Differential effects of interferon alpha-2b and beta on the signaling pathways in human liver cancer cells

Background Interferon (IFN) has been reported to reduce the incidence of hepatocellular carcinoma (HCC) in patients with chronic hepatitis C and the recurrence of HCC after effective treatment. We examined the effect of IFNs on the proliferation and the signaling pathways of human HCC cells.Methods Cellular proliferation was examined by a modified 3-(4,5-dimethylthiazol-2-yl)-2,5 diphenyltetrazolium bromide (MTT) assay. Activities of signaling molecules were evaluated by Western blot analysis.Results Cellular growth was not significantly modulated by IFNα-2b or by IFN-β, even though the HCC cells expressed the IFN receptors. However, extracellular signal-regulated kinase (ERK)1/2 was activated by treatment with IFNα-2b, and both ERK1/2 and AKT were activated by treatment with IFN-β, implying a possible role in resistance to IFNs. Contrary to our expectations, inhibition of mitogen-activated ERK-regulating kinase (MEK) or phosphatidylinositol-3-OH kinase (PI3K) did not modulate the proliferation of HCC cells. Also, abrogation of the ERK1/2 and AKT signaling pathways did not affect cell-cycle arrest at the G1/S phase caused by IFNα-2b.Conclusions IFNα-2b and IFN-β activated ERK1/2 and/or AKT independently of modulating the proliferation of HCC cells and the cell-cycle machinery. A signal transduction-based approach for HCC treatment needs to focus on other possible signaling molecules besides ERK1/2 and AKT when challenged with IFNs.     

Insights into erlotinib action in pancreatic cancer cells using a combined experimental and mathematical approach

AIM:To gain insights into the molecular action of erlotinib in pancreatic cancer (PC) cells. METHODS:Two PC cell lines, BxPC-3 and Capan-1, were treated with various concentrations of erlotinib, the specific mitogen-activated protein kinase kinase (MEK) inhibitor U0126, and protein kinase B (AKT) inhibitor XIV. DNA synthesis was measured by 5-bromo-2'-deoxyuridine (BrdU) assays. Expression and phosphorylation of the epidermal growth factor receptor (EGFR) and downstream signaling molecules were quantified by Western blot analysis. The data were processed to calibrate a mathematical model, based on ordinary differential equations, describing the EGFRmediated signal transduction. RESULTS:Erlotinib significantly inhibited BrdU incorporation in BxPC-3 cells at a concentration of 1 mol/L, whereas Capan-1 cells were much more resistant. In both cell lines, MEK inhibitor U0126 and erlotinib attenuated DNA synthesis in a cumulative manner, whereas the AKT pathway-specific inhibitor did not enhance the effects of erlotinib. While basal phosphorylation of EGFR and extracellular signal-regulated kinase (ERK) did not differ much between the two cell lines, BxPC-3 cells displayed a more than five-times higher basal phospho-AKT level than Capan-1 cells. Epidermal growth factor (EGF) at 10 ng/mL induced the phosphorylation of EGFR, AKT and ERK in both cell lines with similar kinetics. In BxPC-3 cells, higher levels of phospho-AKT and phospho-ERK (normalized to the total protein levels) were observed. Independent of the cell line, erlotinib efficiently inhibited phosphorylation of EGFR, AKT and ERK. The mathematical model successfully simulated the experimental findings and provided predictions regarding phosphoprotein levels that could be verified experimentally. CONCLUSION:Our data suggest basal AKT phosphorylation and the degree of EGF-induced activation of AKT and ERK as molecular determinants of erlotinib efficiency in PC cells.     

