Macrophage stimulating protein: purification, partial amino acid sequence, and cellular activity

Epigenetic scores derived in saliva are associated with gestational age at birth

BACKGROUND

Epigenetic scores (EpiScores), reflecting DNA methylation (DNAm)-based surrogates for complex traits, have been developed for multiple circulating proteins. EpiScores for pro-inflammatory proteins, such as C-reactive protein (DNAm CRP), are associated with brain health and cognition in adults and with inflammatory comorbidities of preterm birth in neonates. Social disadvantage can become embedded in child development through inflammation, and deprivation is overrepresented in preterm infants. We tested the hypotheses that preterm birth and socioeconomic status (SES) are associated with alterations in a set of EpiScores enriched for inflammation-associated proteins.

RESULTS

In total, 104 protein EpiScores were derived from saliva samples of 332 neonates born at gestational age (GA) 22.14 to 42.14 weeks. Saliva sampling was between 36.57 and 47.14 weeks. Forty-three (41%) EpiScores were associated with low GA at birth (standardised estimates |0.14 to 0.88|, Bonferroni-adjusted p-value < 8.3 × 10-3). These included EpiScores for chemokines, growth factors, proteins involved in neurogenesis and vascular development, cell membrane proteins and receptors, and other immune proteins. Three EpiScores were associated with SES, or the interaction between birth GA and SES: afamin, intercellular adhesion molecule 5, and hepatocyte growth factor-like protein (standardised estimates |0.06 to 0.13|, Bonferroni-adjusted p-value < 8.3 × 10-3). In a preterm subgroup (n = 217, median [range] GA 29.29 weeks [22.14 to 33.0 weeks]), SES-EpiScore associations did not remain statistically significant after adjustment for sepsis, bronchopulmonary dysplasia, necrotising enterocolitis, and histological chorioamnionitis.

CONCLUSIONS

Low birth GA is substantially associated with a set of EpiScores. The set was enriched for inflammatory proteins, providing new insights into immune dysregulation in preterm infants. SES had fewer associations with EpiScores; these tended to have small effect sizes and were not statistically significant after adjusting for inflammatory comorbidities. This suggests that inflammation is unlikely to be the primary axis through which SES becomes embedded in the development of preterm infants in the neonatal period.

MSP-RON Pathway: Potential Regulator of Inflammation and Innate Immunity

Macrophage-stimulating protein (MSP), a soluble protein mainly synthesized by the liver, is the only known ligand for recepteur d'origine nantais (RON), which is a member of the MET proto-oncogene family. Recent studies show that the MSP-RON signaling pathway not only was important in tumor behavior but also participates in the occurrence or development of many immune system diseases. Activation of RON in macrophages results in the inhibition of nitric oxide synthesis as well as lipopolysaccharide (LPS)-induced inflammatory response. MSP-RON is also associated with chronic inflammatory responses, especially chronic liver inflammation, and might serve as a novel regulator of inflammation, which may affect the metabolism in the body. Another study provided evidence of the relationship between MSP-RON and autoimmune diseases, suggesting a potential role for MSP-RON in the development of drugs for autoimmune diseases. Moreover, MSP-RON plays an important role in maintaining the stability of the tissue microenvironment and contributes to immune escape in the tumor immune microenvironment. Here, we summarize the role of MSP-RON in immunity, based on recent findings, and lay the foundation for further research.

Hepatocyte Growth Factor and Macrophage-stimulating Protein "Hinge" Analogs to Treat Pancreatic Cancer

Pancreatic cancer (PC) ranks twelfth in frequency of diagnosis but is the fourth leading cause of cancer related deaths with a 5 year survival rate of less than 7 percent. This poor prognosis occurs because the early stages of PC are often asymptomatic. Over-expression of several growth factors, most notably vascular endothelial growth factor (VEGF), has been implicated in PC resulting in dysfunctional signal transduction pathways and the facilitation of tumor growth, invasion and metastasis. Hepatocyte growth factor (HGF) acts via the Met receptor and has also received research attention with ongoing efforts to develop treatments to block the Met receptor and its signal transduction pathways. Macrophage-stimulating protein (MSP), and its receptor Ron, is also recognized as important in the etiology of PC but is less well studied. Although the angiotensin II (AngII)/AT1 receptor system is best known for mediating blood pressure and body water/electrolyte balance, it also facilitates tumor vascularization and growth by stimulating the expression of VEGF. A metabolite of AngII, angiotensin IV (AngIV) has sequence homology with the "hinge regions" of HGF and MSP, key structures in the growth factor dimerization processes necessary for Met and Ron receptor activation. We have developed AngIV-based analogs designed to block dimerization of HGF and MSP and thus receptor activation. Norleual has shown promise as tested utilizing PC cell cultures. Results indicate that cell migration, invasion, and pro-survival functions were suppressed by this analog and tumor growth was significantly inhibited in an orthotopic PC mouse model.

Regulation of Energy Metabolism by Receptor Tyrosine Kinase Ligands

Metabolic diseases, such as diabetes, obesity, and fatty liver disease, have now reached epidemic proportions. Receptor tyrosine kinases (RTKs) are a family of cell surface receptors responding to growth factors, hormones, and cytokines to mediate a diverse set of fundamental cellular and metabolic signaling pathways. These ligands signal by endocrine, paracrine, or autocrine means in peripheral organs and in the central nervous system to control cellular and tissue-specific metabolic processes. Interestingly, the expression of many RTKs and their ligands are controlled by changes in metabolic demand, for example, during starvation, feeding, or obesity. In addition, studies of RTKs and their ligands in regulating energy homeostasis have revealed unexpected diversity in the mechanisms of action and their specific metabolic functions. Our current understanding of the molecular, biochemical and genetic control of energy homeostasis by the endocrine RTK ligands insulin, FGF21 and FGF19 are now relatively well understood. In addition to these classical endocrine signals, non-endocrine ligands can govern local energy regulation, and the intriguing crosstalk between the RTK family and the TGFβ receptor family demonstrates a signaling network that diversifies metabolic process between tissues. Thus, there is a need to increase our molecular and mechanistic understanding of signal diversification of RTK actions in metabolic disease. Here we review the known and emerging molecular mechanisms of RTK signaling that regulate systemic glucose and lipid metabolism, as well as highlighting unexpected roles of non-classical RTK ligands that crosstalk with other receptor pathways.

MSP-RON Signaling Is Activated in the Transition From Pancreatic Intraepithelial Neoplasia (PanIN) to Pancreatic Ductal Adenocarcinoma (PDAC)

Pancreatic ductal adenocarcinoma (PDAC) is among the deadliest epithelial malignancies and remains difficult to treat. Pancreatic intraepithelial neoplasias (PanINs) represent the majority of the pre-cancer lesions in the pancreas. The PDAC microenvironment consists of activated pancreatic stellate cells (PSCs) and immune cells, which are thought to contribute to neoplastic transformation. However, the signaling events involved in driving the transition from the neoplastic precursor to the more advanced and aggressive forms in the pancreas are not well understood. Recepteur d’Origine Nantais (RON) is a c-MET family receptor tyrosine kinase that is implicated in playing a role in cell proliferation, migration and other aspects of tumorigenesis. Macrophage stimulating protein (MSP) is the ligand for RON and becomes activated upon proteolytic cleavage by matriptase (also known as ST14), a type II transmembrane serine protease. In the current study, by immunohistochemistry (IHC) analysis of human pancreatic tissues, we found that the expression levels MSP and matriptase are drastically increased during the transition from the preneoplastic PanIN stages to the more advanced and aggressive PDAC. Moreover, RON is highly expressed in both PDAC and in cancer-associated stellate cells. In contrast, MSP, RON, and matriptase are expressed at low levels, if any, in normal pancreas. Our study underscores an emerging role of MSP-RON autocrine and paracrine signaling events in driving malignant progression in the pancreas.

