Focus
Authors: Scott L. Friedman
Journal: Journal of Hepatology (2012)

Hepatitis C viral protein NS5A induces EMT and participates in oncogenic transformation of primary hepatocyte precursorsJournal of HepatologyVol. 57Issue 5PreviewApicobasal polarity, which is essential for epithelial structure and function, is targeted by several tumour-related pathogens and is generally perturbed in the course of carcinogenesis. Hepatitis C virus (HCV) infection is associated with a strong risk of hepatocellular carcinoma, typically preceded by dysplastic alterations of cell morphology. We investigated the molecular mechanisms and the functional consequences of HCV-driven perturbations of epithelial polarity. Full-Text PDF Sorafenib attenuates monocrotaline-induced sinusoidal obstruction syndrome in rats through suppression of JNK and MMP-9Journal of HepatologyVol. 57Issue 5PreviewSinusoidal obstruction syndrome (SOS) is a drug-induced liver injury that occurs with oxaliplatin treatment and is associated with postoperative morbidity after hepatectomy. The aim of this study was to investigate the effects of sorafenib in a monocrotaline (MCT)-induced model of SOS in rats. Full-Text PDF This issue of the Journal includes two articles that address a couple of important, overlooked pathologic events in liver disease – epithelial mesenchymal transition (EMT), which is implicated in HCV-induced carcinogenesis in the study by Akkari et al., and sinusoidal obstruction syndrome (SOS), in which Nakamura et al. have identified a potential new therapy in sorafenib, a drug currently approved for the treatment of hepatocellular carcinoma. The study by Akkari describes a potential mechanism whereby the NS5A protein of HCV may promote EMT, based on cell culture and animal models. EMT is a well characterized cellular transition in which epithelial cells acquire a phenotype of mesenchymal cells, and in doing so lose their polarity and cell–cell adhesions, and become motile [1Nistico P. Bissell M.J. Radisky D.C. Epithelial-mesenchymal transition: general principles and pathological relevance with special emphasis on the role of matrix metalloproteinases.Cold Spring Harb Perspect Biol. 2012; 4Crossref PubMed Scopus (209) Google Scholar, 2Thiery J.P. Acloque H. Huang R.Y. Nieto M.A. Epithelial-mesenchymal transitions in development and disease.Cell. 2009; 139: 871-890Abstract Full Text Full Text PDF PubMed Scopus (7679) Google Scholar]. The process is critical to normal tissue development, enabling epithelial cells to become untethered, adopt a mesenchymal phenotype, dissociate from their underlying basement membrane, and migrate to create highly specialized tissues. This so-called primary EMT is essential to many developmental processes, including gastrulation, neural crest formation, and heart valve development, among others. Moreover, EMT confers immunologic privilege, allowing new tissues to form without eliciting an inflammatory or immune response. Signals underlying EMT include the soluble cytokine TGFβ1 and the nuclear transcription factors Twist, Snail, and Slug. Those same features that are essential to EMT in development can be hijacked to promote the development and dissemination of cancer. Pathologic EMT in adult tissues can drive the formation of tumor stem cells and alter the microenvironment to promote invasion, while allowing cells to resist apoptosis or immune attack. EMT has been implicated in a range of human tumors including hepatocellular carcinoma (HCC), as well as breast and colon cancers, and squamous cell cancers of the head and neck and the urogenital system. In this context, the study by Akkari et al. provides some evidence that the NS5A protein of HCV promotes EMT in the BMEL hepatocyte progenitor cell line, in a xenograft model, as well as in transgenic mice that have liver-specific expression of HCV proteins (but not active HCV infection). Retroviral transduction of BMEL cells with the HCV NS5A of genotype 1b or genotype 2a led to morphologic changes typical of EMT along with increased motility, which was dependent upon induction of Twist2. These effects were augmented in the presence of Ras overexpression, which is a common feature of HCC. In vivo, livers of mice transgenically expressing NS5A had increased expression of mesenchymal genes that might also indicate EMT in