Cell-derived Growth Factor Research Articles

Stromal cell‐derived factor‐1 and hepatocyte growth factor guide axon projections to the extraocular muscles

Vertebrate eye movements depend on the co-ordinated function of six extraocular muscles that are innervated by the oculomotor, trochlear, and abducens nerves. Here, we show that the diffusible factors, stromal cell-derived factor-1 (SDF-1) and hepatocyte growth factor (HGF), guide the development of these axon projections. SDF-1 is expressed in the mesenchyme around the oculomotor nerve exit point, and oculomotor axons fail to exit the neuroepithelium in mice mutant for the SDF-1 receptor CXCR4. Both SDF-1 and HGF are expressed in or around the ventral and dorsal oblique muscles, which are distal targets for the oculomotor and trochlear nerves, respectively, as well as in the muscles which are later targets for oculomotor axon branches. We find that in vitro SDF-1 and HGF promote the growth of oculomotor and trochlear axons, whereas SDF-1 also chemoattracts oculomotor axons. Oculomotor neurons show increased branching in the presence of SDF-1 and HGF singly or together. HGF promotes the growth of trochlear axons more than that of oculomotor axons. Taken together, these data point to a role for both SDF-1 and HGF in extraocular nerve projections and indicate that SDF-1 functions specifically in the development of the oculomotor nerve, including oculomotor axon branch formation to secondary muscle targets. HGF shows some specificity in preferentially enhancing development of the trochlear nerve.

Secretion of SDF‐1α by bone marrow‐derived stromal cells enhances skin wound healing of C57BL/6 mice exposed to ionizing radiation

Patients treated for cancer therapy using ionizing radiation (IR) have delayed tissue repair and regeneration. The mechanisms mediating these defects remain largely unknown at present, thus limiting the development of therapeutic approaches. Using a wound healing model, we here investigate the mechanisms by which IR exposure limits skin regeneration. Our data show that induction of the stromal cell-derived growth factor 1α (SDF-1α) is severely impaired in the wounded skin of irradiated, compared to non-irradiated, mice. Hence, we evaluated the potential of bone marrow-derived multipotent stromal cells (MSCs), which secrete high levels of SDF-1α, to improve skin regeneration in irradiated mice. Injection of MSCs into the wound margin led to remarkable enhancement of skin healing in mice exposed to IR. Injection of irradiated MSCs into the wound periphery of non-irradiated mice delayed wound closure, also suggesting an important role for the stromal microenvironment in skin repair. The beneficial actions of MSCs were mainly paracrine, as the cells did not differentiate into keratinocytes. Specific knockdown of SDF-1α expression led to drastically reduced efficiency of MSCs in improving wound closure, indicating that SDF-1α secretion by MSCs is largely responsible for their beneficial action. We also found that one mechanism by which SDF-1α enhances wound closure likely involves increased skin vascularization. Our findings collectively indicate that SDF-1α is an important deregulated cytokine in irradiated wounded skin, and that the decline in tissue regeneration potential following IR can be reversed, given adequate microenvironmental support

Increased circulating level of the autocrine growth factor GP88 (PC cell-derived growth factor factor/progranulin) in early- and advanced-stage non-small cell lung cancer and small cell lung cancer.

e18103 Background: GP88, is an 88 kDa glycoprotein autocrine growth factor belonging to a newly identified family of growth modulators characterized by unique cysteine-rich motif and playing a role in the proliferation and survival of human cancers by inhibiting apoptosis, stimulating cell migration and invasiveness, and promoting metastasis. In vitro and in vivo studies have examined the biological activity and expression of GP88 in human breast cancer. In particular, pathological and clinical studies investigating the expression of GP88 in lesions and sera from breast cancer patients demonstrated GP88 expression was associated with clinically poor prognosis. The current study evaluated GP88 in lung cancer. Methods: 28 patients newly diagnosed with SCLC or NSCLC or previously diagnosed lung cancer and undergoing chemotherapeutic regimen change were enrolled. 20 healthy adults with similar background, including history of smoking, were enrolled as control group. Venous blood was collected and serum GP88 was tested by human GP88 ELISA. Results: 28 patients enrolled. 6 SCLC (1 Limited stage SCLC, five extended stage SCLC). 22 NSCLC, stage IV: 16, stage III: 3 and stage I: 3. The mean serum GP88 level in the lung cancer study group was 46.5 ± 15.5 ng/mL while the mean serum GP88 level in the control group was 28.4 ± 5.6 ng/mL, p = 0.0004 (Wilcoxon rank sum test). Conclusions: In patients diagnosed with SCLC/NSCLC, there is a statistically significant increase of serum GP88. Further studies will be planned to explore the role of GP88 as a biomarker for diagnosis and prognosis of lung cancer. We are currently accruing additional pts and analyzing whether GP88 has prognostic or predictive value. No significant financial relationships to disclose.

