Effects of growth and differentiation factors on the epithelial-mesenchymal transition in cultured neonatal rat hepatocytes

Insulin Determines Transforming Growth Factor β Effects on Hepatocyte Nuclear Factor 4α Transcription in Hepatocytes

Loss of hepatocyte nuclear factor 4α (HNF4α) expression is frequently observed in end-stage liver disease and associated with loss of vital liver functions, thus increasing mortality. Loss of HNF4α expression is mediated by inflammatory cytokines, such as transforming growth factor (TGF)-β. However, details of how HNF4α is suppressed are largely unknown to date. Herein, TGF-β did not directly inhibit HNF4α but contributed to its transcriptional regulation by SMAD2/3 recruiting acetyltransferase CREB-binding protein/p300 to the HNF4α promoter. The recruitment of CREB-binding protein/p300 is indispensable for CCAAT/enhancer-binding protein α (C/EBPα) binding, another essential requirement for constitutive HNF4α expression in hepatocytes. Consistent with the in vitro observation, 67 of 98 patients with hepatic HNF4α expressed both phospho-SMAD2 and C/EBPα, whereas 22 patients without HNF4α expression lacked either phospho-SMAD2 or C/EBPα. In contrast to the observed induction of HNF4α, SMAD2/3 inhibited C/EBPα transcription. Long-term TGF-β incubation resulted in C/EBPα depletion, which abrogated HNF4α expression. Intriguingly, SMAD2/3 inhibitory binding to the C/EBPα promoter was abolished by insulin. Two-thirds of patients without C/EBPα lacked membrane glucose transporter type 2 expression in hepatocytes, indicating insulin resistance. Taken together, these data indicate that hepatic insulin sensitivity is essential for hepatic HNF4α expression in the condition of inflammation.

c-Met Signaling Is Essential for Mouse Adult Liver Progenitor Cells Expansion After Transforming Growth Factor-β-Induced Epithelial-Mesenchymal Transition and Regulates Cell Phenotypic Switch

Adult hepatic progenitor cells (HPCs)/oval cells are bipotential progenitors that participate in liver repair responses upon chronic injury. Recent findings highlight HPCs plasticity and importance of the HPCs niche signals to determine their fate during the regenerative process, favoring either fibrogenesis or damage resolution. Transforming growth factor-β (TGF-β) and hepatocyte growth factor (HGF) are among the key signals involved in liver regeneration and as component of HPCs niche regulates HPCs biology. Here, we characterize the TGF-β-triggered epithelial-mesenchymal transition (EMT) response in oval cells, its effects on cell fate in vivo, and the regulatory effect of the HGF/c-Met signaling. Our data show that chronic treatment with TGF-β triggers a partial EMT in oval cells based on coexpression of epithelial and mesenchymal markers. The phenotypic and functional profiling indicates that TGF-β-induced EMT is not associated with stemness but rather represents a step forward along hepatic lineage. This phenotypic transition confers advantageous traits to HPCs including survival, migratory/invasive and metabolic benefit, overall enhancing the regenerative potential of oval cells upon transplantation into a carbon tetrachloride-damaged liver. We further uncover a key contribution of the HGF/c-Met pathway to modulate the TGF-β-mediated EMT response. It allows oval cells expansion after EMT by controlling oxidative stress and apoptosis, likely via Twist regulation, and it counterbalances EMT by maintaining epithelial properties. Our work provides evidence that a coordinated and balanced action of TGF-β and HGF are critical for achievement of the optimal regenerative potential of HPCs, opening new therapeutic perspectives. Stem Cells 2019;37:1108-1118.

Mechanisms of Aquaporin-Facilitated Cancer Invasion and Metastasis

Cancer is a leading cause of death worldwide, and its incidence is rising with numbers expected to increase 70% in the next two decades. The fact that current mainline treatments for cancer patients are accompanied by debilitating side effects prompts a growing demand for new therapies that not only inhibit growth and proliferation of cancer cells, but also control invasion and metastasis. One class of targets gaining international attention is the aquaporins, a family of membrane-spanning water channels with diverse physiological functions and extensive tissue-specific distributions in humans. Aquaporins−1,−2,−3,−4,−5,−8, and−9 have been linked to roles in cancer invasion, and metastasis, but their mechanisms of action remain to be fully defined. Aquaporins are implicated in the metastatic cascade in processes of angiogenesis, cellular dissociation, migration, and invasion. Cancer invasion and metastasis are proposed to be potentiated by aquaporins in boosting tumor angiogenesis, enhancing cell volume regulation, regulating cell-cell and cell-matrix adhesions, interacting with actin cytoskeleton, regulating proteases and extracellular-matrix degrading molecules, contributing to the regulation of epithelial-mesenchymal transitions, and interacting with signaling pathways enabling motility and invasion. Pharmacological modulators of aquaporin channels are being identified and tested for therapeutic potential, including compounds derived from loop diuretics, metal-containing organic compounds, plant natural products, and other small molecules. Further studies on aquaporin-dependent functions in cancer metastasis are needed to define the differential contributions of different classes of aquaporin channels to regulation of fluid balance, cell volume, small solute transport, signal transduction, their possible relevance as rate limiting steps, and potential values as therapeutic targets for invasion and metastasis.

