Transforming Growth Factor-α Inhibits the Intrinsic Pathway of c-Myc-Induced Apoptosis through Activation of Nuclear Factor-κB in Murine Hepatocellular Carcinomas

Hepatotoxicity effects of Ageratina adenophora, as indicated by network toxicology combined with metabolomics and transcriptomics

Ageratina adenophora (A. adenophora), one of the prominent invasive plants in the Asian continent has shown toxicity in animals. However, studies examining the gene expression and metabolic profiles of animals that ingest A. adenophora have not yet been reported in the literature. Therefore, considering the wide distribution of A. adenophora, it is necessary to elucidate the toxic mechanisms of A. adenophora via multiomics approach. In this study, we identified and evaluated the toxic mechanisms of action associated with bioactive compounds in A. adenophora by using network toxicology studies combined with metabolomics and transcriptomics and found that 2-deoxo-2-(acetyloxy)- 9-oxoageraphorone, 10Hβ-9-oxo-agerophorone, 10Hα-9-oxo-agerophorone, nerolidol, 9-oxo-10,11-dehydro-agerophorone were the main active toxic compounds in A. adenophora. In addition, using metabolomics approach we identified differential metabolites such as L-pyroglutamic acid, 1-methylhistidine, prostaglandin F2alpha and hydrocortisone from A. adenophora and these metabolites were involved in amino acid metabolism, lipid metabolism and signal conducting media regulation. Based on network toxicological analysis, we observed that, A. adenophora can affect the Ras signaling, Phospholipase D signaling and MAPK signaling pathways by regulating EGFR, PDGFRB, KIT and other targets. From the results of this study we concluded that A. adenophora induces liver inflammatory damage by activating the EGFR expression and Ras/Raf/MEK/ERK signaling pathways as well as affect nutrients metabolism and neuron conduction.

Pulsatilla vulgaris Inhibits Cancer Proliferation in Signaling Pathways of 12 Reporter Genes

This study aimed to examine if methanolic extracts of Pulsatilla vulgaris Mill. can inhibit HeLa cell proliferation through the modulation of cancer-related signaling pathways. The cytotoxicity and chemical composition of P. vulgaris leaves and root extracts were also determined. Research showed that root extract of P. vulgaris inhibited 12 signaling pathways in a cervical cancer cell line and the most potent activation inhibition was observed for MYC, Notch, Wnt, E2F, Ets, Stat3, Smad, Hdghog, AP-1, and NF-κB, at a concentration of 40 µg/mL. The methanolic extracts of P. vulgaris enhanced apoptotic death and deregulated cellular proliferation, differentiation, and progression toward the neoplastic phenotype by altering key signaling molecules required for cell cycle progression. This is the first study to report the influence of P. vulgaris on cancer signaling pathways. Additionally, our detailed phytochemical analysis of the methanolic extracts of P. vulgaris gives a conclusion that compounds, which strongly suppressed the growth and proliferation of HeLa cancer cells were mainly triterpenoid saponins accompanied by phenolic acids.

Extracts from Pulsatilla patens target cancer-related signaling pathways in HeLa cells

The purpose of this study was to determine if a methanolic extract of the Pulsatilla patens (L.) Mill. can inhibit the progression of cancer through the modulation of cancer-related metabolic signaling pathways. We analyzed a panel of 13 inducible luciferase reporter gene vectors which expression is driven by enhancer elements that bind to specific transcription factors for the evaluation of the activity of cancer signaling pathways. The root extract of P. patens exhibited strong inhibition of several signaling pathways in HeLa cells, a cervical cancer cell line, and was found to be the most potent in inhibiting the activation of Stat3, Smad, AP-1, NF-κB, MYC, Ets, Wnt and Hdghog, at a concentration of 40 µg/mL. The methanolic extracts of P. patens enhanced apoptotic death, deregulated cellular proliferation, differentiation, and progression towards the neoplastic phenotype by altering key signaling molecules required for cell cycle progression. This is the first study to report the influence of Pulsatilla species on cancer signaling pathways. Further, our detailed phytochemical analysis of the methanolic extracts of the P. patens allowed to deduce that compounds, which strongly suppressed the growth and proliferation of HeLa cancer cells were mainly triterpenoid saponins accompanied by phenolic acids.

