HSCs in ethanol-fed mice compared with pair-fed mice. Polyinosinic-polycytidylic acid (Poly I:C) or IFN-gamma treatment inhibited liver fibrosis in pair-fed but not in ethanol-fed mice. Poly I:C activation of NK cell cytotoxicity against HSCs was attenuated in ethanol-fed mice compared with pair-fed mice, which was due to reduced natural killer group 2 member D (NKG2D), tumor necrosis factor-related apoptosis-inducing ligand, and IFN-gamma expression on NK cells from ethanol-fed mice. In vitro, HSCs from ethanol-fed mice were resistant to IFN-gamma-induced cell cycle arrest and apoptosis compared with pair-fed mice. Such resistance was due to diminished IFN-gamma activation of signal transducer and activator of transcription 1 (STAT1) in HSCs from ethanol-fed mice caused by the induction of suppressors of cytokine signaling proteins and the production of oxidative stress. Finally, HSCs from ethanol-fed mice were resistant to NK cell killing, which can be reversed by transforming growth factor-beta1 (TGF-beta1) neutralizing antibody.

CONCLUSIONS

Chronic ethanol consumption attenuates the antifibrotic effects of NK/IFN-gamma/STAT1 in the liver, representing new and different therapeutic targets with which to treat alcoholic liver fibrosis.

Implication of altered proteasome function in alcoholic liver injury

The proteasome is a major protein-degrading enzyme, which catalyzes degradation of oxidized and aged proteins, signal transduction factors and cleaves peptides for antigen presentation. Proteasome exists in the equilibrium of 26S and 20S particles. Proteasome function is altered by ethanol metabolism, depending on oxidative stress levels: low oxidative stress induces proteasome activity, while high oxidative stress reduces it. The proposed mechanisms for modulation of proteasome activity are related to oxidative modification of proteasomal proteins with primary and secondary products derived from ethanol oxidation. Decreased proteolysis by the proteasome results in the accumulation of insoluble protein aggregates, which cannot be degraded by proteasome and which further inhibit proteasome function. Mallory bodies, a common signature of alcoholic liver diseases, are formed by liver cells, when proteasome is unable to remove cytokeratins. Proteasome inhibition by ethanol also promotes the accumulation of pro-apoptotic factors in mitochondria of ethanol-metabolizing liver cells that are normally degraded by proteasome. In addition, decreased proteasome function also induces accumulation of the negative regulators of cytokine signaling (I-κB and SOCS), thereby blocking cytokine signal transduction. Finally, ethanol-elicited blockade of interferon type 1 and 2 signaling and decreased proteasome function impairs generation of peptides for MHC class I-restricted antigen presentation.

Role of the proteasome in ethanol-induced liver pathology

The ubiquitin-proteasome system has come to be known as a vital constituent of mammalian cells. The proteasome is a large nonlysosomal enzyme that acts in concert with an 8.5 kDa polypeptide called ubiquitin and a series of conjugating enzymes, known as E1, E2 and E3, that covalently bind multiple ubiquitin moieties in a polyubiquitin chain to protein substrates in a process called ubiquitylation. The latter process targets protein substrates for unfolding and degradation by the 26S proteasome. This enzyme system specifically recognizes and degrades polyubiquitylated proteins, many of which are key proteins involved in cell cycle regulation, apoptosis, signal transduction, and antigen presentation. The 26S proteasome contains a cylinder-shaped 20S catalytic core that, itself, degrades proteins in an ATP- and ubiquitin-independent manner. The 20S form is actually the predominant enzyme form in mammalian cells. Proteolysis by the constitutive 20S proteasome is vital in removing oxidized, misfolded and otherwise modified proteins. Such degradation is critical as a means of cellular detoxification, as intracellular accumulation of damaged and misfolded proteins is potentially lethal. Studies have shown that inhibition of proteasome activity can lead to cell death. Ethanol and its metabolism cause partial inhibition of the proteasome. This leads to a number of pleiotropic effects that can affect a variety of cellular processes. This critical review describes important aspects of ethanol metabolism and its influence on the proteasome. The review will summarize recent findings on: (1) the interactions between the proteasome and the ethanol metabolizing enzyme, CYP2E1; (2) the dynamics of proteasome inhibition by ethanol in animal models and cultured cells; (3) ethanol-elicited suppression of proteasome activity and its effect on signal transduction; (4) The role of proteasome inhibition in cytokine production by liver cells; and (5) ethanol elicited suppression of peptide hydrolysis and the potential effects on antigen presentation. While the principal focus is on alcohol-induced liver injury, the authors foresee that the findings presented in this review will prompt further research on the role of this proteolytic system in other tissues injured by excessive alcohol consumption.