vivo, although the site(s) of expression were unclear. The findings are provocative and support an earlier study [[3]Battaglia S. Benzoubir N. Nobilet S. Charneau P. Samuel D. Zignego A.L. et al.Liver cancer-derived hepatitis C virus core proteins shift TGF-beta responses from tumor suppression to epithelial-mesenchymal transition.PLoS One. 2009; 4: e4355Crossref PubMed Scopus (103) Google Scholar] that could explain how chronic HCV infection promotes HCC. Moreover, a subset of HCCs can have a stem cell-like signature, which may reflect those in which the EMT program is driving the tumor’s formation [4Yamashita T. Ji J. Budhu A. Forgues M. Yang W. Wang H.Y. et al.EpCAM-positive hepatocellular carcinoma cells are tumor-initiating cells with stem/progenitor cell features.Gastroenterology. 2009; 136: 1012-1024Abstract Full Text Full Text PDF PubMed Scopus (950) Google Scholar, 5Yao Z. Mishra L. Cancer stem cells and hepatocellular carcinoma.Cancer Biol Ther. 2009; 8: 1691-1698Crossref PubMed Scopus (74) Google Scholar, 6Chen X. Lingala S. Khoobyari S. Nolta J. Zern M.A. Wu J. Epithelial mesenchymal transition and hedgehog signaling activation are associated with chemoresistance and invasion of hepatoma subpopulations.J Hepatol. 2011; 55: 838-845Abstract Full Text Full Text PDF PubMed Scopus (173) Google Scholar, 7Dang H. Ding W. Emerson D. Rountree C.B. Snail1 induces epithelial-to-mesenchymal transition and tumor initiating stem cell characteristics.BMC Cancer. 2011; 11: 396Crossref PubMed Scopus (92) Google Scholar] – typically, these tumors have a poorer prognosis. Despite this emerging association between EMT, stem cells, and HCC, the evidence is not ironclad for a role of NS5A in EMT associated with this neoplasm. First, none of the models in this study support HCV replication and therefore the levels of NS5A and their cellular context may not be physiologically relevant. Second, there are no studies identifying features of EMT in livers from patients with HCV, or evidence that EMT correlates with cancer risk or behavior in this cancer. Third, the full program of EMT is not convincingly demonstrated in the Akkari study. Finally, it is not clear how EMT associated with NS5A expression would explain the almost universal requirement for advanced fibrosis or cirrhosis to be present before HCC arises. Does EMT only occur in advanced disease? Is EMT necessary, but not sufficient for HCC, or does it occur in only a subset of tumors? These and other questions await further study. One contribution of EMT to liver disease that is not likely is its potential role in fibrogenesis. A number of earlier studies implicated EMT in hepatic fibrosis, suggesting it leads to the generation of fibrogenic cells from hepatocytes [8Omenetti A. Porrello A. Jung Y. Yang L. Popov Y. Choi S.S. et al.Hedgehog signaling regulates epithelial–mesenchymal transition during biliary fibrosis in rodents and humans.J Clin Invest. 2008; 118: 3331-3342PubMed Google Scholar, 9Zeisberg M. Yang C. Martino M. Duncan M.B. Rieder F. Tanjore H. et al.Fibroblasts derive from hepatocytes in liver fibrosis via epithelial to mesenchymal transition.J Biol Chem. 2007; 282: 23337-23347Crossref PubMed Scopus (672) Google Scholar], and while it appears that EMT fosters fibrogenesis in some way [[10]Rowe R.G. Lin Y. Shimizu-Hirota R. Hanada S. Neilson E.G. Greenson J.K. et al.Hepatocyte-derived Snail1 propagates liver fibrosis progression.Mol Cell Biol. 2011; 31: 2392-2403Crossref PubMed Scopus (104) Google Scholar], it is unlikely to do so by simply generating more matrix-producing cells from epithelium. In fact, several recent studies fail to show true EMT in liver [11Taura K. Miura K. Iwaisako K. Osterreicher C.H. Kodama Y. Penz-Osterreicher M. et al.Hepatocytes do not undergo epithelial–mesenchymal transition in liver fibrosis in mice.Hepatology. 2010; 51: 1027-1036Crossref PubMed Scopus (262) Google Scholar, 12Scholten D. Osterreicher C.H. Scholten A. Iwaisako K. Gu G. Brenner D.A. et al.Genetic labeling does not detect epithelial-to-mesenchymal transition of cholangiocytes in liver fibrosis in mice.Gastroenterology. 2010; 139: 987-998Abstract Full Text Full Text PDF PubMed Scopus (189) Google Scholar, 13Chu A.S. Diaz R. Hui J.J. Yanger K. Zong Y. Alpini G. et al.Lineage tracing demonstrates no evidence of cholangiocyte epithelial-to-mesenchymal transition in murine models of hepatic fibrosis.Hepatology. 