Negative correlation between X-linked inhibitors of apoptosis and second mitochondria-derived activator of caspase expression levels in cervical carcinoma and cervical intraepithelial neoplasia

X-linked inhibitors of apoptosis (XIAP) and second mitochondria-derived activator of caspase (Smac) have been widely reported to serve roles in the development of cervical carcinoma. The present study analyzed the associations between the expression levels of XIAP and Smac in normal cervical epithelium, cervical intraepithelial neoplasia (CIN) and cervical carcinoma. Immunohistochemistry staining of formalin-fixed, paraffin-embedded tissue sections was performed in order to analyze the expression levels of XIAP and Smac in 15 cases of normal cervical tissues, 69 cases of CIN and 76 cases of cervical carcinoma. All the tissue samples were confirmed by pathological diagnosis. The association of XIAP and Smac expression levels was analyzed using one-way analysis of variance, χ² tests and Spearman's ρ for the nonparametric bi-variant correlation analysis. Overall survival was determined using the log-rank test and Kaplan-Meier survival curves. The expression level of XIAP was increased in CIN and cervical carcinoma tissues compared with normal cervical tissues, whereas Smac demonstrated a converse expression pattern to XIAP in these tissues. The positive staining level of XIAP protein was increased in grade 3 CIN compared with that in grade 1–2 CIN, and was significantly higher in the less-differentiated tissue of cervical carcinoma compared with the well- or medium-differentiated tissues (P<0.05). The staining level was also significantly increased in cervical carcinoma with stage 2b-3 compared with tissues from stage 1–2a carcinoma (P<0.05). The expression levels of Smac were in opposition to these results. XIAP was associated with pelvic lymph node metastasis, whereas no association was identified with Smac expression. The expression level of XIAP was significantly and negatively associated with cell survival time in cervical carcinoma, whereas the expression level of Smac was significantly and positively associated with cell survival time in cervical carcinoma. Therefore, XIAP and Smac may participate in the development of cervical cancer. The expression levels of XIAP and Smac were significantly and inversely associated. This may be useful in early diagnosis, evaluation of surgery and chemotherapy and the prognosis of cervical carcinoma.

NF-κB in cancer therapy

The transcription factor nuclear factor kappa B (NF-κB) has attracted increasing attention in the field of cancer research from last few decades. Aberrant activation of this transcription factor is frequently encountered in a variety of solid tumors and hematological malignancies. NF-κB family members and their regulated genes have been linked to malignant transformation, tumor cell proliferation, survival, angiogenesis, invasion/metastasis, and therapeutic resistance. In this review, we highlight the diverse molecular mechanism(s) by which the NF-κB pathway is constitutively activated in different types of human cancers, and the potential role of various oncogenic genes regulated by this transcription factor in cancer development and progression. Additionally, various pharmacological approaches employed to target the deregulated NF-κB signaling pathway, and their possible therapeutic potential in cancer therapy is also discussed briefly.

Inactivation of MYC reverses tumorigenesis

The MYC proto-oncogene is an essential regulator of many normal biological programmes. MYC, when activated as an oncogene, has been implicated in the pathogenesis of most types of human cancers. MYC overexpression in normal cells is restrained from causing cancer through multiple genetically and epigenetically controlled checkpoint mechanisms, including proliferative arrest, apoptosis and cellular senescence. When pathologically activated in the correct epigenetic and genetic contexts, MYC bypasses these mechanisms and drives many of the 'hallmark' features of cancer, including uncontrolled tumour growth associated with DNA replication and transcription, cellular proliferation and growth, protein synthesis and altered cellular metabolism. MYC also dictates tumour cell fate by enforcing self-renewal and by abrogating cellular senescence and differentiation programmes. Moreover, MYC influences the tumour microenvironment, including activating angiogenesis and suppressing the host immune response. Provocatively, brief or even partial suppression of MYC back to its physiological levels of activation can lead to the restoration of intrinsic checkpoint mechanisms, resulting in acute and sustained tumour regression associated with tumour cells undergoing proliferative arrest, differentiation, senescence and apoptosis, as well as remodelling of the tumour microenvironment, recruitment of an immune response and shutdown of angiogenesis. Hence, tumours appear to be addicted to the MYC oncogene because of both tumour cell intrinsic and host-dependent mechanisms. MYC is important for the regulation of both the initiation and maintenance of tumorigenesis.