Hypoxia-inducible factor 1α is Essential for Macrophage-mediated Erythroblast Proliferation in Acute Friend Retrovirus Infection

Macrophages are the frontline of defence against foreign microorganisms, including bacteria, parasites, and viruses. During acute viral infection, macrophages must invade the inflamed tissue toward low oxygen concentrations, where genetic cellular responses depend on hypoxia-inducible factors (HIF). In the study reported here we investigated the role of HIF-1α in macrophage function during acute retroviral infection. Wild-type and myeloid cell-specific HIF-1α knockout mice were infected with Friend retrovirus (FV), and immune response was analysed 7 and 10 days after infection. FV infection led to increased spleen weight in wild-type and knockout mice, whereas a profound proliferation of erythroblasts was seen only in wild-type mice. The number of spleen-infiltrating macrophages was also significantly lower in knockout animals. Macrophage invasion after FV infection in wild-type mice led to elevated amounts of activated macrophage-stimulating 1 protein that resulted in massive proliferation of erythrocyte precursor cells. This proliferation was absent from knockout mice because of impaired invasion capabilities of HIF-1α-deficient macrophages. Our study elucidated a novel mechanism of FV-induced erythrocyte precursor cell proliferation.

Biological roles of hepatocyte growth factor-Met signaling from genetically modified animals

Hepatocyte growth factor (HGF) is produced by stromal and mesenchymal cells, and it stimulates epithelial cell proliferation, motility, morphogenesis and angiogenesis in various organs via tyrosine phosphorylation of its cognate receptor, Met. The HGF-Met signaling pathway contributes in a paracrine manner to the development of epithelial organs, exerts regenerative effects on the epithelium, and promotes the regression of fibrosis in numerous organs. Additionally, the HGF-Met signaling pathway is correlated with the biology of cancer types, neurons and immunity. In vivo analyses using genetic modification have markedly increased the profound understanding of the HGF-Met system in basic biology and its clinical applications. HGF and Met knockout (KO) mice are embryonically lethal. Therefore, amino acids in multifunctional docking sites of Met have been exchanged with specific binding motifs for downstream adaptor molecules in order to investigate the signaling potential of the HGF-Met signaling pathway. Conditional Met KO mice were generated using Cre-loxP methodology and characterization of these mice indicated that the HGF-Met signaling pathway is essential in regeneration, protection, and homeostasis in various tissue types and cells. Furthermore, the results of studies using HGF-overexpressing mice have indicated the therapeutic potential of HGF for various types of disease and injury. In the present review, the phenotypes of Met gene-modified mice are summarized.

Characterization of basic immune function parameters in the fathead minnow (Pimephales promelas), a common model in environmental toxicity testing

The fathead minnow (Pimephales promelas) is an environmental sentinel species, commonly used in toxicity testing. However, there is a lack of data regarding basic immune function in this species. To improve the usefulness of the fathead minnow as a model for basic immune function and immunotoxicity, this study sought to 1) compare the differential expression of immune function genes in naïve fathead minnows and 2) determine the effects of pathogen exposure on immune gene expression and spleen index. To accomplish this, kidney, spleen and liver tissue were collected three days post injection (dpi) from adult male fathead minnows from each of the following groups: 1) uninjected control 2) sham-injected (Hank's balanced salt solution) and 3) pathogen-injected (Yersinia ruckeri). Spleen tissue was also collected at seven and 14 dpi. Differential tissue expression of immune function genes was evaluated in naïve minnows and expression patterns were similar to those found in other fish species, with liver tissue generally having the highest amount of expression. Following pathogen injection, the expression of complement component 3 (c3) (4.4-fold, kidney; 2.5-fold, liver), interleukin 11 (il11) (4.8-fold, kidney; 15.2-fold, liver) and interleukin 1β (il1β) (8.2-fold, kidney; 17.2-fold, spleen; 2.6-fold, liver) were significantly upregulated. Elastase 2 (elas2) was significantly downregulated (5.8-fold) in liver tissue. A significant increase in spleen index at seven dpi was also observed in pathogen-injected minnows. This study has identified endpoints that are part of the normal response to pathogen in fathead minnows, an essential step toward the development of the fathead minnow as a model for immunotoxicity evaluations.

Strategies of targeting the extracellular domain of RON tyrosine kinase receptor for cancer therapy and drug delivery

PURPOSE

Cancer is one of the most important life-threatening diseases in the world. The current efforts to combat cancer are being focused on molecular-targeted therapies. The main purpose of such approaches is based on targeting cancer cell-specific molecules to minimize toxicity for the normal cells. RON (Recepteur d'Origine Nantais) tyrosine kinase receptor is one of the promising targets in cancer-targeted therapy and drug delivery.

METHODS

In this review, we will summarize the available agents against extracellular domain of RON with potential antitumor activities.

RESULTS

The presented antibodies and antibody drug conjugates against RON in this review showed wide spectrum of in vitro and in vivo antitumor activities promising the hope for them entering the clinical trials.

CONCLUSION

Due to critical role of extracellular domain of RON in receptor activation, the development of therapeutic agents against this region could lead to fruitful outcome in cancer therapy.

Microneedles for Transdermal Biosensing: Current Picture and Future Direction

A novel trend is rapidly emerging in the use of microneedles, which are a miniaturized replica of hypodermic needles with length-scales of hundreds of micrometers, aimed at the transdermal biosensing of analytes of clinical interest, e.g., glucose, biomarkers, and others. Transdermal biosensing via microneedles offers remarkable opportunities for moving biosensing technologies and biochips from research laboratories to real-field applications, and envisages easy-to-use point-of-care microdevices with pain-free, minimally invasive, and minimal-training features that are very attractive for both developed and emerging countries. In addition to this, microneedles for transdermal biosensing offer a unique possibility for the development of biochips provided with end-effectors for their interaction with the biological system under investigation. Direct and efficient collection of the biological sample to be analyzed will then become feasible in situ at the same length-scale of the other biochip components by minimally trained personnel and in a minimally invasive fashion. This would eliminate the need for blood extraction using hypodermic needles and reduce, in turn, related problems, such as patient infections, sample contaminations, analysis artifacts, etc. The aim here is to provide a thorough and critical analysis of state-of-the-art developments in this novel research trend, and to bridge the gap between microneedles and biosensors.

Deficiency in macrophage-stimulating protein results in spontaneous intestinal inflammation and increased susceptibility toward epithelial damage in zebrafish

Several genome-wide association studies have identified the genes encoding for macrophage-stimulating protein (MSP) and its receptor RON (Recepteur d'Origine Nantais) as possible susceptibility factors in inflammatory bowel disease. While it has been shown that the MSP-RON signaling pathway is involved in tissue injury responses, current mouse models for MSP and RON deficiency have not clearly demonstrated a role of MSP-RON signaling in the context of intestinal inflammation. In this study, we report that the recently identified zebrafish Msp mutant (msp(t34230)) develops spontaneous intestinal inflammation over time. From 14 to 28 weeks postfertilization Msp-deficient zebrafish show intestinal eosinophilia, increased intestinal expression of inflammatory marker mmp9, and activation of intestinal goblet cells. Moreover, these Msp mutant zebrafish are more susceptible toward ethanol-induced epithelial damage, which resulted in increased infiltration and proliferation of immune cells within the lamina propria and prolonged intestinal proinflammatory cytokine responses in some mutant fish. In light of the recent development of many tools to visualize, monitor, and genetically modify zebrafish, these Msp-deficient zebrafish will enable in-depth in vivo analysis of epithelial and macrophage-specific MSP-RON signaling in the context of intestinal inflammation.

Expression of Hepatocyte Growth Factor-Like Protein in Human Wound Tissue and Its Biological Functionality in Human Keratinocytes

human keratinocyte model, may indicate a role for HGFl in active wound healing.

Multiplexed protein profiling after aneurysmal subarachnoid hemorrhage: characterization of differential expression patterns in cerebral vasospasm

Cerebral vasospasm is a major contributor to delayed morbidity following aneurysmal subarachnoid hemorrhage. We sought to evaluate differential plasma protein levels across time in patients with aneurysmal subarachnoid hemorrhage to identify potential biomarkers and to better understand the pathogenesis of cerebral vasospasm. Nine female patients with aneurysmal subarachnoid hemorrhage underwent serial analysis of 239 different serum protein levels using quantitative, multiplexed immunoassays (DiscoveryMAP 250+ v2.0, Myriad RBM, Austin, TX, USA) on post-hemorrhage days 0 and 5. A repeated measures analysis of variance determined that mean protein concentration decreased significantly in patients who developed vasospasm versus those who did not for alpha-2-macroglobulin (F [1.00,7.00]=16.33, p=0.005), angiogenin (F [1.00,7.00]=7.65, p=0.028), apolipoprotein A-IV (F [1.00,7.00]=6.308, p=0.040), granulocyte colony-stimulating factor (F [1.00,7.00]=9.08, p=0.020), macrophage-stimulating protein (F [1.00,7.00]=24.21, p=0.002), tetranectin (F [1.00,7.00]=5.46, p<0.039), vascular endothelial growth factor receptor 3 (F [1.00,7.00]=6.94, p=0.034), and significantly increased for vitronectin (F [1.00,7.00]=5.79, p=0.047). These biomarkers may be of value in detecting cerebral vasospasm, possibly aiding in the identification of patients at high-risk prior to neurological deterioration.