Human sulfatase‐1 inhibits the migration and proliferation of SMMC‐7721 hepatocellular carcinoma cells by downregulating the growth factor signaling

Aim: The human sulfatase‐1 (hSulf‐1) gene regulates the sulfation of heparan sulfate proteoglycans (HSPG) and suppresses tumorigenesis and angiogenesis by inhibiting several growth factor signaling pathways. Because the serine‐threonine protein kinase (AKT) and extracellular signal‐regulated kinase (ERK) signaling pathways are critical in cell survival, proliferation, migration and angiogenesis, the possible correlation between hSulf‐1 and AKT/ERK signaling in hepatocellular carcinoma (HCC) cells needs further exploration. Methods: Adenovirus Ad5‐hSulf1 carrying the hSulf‐1 gene, and vectors carrying hSulf‐1 shRNA, AKT shRNA and ERK shRNA were constructed and used to manipulate the expression of hSulf‐1, AKT and ERK in SMMC‐7721 cells. The scarification test, transwell and 3‐(4 5‐dimethylthiazol‐2‐yl)‐2 5‐diphenyltetrazolium bromide assays were used to examine the cellular migration and proliferation, and the expression of hSulf‐1 and signaling factors, including the total and phosphorylated AKT and ERK, was analyzed by western blot in SMMC‐7721 cells. Results: After infection with Ad5‐hSulf1, the expression of hSulf‐1 was increased with viral multiplicity of infection in SMMC‐7721 cells. Compared with the control adenovirus Ad5‐EGFP and blank control groups, cells in the Ad5‐hSulf1 group were showed that the phosphorylation of AKT and ERK was decreased. Meanwhile, the cell migration and cell viability were obviously suppressed. Conclusion: The expression of hSulf‐1 mediated by adenovirus in HCC cells could downregulate the activity of AKT and ERK signaling pathways, and inhibit HCC cell migration and proliferation. The hSulf‐1 gene may be considered as a candidate of antitumor factor for cancer gene therapy.     

Molecular aspects of gefitinib antiproliferative and pro-apoptotic effects in PTEN-positive and PTEN-negative prostate cancer cell lines

To date, no effective therapeutic treatment allows abrogation of the progression of prostate cancer (PCa) to more invasive forms. One of the major targets for the therapy in PCa can be epidermal growth factor receptor (EGFR), which signals via the phosphoinositide 3'-kinase (PI3K)/Akt and mitogen-activated protein kinase (MAPK) pathways, among others. Despite multiple reports of overexpression in PCa, the reliance on activated EGFR and its downstream signalling to the PI3K and/or MAPK/extracellular signal-regulated kinase (ERK) pathways has not been fully elucidated. We reported that the EGFR-selective tyrosine kinase inhibitor gefitinib (ZD1839; Iressa) is able to induce growth inhibition, G(1) arrest and apoptosis in PCa cells and that its effectiveness is associated primarily with phosphatase and tensin homologue deleted from chromosome 10 (PTEN) expression (and thus Akt activity). In fact PTEN-negative PCa cells are slowly sensitive to gefitinib treatment, because this molecule is unable to downregulate PI3K/Akt activity. PI3K inhibition, by LY294002 or after PTEN transfection, restores EGFR-stimulated Akt signalling and sensitizes the cells to pro-apoptotic action of gefitinib. The MAPK pathway seems to be involved primarily on cell-growth modulation because dual blockade of EGFR and ERK1/2 phosphorylation potentiates growth inhibition (both not cell apoptosis) in PTEN-positive PCa cells and reduced EGF-mediated growth in PTEN-negative cells. Thus the effectiveness of gefitinib requires growth factor receptor-stimulated PI3K/Akt and MAPK signalling to be intact and functional. The loss of the PTEN activity leads to uncoupling of this signalling pathway, determining a partial gefitinib resistance. Moreover, gefitinib sensitivity may be maintained in these cells through its inhibitory potential in MAPK/ERK pathway activity, modulating proliferative EGFR-triggered events. Therefore, our data suggest that the inhibition of EGFR signalling can result in a significant growth reduction and in increased apoptosis in EGFR-overexpressing PCa cells with different modalities, which are regulated by PTEN status, and this may have relevance in the clinical setting of PCa.     

