Plasminogen-related growth factor and semaphorin receptors: a gene superfamily controlling invasive growth

The Emerging Role of c-Met in Carcinogenesis and Clinical Implications as a Possible Therapeutic Target

Background

c-MET is a receptor tyrosine kinase receptor (RTK) for the hepatocyte growth factor (HGF). The binding of HGF to c-MET regulates several cellular functions: differentiation, proliferation, epithelial cell motility, angiogenesis, and epithelial-mesenchymal transition (EMT). Moreover, it is known to be involved in carcinogenesis. Comprehension of HGF-c-MET signaling pathway might have important clinical consequences allowing to predict prognosis, response to treatment, and survival rates based on its expression and dysregulation. Discussion. c-MET represents a useful molecular target for novel engineered drugs. Several clinical trials are underway for various solid tumors and the development of new specific monoclonal antibodies depends on the recent knowledge about the definite c-MET role in each different malignance. Recent clinical trials based on c-MET molecular targets result in good safety profile and represent a promising therapeutic strategy for solid cancers, in monotherapy or in combination with other target drugs.

Conclusion

The list of cell surface receptors crosslinking with the c-MET signaling is constantly growing, highlighting the importance of this pathway for personalized target therapy. Research on the combination of c-MET inhibitors with other drugs will hopefully lead to discovery of new effective treatment options.

Insights into the regulatory role of Plexin D1 signalling in cardiovascular development and diseases

Plexin D1 (PLXND1), which was previously thought to mediate semaphorin signalling, belongs to the Plexin family of transmembrane proteins. PLXND1 cooperates mostly with the coreceptor neuropilin and participates in many aspects of axonal guidance. PLXND1 can also act as both a tumour promoter and a tumour suppressor. Emerging evidence suggests that mutations in PLXND1 or Semaphorin 3E, the canonical ligand of PLXND1, can lead to serious cardiovascular diseases, such as congenital heart defects, CHARGE syndrome and systemic sclerosis. Upon ligand binding, PLXND1 can act as a GTPase‐activating protein (GAP) and modulate integrin‐mediated cell adhesion, cytoskeletal dynamics and cell migration. These effects may play regulatory roles in the development of the cardiovascular system and disease. The cardiovascular effects of PLXND1 signalling have gradually been elucidated. PLXND1 was recently shown to detect physical forces and translate them into intracellular biochemical signals in the context of atherosclerosis. Therefore, the role of PLXND1 in cardiovascular development and diseases is gaining research interest because of its potential as a biomarker and therapeutic target. In this review, we describe the cardiac effects, vascular effects and possible molecular mechanisms of PLXND1 signalling.

Plasma Level of Placenta-Derived Macrophage-Stimulating Protein -Chain in Preeclampsia before 20 Weeks of Pregnancy

Object

This study aimed to investigate the diagnostic value of placenta-derived macrophage-stimulating protein α-chain (MSP-α) before the 20^th week of gestation for the early diagnosis of preeclampsia (PE).

Methods and Materials

Two parts of this nested case-control study were simultaneously executed, and 1500 pregnant women were recruited. A total of 124 pregnant women were included in the plasma analysis part of this study. The MSP-α plasma level was measured before the 20^th week of gestation, and the participants were followed until delivery. A case group of 62 women with PE and a control group of 62 women matched by gestational age, maternal age, and pre-pregnancy BMI (with normotensive pregnancies) were evaluated. In the placenta analysis part of this nested case-control study, the placentas of 34 pregnant women were randomly obtained. The placental levels of MSP were measured in 17 individuals with PE (case group) and in 17 women with a normotensive pregnancy matched by gestational age and maternal age (control group).