Hepatocyte growth factor: A regulator of inflammation and autoimmunity

Hepatocyte growth factor (HGF) is a pleiotropic cytokine that has been extensively studied over several decades, but was only recently recognized as a key player in mediating protection of many types of inflammatory and autoimmune diseases. HGF was reported to prevent and attenuate disease progression by influencing multiple pathophysiological processes involved in inflammatory and immune response, including cell migration, maturation, cytokine production, antigen presentation, and T cell effector function. In this review, we discuss the actions and mechanisms of HGF in inflammation and immunity and the therapeutic potential of this factor for the treatment of inflammatory and autoimmune diseases.

Hepatocyte Growth Factor Isoforms in Tissue Repair, Cancer, and Fibrotic Remodeling

Hepatocyte growth factor (HGF), also known as scatter factor (SF), is a pleotropic factor required for normal organ development during embryogenesis. In the adult, basal expression of HGF maintains tissue homeostasis and is up-regulated in response to tissue injury. HGF expression is necessary for the proliferation, migration, and survival of epithelial and endothelial cells involved in tissue repair in a variety of organs, including heart, lung, kidney, liver, brain, and skin. The administration of full length HGF, either as a protein or using exogenous expression methodologies, increases tissue repair in animal models of tissue injury and increases angiogenesis. Full length HGF is comprised of an N-terminal hairpin turn, four kringle domains, and a serine protease-like domain. Several naturally occurring alternatively spliced isoforms of HGF were also identified. The NK1 variant contains the N-terminal hairpin and the first kringle domain, and the NK2 variant extends through the second kringle domain. These alternatively spliced forms of HGF activate the same receptor, MET, but they differ from the full length protein in their cellular activities and their biological functions. Here, we review the species-specific expression of the HGF isoforms, their regulation, the signal transduction pathways they activate, and their biological activities.

MSP: an emerging player in metabolic syndrome

MSP (Macrophage Stimulating Protein; also known as Hepatocyte Growth Factor-like protein (HGFL) and MST1) is a secreted protein and the ligand for transmembrane receptor tyrosine kinase Recepteur d'Origine Nantais (RON; also known as MST1R). Since its discovery, MSP has been demonstrated to play a key role in regulating inflammation in the peripheral tissues of multiple disease models. Recent evidences also point toward a beneficial role of MSP in the regulation of hepatic lipid and glucose metabolism, thereby implicating MSP as a crucial regulator in maintaining metabolic homeostasis while simultaneously suppressing inflammatory processes. In this review, we discuss the recent advances that demonstrate the significance of MSP in metabolic syndrome and build a strong case supporting its therapeutic potential.

Structural basis for the binding specificity of human Recepteur d'Origine Nantais (RON) receptor tyrosine kinase to macrophage-stimulating protein

Recepteur d'origine nantais (RON) receptor tyrosine kinase and its ligand, serum macrophage-stimulating protein (MSP), play important roles in inflammation, cell growth, migration, and epithelial to mesenchymal transition during tumor development. The binding of mature MSPαβ (disulfide-linked α- and β-chains) to RON ectodomain modulates receptor dimerization, followed by autophosphorylation of tyrosines in the cytoplasmic receptor kinase domains. Receptor recognition is mediated by binding of MSP β-chain (MSPβ) to the RON Sema. Here we report the structure of RON Sema-PSI-IPT1 (SPI1) domains in complex with MSPβ at 3.0 Å resolution. The MSPβ serine protease-like β-barrel uses the degenerate serine protease active site to recognize blades 2, 3, and 4 of the β-propeller fold of RON Sema. Despite the sequence homology between RON and MET receptor tyrosine kinase and between MSP and hepatocyte growth factor, it is well established that there is no cross-reactivity between the two receptor-ligand systems. Comparison of the structure of RON SPI1 in complex with MSPβ and that of MET receptor tyrosine kinase Sema-PSI in complex with hepatocyte growth factor β-chain reveals the receptor-ligand selectivity determinants. Analytical ultracentrifugation studies of the SPI1-MSPβ interaction confirm the formation of a 1:1 complex. SPI1 and MSPαβ also associate primarily as a 1:1 complex with a binding affinity similar to that of SPI1-MSPβ. In addition, the SPI1-MSPαβ ultracentrifuge studies reveal a low abundance 2:2 complex with ∼ 10-fold lower binding affinity compared with the 1:1 species. These results support the hypothesis that the α-chain of MSPαβ mediates RON dimerization.

Single nucleotide polymorphism and haplotype effects associated with somatic cell score in German Holstein cattle

Background

To better understand the genetic determination of udder health, we performed a genome-wide association study (GWAS) on a population of 2354 German Holstein bulls for which daughter yield deviations (DYD) for somatic cell score (SCS) were available. For this study, we used genetic information of 44 576 informative single nucleotide polymorphisms (SNPs) and 11 725 inferred haplotype blocks.

Results

When accounting for the sub-structure of the analyzed population, 16 SNPs and 10 haplotypes in six genomic regions were significant at the Bonferroni threshold of P ≤ 1.14 × 10^-6. The size of the identified regions ranged from 0.05 to 5.62 Mb. Genomic regions on chromosomes 5, 6, 18 and 19 coincided with known QTL affecting SCS, while additional genomic regions were found on chromosomes 13 and X. Of particular interest is the region on chromosome 6 between 85 and 88 Mb, where QTL for mastitis traits and significant SNPs for SCS in different Holstein populations coincide with our results. In all identified regions, except for the region on chromosome X, significant SNPs were present in significant haplotypes. The minor alleles of identified SNPs on chromosomes 18 and 19, and the major alleles of SNPs on chromosomes 6 and X were favorable for a lower SCS. Differences in somatic cell count (SCC) between alternative SNP alleles reached 14 000 cells/mL.

Conclusions

The results support the polygenic nature of the genetic determination of SCS, confirm the importance of previously reported QTL, and provide evidence for the segregation of additional QTL for SCS in Holstein cattle. The small size of the regions identified here will facilitate the search for causal genetic variations that affect gene functions.

Pathogenesis of RON receptor tyrosine kinase in cancer cells: activation mechanism, functional crosstalk, and signaling addiction

The RON receptor tyrosine kinase, a member of the MET proto-oncogene family, is a pathogenic factor implicated in tumor malignancy. Specifically, aberrations in RON signaling result in increased cancer cell growth, survival, invasion, angiogenesis, and drug resistance. Biochemical events such as ligand binding, receptor overexpression, generation of structure-defected variants, and point mutations in the kinase domain contribute to RON signaling activation. Recently, functional crosstalk between RON and signaling proteins such as MET and EFGR has emerged as an additional mechanism for RON activation, which is critical for tumorigenic development. The RON signaling crosstalk acts either as a regulatory feedback loop that strengthens or enhances tumorigenic phenotype of cancer cells or serves as a signaling compensatory pathway providing a growth/survival advantage for cancer cells to escape targeted therapy. Moreover, viral oncoproteins derived from Friend leukemia or Epstein-Barr viruses interact with RON to drive viral oncogenesis. In cancer cells, RON signaling is integrated into cellular signaling network essential for cancer cell growth and survival. These activities provide the molecular basis of targeting RON for cancer treatment. In this review, we will discuss recent data that uncover the mechanisms of RON activation in cancer cells, review evidence of RON signaling crosstalk relevant to cancer malignancy, and emphasize the significance of the RON signaling addiction by cancer cells for tumor therapy. Understanding aberrant RON signaling will not only provide insight into the mechanisms of tumor pathogenesis, but also lead to the development of novel strategies for molecularly targeted cancer treatment.