Autocrine transforming growth factor-β/activin A-Smad signaling induces hepatic progenitor cells undergoing partial epithelial-mesenchymal transition states

Hepatic progenitor cells (HPCs) are a subpopulation of cells which was usually expanded in chronic liver injury and are contributed to liver regeneration through differentiating into hepatocytes and cholangiocytes. Epithelial-mesenchymal transition is a dynamic process which is important for the progression of liver fibrosis and cancer initiation. This study demonstrated that LE/6 and WB-F344 cells, both of which were HPC derived cell lines, were undergoing partial epithelial-mesenchymal transition states, which was indicated by the co-expression of epithelial markers (E-cadherin and zona occludin 1), and mesenchymal markers (vimentin, fibronectin, collagen 1and α-SMA). Furthermore, autocrine TGF-β and activin A signaling contributed to the maintenance of partial EMT in HPCs. In addition, Smad signaling, a classic downstream signaling cascade of both TGF-β and activin A, also participated in the partial EMT. These findings revealed the existence of partial EMT states in HPCs and confirmed some partial EMT related autocrine signaling cascades, and may help to further the understanding and explore the functional role of HPCs in the process of hepatic fibrosis and liver cancer initiation.

Fate tracing of hepatocytes in mouse liver

Hepatocytes perform most of the functions of the liver and are considered terminally differentiated cells. Recently, it has been suggested that hepatocytes might have the potential to transdifferentiate or dedifferentiate under physiological or pathological conditions in vivo. Epithelial-mesenchymal transition of hepatocytes in liver fibrosis has also been proposed. However, these findings have not been fully confirmed. In this study, hepatocytes were genetically labelled for cell fate tracing using lacZ via the tamoxifen-induced CreERT/loxP system. After induction with tamoxifen, alb + cells were permanently marked by lacZ expression, and all progeny lacZ + cells were derived from a single source with no interference. We did not observe transdifferentiation or dedifferentiation of hepatocytes into cholangiocytes or hepatic progenitor cells under conditions of liver homeostasis or following a 2/3 partial hepatectomy. Meanwhile, lacZ/OPN-positive cells were observed in livers of 3,5-diethoxycarbonyl-1,4-dihydrocollidine-fed mice, and lacZ/alpha-smooth muscle actin-positive cells were detected in carbon tetrachloride-induced chronic liver injury models. These results suggested that some existing differentiated alb + cells might have the potential of transdifferentiation/dedifferentiation or epithelial-to-mesenchymal transition in vivo in some liver injury models, but the proportion of these alb + cells in liver was very low, and their significance and actual function during the pathological process remains to be elucidated.

In Vitro Functionality of Human Fetal Liver Cells and Clonal Derivatives under Proliferative Conditions

Mature human hepatocytes are not suitable for large-scale in vitro applications that rely on hepatocyte function, due to their limited availability and insufficient proliferation capacity in vitro. In contrast, human fetal liver cells (HFLC) can be easily expanded in vitro. In this study we evaluated the hepatic function of HFLCs under proliferative conditions, to determine whether HFLCs can replace mature hepatocytes for in vitro applications. HFLCs were isolated from fetal livers of 16 weeks gestation. Hepatic functions of HFLCs were determined in primary culture and after expansion in vitro. Clonal derivatives were selected and tested for hepatic functionality. Results were compared to primary mature human hepatocytes in vitro. No differences were observed between primary HFLCs and mature human hepatocytes in albumin production and mRNA levels of various liver-specific genes. Ureagenesis was 4.4-fold lower and ammonia elimination was absent in HFLCs. Expanding HFLCs decreased hepatic functions and increased cell stretching. In contrast, clonal derivatives had stable functionality and morphology and responded to differentiation stimuli. Although their hepatic functions were higher than in passaged HFLCs, functionality was at least 20 times lower compared to mature human hepatocytes. HFLCs cannot replace mature human hepatocytes in in vitro applications requiring extensive in vitro expansion, because this is associated with decreased hepatic functionality. Selecting functional subpopulations can, at least partly, prevent this. In addition, defining conditions that support hepatic differentiation is necessary to obtain HFLC cultures suitable for in vitro hepatic applications.

Intrinsic hepatocyte dedifferentiation is accompanied by upregulation of mesenchymal markers, protein sialylation and core alpha 1,6 linked fucosylation

Alterations in N-linked glycosylation have long been associated with cancer but for the most part, the reasons why have remained poorly understood. Here we show that increased core fucosylation is associated with de-differentiation of primary hepatocytes and with the appearance of markers indicative of a transition of cells from an epithelial to a mesenchymal state. This increase in core fucosylation was associated with increased levels of two enzymes involved in α-1,6 linked fucosylation, GDP-mannose 4, 6-dehydratase (Gmds) and to a lesser extent fucosyltransferase 8 (Fut8). In addition, the activation of cancer-associated cellular signaling pathways in primary rat hepatocytes can increase core fucosylation and induce additional glycoform alterations on hepatocyte proteins. Specifically, we show that increased levels of protein sialylation and α-1,6-linked core fucosylation are observed following activation of the β-catenin pathway. Activation of the Akt signaling pathway or induction of hypoxia also results in increased levels of fucosylation and sialylation. We believe that this knowledge will help in the better understanding of the genetic factors associated with altered glycosylation and may allow for the development of more clinically relevant biomarkers.