Type III interferon (IFN) induces a type I IFN-like response in a restricted subset of cells through signaling pathways involving both the Jak-STAT pathway and the mitogen-activated protein kinases

Type III interferon (IFN) is a novel member of the interferon family. Type III IFN utilizes a receptor complex different from that of type I IFN, but both types of IFN induce STAT1, STAT2, and STAT3 activation. Here we describe a detailed comparison of signal transduction initiated by type I and type III IFN. Gene expression array analysis showed that IFN types I and III induced a similar subset of genes. In particular, no genes were induced uniquely by type III IFN. Next, we used chromatin immunoprecipitation (ChIP) analysis to investigate the promoter activation by types I and III IFN. The ChIP assays demonstrated that stimulation of cells with both type I and type III IFN resulted in the recruitment of ISGF3 transcription factor components to the promoter region of responsive genes and in an increase of polymerase II loading and histone acetylation. Whereas IFN type I signaling was observed for a broad spectrum of cell lines, type III IFN signaling was more restricted. The lack of IFN type III signaling was correlated with a low expression of the IL28Ra component of the IFN type III receptor, and IL28Ra overexpression was sufficient to restore IFN type III signaling. We also tested the activation of mitogen-activated protein (MAP) kinases by type III IFN and found that type III IFN relies strongly upon both p38 and JNK MAP kinases for gene induction.

Downregulation of a disintegrin and metalloproteinase 33 by IFN-gamma in human airway smooth muscle cells

BACKGROUND

A disintegrin and metalloproteinase 33 (ADAM33) has been identified as a susceptibility gene for asthma. ADAM33 is expressed in airway smooth muscle (ASM) cells and is suggested to play a role in the function of these cells. However, there is little information on the regulation of ADAM33.

OBJECTIVE

To investigate whether ADAM33 is more highly expressed in ASM cells of patients with asthma than in those of normal subjects, and whether there is any inflammatory mediator (asthma-related cytokine/chemokine) that could modulate the expression of ADAM33 in ASM cells.

METHOD

smRNA and protein expression of ADAM33 in bronchial biopsy specimens was investigated (in situ hybridization and immunohistochemistry). Effects of cytokines on expression of ADAM33 in cultured human ASM cells were evaluated by measuring mRNA (real-time RT-PCR) and protein (Western blotting).

RESULTS

ADAM33 mRNA and protein in biopsied specimens were more highly expressed in ASM cells of patients with asthma than in cells of normal subjects. Cultured ASM cells expressed ADAM33 at both the mRNA and the protein levels. IFN-gamma reduced the mRNA expression dose-dependently and time-dependently, whereas IL-4 and IL-13 or chemokines did not affect the expression. The reduction by IFN-gamma was partially restored by U0126, inhibitor for mitogen-activated protein kinase kinase 1/2, suggesting a role for extracellular signal-regulated kinase pathway. Further studies using cycloheximide and actinomycin-D suggested that the downregulation was at the transcriptional level.

CONCLUSION

The expression of ADAM33 by ASM cells is increased in patients with asthma, and its expression may be regulated by IFN-gamma.

CLINICAL IMPLICATIONS

IFN-gamma might have a role in suppressing ADAM33 in ASM cells.