MSP-RON signalling in cancer: pathogenesis and therapeutic potential

Since the discovery of MSP (macrophage-stimulating protein; also known as MST1 and hepatocyte growth factor-like (HGFL)) as the ligand for the receptor tyrosine kinase RON (also known as MST1R) in the early 1990s, the roles of this signalling axis in cancer pathogenesis has been extensively studied in various model systems. Both in vitro and in vivo evidence has revealed that MSP-RON signalling is important for the invasive growth of different types of cancers. Currently, small-molecule inhibitors and antibodies blocking RON signalling are under investigation. Substantial responses have been achieved in human tumour xenograft models, laying the foundation for clinical validation. In this Review, we discuss recent advances that demonstrate the importance of MSP-RON signalling in cancer and its potential as a therapeutic target.

Macrophage stimulating protein promotes liver metastases of small cell lung cancer cells by affecting the organ microenvironment

The organ microenvironment significantly affects the processes of cancer metastasis. Elucidating the molecular mechanisms of interaction between tumor cells and the organ microenvironment is crucial for the development of effective therapeutic strategies to eradicate cancer metastases. Macrophage stimulating protein (MSP), an activator of macrophages, regulates a pleiotropic array of effects, including proliferation, cellular motility, invasiveness, angiogenesis, and resistance to anoikis. However, the role of MSP in cancer metastasis is still largely unknown. In this study, the action of MSP on the production of metastases was determined in a multiple-organ metastasis model. The murine MSP gene was transfected into two human SCLC cell lines, SBC-5 and H1048, to establish transfectants secreting biologically active MSP. MSP gene transduction did not affect cell proliferation and motility in vitro. Intravenously inoculated MSP transfectants produced significantly larger numbers of liver metastases than parental cells or vector control clones, while there were no significant differences in bone or lung metastases among them. Immunohistochemical analyses of liver metastases revealed that tumor-associated microvessel density and tumor-infiltrating macrophages were significantly increased in lesions produced by MSP transfectants. MSP could stimulate the migration of murine macrophages and endothelial cells in vitro. Consequently, MSP may be one of the major determinants that affects the properties of tumor stroma and that produces a permissive microenvironment to promote cancer metastasis.

Crystal structure of the Sema-PSI extracellular domain of human RON receptor tyrosine kinase

Human RON (Recepteur d’Origine Nantais) receptor tyrosine kinase is a cell surface receptor for Macrophage Stimulating Protein (MSP). RON mediates signal transduction pathways that regulate cell adhesion, invasion, motility and apoptosis processes. Elevated levels of RON and its alternatively spliced variants are implicated in the progression and metastasis of tumor cells. The binding of MSP α/β heterodimer to the extracellular region of RON receptor induces receptor dimerization and activation by autophosphorylation of the intracellular kinase domains. The ectodomain of RON, containing the ligand recognition and dimerization domains, is composed of a semaphorin (Sema), Plexins-Semaphorins-Integrins domain (PSI), and four Immunoglobulins-Plexins-Transcription factor (IPT) domains. High affinity association between MSP and RON is mediated by the interaction between MSP β-chain and RON Sema, although RON activation requires intact RON and MSP proteins. Here, we report the structure of RON Sema-PSI domains at 1.85 Å resolution. RON Sema domain adopts a seven-bladed β-propeller fold, followed by disulfide bond rich, cysteine-knot PSI motif. Comparison with the homologous Met receptor tyrosine kinase reveals that RON Sema-PSI contains distinguishing secondary structural features. These define the receptors’ exclusive selectivity towards their respective ligands, RON for MSP and Met for HGF. The RON Sema-PSI crystal packing generates a homodimer with interface formed by the Sema domain. Mapping of the dimer interface using the RON homology to Met, MSP homology to Hepatocyte Growth Factor (HGF), and the structure of the Met/HGF complex shows the dimer interface overlapping with the putative MSPβ binding site. The crystallographically determined RON Sema-PSI homodimer may represent the dimer assembly that occurs during ligand-independent receptor activation and/or the inhibition of the constitutive activity of RONΔ160 splice variant by the soluble RON splice variant, RONΔ85.

Activation of macrophage-stimulating protein by human airway trypsin-like protease

Macrophage-stimulating protein (MSP) circulates as a proform protein and requires proteolytic processing for activation. Respiratory ciliated cells express the MSP receptor, recepteur d'origine nantais (RON), at the apical surface, which reportedly has an important role in ciliary function. Like RON, human airway trypsin-like protease (HAT) is also expressed at the apical surface of ciliated cells. Here we show that HAT cleaves proMSP at the physiological activation site, Arg483-Val484. MSP processed by HAT could induce chemotactic responses and morphological changes of peritoneal macrophages. In human respiratory epithelial cells, knock down of HAT expression reduced proMSP processing and RON autophosphorylation. We suggest that HAT is important for MSP-RON signaling in the respiratory tract.

Sustained expression of the RON receptor tyrosine kinase by pancreatic cancer stem cells as a potential targeting moiety for antibody-directed chemotherapeutics

Cancer stem cells (CSCs) contribute to pancreatic cancer tumorigenesis through tumor initiation, drug resistance, and metastasis. Currently, therapeutics targeting pancreatic CSCs are under intensive investigation. This study tested a novel strategy that utilizes the RON receptor as a drug delivery moiety for increased therapeutic activity against pancreatic CSCs. CD24(+)CD44(+)ESA(+) triple-positive pancreatic CSCs (CSCs(+24/44/ESA)) were obtained from spheroids of pancreatic L3.6pl cancer cells by sequential magnetic cell sorting methods. These cells displayed a spherical growth pattern, expressed the unique self-renewal marker Bmi-1, redifferentiated into an epithelial phenotype, acquired an epithelial to mesenchymal phenotype, and caused tumor formation in animal models. Among several receptor tyrosine kinases examined, RON was highly expressed and sustained by CSCs(+24/44/ESA). This feature provided the cellular basis for validating the therapeutic effectiveness of anti-RON antibody Zt/c9-directing doxorubicin-immunoliposomes (Zt/c9-Dox-IL). Zt/c9-Dox-IL specifically interacted with CSCs(+24/44/ESA) and rapidly caused RON internalization, which led to the uptake of liposome-coated Dox. Moreover, Zt/c9-Dox-IL was effective in reducing viability of L3.6pl cells and CSCs(+24/44/ESA). The IC(50) values between free Dox (62.0 ± 3.1 μM) and Zt/c9-Dox-IL (95.0 ± 6.1 μM) treated CSCs(+24/44/ESA) were at relatively comparable levels. In addition, Zt/c9-Dox-IL in combination with small molecule inhibitors lapatinib, sunitinib, or dasatinib further reduced the viability of CSCs(+24/44/ESA). In conclusion, RON expression by CSCs(+24/44/ESA) is a suitable molecule for the targeted delivery of chemoagents. The anti-RON antibody-directed delivery of chemotherapeutics is effective in reducing viability of pancreatic CSCs.

Proteolytic activation of pro-macrophage-stimulating protein by hepsin

Macrophage-stimulating protein (MSP) is a plasminogen-related growth factor and ligand for the receptor tyrosine kinase RON. The MSP/RON system promotes wound healing and invasive tumor growth and suppresses proinflammatory immune response. MSP binding to RON requires proteolytic conversion of the inactive single-chain form (pro-MSP) into the disulfide-linked α/β heterodimer. The pro-MSP cleavage sequence (Ser-Lys-Leu-Arg(483)↓Val(484)) closely matches the substrate recognition sequences of hepsin, a type II transmembrane serine protease, that is overexpressed in several cancers. Here, we show that recombinant hepsin cleaves pro-MSP at the consensus site Arg(483)-Val(484) with superior efficiency compared with the known activators MT-SP1 and hepatocyte growth factor activator (HGFA). At least 50% of pro-MSP was processed within 1 hour at a hepsin concentration of 2.4 nmol/L and at a molar enzyme to substrate ratio of 1:500. An uncleavable single-chain variant of MSP weakly bound to a RON-Fc fusion protein, whereas hepsin-cleaved MSP bound with a K(D) of 10.3 nmol/L, suggesting that the high-affinity binding site in MSP β-chain was properly formed. LNCaP prostate cancer cells overexpressing hepsin on the cell surface efficiently activated pro-MSP, which was blocked by a specific anti-hepsin antibody. Incubation of pro-MSP with hepsin led to robust RON-mediated phosphorylation of mitogen-activated protein kinase, ribosomal S6 protein, and Akt in human A2780 ovarian carcinoma cells stably expressing RON protein. In macrophages, pro-MSP with hepsin induced chemotaxis and attenuated lipopolysaccharide-dependent production of nitric oxide. These findings suggest that the MSP/RON signaling pathway may be regulated by hepsin in tissue homeostasis and in disease pathologies, such as in cancer and immune disorders.