Results

The plasma level of MSP-α was higher in the PE group than in the control group before the 20^th week of gestation (p < 0.001). In addition, compared to the women with severe features in the PE group, those without severe features had a significantly higher plasma MSP-α level before the 20^th week of gestation (p < 0.001). The area under the receiver operating characteristic curve (AUC) of MSP-α before the 20^th week of gestation was 0.905 (95% CI, 0.811–0.962) for the women with early-onset PE without severe features. With regard to the placenta, the PE group (accumulated optical density, IOD [SUM] = 8862.37 ± 2064.42) exhibited increased MSP staining (more intense MSP staining or more extensive staining) compared with the control group (normal pregnancies (IOD [SUM] = 447.92 ± 114.72, P < 0.001). Furthermore, increased MSP staining was detected among the women without severe features compared with those with severe features in the PE group (IOD [SUM]: 12192.65 ± 5325.56 vs. 4104.83 ± 2383.06, P = 0.021).

Conclusion

According to the findings of this study, the plasma level of MSP-α may be associated with PE, and MSP-α may be considered a candidate protein for further analysis in studies of PE. Multicenter studies with larger sample sizes must be performed in the future to obtain accurate results regarding the predictive value of MSP-α in combination with other protein factors for the early diagnosis of PE.

Design and biological evaluation of novel 4-(2-fluorophenoxy)quinoline derivatives bearing an imidazolone moiety as c-Met kinase inhibitors

A series of 4-(2-fluorophenoxy)quinoline derivatives containing an imidazolone moiety were designed, synthesized and evaluated for their in vitro biological activities against c-Met kinase and four cancer cell lines (A549, H460, HT-29 and MKN-45). Most compounds showed moderate to excellent activities in enzyme and cellular assays. The most promising analog, 58 (c-Met IC50=1.42 nM), displayed 2.1-, 8.6-fold increase against H460, and MKN-45 cell lines, respectively, compared with foretinib. An analysis of structure-activity relationships revealed that an ortho substituted phenyl ring as well as an N-unsubstituted imidazolone linker is favorable for antitumor activity.

The monoclonal antibody Zt/f2 targeting RON receptor tyrosine kinase as potential therapeutics against tumor growth-mediated by colon cancer cells

Background

Overexpression of the RON receptor tyrosine kinase contributes to epithelial cell transformation, malignant progression, and acquired drug resistance. RON also has been considered as a potential target for therapeutic intervention. This study determines biochemical features and inhibitory activity of a mouse monoclonal antibody (mAb) Zt/f2 in experimental cancer therapy.

Results

Zt/f2 is a mouse IgG2a mAb that is highly specific and sensitive to human RON and its oncogenic variants such as RON160 (ED₅₀ = 2.3 nmol/L). Receptor binding studies revealed that Zt/f2 interacts with an epitope(s) located in a 49 amino acid sequence coded by exon 11 in the RON β-chain extracellular sequences. This sequence is critical in regulating RON maturation and phosphorylation. Zt/f2 did not compete with ligand macrophage-stimulating protein for binding to RON; however, its engagement effectively induced RON internalization, which diminishes RON expression and impairs downstream signaling activation. These biochemical features provide the cellular basis for the use of Zt/f2 to inhibit tumor growth in animal model. Repeated administration of Zt/f2 as a single agent into Balb/c mice results in partial inhibition of tumor growth caused by transformed NIH-3T3 cells expressing oncogenic RON160. Colon cancer HT-29 cell-mediated tumor growth in athymic nude mice also was attenuated following Zt/f2 treatment. In both cases, ~50% inhibition of tumor growth as measured by tumor volume was achieved. Moreover, Zt/f2 in combination with 5-fluorouracil showed an enhanced inhibition effect of ~80% on HT-29 cell-mediated tumor growth in vivo.

Conclusions

Zt/f2 is a potential therapeutic mAb capable of inhibiting RON-mediated oncogenesis by colon cancer cells in animal models. The inhibitory effect of Zt/f2 in vivo in combination with chemoagent 5-fluorouracil could represent a novel strategy for future colon cancer therapy.