Selective Regulation of IL-10 Signaling and Function by Zymosan

Balanced activity of pro- and anti-inflammatory cytokines during innate immune responses is required to allow effective host defense while avoiding tissue damage and autoimmunity. Induction of cytokine production after recognition of pathogen-associated molecular patterns (PAMPs) by innate immune cells has been well demonstrated, but modulation of cytokine function by PAMPs is not well understood. In this study we show that stimulation of macrophages with zymosan, which contains PAMPs derived from yeast, rapidly extinguished macrophage responses to IL-10, a suppressive cytokine that limits inflammatory tissue damage but also compromises host defense. The mechanism of inhibition involved protein kinase Cbeta and internalization of IL-10R, and was independent of TLR2 and phagocytosis. Inhibition of IL-10 signaling and function required direct contact with zymosan, and cells in an inflammatory environment that had not contacted zymosan remained responsive to the paracrine activity of zymosan-induced IL-10. These results reveal a mechanism that regulates IL-10 function such that antimicrobial functions of infected macrophages are not suppressed, but the activation of surrounding noninfected cells and subsequent tissue damage are limited. The fate of individual cells in an inflammatory microenvironment is thus specified by dynamic interactions among host cells, microbes, and cytokines that determine the balance between protection and pathology.

Inhibition of IFN-alpha signaling by a PKC- and protein tyrosine phosphatase SHP-2-dependent pathway

Cytokine signaling by the Jak-STAT pathway is subject to complex negative regulation that limits the amplitude and duration of signal transduction. Inhibition of signaling also mediates negative crosstalk, whereby factors with opposing biological activities crossinhibit each other's function. Here, we investigated a rapidly inducible mechanism that inhibited Jak-STAT activation by IFN-alpha, a cytokine that is important for antiviral responses, growth control, and modulation of immune responses. IFN-alpha-induced signaling and gene activation were inhibited by ligation of Fc receptors and Toll-like receptors 7 and 8 in a PKCbeta-dependent manner. Neither PKCbeta nor PKCdelta influenced responses of cells treated with IFN-alpha alone. Inhibition of IFN-alpha signaling correlated with suppression of IFN-alpha-dependent antiviral responses. PKC-mediated inhibition did not require de novo gene expression but involved the recruitment of PKCbeta to the IFN-alpha receptor and interaction with protein tyrosine phosphatase SHP-2, resulting in augmented phosphatase activity. PKC-mediated inhibition of IFN-alpha signaling was abolished in SHP-2-deficient cells, demonstrating a pivotal role for SHP-2 in this inhibitory pathway. Together, our data describe a rapidly inducible, direct mechanism of inhibition of Jak-STAT signaling mediated by a PKCbeta-SHP-2 signaling pathway.

Enhanced human beta-defensin-2 (hBD-2) expression by corticosteroids is independent of NF-kappaB in colonic epithelial cells (CaCo2)

Beta-defensins are small cationic peptides with antimicrobial properties that contribute to innate host defense. Unlike human beta-defensin-1 (hBD-1), which is produced constitutively, human beta-defensin-2 (hBD-2) is expressed after adequate stimulation by cytokines and/or bacterial endotoxins in epithelial tissue and mononuclear phagocytes but may be deficient in patients with Crohn's disease. To further elucidate the role of the intestinal epithelium in antimicrobial host defense, gene regulation of hBD-2 and the interaction with NF-kappaB were analyzed in a cell culture model. Human colonic epithelial cells (CaCo2) were stimulated by pro-inflammatory cytokines (IL-1beta, TNF-alpha, IF-gamma) to induce hBD-2 mRNA transcription. Interactions with NF-kappaB were analyzed using specific inhibitors (sulfasalazine, gliotoxine, dexamethasone) at different concentrations. Defensin mRNA expression was quantified by competitive RT-PCR and antibacterial capacity of supernatants was determined by an antimicrobial assay. HBD-2 mRNA transcription and antimicrobial activity of CaCo2 cells were induced by stimulation with pro-inflammatory cytokines. Induction was not inhibited by sulfasalazine or gliotoxine, whereas dexamethasone further enhanced both gene transcription and antimicrobial capacity. The lack of inhibition of induced hBD-2 expression by specific NF-kappaB antagonists suggests an additional pathway of activation, independent of NF-kappaB. The induction of hBD-2 expression in cytokine-stimulated CaCo2 cells by corticosteroids indicates further immunomodulatory ability of steroid hormones not yet understood.