Ron receptor regulates Kupffer cell-dependent cytokine production and hepatocyte survival following endotoxin exposure in mice

Previous studies demonstrated that targeted deletion of the Ron receptor tyrosine kinase (TK) domain in mice leads to marked hepatocyte protection in a well-characterized model of lipopolysaccharide (LPS)-induced acute liver failure in D-galactosamine (GalN)-sensitized mice. Hepatocyte protection in TK-/- mice was observed despite paradoxically elevated serum levels of tumor necrosis factor alpha (TNF-α). To understand the role of Ron in the liver, purified populations of Kupffer cells and hepatocytes from wildtype (TK+/+) and TK-/- mice were studied. Utilizing quantitative reverse-transcription polymerase chain reaction (RT-PCR), we demonstrated that Ron is expressed in these cell types. Moreover, we also recapitulated the protected hepatocyte phenotype and exaggerated cytokine production observed in the TK-/- mice in vivo through the use of purified cultured cells ex vivo. We show that isolated TK-/- Kupffer cells produce increased levels of TNF-α and select cytokines compared to TK+/+ cells following LPS stimulation. We also show that conditioned media from LPS-treated TK-/- Kupffer cells was more toxic to hepatocytes than control media, suggesting the exaggerated levels of cytokines produced from the TK-/- Kupffer cells are detrimental to wildtype hepatocytes. In addition, we observed that TK-/- hepatocytes were more resistant to cell death compared to TK+/+ hepatocytes, suggesting that Ron functions in both the epithelial and inflammatory cell compartments to regulate acute liver injury. These findings were confirmed in vivo in mice with hepatocyte and macrophage cell-type-specific conditional Ron deletions. Mice with Ron loss selectively in hepatocytes exhibited less liver damage and increased survival compared to mice with Ron loss in macrophages.

CONCLUSION

We dissected cell-type-specific roles for Ron such that this receptor modulates cytokine production from Kupffer cells and inhibits hepatocyte survival in response to injury.

Ron receptor tyrosine kinase activation confers resistance to tamoxifen in breast cancer cell lines

Although tamoxifen treatment is associated with improved survival in patients with estrogen receptor (ER)-positive breast tumors, resistance remains an important clinical obstacle. Signaling through growth factor signaling pathways, in particular through receptor tyrosine kinases, has been demonstrated to confer tamoxifen resistance in an estradiol-independent manner. The Ron receptor tyrosine kinase, a member of the c-Met family of receptors, is expressed in a number of human epithelial tumors, and elevated expression of Ron is associated with poor prognosis in women with breast cancer. In this report, we evaluated the role of Ron receptor activation in conferring resistance to tamoxifen in human and murine breast cancer cell lines. Activation of Ron by its ligand, hepatocyte growth factor-like protein (HGFL) was associated with partial rescue from tamoxifen-induced growth inhibition in Ron-expressing cell lines. Western analysis revealed that treatment of the T47D human breast cancer cell line with tamoxifen and HGFL was associated with increased phosphorylation of mitogen-activated protein kinase (MAPK) 1/2 and phosphorylation of serine residue 118 of ER. Expression of ER-dependent genes was increased in cells treated with tamoxifen and HGFL by quantitative reverse transcription-polymerase chain reaction. All of these effects were inhibited by treatment with either a Ron-neutralizing antibody or a MEK1 inhibitor, suggesting the specificity of the effect to Ron, and the involvement of the MAPK 1/2 signaling pathway. In summary, these results illustrate a novel connection between the Ron receptor tyrosine kinase and an important mechanism of tamoxifen resistance in breast cancer.

Mechano-biology of skeletal muscle hypertrophy and regeneration: possible mechanism of stretch-induced activation of resident myogenic stem cells

In undamaged postnatal muscle fibers with normal contraction and relaxation activities, quiescent satellite cells of resident myogenic stem cells are interposed between the overlying external lamina and the sarcolemma of a subjacent mature muscle fiber. When muscle is injured, exercised, overused or mechanically stretched, these cells are activated to enter the cell proliferation cycle, divide, differentiate, and fuse with the adjacent muscle fiber, and are responsible for regeneration and work-induced hypertrophy of muscle fibers. Therefore, a mechanism must exist to translate mechanical changes in muscle tissue into chemical signals that can activate satellite cells. Recent studies of satellite cells or single muscle fibers in culture and in vivo demonstrated the essential role of hepatocyte growth factor (HGF) and nitric oxide (NO) radical in the activation pathway. These experiments have also reported that mechanically stretching satellite cells or living skeletal muscles triggers the activation by rapid release of HGF from its extracellular tethering and the subsequent presentation to the receptor c-met. HGF release has been shown to rely on calcium-calmodulin formation and NO radical production in satellite cells and/or muscle fibers in response to the mechanical perturbation, and depend on the subsequent up-regulation of matrix metalloproteinase (MMP) activity. These results indicate that the activation mechanism is a cascade of events including calcium ion influx, calcium-calmodulin formation, NO synthase activation, NO radical production, MMP activation, HGF release and binding to c-met. Better understanding of 'mechano-biology' on the satellite cell activation is essential for designing procedures that could enhance muscle growth and repair activities in meat-animal agriculture and also in neuromuscular disease and aging in humans.

An unusual function of RON receptor tyrosine kinase as a transcriptional regulator in cooperation with EGFR in human cancer cells

Homodimerization of RON (MST1R), a receptor tyrosine kinase, usually occurs in cells stimulated by a ligand and leads to the downstream activation of signaling pathways. Here we report that bladder cancer cells, in response to physiological stress, use an alternative mechanism for signaling activation. Time-course studies indicated that RON migrated directly from the membrane to the nucleus of bladder cancer cells in response to serum starvation. Biochemical and genetic studies implied that this nuclear internalization was complexed with epidermal growth factor receptor (EGFR) and required the docking of importins. In vivo analysis confirmed that nuclear RON was present in 38.4% (28/73) of primary bladder tumors. Chromatin immunoprecipitation (ChIP) on microarray analysis further revealed that this internalized complex bound to at least 134 target genes known to participate in three stress-responsive networks: p53, stress-activated protein kinase/c-jun N-terminal kinase and phosphatidylinositol 3-kinase/Akt. These findings suggest that RON, in a complex with EGFR, acts as a transcriptional regulator in response to acute disturbances (e.g. serum starvation) imposed on cancer cells. In an attempt to re-establish homeostasis, these cells bypass regular mechanisms required by ligand stimulation and trigger the RON-directed transcriptional response, which confers a survival advantage.

Role of STK in mouse liver macrophage and endothelial cell responsiveness during acute endotoxemia

Acute endotoxemia is associated with excessive production of proinflammatory mediators by hepatic macrophages and endothelial cells, which have been implicated in liver injury and sepsis. In these studies, we analyzed the role of MSP and its receptor STK in regulating the activity of these cells. Acute endotoxemia, induced by administration of LPS (3 mg/kg) to mice, resulted in increased expression of STK mRNA and protein in liver macrophages and endothelial cells, an effect that was dependent on TLR-4. This was correlated with decreased MSP and increased pro-MSP in serum. In Kupffer cells, but not endothelial cells, MSP suppressed LPS-induced NOS-2 expression, with no effect on COX-2. LPS treatment of mice caused a rapid (within 3 h) increase in the proinflammatory proteins NOS-2, IL-1beta, and TNF-alpha, as well as TREM-1 and TREM-3 and the anti-inflammatory cytokine IL-10 in liver macrophages and endothelial cells. Whereas LPS-induced expression of proinflammatory proteins was unchanged in STK-/- mice, IL-10 expression was reduced significantly. Enzymes mediating eicosanoid biosynthesis including COX-2 and mPGES-1 also increased in macrophages and endothelial cells after LPS administration. In STK-/- mice treated with LPS, mPGES-1 expression increased, although COX-2 expression was reduced. LPS-induced up-regulation of SOD was also reduced in STK-/- mice in liver macrophages and endothelial cells. These data suggest that MSP/STK signaling plays a role in up-regulating macrophage and endothelial cell anti-inflammatory activity during hepatic inflammatory responses. This may be important in protecting the liver from tissue injury.