Drug resistance originating from a TGF-β/FGF-2-driven epithelial-to-mesenchymal transition and its reversion in human lung adenocarcinoma cell lines harboring an EGFR mutation

Epithelial-to-mesenchymal transition (EMT) is a malignant cancer phenotype characterized by augmented invasion and metastasis, chemoresistance, and escape from host-immunity. This study sought to identify efficient methods for inducing EMT reversion, to evaluate alterations in chemosensitivity and immune-protectiveness, and to elucidate the underlying mechanisms. In this study, the human lung adenocarcinoma cell lines PC-9 and HCC-827, harboring an EGFR mutation, were treated with TGF-β and FGF-2 to induce EMT. The phenotypic alterations were evaluated by RT-PCR, fluorescent immunohistochemistry, cell-mobility, and flow cytometry. Chemosensitivity to gefitinib and cisplatin was evaluated using an MTT assay and apoptosis. Immune-protectiveness was evaluated by PD-L1 expression. A combination of TGF-β and FGF-2 efficiently induced EMT in both cell lines: through Smad3 pathway in PC-9, and through Smad3, MEK/Erk, and mTOR pathways in HCC-827. The mTOR inhibitor PP242, metformin, and DMSO reverted EMT to different extent and through different pathways, depending on the cell lines. EMT induction reduced the sensitivity to gefitinib in both cell lines and to cisplatin in HCC-827, and it increased PD-L1 expression in both cell lines. EMT reversion using each of the 3 agents partly restored chemosensitivity and suppressed PD-L1 expression. Thus, chemoresistance and increased PD-L1 expression caused by EMT can be successfully reverted by EMT-reverting agents.

Local control of hepatic phenotype with growth factor-encoded surfaces

The goal of the present study was to modulate the phenotype expression of hepatocytes in vitro on surfaces imprinted with growth factors (GFs). Hepatocyte growth factor (HGF) or transforming-growth factor-β1 (TGF-β1) were mixed with collagen (I) and robotically printed onto standard glass slides to create arrays of 300 μm or 500 μm diameter spots. Primary rat hepatocytes were seeded on top of the arrays, forming clusters corresponding in size to the underlying protein spots. The TGF-β1 spots appeared to downregulate markers of hepatic (epithelial) phenotype while upregulating expression of mesenchymal markers. Conversely, hepatocytes cultured on HGF spots maintained high level of epithelial markers. When hepatocytes were seeded onto alternating spots of HGF and TGF-β1, their phenotype was found to depend on center-to-center distance between the spots. At shorter distances cross-expression of epithelial and mesenchymal markers was observed while at distances exceeding 1.25 mm divergence of phenotypes, epithelial on HGF and mesenchymal on TGF-β was seen. Overall, our results demonstrate that GF-encoded surfaces can modulate phenotype within groups of cells cultured on the same surface. Given the importance of phenotype switching in development, fibrosis and cancer, this platform may be used to gain useful insights into the mechanisms of processes such as epithelial-to-mesenchymal transition or stem cell fate selections.

Platelets, selectins, and the control of tumor metastasis

The significant role of platelets and P-selectin in assisting tumor cell metastasis to the lungs has been frequently reported and reviewed. However, evidence recently has come to light on other pro-metastatic mechanisms of platelets beyond that of tumor cell protection from immune cell attack and aiding extravasation, such as promoting epithelial to mesenchymal transition in tumor cells and conveying signals from the primary tumor to distant tissues that optimize conditions for metastasis. Moreover, the role of platelets and selectins in hematogenous metastasis to frequently targeted organs other than the lungs has been less well examined. This review aims to summarize the literature on the roles of platelets in all stages of the metastatic process and to examine the participation of platelets and selectins in hematogenous metastasis to the lungs, liver, bone, and brain. In the light of the available evidence, potential therapeutic avenues for the control of metastasis are also discussed.

Epithelial-mesenchymal transition delayed by E-cad to promote tissue formation in hepatic differentiation of mouse embryonic stem cells in vitro