2011; 53: 1685-1695Crossref PubMed Scopus (180) Google Scholar], and there is a growing appreciation that EMT can readily occur in culture, but this does not reflect its capacity to occur in vivo [[14]Wells R.G. The epithelial-to-mesenchymal transition in liver fibrosis: here today, gone tomorrow?.Hepatology. 2010; 51: 737-740PubMed Google Scholar]. Sinusoidal obstruction syndrome (SOS), previously called veno-occlusive disease, is a catastrophic illness in which severe injury to the sinusoidal endothelial cells in the pericentral region leads to sinusoidal fibrosis, necrosis of pericentral hepatocytes, and narrowing, then fibrosis of central veins [[15]DeLeve L.D. Shulman H.M. McDonald G.B. Toxic injury to hepatic sinusoids: sinusoidal obstruction syndrome (veno-occlusive disease).Semin Liver Dis. 2002; 22: 27-42Crossref PubMed Scopus (557) Google Scholar]. The syndrome typically occurs in response to chemotherapeutic alkylating agents (e.g., oxaliplatin) used for metastatic colon or breast cancer, and presents clinically with rapid onset of abdominal pain, ascites, and jaundice, owing to the sudden obstruction to outflow of blood from the hepatic parenchyma. Drs. George McDonald and Laurie DeLeve have been among the leaders in characterizing the clinical and cellular features of this illness, respectively, and in 1999 Dr. DeLeve described a new animal model of SOS due to administration of the toxin monocrotaline [[16]DeLeve L.D. McCuskey R.S. Wang X. Hu L. McCuskey M.K. Epstein R.B. et al.Characterization of a reproducible rat model of hepatic veno-occlusive disease.Hepatology. 1999; 29: 1779-1791Crossref PubMed Scopus (284) Google Scholar], which leads to specific injury to sinusoidal endothelial cells, liberating the enzyme matrix metalloproteinase-9 as well as leading to loss of the vasodilator nitric oxide [[17]DeLeve L.D. Wang X. Kanel G.C. Ito Y. Bethea N.W. McCuskey M.K. et al.Decreased hepatic nitric oxide production contributes to the development of rat sinusoidal obstruction syndrome.Hepatology. 2003; 38: 900-908Crossref PubMed Google Scholar]. In the study by Nakamura et al. in this issue of the Journal, the authors reasoned that because SOS is also associated with elevated circulating levels of the angiogenic cytokine VEGF, then antagonizing its signaling with the approved drug sorafenib, might improve the syndrome. Indeed, rats pretreated with standard doses of sorafenib either 12 and 36 h before monocrotaline administration had marked attenuation of SOS features, associated with reduced injury and improved survival after partial hepatectomy. In addition, expression and activity of MMP-9 and the intracellular kinase c-jun N-terminal kinase (JNK) were both reduced by sorafenib. While these results are largely descriptive, they are hopeful nonetheless, first by drawing much-needed attention to this neglected syndrome and second, by providing a practical approach that might merit studies in humans, since sorafenib is already approved for use in HCC. However, in this rodent study the drug was administered prophylactically, and although this might be possible for patients at risk for SOS, sorafenib is not without some adverse symptoms that might be difficult for patients undergoing metastatic colorectal or breast cancer treatment. Moreover, the apparent salutary effect on MMP-9 and JNK does not definitely link these mediators to the cause of attenuated disease. Additionally, the cellular and molecular target(s) of sorafenib and the sources of MMP-9 and JNK are not clear, and could derive from a number of resident cell types besides sinusoidal endothelial cells, in particular hepatic stellate cells. Despite these limitations, efforts like this study to repurpose approved drugs for new indications such as SOS are part of an accelerating trend in biomedicine, and have been the recent focus of an effort in the U.S. by the National Center for Advancing Translational Sciences (www.ncats.nih.gov/research/reengineering/rescue-repurpose/therapeutic-uses/therapeutic-uses.html). In the case of SOS, this effort to find new treatments cannot come a moment too soon. The Author declared that he does not have anything to disclose regarding funding or conflict of interest with respect to this manuscript.