Hepatocyte growth factor inhibits CNS autoimmunity by inducing tolerogenic dendritic cells and CD25+Foxp3+ regulatory T cells

Immune-mediated diseases of the CNS, such as multiple sclerosis and its animal model, experimental autoimmune encephalitis (EAE), are characterized by the activation of antigen-presenting cells and the infiltration of autoreactive lymphocytes within the CNS, leading to demyelination, axonal damage, and neurological deficits. Hepatocyte growth factor (HGF) is a pleiotropic factor known for both neuronal and oligodendrocytic protective properties. Here, we assess the effect of a selective overexpression of HGF by neurons in the CNS of C57BL/6 mice carrying an HGF transgene (HGF-Tg mice). EAE induced either by immunization with myelin oligodendrocyte glycoprotein peptide or by adoptive transfer of T cells was inhibited in HGF-Tg mice. Notably, the level of inflammatory cells infiltrating the CNS decreased, except for CD25(+)Foxp3(+) regulatory T (T(reg)) cells, which increased. A strong T-helper cell type 2 cytokine bias was observed: IFN-gamma and IL-12p70 decreased in the spinal cord of HGF-Tg mice, whereas IL-4 and IL-10 increased. Antigen-specific response assays showed that HGF is a potent immunomodulatory factor that inhibits dendritic cell (DC) function along with differentiation of IL-10-producing T(reg) cells, a decrease in IL-17-producing T cells, and down-regulation of surface markers of T-cell activation. These effects were reversed fully when DC were pretreated with anti-cMet (HGF receptor) antibodies. Our results suggest that, by combining both potentially neuroprotective and immunomodulatory effects, HGF is a promising candidate for the development of new treatments for immune-mediated demyelinating diseases associated with neurodegeneration such as multiple sclerosis.

Gene expression patterns associated with chicken jejunal development

Jejunal development occurs in a spatio-temporal pattern and is characterized by morphological and functional changes. To investigate jejunal development at the transcriptomic level, we performed microarray studies in 1-21-day-old chickens. Nine gene clusters were identified, each with a specific gene expression pattern. Subsequently, groups of genes with similar functions could be identified. Genes involved in morphological and functional development were highly expressed immediately after hatch with declining expression patterns afterwards. Immunological development can be roughly divided based on expression patterns into three processes over time; first innate response and immigration of immune cells, secondly differentiation and specialization, and thirdly maturation and immune regulation. We conclude that specific gene expression patterns coincide with the immunological, morphological, and functional development as measured by other methods. Our data show that transcriptomic approaches provide more detailed information on the biological processes underlying jejunal development.

Hepatocyte growth factor activator is a serum activator of single-chain precursor macrophage-stimulating protein

Macrophage-stimulating protein (MSP) is a plasma protein that circulates as a single-chain proform. It acquires biological activity after proteolytic cleavage at the Arg483-Val484 bond, a process in which serum and cell surface serine proteinases have been implicated. In this article, we report that hepatocyte growth factor activator (HGFA), a serum proteinase which activates hepatocyte growth factor in response to tissue injury, may have a critical role in the activation of pro-MSP. In vitro analysis has revealed that human HGFA efficiently cleaves human pro-MSP at the physiological activation site without further degradation, resulting in biologically active MSP, as measured by the chemotactic response and MSP-induced morphological change of peritoneal macrophages. The processing of pro-MSP by HGFA is 10-fold more efficient than processing by factor XIa. To search for a role of HGFA in pro-MSP activation, we analyzed the processing of mouse pro-MSP in sera from HGFA-knockout (HGFA(-/-)) mice. The proform of MSP was the predominant molecular form in the plasma of both wild-type and HGFA(-/-) mice. In wild-type sera, endogenous pro-MSP was progressively converted to the mature two-chain form during incubation at 37 degrees C. However, this conversion was significantly impaired in sera from HGFA(-/-) mice. The addition of recombinant HGFA to HGFA-deficient serum restored pro-MSP convertase activity in a dose-dependent manner, and a neutralizing antibody to HGFA significantly reduced the conversion of pro-MSP in wild-type serum. Moreover, initial infiltration of macrophages into the site of mechanical skin injury was delayed in HGFA(-/-) mice. We suggest that HGFA is a major serum activator of pro-MSP.

Ketohexokinase-dependent metabolism of fructose induces proinflammatory mediators in proximal tubular cells

Increased consumption of fructose may play an important role in the epidemic of metabolic syndrome and may presage the development of diabetes, cardiovascular disease, and chronic kidney disease. Once in the cell, fructose is phosphorylated by ketohexokinase (KHK), leading to consumption of ATP, formation of AMP, and generation of uric acid through xanthine oxidoreductase (XOR). This study aimed to examine the direct effects of fructose in human kidney proximal tubular cells (HK-2) and whether they are mediated by the fructose metabolism via KHK. At a similar concentration to that observed in peripheral blood after a meal, fructose induced production of monocyte chemotactic protein 1 (MCP-1) and reactive oxygen species in HK-2 cells. Knockdown of KHK by stable transfection with small hairpin RNA demonstrated that these processes were KHK dependent. Several antioxidants, including specific inhibitors of NADPH oxidase and XOR, prevented MCP-1 secretion. We detected XOR mRNA in HK-2 cells and confirmed its activity by identifying uric acid by mass spectrometry. Fructose increased intracellular uric acid, and uric acid induced production of MCP-1 as well. In summary, postprandial concentrations of fructose stimulate redox- and urate-dependent inflammatory mediators in proximal tubular cells.

The RON receptor tyrosine kinase regulates IFN-gamma production and responses in innate immunity

Receptor tyrosine kinases are emerging as a class of key regulators of innate immune responses. We have shown previously that the RON receptor tyrosine kinases (murine Stk), expressed on tissue-resident macrophages, inhibit classical macrophage activation while promoting hallmarks of alternative activation, thus regulating the critical balance between the inflammatory and wound-healing properties of activated macrophages. We have also shown previously that RON(-/-) mice are more susceptible to in vivo endotoxin challenge than wild-type mice, suggesting that the expression of this receptor confers a degree of endotoxin resistance to these animals. Here we demonstrate that, in response to in vivo LPS challenge, RON(-/-) mice harbor significantly increased systemic levels of IFN-gamma and IL-12p70 and increased levels of IL-12p40 transcript in their spleen. This elevation of IFN-gamma can be attributed to splenic NK cells responding to the elevated levels of IL-12. Analysis of RON and IFN-gamma receptor double-knockout mice indicates that the enhanced susceptibility of RON(-/-) mice to endotoxin challenge is dependent on IFN-gamma-mediated signals. In vitro studies demonstrate that stimulation of primary peritoneal macrophages with macrophage-stimulating protein, the ligand for RON, inhibits IFN-gamma-induced STAT1 phosphorylation and CIITA expression, resulting in reduced surface levels of MHC class II. Further studies demonstrating the induction of suppressor of cytokine signaling 1 via macrophage-stimulating protein/RON signaling provide a potential mechanistic insight into this regulatory pathway. These results indicate that the RON receptor regulates both the production of and response to IFN-gamma, resulting in enhanced susceptibility to endotoxin challenge.

