HGF-mediated apoptosis via p53/bax-independent pathway activating JNK1

Comparative effects of hepatocyte growth factor and tacrolimus on acute liver allograft early tolerance

Allostimulated CD8+ T cells (aCD8+ T cells), as the main mediators of acute liver rejection (ARJ), are hyposensitive to apoptosis due to the inactivation of death receptor FAS-mediated pathways and fail to allow tolerance induction, eventually leading to acute graft rejection. Although tacrolimus (FK506), the most commonly used immunosuppressant (IS) in the clinic, allows tolerance induction, its use is limited because its target immune cells are unknown and it is associated with increased incidences of malignancy, infection, and nephrotoxicity, which substantially impact long-term liver transplantation (LTx) outcomes. The dark agouti (DA)-to-Lewis rat LTx model is a well-known ARJ model and was hence chosen for the present study. We show that both hepatocyte growth factor (HGF) (cHGF, containing the main form of promoting HGF production) and recombinant HGF (h-rHGF) exert immunoregulatory effects mainly on allogeneic aCD8+ T cell suppression through FAS-mediated apoptotic pathways by inhibiting cMet to FAS antagonism and Fas trimerization, leading to acute tolerance induction. We also showed that such inhibition can be abrogated by treatment with neutralizing antibodies against cMet (HGF-only receptor). In contrast, we did not observe these effects in rats treated with FK506. However, we observed that the effect of anti-rejection by FK506 was mainly on allostimulated CD4+ T cell (aCD4+ T cell) suppression and regulatory T cell (Treg) promotion, in contrast to the mechanism of HGF. In addition, the protective mechanism of HGF in FK506-mediated nephrotoxicity was addressed. Therefore, HGF as a tolerance inducer, whether used in combination with FK506 or as monotherapy, may have good clinical value. Additional roles of these T-cell subpopulations in other biological systems and studies in these fields will also be meaningful.

Hepatocyte Growth Factor Overexpression Slows the Progression of 4NQO-Induced Oral Tumorigenesis

Objectives

To investigate the role of hepatocyte growth factor (HGF)/c-Met signaling in oral malignant transformation.

Methods

We used immunohistochemistry to investigate HGF and c-Met expression in 53 oral squamous cell carcinoma (OSCC) specimens and 21 adjacent nontumor specimens and evaluated the associations between HGF and c-Met expression and clinicopathological parameters. Additionally, HGF-overexpression transgenic (HGF-Tg) and wild-type (Wt) mice were treated with 4-nitroquinoline-1-oxide (4NQO) to induce oral carcinogenesis for 16 weeks. At 16, 20, and 24 weeks, tongue lesions were collected for clinical observation; estimation of HGF, c-Met, and PCNA expression; apoptosis (TUNEL) assays; and RNA sequencing (RNA-seq).

Results

HGF and c-Met were positively expressed in 92.5% and 64% of OSCC samples, respectively. High HGF expression was significantly associated with smaller tumor size (p = 0.006) and inferior TNM stage (p = 0.032). No correlation between HGF and c-Met levels and other clinical parameters or prognosis was noted. In addition, HGF and c-Met expression was elevated in 4NQO-induced lesions of Wt mice. Compared with Wt mice, HGF-Tg mice have lower tumor incidence, number, volume, and lesion grade. In addition, the percentage of PCNA-positive cells in Wt mice was significantly higher than that in HGF-Tg mice at different time points. At 16 weeks, HGF-Tg mice exhibited less apoptotic cells compared with Wt mice (p < 0.000), and these levels gradually increased until the levels were greater than that of Wt mice at 24 weeks (p < 0.000). RNA-seq data revealed that 140 genes were upregulated and 137 genes were downregulated in HGF-Tg mice. KEGG enrichment analysis showed that upregulated differentially expressed genes (DEGs) are highly correlated with oxidative and metabolic signaling and that downregulated DEGs are related to MAPK and PI3K-AKT signaling.

Conclusions

HGF and c-Met expression is upregulated in OSCC tissues and is associated with the occurrence and development of OSCC. HGF overexpression in normal oral epithelial tissue can inhibit 4NQO-induced tumorigenesis potentially through inhibiting proliferation and accelerating apoptosis via MAPK and PI3K-AKT signaling.

Aloe emodin induces hepatotoxicity by activating NF-κB inflammatory pathway and P53 apoptosis pathway in zebrafish

The aim of this study was to investigate the hepatotoxic effect and its underlying mechanism of aloe emodin (AE). AE was docked with the targets of NF-κB inflammatory pathway and P53 apoptosis pathway respectively by using molecular docking technique. To verify the results of molecular docking and further investigate the hepatotoxicity mechanism of AE, the zebrafish Tg (fabp10: EGFP) was used as an animal model in vivo. The pathological sections of zebrafish liver were analyzed to observe the histopathological changes and Sudan black B was used to study whether there were inflammatory reactions in zebrafish liver or not. Then TdT-mediated dUTP Nick-End Labeling (TUNEL) was used to detect the apoptotic signal of zebrafish liver cells, finally the mRNA expression levels as well as the protein expression levels of the targets in NF-κB and P53 pathways in zebrafish were measured by quantitative Real-Time PCR (qRT-PCR) and western blot. Molecular docking results showed that AE could successfully dock with all the targets of NF-κB and P53 pathways, and the docking scores of most of the targets were equal to or higher than that of the corresponding ligands. Pathological sections showed AE could cause zebrafish liver lesions and the result of Sudan black B staining revealed that AE blackened the liver of zebrafish with Sudan black B. Then TUNEL assay showed that a large number of dense apoptotic signals were observed in AE group, mainly distributed in the liver and yolk sac of zebrafish. The results of qRT-PCR and western blot showed that AE increased the mRNA and protein expression levels of pro-inflammatory and pro-apoptotic targets in NF-κB and P53 pathways. AE could activate the NF-κB inflammatory pathway and the P53 apoptosis pathway, and its hepatotoxic mechanism was related to activation of NF-κB-P53 inflammation-apoptosis pathways.

Angiogenic factor screening in women with mild preeclampsia - New and significant proteins in plasma

INTRODUCTION

The aim of this study was to analyse a panel of 60 angiogenic factors (pro-angiogenic and antiangiogenic) in the plasma of women with mild preeclampsia.

MATERIALS AND METHODS

We recruited 21 women between 25 and 40 weeks gestation with diagnosed mild preeclampsia into the study group and 27 healthy women with uncomplicated pregnancies of corresponding gestational age to that of the study to the control group. We used a quantitative protein macroarray method that allowed for analysis of 60 angiogenic proteins per sample simultaneously.

RESULTS

We showed a statistically significant increase in the concentration of 8 proteins, interferon gamma (IFN-γ), interleukin 6 (IL-6), leukaemia inhibitory factor (LIF), heparin-binding EGF-like growth factor (HB-EGF), hepatocyte growth factor (HGF), C-X-C motif chemokine 10 (IP-10), leptin and platelet-derived growth factor BB (PDGF-BB), as well as a significant decrease in the concentration of 3 proteins, vascular endothelial growth factor (VEGF), placental growth factor (PlGF) and follistatin, in the plasma of women with preeclampsia.