MYC activation is a hallmark of cancer initiation and maintenance

The MYC proto-oncogene has been implicated in the pathogenesis of most types of human tumors. MYC activation alone in many normal cells is restrained from causing tumorigenesis through multiple genetic and epigenetically controlled checkpoint mechanisms, including proliferative arrest, apoptosis, and cellular senescence. When pathologically activated in a permissive epigenetic and/or genetic context, MYC bypasses these mechanisms, enforcing many of the "hallmark" features of cancer, including relentless tumor growth associated with DNA replication and transcription, cellular proliferation and growth, protein synthesis, and altered cellular metabolism. MYC mandates tumor cell fate, by inducing stemness and blocking cellular senescence and differentiation. Additionally, MYC orchestrates changes in the tumor microenvironment, including the activation of angiogenesis and suppression of the host immune response. Provocatively, brief or even partial suppression of MYC back to its physiological levels of activation can result in the restoration of intrinsic checkpoint mechanisms, resulting in acute and sustained tumor regression, associated with tumor cells undergoing proliferative arrest, differentiation, senescence, and apoptosis, as well as remodeling of the tumor microenvironment, recruitment of an immune response, and shutdown of angiogenesis. Hence, tumors appear to be "addicted" to MYC because of both tumor cell-intrinsic, cell-autonomous and host-dependent, immune cell-dependent mechanisms. Both the trajectory and persistence of many human cancers require sustained MYC activation. Multiscale mathematical modeling may be useful to predict when tumors will be addicted to MYC. MYC is a hallmark molecular feature of both the initiation and maintenance of tumorigenesis.

The EGFR signalling system in the liver: from hepatoprotection to hepatocarcinogenesis

The liver displays an outstanding wound healing and regenerative capacity unmatched by any other organ. This reparative response is governed by a complex network of inflammatory mediators, growth factors and metabolites that are set in motion in response to hepatocellular injury. However, when liver injury is chronic, these regenerative mechanisms become dysregulated, facilitating the accumulation of genetic alterations leading to unrestrained cell proliferation and the development of hepatocellular carcinoma (HCC). The epidermal growth factor receptor (EGFR or ErbB1) signaling system has been identified as a key player in all stages of the liver response to injury, from early inflammation and hepatocellular proliferation to fibrogenesis and neoplastic transformation. The EGFR system engages in extensive crosstalk with other signaling pathways, acting as a true signaling hub for other growth factors, cytokines and inflammatory mediators. Here, we briefly review essential aspects of the biology of the EGFR, the other ErbB receptors, and their ligands in liver injury, regeneration and HCC development. Some aspects of the preclinical and clinical experience with EGFR therapeutic targeting in HCC are also discussed.

Polygenic effects of common single-nucleotide polymorphisms on life span: when association meets causality

Recently we have shown that the human life span is influenced jointly by many common single-nucleotide polymorphisms (SNPs), each with a small individual effect. Here we investigate further the polygenic influence on life span and discuss its possible biological mechanisms. First we identified six sets of prolongevity SNP alleles in the Framingham Heart Study 550K SNPs data, using six different statistical procedures (normal linear, Cox, and logistic regressions; generalized estimation equation; mixed model; gene frequency method). We then estimated joint effects of these SNPs on human survival. We found that alleles in each set show significant additive influence on life span. Twenty-seven SNPs comprised the overlapping set of SNPs that influenced life span, regardless of the statistical procedure. The majority of these SNPs (74%) were within genes, compared to 40% of SNPs in the original 550K set. We then performed a review of current literature on functions of genes closest to these 27 SNPs. The review showed that the respective genes are largely involved in aging, cancer, and brain disorders. We concluded that polygenic effects can explain a substantial portion of genetic influence on life span. Composition of the set of prolongevity alleles depends on the statistical procedure used for the allele selection. At the same time, there is a core set of longevity alleles that are selected with all statistical procedures. Functional relevance of respective genes to aging and major diseases supports causal relationships between the identified SNPs and life span. The fact that genes found in our and other genetic association studies of aging/longevity have similar functions indicates high chances of true positive associations for corresponding genetic variants.

