Activation of mitogen-activated protein kinases/extracellular signal-regulated kinases in human hepatocellular carcinoma

Effect of hepatitis C virus nonstructural protein NS3 on proliferation and MAPK phosphorylation of normal hepatocyte line

AIM: To study the effect of hepatitis C virus nonstructural region 3 (HCV NS3) protein on proliferation and transformation of normal human liver cell line.

METHODS: QSG7701 cells were transfected with pRcHCNS3-5’, pRcHCNS3-3’ and pRcCMV using lipofectamine transfecting technique and selected with G418 method. Expression of HCV NS3 protein was determined by immunohistochemistry. Biologic characteristics of transfected cells were evaluated by population doubling time and soft agar assays. Activation of MAPK was analyzed using Western blot with phosphospecific monoclonal antibody against dually phosphorylated MAPK.

RESULTS: QSG7701 cells transfected with pRcHCNS3-5’ showed strong intracellular expression of HCVNS3 protein, and the positive signal was localized in cytoplasm. The expressing strength of HCVNS3 protein in pRcHCNS3-3’-transfected cells was weaker than that in pRcHCNS3-5’-transfected cells. The population doubling time in the transfected cells with pRcHCNS3-5’ (12 h) was much shorter than those with pRcHCNS3-3’, pRcCMV and normal cells (24, 26, 28 h, respectively) (P<0.01). The transfected cells with pRcHCNS3-5’ showed much more anchorage independent colonies than that in those with pRcHCNS3-3’ and pRcCMV (P<0.01). The cloning efficiencies of transfected cells with pRcHCNS3-5’, pRcHCNS3-3’, pRcCMV and controls were 33%, 1.33%, 1.46%, 1.11% respectively. The level of phosphorylated MAPK in the cells with pRcHCNS3-5’ was much higher than that in those with pRcHCNS3-3’and pRcCMV and normal cells (P<0.01).

CONCLUSION: The results suggest that (1) QSG7701 cells are a better human liver cell line for investigating the pathogenesis of HCV NS3 protein. (2) 5’ region of the HCV genome segment encoding HCV NS3 is involved in cell growth and cell phenotype. (3) HCV NS3 N-terminal peptide may up-regulate the activation of MAPK, but not affect the expression of MAPK.

Integration of Ras subeffector signaling in TGF-beta mediated late stage hepatocarcinogenesis

Immortalized p19(ARF) null hepatocytes (MIM) feature a high degree of functional differentiation and are susceptible to transforming growth factor (TGF)-beta driven growth arrest and apoptosis. In contrast, polarized MIM hepatocytes expressing hyperactive Ha-Ras continue proliferation in cooperation with TGF-beta, and adopt an invasive phenotype by executing an epithelial to mesenchymal transition (EMT). In this study, we analyzed the involvement of Ras subeffectors in TGF-beta mediated hepatocellular EMT by employing MIM hepatocytes, which express Ras mutants allowing selective activation of either mitogen-activated protein kinase (MAPK) signaling (V12-S35) or phosphoinositide 3-OH (PI3)3 kinase (PI3K) signaling (V12-C40). We found that MAPK signaling in MIM-S35 hepatocytes was necessary and sufficient to promote resistance to TGF-beta mediated inhibition of proliferation in vitro and in vivo. MIM-S35 hepatocytes showed also PI3K activation during EMT, however, MAPK signaling on its own protected hepatocytes from apoptosis. Yet, MIM-C40 hepatocytes failed to form tumors and required additional MAPK stimulation to overcome TGF-beta mediated growth arrest. In vivo, the collaboration of MAPK signaling and TGF-beta activity drastically accelerated the cell-cycle progression of the hepatocytes, leading to vast tumor formation. From these data we conclude that MAPK is crucial for the cooperation with TGF-beta to regulate the proliferation as well as the survival of hepatocytes during EMT, and causes the fatal increase in hepatocellular tumor progression.

Increased expression of mitogen-activated protein kinase and its upstream regulating signal in human gastric cancer

AIM: To investigate the expression of mitogen-activated protein kinases (MAPKs) and its upstream protein kinase in human gastric cancer and to evaluate the relationship between protein levels and clinicopathological parameters.

METHODS: Western blot was used to measure the expression of extracellular signal-regulated kinase (ERK)-1, ERK-2, ERK-3, p38 and mitogen or ERK activated protein kinaseMEK-1 proteins in surgically resected gastric carcinoma, adjacent normal mucosa and metastatic lymph nodes from 42 patients. Immunohistochemistry was employed for their localization.

RESULTS: Compared with normal tissues, the protein levels of ERK-1 (integral optical density value 159526±65760 vs 122807±65515, P = 0.001), ERK-2 (168471±95051 vs 120469±72874, P<0.001), ERK-3 (118651±71513 vs 70934±68058, P<0.001), P38 (104776±51650 vs 82930±40392, P = 0.048) and MEK-1 (116486±45725 vs 101434±49387, P = 0.027) were increased in gastric cancer tissues. Overexpression of ERK-3 was correlated to TNM staging [average ratio of integral optic density (IOD)_tumor: IOD_normal in TNM I, II, III, IV tumors was 1.43±0.34, 5.08±3.74, 4.99±1.08, 1.44±1.02, n = 42, P = 0.023] and serosa invasion (4.31±4.34 vs 2.00±2.03, P = 0.037). In poorly differentiated cancers (n = 33), the protein levels of ERK-1 and ERK-2 in stage III and IV tumors were higher than those in stage I and II tumors (2.64±3.01 vs 1.01±0.33, P = 0.022; 2.05±1.54 vs 1.24±0.40, P = 0.030). Gastric cancer tissues with either lymph node involvement (2.49±2.91 vs 1.03±0.36, P = 0.023; 1.98±1.49 vs 1.24±0.44, P = 0.036) or serosa invasion (2.39±2.82 vs 1.01±0.35, P = 0.022; 1.95±1.44 vs 1.14±0.36, P = 0.015) expressed higher protein levels of ERK-1 and ERK-2. In Borrmann II tumors, expression of ERK-2 and ERK-3 was increased compared with Borrmann III tumors (2.57±1.86 vs 1.23±0.60, P = 0.022; 5.50±5.05 vs 1.83±1.21, P = 0.014). Borrmann IV tumors expressed higher p38 protein levels. No statistically significant difference in expression of MAPKs was found when stratified to tumor size or histological grade (P>0.05). Protein levels of ERK-2, ERK-3 and MEK-1 in metastatic lymph nodes were 2-7 folds higher than those in adjacent normal mucosa. The immunohistochemistry demonstrated that ERK-1, ERK-2, ERK-3, p38 and MEK-1 proteins were mainly localized in cytoplasm. The expression of MEK-1 in gastric cancer cells metastasized to lymph nodes was higher than that of the primary site.

CONCLUSION: MAPKs, particularly ERK subclass are overexpressed in the majority of gastric cancers. Overexpression of ERKs is correlated to TNM staging, serosa invasion, and lymph node involvement. The overexpression of p38 most likely plays a prominent role in certain morphological subtypes of gastric cancers. MEK-1 is also overexpressed in gastric cancer, particularly in metastatic lymph nodes. Upregulation of MAPK signal transduction pathways may play an important role in tumorigenesis and metastatic potential of gastric cancer.