CONCLUSION

Based on our findings, it seems that protein factors may play an important role in the pathogenesis of preeclampsia, and there are many proteins that have not been studied in PE to date. There are no previous studies assessing the LIF, follistatin, HGF, HB-EGF and PDGF-BB concentrations in the plasma of women with PE; therefore, our obtained results indicate that these proteins are new factors that can play an important role in the pathomechanisms of PE.

Stem Cell Differentiation Stage Factors from Zebrafish Embryo: A Novel Strategy to Modulate the Fate of Normal and Pathological Human (Stem) Cells

In spite of the growing body of evidence on the biology of the Zebrafish embryo and stem cells, including the use of Stem Cell Differentiation Stage Factors (SCDSFs) taken from Zebrafish embryo to impact cancer cell dynamics, comparatively little is known about the possibility to use these factors to modulate the homeostasis of normal human stem cells or to modulate the behavior of cells involved in different pathological conditions. In the present review we recall in a synthetic way the most important researches about the use of SCDSFs in reprogramming cancer cells and in modulating the high speed of multiplication of keratinocytes which is characteristic of some pathological diseases like psoriasis. Moreover we add here the results about the capability of SCDSFs in modulating the homeostasis of human adiposederived stem cells (hASCs) isolated from a fat tissue obtained with a novel-non enzymatic method and device. In addition we report the data not yet published about a first protein analysis of the SCDSFs and about their role in a pathological condition like neurodegeneration.

Basic fibroblast growth factor-treated adipose tissue-derived mesenchymal stem cell infusion to ameliorate liver cirrhosis via paracrine hepatocyte growth factor

BACKGROUND AND AIM

Recent studies show that adipose tissue-derived mesenchymal stem cells have potential clinical applications. However, the mechanism has not been fully elucidated yet. Here, we investigated the effect of basic fibroblast growth factor-treated adipose tissue-derived mesenchymal stem cells infusion on a liver fibrosis rat model and elucidated the underlying mechanism.

METHODS

Adipose tissue-derived mesenchymal stem cells were infused into carbon tetrachloride-induced hepatic fibrosis rats through caudal vein. Liver functions and pathological changes were assessed. A co-culture model was used to clarify the potential mechanism.

RESULTS

Basic fibroblast growth factor treatment markedly improved the proliferation, differentiation, and hepatocyte growth factor expression ability of adipose tissue-derived mesenchymal stem cells. Although adipose tissue-derived mesenchymal stem cells infusion alone slightly ameliorated liver functions and suppressed fibrosis progression, basic fibroblast growth factor-treatment significantly enhanced the therapeutic effect in association with elevated hepatocyte growth factor expression. Moreover, double immunofluorescence staining confirmed that the infused cells located in fibrosis area. Furthermore, co-culture with adipose tissue-derived mesenchymal stem cell led to induction of hepatic stellate cell apoptosis and enhanced hepatocyte proliferation. However, these effects were significantly weakened by knockdown of hepatocyte growth factor. Mechanism investigation revealed that co-culture with adipose tissue-derived mesenchymal stem cells activated c-jun N-terminal kinase-p53 signaling in hepatic stellate cell and promoted apoptosis.

CONCLUSIONS

Basic fibroblast growth factor treatment enhanced the therapeutic effect of adipose tissue-derived mesenchymal stem cells, and secretion of hepatocyte growth factor from adipose tissue-derived mesenchymal stem cells plays a critical role in amelioration of liver injury and regression of fibrosis.

c-MET receptor tyrosine kinase as a molecular target in advanced hepatocellular carcinoma

c-MET is the membrane receptor for hepatocyte growth factor (HGF), also known as scatter factor or tumor cytotoxic factor, a mitogenic growth factor for hepatocytes. HGF is mainly produced by cells of mesenchymal origin and it mainly acts on neighboring epidermal and endothelial cells, regulating epithelial growth and morphogenesis. HGF/MET signaling has been identified among the drivers of tumorigenesis in human cancers. As such, c-MET is a recognized druggable target, and against it, targeted agents are currently under clinical investigation. c-MET overexpression is a common event in a wide range of human malignancies, including gastric, lung, breast, ovary, colon, kidney, thyroid, and liver carcinomas. Despite c-MET overexpression being reported by a large majority of studies, no evidence for a c-MET oncogenic addiction exists in hepatocellular carcinoma (HCC). In particular, c-MET amplification is a rare event, accounting for 4%–5% of cases while no mutation has been identified in c-MET oncogene in HCC. Thus, the selection of patient subgroups more likely to benefit from c-MET inhibition is challenging. Notwithstanding, c-MET overexpression was reported to be associated with increased metastatic potential and poor prognosis in patients with HCC, providing a rationale for its therapeutic inhibition. Here we summarize the role of activated HGF/MET signaling in HCC, its prognostic relevance, and the implications for therapeutic approaches in HCC.

FAK activity is required for HGF to suppress TGF-β1-induced cellular proliferation

Due to the complex nature of the tendon architecture, the regeneration of these tissues results in the formation of scars. As a direct result of scar formation, the ability of the tendon tissues to function is impaired and often results in further damage that has been afflicted to the tendon architecture. The growth and proliferation of tendon fibroblasts involve a complex network of signalling molecules. To understand and aid in the proper repair of this complex tissue network, a more in-depth understanding is required in the events that induce the growth of tendon cells. Several studies have shown the apoptotic mechanisms induced by the mitogen, hepatocyte growth factor, in multiple biological and pathological systems. In our recent research, we have described a mechanism where hepatocyte growth factor (HGF) is able to inhibit the proliferative effects of transforming growth factor-β1 (TGF-β1) and induce apoptosis in rat tendon fibroblasts. Transforming growth factor-β1 is able to induce the proliferation of fibroblast cells by increasing both the gene expression and protein levels of α-smooth muscle actin (α-SMA) and c-MET. We have also shown that inhibition of extracellular signal-regulated kinase 1/2 does not block hepatocyte growth factor-induced growth arrest. However, we have shown that blocking the activity of focal adhesion kinase can prevent the growth inhibition ability of hepatocyte growth factor in tendon fibroblasts. Collectively, our studies show growth inhibitory pathway in tendon fibroblasts induced by hepatocyte growth factor and mediated focal adhesion kinase.

Novel therapeutic strategies for cardioprotection

The morbidity and mortality from ischemic heart disease (IHD) remain significant worldwide. The treatment for acute myocardial infarction has improved over the past decades, including early reperfusion of occluded coronary arteries. Although it is essential to re-open the artery as soon as possible, paradoxically this leads to additional myocardial injury, called acute ischemia-reperfusion injury (IRI), for which currently no effective therapy is available. Therefore, novel therapeutic strategies are required to protect the heart from acute IRI in order to reduce myocardial infarction size, preserve cardiac function and improve clinical outcomes in patients with IHD. In this review article, we will first outline the pathophysiology of acute IRI and review promising therapeutic strategies for cardioprotection. These include novel aspects of mitochondrial function, epigenetics, circadian clocks, the immune system, microvesicles, growth factors, stem cell therapy and gene therapy. We discuss the therapeutic potential of these novel cardioprotective strategies in terms of pharmacological targeting and clinical application.