Targeting EGFR activity in blood vessels is sufficient to inhibit tumor growth and is accompanied by an increase in VEGFR-2 dependence in tumor endothelial cells

Epidermal growth factor receptor (EGFR) targeting agents such as kinase inhibitors reduce tumor growth and progression. We have previously reported that EGFR is not only expressed by the tumor cells but by the tumor endothelial cells (EC) as well (Amin, D. N., Hida, K., Bielenberg, D. R., Klagsbrun, M., 2006. Tumor endothelial cells express epidermal growth factor receptor (EGFR) but not ErbB3 and are responsive to EGF and to EGFR kinase inhibitors. Cancer Res. 66, 2173–80). Thus, targeting tumor blood vessel EGFR may be a viable strategy for tumor growth inhibition. We describe here a melanoma xenograft model where the tumor cells express very little or no EGFR but the tumor blood vessels express activated EGFR. The EGFR kinase inhibitor, gefitinib (Iressa), retarded tumor growth with a size decrease of 38% compared to control mice, ostensibly due to targeting of the blood vessels. EC were isolated from tumors of gefitinib-treated mice. These EC were unable to proliferate in response to EGF and displayed relatively weaker activation of MAPK and AKT signaling in response to EGF compared to tumor EC isolated from vehicle-treated mice. In contrast, the tumor EC from gefitinib-treated mice expressed higher levels of VEGFR-2 both at the mRNA and protein level. In addition, these cells were less sensitive to EGFR kinase inhibitors in vitro but more sensitive to a VEGFR-2 kinase inhibitor. These results suggest that in tumor EC from gefitinib-treated mice there is a switch from dependence on EGFR activity to signaling via VEGFR-2. Our data provide a molecular rationale for combination therapies targeting both EGF and VEGF signaling on the tumor vasculature.     

Angiotensin II and epidermal growth factor receptor cross-talk mediated by a disintegrin and metalloprotease accelerates tumor cell proliferation of hepatocellular carcinoma cell lines.

Aim: The cross-talk pathway between angiotensin II (AngII) and the epidermal growth factor receptor (EGFR) mediated by epidermal growth factor (EGF)-like ligands cleaved by a disintegrin and metalloprotease (ADAM) has been elucidated in several cell types. Even though the liver is a representative angiotensinogen-producing organ, such cross-talk has never been elucidated in hepatocellular carcinomas (HCCs). We investigated whether AngII exerted a mitogenic effect on HCC cell lines through the AngII-EGFR cross-talk pathway. Methods: We determined the expression and/or phosphorylation status of AngII receptor type 1 (AGTR1), ADAM9, ADAM17, ERK1/2, STAT3, AKT and EGFR in five HCC cell lines using Western blotting. Proliferation and invasion activities were measured by ATP and Matrigel invasion assays, respectively. Results: AGTR1 was expressed ubiquitously in HCC cell lines. EGFR expression in HepG2 was relatively weaker than that in the remaining HCC cell lines. The phosphorylation status of EGFR, ERK1/2, STAT3 and AKT was upregulated by AngII treatment in two EGFR-overexpressing cell lines (Huh7 and PLC/PRF/5), but not in HepG2 (showing weak EGFR expression). AngII stimulation significantly accelerated proliferation and invasion activities in Huh7 and PLC/PRF/5, and was inhibited by pretreatment with an ADAM inhibitor. A selective AGTR1 blocker significantly repressed proliferation activity in both cell lines, but did not significantly repress the invasion activity. Both chemical agents and neutralizing antibodies against ADAMs (ADAM9 and ADAM17) and EGF-like ligands suppressed EGFR transactivation and/or subsequent phosphorylation of ERK1/2, STAT3 and AKT. Conclusion: These results suggest that AngII-EGFR cross-talk signaling mediated by ADAMs is involved in the proliferation and invasion activities of several HCC cell lines.     