Hepatocyte growth factor activator (HGFA): a serine protease that links tissue injury to activation of hepatocyte growth factor

Growth factors are a group of proteins that regulate a wide variety of cellular processes, including proliferation, differentiation, motility, adhesion, and apoptosis of target cells. They play crucial roles in the formation and maintenance of tissue architecture in embryonic development and adult tissue homeostasis. Because aberrations in growth factor signaling often result in pathological conditions, the activities of growth factors are tightly controlled by extracellular and intracellular regulators. Hepatocyte growth factor (HGF) is a mesenchymal cell-derived growth factor that affects various target cells, including epithelial and endothelial cells. HGF is synthesized and secreted as a latent form, and is proteolytically activated in response to tissue injury, thus participating in tissue regeneration and repair. Interestingly, HGF has a unique structural feature: it is homologous to plasminogen, a key enzyme in the fibrinolytic system. Elucidation of the regulatory mechanisms of HGF activity has revealed that a blood coagulation factor XII-like serine protease, hepatocyte growth factor activator, efficiently converts HGF from the latent form to the active form. Hepatocyte growth factor activator itself is activated downstream of the blood coagulation cascade, and links tissue injury to activation of HGF. HGF thus has structural as well as functional relevance to the blood coagulation/fibrinolytic system.

Cerebral Malaria: A Vasculopathy

Cerebral Malaria: A Vasculopathy

Improved Function and Myocardial Repair of Infarcted Heart by Intracoronary Injection of Mesenchymal Stem Cell-Derived Growth Factors

Transplantation of mesenchymal stem cells (MSC) improves repair and function recovery following myocardial infarction (MI), but underlying mechanisms remain to be elucidated. We hypothesize that MSC could achieve protection by paracrine effects through released mediators rather than direct cardiac regeneration. We sought to characterize the effects of MSC-secreted growth factors on extent of early recovery from MI. Swine subjected to acute MI by temporary balloon occlusion of the left anterior descending coronary artery using percutaneous techniques received intracoronary injection of either concentrated MSC-derived growth factors or control medium. Animals were killed at 7 days to evaluate early effects. Treatment with MSC-derived factors significantly reduced cardiac troponin-T elevation and improved echocardiographic parameters, including fractional area shortening, stroke volume, cardiac output, and wall motion score index. Quantitative evaluation of fibrosis by Verhoff staining revealed a reduction of the fibrotic area in the infarcted zone. Similarly, Masson's trichrome staining revealed reduced myocardial damage as demonstrated by areas of relatively preserved myocardium in the infarcted area. TUNEL assay demonstrated less cardiomyocyte apoptosis. Protein array detected the presence of angiogenic (vascular endothelial growth factor, endothelin, and epiregulin), anti-apoptotic (Galectin-3, Smad-5, sRFP-1, and sRFP-4) and anti-remodeling factors. Reverse transcription polymerase chain reaction confirmed the expression of these factors. In summary, a single intracoronary injection of concentrated biologically active factors secreted by MSC could achieve early protection of ischemic myocardium and improve cardiac repair and contractility. MSC-derived growth factors injection (rather than MSC themselves) should be evaluated as a novel therapy to treat ischemic heart disease, avoiding many practical and technical issues of cell therapy.

Loss of myeloid cell-derived vascular endothelial growth factor accelerates fibrosis

Tissue injury initiates a complex series of events that act to restore structure and physiological homeostasis. Infiltration of inflammatory cells and vascular remodeling are both keystones of this process. However, the role of inflammation and angiogenesis in general and, more specifically, the significance of inflammatory cell-derived VEGF in this context are unclear. To determine the role of inflammatory cell-derived VEGF in a clinically relevant and chronically inflamed injury, pulmonary fibrosis, we deleted the VEGF-A gene in myeloid cells. In a model of pulmonary fibrosis in mice, deletion of VEGF in myeloid cells resulted in significantly reduced formation of blood vessels; however, it causes aggravated fibrotic tissue damage. This was accompanied by a pronounced decrease in epithelial cell survival and a striking increase in myofibroblast invasion. The drastic increase in fibrosis following loss of myeloid VEGF in the damaged lungs was also marked by increased levels of hypoxia-inducible factor (HIF) expression and Wnt/beta-catenin signaling. This demonstrates that the process of angiogenesis, driven by myeloid cell-derived VEGF, is essential for the prevention of fibrotic damage.