Mitogen-activated protein kinase phosphatase-1 is overexpressed in non-small cell lung cancer and is an independent predictor of outcome in patients

PURPOSE

An increase in the activity of the mitogen-activated protein kinases (MAPKs) has been correlated with a more malignant phenotype in several tumor models in vitro and in vivo. A key regulatory mechanism of the MAPKs [extracellular signal-regulated kinase (ERK); c-jun NH(2)-terminal kinase (JNK); and p38] is the dual specificity phosphatase CL100, also called MAPK phosphatase-1 (MKP-1). This study was designed to examine the involvement of CL100/MKP-1 and stress-related MAPKs in lung cancer.

EXPERIMENTAL DESIGN

We assessed the expression of CL100/MKP-1 and the activation of the MAPKs in a panel of 18 human cell lines [1 primary normal bronchial epithelium, 8 non-small cell lung cancer (NSCLC), 7 small cell lung cancer (SCLC), and 2 carcinoids] and in 108 NSCLC surgical specimens.

RESULTS

In the cell lines, CL100/MKP-1 expression was substantially higher in NSCLC than in SCLC. P-ERK, P-JNK, and P-p38 were activated in SCLC and NSCLC, but the degree of their activation was variable. Immunohistochemistry in NSCLC resection specimens showed high levels of CL100/MKP-1 and activation of the three MAPK compared with normal lung. In univariate analysis, no relationship was found among CL100/MKP-1 expression and P-ERK, P-JNK, or P-p38. Interestingly, high CL100/MKP-1 expression levels independently predicted improved survival in multivariate analysis. JNK activation associated with T(1-2) and early stage, whereas ERK activation correlated with late stages and higher T and N. Neither JNK nor ERK activation were independent prognostic factors when studied for patient survival.

CONCLUSIONS

Our data indicate the relevance of MAPKs and CL100/MKP-1 in lung cancer and point at CL100/MKP-1 as a potential positive prognostic factor in NSCLC. Finally, our study supports the search of new molecular targets for lung cancer therapy within the MAPK signaling pathway.

Overexpression of extracellular signal-regulated protein kinase and its correlation with proliferation in human hepatocellular carcinoma

BACKGROUND

Dysregulation of cell proliferation is one of the most important features of human cancers including hepatocellular carcinoma (HCC). However, the molecular basis underlying the proliferation of HCC has not been fully clarified. Because a previous study reported that overexpression of extracellular signal-regulated protein kinase (ERK), which transduces extracellular growth stimuli to the nuclei, was frequently observed in several human cancers, this study was performed to analyze the expression of ERK in human HCC and its correlation with HCC proliferation.

METHODS

Twenty-four paired samples of primary HCCs and corresponding noncancerous liver tissues, and six samples of histologically normal liver tissue were obtained from surgically resected materials. The expression of ERK was examined by immunoblotting and immunohistochemical analysis. Proliferative activity of each HCC was examined by immunohistochemical demonstration of proliferative cell nuclear antigen (PCNA).

RESULTS

The ERK1 and ERK2 expression in HCCs was significantly higher than that in noncancerous liver tissues, and the ERK1 expression in noncancerous liver tissues from patients with HCC was higher than that in tissue from normal liver. Immunohistochemical examination revealed enhanced accumulation of ERK1 in the nuclei of HCC cells. Regression analysis revealed a significant correlation between ERK expression and PCNA labeling index in HCC.

CONCLUSIONS

Our findings suggest that ERK overexpression contributes to the proliferation of HCC.

An evaluation of the role of insulin-like growth factors (IGF) and of type-I IGF receptor signalling in hepatocarcinogenesis and in the resistance of hepatocarcinoma cells against drug-induced apoptosis

Strong evidence emphasizes the role of the insulin-like growth factor (IGF) system and of type-I IGF receptor (IGF-IR) signalling in tumourigenesis. In this connection: (i) changes in the expression pattern of components of the IGF system (autocrine/paracrine expression of IGF-I and -II, overexpression of IGF-IR, decreased expression of IGF-binding proteins (IGFBPs) and of type-II IGF receptor/cation-independent mannose-6-phosphate receptor (IGF-II/M6PR) and (ii) increased serum concentrations of proteases that cleave the IGFBPs (e.g., cathepsin D) were observed in patients with hepatocellular carcinomas (HCC), in human hepatoma cell lines and in their conditioned culture medium, as well as in rodent models of hepatocarcinogenesis. Accordingly, studies carried out with animal models do suggest that the IGF system and IGF-IR signalling may play a role in hepatocarcinogenesis and in deregulated proliferation and apoptosis of HCC cells. Finally the instrumental role of Raf/MEK/ERK, one of the signalling cascades stimulated by IGF-IR, in anthracycline-induced apoptosis of HepG2 and Huh-7 human hepatoma cell lines emphasizes that care must be taken when designing combinations of antitumoural molecules for antineoplastic treatment. This review addresses the putative roles of the IGF system in primary HCC, with a special focus on the underlying molecular mechanisms. In a second part it emphasizes the putative interference of IGF-IR signalling with chemotherapeutic drug-induced apoptosis in human hepatoma cells.

Dual blockade of EGFR and ERK1/2 phosphorylation potentiates growth inhibition of breast cancer cells

One of the major targets for breast cancer therapy is the epidermal growth factor receptor (EGFR) and related receptors, which signal via different signal transduction pathways including the mitogen-activated protein kinase (MAPK) pathway. This study determined whether there is a correlation between EGFR/HER2 status and MAPK (ERK1/2) phosphorylation in breast cancer cells, and how this affects the response to an inhibitor of the receptors. Expression of EGFR, HER2 and phosphorylated ERK1/2 were measured by immunoblotting in a panel of breast cancer cell lines. Several lines expressed high levels of pERK1/2, with no obvious correlation with the level of EGFR/HER2. The EGFR tyrosine kinase inhibitor PKI166 inhibited growth and induced apoptosis in some cells with high levels of growth factor receptors (MDA-MB-468, SUM149, SKBR3), but was less effective in cells that also had high basal ERK1/2 activity (MDA-MB-231). The combination of an inhibitor of MAPK signalling (U0126) and PKI166 produced significantly more inhibition and apoptosis than either agent alone. This suggests that constitutive activation of the MAPK pathway may bypass inhibition of EGFR/HER2 tyrosine kinases, and lead to insensitivity to agents targeting the receptors. However, inhibiting both EGFR/HER2 and MAPK signalling can result in significant growth inhibition and apoptosis of EGFR-expressing breast cancer cells.

Hepatitis C virus NS5A-regulated gene expression and signaling revealed via microarray and comparative promoter analyses

Most individuals exposed to hepatitis C virus (HCV) become chronically infected and are predisposed to liver disease. The mechanisms underlying viral persistence and disease progression are unknown. A role for the HCV NS5A protein in viral replication and interferon resistance has been demonstrated. To identify mechanisms affected by NS5A, we analyzed the gene expression of Huh7 cells expressing NS5A and control cells using oligonucleotide microarrays. A set of 103 genes (43 up-regulated, 60 down-regulated) whose expression was modified by at least twofold was selected. These included genes involved in cell adhesion and motility, calcium homeostasis, lipid transport and metabolism, and genes regulating immune responses. The finding of modulated expression of genes related to the TGF-beta superfamily and liver fibrosis was observed. Interestingly, both the tumor necrosis factor and lymphotoxin beta receptors were down-regulated by NS5A. Similar data were obtained following expression of four NS5A mutants obtained from patients who were not responsive or were sensitive to interferon therapy. Through computational analysis, we determined that 39 of the 43 genes up-regulated by NS5A contained one or more nuclear factor kappaB (NF-kappaB) binding sites within their promoter region. Using the Gibbs sampling method, we also detected enrichment of NF-kappaB consensus binding sites in the upstream regions of the 43 coexpressed genes. Activation of NF-kappaB by NS5A was subsequently demonstrated in luciferase reporter assays. Adenovirus-mediated expression of IkappaBalpha reverted NS5A mediated up-regulation of gene expression. In conclusion, this study suggests a role of NS5A and NF-kappaB in HCV pathogenesis and related liver disease. Supplementary material for this article can be found on the HEPATOLOGY website (http://interscience.wiley.com/jpages/0270-9139/suppmat/index.html).