Targeting the epidermal growth factor receptor by gefitinib for treatment of hepatocellular carcinoma

BACKGROUND/AIMS: Hepatocellular carcinoma (HCC) is one of the most common cancer-related causes of death worldwide. Due to very poor 5-year-survival new therapeutic approaches are mandatory. Gefitinib, an inhibitor of epidermal growth factor receptor tyrosine kinase (EGFR-TK), potently suppresses the growth of various tumors, but its effect on HCC remains unexplored. We therefore studied the antineoplastic potency of gefitinib in human HCC cells. RESULTS: Gefitinib induced a time- and dose-dependent growth inhibition of the human HCC cell lines Huh-7 and HepG2. Gefitinib-treatment induced both mitochondria-dependent and -independent apoptosis. Changes in mitochondrial membrane potential and caspase-8 activation, followed by caspase-3 activation and nuclear degradation, were detected. Moreover, gefitinib induced cell cycle arrest at the G1/S checkpoint and decreased the phosphorylation of mitogen-activated protein kinase ERK1/2. Finally, gefitinib suppressed the expression of antiapoptotic Bcl-2 and Bcl-X(L), further rendering HCC cells prone to apoptosis. CONCLUSIONS: Our data demonstrate that the inhibition of EGFR-TK by gefitinib induced growth inhibition, apoptosis and cell cycle arrest in human HCC cells. Thus, EGFR-TK inhibition appears to be a promising novel approach for future treatment strategies of HCC.     

Lapatinib,a dual inhibitor of epidermal growth factor receptor and human epidermal growth factor receptor 2, potentiates the antitumor effects of cisplatin on esophageal carcinoma

Epidermal growth factor receptor (EGFR) and human epidermal growth factor receptor 2 (HER2) overexpression occurs in over 30% of esophageal carcinomas. Combination therapies of EGFR‐ and HER2‐targeting agents with cytotoxic agents are considered a potential therapeutic strategy for esophageal cancer. The antitumor effects of lapatinib, a dual tyrosine kinase inhibitor of EGFR and HER2, cisplatin alone, and the combination of the two drugs on esophageal cancer cells were evaluated. The growth inhibition activity of lapatinib, cisplatin, and lapatinib plus cisplatin was measured by 3‐(4,5)‐dimethylthiahiazo(‐z‐y1)‐3,5‐di‐phenytetrazoliumromide (MTT) assays, and the combination index values were calculated. Additionally, cell cycle distribution and cell apoptosis treated with lapatinib or cisplatin alone and the combination of the two drugs were detected by flow cytometry analysis. The activation of EGFR and HER2 signaling pathways was monitored by Western blot analysis. These experimental data showed that the combination of lapatinib and cisplatin synergistically inhibited cell proliferation and exhibited an enhanced pro‐apoptotic effect on esophageal cancer cells. The underlying mechanisms of potentiated effects of combined treatment were associated with reduced phosphorylation of EGFR and HER2, and the downstream signaling molecules AKT and extracellular regulated protein kinases (ERK). Our findings indicated that the combination of lapatinib and cisplatin is one of the promising treatment strategies for esophageal carcinomas with EGFR and HER2 overexpression.     

The antiepidermal growth factor receptor agent gefitinib (ZD1839/Iressa) improves antihormone response and prevents development of resistance in breast cancer in vitro

Although many estrogen receptor-positive breast cancers initially respond to antihormones, responses are commonly incomplete with resistance ultimately emerging. Delineation of signaling mechanisms underlying these phenomena would allow development of therapies to improve antihormone response and compromise resistance. This in vitro investigation in MCF-7 breast cancer cells examines whether epidermal growth factor receptor (EGFR) signaling limits antiproliferative and proapoptotic activity of antihormones and ultimately supports development of resistance. It addresses whether the anti-EGFR agent gefitinib (ZD1839/Iressa; TKI: 1 mum) combined with the antihormones 4-hydroxytamoxifen (TAM: 0.1 mum) or fulvestrant (Faslodex; 0.1 mum) enhances growth inhibition and prevents resistance. TAM significantly suppressed MCF-7 growth over wk 2-5, reducing proliferation detected by immunocytochemistry and fluorescence-activated cell sorter cell cycle analysis. A modest apoptotic increase was observed by fluorescence-activated cell sorter and fluorescence microscopy, with incomplete bcl-2 suppression. EGFR induction occurred during TAM response, as measured by immunocytochemistry and Western blotting, with EGFR-positive, highly proliferative resistant growth subsequently emerging. Although TKI alone was ineffective on growth, TAM plus TKI cotreatment exhibited superior antigrowth activity vs. TAM, with no viable cells by wk 12. Cotreatment was more effective in inhibiting proliferation, promoting apoptosis, and eliminating bcl-2. Cotreatment blocked EGFR induction, markedly depleted ERK1/2 MAPK and protein kinase B phosphorylation, and prevented emergence of EGFR-positive resistance. Faslodex plus TKI cotreatment was also a superior antitumor strategy. Thus, increased EGFR evolves during treatment with antihormones, limiting their efficacy and promoting resistance. Gefitinib addition to antihormonal therapy could prove more effective in treating estrogen receptor-positive breast cancer and may combat development of resistance.     