Protection against radiation-induced hematopoietic damage in bone marrow by hepatocyte growth factor gene transfer

PURPOSE

To investigate whether adenovirus-mediated delivery of the human hepatocyte growth factor (HGF) gene could prevent radiation-induced hematopoietic damage.

MATERIALS AND METHODS

Thirty C57BL/6 mice were randomized into three groups, in which phosphate buffer saline (PBS), mock adenovirus vector (Ad-null) or adenovirus vector containing HGF (Ad-HGF) were injected into the tail vein of each group, respectively. After 48 hours, the mice received a single irradiation dose of 6.5 Gy (60)Co gamma rays. Blood samples were extracted via the tail vein at day 0, 4, 7, 10, 14, 21, 24 and 30 after irradiation, for red blood cell (RBC) and white blood cell (WBC) and cluster of differentiation4 (CD4)/cluster of differentiation8 (CD8) ratio assessment. At weekly intervals following irradiation, serum erythropoietin (EPO), Interleukin-6 (IL-6) and Interferon-gamma (IFN-γ) levels were measured using enzyme-linked immunosorbent assay (ELISA). On post-irradiation day 30, the mice were autopsied and erythroid burst-forming units (BFU-E) were evaluated.

RESULTS

Adenovirus-mediated HGF gene transfer could increase human HGF level in serum and have a significant elevation in RBC and WBC count. Ad-HGF increased EPO and IL-6 levels and prompted BFU-E formation. Ad-HGF decreased radiation- induced micronucleus frequency in the mouse bone marrow (BM). Most evidence of radiation-induced hematopoietic damage was observed morphologically in bone marrow specimen four weeks after irradiation. Ad-HGF protected against radiation-induced BM failure and increased survival. Finally, Ad-HGF increased the thymic index and enhanced immune function in the irradiated C57BL/6 mice.

CONCLUSIONS

This is the first report to date that demonstrates the potential of HGF gene transfer to prevent radiation-induced hematopoietic damage.

Paradoxical action of growth factors: antiproliferative and proapoptotic signaling by HGF/c-MET

Hepatocyte growth factor (HGF)/mesenchymal-epithelial transition factor (c-MET) signaling is usually associated with the promotion of cellular growth and often with progression of tumors. Nevertheless, under certain conditions HGF can also act as an antiproliferative and proapoptotic factor and can sensitize various cancer cells, treated with anticancer drugs, to apoptosis. Not only HGF but also its various truncated forms as well as intracellular fragments of its membrane receptor, c-MET, may act as antiproliferative and proapoptotic factors toward various cells. This review focuses on different mechanisms responsible for such paradoxical action of the known typical growth factor. It also points toward the possibilities of usage of this information in anticancer therapy.

Therapeutic effect of transplanting beta(2)m(-)/Thy1(+) bone marrow-derived hepatocyte stem cells transduced with lentiviral-mediated HGF gene into CCl(4)-injured rats

BACKGROUND

beta(2)m(-)/Thy1(+) bone marrow-derived hepatocyte stem cells (BDHSCs) isolated from the bone marrow of cholestatic rats by magnetic bead cell sorting consistently express characteristics of both stem and liver cells. These stem cells may be good vehicles for gene transfer. Administration of exogenous hepatocyte growth factor (HGF) may be potentially useful for the treatment of liver fibrosis. Because lentiviral vectors integrate stably into the host-cell genome of nondividing and dividing cells, it may efficiently transfect beta(2)m(-)/Thy1(+) BDHSCs in vitro and secrete high-level HGF consistently. Transplantation of beta(2)m(-)/Thy1(+) BDHSCs transduced with lentiviral vectors containing the HGF gene may reduce liver fibrosis in rats.

METHODS

Lentiviral vectors expressing HGF were constructed and used to transduce beta(2)m(-)/Thy1(+) BDHSCs sorted from cholestatic rats in vitro. Transduction efficiency was evaluated and then these cells were transplanted into rats through the portal vein. Liver function as well as histological and immunohistochemical examinations were carried out to assess the therapeutic efficacy on liver fibrosis.

RESULTS

We demonstrated that high-level exogenous HGF was detected in supernatants after beta(2)m(-)/Thy1(+) BDHSCs were transfected with lentiviral vectors expressing HGF. Transplantation of transduced beta(2)m(-)/Thy1(+) BDHSCs significantly enhanced liver function and attenuated liver fibrosis in vivo.

CONCLUSIONS

The present study indicates that transplantation of beta(2)m(-)/Thy1(+) BDHSCs overexpressing the HGF gene may offer a novel approach for promoting liver function and reverse liver fibrosis.

Hypoxia-induced Bcl-2 expression in endothelial cells via p38 MAPK pathway

Angiogenesis and apoptosis are reciprocal processes in endothelial cells. Bcl-2, an anti-apoptotic protein, has been found to have angiogenic activities. The purpose of this study was to determine the role of Bcl-2 in hypoxia-induced angiogenesis in endothelial cells and to investigate the underlying mechanisms. Human aortic endothelial cells (HAECs) were exposed to hypoxia followed by reoxygenation. Myocardial ischemia and reperfusion mouse model was used and Bcl-2 expression was assessed. Bcl-2 expression increased in a time-dependent manner in response to hypoxia from 2 to 72h. Peak expression occurred at 12h (3- to 4-fold, p<0.05). p38 inhibitor (SB203580) blocked hypoxia-induced Bcl-2 expression, whereas PKC, ERK1/2 and PI3K inhibitors did not. Knockdown of Bcl-2 resulted in decreased HAECs' proliferation and migration. Over-expression of Bcl-2 increased HAECs' tubule formation, whereas knockdown of Bcl-2 inhibited this process. In this model of myocardial ischemia and reperfusion, Bcl-2 expression was increased and was associated with increased p38 MAPK activation. Our results showed that hypoxia induces Bcl-2 expression in HAECs via p38 MAPK pathway.

Hepatocyte growth factor enhances death receptor-induced apoptosis by up-regulating DR5

BACKGROUND

Hepatocyte growth factor (HGF) and its receptor c-MET are commonly expressed in malignant gliomas and embryonic neuroectodermal tumors including medulloblastoma and appear to play an important role in the growth and dissemination of these malignancies. Dependent on cell context and the involvement of specific downstream effectors, both pro- and anti-apoptotic effects of HGF have been reported.

METHODS

Human medulloblastoma cells were treated with HGF for 24-72 hours followed by death receptor ligand TRAIL (Tumor necrosis factor-related apoptosis-inducing ligand) for 24 hours. Cell death was measured by MTT and Annexin-V/PI flow cytometric analysis. Changes in expression levels of targets of interest were measured by Northern blot analysis, quantitative reverse transcription-PCR, Western blot analysis as well as immunoprecipitation.

RESULTS

In this study, we show that HGF promotes medulloblastoma cell death induced by TRAIL. TRAIL alone triggered apoptosis in DAOY cells and death was enhanced by pre-treating the cells with HGF for 24-72 h prior to the addition of TRAIL. HGF (100 ng/ml) enhanced TRAIL (10 ng/ml) induced cell death by 36% (P<0.001). No cell death was associated with HGF alone. Treating cells with PHA-665752, a specific c-Met receptor tyrosine kinase inhibitor, significantly abrogated the enhancement of TRAIL-induced cell death by HGF, indicating that its death promoting effect requires activation of its canonical receptor tyrosine kinase. Cell death induced by TRAIL+HGF was predominately apoptotic involving both extrinsic and intrinsic pathways as evidenced by the increased activation of caspase-3, 8, 9. Promotion of apoptosis by HGF occurred via the increased expression of the death receptor DR5 and enhanced formation of death-inducing signal complexes (DISC).