Stromal Cell Biology - A Way to Understand the Evolution of Cardiovascular Diseases -

Stromal cells, composed of fibroblasts, microvascular endothelial cells, immune cells and inflammatory cells, are critical determinants of the mechanical properties and function of the heart and vasculature, and the mechanisms whereby these types of cells are activated are important to understand the progression of cardiovascular diseases. Emerging studies have suggested that the activation of autocrine and paracrine signaling pathways by stromal cell-derived growth factors, cytokines and bioactive molecules contributes to disease progression. Disruption of the stromal network will result in alterations in the geometry and function in these organs. Interventions targeting the stromal cells (eg, myofibroblasts, microvascular endothelial cells, inflammatory cells) by pharmacological agents or direct gene delivery/small interfering RNA would be potential novel therapeutic strategies to prevent/attenuate the progression of cardiovascular disorders.

Intrahypothalamic Injection of the HIV-1 Envelope Glycoprotein Induces Fever via Interaction with the Chemokine System

Wasting syndrome is a common complication of HIV infection and is marked by progressive weight loss and weakness, often associated with fever. The mechanisms involved in the pathogenesis of these syndromes are not well defined, and neither are the brain areas involved. The present study tests a new hypothesis: that the preoptic anterior hypothalamus (POAH), the main brain area for thermoregulation and fever, has a role in the pathogenesis of fever induced by glycoprotein 120 (gp120), the surface envelope protein used by the HIV to gain access into immune cells, and that the CXC chemokine receptors (CXCR4) that serve as a coreceptor for HIV entry mediate the effect. A sterilized stainless steel C313G cannula guide was implanted into the POAH, and a biotelemetry system was used to monitor the body temperature (Tb) changes. The administration of gp120 into the POAH induced fever in a dose-dependent manner. To demonstrate possible links between the gp120 and CXCR4 in generating the fever, we pretreated the rats with 1,1'-[1,4-phenylenebis(methylene)]bis[1,4,8,11-tetraazacyclotetradecane] octohydrobromide dihydrate (AMD 3100), an antagonist of stromal cell-derived growth factor (SDF)-1alpha/CXCL12, acting at its receptor, CXCR4, 30 min before administration of gp120. AMD 3100 significantly reduced the gp120-induced fever. The present studies show that the presence of HIV-1 envelope glycoprotein gp120 in the POAH provokes fever via interaction CXCR4 pathway.

CATALYTIC RECEPTORS

CATALYTIC RECEPTORS

A distinct subset of submucosal mast cells undergoes hyperplasia following neonatal maternal separation: a role in visceral hypersensitivity?

We recently read with great interest the article published by Barreau et al ( Gut 2008; 57 :582–90) who report, as one of their primary findings, mast cell hyperplasia and...

AP-1-Controlled Hepatocyte Growth Factor Activation Promotes Keratinocyte Migration via CEACAM1 and Urokinase Plasminogen Activator/Urokinase Plasminogen Receptor

Keratinocyte migration is essential for the rapid closure of the epidermis in the process of wound healing. Mesenchymal cell-derived hepatocyte growth factor (HGF) is a central regulator of this process. However, the molecular mechanisms and relevant genes that facilitate this cellular response are still poorly defined. We used heterologous cocultures combining primary human keratinocytes and genetically modified murine fibroblasts to identify key factors mediating HGF-induced epidermal cell migration. The absence of c-Jun activity in fibroblasts completely abolished the expression of HGF in these cells and consequently altered the behavior of keratinocytes. Time-resolved expression series of keratinocytes stimulated with HGF disclosed target genes regulating HGF-dependent motility. In addition to well-established HGF-dependent wound healing-associated genes, carcinoembryogenic antigen-related cell adhesion molecule (CEACAM)-1 and the urokinase plasminogen activator (uPA)/uPA-receptor (uPAR) pathway were identified as possible mediators in HGF-induced keratinocyte migration. The functional relevance of CEACAM-1 and uPA/uPAR on epidermal cell motility was demonstrated using the HaCaT cell culture model. In conclusion, the distinct spatiotemporal regulation of genes by HGF is essential for proper epidermal cell migration in cutaneous wound healing.