Phosphatidylethanol in high density lipoproteins increases the vascular endothelial growth factor in smooth muscle cells

To study whether qualitative changes in high density lipoprotein (HDL) phospholipids mediate part of the advantageous effects of ethanol on atherosclerosis, we investigated whether HDL associated phosphatidylethanol (PEth) affects the secretion of vascular endothelial growth factor (VEGF) from cultured human smooth muscle cells. Serum-starved human umbilical vein HUVS-112D smooth muscle cells were incubated in the presence of PEth-HDL, HDL, or buffer. The phosphorylation of protein kinase C (PKC) and mitogen activated protein kinase (p44/42 MAPK) was determined by specific antibodies against phosphorylated and total proteins. VEGF concentrations were measured from cell culture medium of the cells. PEth increased the secretion of VEGF into the culture medium of HUVS cells. PEth-HDL increased the PKC phosphorylation by 2.1-fold and p44/42 MAPK phosphorylation by 3.3-fold compared with HDL, indicating that PEth-containing HDL particles influence vascular smooth muscle cells by PKC and p44/42 MAPK signalling. This may mediate the effects of ethanol on vascular wall by increasing the VEGF secretion from smooth muscle cells. The secreted VEGF may inhibit the formation of neointima and in doing so helps prevent atherosclerosis.

Intestinal Na+-K+-ATPase activity and molecular events downstream of interferon-gamma receptor stimulation

This study evaluated the effects of human interferon-gamma (IFN-gamma) on Na(+)-K(+)-ATPase activity and the intracellular signaling pathways involved in human intestinal epithelial Caco-2 cells. Na(+)-K(+)-ATPase activity was determined as the difference between total and ouabain-sensitive ATPase. p38 MAP kinase activity was analyzed by Western blotting using the p38 MAP kinase assay kit. Total and phosphorylated STAT1 protein levels were detected using the PhosphoPlus Stat1. IFN-gamma decreased Na(+)-K(+)-ATPase activity in a time- and concentration-dependent manner. The IFN-gamma-induced decrease in Na(+)-K(+)-ATPase activity was accompanied by no changes in the abundance of alpha(1) subunit Na(+)-K(+)-ATPase. Downregulation of protein kinase C (PKC) with phorbol-12,13-dibutyrate (PDBu) prevented the inhibitory effect of IFN-gamma on Na(+)-K(+)-ATPase activity. Inhibition of Raf-1, mitogen-activated protein kinase kinase (MAPKK/MEK), p38 MAPK and STAT1 with, respectively, GW 5074, PD 98059, SB 203580 and epigallocatechin gallate prevented inhibition of Na(+)-K(+)-ATPase activity by IFN-gamma. Treatment with IFN-gamma markedly increased the expression of total and phospho-STAT1, this being accompanied by activation of p38 MAPK. Activation of phospho-STAT1 by IFN-gamma was almost abolished by epigallocatechin gallate and markedly reduced by SB 203580, but insensitive to downregulation of PKC. The increase in short circuit current (I(sc)) by 1.0 and 2.5 micrograms ml(-1) amphotericin B was markedly attenuated in IFN-gamma-treated cells. However, the inhibitory effect of PDBu on the amphotericin B-induced increase in I(sc) was of similar magnitude in vehicle- and IFN-gamma-treated cells. It is concluded that IFN-gamma markedly attenuates Na(+)-K(+)-ATPase activity. The transduction mechanisms set into motion by IFN-gamma involve the activation of PKC downstream STAT1 phosphorylation and Raf-1, MEK, ERK2 and p38 MAPK pathways, in a complex sequence of events.

