[Show abstract][Hide abstract] ABSTRACT: Pre-mRNA splicing is an essential step in the process of gene expression in eukaryotes and consists of the removal of introns and the linking of exons to generate mature mRNAs. This is a highly regulated mechanism that allows the alternative usage of exons, the retention of intronic sequences and the generation of exonic sequences of variable length. Most human genes undergo splicing events, and disruptions of this process have been associated with a variety of diseases, including cancer. Hepatocellular carcinoma (HCC) is a molecularly heterogeneous type of tumor that usually develops in a cirrhotic liver. Alterations in pre-mRNA splicing of some genes have been observed in liver cancer, and although still scarce, the available data suggest that splicing defects may have a role in hepatocarcinogenesis. Here we briefly review the general mechanisms that regulate pre-mRNA splicing, and discuss some examples that illustrate how this process is impaired in liver tumorigenesis, and may contribute to HCC development. We believe that a more thorough examination of pre-mRNA splicing is still needed to accurately draw the molecular portrait of liver cancer. This will surely contribute to a better understanding of the disease and to the development of new effective therapies.
World Journal of Gastroenterology 07/2010; 16(25):3091-102. · 2.55 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The modulation of the hepatic acute-phase reaction (APR) that occurs during inflammation and liver regeneration is important for allowing normal hepatocellular proliferation and the restoration of homeostasis. Activation of acute-phase protein (APP) gene expression by interleukin-6 (IL-6)-type cytokines is thought to be counteracted by growth factors released during hepatic inflammation and regeneration. The epidermal growth factor receptor (EGFR) ligand amphiregulin (AR) is readily induced by inflammatory signals and plays a nonredundant protective role during liver injury. In this paper, we investigated the role of AR as a modulator of liver APP gene expression.
Expression of APP genes was measured in the livers of AR(+/+) and AR(-/-)mice during inflammation and regeneration and in cultured liver cells treated with AR and oncostatin M (OSM). Crosstalk between AR and OSM signalling was studied.
APP genes were overexpressed in the livers of AR(-/-) mice during inflammation and hepatocellular regeneration. In cultured AR-null hepatocytes and human hepatocellular carcinoma (HCC) cells after AR knockdown, APP gene expression is enhanced. AR counteracts OSM-triggered signal transducer and activator of transcription 3 signalling in hepatocytes and attenuates APP gene transcription.
Our data support the relevance of EGFR-mediated signalling in the modulation of cytokine-activated pathways. We have identified AR as a key regulator of hepatic APP gene expression during inflammation and liver regeneration.
Journal of Hepatology 09/2009; 51(6):1010-20. · 9.86 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Inactivation of the product of the tumor suppressor gene TP73 does not usually occur by mutation but rather through expression of truncated isoforms that have dominant-negative effects on p73 and p53. The truncated oncogenic isoform DeltaEx2p73 is expressed in hepatocellular carcinomas (HCC) and is produced through the alternative splicing of p73 pre-messenger RNA (pre-mRNA); however, the underlying mechanisms regulating this process are unknown.
We used human normal and diseased liver tissue samples, as well as human HCC cell lines, to examine the association between activation of epidermal growth factor receptor (EGFR) by its ligand amphiregulin (AR) and the alternative splicing of p73 pre-mRNA into the tumorigenic isoform DeltaEx2p73, via c-Jun N-terminal-kinase-1-mediated signaling.
DeltaEx2p73 was expressed in a subset of premalignant cirrhotic livers and in otherwise healthy livers that harbored a primary tumor, as well as in HCC tissues. DeltaEx2p73 expression was correlated with that of the EGFR ligand AR, which was previously shown to have a role in hepatocarcinogenesis. Autocrine activation of the EGFR by AR triggered c-Jun N-terminal kinase-1 activity and inhibited the expression of the splicing regulator Slu7, leading to the accumulation of DeltaEx2p73 transcripts in HCC cells.
This study provided a mechanism for the generation of protumorigenic DeltaEx2p73 during liver tumorigenesis, via activation of EGFR signaling by AR and c-Jun N-terminal kinase-1 activity, leading to inhibition of the splicing regulator Slu7.