Hormonal regulation and distinct functions of semaphorin-3B and semaphorin-3F in ovarian cancer

Semaphorins comprise a family of molecules that influence neuronal growth and guidance. Class-3 semaphorins, semaphorin-3B (SEMA3B) and semaphorin-3F (SEMA3F), illustrate their effects by forming a complex with neuropilins (NP-1 or NP-2) and plexins. We examined the status and regulation of semaphorins and their receptors in human ovarian cancer cells. A significantly reduced expression of SEMA3B (83 kDa), SEMA3F (90 kDa), and plexin-A3 was observed in ovarian cancer cell lines when compared with normal human ovarian surface epithelial cells. The expression of NP-1, NP-2, and plexin-A1 was not altered in human ovarian surface epithelial and ovarian cancer cells. The decreased expression of SEMA3B, SEMA3F, and plexin-A3 was confirmed in stage 3 ovarian tumors. The treatment of ovarian cancer cells with luteinizing hormone, follicle-stimulating hormone, and estrogen induced a significant upregulation of SEMA3B, whereas SEMA3F was upregulated only by estrogen. Cotreatment of cell lines with a hormone and its specific antagonist blocked the effect of the hormone. Ectopic expression of SEMA3B or SEMA3F reduced soft-agar colony formation, adhesion, and cell invasion of ovarian cancer cell cultures. Forced expression of SEMA3B, but not SEMA3F, inhibited viability of ovarian cancer cells. Overexpression of SEMA3B and SEMA3F reduced focal adhesion kinase phosphorylation and matrix metalloproteinase-2 and matrix metalloproteinase-9 expression in ovarian cancer cells. Forced expression of SEMA3F, but not SEMA3B in ovarian cancer cells, significantly inhibited endothelial cell tube formation. Collectively, our results suggest that the loss of SEMA3 expression could be a hallmark of cancer progression. Furthermore, gonadotropin- and/or estrogen-mediated maintenance of SEMA3 expression could control ovarian cancer angiogenesis and metastasis.

Hepatocyte growth factor (HGF) modulates GABAergic inhibition and seizure susceptibility

Disrupted ontogeny of forebrain inhibitory interneurons leads to neurological disorders, including epilepsy. Adult mice lacking the urokinase plasminogen activator receptor (Plaur) have decreased numbers of neocortical GABAergic interneurons and spontaneous seizures, attributed to a reduction of hepatocyte growth factor/scatter factor (HGF/SF). We report that by increasing endogenous HGF/SF concentration in the postnatal Plaur null mouse brain maintains the interneuron populations in the adult, reverses the seizure behavior and stabilizes the spontaneous electroencephalogram activity. The perinatal intervention provides a pathway to reverse potential birth defects and ameliorate seizures in the adult.

Identification of a novel recepteur d'origine nantais/c-met small-molecule kinase inhibitor with antitumor activity in vivo

Recepteur d'origine nantais (RON) is a receptor tyrosine kinase closely related to c-Met. Both receptors are involved in cell proliferation, migration, and invasion, and there is evidence that both are deregulated in cancer. Receptor overexpression has been most frequently described, but other mechanisms can lead to the oncogenic activation of RON and c-Met. They include activating mutations or gene amplification for c-Met and constitutively active splicing variants for RON. We identified a novel inhibitor of RON and c-Met, compound I, and characterized its in vitro and in vivo activities. Compound I selectively and potently inhibited the kinase activity of RON and c-Met with IC(50)s of 9 and 4 nmol/L, respectively. Compound I inhibited hepatocyte growth factor-mediated and macrophage-stimulating protein-mediated signaling and cell migration in a dose-dependent manner. Compound I was tested in vivo in xenograft models that either were dependent on c-Met or expressed a constitutively active form of RON (RONDelta160 in HT-29). Compound I caused complete tumor growth inhibition in NIH3T3 TPR-Met and U-87 MG xenografts but showed only partial inhibition in HT-29 xenografts. The effect of compound I in HT-29 xenografts is consistent with the expression of the activating b-Raf V600E mutation, which activates the mitogen-activated protein kinase pathway downstream of RON. Importantly, tumor growth inhibition correlated with the inhibition of c-Met-dependent and RON-dependent signaling in tumors. Taken together, our results suggest that a small-molecule dual inhibitor of RON/c-Met has the potential to inhibit tumor growth and could therefore be useful for the treatment of patients with cancers where RON and/or c-Met are activated.