MAP kinase signaling in diverse effects of ethanol

Chronic ethanol abuse is associated with liver injury, neurotoxicity, hypertension, cardiomyopathy, modulation of immune responses and increased risk for cancer, whereas moderate alcohol consumption exerts protective effect on coronary heart disease. However, the signal transduction mechanisms underlying these processes are not well understood. Emerging evidences highlight a central role for mitogen activated protein kinase (MAPK) family in several of these effects of ethanol. MAPK signaling cascade plays an essential role in the initiation of cellular processes such as proliferation, differentiation, development, apoptosis, stress and inflammatory responses. Modulation of MAPK signaling pathway by ethanol is distinctive, depending on the cell type; acute or chronic; normal or transformed cell phenotype and on the type of agonist stimulating the MAPK. Acute exposure to ethanol results in modest activation of p42/44 MAPK in hepatocytes, astrocytes, and vascular smooth muscle cells. Acute ethanol exposure also results in potentiation or prolonged activation of p42/44MAPK in an agonist selective manner. Acute ethanol treatment also inhibits serum stimulated p42/44 MAPK activation and DNA synthesis in vascular smooth muscle cells. Chronic ethanol treatment causes decreased activation of p42/44 MAPK and inhibition of growth factor stimulated p42/44 MAPK activation and these effects of ethanol are correlated to suppression of DNA synthesis, impaired synaptic plasticity and neurotoxicity. In contrast, chronic ethanol treatment causes potentiation of endotoxin stimulated p42/44 MAPK and p38 MAPK signaling in Kupffer cells leading to increased synthesis of tumor necrosis factor. Acute exposure to ethanol activates pro-apoptotic JNK pathway and anti-apoptotic p42/44 MAPK pathway. Apoptosis caused by chronic ethanol treatment may be due to ethanol potentiation of TNF induced activation of p38 MAPK. Ethanol induced activation of MAPK signaling is also involved in collagen expression in stellate cells. Ethanol did not potentiate serum stimulated or Gi-protein dependent activation of p42/44 MAPK in normal hepatocytes but did so in embryonic liver cells and transformed hepatocytes leading to enhanced DNA synthesis. Ethanol has a 'triangular effect' on MAPK that involve direct effects of ethanol, its metabolically derived mediators and oxidative stress. Acetaldehyde, phosphatidylethanol, fatty acid ethyl ester and oxidative stress, mediate some of the effects seen after ethanol alone whereas ethanol modulation of agonist stimulated MAPK signaling appears to be mediated by phosphatidylethanol. Nuclear MAPKs are also affected by ethanol. Ethanol modulation of nuclear p42/44 MAPK occurs by both nuclear translocation of p42/44 MAPK and its activation in the nucleus. Of interest is the observation that ethanol caused selective acetylation of Lys 9 of histone 3 in the hepatocyte nucleus. It is plausible that ethanol modulation of cross talk between phosphorylation and acetylations of histone may regulate chromatin remodeling. Taken together, these recent developments place MAPK in a pivotal position in relation to cellular actions of ethanol. Furthermore, they offer promising insights into the specificity of ethanol effects and pharmacological modulation of MAPK signaling. Such molecular signaling approaches have the potential to provide mechanism-based therapy for the management of deleterious effects of ethanol or for exploiting its beneficial effects.