[Show abstract][Hide abstract] ABSTRACT: Epidemiological studies have established that many tumours occur in association with persistent inflammation. One clear example of inflammation-related cancer is hepatocellular carcinoma (HCC). HCC slowly unfolds on a background of chronic inflammation triggered by exposure to infectious agents (hepatotropic viruses), toxic compounds (ethanol), or metabolic impairment. The molecular links that connect inflammation and cancer are not completely known, but evidence gathered over the past few years is beginning to define the precise mechanisms. A central role for cytokines such as interleukin-6 (IL-6) and IL-1 (alpha and beta) in liver cancer has been established in experimental models. Besides these inflammatory mediators, mounting evidence points to the dysregulation of specific growth and survival-related pathways in HCC development. Among them is the pathway governed by the epidermal growth factor receptor (EGFR), which can be bound and activated by a broad family of ligands. Of special relevance is the fact that the EGFR engages in extensive crosstalk with other signaling pathways, serving as a "signaling hub" for an increasing list of growth factors, cytokines, and inflammatory mediators. In this review, we summarize the most recent evidences supporting a role for the EGFR system in inflammation-related cell signaling, with special emphasis in liver inflammation and HCC. The molecular dissection of the pathways connecting the inflammatory reaction and neoplasia will facilitate the development of novel and more effective antitumor strategies.
Experimental Biology and Medicine 06/2009; 234(7):713-25. · 2.80 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The Wilms' tumor 1 gene (WT1) encodes a transcription factor involved in cell growth and development. As we previously reported, WT1 expression is hardly detectable in normal hepatic tissue but is induced in liver cirrhosis. Although WT1 has been found to be overexpressed in a number of malignancies, the role of WT1 in hepatocarcinogenesis has not been clarified. We found that WT1 is expressed in several human hepatocellular carcinoma (HCC) cell lines, including PLC/PRF/5 and HepG2, and in HCC tumor tissue in 42% of patients. WT1 small interfering RNAs did not affect proliferation rate of HCC cells but abrogated their resistance to anoikis. Transcriptome analysis of PLC/PRF/5 cells after WT1 knockdown showed up-regulation of 251 genes and down-regulation of 321. Ninety percent of the former corresponded to metabolic genes, mostly those characterizing the mature hepatocyte phenotype. On the contrary, genes that decreased upon WT1 inhibition were mainly related to defense against apoptosis, cell cycle, and tumor progression. In agreement with these findings, WT1 expression increased the resistance of liver tumor cells to doxorubicin, a compound used to treat HCC. Interestingly, doxorubicin strongly enhanced WT1 expression in both HCC cells and normal human hepatocytes. Among different chemotherapeutics, induction of WT1 transcription was restricted to topoisomerase 2 inhibitors. When WT1 expression was prohibited, doxorubicin caused a marked increase in caspase-3 activation. In conclusion, WT1 is expressed in a substantial proportion of HCC contributing to tumor progression and resistance to chemotherapy, suggesting that WT1 may be an important target for HCC treatment.
Cancer Research 03/2009; 69(4):1358-67. · 9.28 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The hepatic wound-healing response to chronic noxious stimuli may lead to liver fibrosis, a condition characterized by excessive deposition of extracellular matrix. Fibrogenic cells, including hepatic stellate cells and myofibroblasts, are activated in response to a variety of cytokines, growth factors, and inflammatory mediators. The involvement of members of the epidermal growth factor family in this process has been suggested. Amphiregulin (AR) is an epidermal growth factor receptor (EGFR) ligand specifically induced upon liver injury. Here, we have addressed the in vivo role of AR in experimental liver fibrosis. To this end, liver fibrosis was induced in AR+/+ and AR-/- mice by chronic CCl(4) administration. Histological and molecular markers of hepatic fibrogenesis were measured. Additionally, the response of cultured human and mouse liver fibrogenic cells to AR was evaluated. We observed that AR was expressed in isolated Kupffer cells and liver fibrogenic cells in response to inflamatory stimuli and platelet-derived growth factor, respectively. We demonstrate that the expression of alpha-smooth muscle actin and collagen deposition were markedly reduced in AR-/- mice compared to AR+/+ animals. AR-/- mice also showed reduced expression of tissue inhibitor of metalloproteinases-1 and connective tissue growth factor, two genes that responded to AR treatment in cultured fibrogenic cells. AR also stimulated cell proliferation and exerted a potent antiapoptotic effect on isolated fibrogenic cells. CONCLUSION: These results indicate that among the different EGFR ligands, AR plays a specific role in liver fibrosis. AR may contribute to the expression of fibrogenic mediators, as well as to the growth and survival of fibrogenic cells. Additionally, our data lend further support to the role of the EGFR system in hepatic fibrogenesis.
[Show abstract][Hide abstract] ABSTRACT: 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.