Hepatic differentiation of embryonic stem cells (ESCs) usually results in a single cell lineage, and the formation of liver tissues remains difficult. Here, we examine the role of epithelial-mesenchymal transition (EMT) that is regulated by epithelial cadherin (E-cad) expression in hepatic tissue formation from ESCs. E-cad was transfected into mouse ESCs to enable a stable expression of E-cad. Hepatic differentiation of ESCs was then induced by hepatic growth factors. Wnt/β-catenin signaling and EMT speed were examined to determine the differentiation process. Hepatic and angiogenesis markers, as well as differentiated cell-adhesive force were also examined to identify the hepatic tissue differentiation. In our results, E-cad expression gradually decreased in normal ESC (N-ESC) differentiation, but remained stable in the E-cad transfected ESC (EC-ESC) group. In EC-ESC differentiation, expressions of cytoplastic β-catenin and EMT were much lower and significantly prolonged. Angiogenesis markers vascular endothelial growth factor receptor-1 (VEGFR-1) and CD31/PECAM-1 were expressed only on day 5-13 in N-ESC differentiation, whereas VEGFR-1 and CD31/PECAM-1 were expressed prolonged on day 5-17 in the EC-ESC group and were coincident with the expression of hepatic markers. Finally, EC-ESC differentiation maintained multilayer-growth patterns, and abundant vascular network structures appeared and migrated in albumin-positive cell areas. The cellular adhesion forces between embryonic body cells in EC-ESC differentiation during day 13-17 were similar to those of mouse liver tissue. In conclusion, accelerated EMT due to the decreased E-cad expression may partially contribute to the failure of hepatic tissue formation in N-ESC differentiation. E-cad can act in synergy with hepatic growth factors and facilitate the early-stage formation of hepatic tissues through down-regulating Wnt/β-catenin signaling and delaying EMT. This work provides a new insight into hepatic tissue differentiation that is mediated by E-cad from ESC.

The existence of multipotent stem cells with epithelial-mesenchymal transition features in the human liver bud

During early stage of embryonic development, the liver bud, arising from the foregut endoderm, is the beginning for the formation of future liver three-dimensional structure. While the gene expression profiles associated with this developmental stage have been well explored, the detailed cellular events are not as clear. Epithelial-mesenchymal transition (EMT) was thought to be essential for cell migration in the early vertebrate embryo but seldom demonstrated in human liver development. In this study, we tried to identify the cell populations with both stem cell and EMT features in the human liver bud. Our in situ studies show that the phenotype of EMT occurs at initiation of human liver development, accompanied by up-regulation of EMT associated genes. A human liver bud derived stem cell line (hLBSC) was established, which expressed not only genes specific to both mesenchymal cells and hepatic cells, but also octamer-binding protein 4 (OCT4) and nanog. Placed in appropriate media, hLBSC differentiated into hepatocytes, adipocytes, osteoblast-like cells and neuron-like cells in vitro. When transplanted into severe combined immunodeficiency mice pre-treated by carbon tetrachloride, hLBSC engrafted into the liver parenchyma and proliferated. These data suggests that there are cell populations with stem cell and EMT-like properties in the human liver bud, which may play an important role in the beginning of the spatial structure construction of the liver.

Growth factor- and cytokine-driven pathways governing liver stemness and differentiation

Liver is unique in its capacity to regenerate in response to injury or tissue loss. Hepatocytes and other liver cells are able to proliferate and repopulate the liver. However, when this response is impaired, the contribution of hepatic progenitors becomes very relevant. Here, we present an update of recent studies on growth factors and cytokine-driven intracellular pathways that govern liver stem/progenitor cell expansion and differentiation, and the relevance of these signals in liver development, regeneration and carcinogenesis. Tyrosine kinase receptor signaling, in particular, c-Met, epidermal growth factor receptors or fibroblast growth factor receptors, contribute to proliferation, survival and differentiation of liver stem/progenitor cells. Different evidence suggests a dual role for the transforming growth factor (TGF)-β signaling pathway in liver stemness and differentiation. On the one hand, TGF-β mediates progression of differentiation from a progenitor stage, but on the other hand, it contributes to the expansion of liver stem cells. Hedgehog family ligands are necessary to promote hepatoblast proliferation but need to be shut off to permit subsequent hepatoblast differentiation. In the same line, the Wnt family and β-catenin/T-cell factor pathway is clearly involved in the maintenance of liver stemness phenotype, and its repression is necessary for liver differentiation during development. Collectively, data indicate that liver stem/progenitor cells follow their own rules and regulations. The same signals that are essential for their activation, expansion and differentiation are good candidates to contribute, under adequate conditions, to the paradigm of transformation from a pro-regenerative to a pro-tumorigenic role. From a clinical perspective, this is a fundamental issue for liver stem/progenitor cell-based therapies.

Epithelial-mesenchymal transition: from molecular mechanisms, redox regulation to implications in human health and disease

Epithelial to mesenchymal transition (EMT) is a fundamental process, paradigmatic of the concept of cell plasticity, that leads epithelial cells to lose their polarization and specialized junctional structures, to undergo cytoskeleton reorganization, and to acquire morphological and functional features of mesenchymal-like cells. Although EMT has been originally described in embryonic development, where cell migration and tissue remodeling have a primary role in regulating morphogenesis in multicellular organisms, recent literature has provided evidence suggesting that the EMT process is a more general biological process that is also involved in several pathophysiological conditions, including cancer progression and organ fibrosis. This review offers first a comprehensive introduction to describe major relevant features of EMT, followed by sections dedicated on those signaling mechanisms that are known to regulate or affect the process, including the recently proposed role for oxidative stress and reactive oxygen species (ROS). Current literature data involving EMT in both physiological conditions (i.e., embryogenesis) and major human diseases are then critically analyzed, with a special final focus on the emerging role of hypoxia as a relevant independent condition able to trigger EMT.