Involvement of cell cycle regulatory proteins and MAP kinase signaling pathway in growth inhibition and cell cycle arrest by a selective cyclooxygenase 2 inhibitor, etodolac, in human hepatocellular carcinoma cell lines

Recent studies have shown that selective cyclooxygenase-2 (COX-2) inhibitors induce growth inhibition and cell cycle arrest in hepatocellular carcinoma (HCC) cell lines. However, the mechanism by which COX-2 inhibitors regulate the cell cycle and whether or not growth signal pathways are involved in the growth inhibition remain unclear. In this study, we investigated the mechanisms of growth inhibition and cell cycle arrest by etodolac, a selective COX-2 inhibitor, in HCC cell lines, HepG2 and PLC/PRF/5, by studying cell cycle regulatory proteins, and the MAP kinase and PDK1-PKB/AKT signaling pathways. Etodolac inhibited growth and PCNA expression and induced cell cycle arrest in both HCC cell lines. Etodolac induced p21WAF1/Cip1 and p27Kip1 expression and inhibited CDK2, CDK4, CDC2, cyclin A and cyclin B1 expression, but did not affect cyclin D1 or cyclin E. HGF and 10% FBS induced ERK phosphorylation, but phosphorylation of p38, JNK and AKT was down-regulated by etodolac. PD98059, a selective inhibitor of ERK phosphorylation, induced growth inhibition, the expression of p27Kip1 and cell cycle arrest. In conclusion, p21WAF1/Cip1, p27Kip1, CDK2, CDK4, CDC2, cyclin A, cyclin B1 and the MAP kinase signaling pathway are involved in growth inhibition and cell cycle arrest by a selective COX-2 inhibitor in HCC cell lines.

Disruption of hepatocellular tight junctions by vascular endothelial growth factor (VEGF): a novel mechanism for tumor invasion

BACKGROUND/AIMS

Vascular endothelial growth factor (VEGF) is expressed by many tumors, including hepatocellular carcinoma (HCC) and is involved in tumor angiogenesis. Little is known about its role for HCC infiltration into normal liver parenchyma.

METHODS

The effects of VEGF on the integrity of tight junctions were studied in HepG2 cells and human HCC by means of confocal laser scanning microscopy.

RESULTS

VEGF induced within 45 min a marked loss of pseudocanaliculi and disruption of occludin-delineated tight junctions. This effect of VEGF was mimicked by phorbol-12-myristate-13-acetate (PMA) and was sensitive to protein kinase C (PKC) inhibition by Gö6850. VEGF induced within 15 min the translocation of the PKC alpha-isoform to the plasma-membrane, but had no effect on the activity of Erks and p38(MAPK). Sections from surgically removed HCC showed expression of VEGF in the tumor and occludin disassembly in normal liver parenchyma next to the tumor.

CONCLUSIONS

VEGF induces disruption of tight junctions in a PKC-alpha dependent manner. In addition to its known angioneogenic properties, VEGF may promote HCC spreading into normal liver parenchyma. The data may provide another rationale for the use of VEGF antagonists for tumor therapy.

Exposure of melanoma cells to dacarbazine results in enhanced tumor growth and metastasis in vivo

PURPOSE

In recent years, the incidence of cutaneous melanoma has increased more than that of any other cancer. Dacarbazine is considered the gold standard for treatment, having a response rate of 15% to 20%, but most responses are not sustained. Previously, we have shown that short exposure of primary cutaneous melanoma cells to dacarbazine resulted in the upregulation of interleukin-8 (IL-8) and vascular endothelial growth factor (VEGF). The purpose of the present study was to determine how long-term exposure of melanoma cells to dacarbazine would affect their tumorigenic and metastatic potential in vivo.

MATERIALS AND METHODS

The primary cutaneous melanoma cell lines SB2 and MeWo were repeatedly exposed in vitro to increasing concentrations of dacarbazine, and dacarbazine-resistant cell lines SB2-D and MeWo-D were selected and examined for their ability to grow and metastasize in nude mice.

RESULTS

The dacarbazine-resistant cell lines SB2-D and MeWo-D exhibited increased tumor growth and metastatic behavior in vivo. This increase could be explained by the activation of RAF, MEK, and ERK, which led to the upregulation of IL-8 and VEGF. More IL-8, VEGF, matrix metalloproteinase-2 (MMP-2), and microvessel density (CD-31) were found in tumors produced by SB2-D and MeWo-D in vivo than in those produced by their parental counterparts. No mutations were observed in BRAF.

CONCLUSION

Our results have significant clinical implications. Treatment of melanoma patients with dacarbazine could select for a more aggressive melanoma phenotype. We propose that combination treatment with anti-VEGF/IL-8 or MEK inhibitors may potentiate the therapeutic effects of dacarbazine.

Mice deficient for the gap junction protein Connexin32 exhibit increased radiation-induced tumorigenesis associated with elevated mitogen-activated protein kinase (p44/Erk1, p42/Erk2) activation

Loss of connexin expression/gap junction intercellular communication (GJIC) has been correlated with decreased growth control and increased tumorigenesis. Studies utilizing Connexin32 (Cx32)-deficient knockout mice have demonstrated that loss of Cx32 increases susceptibility to chemically induced liver tumorigenesis. Here, in addition to dramatically increased liver tumorigenesis, we show that tumor induction utilizing X-ray radiation resulted in a statistically significant increase in overall tumor burden in Cx32-deficient mice compared with wild-type mice due to tumorigenesis in several other tissues (lung, adrenal, lymph and small intestine) even when excluding prevalent liver tumors. Irradiated Cx32-deficient mice were particularly sensitive to liver tumorigenesis (46% incidence compared with 18% in wild-type mice, P = 0.007) demonstrating that Cx32 functions as a hepatic tumor suppressor in response to radiation-associated mutation events. Cx32-deficient mice also exhibited increased lung tumorigenesis (bronchioloalveolar) with an increased progression to carcinoma when compared with wild-type mice. Two Cx32-deficient mice developed an uncommon, invasive medullary adrenal tumor type (pheochromocytoma) not observed in irradiated wild-type mice. Immunohistochemical analysis revealed increased levels of activated mitogen-activated protein kinase (MAPK) (p44/Erk1, p42/Erk2) in Cx32-deficient mouse liver tumors (P = 0.006), lung tumors (P = 0.056) and adrenal tumors (primary and metastases) compared with wild-type counterparts implicating elevated activation of MAPK-interacting pathways in Cx32-deficient tumorigenesis. Interestingly, lung tumors from Cx32-deficient mice also demonstrated decreased p27Kip1 levels compared with wild-type lung tumors (P = 0.05). This study demonstrates that loss of Cx32/GJIC plays a significant role in radiation-induced tumorigenesis of the liver and importantly that Cx32 may also play a role in tumor suppression and/or tumor progression in other tissue types such as lung and adrenal gland. Additionally, this mouse model suggests that MAPK-related pathways may be preferentially activated or conversely that tumors harboring activated MAPK pathways may selectively progress towards more advanced tumor states in the absence of Cx32-mediated GJIC.