Met-related receptor tyrosine kinase Ron in tumor growth and metastasis

The Ron receptor is a member of the Met family of cell surface receptor tyrosine kinases and is primarily expressed on epithelial cells and macrophages. The biological response of Ron is mediated by binding of its ligand, hepatocyte growth factor-like protein/macrophage stimulating-protein (HGFL). HGFL is primarily synthesized and secreted from hepatocytes as an inactive precursor and is activated at the cell surface. Binding of HGFL to Ron activates Ron and leads to the induction of a variety of intracellular signaling cascades that leads to cellular growth, motility and invasion. Recent studies have documented Ron overexpression in a variety of human cancers including breast, colon, liver, pancreas, and bladder. Moreover, clinical studies have also shown that Ron overexpression is associated with both worse patient outcomes as well as metastasis. Forced overexpression of Ron in transgenic mice leads to tumorigenesis in both the lung and the mammary gland and is associated with metastatic dissemination. While Ron overexpression appears to be a hallmark of many human cancers, the mechanisms by which Ron induces tumorigenesis and metastasis are still unclear. Several strategies are currently being undertaken to inhibit Ron as a potential therapeutic target; current strategies include the use of Ron blocking proteins, small interfering RNA (siRNA), monoclonal antibodies, and small molecule inhibitors. In total, these data suggest that Ron is a critical factor in tumorigenesis and that inhibition of this protein, alone or in combination with current therapies, may prove beneficial in the treatment of cancer patients.

HGF–MSP chimera protects kidneys from ischemia–reperfusion injury

Renal ischemia-reperfusion (I/R) injury is inevitable in transplantation and is related to long-term graft function. MF-1, a bifunctional hepatocyte growth factor (HGF)-macrophage-stimulating protein (MSP) (HGF-MSP) chimera was recently reported to prevent apoptosis. We therefore hypothesized that treatment with MF-1 would protect kidneys from I/R injury by inhibiting tubular epithelial apoptosis. MF-1 directly guarded cultured proximal tubular epithelial cells from hypoxia-induced necrosis and apoptosis in vitro. In addition, the therapeutic effects of MF-1 were evaluated using a rat I/R injury model in vivo. Saline-treated kidneys had increased creatinine and BUN, and exhibited tubular epithelial apoptosis with activated caspase 3 expression. In contrast, MF-1 treatment up-regulated Akt phosphorylation, and inhibited caspase 3 activation and tubular apoptosis, thereby ameliorating renal dysfunction. Of particular interest is that macrophage infiltration was suppressed in the MF-1-treated kidney. In conclusion, we identified a novel therapeutic approach using MF-1 to protect kidneys from I/R injury.

Multiple variants of the RON receptor tyrosine kinase: Biochemical properties, tumorigenic activities, and potential drug targets

Aberrant expression of the RON (Recepteur d'Origine Nantais) receptor tyrosine kinase, accompanied by generation of multiple splicing or truncated variants, contributes to pathogenesis of epithelial cancers. Currently, six variants including RONDelta170, Delta165, Delta160, Delta155, Delta110, and Delta55 with various deletions or truncations in the extracellular or intracellular regions have been identified. The extracellular sequences contain functional structures such as sema domain, PSI motif, and IPT units. The deletion or truncation results in constitutive phosphorylation and increased kinase activities. Oncogenic RONDelta160, generated by exclusion of the first IPT unit, is a typical example. In contrast, the deletion adjacent to the conserved MET(1254) in the kinase domain converts RON into a dominant negative agent. Among three mechanisms underlying isoform production, the switch from constitutive to alternative pre-mRNA splicing is the major event in producing RON variants in cancer cells. Most of the RON variants have the ability to activate multiple signaling cascades with a different substrate specificity and phosphorylation profile. They regulate cell migration, invasion, and proliferation, which contribute to the invasive phenotype and promote the malignant progression. Thus, determining the pathogenesis of RON variants is critical in understanding the mechanisms underlying cancer initiation and progression. Targeting oncogenic signals elicited by RON or its variants by special antibody or small interfering RNA could provide a novel strategy for the treatment of malignant epithelial cancers.

Neutralization of macrophage-stimulating protein ameliorates renal injury in anti-thy 1 glomerulonephritis

Macrophage-stimulating protein (MSP) is a scatter factor that causes cell proliferation and migration, and receptor origin nantaise (RON) is its receptor. RON is expressed in macrophages and mesangial cells, and MSP is produced by renal tubular cells. This study investigated whether MSP/RON participate in the pathogenesis of anti-Thy 1 nephritis, a glomerular disease that is characterized by invasion of circulating monocytes into glomeruli and migration and proliferation of mesangial cells. In vivo, renal function and histopathology were studied in rats that had anti-Thy 1 disease and were untreated and treated with a neutralizing anti-MSP antibody. In vitro, whether monocytes express RON and whether MSP has a chemotactic effect on monocytes were studied. In vivo, in anti-Thy 1 disease, MSP was expressed de novo in glomeruli, and neutralization of MSP attenuated the rise in serum creatinine and proteinuria, stopped glomerular neutrophil and monocyte influx, protected from glomerular injury, and lessened mesangial cell overgrowth. In vitro, unstimulated monocytes did not express RON, but the stimulation with LPS induced de novo RON expression. LPS-stimulated monocytes were attracted by MSP. These results demonstrate a pathogenic role of the MSP/RON system in anti-Thy 1 nephritis.

Coordinate expression and functional profiling identify an extracellular proteolytic signaling pathway

A multidisciplinary method combining transcriptional data, specificity profiling, and biological characterization of an enzyme may be used to predict novel substrates. By integrating protease substrate profiling with microarray gene coexpression data from nearly 2,000 human normal and cancerous tissue samples, three fundamental components of a protease-activated signaling pathway were identified. We find that MT-SP1 mediates extracellular signaling by regulating the local activation of the prometastatic growth factor MSP-1. We demonstrate MT-SP1 expression in peritoneal macrophages, and biochemical methods confirm the ability of MT-SP1 to cleave and activate pro-MSP-1 in vitro and in a cellular context. MT-SP1 induced the ability of MSP-1 to inhibit nitric oxide production in bone marrow macrophages. Addition of HAI-1 or an MT-SP1-specific antibody inhibitor blocked the proteolytic activation of MSP-1 at the cell surface of peritoneal macrophages. Taken together, our work indicates that MT-SP1 is sufficient for MSP-1 activation and that MT-SP1, MSP-1, and the previously shown MSP-1 tyrosine kinase receptor RON are required for peritoneal macrophage activation. This work shows that this triad of growth factor, growth factor activator protease, and growth factor receptor is a protease-activated signaling pathway. Individually, MT-SP1 and RON overexpression have been implicated in cancer progression and metastasis. Transcriptional coexpression of these genes suggests that this signaling pathway may be involved in several human cancers.

Short-form Ron receptor is required for normal IFN-gamma production in concanavalin A-induced acute liver injury

Abrogation of Ron receptor tyrosine kinase function results in defects in macrophage activation and dysregulated acute inflammatory responses in vivo. Several naturally occurring constitutively active alternative forms of Ron have been identified, including from primary human tumors and tumor cell lines. One of these alternative forms, short-form (SF) Ron, is generated from an alternative start site in intron 10 of the Ron gene that eliminates most of the extracellular portion of the receptor and is overexpressed in several human cancers. To test the physiological significance of SF-Ron in vivo, mice were generated that solely express the full-length form of Ron (FL-Ron). Our results show that elimination of the capacity to express SF-Ron in vivo leads to augmented production of IFN-gamma from splenocytes following stimulation ex vivo with either concanavalin A or anti-CD3/T cell receptor monoclonal antibody. Moreover, in a concanavalin A-induced murine model of acute liver injury, FL-Ron mice have increased production of serum INF-gamma and serum alanine aminotransferase levels and worsened liver histology and overall survival compared with wild-type control mice. Taken together, these results suggest for the first time that SF-Ron impacts the progression of inflammatory immune responses in vivo and further support a role for the Ron receptor and its various forms in liver pathophysiology.

The Met pathway: master switch and drug target in cancer progression

It has been recognized for more than a century that most tumors tend to become more aggressive in clinical behavior over time, although this time course may be variable. This phenomenon has been termed "cancer progression," a process that appears to develop in a stepwise fashion through qualitatively different stages. Cancer progression relies on the ability of neoplastic cells to abandon their primary site of accretion, trespass tissue boundaries, and penetrate into the vasculature to colonize and repopulate distant sites. Among the various properties associated with cancer progression, the acquisition by neoplastic cells of the capacity to invade locally and to metastasize is of great clinical significance, and is still the fundamental definition of malignancy. This process represents the aberrant counterpart of a physiological morphogenetic program, known as invasive growth, occurring during embryo development and, in some instances, in adulthood for the generation and maintenance of normal organ complexity and architecture. Here we summarize some of the strategies adopted to inhibit cancer cell growth and spreading. We also review the current findings about cancer and metastasis inhibitors. As we suggest possible directions for drug development, we propose the receptor for the hepatocyte growth factor, Met, as an ideal target for tackling cancer progression.