Upregulation of the NADPH oxidase NOX4 by TGF-beta in hepatocytes is required for its pro-apoptotic activity

BACKGROUND/AIMS

The transforming growth factor-beta (TGF-beta) induces apoptosis in hepatocytes through an oxidative stress process. Here, we have analyzed the role of different NADPH oxidase isoforms in the intracellular signalling induced by TGF-beta in hepatocytes, to later explore whether this mechanism is altered in liver tumor cells.

METHODS

Primary cultures of rat and human hepatocytes, HepG2 and Hep3B cells were used in in vitro studies to analyze the TGF-beta response.

RESULTS

TGF-beta-induced apoptosis in rat hepatocytes does not require Rac-dependent NADPH oxidases. TGF-beta upregulates the Rac-independent Nox4, which correlates with its pro-apoptotic activity. Regulation of Nox4 occurs at the transcriptional level and is counteracted by intracellular survival signals. siRNA targeted knock-down of Nox4 attenuates NADPH oxidase activity, caspase activation and cell death in rat hepatocytes. NOX4 upregulation by TGF-beta is also observed in human hepatocytes, coincident with apoptosis. In human hepatocellular carcinoma (HCC) cell lines, NOX4 upregulation by TGF-beta is only observed in cells that are sensitive to its cytotoxic effect, such as Hep3B cells. siRNA targeted knock-down of NOX4 in these cells impairs TGF-beta-induced apoptosis.

CONCLUSIONS

Upregulation of NOX4 by TGF-beta is required for its pro-apoptotic activity in hepatocytes. Impairment of this TGF-beta-induced response might confer apoptosis resistance in HCC cells.

Hepatic fibrogenesis: from within and outwith

Liver disease is now the fifth commonest cause of death in the United Kingdom and the incidence is increasing. Chronic injury to the liver typically due to toxic insult, viral infection, immunological or metabolic diseases usually results in a stereotypical response with both parenchymal regeneration and wound healing. Chronic hepatic injury results in liver fibrosis with eventual progression to cirrhosis and end stage liver disease. At this point the majority of the clinical complications arise such as portal hypertension and the development of liver cancer. If the causative disease can be effectively treated the liver can regenerate and at the least partial resolution of liver fibrosis may occur. Unfortunately, unless the primary disease can be eradicated there are no specific anti-fibrotic treatments in routine clinical use. This highlights the urgent need to both increase our understanding of the mechanisms of hepatic fibrogenesis and to develop novel therapies to arrest or reverse the fibrotic process. This article initially outlines the main cellular pathway of fibrogenesis within the liver-the activation of the quiescent hepatic stellate cell into an activated myofibroblast phenotype, resulting in the production of fibrillar collagen. We will then discuss newly emerging sources of scar forming cells during hepatic injury together with the role of hepatic macrophages which have a regulatory function in both the formation and resolution of liver fibrosis.

Evidence for the epithelial to mesenchymal transition in biliary atresia fibrosis

The epithelial to mesenchymal transition has recently been implicated as a source of fibrogenic myofibroblasts in organ fibrosis, particularly in the kidney. There is as yet minimal evidence for the epithelial to mesenchymal transition in the liver. We hypothesized that this process in biliary epithelial cells plays an important role in biliary fibrosis and might be found in patients with especially rapid forms, such as is seen in biliary atresia. We therefore obtained liver tissue from patients with biliary atresia as well as a variety of other pediatric and adult liver diseases. Tissues were immunostained with antibodies against the biliary epithelial cell marker CK19 as well as with antibodies against proteins characteristically expressed by cells undergoing the epithelial to mesenchymal transition, including fibroblast-specific protein 1, the collagen chaperone heat shock protein 47, the intermediate filament protein vimentin, and the transcription factor Snail. The degree of colocalization was quantified using a multispectral imaging system. We observed significant colocalization between CK19 and other markers of the epithelial to mesenchymal transition in biliary atresia as well as other liver diseases associated with significant bile ductular proliferation, including primary biliary cirrhosis. There was minimal colocalization seen in healthy adult and pediatric livers, or in livers not also demonstrating bile ductular proliferation. Multispectral imaging confirmed significant colocalization of the different markers in biliary atresia. In conclusion, we present significant histologic evidence suggesting that the epithelial to mesenchymal transition occurs in human liver fibrosis, particularly in diseases such as biliary atresia and primary biliary cirrhosis with prominent bile ductular proliferation.

Liver fibrosis: cellular mechanisms of progression and resolution

Liver fibrosis represents a major worldwide health care burden. The last 15 years have seen a rapid growth in our understanding of the pathogenesis of this clinically relevant model of inflammation and repair. This work is likely to inform the design of effective antifibrotic therapies in the near future. In this review, we examine how the innate and adaptive immune response interacts with other key cell types in the liver, such as the myofibroblast, regulating the process of hepatic fibrosis and, where relevant, resolution of fibrosis with remodelling. Emphasis is placed on the increasing knowledge that has been generated by the use of transgenic animals and animals in which specific cell lines have been deleted. Additionally, we review the increasing evidence that, although significant numbers of wound-healing myofibroblasts are derived from the hepatic stellate cell, significant contributions may occur from other cell lineages, including those from distant sites such as bone marrow stem cells.