Postnatal liver growth and regeneration are independent of c-myc in a mouse model of conditional hepatic c-myc deletion

BACKGROUND

The transcription factor c-myc regulates genes involved in hepatocyte growth, proliferation, metabolism, and differentiation. It has also been assigned roles in liver development and regeneration. In previous studies, we made the unexpected observation that c-Myc protein levels were similar in proliferating fetal liver and quiescent adult liver with c-Myc displaying nucleolar localization in the latter. In order to investigate the functional role of c-Myc in adult liver, we have developed a hepatocyte-specific c-myc knockout mouse, c-mycfl/fl;Alb-Cre.

RESULTS

Liver weight to body weight ratios were similar in control and c-myc deficient mice. Liver architecture was unaffected. Conditional c-myc deletion did not result in compensatory induction of other myc family members or in c-Myc's binding partner Max. Floxed c-myc did have a negative effect on Alb-Cre expression at 4 weeks of age. To explore this relationship further, we used the Rosa26 reporter line to assay Cre activity in the c-myc floxed mice. No significant difference in Alb-Cre activity was found between control and c-mycfl/fl mice. c-myc deficient mice were studied in a nonproliferative model of liver growth, fasting for 48 hr followed by a 24 hr refeeding period. Fasting resulted in a decrease in liver mass and liver protein, both of which recovered upon 24 h of refeeding in the c-mycfl/fl;Alb-Cre animals. There was also no effect of reducing c-myc on recovery of liver mass following 2/3 partial hepatectomy.

CONCLUSIONS

c-Myc appears to be dispensable for normal liver growth during the postnatal period, restoration of liver mass following partial hepatectomy and recovery from fasting.

c-Myc induction of programmed cell death may contribute to carcinogenesis: a perspective inspired by several concepts of chemical carcinogenesis

The c-Myc protein, encoded by c-myc gene, in its wild-type form can induce tumors with a high frequency and can induce massive programmed cell death (PCD) in most transgenic mouse models, with greater efficiency than other oncogenes. Evidence also indicates that c-Myc can cause proliferative inhibition, i.e. mitoinhibition. The c-Myc-induced PCD and mitoinhibition, which may be attributable to its inhibition of cyclin D1 and induction of p53, may impose a pressure of compensatory proliferation, i.e. regeneration, onto the initiated cells (cancer progenitor cells) that occur sporadically and are resistant to the mitoinhibition. The initiated cells can thus proliferate robustly and progress to a malignancy. This hypothetical thinking, i.e. the concurrent PCD and mitoinhibition induced by c-Myc can promote carcinogenesis, predicts that an optimal balance is achieved between cell death and ensuing regeneration during oncogenic transformation by c-Myc, which can better promote carcinogenesis. In this perspective, we summarize accumulating evidence and challenge the current model that oncoprotein induces carcinogenesis by promoting cellular proliferation and/or inhibiting PCD. Inspired by c-myc oncogene, we surmise that many tumor-suppressive or growth-inhibitory genes may also be able to promote carcinogenesis in a similar way, i.e. by inducing PCD and/or mitoinhibition of normal cells to create a need for compensatory proliferation that drives a robust replication of initiating cells.