ERK1/2 is activated in non-small-cell lung cancer and associated with advanced tumours

Activation of the ERK1/2 pathway is involved in malignant transformation both in vitro and in vivo. Little is known about the role of activated ERK1/2 in non-small cell lung cancer (NSCLC). The purpose of this study was to characterise the extent of the activation of ERK1/2 by immunohistochemistry in patients with NSCLC, and to determine the relationship of ERK1/2 activation with clinicopathological variables. Specimens from 111 patients with NSCLC (stages I-IV) were stained for P-ERK. Staining for epidermal growth factor receptor (EGFR) and Ki-67 was also performed. In all, 34% of the tumour specimens showed activation for ERK1/2, while normal lung epithelial tissue was consistently negative. There was a strong statistical correlation between nuclear and cytoplasmic P-ERK staining and advanced stages (P<0.05 and P<0.001, respectively), metastatic hilar or mediastinal lymph nodes (P<0.01, P<0.001), and higher T stages (P<0.01, P<0.001). We did not find correlation of nuclear or cytoplasmic P-ERK staining with either EGFR expression or Ki-67 expression. Total ERK1/2 expression was evaluated with a specific ERK1/2 antibody and showed that P-ERK staining was not due to ERK overexpression but rather to hyperactivation of ERK1/2. Patients with a positive P-ERK cytoplasmic staining had a significant lower survival (P<0.05). However, multivariate analysis did not show significant survival difference. Our study indicates that nuclear and cytoplasmic ERK1/2 activation positively correlates with stage, T and lymph node metastases, and thus, is associated with advanced and aggressive NSCLC tumours.

Multiple anticancer effects of blocking MEK-ERK signaling in hepatocellular carcinoma

BACKGROUND

Human hepatocellular carcinoma (HCC) is associated with increased expression and activity of mitogen-activated protein kinase (MAPK) signaling intermediates (ie, MEK, ERK).

STUDY DESIGN

We determined the effects of MEK-ERK signaling on proliferation, cell cycle, apoptosis, and tumorigenicity of HCC in vitro. HCC cell lines were treated with MEK enzyme-specific inhibitors, PD098059 and U0126, and ERK1,2 oligonucleotide antisense.

RESULTS

In the HCC cells examined, MEK inhibitors blocked ERK1,2 phosphorylation without a change in total ERK expression. ERK1,2 oligonucleotide antisense inhibited ERK1,2 protein expression. PD098059, U0126, and ERK1,2 oligonucleotide antisense each inhibited HCC cellular proliferation in a concentration-dependent manner. Cell cycle, apoptosis, and tumorigenicity were examined in Hep3B and HepG2 cell lines. MEK enzyme inhibition resulted in anticancer effects through cell cycle arrest, increased apoptosis, and decreased tumorigenicity in these cell lines. U0126 exhibited more potent inhibition of ERK1,2 phosphorylation and had more pronounced anticancer effects in both cell lines. Correspondingly, HepG2 cells, the cell line more sensitive to ERK1,2 phosphorylation inhibition, sustained more pronounced anticancer effects with treatment. But Hep3B cells were more sensitive to ERK1,2 antisense-mediated decreases in ERK1,2 protein expression and correspondingly, their growth was inhibited to a greater degree than the HepG2 cells. MEK enzyme inhibition had downstream effects on the expression of the antiapoptotic protein survivin in both cell lines.

CONCLUSIONS

These data suggest that there are multiple anticancer effects of blocking MEK-ERK signaling, and that these depend on both the susceptibility of the cells and the ability of the treatment to effect a selective block of MEK-ERK signaling in HCC cells.

The proto-oncoprotein c-Fos negatively regulates hepatocellular tumorigenesis

Hepatocytes adopt an invasive and metastatic phenotype caused by the cooperation of transforming growth factor (TGF)-beta and oncogenic Ha-Ras. In the initial phase of this process, c-Fos is rapidly induced by TGF-beta, but then decreases to undetectable levels. Here, we investigated the functional implications of c-Fos activation and its contribution to hepatocellular tumorigenesis. By employing conditional c-Fos expression, we observed that continuous activation of c-Fos and consequently AP-1 activity leads to depolarization of differentiated murine epithelial hepatocytes. Most remarkably, this change in morphology was associated with inhibition of proliferation and induction of cell death. Coexpression of antiapoptotic Bcl-XL or scavenging of reactive oxygen species was sufficient to prevent the c-Fos-mediated phenotype. In contrast, the cooperation of c-Fos with oncogenic Ha-Ras or a Ras mutant selectively activating the MAPK pathway even enhanced c-Fos-induced effects. Showing the negative role in hepatocellular tumorigenesis, c-Fos repressed oncogenic Ras-driven anchorage-independent growth in vitro and strongly suppressed tumour formation in vivo. Taken together, we demonstrate that c-Fos modulates plasticity of epithelial hepatocytes and acts tumour suppressive in neoplastic hepatocytes by stimulating cell cycle inhibition and cell death.

Hepatitis C virus core protein activates ERK and p38 MAPK in cooperation with ethanol in transgenic mice

In human chronic hepatitis C, alcohol intake is a synergistic factor for the acceleration of hepatocarcinogenesis. Recently, we showed a significant increase of reactive oxygen species (ROS) in hepatitis C virus (HCV) core-transgenic mice fed ethanol-containing diets. Because previous studies indicated that ROS is closely associated with mitogen-activated protein kinases (MAPK), we examined activities of c-Jun N-terminal kinase, p38 MAPK, and extracellular signal-regulated kinase (ERK) in the liver of core-transgenic and nontransgenic mice with short-term ethanol feeding. Activity of ERK and p38 MAPK was increased in core-transgenic mice compared with nontransgenic mice, whereas neither ERK nor p38 MAPK was activated in core-transgenic mice with normal diets. In addition, activity of cyclic-AMP and serum responsive element, downstream pathways of p38 MAPK and ERK, was also increased. Comparison of gene expression profiles by cDNA microarray and real-time PCR revealed that galectin-1, which is associated with cell transformation, was significantly increased in ethanol-fed core-transgenic mice. On the other hand, glutathione S-transferase (GST), which plays a key role in protecting cells from oxidative stress, was decreased. In conclusion, these results suggest that HCV core protein cooperates with ethanol for the activation of some MAPK pathways, and leads to the modulation of several genes, contributing to the pathogenesis of liver disease of HCV-infected patients with high ethanol consumption.

Nitric oxide-mediated promotion of mammary tumour cell migration requires sequential activation of nitric oxide synthase, guanylate cyclase and mitogen-activated protein kinase