Semaphorins and their receptors in lung cancer

Semaphorins are a large family of secreted, transmembrane and GPI-linked proteins initially characterized in the development of the nervous system and axonal guidance. Semaphorins are expressed in many tissues where they regulate normal development, organ morphogenesis, immunity and angiogenesis. They affect the cytoskeleton, actin filament organization, microtubules and cell adhesion. Semaphorin signaling is transduced by plexins, which in the case of most class-3 semaphorins requires high-affinity neuropilin receptors. The neuropilins also function as receptors for VEGF and other growth factors, and their expression is often abnormal in tumors. In cancer, semaphorins have both tumor suppressor and tumor promoting functions. We review here the current status of semaphorins and their receptors in tumor development with a focus on lung cancer.

Regulation of epithelial cell adhesion and repulsion: role of endocytic recycling

A proper balance between cell adhesion and repulsion is essential for cellular morphogenesis during epithelial-mesenchymal transition and mesenchymal-epithelial transition. A number of ligand-receptor pairs including hepatocyte growth factor/scatter factor-Met and semaphorin-plexin are known to control this balance through the complex intracellular signaling pathways. Cell adhesion to other cells and extracellular matrix (ECM) is mediated by cell adhesion molecules (CAMs) and ECM receptors, respectively, which are associated with cytoskeleton through a variety of plaque proteins strengthening and/or weakening adhesion activities. Cell repulsion requires the downregulation of cell adhesion and the extensive changes in cytoskeletal dynamics. The endocytic recycling of CAMs and ECM receptors has recently emerged as an important mechanism to control the balance between cell adhesion and repulsion. Molecule interacting with CasL (MICAL) family proteins are originally identified as a plaque protein associated with ECM receptors integrins and implicated in semaphorin-plexin dependent repulsive axon guidance. We have recently shown that MICAL family protein JRAB/MICAL-L2 functions as an effector protein for Rab family small G protein Rab13 and regulates the endocytic recycling of tight junctional CAM occludin and controls the adhesion and repulsion of epithelial cells.

Ron-receptor tyrosine kinase in tumorigenesis and metastasis

The Ron-receptor tyrosine kinase has been increasingly recognized for its tumorigenic potential in the last decade. Ron-receptor activation leads to the activation of common receptor tyrosine kinase downstream-signaling pathways, and most prominently in tumor models, activation of MAPK, PI3K and beta-catenin. Numerous experimental models of mammalian tumorigenesis have demonstrated that increased Ron-receptor activity correlates with increased tumorigenesis in a variety of organs of epithelial origin. The evidence for Ron as an oncogene in human tumor biology is growing. The Ron receptor is overexpressed and over activated in a large number of human tumors, and overexpression of Ron correlates with a worse clinical outcome for patients in at least two human cancer states, namely breast and bladder cancer. Several experimental approaches have been demonstrated to successfully block Ron activity and function, and given these convincing data, approaches to block Ron-receptor activity in targeted human cancers should prove to be fruitful in the setting of future clinical research trials.

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.

Molecular biology of malignant mesothelioma: a review

Malignant mesothelioma (MM) is an uncommon tumor with high mortality and morbidity rates. It arises from mesothelial cells that line the pleural, pericardial, peritoneal, and testicular cavities. This is a disease with an indolent course because tumors arise 20 to 40 years after exposure to an inciting agent. Extensive research has shown that mesothelial cells are transformed into MM cells through various chromosomal and cellular pathway defects. These changes alter the normal cells' ability to survive, proliferate, and metastasize. This article discusses the alterations that occur in transforming normal mesothelial cells into MM. It also details some of the signal transduction pathways that seem to be important in MM with the potential for novel targeted therapeutics.

DNA microarray analysis of gene expression in eutopic endometrium from patients with deep endometriosis using laser capture microdissection

OBJECTIVE

To investigate differentially expressed genes in epithelial and stromal cells of eutopic endometrium from patients with deep endometriosis and women with normal pelvic cavities using laser capture microdissection and complementary DNA microarrays.

DESIGN

Prospective study.

SETTING

University hospital.

PATIENT(S)

Patients with deep endometriosis and fertile women who underwent laparoscopic tubal ligation or reversal of tubal sterilization.