STAT1 deficiency unexpectedly and markedly exacerbates the pathophysiological actions of IFN-alpha in the central nervous system

Although signal transducer and activator of transcription 1 (STAT1) is an essential signaling molecule in many IFN-alpha-regulated processes, some biological responses to IFN-alpha can occur independently of STAT1. To establish the role of STAT1 in mediating the biological actions of IFN-alpha in the CNS, transgenic mice [termed glial fibrillary acidic protein (GFAP)-IFN-alpha] with astrocyte production of IFN-alpha were bred to be null for the STAT1 gene. Surprisingly, GFAP-IFN-alpha mice deficient for STAT1 developed earlier onset and more severe neurological disease with increased lethality compared with GFAP-IFN-alpha mice sufficient for STAT1. Whereas the brain of 2- to 3-month-old GFAP-IFN-alpha mice showed little, if any abnormality, the brain from GFAP-IFN-alpha mice deficient for STAT1 had severe neurodegeneration, inflammation, calcification with increased apoptosis, and glial activation. However, the cerebral expression of a number of IFN-regulated STAT1-dependent genes increased in GFAP-IFN-alpha mice but was reduced markedly in GFAP-IFN-alpha STAT1-null mice. Of many other signaling molecules examined, STAT3 alone was activated significantly in the brain of GFAP-IFN-alpha STAT1-null mice. Thus, in the absence of STAT1, alternative signaling pathways mediate pathophysiological actions of IFN-alpha in the living brain, giving rise to severe encephalopathy. Finally, STAT1 or a downstream component of the JAKSTAT pathway may protect against such IFN-alpha-mediated injury in the CNS.

Interaction of alcohol and hepatitis viral proteins: implication in synergistic effect of alcohol drinking and viral hepatitis on liver injury

Alcohol drinking and viral hepatitis are both recognized as major causes of liver disease worldwide, and they frequently coexist and synergistically cause liver injury in patients with chronic liver disease. Several mechanisms have been implicated in exacerbation of liver injury in patients with alcohol drinking and viral hepatitis. These include impairment of host defense and liver regeneration by alcohol consumption. The findings obtained from my laboratory have demonstrated that alcohol potentiates cooperatively several signals activated by hepatitis B virus X protein (HBX) or hepatitis C virus core protein, and HBX sensitizes hepatocytes to tumor necrosis factor-alpha (TNF-alpha)- and ethanol-induced apoptosis by a caspase-3-dependent mechanism, which may also contribute to the synergistic effect of alcohol drinking and viral hepatitis on liver injury.

Ethanol inhibits the JAK-STAT signaling pathway in freshly isolated rat hepatocytes but not in cultured hepatocytes or HepG2 cells: evidence for a lack of involvement of ethanol metabolism

OBJECTIVES

To understand the molecular mechanism underlying alcoholic liver injury, effects of acute ethanol on the Janus kinase-signal transducer and activator transcription factor (JAK-STAT) signaling in hepatic cells were studied.

DESIGNS AND METHODS

Effects of acute ethanol on the JAK-STAT signaling in freshly isolated, cultured rat hepatocytes, and HepG2 cells were explored.

RESULTS

Acute ethanol exposure inhibited IL-6- or IFN-activated STAT in freshly isolated hepatocytes but not in cultured hepatocytes, HepG2 cells, or HepG2 cells transfected with alcohol dehydrogenase (ADH) or cytochrome P450(2E1). The inhibitory action of ethanol in freshly isolated hepatocytes was not antagonized by the ADH inhibitor 4-methylpyrazole (4-MP). Acute exposure of hepatocytes to acetaldehyde or hydrogen peroxide did not suppress STAT activation. Further studies indicated that the loss of response to the inhibitory effect of ethanol was not due to hepatocyte proliferation and collagen contact.

CONCLUSIONS

Freshly isolated hepatocytes are more susceptible to the inhibitory action of ethanol on the JAK-STAT signaling than cultured hepatocytes or HepG2 cells, which may be implicated in pathogenesis and progression of alcoholic liver disease.