Cerebral Malaria Is Associated with Low Levels of Circulating Endothelial Progenitor Cells in African Children

Damage to the cerebral microvasculature is a feature of cerebral malaria. Circulating endothelial progenitor cells are needed for microvascular repair. Based on this knowledge, we hypothesized that the failure to mobilize sufficient circulating endothelial progenitor cells to the cerebral microvasculature is a pathophysiologic feature of cerebral malaria. To test this hypothesis, we compared peripheral blood levels of CD34 (+)/VEGFR2(+) and CD34 (+)/CD133(+) cells and plasma levels of the chemokine stromal cell-derived growth factor 1 (SDF-1) in 214 children in Accra, Ghana. Children with cerebral malaria had lower levels of CD34 (+)/VEGFR2(+) and CD34 (+)/CD133(+) cells compared with those with uncomplicated malaria, asymptomatic parasitemia, or healthy controls. SDF-1 levels were higher in children with acute malaria compared with healthy controls. Together, these results uncover a potentially novel role for endothelial progenitor cell mobilization in the pathophysiology of cerebral malaria.

Proepithelin Regulates Prostate Cancer Cell Biology by Promoting Cell Growth, Migration, and Anchorage-Independent Growth

The growth factor proepithelin has recently emerged as an important regulator of transformation in several physiological and pathological systems. In this study, we determined the biological roles of proepithelin in prostate cancer cells using purified human recombinant proepithelin as well as proepithelin-depletion strategies. Proepithelin promoted the migration of androgen-dependent and -independent human prostate cancer cells; androgen-independent DU145 cells were the more responsive. In these cells, proepithelin additionally stimulated wound closure, invasion, and promotion of cell growth in vitro. These effects required the activation of both the Akt and mitogen-activated protein kinase pathways. We have analyzed proepithelin expression levels in different available prostate cancer microarray studies using the Oncomine database and found a statistically significant increase in proepithelin mRNA expression levels in prostate cancers compared with nonneoplastic controls. Notably, depletion of endogenous proepithelin by siRNA and antisense strategies impaired the ability of DU145 cells to grow and migrate after serum withdrawal and inhibited anchorage-independent growth. Our results provide the first evidence for a role of proepithelin in stimulating the migration, invasion, proliferation, and anchorage-independent growth of prostate cancer cells. This study supports the hypothesis that proepithelin may play a critical role as an autocrine growth factor in the establishment and initial progression of prostate cancer. Furthermore, proepithelin may prove to be a useful clinical marker for the diagnosis of prostate tumors.

Inhibitory effects of an antisense PCDGF vector on proliferation and invasion of highly malignant ovarian cancer cells and the related mechanism

To investigate the inhibitory effects of an antisense PC cell derived growth factor (PCDGF) vector on proliferation and invasion of highly malignant ovarian cancer cell lines Sw626 and A2780 cells, and preliminarily explore the related mechanisms. MTT assay and Boyden chamber in vitro invasion assay were employed to detect the changes of proliferation and invasion ability in the Sw626 and A2780 cells transfected with anti-sense PCDGF. The expression levels of cyclin D1 and CDK4 proteins before and after transfection were detected by Western blotting. The effects on the expression and activity of MMP-2 were evaluated by quantitative RT-PCR and zymography, respectively. Comparing with the blank group, the proliferation inhibition rate of the Sw626 and A2780 cells transfected with anti-sense PCDGF was 72.9% and 70.9%, respectively, and the invasion ability was inhibited by 62.9% and 59.0%, respectively. The levels of cyclin D1 and CDK4 protein expression in antisense PCDGF transfected cells were 0.38 +/- 0.08 and 0.37 +/- 0.13, respectively, all significantly lower than 0.84 +/- 0.11 and 0.64 +/- 0.11, respectively, in the blank group (P < 0.01). The MMP-2 mRNA expression level in antisense PCDGF transfected cell group was 0.66 +/- 0.11, not significantly decreased in comparison with 0.89 +/- 0.09 in the blank group (P > 0.05), but the activity of MMP-2 was inhibited significantly. The antisense PCDGF vector may inhibit markedly the proliferation and invasion of highly malignant ovarian cancer cells, and partially reverses their malignant phenotype. It seems to be related with down-regulating the expression of cyclin D1 and CDK4 and inhibiting the activity of MMP-2. Our findings indicate that PCDGF may become a new target for antisense gene therapy of ovarian cancer.