Non-mammalian fat-1 gene prevents neoplasia when introduced to a mouse hepatocarcinogenesis model: Omega-3 fatty acids prevent liver neoplasia

We investigated the effect of a non-mammalian omega-3 desaturase in a mouse hepatocarcinogenesis model. Mice containing double mutations (DM) in c-myc and TGF-alpha (transforming growth factor-alpha), leading to liver neoplasia, were crossed with mice containing omega-3 desaturase. MRI analysis of triple mutant (TM) mice showed the absence of neoplasia at all time points for 92% of mice in the study. Pathological changes of TM (TGFalpha/c-myc/fat-1) mouse liver tissue was similar to control mouse liver tissue. Magnetic resonance spectroscopy (MRS) measurements of unsaturated fatty acids found a significant difference (p<0.005) between DM and TM transgenic (Tg) mice at 34 and 40 weeks of age. HPLC analysis of mouse liver tissue revealed markedly decreased levels of omega-6 fatty acids in TM mice when compared to DM (TGFalpha/c-myc) and control (CD1) mice. Mass spectrometry (MS) analysis indicated significantly decreased 16:0/20:4 and 18:1/20:4 and elevated 16:0/22:6 fatty acyl groups in both GPCho and GPEtn, and elevated 16:0/20:5, 18:0/18:2, 18:0/18:1 and 18:0/22:6 in GPCho, within TM mice compared to DM mice. Total fatty acid analysis indicated a significant decrease in 18:1n9 in TM mice compared to DM mice. Western blot analysis of liver tissue showed a significant (p<0.05) decrease in NF-kappaB (nuclear factor-kappaB) levels at 40 weeks of age in TM mice compared to DM mice. Microarray analysis of TM versus DM mice livers at 40 weeks revealed alterations in genes involved in cell cycle regulation, cell-to-cell signaling, p53 signaling, and arachidonic acid (20:4) metabolism. Endogenous omega-3 fatty acids were found to prevent HCC development in mice.

Advances in the understanding of MYC-induced lymphomagenesis

Up to 70% of all human malignancies show elevated expression of MYC. MYC is a pleiotropic transcription factor involved in many aspects of cellular development and physiology. Besides direct regulation of target genes involved in proliferation and growth MYC is implicated in controlling the complex networks of microRNAs and apoptosis mediators. The mode of MYC deregulation varies between different tumor entities. In most types of cancer high MYC levels are secondary to alterations in cell signalling pathways, leading to enhanced proliferation of the transformed cells. In some haematological malignancies, like Burkitt lymphoma (BL) and subsets of diffuse large B-cell lymphomas, elevated MYC levels are a direct consequence of genomic aberrations involving the MYC locus. BL is considered the prime example for MYC-induced lymphomagenesis. In comparison to other haematological malignancies it has the highest MYC-expression and is often connected to Epstein-Barr virus (EBV) infection. Over the past five decades BL has provided an invaluable tool for the entire discipline of oncology, helping to decipher many aspects of tumor biology. This review summarizes recent advances in the research on MYC-induced lymphomagenesis, focusing on the regulation of microRNAs and apoptosis, and possible contributions of EBV for lymphoma development.

Assessment of the effect of betaine on p16 and c-myc DNA methylation and mRNA expression in a chemical induced rat liver cancer model

Background

The development and progression of liver cancer may involve abnormal changes in DNA methylation, which lead to the activation of certain proto-oncogenes, such as c-myc, as well as the inactivation of certain tumor suppressors, such as p16. Betaine, as an active methyl-donor, maintains normal DNA methylation patterns. However, there are few investigations on the protective effect of betaine in hepatocarcinogenesis.

Methods

Four groups of rats were given diethylinitrosamine (DEN) and fed with AIN-93G diets supplemented with 0, 10, 20 or 40 g betaine/kg (model, 1%, 2%, and 4% betaine, respectively), while the control group, received no DEN, fed with AIN-93G diet. Eight or 15 weeks later, the expression of p16 and c-myc mRNA was examined by Real-time PCR (Q-PCR). The DNA methylation status within the p16 and c-myc promoter was analyzed using methylation-specific PCR.

Results

Compared with the model group, numbers and areas of glutathione S-transferase placental form (GST-p)-positive foci were decreased in the livers of the rats treated with betaine (P < 0.05). Although the frequency of p16 promoter methylation in livers of the four DEN-fed groups appeared to increase, there is no difference among these groups after 8 or 15 weeks (P > 0.05). Betaine supplementation attenuated the down-regulation of p16 and inhibited the up-regulation of c-myc induced by DEN in a dose-dependent manner (P < 0.01). Meanwhile, increases in levels of malondialdehyde (MDA) and glutathione S-transferase (GST) in model, 2% and 4% betaine groups were observed (P < 0.05). Finally, enhanced antioxidative capacity (T-AOC) was observed in both the 2% and 4% betaine groups.