Differentiation therapy of human cancer: basic science and clinical applications

Current cancer therapies are highly toxic and often nonspecific. A potentially less toxic approach to treating this prevalent disease employs agents that modify cancer cell differentiation, termed 'differentiation therapy.' This approach is based on the tacit assumption that many neoplastic cell types exhibit reversible defects in differentiation, which upon appropriate treatment, results in tumor reprogramming and a concomitant loss in proliferative capacity and induction of terminal differentiation or apoptosis (programmed cell death). Laboratory studies that focus on elucidating mechanisms of action are demonstrating the effectiveness of 'differentiation therapy,' which is now beginning to show translational promise in the clinical setting.

Cross-talk between interleukin 1beta (IL-1beta) and IL-6 signalling pathways: IL-1beta selectively inhibits IL-6-activated signal transducer and activator of transcription factor 1 (STAT1) by a proteasome-dependent mechanism

Interleukin 1beta (IL-1beta) suppresses the IL-6-dependent induction of type II acute-phase response genes, but the underlying mechanism for this suppression remains uncertain. Here we report that treatment of human hepatocullular carcinoma HepG2 cells with IL-1beta inhibited the IL-6-dependent binding of signal transducer and activator of transcription factor (STAT)1, but not that of STAT3, to the high-affinity serum-inducible element ('SIE'). Furthermore, IL-1beta selectively down-regulated the IL-6-induced tyrosine phosphorylation of STAT1 without affecting the level of STAT1 or tyrosine phosphorylation of STAT3. Kinase assays in vitro indicated that the inhibition of STAT1 phosphorylation by IL-1beta was not due to an upstream blockade of Janus kinase (JAK1 or JAK2) activation. However, pretreatment with the proteasome inhibitor MG132 under conditions that prevented the IL-1beta-dependent activation of the nuclear factor NF-kappaB also blocked the inhibitory effect of IL-1beta on IL-6-activated STAT1. In related experiments, the protein tyrosine phosphatase inhibitor Na(3)VO(4) also antagonized the inhibitory effect of IL-1beta on the activation of STAT1 by IL-6. Taken together, these findings indicate that, by using a proteasome-dependent mechanism, IL-1beta concomitantly induces NF-kappaB activation and dephosphorylates IL-6-activated STAT1; the latter might partly account for the inhibition by IL-1beta of the IL-6-dependent induction of type II acute-phase genes.

IL-1 beta attenuates IFN-alpha beta-induced antiviral activity and STAT1 activation in the liver: involvement of proteasome-dependent pathway

IFN-alphabeta is the only established treatment for viral hepatitis; however, more than 60% of patients are poorly responsive. Because viral hepatitis is associated with inflammation, we hypothesized that inflammation may attenuate the efficacy of IFN therapy. To test this hypothesis, the effect of IL-1beta, one of the major proinflammatory cytokines, on IFN signaling pathway in the liver was examined. Administration of IL-1beta in vivo attenuated IFN-alphabeta-induced STAT1 tyrosine phosphorylation in the liver but not in the spleen. The inhibitory action of IL-1beta in vivo was not affected by depleting hepatic Kupffer cells, suggesting that IL-1beta may directly target IFN-alphabeta signaling in hepatocytes. Indeed, pretreatment of human hepatocellular carcinoma HepG2 cells with IL-1beta suppressed IFN-alphabeta-induced antiviral activity and antiviral protein MxA mRNA expression. Furthermore, IL-1beta attenuated IFN-alphabeta-induced STAT1 binding and tyrosine phosphorylation without affecting the level of STAT1 protein. This inhibitory effect can be reversed by pretreatment with either proteasome inhibitors or transfection of dominant negative NF-kappaB inducing kinase mutants. Taken together, these findings suggest that IL-1beta attenuates IFN-alphabeta-induced STAT1 activation by a proteasome-dependent mechanism. In view of high levels of IL-1beta in the serum or within the liver of patients with chronic liver diseases, attenuation of IFN-alphabeta signaling in the liver by IL-1beta could be one of the mechanisms underlying the resistance to IFN therapy in chronic hepatitis C, and IL-1beta could be a potential therapeutic target for improving the efficacy of IFN therapy.