INTERVENTION(S)

Endometrial tissue biopsies during the late proliferative phase and early, mid-, and late secretory phases.

MAIN OUTCOME MEASURE(S)

Genes that were regulated with a change greater than threefold were selected as differentially expressed genes. Validation was performed with real-time reverse transcriptase-polymerase chain reaction (RT-PCR).

RESULT(S)

Microarray analysis identified up-regulation during the late secretory phase (patients with endometriosis vs. controls) of several genes in two important signaling pathways: RAS/RAF/MAPK and PI3K. This included the genes RON, SOS, 14-3-3 protein eta, and uPAR in epithelial cells and KSR and PI3K p85 regulatory subunit alpha in stromal cells; real-time RT-PCR analysis validated up-regulation of all six genes.

CONCLUSION(S)

The RAS/RAF/MAPK and PI3K pathways may be involved in initial development of endometriosis.

RON, a Tyrosine Kinase Receptor Involved in Tumor Progression and Metastasis

Tyrosine kinase receptors mediate many critical cellular functions that contribute to tumor progression and metastasis and thus are potential targets for molecular-based cancer therapy. As has been found for many receptor tyrosine kinases, RON (recepteur d'origine nantais) and its ligand, macrophage-stimulating protein, have recently been implicated in the progression and metastasis of tumors. In in vitro experiments using colon and breast cancer cell lines, overexpression of RON led to increased invasion and migration of cancer cells and prevented apoptosis and anoikis. In addition, transgenic mice engineered to overexpress RON in the lung epithelium developed multiple pulmonary tumors, suggesting a role for RON in tumorigenesis. In human cancer specimens, increased RON expression has been demonstrated in colon, breast, ovarian, and lung tumors. Therefore, therapies designed to inhibit RON activation may hinder critical tumor survival mechanisms and play a role in the treatment of advanced disease.

The macrophage stimulating protein/RON system: a potential novel target for prevention and treatment of endometriosis

Our recent DNA microarray analysis using tissue obtained by laser capture microdissection (LCM) identified up-regulation of RON (a tyrosine kinase receptor) during the late secretory phase in eutopic endometrial epithelial cells from patients with deep endometriosis compared with control endometrium from women with macroscopically normal pelvic cavities. In the present study, we further investigated mRNA expression of RON and its ligand, macrophage stimulating protein (MSP), in deep endometriotic lesions, eutopic endometrium from patients with deep endometriosis and control endometrium by using LCM and quantitative real-time RT-PCR. MSP mRNA expression in endometrial epithelial cells was significantly up-regulated in endometriosis patients during the late secretory phase compared with expression in controls. Furthermore, we detected up-regulation of MSP mRNA in ectopic endometrial epithelial cells compared with matched eutopic endometrial epithelial cells within the same patients regardless of the menstrual phase. MSP has an intrinsically dual functional nature through its receptor RON-it is a trophic cytokine preventing apoptosis and a scatter factor promoting invasion, both of which may be necessary for the initial development and growth of endometriosis. The present findings suggest that the MSP/RON system may be involved in the pathophysiology of endometriosis.

Integrin alpha6beta4-erbB2 complex inhibits haptotaxis by up-regulating E-cadherin cell-cell junctions in keratinocytes