CONCLUSION

Taken together, these and previous findings indicate that HGF:c-Met pathway either promotes or inhibits medulloblastoma cell death via pathway and context specific mechanisms.

Promotion of Fas-mediated apoptosis in Type II cells by high doses of hepatocyte growth factor bypasses the mitochondrial requirement

The death receptor pathway is coupled to the mitochondria apoptosis pathway. However, mitochondrial participation, which is stimulated by Bid but suppressed by Bcl-2/Bcl-x(L), is required in certain cells (Type II), but not in others (Type I). While these differences were originally characterized in the lymphoid cell lines, the typical Type II cells are represented by hepatocytes in vivo. The molecular mechanisms that distinguish Type II from Type I cells and the regulation are not fully understood. Fas can be sequestered by the HGF receptor c-Met and high doses of HGF can promote cell death by freeing Fas from c-Met complex. We thus reasoned that treatment of the Type II cells with high doses of HGF could enhance Fas-mediated apoptosis and spare the mitochondria amplification. Indeed, such treatment led to increased apoptosis in Type II lymphoid cells, which could not be blocked by Bcl-x(L). Moreover, significant hepatocyte apoptosis was induced by this scheme in the absence of Bid with increased dissociation of Fas from c-Met. These findings indicate that high doses of HGF could be used to promote apoptosis in Type II cells bypassing the requirement for mitochondria activation.

Grb2-associated binder-1 plays a central role in the hepatocyte growth factor enhancement of hepatoma growth inhibition by K vitamin analog compound 5

Compound 5 (Cpd 5), a K vitamin analog, has been shown to inhibit Hep3B human hepatoma cell growth in cultures and rat hepatoma growth in vivo through prolonged epidermal growth factor receptor (EGFR)-extracellular response kinase (ERK) phosphorylation, and hepatocyte growth factor (HGF) synergizes with Cpd 5 to enhance the inhibition of Hep3B cell and rat hepatoma growth. To explore the mechanisms mediating the HGF/Cpd 5 synergy, we examined the possible involvement of the Grb2-associated binder-1 (Gab1) docking protein because it interacts with both EGFR and HGF receptor c-Met pathways. We found that HGF enhanced Cpd 5-induced c-Met phosphorylation at Tyr-1349, a binding site for Gab1, resulting in increased c-Met binding to Gab1, and induced strong and prolonged Gab1 tyrosine phosphorylation. Prolonged Gab1 phosphorylation by HGF/Cpd 5 in turn enhanced the ability of Gab1 to bind to protein tyrosine phosphatase SHP2 and enhanced the activation of its downstream mitogen-activated protein kinase pathway. In contrast, this same HGF/Cpd 5 treatment inhibited Gab1 binding to phosphatidylinositol 3-kinase (PI3K), leading to the inactivation of the PI3K-Akt pathway. The inhibition of Akt phosphorylation by HGF/Cpd 5 further activated the Raf-MEK-ERK signaling cascade via an Akt-Raf1 interaction, leading to strong and prolonged ERK phosphorylation. The transfection of Hep3B cells with mutated Gab1 (Gab1 Y627F), which had lost its ability to bind SHP2, antagonized HGF/Cpd 5-induced ERK phosphorylation, whereas the transfection of Hep3B cells with mutated Gab1 3YF, which lost its ability to bind PI3K, further enhanced HGF/Cpd 5-induced ERK phosphorylation and cell growth inhibition.

CONCLUSION

Gab1 plays a central role in regulating HGF/Cpd 5 synergy in their actions on Hep3B cell growth inhibition.

Effects of hepatocyte growth factor on glutathione synthesis, growth, and apoptosis is cell density-dependent

Hepatocyte growth factor (HGF) is a potent hepatocyte mitogen that exerts opposing effects depending on cell density. Glutathione (GSH) is the main non-protein thiol in mammalian cells that modulates growth and apoptosis. We previously showed that GSH level is inversely related to cell density of hepatocytes and is positively related to growth. Our current work examined whether HGF can modulate GSH synthesis in a cell density-dependent manner and how GSH in turn influence HGF's effects. We found HGF treatment of H4IIE cells increased cell GSH levels only under subconfluent density. The increase in cell GSH under low density was due to increased transcription of GSH synthetic enzymes. This correlated with increased protein levels and nuclear binding activities of c-Jun, c-Fos, p65, p50, Nrf1 and Nrf2 to the promoter region of these genes. HGF acts as a mitogen in H4IIE cells under low cell density and protects against tumor necrosis factor alpha (TNFalpha)-induced apoptosis by limiting JNK activation. However, HGF is pro-apoptotic under high cell density and exacerbates TNFalpha-induced apoptosis by potentiating JNK activation. The increase in cell GSH under low cell density allows HGF to exert its full mitogenic effect but is not necessary for its anti-apoptotic effect.

p38 MAPK turns hepatocyte growth factor to a death signal that commits ovarian cancer cells to chemotherapy-induced apoptosis

We recently showed that Hepatocyte Growth Factor (HGF), known as a survival factor, unexpectedly enhances apoptosis in human ovarian cancer cells treated with the front-line chemotherapeutics cisplatin (CDDP) and paclitaxel (PTX). Here we demonstrate that this effect depends on the p38 mitogen-activated kinase (MAPK). In fact, p38 MAPK activity is stimulated by HGF and further increased by the combined treatment with HGF and either CDDP or PTX. The expression of a dominant negative form of p38 MAPK abrogates apoptosis elicited by drugs, alone or in combination with HGF. HGF and drugs also activate the ERK1/2 MAPKs, the PI3K/AKT and the AKT substrate mTOR. However, activation of these survival pathways does not hinder the ability of HGF to enhance drug-dependent apoptosis. Altogether data show that p38 MAPK is necessary for HGF sensitization of ovarian cancer cells to low-doses of CDDP and PTX and might be sufficient to overcome activation of survival pathways. Therefore, the p38 MAPK pathway might be a suitable target to improve response to conventional chemotherapy in human ovarian cancer.