Using clonal derivatives of spontaneous mammary tumours in C3H/HeJ mice, we had earlier shown that tumour-derived nitric oxide (NO), resulting from endothelial type (e) NO synthase (NOS) expression by tumour cells, promoted tumour growth and metastasis by multiple mechanisms: stimulation of tumour cell invasiveness, migration and angiogenesis. Our present study examined the signaling mechanisms underlying NO-mediated promotion of tumour cell migration in a highly metastatic and high eNOS-expressing C3H/HeJ mammary tumour cell line, C3L5. C3L5 cell migration was reduced in the presence of N(G)-nitro-L-arginine methyl ester (L-NAME, NOS inhibitor) in a concentration-dependent manner and restored in the additional presence of excess L-arginine (NOS substrate), confirming a migration-promoting role of endogenous NO. Migratory capacity of C3L5 cells was reduced after treatment with the guanylate cyclase (GC) inhibitor 1-H-[1,2,4]oxadiaxolo[4,3-a]quinolalin-1-one (ODQ) and restored in the additional presence of 8-bromoguanosine 3'5'-cyclic monophosphate (8-Br cGMP, cGMP analogue), demonstrating a pivotal role for GC in C3L5 cell migration. Mitogen-activated protein kinase kinase (MAPKK; MEK) inhibitor, UO126, blocked migration, demonstrating MEK involvement in C3L5 cell migration. Furthermore, both ODQ and UO126 blocked migration-restoring effects of L-arginine in L-NAME-treated cells, indicating that GC and MAPK pathways are required for endogenous NO-mediated migratory responses. Similarly, L-NAME reduced and additional treatment with excess L-arginine or sodium nitroprusside (SNP, NO donor) stimulated phosphorylation of extracellular signal-regulated kinases (ERK(1/2)), demonstrating a role for endogenous and exogenous NO in ERK(1/2) activation. ODQ inhibited ERK(1/2) activation, whereas 8-Br cGMP stimulated ERK(1/2) phosphorylation in L-NAME-treated cells, indicating that cGMP is a downstream effector of NOS for ERK(1/2) activation. Finally, both ODQ and UO126 blocked the capacity of L-arginine to restore ERK(1/2) phosphorylation in L-NAME-treated cells, demonstrating that GC and MEK are both required for endogenous NO-mediated MAPK activation. Together, these results indicate sequential activation of NOS, GC and MAPK pathways in mediating signals for C3L5 cell migration, an essential step in invasion and metastasis. Since NOS activity is positively associated with human breast cancer progression, the present results are relevant for development of therapeutic modalities for this disease.

Downregulation of stomach cancer-associated protein tyrosine phosphatase-1 (SAP-1) in advanced human hepatocellular carcinoma

SAP-1 (stomach cancer-associated protein tyrosine phosphatase-1) is a transmembrane-type protein tyrosine phosphatase that has been implicated as a negative regulator of integrin-mediated signaling. The potential role of this enzyme in hepatocarcinogenesis has now been investigated by examining its expression in 32 surgically excised human hepatocellular carcinoma (HCC) specimens. Both immunohistochemical and immunoblot analyses revealed that normal liver tissue, as well as tissue affected by chronic hepatitis or cirrhosis, contained substantial amounts of SAP-1. The expression level of SAP-1 in 75% of well-differentiated HCCs was similar to or higher than that observed in the surrounding noncancerous tissue. In contrast, the abundance of SAP-1 in 85.7% of moderately differentiated HCCs and in all poorly differentiated HCCs was greatly reduced compared with that in the adjacent tissue. Indeed, SAP-1 was almost undetectable in 83.3% of poorly differentiated HCCs. Furthermore, expression of recombinant SAP-1 in two highly motile human HCC cell lines resulted in a change in morphology and a marked reduction in both migratory activity and growth rate. In conclusion, these results indicate that SAP-1 expression is downregulated during the dedifferentiation of human HCC, and that this downregulation may play a causal role in disease progression.

Involvement of the p38 mitogen-activated protein kinase cascade in hepatocellular carcinoma

BACKGROUND

The mitogen-activated protein kinase (MAPK) cascade is activated in response to various extracellular stimuli. The authors investigated the involvement of the p38 MAPK, a member of the MAPK superfamily, cascade in hepatoma cell lines and in human hepatocellular carcinoma (HCC) tissue specimens.

METHODS

Constitutively active mutant of MAPK kinase 6 (MKK6), which is upstream of p38 MAPK, was transfected into the HepG2 and HuH7 human hepatoma cell lines. The constitutive active mutant was constructed by replacing Ser-189 and Thr-193 with Glu. The growth and death of mutant MKK6-transfected hepatoma cells were analyzed by the WST-1 and sub-G1 assays. The surgically resected livers of 20 HCC patients were divided histologically into tumorous (T) and nontumorous (NT) lesions. p38 MAPK activity was analyzed using in vitro kinase assay and MKK6 activity was measured using Western blot analysis.

RESULTS

Mutant MKK6 transfection increased p38 MAPK activity, cytochrome c release from the mitochondria to the cytosol, and caspase-3 activity, accompanied by apoptosis. In contrast, SB203580, a p38 MAPK-specific inhibitor, prevented MKK6-induced apoptosis in hepatoma cell lines. In the T lesions of 20 HCC parients, p38 MAPK and MKK6 activities were significantly lower compared with NT lesions (P < 0.05). There was a significant positive correlation between p38 MAPK and MKK6 activity (r = 0.507, P < 0.05). Larger tumors (> 20 mm) exhibited lower levels of p38 MAPK and MKK6 activity than did smaller tumors (P < 0.05).

CONCLUSIONS

These findings suggested that reduction of the p38 MAPK cascade may account, in part, for the resistance to apoptosis, leading to the unrestricted cell growth of human HCC.

Extracellular signal-regulated kinase in liver fibrogenesis of rat

AIM

To explore the role of ERK signal transduction pathway in the pathogenesis of liver fibrosis via investigating the expression and distribution of ERK1 in rats with liver fibrosis.

METHODS

Liver fibrosis model of rats were made by subcutaneously injecting with CCl4. Thirty-two male SD rats (weight 250-300 g) were randomly scarified at 1, 4 and 8 weeks after injection of CCl4 respectively, and their liver were used to detect ERK1 expression by immunohistochemical staining.

RESULTS

The expression of ERK1 in rats after injection with CCl4 were found chiefly in hepatic stellate cells(HSC)and all significantly higher than those in normal rats(P<0.05). Moreover, it presented with a progressive tendency for the expression of ERK1 in rats respectively at 1st, 4th and 8th week after injection with CCl4 (P<0.05).

CONCLUSION

The activation of ERK signal transduction pathway enhances HSC proliferation, and it may play an important role in liver fibrogenesis in rat.

Constitutive over-expression of the insulin receptor substrate-1 causes functional up-regulation of Fas receptor

BACKGROUND/AIMS

Insulin- and insulin growth factor-1 stimulated signaling through the insulin receptor substrate-1 (IRS-1) promotes hepatocellular proliferation and survival. IRS-1 over-expression in transgenic (Tg) mouse livers caused constitutive activation of Erk mitogen activated protein kinase (MAPK) and phosphatidylinositol-3 kinase (PI3K) resulting in significantly increased levels of DNA synthesis and larger hepatic masses relative to non-transgenic (non-Tg) littermates. However, the livers eventually ceased to grow but remained approximately 25% larger than non-Tg livers. We hypothesized that this growth homeostasis was achieved by parallel activation of pro-apoptosis pathways.

METHODS

Since Fas-mediated apoptosis is a common mechanism of hepatocyte destruction, we investigated the potential role of Fas receptor as a regulator of hepatic mass in IRS-1 transgenic mice.

RESULTS

Significantly increased Fas-receptor levels were detected in the livers of IRS-1 Tg compared to non-Tg mice by Western blot analysis. Functional activation of Fas-receptor in IRS-1 Tg livers was demonstrated by increased hepatocellular apoptosis caused by intravenous injection of anti-Fas (Jo-2).

CONCLUSIONS

These findings suggest that the increased growth caused by IRS-1 over-expression is balanced by constitutive activation of pro-death mechanisms. Failure of the IRS-1 Tg mice to develop liver cancer may be due to preservation of pro-growth, pro-death homeostasis mechanisms.