Conclusion

Our data suggest that betaine attenuates DEN-induced damage in rat liver and reverses DEN-induced changes in mRNA levels.

Hepatocarcinogenesis following pancreatic islet transplantation in streptozotocin- and autoimmune-diabetic rats

Epidemiological studies assign a role to insulin signalling deregulation and diabetes mellitus in human hepatocarcinogenesis. The underlying mechanisms, however, remain largely unknown. To unravel the molecular pathogenesis of insulin-induced hepatocarcinogenesis, we generated an experimental animal model: after transplantation of only a low number of isologous pancreatic islets into the livers of diabetic rats, mild diabetes persists and the beta cells are maximally stimulated to permanently secrete insulin. As a consequence, liver acini, draining the hyperinsulinemic blood from islet grafts, show insulin-induced adaptive alterations simultaneously resembling preneoplastic foci of chemically-induced hepatocarcinogenesis models. These lesions progress to hepatocellular tumours within 6 and 24 months. Hepatocarcinogenesis is accompanied by alterations in hepatocytes metabolisms and changes in signal transduction pathways that, in the beginning, can be attributed solely to insulin action. In this review, we summarize our findings that may help understanding the oncogenic potential of diabetes mellitus in the human liver.

Nuclear-factor-kappaB (NF-kappaB) and radical oxygen species play contrary roles in transforming growth factor-beta1 (TGF-beta1)-induced apoptosis in hepatocellular carcinoma (HCC) cells

Nuclear-Factor-kappaB (NF-kappaBeta can counteract transforming growth factor-beta1 (TGF-beta1)-induced apoptosis in malignant hepatocytes through up-regulation of its downstream genes, such as X-linked inhibitor of apoptosis protein (XIAP). Reports have demonstrated that TGF-beta1 can induce oxidative stress, and c-Jun N-terminal Kinase1 (JNK1) is indispensable for TGF-beta1-induced apoptosis pathway, but the relationship between radical oxygen species (ROS) and the activation of JNKs is still unclear. In the present study, we found that ROS can induce JNK activation in TGF-beta1 mediated apoptosis in hepatocytes. The inhibitors of hydrogen peroxide and superoxide, which were produced by mitochondria under stress, could inhibit the phosphorylation of c-Jun in XIAP knockdown cells. In conclusion, it is the first time to show that both NF-kappaB and antioxidants can counteract TGF-beta1-induced apoptosis in hepatic cell death through JNK1 pathway.

Histological complexities of pancreatic lesions from transgenic mouse models are consistent with biological and morphological heterogeneity of human pancreatic cancer

Although pancreatic cancer is the fourth leading cause of cancer death, it has received much less attention compared to other malignancies. There are several transgenic animal models available for studies of pancreatic carcinogenesis, but most of them do not recapitulate, histologically, human pancreatic cancer. Here we review some detailed molecular complexity of human pancreatic cancer and their reflection in histomorphological complexities of pancreatic lesions developed in various transgenic mouse models with a special concern for studying the effects of chemotherapeutic and chemopreventive agents. These studies usually require a large number of animals that are at the same age and gender and should be either homozygote or heterozygote but not a mixture of both. Only single-transgene models can meet these special requirements, but many currently available models require a mouse to simultaneously bear several transgene alleles. Thus it is imperative to identify new gene promoters or enhancers that are specific for the ductal cells of the pancreas and are highly active in vivo so as to establish new single-transgene models that yield pancreatic ductal adenocarcinomas for chemotherapeutic and chemopreventive studies.