Transcriptional targets of hepatocyte growth factor signaling and Ki-ras oncogene activation in colorectal cancer

Both Ki-ras mutation and hepatocyte growth factor (HGF) receptor Met overexpression occur at high frequency in colon cancer. This study investigates the transcriptional changes induced by Ki-ras oncogene and HGF/Met signaling activation in colon cancer cell lines in vitro and in vivo. The model system used in these studies included the DLD-1 colon cancer cell line with a mutated Ki-ras allele, and the DKO-4 cell line generated from DLD-1, with its mutant Ki-ras allele inactivated by targeted disruption. These cell lines were transduced with cDNAs of full-length Met receptor. Microarray transcriptional profiling was conducted on cell lines stimulated with HGF, as well as on tumor xenograft tissues. Overlapping genes between in vitro and in vivo microarray data sets were selected as a subset of HGF/Met and Ki-ras oncogene-regulated targets. Using the Online Predicted Human Interaction Database, novel HGF/Met and Ki-ras regulated proteins with putative functional linkage were identified. Novel proteins identified included histone acetyltransferase 1, phosphoribosyl pyrophosphate synthetase 2, chaperonin containing TCP1, subunit 8, CSE1 chromosome segregation 1-like (yeast)/cellular apoptosis susceptibility (mammals), CCR4-NOT transcription complex, subunit 8, and cyclin H. Transcript levels for these Met-signaling targets were correlated with Met expression levels, and were significantly elevated in both primary and metastatic human colorectal cancer samples compared to normal colorectal mucosa. These genes represent novel Met and/or Ki-ras transcriptionally coregulated genes with a high degree of validation in human colorectal cancers.

Ubiquitin-dependent degradation of p53 protein despite phosphorylation at its N terminus by acetaminophen

We previously reported that acetaminophen (APAP, 4-hydroxyacetanilide) caused apoptosis of C6 glioma cells. Therefore, we hypothesized that the level of p53, which usually stimulates apoptosis, might be increased after APAP exposure. However, APAP exposure for 24 h markedly decreased the p53 content and its downstream target p21 in a concentration-dependent manner. Reduction of p53 was not accompanied by a decrease in p53 mRNA in C6 glioma cells, suggesting that p53 was mainly affected at the protein level. Unexpectedly, APAP stimulated phosphorylation of p53 at Ser15, Ser20, and Ser37, which usually elevates p53 content. However, phosphorylation of these residues did not prevent APAP-induced decrease in p53. The p53 reduction was independent from the level of phospho-Akt, which is known to promote p53 degradation. Immunoblot analysis of the immunoprecipitated p53 revealed that increased amounts of murine double minute 2 (mdm2) and ubiquitin were bound to p53 during its degradation. Lactacystin and N-benzoyloxycarbonyl (Z)-Leu-Leu-leucinal (MG132), inhibitors of proteasomal proteolysis, prevented the decrease, supporting the proteasomal degradation of p53 upon APAP exposure. Pretreatment with chlormethiazole, an inhibitor of ethanol-inducible CYP2E1, significantly lowered the CYP2E1 enzyme activity and the rate of APAP-induced cell death while it prevented the reduction of p53 and p21 in C6 glioma cells. A nontoxic analog of APAP, 3-hydroxyacetanilde, did not reduce p53 and p21 contents in C6 glioma cells and LLC-PK1 porcine kidney cells. Taken together, our results show that APAP or its reactive metabolite(s) can directly reduce the p53 content through mdm2-mediated ubiquitin conjugation, despite phosphorylation of p53 at its N terminus.

Increased apoptosis in cervical intraepithelial neoplasia associated with HIV infection: implication of oncogenic human papillomavirus, caspases, and Langerhans cells

PURPOSE

Increasing risk of squamous cervical intraepithelial neoplasia (CIN) exits in HIV-infected women. However, the relatively low incidence of invasive carcinoma in the untreated HIV-infected population suggests an imbalance between cell proliferation and apoptosis. We investigated apoptosis and caspases in cervical samples from this population comparatively to non-HIV-infected and control subjects.

EXPERIMENTAL DESIGN

Apoptotic terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling method, immunohistochemistry for caspase-2, caspase-3, caspase-8, caspase-9, and other apoptosis markers were done on 12 normal cervical samples and 103 low- and high-grade cervical lesions, containing human papillomavirus(es) from 35 HIV-negative and 33 HIV-positive women before tritherapy advent.

RESULTS

(a) The apoptotic index (AI) in epithelial cells did not vary between normal mucosa and condyloma acuminata infected or not with HIV. (b) AI augmented with the CIN severity in HIV-positive and HIV-negative women. (c) AI dramatically increased in oncogenic human papillomavirus-infected CIN of HIV-positive population compared with the CIN of similar grade in HIV-negative one. This was associated with a greater expression of caspase-8, active caspase-9, and active caspase-3 in those samples. Moreover, densities of Langerhans' cells, involved in apoptotic bodies engulfment, were greatly reduced in CIN of HIV-positive women. In samples, these densities were highly inversely correlated with AI (r = -0.88, P < 0.002).

CONCLUSIONS

This study provides the first evidence for the strongly enhanced apoptosis levels and caspase expression in CIN of untreated HIV-infected women. We suggest that the reduction in Langerhans' cell number could contribute at least partly to apoptotic cell accumulation.

Growth inhibition and apoptosis in liver myofibroblasts promoted by hepatocyte growth factor leads to resolution from liver cirrhosis

Liver cirrhosis is characterized by hepatic dysfunction with extensive accumulation of fibrous tissue in the liver. In response to chronic hepatic injury, hepatic portal myofibroblasts and activated hepatic stellate cells (HSCs) play a role in liver fibrosis. Although administration or gene expression of hepatocyte growth factor (HGF) leads to improvement in hepatic fibrosis/cirrhosis, the related mechanisms are not fully understood. We investigated mechanisms involved in resolution from liver cirrhosis by HGF, focusing on growth regulation and apoptosis in portal myofibroblasts. Cultured rat HSCs could not proliferate, were withdrawn after passage, and were replaced by proliferating portal myofibroblasts during the passages. In quiescent HSCs, c-Met receptor expression was undetected whereas c-Met receptor expression was detected in activated HSCs and liver myofibroblasts expressing alpha-smooth muscle actin (alpha-SMA), suggesting that activated HSCs and portal myofibroblasts are targets of HGF. For cultured rat portal myofibroblasts, HGF counteracted phosphorylation of extracellular signal-regulated kinase (Erk) 1/2 and mitogenic stimulus induced by platelet-derived growth factor, induced c-jun N-terminal kinase (JNK) 1 phosphorylation, and promoted apoptotic cell death. In the dimethylnitrosamine rat model of liver cirrhosis, administration of HGF suppressed proliferation while promoting apoptosis of alpha-SMA-positive cells in the liver, events that were associated with reduced hepatic expressions of alpha-SMA and histological resolution from liver cirrhosis. Growth inhibition and enhanced apoptosis in portal myofibroblasts by HGF are newly identified mechanisms aiding resolution from liver fibrosis/cirrhosis by HGF.