Oncogenesis of RON receptor tyrosine kinase: a molecular target for malignant epithelial cancers

Recepteur d'origine nantais (RON) belongs to a subfamily of receptor tyrosine kinases (RTK) with unique expression patterns and biological activities. RON is activated by a serum-derived growth factor macrophage stimulating protein (MSP). The RON gene transcription is essential for embryonic development and critical in regulating certain physiological processes. Recent studies have indicated that altered RON expression contributes significantly to cancer progression and malignancy. In primary tumors, such as colon and breast cancers, overexpression of RON exists in large numbers and is often accompanied by the generation of different splicing variants. These RON variants direct a unique program that controls cell transformation, growth, migration, and invasion, indicating that altered RON expression has the ability to regulate motile/invasive phenotypes. These activities were also seen in transgenic mice, in which targeted expression of RON in lung epithelial cells resulted in numerous tumors with pathological features of human bronchioloalveolar carcinoma. Thus, abnormal RON activation is a pathogenic factor that transduces oncogenic signals leading to uncontrolled cell growth and subsequent malignant transformation. Considering these facts, RON and its variants can be considered as potential targets for therapeutic intervention. Experiments using small interfering RNA and neutralizing monoclonal antibodies demonstrated that suppressing RON expression and activation decreases cancer cell proliferation, increases apoptotic death, prevents tumor formation in nude mice, and reduces malignant phenotypes. Thus, blocking RON expression and activation has clinical significance in reversing malignant phenotypes and controlling tumor growth.

Mechanisms of cytoplasmic {beta}-catenin accumulation and its involvement in tumorigenic activities mediated by oncogenic splicing variant of the receptor originated from Nantes tyrosine kinase

The beta-catenin pathway plays a critical role in the pathogenesis of certain types of cancers. To gain insight into mechanisms by which altered receptor tyrosine kinases regulate cytoplasmic beta-catenin accumulation, the effect of an oncogenic receptor originated from Nantes (RON) variant on beta-catenin accumulation and the role of beta-catenin in RON-mediated tumorigenic activities were studied. In NIH3T3 cells harboring oncogenic variant RONDelta160, increased beta-catenin accumulation with tyrosine phosphorylation and nuclear translocation was observed. Overexpression of RONDelta160 also resulted in increased expression of beta-catenin target genes c-myc and cyclin D1. By analyzing cellular proteins that regulate beta-catenin stabilities, it was found that RONDelta160 activates the protein disheveled (DVL) and inactivates glycogen synthase kinase-3beta by Ser-9 residue phosphorylation. These effects were channeled by RONDelta160-activated PI 3-kinase-AKT pathways that are sensitive to specific inhibitors, such as wortmannin, but not to other chemical inhibitors. Silencing RONDelta160 expression by specific small interfering RNA blocked not only beta-catenin expression but also c-myc and cyclin D1 expression, suggesting that RON expression is required for the activation of the beta-catenin signaling pathway. Moreover, it was found that knockdown of the beta-catenin gene expression by small interfering RNA techniques reduces significantly the RONDelta160-mediated NIH3T3 cell proliferation, focus-forming activities and anchorage-independent growth. Thus, the oncogenic RON variant regulates beta-catenin stabilities through activation of DVL and inactivation of glycogen synthase kinase-3beta. The activated beta-catenin cascade is one of the pathways involved in tumorigenic activities mediated by the oncogenic RON variant.

RNA-mediated gene silencing of the RON receptor tyrosine kinase alters oncogenic phenotypes of human colorectal carcinoma cells

Altered expression of receptor tyrosine kinases contributes to tumorigenic behaviors of epithelial cancers. In this study, the pathogenic roles of receptor tyrosine kinase RON (recepteur d'origine nantais) in regulating oncogenic phenotypes in colorectal epithelial cells were studied. Increased expression of RON and its variants resulted in colony formation and motile activities of colonic epithelial AA/C1 cells as evident in soft-agar and migration assays, respectively. These results suggest that overexpression of wild-type RON mediates the transformed phenotypes in immortalized colon epithelial cells. In colorectal cancer cells (HT-29, HCT116, and SW620) that naturally express RON, the RON gene expression was silenced by RNA interference. The introduction of RON-specific small interfering (si) RNA significantly affected cancer cell proliferation, motility, and led to increased apoptotic cell death. Focus-forming activities and anchorage-independent growth of colon cancer cells were also dramatically reduced. Moreover, it was demonstrated in tumor growth assays that silencing RON gene expression significantly reduces tumorigenic activities of SW620 cells in vivo. By analysing signaling proteins involved in colon carcinogenesis, we found that the effect of RON-specific siRNA is associated with diminished expression of beta-catenin, a critical component in the Wnt signaling pathway. Taken together, our results demonstrate that altered expression of RON in colon cancer cells is required to maintain tumorigenic phenotypes. Thus, silencing RON gene expression could have potential to reverse malignant activities of colon tumors in vivo.

Rapamycin attenuates vascular wall inflammation and progenitor cell promoters after angioplasty

Rapamycin combines antiproliferative and antiinflammatory properties and reduces neointima formation after angioplasty in patients. Its effect on transcriptional programs governing neointima formation has not yet been investigated. Here, we systematically analyzed the effect of rapamycin on gene expression during neointima formation in a human organ culture model. After angioplasty, renal artery segments were cultured for 21 or 56 days in absence or presence of 100 ng/ml rapamycin. Gene expression analysis of 2312 genes revealed 264 regulated genes with a peak alteration after 21 days. Many of those were associated with recruitment of blood cells and inflammatory reactions of the vessel wall. Likewise, chemokines and cytokines such as M-CSF, IL-1beta, IL-8, beta-thromboglobulin, and EMAP-II were found up-regulated in response to vessel injury. Markers indicative for a facilitated recruitment and stimulation of hematopoetic progenitor cells (HPC), including BST-1 and SDF-1, were also induced. In this setting, rapamycin suppressed the coordinated proadhesive and proinflammatory gene expression pattern next to down-regulation of genes related to metabolism, proliferation, and apoptosis. Our study shows that mechanical injury leads to induction of a proinflammatory, proadhesive gene expression pattern in the vessel wall even in absence of leukocytes. These molecular events could provide a basis for the recruitment of leukocytes and HPC. By inhibiting the expression of such genes, rapamycin may lead to a reduced recruitment of leukocytes and HPC after vascular injury, an effect that may play a decisive role for its effectiveness in reducing restenosis.

Macrophage-Stimulating Protein Promotes Hair Growth Ex Vivo and Induces Anagen from Telogen Stage Hair Follicles In Vivo

Hepatocyte growth factor (HGF) is a promoter of hair follicle growth. We examined another HGF family member, macrophage-stimulating protein (MSP), for its hair follicle-modulating properties. Western blotting revealed presence of mature MSP in cultured human dermal papilla (DP) cells and bulbar dermal sheath (DS) cells, but not non-bulbar DS cells. Immunohistology demonstrated expression of MSP receptor RON in the outer and inner root sheaths, hair matrix cells, DP, and bulbar DS whereas non-follicular epithelium and some cells of the sweat glands exhibited low-level receptor expression. Human hair follicles exposed in vitro for 8 d to 0.1, 1, 10, and 100 ng per mL MSP all yielded a mean net increase in hair follicle length in excess of the mean baseline growth observed in controls. MSP was incubated with agarose beads and injected subcutaneously into mice all 70 d old when a uniform telogen state in dorsal skin was apparent. All eight mice receiving 1 microg MSP, and four of eight receiving 100 ng MSP showed induction of anagen hair growth at the site of bead implantation by 16 d whereas eight mice implanted with saline incubated beads had no hair growth. The data identify MSP as a modulator of hair growth.