Liver international: official journal of the International Association for the Study of the Liver 04/2007; 27(2):174-85. · 3.87 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Hepatocellular carcinoma is a major cause of cancer-related deaths. Current treatments are not effective, and the identification of relevant pathways and novel therapeutic targets are much needed. Increasing evidences point to the activation of the epidermal growth factor receptor (EGFR) as an important mechanism in the development of hepatocarcinoma. We previously described that amphiregulin (AR), a ligand of the EGFR, is not expressed in healthy liver but is up-regulated during chronic liver injury, the background on which most liver tumors develop. Now, we have studied the expression and role of AR in human hepatocarcinoma. AR expression and function was studied in human liver tumors and cell lines. AR is expressed in human hepatocellular carcinoma tissues and cell lines and behaves as a mitogenic and antiapoptotic growth factor for hepatocarcinoma cells. We provide several lines of evidence, including AR silencing by small interfering RNAs and inhibition of amphiregulin by neutralizing antibodies, showing the existence of an AR-mediated autocrine loop that contributes to the transformed phenotype. Indeed, interference with endogenous AR production resulted in reduced constitutive EGFR signaling, inhibition of cell proliferation, anchorage-independent growth, and enhanced apoptosis. Moreover, knockdown of AR potentiated transforming growth factor-beta and doxorubicin-induced apoptosis. Conversely, overexpression of AR in SK-Hep1 cells enhanced their proliferation rate, anchorage-independent growth, drug resistance, and in vivo tumorigenic potential. These observations suggest that AR is involved in the acquisition of neoplastic traits in the liver and thus constitutes a novel therapeutic target in human hepatocarcinoma.
Cancer Research 07/2006; 66(12):6129-38. · 8.65 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Clinically, the Fas and Fas ligand system plays a central role in the development of hepatocyte apoptosis, a process contributing to a broad spectrum of liver diseases. Therefore, the development of therapies aimed at the inhibition of hepatocyte apoptosis is a major issue. Activation of the epidermal growth factor receptor has been shown to convey survival signals to the hepatocyte. To learn about the endogenous response of epidermal growth factor receptor ligands during Fas-mediated liver injury we investigated the expression of epidermal growth factor, transforming growth factor alpha, heparin-binding epidermal growth factor-like growth factor, betacellulin, epiregulin, and amphiregulin in the liver of mice challenged with Fas-agonist antibody. Amphiregulin expression, barely detectable in healthy liver, was significantly up-regulated. Amphiregulin administration abrogated Fas-mediated liver injury in mice and showed direct anti-apoptotic effects in primary hepatocytes. Amphiregulin activated the Akt and signal transducer and activator of transcription-3 survival pathways, and up-regulated Bcl-xL expression. Amphiregulin knock-out mice showed signs of chronic liver damage in the absence of any noxious treatment, and died faster than wild type mice in response to lethal doses of Fas-agonist antibody. In contrast, these mice were more resistant against sublethal liver damage, supporting the hypothesis that chronic liver injury can precondition hepatocytes inducing resistance to subsequent cell death. These results show that amphiregulin is a protective factor induced in response to liver damage and that it may be therapeutic in liver diseases.
Journal of Biological Chemistry 06/2005; 280(19):19012-20. · 4.65 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Liver regeneration is a unique response directed to restore liver mass after resection or injury. The survival and proliferative signals triggered during this process are conveyed by a complex network of cytokines and growth factors acting in an orderly manner. Activation of the epidermal growth factor receptor is thought to play an important role in liver regeneration. Amphiregulin is a member of the epidermal growth factor family whose expression is not detectable in healthy liver. We have investigated the expression of amphiregulin in liver injury and its role during liver regeneration after partial hepatectomy.
Amphiregulin gene expression was examined in healthy and cirrhotic human and rat liver, in rodent liver regeneration after partial hepatectomy, and in primary hepatocytes. The proliferative effects and intracellular signaling of amphiregulin were studied in isolated hepatocytes. The in vivo role of amphiregulin in liver regeneration after partial hepatectomy was analyzed in amphiregulin-null mice.
Amphiregulin gene expression is detected in chronically injured human and rat liver and is rapidly induced after partial hepatectomy in rodents. Amphiregulin expression is induced in isolated hepatocytes by interleukin 1beta and prostaglandin E(2), but not by hepatocyte growth factor, interleukin 6, or tumor necrosis factor alpha. We show that amphiregulin behaves as a primary mitogen for isolated hepatocytes, acting through the epidermal growth factor receptor. Finally, amphiregulin-null mice display impaired proliferative responses after partial liver resection.
Our findings indicate that amphiregulin is an early-response growth factor that may contribute to the initial phases of liver regeneration.