The p105/50 NF-kappaB pathway is essential for Mallory body formation

To determine if nuclear factor-kappaB (NF-kB) plays a role in Mallory body (MB) formation, quantitative real-time RT-PCR assay was used to measure liver NF-kappaB1/p105 mRNA levels in 4 different groups of mice. Group 1: mice given IP saline for 15 weeks; group 2: mice fed diethyl 1,4-dihydro-2,4,6,-trimethyl-3,5-pyridinedicarboxylate (DDC) for 10 weeks when MBs were formed; group3: mice fed DDC 10 weeks, then withdrawn 5 weeks when MBs disappeared; group 4: mice fed DDC 10 weeks, withdrawn 4 weeks, then fed DDC+chlormethiazole (CMZ) for 1 week when MBs again formed. The mRNA for p105 NF-kappaB expression was significantly increased in the livers of mice treated with DDC (group 2) and DDC+CMZ (group 4) compared with the control livers (group 1) as well as the drug-withdrawal livers (group 3). Primary cultures of hepatocytes from drug-primed mice (the group 4 mice were withdrawn for another 4 weeks when the MBs had disappeared) were studied. The hepatocytes from drug-primed mice were MB free when isolated and used for primary culture. MBs began to form spontaneously within their cytoplasm after 2-3 days of culture. The NF-kappaB inhibitor (NF-kappaBi), a cell-permeable quinazoline compound that acts as a potent inhibitor of NF-kappaB transcriptional activation, was added to the medium 3 h after planting the cultures of liver cells. No MBs formed in the cells treated with 10 microM, 1 microM, and 0.1 microM NF-kappaBi for 6 days. MBs still formed in the cells treated with 10 nM NF-kappaBi for 6 days. Both DDC-primed and normal control liver cells began to enlarge and elongate after a few hours of culture. In contrast, the cells treated with NF-kappaBi stayed polyhedral in shape just as they appeared prior to culturing. The level of NF-kappaB1/p105 mRNA significantly increased in DDC-primed hepatocytes after 24 h of culture and in normal control hepatocytes after 48 h of culture. In DDC-primed hepatocytes, NF-kappaBi 0.1 muM treatment for 6 days significantly decreased mRNA expression of Src, p105/NF-kappaB1, ERK1, MEKK1, and JNK1/2. In normal control liver cells, NF-kappaBi treatment decreased mRNA expression of Src and JNK1 and stimulated the mRNA expression of p105/NF-kappaB1 and Junk2. NF-kappaBi treatment significantly decreased the total ERK1/2 protein and further decreased the phosphorylated (activated) form of ERK1/2 in the cultured hepatocytes. The results indicate that the p105 NF-kappaB pathway which putatively regulates ERK at both the transcriptional and post-translational levels regulates MB formation by way of changes in gene expression.

Hepatocyte growth factor enhances protein phosphatase Cdc25A inhibitor compound 5-induced hepatoma cell growth inhibition via Akt-mediated MAPK pathway

We have previously shown that Compound 5 (Cpd 5), an inhibitor of protein phosphatase Cdc25A, inhibits Hep3B human hepatoma cell growth. We now show that hepatocyte growth factor (HGF), a hepatocyte growth stimulant, can strongly enhance Cpd 5-induced growth inhibition in Hep3B cells, and this enhancement in cell growth inhibition is correlated with a much stronger ERK phosphorylation when compared to cells treated with Cpd 5 or HGF separately. We found that HGF/Cpd 5-induced ERK phosphorylation and cell growth inhibition were mediated by Akt (protein kinase B) pathway, since combination HGF/Cpd 5 treatment of Hep3B cells inhibited Akt phosphorylation at Ser-473 and its kinase activity, which led to the suppression of Raf-1 phosphorylation at Ser-259. The suppression of Raf-1 Ser-259 phosphorylation caused the induction of Raf-1 kinase activity, as well as hyper-ERK phosphorylation. Transient transfection of Hep3B cells with dominant negative Akt c-DNA further enhanced both Cpd 5- and HGF/Cpd 5-induced ERK phosphorylation, while over-expression of wild-type Akt c-DNA diminished their effects. In contrast, HGF antagonized the growth inhibitory actions of Cpd 5 on normal rat hepatocytes, thus showing a selective effect on tumor cells compared to normal cells. Our data suggest that Akt kinase negatively regulates MAPK activity at the Akt-Raf level. Suppression of Akt activity by either combination HGF/Cpd 5 treatment or by dominant negative Akt c-DNA transfection antagonizes the Akt inhibitory effect on Raf-1, resulting in an enhancement of Cpd 5-induced MAPK activation and cell growth inhibition.

Novel interaction partners of the TPR/MET tyrosine kinase

A large variety of biological processes is mediated by stimulation of the receptor tyrosine kinase MET. Screening a mouse embryo cDNA library, we were able to identify several novel, putative intracellular TPR/MET-substrates: SNAPIN, DCOHM, VAV-1, Sorting nexin 2, Death associated protein kinase 3, SMC-1, Centromeric protein C, and hTID-1. Interactions as identified by yeast two-hybrid analysis were validated in vitro and in vivo by mammalian two-hybrid studies, a far-western assay and coimmunoprecipitation. Participation in apoptosis-regulating mechanisms through interaction with DAPK-3 and cell cycle control via binding to nuclear proteins such as CENPC and SMC-1 are possible new aspects of intracellular MET signaling.

Local administration of hepatocyte growth factor gene enhances the regeneration of dermis in acute incisional wounds

Hepatocyte growth factor (HGF) has a number of biological activities, e.g., mitogenic, motogenic, antiapoptotic, antifibrous, and morphogenic. It also has angiogenic and angioprotective activities for endothelial cells. The aim of this study was to characterize the role of HGF in wound healing by administering the HGF gene locally to acute incisional skin wounds created on the backs of rats. To create wounds, the backs of Wistar rats were clipped and three 2-cm-long incisional wounds were made deep to the fascia. The wounds contained pannicrus carnosum and were created at intervals of 2 cm. After suturing, the HGF gene was then administered intradermally. Apoptotic cells in wound lesions were identified by TUNEL method as well as by immunological detection of active caspase-3. In the HGF-treated animals, we found almost complete suppression of apoptosis and well-organized wound healing. Histopathological examination revealed that the proliferation of fibroblasts was suppressed and that scar formation was less apparent in the HGF-treated animals compared to the controls. It is thought that administration of the HGF gene immediately after surgery may enhance the healing process through suppressing apoptosis, which occurred in the controls 1 week after suturing the incisional wound. In addition, locally increased HGF expression due to the introduction of the HGF gene to cells around wounds enhances dermal regeneration, possibly by promoting regeneration of dermal tissue, which results in less scarring due to its antifibrotic effect. Thus, HGF supplementation through gene therapy may be an effective strategy for treating wounds, as it increases the regeneration of the dermis to allow for "scarless wound healing."

Hepatocyte growth factor induces Mcl-1 in primary human hepatocytes and inhibits CD95-mediated apoptosis via Akt

CD95 (APO-1/Fas)-mediated apoptosis of hepatocytes plays a central role in the pathophysiology of various human liver diseases. Hepatocyte growth factor (HGF) was shown to exert antiapoptotic functions in rodent hepatocytes. We previously showed that primary human hepatocytes (PHH) are a valuable tool for the investigation of apoptotic processes in liver cells. In this study, we analyzed the influence of HGF on CD95-mediated apoptosis of PHH and its molecular determinants. HGF significantly inhibited CD95-mediated apoptosis of PHH as well as cleavage of caspase-8 and poly (ADP-ribose)polymerase. HGF transcriptionally induced the expression of the anti-apoptotic Bcl-2 family member myeloid cell leukemia-1 (Mcl-1). In contrary, HGF did not alter the expression levels of Bcl-2 or Bcl-x(L). HGF activated survival pathways such as the phosphatidylinositol-3 kinase (PI3K)/Akt pathway, the mitogen-activated protein kinase/extracellular signal-regulated kinase (ERK) kinase/ERK and the signal transducer and activator of transcription 3 (STAT3) pathway. Notably, HGF triggered serine(727)--but not tyrosine(705)--phosphorylation of STAT3. Pretreatment of PHH with the PI3K inhibitor LY294002 as well as adenoviral transduction of dominant negative Akt1 prevented HGF-mediated Mcl-1 induction and reversed the antiapoptotic effects of HGF. In conclusion, HGF confers survival of PHH by activation of the PI3K/Akt pathway. PI3K/Akt activation by HGF results in the induction of antiapoptotic proteins such as Mcl-1. Thus, application of HGF may be a therapeutic approach to prevent CD95-mediated hepatocellular damage in human liver diseases.