P68 RNA helicase mediates PDGF-induced epithelial mesenchymal transition by displacing Axin from beta-catenin

The nuclear p68 RNA helicase (referred to as p68) is a prototypical member of the DEAD box family of RNA helicases. The protein plays a very important role in early organ development. In the present study, we characterized the tyrosine phosphorylation of p68 under platelet-derived growth factor (PDGF) stimulation. We demonstrated that tyrosine phosphorylation of p68 at Y593 mediated PDGF-stimulated epithelial-mesenchymal transition (EMT). We showed that PDGF treatment led to phosphorylation of p68 at Y593 in the cell nucleus. The Y593-phosphorylated p68 (referred to as phosphor-p68) promotes beta-catenin nuclear translocation via a Wnt-independent pathway. The phosphor-p68 facilitates beta-catenin nuclear translocation by blocking phosphorylation of beta-catenin by GSK-3beta and displacing Axin from beta-catenin. The beta-catenin nuclear translocation and subsequent interaction with the LEF/TCF was required for the EMT process. These data demonstrated a novel mechanism of phosphor-p68 in mediating the growth factor-induced EMT and uncovered a new pathway to promote beta-catenin nuclear translocation.

Production of infectious hepatitis C virus by well-differentiated, growth-arrested human hepatoma-derived cells

Dimethyl sulfoxide (DMSO) has been shown to induce the differentiation of primary hepatocytes in vitro. When actively dividing poorly differentiated human hepatoma-derived (Huh7) cells were cultured in the presence of 1% DMSO, cells became cytologically differentiated and transitioned into a nondividing state, characterized by the induction of hepatocyte-specific genes. Moreover, these cells were highly permissive for acute hepatitis C virus (HCV) infection, and persistent long term infection of these cultures could also be achieved. As HCV naturally replicates in highly differentiated nondividing human hepatocytes, this system may more accurately mimic the conditions under which HCV replicates in vivo than previous models using poorly differentiated rapidly dividing hepatoma cells.

Effects of liver growth factors on hepadnavirus replication in chronically infected duck hepatocytes

BACKGROUND/AIMS

Duck hepatitis B virus (DHBV) replication is up-regulated by cell cycle during the early infection of primary duck but the effect of cell cycle on DHBV replication in chronically infected hepatocyte is not known.

METHODS

Hepatocytes obtained from DHBV congenitally infected embryos were used. Cell proliferation was controlled by addition of liver growth factors and the impact on viral replication analyzed.

RESULTS

EGF induced cell proliferation is associated with a slight increase in CCC DNA synthesis and a decrease in viral transcription. Conversely, TGFbeta blocked cell cycle progression, diminished CCC DNA synthesis but increased viral transcription.

CONCLUSIONS

Cell proliferation decreases DHBV transcription but this effect seems to be compensated by an opposite effect on the synthesis of CCC DNA resulting in a global moderate effect on viral replication. Our results also indicate that after division of chronically infected hepatocytes both daughter cells are infected, confirming that liver regeneration is not sufficient to induce CCC DNA eradication as suggested by the lack of effect of some long term anti-HBV therapies.

Hepatocyte growth factor attenuates liver fibrosis induced by bile duct ligation

Hepatic fibrosis is a common outcome of a variety of chronic liver diseases. Here we evaluated the therapeutic efficacy of hepatocyte growth factor (HGF) on liver fibrosis induced by bile duct ligation (BDL) and investigated potential mechanisms. Mice underwent BDL, followed by intravenous injections of naked HGF expression plasmid or control vector. HGF gene therapy markedly ameliorated hepatic fibrotic lesions, as demonstrated by reduced alpha-smooth muscle actin (alphaSMA) expression, attenuated deposition of type I and type III collagen, and normalized total hydroxyproline content. HGF also suppressed transforming growth factor-beta1 (TGF-beta1) expression. Interestingly, colocalization of alphaSMA and cytokeratin-19 in bile duct epithelium was observed, suggesting the possibility of biliary epithelial to myofibroblast transition after BDL. Cells that were still positive for cytokeratin-19 but actively producing type I collagen were found in the biliary epithelia and periductal region. Laminin staining revealed an impaired basement membrane of the bile duct epithelium in diseased liver. These lesions were largely prevented by HGF administration. In vitro, treatment of human biliary epithelial cells with TGF-beta1 induced alphaSMA and fibronectin expression and suppressed cytokeratin-19. HGF abolished the phenotypic conversion of biliary epithelial cells induced by TGF-beta1. These results suggest that HGF ameliorates hepatic biliary fibrosis in part by blocking bile duct epithelial to mesenchymal transition.