Activation of NADPH oxidase by transforming growth factor-beta in hepatocytes mediates up-regulation of epidermal growth factor receptor ligands through a nuclear factor-kappaB-dependent mechanism

The TGF-beta (transforming growth factor-beta) induces survival signals in foetal rat hepatocytes through transactivation of EGFR (epidermal growth factor receptor). The molecular mechanism is not completely understood, but both activation of the TACE (tumour necrosis factor alpha-converting enzyme)/ADAM17 (a disintegrin and metalloproteinase 17; one of the metalloproteases involved in shedding of the EGFR ligands) and up-regulation of TGF-alpha and HB-EGF (heparin-binding epidermal growth factor-like growth factor) appear to be involved. In the present study, we have analysed the molecular mechanisms that mediate up-regulation of the EGFR ligands by TGF-beta in foetal rat hepatocytes. The potential involvement of ROS (reactive oxygen species), an early signal induced by TGF-beta, and the existence of an amplification loop triggered by initial activation of the EGFR, have been studied. Results indicate that DPI (diphenyleneiodonium) and apocynin, two NOX (NADPH oxidase) inhibitors, and SB431542, an inhibitor of the TbetaR-I (TGF-beta receptor I), block up-regulation of EGFR ligands and Akt activation. Different members of the NOX family of genes are expressed in hepatocytes, included nox1, nox2 and nox4. TGF-beta up-regulates nox4 and increases the levels of Rac1 protein, a known regulator of both Nox1 and Nox2, in a TbetaR-I-dependent manner. TGF-beta mediates activation of the nuclear factor-kappaB pathway, which is inhibited by DPI and is required for up-regulation of TGF-alpha and HB-EGF. In contrast, EGFR activation is not required for TGF-beta-induced up-regulation of those ligands. Considering previous work that has established the role of ROS in apoptosis induced by TGF-beta in hepatocytes, the results of the present study indicate that ROS might mediate both pro- and anti-apoptotic signals in TGF-beta-treated cells.

New molecular targets for hepatocellular carcinoma: the ErbB1 signaling system

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

Survival and apoptosis: a dysregulated balance in liver cancer

BACKGROUND/AIMS

Dysregulation of the balance between proliferation and cell death represents a protumorigenic principle in human hepatocarcinogenesis. This article aims to provide a review of the current findings about how physiological hepatocyte apoptosis is regulated and whether or not its dysregulation might contribute to the progression towards a hepatocellular carcinoma (HCC) process.

RESULTS

Although some physiological proapoptotic molecules are downregulated or inactivated in HCC, such as Fas, p53, Bax or Bid, dysregulation of the balance between death and survival is mainly due to overactivation of antiapoptotic signals. Thus, some growth factors that mediate cell survival are upregulated in HCC, as well as the molecules involved in the machinery responsible for cleavage of their proforms to an active peptide. The expression of the pten gene is reduced or absent in almost half the HCCs and the Spred family of Ras/ERK inhibitors is also dysregulated in HCC, which consequently lead to the overactivation of relevant survival kinases: AKT and ERKs. Alterations in the expression and/or activity of molecules involved in counteracting apoptosis, such as NF-kappaB, Bcl-X(L), Mcl-1 or c-IAP1, have also been observed in HCC.

CONCLUSIONS

Therefore, therapeutic strategies to inhibit selectively antiapoptotic signals in tumour cells have the potential to provide powerful tools to treat liver cancer.

Differential intracellular signalling induced by TGF-beta in rat adult hepatocytes and hepatoma cells: implications in liver carcinogenesis

The transforming growth factor-beta (TGF-beta) regulates hepatocyte growth, inhibiting proliferation and inducing apoptosis. Indeed, escaping from the TGF-beta suppressor actions might be a prerequisite for liver tumour progression. In this work we show that TGF-beta plays a dual role in regulating apoptosis in FaO rat hepatoma cells, since, in addition to its pro-apoptotic effect, TGF-beta also activates survival signals, such as AKT, the epidermal growth factor receptor (EGFR) being required for its activation. TGF-beta induces the expression of the EGFR ligands transforming growth factor-alpha (TGF-alpha) and heparin-binding EGF-like growth factor (HB-EGF) and induces intracellular re-localization of the EGFR. Cells that overcome the apoptotic effects of TGF-beta undergo morphological changes reminiscent of an epithelial-mesenchymal transition (EMT) process. In contrast, TGF-beta does not activate AKT in adult hepatocytes, which correlates with lack of EGFR transactivation and no response to EGFR inhibitors. Although TGF-beta induces TGF-alpha and HB-EGF in adult hepatocytes, these cells show very low expression of TACE/ADAM 17 (TNF-alpha converting enzyme), which is required for EGFR ligand proteolysis and activation. Furthermore, adult hepatocytes do not undergo EMT processes in response to TGF-beta, which might be due, at least in part, to the fact that F-actin re-organization induced by TGF-beta in FaO cells require the EGFR pathway. Finally, results indicate that EGFR transactivation does not block TGF-beta-induced cell cycle arrest in FaO cells, but must be interfering with the pro-apoptotic signalling. In conclusion, TGF-beta is a suppressor factor for adult quiescent hepatocytes, but not for hepatoma cells, where it plays a dual role, both suppressing and promoting carcinogenesis.