Novel MMP-9 Substrates in Cancer Cells Revealed by a Label-free Quantitative Proteomics Approach

Matrix metalloproteinase-9 (MMP-9) is implicated in tumor metastasis as well as a variety of inflammatory and pathological processes. Although many substrates for MMP-9, including components of the extracellular matrix, soluble mediators such as chemokines, and cell surface molecules have been identified, we undertook a more comprehensive proteomics-based approach to identify new substrates to further understand how MMP-9 might contribute to tumor metastasis. Previous proteomics approaches to identify protease substrates have depended upon differential labeling of each sample. Instead we used a label-free quantitative proteomics approach based on ultraperformance LC-ESI-high/low collision energy MS. Conditioned medium from a human metastatic prostate cancer cell line, PC-3ML, in which MMP-9 had been down-regulated by RNA interference was compared with that from the parental cells. From more than 200 proteins identified, 69 showed significant alteration in levels after depletion of the protease (>+/-2-fold), suggesting that they might be candidate substrates. Levels of six of these (amyloid-beta precursor protein, collagen VI, leukemia inhibitory factor, neuropilin-1, prostate cancer cell-derived growth factor (PCDGF), and protease nexin-1 (PN-1)) were tested in the conditioned media by immunoblotting. There was a strong correlation between results by ultraperformance LC-ESI-high/low collision energy MS and by immunoblotting giving credence to the label-free approach. Further information about MMP-9 cleavage was obtained by comparison of the peptide coverage of collagen VI in the presence and absence of MMP-9 showing increased sensitivity of the C- and N-terminal globular regions over the helical regions. Susceptibility of PN-1 and leukemia inhibitory factor to MMP-9 degradation was confirmed by in vitro incubation of the recombinant proteins with recombinant MMP-9. The MMP-9 cleavage sites in PN-1 were sequenced. This study provides a new label-free method for degradomics cell-based screening leading to the identification of a series of proteins whose levels are affected by MMP-9, some of which are clearly direct substrates for MMP-9 and become candidates for involvement in metastasis.

Multiple Mechanisms Are Responsible for Transactivation of the Epidermal Growth Factor Receptor in Mammary Epithelial Cells

The number of distinct signaling pathways that can transactivate the epidermal growth factor receptor (EGFR) in a single cell type is unclear. Using a single strain of human mammary epithelial cells, we found that a wide variety of agonists, such as lysophosphatidic acid (LPA), uridine triphosphate, growth hormone, vascular endothelial growth factor, insulin-like growth factor-1 (IGF-1), and tumor necrosis factor-alpha, require EGFR activity to induce ERK phosphorylation. In contrast, hepatocyte growth factor can stimulate ERK phosphorylation independent of the EGFR. EGFR transactivation also correlated with an increase in cell proliferation and could be inhibited with metalloprotease inhibitors. However, there were significant differences with respect to transactivation kinetics and sensitivity to different inhibitors. In particular, IGF-1 displayed relatively slow transactivation kinetics and was resistant to inhibition by the selective ADAM-17 inhibitor WAY-022 compared with LPA-induced transactivation. Studies using anti-ligand antibodies showed that IGF-1 transactivation required amphiregulin production, whereas LPA was dependent on multiple ligands. Direct measurement of ligand shedding confirmed that LPA treatment stimulated shedding of multiple EGFR ligands, but paradoxically, IGF-1 had little effect on the shedding rate of any ligand, including amphiregulin. Instead, IGF-1 appeared to work by enhancing EGFR activation of Ras in response to constitutively produced amphiregulin. This enhancement of EGFR signaling was independent of both receptor phosphorylation and PI-3-kinase activity, suggestive of a novel mechanism. Our studies demonstrate that within a single cell type, the EGFR autocrine system can couple multiple signaling pathways to ERK activation and that this modulation of EGFR autocrine signaling can be accomplished at multiple regulatory steps.