E-cadherin synergistically induces hepatospecific phenotype and maturation of embryonic stem cells in conjunction with hepatotrophic factors

Since effective cell sourcing is a major challenge for the therapeutic management of liver disease and liver failure, embryonic stem (ES) cells are being widely investigated as a promising source of hepatic-like cells with their proliferative and pluripotent capacities. Cell-cell interactions are crucial in embryonic development modulating adhesive and signaling functions; specifically, the cell-cell adhesion ligand, cadherin is instrumental in gastrulation and hepatic morphogenesis. Inspired by the role of cadherins in development, we investigated the role of expression of E-cadherin in cultured murine ES cells on the induction of hepatospecific phenotype and maturation. The cadherin-expressing embryonic stem (CE-ES) cells intrinsically formed pronounced cell aggregates and cuboidal morphology whereas cadherin-deficient cadherin-expressing embryonic stem (CD-ES) cells remained more spread out and corded in morphology. Through controlled stimulation with single or combined forms of hepatotrophic growth factors; hepatocyte growth factor (HGF), dexamethasone (DEX) and oncostatin M (OSM), we investigated the progressive maturation of CE-ES cells, in relation to the control, CD-ES cells. Upon growth factor treatment, the CE-ES cells adopted a more compacted morphology, which exhibited a significant hepatocyte-like cuboidal appearance in the presence of DEX-OSM-HGF. In contrast, the CD-ES cells exhibited a mixed morphology and appeared to be more elongated in the presence of DEX-OSM-HGF. Reverse-transcriptase polymerase chain reaction was used to delineate the most differentiating condition in terms of early (alpha-fetoprotein (AFP)), mid (albumin), and late-hepatic (glucose-6-phosphatase) markers in relation to growth factor presentation for both CE-ES and CD-ES cells. We report that following the most differentiating condition of DEX-OSM-HGF stimulation, CE-ES cells expressed increased levels of albumin and glucose-6-phosphatase, whereas the CD-ES cells showed low levels of AFP and marginal levels of albumin and glucose-6-phosphatase. These trends suggest that the membrane expression of E-cadherin in ES cells can elicit a marked response to growth factor stimulation and lead to the induction of later stages of hepatocytic maturation. Thus, cadherin-engineered ES cells could be used to harness the cross-talk between the hepatotrophic and cadherin-based signaling pathways for controlled acceleration of ES hepatodifferentiation.

Interferon-gamma induces neuroendocrine-like differentiation of human prostate basal-epithelial cells

BACKGROUND

Prostatic neuroendocrine (NE) cells are intraglandular hybrid epithelial-neural-endocrine cells that express and secrete numerous hormones and neuropeptides, which presumably regulate growth, differentiation, and secretory activity of the prostatic epithelium. This specialized cell type appears to differentiate from a common basal/precursor/stem cell that also gives rise to the secretory epithelium. In order to elucidate mechanisms of NE-differentiation the effects of type 1 (alpha, beta) and type 2 (gamma) interferons (IFNs) on human prostate basal cells (PrECs) were evaluated.

METHODS AND RESULTS

Application of alpha/beta IFN increased the expression of the cell-cycle inhibitor p21(CIP1) and inhibited DNA synthesis, while only IFN-gamma led to increased apoptosis, cell-cycle inhibitor p27(KIP1) upregulation, and differentiation of PrECs into NE-like cells. In vitro differentiated NE-like cells expressed the glycolytic enzyme neuron-specific enolase (NSE) and chromogranin A (CgA), known markers of NE-cells in vivo in the prostate. These NE-like cells also changed cytokeratin (CK) expression patterns by upregulating CK 8/18, predominantly found in terminally-differentiated secretory luminal/NE epithelial cells.

CONCLUSIONS

IFN-gamma produced locally in the prostate by basal cells and, under proinflammatory conditions, by infiltrating lymphocytes could support NE cell differentiation and play a role in NE differentiation processes of tumor cells in hormone-refractory prostate cancer.

Effects of growth factors on the growth and differentiation of mouse fetal liver epithelial cells in primary cultures

BACKGROUND AND AIMS

Growth factors (GF) are thought to affect the growth and differentiation of hepatocytes during liver development. However, in the midfetal liver, little is known concerning the role of GF.

METHODS

The DNA synthesis of fetal liver epithelial cells (FLEC) in monolayer culture and the liver-specific gene expressions of FLEC in 3-D culture were examined in medium supplemented with various GF.

RESULTS

DNA synthesis of FLEC was higher than that of adult hepatocytes without GF, and was increased by hepatocyte growth factor (HGF), heparin-binding epidermal growth factor-like growth factor (HB-EGF), basic fibroblast growth factor (bFGF), epidermal growth factor (EGF) or transforming growth factor-alpha (TGF-alpha). However, FLEC responded less to GF in terms of DNA synthesis than adult hepatocytes. The liver-specific gene expressions were increased in the presence of HGF, HB-EGF, bFGF and EGF. In embryonic day (E) 13.5 FLEC, this increase was more apparent in the presence of HB-EGF, whereas in E14.5 FLEC, it was more apparent in the presence of HGF.