Role of Extracellular Signal-Regulated Kinase, p38 Kinase, and Activator Protein-1 in Transforming Growth Factor-β1–Induced Alpha Smooth Muscle Actin Expression in Human Fetal Lung Fibroblasts In Vitro

Myofibroblasts characterized by alpha smooth muscle actin(α-SMA) expression play a key role in pulmonary fibrosis. Transforming growth factor-beta1 (TGF-β1) is likely to be involved in the emergence of myofibroblasts, but the intracellular signal pathways for this process have not been well determined. The aim of the present study was to investigate the role of mitogen-activated protein kinase (MAPK)/activator protein-1 (AP-1) signaling pathways in TGF-β1–induced α-SMA expression in human fetal lung fibroblasts (HLF-02). We found that TGF-β1 treatment activated p38 kinase and extracellular signal-regulated kinase (Erk) in HLF-02 cells. The induction of α-SMA by TGF-β1 was suppressed by p38 kinase inhibitor (SB203580) and Erk inhibitor (PD98059). AP-1 inhibitor curcumin also inhibited TGF-β1–induced α-SMA expression. In addition, dominant negative mutant c-Jun (TAM67) downregulated TGF-β1–induced AP-1 transactivation and α-SMA expression. In additional, PD98059 but not SB203580 inhibited the AP-1 DNA binding activity induced by TGF-β1. Based on these findings, we conclude that p38 kinase, Erk, and AP-1 are responsible for the α-SMA expression induced by TGF-β1 in human fetal lung fibroblasts. Erk is involved in inducing α-SMA expression via AP-1 activation.     

Irreversible inhibitors of the EGF receptor may circumvent acquired resistance to gefitinib

Non-small cell lung cancers (NSCLCs) with activating mutations in the kinase domain of the epidermal growth factor receptor (EGFR) demonstrate dramatic, but transient, responses to the reversible tyrosine kinase inhibitors gefitinib (Iressa) and erlotinib (Tarceva). Some recurrent tumors have a common secondary mutation in the EGFR kinase domain, T790M, conferring drug resistance, but in other cases the mechanism underlying acquired resistance is unknown. In studying multiple sites of recurrent NSCLCs, we detected T790M in only a small percentage of tumor cells. To identify additional mechanisms of acquired resistance to gefitinib, we used NSCLC cells harboring an activating EGFR mutation to generate multiple resistant clones in vitro. These drug-resistant cells demonstrate continued dependence on EGFR and ERBB2 signaling for their viability and have not acquired secondary EGFR mutations. However, they display increased internalization of ligand-activated EGFR, consistent with altered receptor trafficking. Although gefitinib-resistant clones are cross-resistant to related anilinoquinazolines, they demonstrate sensitivity to a class of irreversible inhibitors of EGFR. These inhibitors also show effective inhibition of signaling by T790M-mutant EGFR and killing of NSCLC cells with the T790M mutation. Both mechanisms of gefitinib resistance are therefore circumvented by irreversible tyrosine kinase inhibitors. Our findings suggest that one of these, HKI-272, may prove highly effective in the treatment of EGFR-mutant NSCLCs, including tumors that have become resistant to gefitinib or erlotinib.     