Antisense protein tyrosine phosphatase 1B reverses activation of p38 mitogen-activated protein kinase in liver of ob/ob mice

Phosphorylation of stress-activated kinase p38, a MAPK family member, was increased in liver of ob/ob diabetic mice relative to lean littermates. Treatment of ob/ob mice with protein tyrosine phosphatase 1B (PTP1B) antisense oligonucleotides (ASO) reduced phosphorylation of p38 in liver-to below lean littermate levels-and normalized plasma glucose while reducing plasma insulin. Phosphorylation of ERK, but not JNK, was also decreased in ASO-treated mice. PTP1B ASO decreased TNFalpha protein levels and phosphorylation of the transcription factor cAMP response element binding protein (CREB) in liver, both of which can occur through decreased phosphorylation of p38 and both of which have been implicated in insulin resistance or hyperglycemia. Decreased p38 phosphorylation was not directly due to decreased phosphorylation of the kinases that normally phosphorylate p38-MKK3 and MKK6. Additionally, p38 phosphorylation was not enhanced in liver upon insulin stimulation of ASO-treated ob/ob mice (despite increased activation of other signaling molecules) corroborating that p38 is not directly affected via the insulin receptor. Instead, decreased phosphorylation of p38 may be due to increased expression of MAPK phosphatases, particularly the p38/ERK phosphatase PAC1 (phosphatase of activated cells). This study demonstrates that reduction of PTP1B protein using ASO reduces activation of p38 and its substrates TNFalpha and CREB in liver of diabetic mice, which correlates with decreased hyperglycemia and hyperinsulinemia.

Overexpression of mitogen-activated protein kinase phosphatases MKP1, MKP2 in human breast cancer

Expression and activity of c-Jun N-terminal and p38 protein kinases were explored in malignant and non-malignant tissue samples from patients with primary breast cancer. Differential expression was observed for p38 and c-Jun N-terminal protein kinases (JNK) in samples from 14 patients in whom there were sufficient malignant and non-malignant tissue to perform the entire assays. As previously noted, Erk1,2 expression and activity were increased sharply in the malignant tissue. The p38 kinase expression and activity were increased 3-fold in breast cancer. The expression of c-Jun N-terminal protein kinase JNK1, but not JNK2, was increased 2.5-fold in malignant as compared to normal breast tissue. Immunohistochemical analysis in situ with antibodies to JNK1 revealed intense staining in samples of cancerous epithelium. In spite of a 3-fold increase in expression, malignant samples displayed a 35% decrease in the activity of this pro-apoptotic protein kinase. The expression of mitogen and extracellularly-activated protein kinase kinase (MEK)2 and MEK3, upstream protein kinases of Erkl,2 and p38, respectively, was elevated 4- to 5-fold. The upstream regulator of JNK (e.g., MEK4), however, displayed normal levels of expression, providing no basis for the reduction in JNK activity observed for breast cancer. Mitogen-activated protein kinase phosphatases (MKP)1 and MKP2 were assayed and the expression was found to be increased 5-fold and 3-fold, respectively, in malignant as compared to non-malignant samples. The reduced activity of JNK1, in spite of its overexpression, appears to reflect increased MKP activity associated with primary breast cancer. Suppression of MKP activity therapeutically may enable the expression of the pro-apoptotic signals from JNK in malignant cells.

Cyclins and cyclin-dependent kinases: comparative study of hepatocellular carcinoma versus cirrhosis

Increasing evidence has indicated that perturbation of cyclins is one of the major factors leading to cancer. The aim of this study was not only to investigate various cell cycle-related kinase activities in hepatocellular carcinoma (HCC), but also to analyze the difference of cell cycle-related kinase activity levels between hepatitis C virus (HCV)-induced HCC and HCV-induced cirrhosis. The protein levels of cyclins D1, E, A, and H, and of cyclin dependent kinase 1 (Cdk1), Cdk2, Cdk4, Cdk6, and Cdk7 in HCC and in surrounding nontumorous cirrhosis were determined by Western blot. The enzymatic activities of cyclins D1, E, A, Cdk1, Cdk4, Cdk6, Cdk7, and Wee1 were measured using in vitro kinase assays. Protein levels and kinase activities of cyclin D1, Cdk4, cyclin E, cyclin A, and Wee1 were significantly elevated in HCC compared with surrounding cirrhotic tissues. The enhanced cyclin D1-related kinase activity in HCC was accompanied by the up-regulation of Cdk4 activity, but not Cdk6 activity. The kinase activities of Cdk6, Cdk7, and Cdk1 did not differ between HCC and surrounding cirrhotic tissues. In addition, the protein levels and kinase activities of cyclin D1, Cdk4, and cyclin E were higher in poorly differentiated HCC and advanced HCC. In conclusion, the increases of cyclin D1, Cdk4, cyclin E, cyclin A, and Wee1 play an important role in the development of HCC from cirrhosis. Cyclin D1, Cdk4, and cyclin E activation may be closely related to the histopathologic grade and progression of HCC.

Activation of NF-kappa B, AP-1 and STAT transcription factors is a frequent and early event in human hepatocellular carcinomas

BACKGROUND/AIMS

Hepatitis B and C viruses, two inducers of hepatocarcinomas, have been shown to activate AP-1, NF-kappa B and STAT in vitro, but no detailed information on the activity of these transcription factors in vivo have been provided.

METHODS

We have measured the DNA binding activity of these transcription factors in the peri-tumoral and the tumoral parts of 15 primary liver cancers, of viral or non-viral etiologies, and in five hepatic metastases using electrophoretic mobility shift assays.

RESULTS

AP-1, NF-kappa B and STAT binding activities were increased in the peritumoral tissue, compared with histologically normal livers in 73, 87 and 70%, respectively, of the cases. A further activation of AP-1, NF-kappa B, but not STAT binding in the tumoral parts was detected in 40 and 80%, respectively, of the cases. A close correlation was found between JunD and c-Jun levels and AP-1 binding activity at the tumoral stage. By contrast, AP-1 and NF-kappa B binding activities were low or only slightly elevated in the peri-tumoral and the tumoral tissue of metastases.

CONCLUSIONS

Early activation of AP-1, NF-kappa B and STAT contributes probably to the acquisition of a transformed phenotype during hepatocarcinogenesis, whatever the etiology.

Hepatitis C virus core protein induces cell proliferation and activates ERK, JNK, and p38 MAP kinases together with the MAP kinase phosphatase MKP-1 in a HepG2 Tet-Off cell line

Hepatitis C virus (HCV) core protein is a multifunctional protein interacting with cellular and viral proteins and promoters. A tetracycline-regulated system was used to generate a HepG2 Tet-Off cell line allowing regulated expression of a full-length (191 aa) and an N(c)-truncated core protein (160 aa). In this system HCV core protein expression activates extracellular signal-regulated kinase (ERK), c-jun N-terminal kinase (JNK), and p38 mitogen-activated protein (MAP) kinase, induces MAP kinase phosphatase MKP-1 expression, and increases cell proliferation. This was accompanied by an activation of c-Jun and ATF-2, but not Elk-1 and c-Fos. Furthermore, AP-1 activation was independent of c-Fos. Full-length and N(c)-truncated HCV core proteins exerted similar effects.