CONCLUSIONS

Hepatocyte growth factor, HB-EGF, bFGF, EGF and TGF-alpha increased DNA synthesis of FLEC. HGF, HB-EGF, bFGF and EGF led to an increase in liver-specific gene expressions; and their effects on differentiation differ as a function of gestation age.

Dimethyl Sulfoxide and Oxidative Stress On Cultures of Human Keratinocytes

Objectives:

The aim of the present study was to examine the protective action of the antioxidant dimethyl sulfoxide (DMSO) against the oxidative stress on keratinocyte cultures caused by glucose deprivation and hypoxia, using the concentration of malonyl dialdehyde existing in the cell culture as an indicator of the oxidative stress level.

Methods:

Eighty flasks with cultured human keratinocytes in a confluent layer were divided into eight groups, including the following: culture medium with and without glucose, culture medium with and without the addition of DMSO, culture medium subjected and not subjected to hypoxia, and culture medium with a combination of these factors.

Results and Conclusions:

The statistical analysis of the results showed that DMSO proved to be an effective agent against the oxidative stress on cultures of keratinocytes under the experimental conditions studied.

Proliferation and hepatic differentiation of adult-derived progenitor cells

Hepatic progenitor cells, capable of maturing into hepatocytes and biliary cells, are hypothesized to be involved in all forms of liver regeneration and may prove clinically useful at reconstituting damaged livers. A murine hepatic progenitor cell population from young adult liver tissue has been isolated and characterized to establish a model for the development of liver cell therapies and for analysis of immune responses after transplantation. Hepatic progenitor cells were isolated from 3- to 6-week-old C57BL/6 mice using modifications of a two-stage liver perfusion technique followed by low speed centrifugation. Cellular analysis by phase contrast, fluorescent and confocal microscopy demonstrated that the hepatic progenitors (1) formed ex vivo colonies with a morphological appearance similar to committed hepatocytic progenitors isolated from embryonic mice and rats; (2) they are smaller than mature hepatocytes; (3) in culture they demonstrated peak expression of an oval cell marker at day 14, whereas albumin expression continued to increase beyond day 21 of culture, and (4) a subset of the progenitors phenotypically differentiated into mature hepatocytes or biliary cells. The unique antigenic profile of these hepatic progenitor cells and their ability to differentiate suggests that purification of the cells should allow for their potential use in transplantation.

Fetal liver stroma consists of cells in epithelial-to-mesenchymal transition

Liver becomes the predominant site of hematopoiesis by 11.5 dpc (days after coitus) in the mouse and 15 gestational weeks in humans and stays so until the end of gestation. The reason the liver is the major hematopoietic site during fetal life is not clear. In this work, we tried to define which of the fetal liver microenvironmental cell populations would be associated with the development of hematopoiesis and found that a population of cells with mixed endodermal and mesodermal features corresponded to hematopoietic-supportive fetal liver stroma. Stromal cells generated from primary cultures or stromal lines from mouse or human fetal liver in the hematopoietic florid phase expressed both mesenchymal markers (vimentin, osteopontin, collagen I, alpha smooth muscle actin, thrombospondin-1, EDa fibronectin, calponin, Stro-1 antigens, myocyte-enhancer factor 2C) and epithelial (alpha-fetoprotein, cytokeratins 8 and 18, albumin, E-cadherin, hepatocyte nuclear factor 3 alpha) markers. Such a cell population fits with the description of cells in epithelial-to-mesenchymal transition (EMT), often observed during development, including that of the liver. The hematopoietic supportive capacity of EMT cells was lost after hepatocytic maturation, induced by oncostatin M in the cell line AFT024. EMT cells were observed in the fetal liver microenvironment during the hematopoietic phase but not in nonhematopoietic liver by the end of gestation and in the adult. EMT cells represent a novel stromal cell type that may be generated from hepatic endodermal or mesenchymal stem cells or even from circulating hematopoietic stem cells (HSCs) seeding the liver rudiment.

Fibroblast subpopulations in intra-oral wound healing

The objective of this study was to characterize fibroblasts at sequential time points during intra-oral wound healing in the rat. Experimental wounds were made at several time points in the mucoperiosteum of the palate of 35-day-old Wistar rats. Fibroblasts were cultured from the biopsies under standard conditions for the same number of passages. The expression of the integrin subunits alpha 1, alpha 6, and beta 1; and the intermediate filaments alpha-smooth muscle actin and vimentin were analyzed by flow cytometry. Western blot analysis was performed at 0, 8, and 60 days postwounding to confirm the expression of both intermediate filaments. The phenotypic profiles of fibroblasts cultured from subsequent stages in the wound healing process differed considerably. We conclude that distinct fibroblast phenotypes can be isolated from different stages in wound healing. These phenotypes remained stable during in vitro culturing. In addition, cryosections of the wound areas were made at identical time points and were immunohistochemically stained for the same antigens. The immunohistochemical staining correlated well to the flow-cytometric data. These results suggest the occurrence of multiple subpopulations of fibroblasts with a specialized function during wound healing. We hypothesize that undesirable consequences of wound healing might be prevented through the modulation of specific fibroblast subpopulations.