Gefitinib, an EGFR inhibitor, prevents hepatocellular carcinoma development in the rat liver with cirrhosis

Epidermal growth factor receptor (EGFR) binds transforming growth factor alpha (TGF-alpha) which is mitogenic for hepatocytes. Diverse lines of evidence suggest that activation of the TGF-alpha /EGFR pathway contributes to hepatocellular carcinoma (HCC) formation. Herein, we developed an experimental model of cirrhosis giving rise to HCC and tested the antitumoral effect of gefitinib, a selective EGFR tyrosine kinase inhibitor, in this model. Rats received weekly intraperitoneal injections of diethylnitrosamine (DEN) followed by a 2-week wash-out period that caused cirrhosis in 14 weeks and multifocal HCC in 18 weeks. Hepatocyte proliferation was increased in diseased tissue at 14 weeks compared with control liver and at even higher levels in HCC nodules compared with surrounding diseased tissues at 18 weeks. Increased proliferation was paralleled by upregulation of TGF-alpha messenger RNA expression. A group of DEN-treated rats received daily intraperitoneal injections of gefitinib between weeks 12 and 18. In rats treated with gefitinib, the number of HCC nodules was significantly lower than in untreated rats (18.1 +/- 2.4 vs. 3.7 +/- 0.45; P < .05), while EGFR was activated to a lesser extent in the diseased and tumoral tissues of these animals compared with untreated rats. HCC nodules from both untreated and gefitinib-treated animals displayed insulin-like growth factor 2 overexpression that contributed to tumor formation in treated animals. In conclusion, the blockade of EGFR activity by gefitinib has an antitumoral effect on the development of HCC in DEN-exposed rats, suggesting that it may provide benefit for the chemoprevention of HCC.     

Menetrier’s disease

Opinion statement Menetrier’s disease is a rare acquired disorder of the fundus and body of the stomach (ie, oxyntic mucosa) characterized by giant hyperplastic folds, protein-losing gastropathy, hypoalbuminemia, increased mucus secretion, and hypochlorhydria. Recent research implicates overproduction of transforming growth factor-α with increased signaling of the epidermal growth factor receptor (EGFR) in the pathogenesis. Activation of the EGFR, a transmembrane receptor with tyrosine kinase activity, triggers a cascade of downstream, intracellular signaling pathways that leads to expansion of the proliferative compartment within the isthmus of the oxyntic gland. The diagnosis of Menetrier’s disease is based upon characteristic histologic changes, including foveolar hyperplasia, cystic dilation of pits, and reduced numbers of parietal and chief cells. The best treatment for Menetrier’s disease is not clear. It seems reasonable to test and treat for cytomegalovirus and Helicobacter pylori, as 1) in children, evidence exists that the disease may be due to cytomegalovirus infection in up to one third of patients; and 2) in adults, there are anecdotal reports of resolution upon H. pylori eradication. More recently, therapies targeting increased signaling of the EGFR have shown promise, including somatostatin analogues and monoclonal antibodies (eg, cetuximab) directed against the EGFR. In refractory cases, gastrectomy is curative.     

TGF-alpha exerts biphasic effects on estrogen--and phytoestrogen-mediated gene expression in breast cancer cells

Transforming growth factor-α (TGF-α) contributes to the progression of mammary carcinogenesis in part through synergistic augmentation of estradiol (E₂) action. To investigate this further, we sought to determine (1) whether the duration of TGF-α treatment might influence the nature of the TGF-α/E₂ interaction, and (2) whether TGF-α would behave in a similar manner when combined with phytoestrogens. To this end, we transfected T47-D breast cancer cells with an estrogen-responsive reporter and then treated the cells (for 4–48 h) with varying concentrations of TGF-α, E₂, the antiestrogen 4-hydroxy-tamoxifen (HOT), and/or one of three phytoestrogens. Our findings revealed that TGF-α has short-term synergistic and long-term inhibitory effects on E₂-and phytoestrogen-regulated gene expression. Furthermore, this secondary inhibition of E₂ action by TGF-α was similar in magnitude to that imposed by HOT. These findings demonstrate a novel role for TGF-α and invite reevaluation of current models regarding TGF-αs interactions with E₂ inbreast cancer cells. Our results also raise the possibility that phytoestrogens, which interact with TGF-α in a manner conceptually identical to that of E₂, may subserve a regulatory function in breast cancer cells.     