Keratinocyte integrins alpha6beta4 and alpha3beta1 bind laminin-5, a component of basement membranes. We previously demonstrated that in keratinocytes, haptotactic migration on laminin-5 was stimulated by anti-beta1 integrin-activating antibody TS2/16, whereas antibodies to alpha6 and beta4, respectively, blocked TS2/16-induced, alpha3beta1-dependent migration. Moreover, alpha6beta4-associated haptotaxis inhibition was linked to a phosphatidylinositol 3-kinase (PI3K) pathway and required erbB2 activation. erbB2, the ligand-less member of the epidermal growth factor receptor family, was shown to form a complex with the hemidesmosomal integrin alpha6beta4. Here, we demonstrate that alpha6beta4 inhibitory effects on haptotaxis are abolished by an anti-E-cadherin antibody, which interferes with cell-cell adhesion. Furthermore, antibodies to alpha6 and beta4 stimulated adhesion to an E-cadherin-Fc recombinant protein. In addition, anti-alpha6/beta4 antibodies increased colony size in plated cells, stimulated cell-cell aggregation, and up-regulated E-cadherin localization to cell-cell contacts. These effects were abolished when erbB2 or PI3K were blocked. These results indicate that stimulation of alpha6beta4 increases E-cadherin-mediated cell-cell adhesion and that this mechanism depends on erbB2 activation. The molecule that links alpha6beta4 with E-cadherin may be the small GTPase cdc42, an effector of PI3K, because dominant-negative cdc42 abolished the inhibitory effect of anti-alpha6/beta4 antibodies and increased basal migration, whereas constitutively active cdc42 prevented the TS2/16-induced increase in haptotaxis. These findings suggest a model whereby alpha6beta4 can augment cell-cell adhesion and slow down haptotaxis over laminin-5 and point to the alpha6beta4-erbB2 heterodimer as an important signaling complex for the formation of cohesive keratinocyte layers.

Catalytically inactive human cathepsin D triggers fibroblast invasive growth

The aspartyl-protease cathepsin D (cath-D) is overexpressed and hypersecreted by epithelial breast cancer cells and stimulates their proliferation. As tumor epithelial-fibroblast cell interactions are important events in cancer progression, we investigated whether cath-D overexpression affects also fibroblast behavior. We demonstrate a requirement of cath-D for fibroblast invasive growth using a three-dimensional (3D) coculture assay with cancer cells secreting or not pro-cath-D. Ectopic expression of cath-D in cath-D-deficient fibroblasts stimulates 3D outgrowth that is associated with a significant increase in fibroblast proliferation, survival, motility, and invasive capacity, accompanied by activation of the ras-MAPK pathway. Interestingly, all these stimulatory effects on fibroblasts are independent of cath-D proteolytic activity. Finally, we show that pro-cath-D secreted by cancer cells is captured by fibroblasts and partially mimics effects of transfected cath-D. We conclude that cath-D is crucial for fibroblast invasive outgrowth and could act as a key paracrine communicator between cancer and stromal cells, independently of its catalytic activity.

Both Sp1 and Smad participate in mediating TGF-β1-induced HGF receptor expression in renal epithelial cells

Hepatocyte growth factor (HGF) receptor is a transmembrane receptor tyrosine kinase encoded by the c-met protooncogene. In this study, we demonstrated that c-met expression was upregulated in the kidney after obstructive injury in mice. Because the pattern of c-met induction was closely correlated with transforming growth factor-β1 (TGF-β1) expression in vivo, we further investigated the regulation of c-met expression in renal tubular epithelial (HKC) cells by TGF-β1 in vitro. Real-time RT-PCR and Northern and Western blot analyses revealed that TGF-β1 significantly induced c-met expression in HKC cells, which primarily took place at the gene transcriptional level. Overexpression of inhibitory Smad7 completely abolished c-met induction, indicating its dependence on Smad signaling. Interestingly, TGF-β1-induced c-met expression was also contingent on a functional Sp1, as ablation of Sp1 binding with mithramycin A abrogated c-met induction in HKC cells. Transfection and sequence analysis identified a cis-acting TGF-β1-responsive region in the c-met promoter, in which resided a putative Smad-binding element (SBE) and an adjacent Sp1 site. TGF-β1 not only induced Smad binding to the SBE/Sp1 sites in the c-met promoter, but also enhanced the binding of Sp proteins. Furthermore, Sp1 could form a complex with Smads in a TGF-β1-dependent fashion. These results suggest a novel regulatory mechanism controlling c-met expression by TGF-β1 in renal epithelial cells, in which both Smad and Sp proteins participate and cooperate in activating c-met gene transcription.