The Oscar-worthy role of Myc in apoptosis

The discovery that the Myc oncoprotein could drive cells to undergo apoptosis in addition to its well-established role in cellular proliferation came in the early 1990s, at the beginning of a period of explosive research on cell death. Experimental evidence revealed that Myc sensitises cells to a wide range of death stimuli and abrogating this biological activity plays a profound role in tumorigenesis. Our understanding of the molecular mechanism and genetic programme of Myc-induced apoptosis remains shrouded in mystery and the focus of much attention. In this review, we will discuss established data, recent advances and future objectives regarding the regulatory processes and the functional cooperators that effect and abrogate apoptosis induced by Myc.

Autocrine production of TGF-beta confers resistance to apoptosis after an epithelial-mesenchymal transition process in hepatocytes: Role of EGF receptor ligands

Transforming growth factor-beta (TGF-beta) induces apoptosis in fetal rat hepatocytes. However, a subpopulation of these cells survives, concomitant with changes in phenotype, reminiscent of an epithelial-mesenchymal transition (EMT). We have previously suggested that EMT might confer cell resistance to apoptosis (Valdés et al., Mol. Cancer Res., 1: 68-78, 2002). However, the molecular mechanisms responsible for this resistance are not explored yet. In this work, we have isolated and subcultured the population of hepatocytes that suffered the EMT process and are resistant to apoptosis (TGF-beta-treated fetal hepatocytes: TbetaT-FH). We prove that they secrete mitogenic and survival factors, as analyzed by the proliferative and survival capacity of conditioned medium. Inhibition of the epidermal growth factor receptor (EGFR) sensitizes TbetaT-FH to die after serum withdrawal. TbetaT-FH expresses high levels of transforming growth factor-alpha (TGF-alpha) and heparin-binding EGF-like growth factor (HB-EGF) and shows constitutive activation of the EGFR pathway. A blocking anti-TGF-alpha antibody restores the capacity of cells to die. TGF-beta, which is expressed by TbetaT-FH, mediates up-regulation of TGF-alpha and HB-EGF expression in those cells. In summary, results suggest that an autocrine loop of TGF-beta confers resistance to apoptosis after an EMT process in hepatocytes, through the increase in the expression of EGFR ligands.

Nuclear factor-kappaB and liver carcinogenesis

Hepatocellular carcinoma (HCC) is the third deadliest and fifth most common human cancer worldwide. Hepatitis C virus (HCV) and hepatitis B virus (HBV) infections along with alcohol and aflatoxin B1 intake are widely recognized etiological agents in HCCs. It is anticipated that HCCs will constitute a major health problem in the next two decades because of the rising incidence of HCV infections in the US. The poor survival rate achieved by current surgical procedures and chemotherapy treatment has prompted the scientific community to gain a better understanding of the molecular events involved in hepatocarcinogenesis in order to define new targets for more effective treatment. Recent findings from several laboratories have implicated constitutive activation of the transcription factor NF-kappaB as one of the early key events involved in neoplastic progression of the liver. Data is summarized here from recently published studies illustrating a crucial role of NF-kappaB in bridging the action of growth factors and inflammation to hepatic oncogenesis. Although additional work is needed to fully understand the precise role of NF-kappaB in the regulation of the various transitions of HCC development, these new findings raise the intriguing possibility that pharmacologic inhibition of NF-kappaB in the liver could selectively eradicate malignant liver cells without affecting normal liver homeostasis.