非小细胞肺癌表皮生长因子受体酪氨酸激酶抑制剂耐药机制研究进展

以吉非替尼和厄罗替尼为代表的表皮生长因子受体酪氨酸激酶抑制剂在部分非小细胞肺癌患者中的治疗效果显著,但几乎所有患者最终均表现为耐药.因此,为提高该类药物的效用,对耐药性的研究便显得至关重要.基因突变、细胞表型改变、受体内化、信号通路成分及其调节因子的基因表达改变等都可以导致肿瘤细胞摆脱对表皮生长因子受体信号通路的专一性依赖而产生耐药.     

Wnt/β-catenin signaling regulates MAPK and Akt1 expression and growth of hepatocellular carcinoma cells

In hepatocellular carcinoma (HCC), Wnt/β-catenin, Ras/MAPK and PI3K/AKT signaling pathways form a complex network and play important roles during HCC genesis and development. To study their relationship and the influence on cell growth, the siRNA directed against β-catenin was transfected into HCC HepG2 cells. β-catenin mRNA and protein levels were measured respectively at various times by RT-PCR and Western blot. Furthermore, HCC cell growth was measured by MTT assay. Finally, MAPK family and Akt1 protein levels were also measured by Western blot. After the transfection, β-catenin mRNA levels were markedly inhibited at 24 h and increased gradually at 48, 72 and 96 h; β-catenin protein levels decreased gradually at 24, 48 and 72 h and slightly increased at 96 h. HCC cell growth was inhibited from 24-72 h, but this inhibition decreased at 96 h. ERK1/2 (p42/p44 MAPK), JNK/SAPK, p38 MAPK, and Akt1 protein levels showed no change following transfection, while their phosphorylated protein levels showed changes. Thus, siRNA directed against β-catenin markedly decreased β-catenin gene expression and inhibited cell growth. Wnt/β-catenin signaling pathway might regulate Ras/MAPK and PI3K/Akt signaling pathways through regulation of the phosphorylation state of ERK1/2, JNK/SAPK and Akt1 protein in HCC HepG2 cells. These pathways might compensate for the inhibitory effect of β-catenin, thereby affecting tumor cell growth and others downstream factors.     

Clostridium difficile toxin B activates the EGF receptor and the ERK/MAP kinase pathway in human colonocytes

BACKGROUND & AIMS: Clostridium difficile toxin B (TxB) mediates acute inflammatory diarrhea characterized by neutrophil infiltration and intestinal mucosal injury. In a xenograft animal model, TxB was shown to induce interleukin (IL)-8 gene expression in human colonic epithelium. However, the precise mechanisms of this TxB response are unknown. The aim of this study was to investigate the TxB-mediated proinflammatory pathway in colonocytes. METHODS: The effect of TxB on epidermal growth factor receptor (EGFR), extracellular signal-regulated kinase (ERK) 1/2 signaling pathway and IL-8 gene expression was assessed in nontransformed human colonic epithelial NCM460 cells. TxB regulation of EGFR-ERK1/2 signaling pathways was determined using immunoblot analysis, confocal microscopy, and enzyme-linked immunosorbent assay, whereas IL-8 gene expression was measured by luciferase promoter assay. RESULTS: TxB activates EGFR and ERK1/2 phosphorylation with subsequent release of IL-8 from human colonocytes. Pretreatment with either the EGFR tyrosine kinase inhibitor, AG1478, or an EGFR-neutralizing antibody blocked both TxB-induced EGFR and ERK activation. By using neutralizing antibodies against known ligands of EGFR, we found that the activation of EGFR and ERK1/2 phosphorylation was mediated by transforming growth factor-alpha (TGF-alpha). Inhibition of matrix metalloproteinase (MMP) decreased TGF-alpha secretion and TxB-induced EGFR and ERK activation. Inhibition of MMP, EGFR, and ERK activation significantly decreased TxB-induced IL-8 expression. CONCLUSIONS: TxB signals acute proinflammatory responses in colonocytes by transactivation of the EGFR and activation of the ERK/MAP kinase pathway.     