Inhibition of NF-kappaB sensitizes A431 cells to epidermal growth factor-induced apoptosis, whereas its activation by ectopic expression of RelA confers resistance

Epidermal growth factor (EGF) is a well known mitogen, but it paradoxically induces apoptosis in cells that overexpress its receptor. We demonstrate for the first time that the EGF-induced apoptosis is accelerated if NF-kappaB is inactivated. To inactivate NF-kappaB, human epidermoid carcinoma cells (A431) that overexpress EGF receptor were stably transfected with an IkappaB-alpha double mutant construct. Under the NF-kappaB-inactivated condition, A431 cells were more sensitive to EGF with decreased cell viability and increased externalization of phosphatidylserine on the cell surface, DNA fragmentation, and activation of caspases (3 and 8 but not 9), typical features of apoptosis. These results were further supported by the potentiation of the growth inhibitory effects of EGF by chemical inhibitors of NF-kappaB (curcumin and sodium salicylate) and the protective role of RelA evidenced by the resistance of A431-RelA cells (stably transfected with RelA) to EGF-induced apoptosis. EGF treatment or ectopic expression of RelA in A431 cells induced DNA binding activity of NF-kappaB (p50 and RelA) and the expression of c-IAP1, a downstream target of NF-kappaB. A431-RelA cells exhibited spontaneous phosphorylation of Akt (a downstream target of phosphatidylinositol 3-kinase and regulator of NF-kappaB) and EGF treatment stimulated it further. Blocking this basal Akt phosphorylation with LY294002, an inhibitor of phosphatidylinositol 3-kinase, did not affect their viability but blocking of EGF-induced phosphorylation of Akt sensitized the otherwise resistant A431-RelA cells to EGF-mediated growth inhibition. Our results favor an anti-apoptotic role for NF-kappaB in the regulation of EGF-induced apoptosis.

Influence of oxygen tension on apoptosis and hatching in bovine embryos cultured in vitro

Various oxygen tensions are employed for in vitro embryo production. Since it is known that oxygen tension can influence the efficiency of embryo production and embryo quality, the aim of our study was to define an optimal oxygen concentration for bovine embryo production in vitro in synthetic oviduct fluid (SOF). Embryo quality criteria were hatching ability and the degree of apoptosis as assessed by TUNEL staining and Bax gene expression. In Experiment 1, the effects of 2, 5 and 20% O(2) tensions on embryo development were compared. The highest rate of eight-cell embryos (47%) at 72 hpi was obtained under 20% O(2). However, it seemed that 2 and 5% O(2) were also suitable as assessed by embryo survival rates at 144 hpi (29 and 30% at morula stage), 168 hpi (21 and 19% at blastocyst stage) and 216 hpi (14 and 17% at hatched blastocyst stage). In Experiment 2, comparisons were made between effects of 5, 20% and alternating O(2) (20% O(2) to 72 hpi and then changed to 5% O(2) up to 216 hpi) on embryo development. Alternating the O(2) tension significantly reduced the number of hatching blastocysts to 7%. Staining with TUNEL revealed that apoptosis occurred in all tested hatched blastocysts, but a significantly lower apoptotic cell ratio was found in embryos cultured under 5% O(2) (P<0.05). Total cell number of embryos cultured under 5% and alternating oxygen was significantly higher than that of other groups (P<0.05). Bax gene expression was detected by means of RT-PCR in only 2 of 66 hatched blastocysts. It can be concluded that 5% oxygen is optimal for bovine embryo culture in cell free media. Moreover, it is very likely that the apoptosis detected by TUNEL staining in this study is Bax-independent.

Mechanism of beta 1-integrin-mediated hepatoma cell growth involves p27 and S-phase kinase-associated protein 2

Although cooperative interactions between growth factors and integrins, cell surface receptors for extracellular matrices (ECM), have been reported, little is known about the interaction between hepatocyte growth factor (HGF) and integrin in hepatoma cells. We investigated the effects and mechanisms of integrin on the proliferation of hepatoma cells regulated by HGF. Human HepG2 hepatoma cells stably transfected with beta 1-integrin were treated with HGF and compared with parental and mock-transfected control cells. Cell proliferation and expression of cyclin-dependent kinase (Cdk) inhibitors and S-phase kinase-associated protein 2 (Skp2), were investigated. HGF dose-dependently suppressed the proliferation of parental and mock-transfected HepG2 cells. However, cells overexpressing beta 1-integrin exhibited increased proliferation in response to HGF. Although HGF increased p27 and decreased Skp2 expression in the parental and mock-transfected cells, the p27 and Skp2 levels in cells overexpressing beta 1-integrin were not altered by HGF. Interestingly, HepG2 cells overexpressing beta 1-integrin showed increased Skp2 expression. Furthermore, HGF did not reduce the proliferation of HepG2 cells transfected with antisense p27 or sense Skp2. Thus, HGF suppresses HepG2 cell proliferation by directly increasing p27 expression and indirectly decreasing Skp2 expression, and beta 1-integrin modulates the responsiveness of hepatoma cells to HGF via a p27-dependent manner by increasing Skp2. In conclusion, these results strongly suggest that integrin-mediated signals from the ECM can modulate growth factor-mediated signals in hepatoma cells, and may contribute to the growth of hepatocellular carcinomas.

Portacaval shunt causes apoptosis and liver atrophy in rats despite increases in endogenous levels of major hepatic growth factors

BACKGROUND/AIMS

The response to the liver damage caused by portacaval shunt (PCS) is characterized by low-grade hyperplasia and atrophy. To clarify mechanisms of this dissociation, we correlated the expression of 'hepatotrophic factors' and the antihepatotrophic and proapoptotic peptide, transforming growth factor (TGF)-beta, with the pathologic changes caused by PCS in rats.

METHODS

PCS was created by side-to-side anastomosis between the portal vein and inferior vena cava, with ligation of the hilar portal vein. Hepatic growth mediators were measured to 2 months.

RESULTS

The decrease in the liver/body weight ratio during the first 7 days which stabilized by day 15, corresponded to parenchymal cell apoptosis and increases in hepatic TGF-beta concentration that peaked at 1.4 x baseline at 15 days before returning to control levels by day 30. Variable increases in the concentrations of growth promoters (hepatocyte growth factor, TGF-alpha and augmenter of liver regeneration) also occurred during the period of hepatocellular apoptosis.

CONCLUSIONS

The development of hepatic atrophy was associated with changes in TGF-beta concentration, and occurred despite increased expression of multiple putative growth promoters. The findings suggest that apoptosis set in motion by TGF-beta constrains the amount of hepatocyte proliferation independently from control of liver volume.