Sustained activation of mitogen-activated protein kinases and activator protein 1 by the hepatitis B virus X protein in mouse hepatocytes in vivo

Transcriptional activation of diverse cellular genes by the X protein (HBx) of hepatitis B virus (HBV) has been suggested as one of the mechanisms for HBV-associated hepatocellular carcinoma. However, such functions of HBx have been studied using transformed cells in culture and have not been examined in the normal adult hepatocytes, a natural host of HBV. Using an efficient hepatocyte-specific virus-based gene delivery system developed in our laboratory earlier, we studied the HBx action in vivo. We demonstrate that following virosome-mediated delivery of HBx DNA, a large population (>50%) of hepatocytes express the HBx protein in a dose-dependent manner, which induces a significant increase in the activity of extracellular signal-regulated kinases (ERKs) in the livers of HBx-transfected mice. Inhibition of HBx-induced ERK activation following intravenous administration of PD98059, a mitogen-activated protein kinase kinase kinase (MEK) inhibitor, confirmed the requirement for MEK in the activation of ERKs by HBx. Induction of ERK activity by HBx was sustained for up to 30 days. Interestingly, sustained activation of c-Jun N-terminal kinases (JNKs) for up to 30 days was also noted. Such constitutive ERK and JNK activation as a consequence of continued HBx expression also led to sustained stimulation of further downstream events, such as increased levels of c-Jun and c-Fos proteins along with the persistent induction of activator protein 1 binding activity. Taken together, our data suggest a critical role of these molecules in HBx-mediated cell transformation.

Cytosolic phospholipase A(2)-mediated ICAM-1 expression is calcium dependent

BACKGROUND

Some human malignancies such as virus-related hepatocellular cancer arise in a setting of chronic inflammation. Upregulation of ICAM-1 is a seminal late event in malignant transformation following chronic inflammation. Cytosolic phospholipase A(2) (cPLA(2)) is a lipid-mediator activated by inflammatory stimuli, which has been shown to mediate ICAM-1 upregulation. As lipid mediators are known to work via calcium-dependent mechanisms in nearly all mammalian cells, we hypothesize that inflammatory-mediated ICAM-1 upregulation is dependent on both cPLA(2) and intracellular calcium.

MATERIALS AND METHODS

HUVEC were chosen as a representative cell line as they emulate hepatic sinusoids and are a well-established cell model. These were grown to confluence in T-25 flasks and stimulated with TNF-alpha or LPS for 6 h. Additional groups were preincubated with AACOCF3 (a specific cPLA(2) inhibitor) or BAPTA A.M. (a specific inhibitor of intracellular Ca(2+)) prior to being exposed to inflammatory stimuli. ICAM-1 expression was determined by mean fluorescent intensity (MFI) as measured by FITC-labeled moAb to ICAM-1 via FACS. The role of intracellular Ca(2+) on cPLA(2) activity was determined by thin-layer chromatography. Groups were compared using ANOVA with Scheffe's post hoc analysis; *P < 0.05 vs control, daggerP < 0.05 vs LPS and TNF-alpha was considered significant; N > or = 4 all experimental groups.

RESULTS

Both cPLA(2) and Ca(2+) inhibition significantly inhibited inflammatory upregulation of ICAM-1. Pretreatment with BAPTA A.M. attenuated HUVEC cPLA(2) activity in response to LPS. These findings suggest that appropriate molecular target suppression may prevent malignant degeneration in the presence of chronic inflammation.

Sustained activation of the Raf/MEK/Erk pathway in response to EGF in stable cell lines expressing the Hepatitis C Virus (HCV) core protein

Chronic hepatitis C virus (HCV) infection is a leading cause of liver cirrhosis and hepatocellular carcinoma (HCC) worldwide. The HCV capside core is a multifunctional protein with regulatory functions that affects transcription and cell growth in vitro and in vivo. Here, we show that both HCV genotype 1a and 3 core proteins activate MEK1 and Erk1/2 MAP kinases and that the costitutive expression of the HCV core results in a high basal activity of Raf1 and MAP/kinase/kinase, as determined by endogenous Raf1 in vitro kinase assay and immunodetection of hyperphosphorylated Erk1 and Erk2 even after a serum starvation. Moreover, the activation of both Erk1/2 and the downstream transcription factor Elk-1 in response to the mitogenic stimulus EGF is significantly prolonged. The sustained response to EGF in cells expressing the HCV core occurs despite a normal induction of the MAP phosphatases MKP regulatory feedback and is likely due to the costitutive activation of Raf-1 activity. The ability of HCV core proteins to directly activate the MAP kinase cascade and to prolong its activity in response to mitogenic stimuli may contribute to the neoplastic transformation of HCV infected liver cells.

Effect of phosphorylation of MAPK and Stat3 and expression of c-fos and c-jun proteins on hepatocarcinogenesis and their clinical significance

AIM: To study the effect of phosphorylation of MAPK and Stat3 and the expression of c-fos and c-jun proteins on hepatocellular carcinogenesis and their clinical significance.

METHODS: SP immunohistochemistry was used to detect the expression of p42/44^MAPK, p-Stat3, ca2fos and c-jun proteins in 55 hepatocellular carcinomas (HCC) and their surrounding liver tissues.

RESULTS: The positive rates and expression levels of p42/44^MAPK, p-Stat3, c-fos and c-jun proteins in HCCs were significantly higher than those in pericarcinomatous liver tissues (PCLT). A positive correlation was observed between the expression of p42/44^MAPK and c-fos proteins, and between pa2Stat3 and c-jun, but there was no significant correlation between p42/44^MAPK and p-Stat3 in HCCs and their surrounding liver tissues.

CONCLUSION: The abnormalities of Ras/Raf/MAPK and JAKs/Stat3 cascade reaction may contribute to malignant transformation of hepatocytes.Hepatocytes which are positive for p42/44^MAPK, c-fos or c-jun proteins may be potential malignant pre-cancerous cells. Activation of MAPK and Stat3 proteins may be an early event in hepatocellular carcinogenesis.

Hepatitis C virus core protein activates the MAPK/ERK cascade synergistically with tumor promoter TPA, but not with epidermal growth factor or transforming growth factor alpha

Persistent hepatitis C virus (HCV) infection is associated with the development of human hepatocellular carcinoma (HCC), although the mechanism of HCV-related hepatocarcinogenesis remains unclear. Recently, however, the close relationships between the development of HCC and the mitogen-activated protein kinase (MAPK)/extracellular signal-regulated protein kinase (ERK) cascade have been described. In the present study, we investigated the effects of HCV core protein on this MAPK/ERK cascade. HCV core protein significantly activated the MAPK/ERK cascade, including Elk1. We also examined whether HCV core protein acted synergistically along with hepatocyte mitogen-mediated MAPK/ERK activation. Interestingly, Elk-1 activities were further enhanced by the tumor promoter, 12-O-tetradecanoyl phorbol 13-acetate (TPA), but not by hepatocyte mitogens (epidermal growth factor [EGF] and transforming growth factor alpha [TGF-alpha]) in NIH3T3 cells and HepG2 cells expressing HCV core protein. Moreover, the MAPK/ERK activation by HCV core protein was blocked in the presence of the specific MEK1 inhibitor, PD98059. These results indicate that ERK activation by HCV core protein may be independent of hepatocyte mitogen-mediated signaling but synergistic with TPA, and HCV core protein may function at MEK1 or farther upstream of that component.