KSHV LANA inhibits TGF-beta signaling through epigenetic silencing of the TGF-beta type II receptor

Signaling through the transforming growth factor–β (TGF-β) pathway results in growth inhibition and induction of apoptosis in various cell types. We show that this pathway is blocked in Kaposi sarcoma herpesvirus (KSHV)–infected primary effusion lymphoma through down-regulation of the TGF-β type II receptor (TβRII) by epigenetic mechanisms. Our data also suggest that KSHV infection may result in lower expression of TβRII in Kaposi sarcoma and multicentric Castleman disease. KSHV-encoded LANA associates with the promoter of TβRII and leads to its methylation and to the deacetylation of proximal histones. Reestablishment of signaling through this pathway reduces viability of these cells, inferring that KSHV-mediated blockage of TGF-β signaling plays a role in the establishment and progression of KSHV-associated neoplasia. These data suggest a mechanism whereby KSHV evades both the antiproliferative effects of TGF-β signaling by silencing TβRII gene expression and immune recognition by suppressing TGF-β–responsive immune cells through the elevated secretion of TGF-β1.     

Extracellular signal-regulated kinase 1/2 activation by myometrial oxytocin receptor involves Galpha(q)Gbetagamma and epidermal growth factor receptor tyrosine kinase activation

The mechanisms by which oxytocin (OT) stimulates extracellular signal-regulated kinase 1/2 (ERK1/2) are only partially understood. OT receptor (OTR) signals predominantly through Galpha(q), but ERK1/2 phosphorylation (ERK1/2-P) in PHM1 myometrial cells was not eliminated by inhibition of downstream effectors such as phospholipase C or protein kinase C. Inconsistent with a Galpha(i)-coupled response, pertussis toxin inhibition of OT-induced ERK1/2-P was reversed by the protein kinase A inhibitors Rp-cAMPS and KT5720. Consistent with an inhibitory role for protein kinase A, pertussis toxin pretreatment raised cellular cAMP and 8-(4-chlorophenylthio)-cAMP inhibited OT-induced ERK1/2-P. Attenuation of the OT response by the Gbetagamma scavenger carboxyl terminus of the beta-adrenergic receptor kinase implicated a Gbetagamma-mediated pathway. In both COSM6 cells overexpressing OTR (OTR-COSM6) and in PHM1 cells, the epidermal growth factor receptor (EGFR) tyrosine kinase inhibitor AG1478 markedly reduced OT-induced ERK1/2-P, whereas the platelet-derived growth factor receptor tyrosine kinase inhibitor AG1296 had no effect. Furthermore, OT increased EGFR tyrosine phosphorylation in OTR-COSM6 cells, which was inhibited by AG1478 or EGTA plus thapsigargin pretreatment. AG1478 did not affect inositol 1,4,5-triphosphate production by OT or protein kinase C-stimulated ERK1/2-P but completely blocked ionomycin-induced ERK1/2-P and EGFR tyrosine phosphorylation. In both OTR-COSM6 and PHM1 cells, EGTA reduced OT-stimulated ERK1/2-P; no ERK1/2-P was observed when intracellular calcium increases were blocked by pretreatment with thapsigargin plus EGTA. These data are consistent with activation of a Gbetagamma-mediated pathway as a consequence of Galpha(q) activation in myometrium and OTR-COSM6 cells that results in increased ERK1/2-P. This pathway involves both EGFR activation and an influence of calcium.