A mechanism of cell survival: sequestration of Fas by the HGF receptor Met

Death receptors such as Fas are present in a variety of organs including liver and play an important role in homeostasis. What prevents these harmful receptors from forming homooligomers, clustering, and initiating the apoptotic pathway is not known. Here, we report the discovery of a cell survival mechanism by which Met, a growth factor receptor tyrosine kinase, directly binds to and sequesters the death receptor Fas in hepatocytes. This interaction prevents Fas self-aggregation and Fas ligand binding, thus inhibiting Fas activation and apoptosis. Our results describe a direct link between growth factor tyrosine kinase receptors and death receptors to establish a novel paradigm in growth regulation.

Anti-apoptotic signaling by hepatocyte growth factor/Met via the phosphatidylinositol 3-kinase/Akt and mitogen-activated protein kinase pathways

Hepatocyte growth factor (HGF) is a ligand of the receptor tyrosine kinase encoded by the c-Met protooncogene. HGF/Met signaling has multifunctional effects on various cell types. We sought to determine the role of HGF/Met in apoptosis and identify signal transducers involved in this process. In experiments with human SK-LMS-1 leiomyosarcoma cells, we show that the Akt kinase is activated by HGF in a time- and dose-dependent manner by phosphatidylinositol 3-kinase (PI3-kinase). Akt is also activated by active tumorigenic forms of Met, i.e., ligand-independent Tpr-Met, a truncated and constitutively dimerized form of Met, and a mutationally activated version of Met corresponding to that found in human hereditary papillary renal carcinoma. In NIH 3T3 cells transfected with wild-type Met, HGF inhibits apoptosis induced by serum starvation and UV irradiation. HGF-induced survival correlates with Akt activity and is inhibited by the specific PI3-kinase inhibitor LY294002, indicating that HGF inhibits cell death through the PI3-kinase/Akt signal transduction pathway. Furthermore, transiently transfected Tpr-Met activates Akt (both Akt1 and Akt2) and protects cells from apoptosis. Mitogen-activated protein kinase (MAPK) also is activated by HGF and rescues cells from apoptosis, although the cytoprotective effect is less marked than for PI3-kinase/Akt. Blocking MAPK with the specific MAPK kinase inhibitor PD098059 impairs the ability of HGF to promote cell survival. Similar results were obtained with NIH 3T3 cells expressing the fusion protein Trk-Met and stimulated with nerve growth factor, the Trk ligand. These results demonstrate that HGF/Met is capable of protecting cells from apoptosis by using both PI3-kinase/Akt and, to a lesser extent, MAPK pathways.

Hepatocyte growth factor induces pro-apoptotic genes in HepG2 hepatoma but not in B16-F1 melanoma cells

Hepatocyte growth factor (HGF) exerts a cytostatic effect on HepG2 and B16-F1 cell lines. To evaluate the possible involvement of the apoptotic process in this effect, we performed studies at cellular and molecular levels. HGF induced apoptosis only in HepG2 hepatoma cells at day 3 in about 20% of the cells undergoing growth inhibition, while hallmarks of apoptosis did not occur in B16-F1 melanoma cells. During the first 24 h after HGF treatment, enhanced expression of the pro-apoptotic genes bax and c-Myc was observed at level of mRNA and protein. Concomitant induction of antizyme (AZ) might lower ornithine decarboxylase (ODC) protein level though a huge increase in ODC mRNA level took place. This was suggested as a signal for apoptosis decisional phase. The levels of the proteins examined except that of AZ fell down thereafter when HepG2 cells underwent apoptosis. In B16-F1 cells, only ODC and AZ protein levels were elevated probably in relation to the initial elevated growth rate and the absence of apoptosis involvement in the following cytostatic effect of HGF in melanoma cells. Consistent with this hypothesis, bax mRNA and protein levels were unchanged or even lower relative to control values.

Anti-apoptotic signaling by hepatocyte growth factor/Met via the phosphatidylinositol 3-kinase/Akt and mitogen-activated protein kinase pathways

Hepatocyte growth factor (HGF) is a ligand of the receptor tyrosine kinase encoded by the c-Met protooncogene. HGF/Met signaling has multifunctional effects on various cell types. We sought to determine the role of HGF/Met in apoptosis and identify signal transducers involved in this process. In experiments with human SK-LMS-1 leiomyosarcoma cells, we show that the Akt kinase is activated by HGF in a time- and dose-dependent manner by phosphatidylinositol 3-kinase (PI3-kinase). Akt is also activated by active tumorigenic forms of Met, i.e., ligand-independent Tpr-Met, a truncated and constitutively dimerized form of Met, and a mutationally activated version of Met corresponding to that found in human hereditary papillary renal carcinoma. In NIH 3T3 cells transfected with wild-type Met, HGF inhibits apoptosis induced by serum starvation and UV irradiation. HGF-induced survival correlates with Akt activity and is inhibited by the specific PI3-kinase inhibitor LY294002, indicating that HGF inhibits cell death through the PI3-kinase/Akt signal transduction pathway. Furthermore, transiently transfected Tpr-Met activates Akt (both Akt1 and Akt2) and protects cells from apoptosis. Mitogen-activated protein kinase (MAPK) also is activated by HGF and rescues cells from apoptosis, although the cytoprotective effect is less marked than for PI3-kinase/Akt. Blocking MAPK with the specific MAPK kinase inhibitor PD098059 impairs the ability of HGF to promote cell survival. Similar results were obtained with NIH 3T3 cells expressing the fusion protein Trk-Met and stimulated with nerve growth factor, the Trk ligand. These results demonstrate that HGF/Met is capable of protecting cells from apoptosis by using both PI3-kinase/Akt and, to a lesser extent, MAPK pathways.

Lipopolysaccharide potentiates the effect of hepatocyte growth factor on hepatocyte replication in rats by augmenting AP-1 activity

The liver regenerates by replication of differentiated hepatocytes after damage or removal of part of the liver. Although several growth factors and signaling pathways are activated during regeneration, it is unclear as to which of these are essential for hepatocyte replication. We show here that low- (1 mg/kg) and high- (10 mg/kg) dose hepatocyte growth factor (HGF) induced replication of 2.1% and 11.1% of hepatocytes in rats, respectively. Lipopolysaccharide (LPS), an inducer of the acute phase response, augmented hepatocyte replication in response to low- and high-dose HGF by 4- and 2-fold, respectively. HGF alone induced moderate levels of c-Jun-N-terminal kinase (JNK) and p44/p42 mitogen-activated protein kinase (MAPK), resulting in moderate levels of AP-1-DNA binding activity. The combination of LPS + HGF increased JNK and AP-1-DNA binding activity more than levels seen with LPS or HGF alone. The activation of Stat3 that was observed after administration of LPS + HGF, but not HGF alone, could contribute to increased transcription of AP-1 components. Because phosphorylation of the c-Jun component of AP-1 by JNK increases its ability to activate transcription, the AP-1 in hepatocytes from animals treated with LPS + HGF may be more active than in rats treated with LPS or HGF alone. LPS may contribute to hepatocyte replication by potentiating the effect of HGF on the activation of both AP-1-DNA binding and transcriptional activity.