Hepatocellular carcinoma cell cycle: study of Long-Evans cinnamon rats

Amplification found in a number of cyclin genes, especially in cyclin D and E, is an important event process that takes place in cancers, including hepatocellular carcinoma (HCC). The activities of a wide range of cell cycle-related kinases remain obscure in HCC. The purpose of the present study is to determine the cyclins and kinase activities of HCC in Long-Evans Cinnamon (LEC) rats. Cyclin D1, E, A, H, Cdk1(cyclin-dependent kinase; Cdc2), Cdk4, and Cdk6 protein levels were determined by Western blot analysis at different pathologic stages of liver tissues exhibiting HCC. Enzymatic activities of cyclin D1, E, A, Cdk4, Cdk6, Cdc2, Cdk7, and Wee1 kinase were measured by in-gel kinase assay. Protein levels and kinase activities of cyclin D1, E, Cdk4, cyclin A, and Wee1 increased proportionally with the development of HCC, especially in the transition process from chronic hepatitis to HCC. Although Cdc2 kinase activity was found to increase slightly from normal liver to chronic hepatitis, its activity remained unchanged in the process from chronic hepatitis to HCC. Cdk6 and Cdk7 activities remained unchanged in the process from normal liver to HCC. These data suggest that the increase in Cdc2 kinase may play a role in the process from normal liver to chronic hepatitis, whereas the predominant increase in cyclin D1, Cdk4, cyclin E, cyclin A, and Wee1 suggests involvement not only in the process from normal liver to chronic hepatitis, but also during transition into HCC.

The role of wild-type and mutated N-ras in the malignant transformation of liver cells

In order to determine the role of N-ras overexpression and mutation in malignant liver cell transformation, wild-type and mutated N-ras were transfected into the rat liver epithelial cell line OC/CDE 22, and N-ras expression, growth kinetics, growth in soft agar, and tumorigenicity in vivo as well as the involvement of the mitogen-activated protein kinase (MAPK) signal transduction pathway in the expression of the malignant phenotype were analyzed. Although OC/CDE 22 cells transfected with wild-type N-ras showed a high expression of N-ras at the mRNA and protein levels, the cells did not grow in soft agar and were not tumorigenic in vivo. In contrast, OC/CDE 22 cells transfected with mutated N-ras showed anchorage-independent growth and were tumorigenic. When cultured in fetal bovine serum-supplemented medium, OC/CDE 22 cells expressing mutant N-ras showed a higher proliferation rate than nontransfected OC/CDE 22 cells or OC/CDE 22 cells transfected with wild-type N-ras. When held in serum-free medium, untreated OC/CDE 22 cells did not grow at all, while OC/CDE 22 cells transfected with wild-type or mutant N-ras proliferated at a similar rate, which can be explained by the high MAPK activity in these cells. Selective inhibition of the MAPK cascade abolished the growth of OC/CDE 22 cells carrying mutant N-ras in soft agar; furthermore, these cells ceased pile up and formed monolayers on Petri dishes. Thus, activation of the MAPK signaling pathway, though alone not sufficient to malignantly transform liver cells (as shown in liver cells overexpressing wild-type N-ras), is not only essential for growth control but also for the expression of the malignant phenotype (as demonstrated in liver cells transformed by mutated N-ras).

Hepatitis C virus core protein interacts with 14-3-3 protein and activates the kinase Raf-1

Persistent hepatitis C virus (HCV) infection is a major cause of chronic liver dysfunction in humans and is epidemiologically closely associated with the development of human hepatocellular carcinoma. Among HCV components, core protein has been reported to be implicated in cell growth regulation both in vitro and in vivo, although mechanisms explaining those effects are still unclear. In the present study, we identified that members of the 14-3-3 protein family associate with HCV core protein. 14-3-3 protein bound to HCV core protein in a phosphoserine-dependent manner. Introduction of HCV core protein caused a substantial increase in Raf-1 kinase activity in HepG2 cells and in a yeast genetic assay. Furthermore, the HCV core-14-3-3 interaction was essential for Raf-1 kinase activation by HCV core protein. These results suggest that HCV core protein may represent a novel type of Raf-1 kinase-activating protein through its interaction with 14-3-3 protein and may contribute to hepatocyte growth regulation.

Increased activity and expression of MAP kinase in HCC model rats induced by 3'-methyl-4-dimethylamino-azobenzene

BACKGROUND/AIMS

The ras-mitogen-activated protein kinase (MAPK) cascade plays an important role not only in the mitogenic signal transduction pathway but also in the development of cancer, and it is believed to be one of the important regulators in normal hepatocytes and hepatocellular carcinoma. The aim of this study was to determine the role of insulin receptor substrate-1 and the MAPK cascade in rats with hepatocellular carcinoma induced by 3'-methyl-4-dimethylamino-azobenzene (3'-MeDAB).

METHODS

Liver cancer was induced in rats by feeding 3'-MeDAB, and the changes in expression of IRS-1 and MAPK were analyzed in tumorous, non-tumorous and control liver.

RESULTS

Expression of insulin receptor substrate-1 (IRS-1) showed a 1.4-fold increase at protein level in the tumors (p<0.01), but the tyrosine phosphorylation of IRS-1 did not differ between the tumor and control liver. Expression of MAPK and its activity were elevated 4.5-7.5-fold (p<0.01) and 4.6-fold (p<0.01) in the tumor compared with control liver. In non-tumorous lesions from rats fed with 3'-MeDAB, expression of MAPK, but not IRS-1, increased significantly (p<0.01). Between tumorous and adjacent non-tumorous lesions, there was a significant difference in MAPK expression (p<0.05) and activities (p<0.05).

CONCLUSIONS

The increased expression of MAPK may play an important role in the progression or initiation of HCC in this rat model.

The mitogen-activated protein kinase kinase/extracellular signal-regulated kinase cascade activation is a key signalling pathway involved in the regulation of G(1) phase progression in proliferating hepatocytes

In this study, activation of the mitogen-activated protein kinase kinase (MEK)/extracellular signal-regulated kinase (ERK) signalling pathway was analyzed in proliferating rat hepatocytes both in vivo after partial hepatectomy and in vitro following epidermal growth factor (EGF)-pyruvate stimulation. First, a biphasic MEK/ERK activation was evidenced in G(1) phase of hepatocytes from regenerating liver but not from sham-operated control animals. One occurred in early G(1) (30 min to 4 h), and the other occurred in mid-late G(1), peaking at around 10.5 h. Interestingly, the mid-late G(1) activation peak was located just before cyclin D1 induction in both in vivo and in vitro models. Second, the biological role of the MEK/ERK cascade activation in hepatocyte progression through the G(1)/S transition was assessed by adding a MEK inhibitor (PD 98059) to EGF-pyruvate-stimulated hepatocytes in primary culture. In the presence of MEK inhibitor, cyclin D1 mRNA accumulation was inhibited, DNA replication was totally abolished, and the MEK1 isoform was preferentially targeted by this inhibition. This effect was dose dependent and completely reversed by removing the MEK inhibitor. Furthermore, transient transfection of hepatocytes with activated MEK1 construct resulted in increased cyclin D1 mRNA accumulation. Third, a correlation between the mid-late G(1) MEK/ERK activation in hepatocytes in vivo after partial hepatectomy and the mitogen-independent proliferation capacity of these cells in vitro was established. Among hepatocytes isolated either 5, 7, 9, 12 or 15 h after partial hepatectomy, only those isolated from 12- and 15-h regenerating livers were able to replicate DNA without additional growth stimulation in vitro. In addition, PD 98059 intravenous administration in vivo, before MEK activation, was able to inhibit DNA replication in hepatocytes from regenerating livers. Taken together, these results show that (i) early induction of the MEK/ERK cascade is restricted to hepatocytes from hepatectomized animals, allowing an early distinction of primed hepatocytes from those returning to quiescence, and (ii) mid-late G(1) MEK/ERK activation is mainly associated with cyclin D1 accumulation which leads to mitogen-independent progression of hepatocytes to S phase. These results allow us to point to a growth factor dependency in mid-late G(1) phase of proliferating hepatocytes in vivo as observed in vitro in proliferating hepatocytes and argue for a crucial role of the MEK/ERK cascade signalling pathway.