Expression of PC cell-derived growth factor and vascular endothelial growth factor in esophageal squamous cell carcinoma and their clinicopathologic significance

Esophageal carcinoma is a common kind of malignant tumor and about 90% of which is esophageal squamous cell carcinoma (ESCC), and it has a high incidence in China. In recent years it has been argued that angiogenesis plays a key role in tumor growth and metastasis and it is a complex process influenced by many factors. This study was aimed to investigate the expression of PC cell-derived growth factor (PCDGF or progranulin) and vascular endothelial growth factor (VEGF) in ESCC tissue and their relationship with clinical pathological parameters of ESCC, clarify the role of PCDGF and VEGF in the angiogenesis of ESCC. The expression of PCDGF and VEGF in 50 surgical specimens from patients with ESCC and 20 with normal esophageal mucosa were detected by immunohistochemistry. The vascular endothelial cells in tumor tissues were labeled by antibody to CD105 for counting microvessel density (MVD). The expression of PCDGF and VEGF in ESCC was significantly higher than that in normal mucosa. Expression correlated with the depth of tumor invasion, lymph node metastasis, and TNM (classification tumor, nodes, metastasis). In ESCC, both the expression level of PCDGF and VEGF had a positive correlation with MVD and the expression of PCDGF had a significant correlation with the expression of VEGF. These results show that both of PCDGF and VEGE have higher expression in ESCC, which indicate that they have a close relationship with angiogenesis. They may be involved in tumor growth, infiltration and metastasis through promoting tumor angiogenesis and may be an important index reflecting biological behavior and prognosis of ESCC.

First in Vivo Evidence for a Functional Interaction between Chemokine and Cannabinoid Systems in the Brain

Growing evidence supports the idea that in addition to their well established role in the immune system, chemokines might play a role in both normal and pathological brain function, and the chemokine network could interact with other neuromodulators. The chemokine stromal cell-derived growth factor (SDF)-1alpha/CXCL12, a member of the CXC chemokine family, was tested for its possible effect on the analgesic responses of the cannabinoid receptor agonist aminoalkylindole 4,5-dihydro-2-methyl-4-(4-morpholinylmethyl)-1-(1-naphthalenyl-carbonyl)-6H-pyrrolo-[3,2,1ij]quinolin-6-one [(+)-WIN 55,212-2, hereafter WIN 55,212-2] at the level of the periaqueductal gray (PAG), a brain region critical to the processing of pain signals, and a primary site of action of many analgesic compounds. The administration of WIN 55,212-2 (0.1-0.4 microg/microl) into the PAG resulted in antinociception in a dose-dependent manner. The selective cannabinoid (CB)1 antagonist N-(piperidin-1-yl)-5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-4-methyl-1H-pyrazole-3-carboxamide hydrochloride (SR 141716A; 1-10 microg) given into the PAG blocked the WIN 55,212-2-induced antinociception. In contrast, the selective CB2 antagonist N-[(1S)-endo-1,3,3-trimethyl bicyclo heptan-2-yl]-5-(4-chloro-3-methylphenyl)-1-(4-methylbenzyl)-pyrazole-3-carboxamide (SR144528; 10 microg) did not alter the WIN 55,212-2-induced antinociception. Pretreatment with SDF-1alpha/CXCL12 (100 ng) caused a reduction in antinociceptive responses of WIN 55,212-2. The inhibitory effect of SDF-1alpha/CXCL12 on WIN 55,212-2-induced antinociception was reversed by octahydrochloride [corrected] hydrate (AMD 3100) (10-50 ng), an antagonist of the SDF-1alpha/CXCL12, acting at its receptor, CXCR4. This study reports the first in vivo evidence of a functional interaction between chemokine and cannabinoid systems in the brain, showing that the activation of SDF-1alpha/CXCL12 receptors (CXCR4) in the PAG interferes with the analgesic effects of WIN 55212-2.

Differentiation of mouse embryonic stem cells to hepatocyte-like cells by co-culture with human liver nonparenchymal cell lines

This protocol describes a co-culture system for the in vitro differentiation of mouse embryonic stem cells into hepatocyte-like cells. Differentiation involves four steps: (i) formation of embryoid bodies (EB), (ii) induction of definitive endoderm from 2-d-old EBs, (iii) induction of hepatic progenitor cells and (iv) maturation into hepatocyte-like cells. Differentiation is completed by 16 d of culture. EBs are formed, and cells can be induced to differentiate into definitive endoderm by culture in Activin A and fibroblast growth factor 2 (FGF-2). Hepatic differentiation and maturation of cells is accomplished by withdrawal of Activin A and FGF-2 and by exposure to liver nonparenchymal cell-derived growth factors, a deleted variant of hepatocyte growth factor (dHGF) and dexamethasone. Approximately 70% of differentiated embryonic stem (ES) cells express albumin and can be recovered by albumin promoter-based cell sorting. The sorted cells produce albumin in culture and metabolize ammonia, lidocaine and diazepam at approximately two-thirds the rate of primary mouse hepatocytes.