Novel interaction partners of the TPR/MET tyrosine kinase

A large variety of biological processes is mediated by stimulation of the receptor tyrosine kinase MET. Screening a mouse embryo cDNA library, we were able to identify several novel, putative intracellular TPR/MET-substrates: SNAPIN, DCOHM, VAV-1, Sorting nexin 2, Death associated protein kinase 3, SMC-1, Centromeric protein C, and hTID-1. Interactions as identified by yeast two-hybrid analysis were validated in vitro and in vivo by mammalian two-hybrid studies, a far-western assay and coimmunoprecipitation. Participation in apoptosis-regulating mechanisms through interaction with DAPK-3 and cell cycle control via binding to nuclear proteins such as CENPC and SMC-1 are possible new aspects of intracellular MET signaling.

Hepatocyte growth factor/c-met signaling pathway is required for efficient liver regeneration and repair

Hepatocyte growth factor/scatter factor c-met signaling pathway is of central importance during development as well as in tumorigenesis. Because homozygous null mice for either hgf/sf or c-met die in utero, we used Cre/loxP-mediated gene targeting to investigate the function of c-met specifically in the adult liver. Loss of c-met appeared not to be detrimental to hepatocyte function under physiological conditions. Nonetheless, the adaptive responses of the liver to injury were dramatically affected. Mice lacking c-met gene in hepatocytes were hypersensitive to Fas-induced apoptosis. When injected with a low dose of anti-Fas antibody, the majority of these mice died from massive apoptosis and hemorrhagic necrosis, whereas all wild-type mice survived with signs of minor injury. After a challenge with a single necrogenic dose of CCl4, c-met conditional knockout mice exhibited impaired recovery from centrolobular lesions rather than a deficit in hepatocyte proliferation. The delayed healing was associated with a persistent inflammatory reaction, over-production of osteopontin, early and prominent dystrophic calcification, and impaired hepatocyte scattering/migration into diseased areas. These studies provide direct genetic evidence in support of the critical role of c-met in efficient liver regeneration and suggest that disruption of c-met affects primarily hepatocyte survival and tissue remodeling.

Collaborative activities of macrophage-stimulating protein and transforming growth factor-beta1 in induction of epithelial to mesenchymal transition: roles of the RON receptor tyrosine kinase

Epithelial to mesenchymal transition (EMT) is a process occurring during embryonic development and cancer progression. Using recepteur d'origine nantais (RON)-expressing epithelial cells as a model, we showed that RON activation causes spindle-shaped morphology with increased cell motilities. These activities resemble those observed in EMT induced by transforming growth factor (TGF)-beta1 or by Ras-Raf signaling. By immunofluorescent and Western blot analyses, we found that constitutive RON expression results in diminished expression of E-cadherin, redistribution of beta-catenin, reorganization of actin cytoskeleton, and increased expression of vimentin, a mesenchymal filament. RON expression is also essential for TGF-beta1-induced expression of alpha-smooth muscle actin (alpha-SMA), a specialized mesenchymal marker. In the study of signaling pathways responsible for RON-mediated EMT, it was found that PD98059, a MAP kinase inhibitor, blocks the collaborative activities of RON and TGF-beta1 in induction of alpha-SMA expression and restores epithelial cells to their original morphology. Moreover, we showed that RON expression increases Smad2 gene promoter activities and protein expression, which significantly lowers TGF-beta1 threshold for EMT induction. These results suggest that persistent RON expression and activation cause the loss of epithelial phenotypes. These changes, collaborating with TGF-beta1 signaling, could play a critical role in epithelial transdifferentiation towards invasiveness and metastasis of certain cancers.

The role of Ras superfamily proteins in bladder cancer progression

PURPOSE

The prognosis of patients with bladder cancer is strongly dependent on whether the lesion is superficial or invasive at initial presentation. In addition, a significant fraction of patients presenting with superficial disease have invasive tumor during followup. Understanding how superficial bladder cancer progresses to invasive forms of the disease is of paramount importance for early diagnosis and successful treatment. Molecular mechanisms underlying bladder cancer progression are being elucidated. We reviewed the roles that members of the Ras superfamily of monomeric G proteins, an important class of cellular regulator, have in bladder cancer and its progression.

MATERIALS AND METHODS

We performed MEDLINE searches focusing on members of the Ras superfamily of monomeric G proteins and their involvement in transitional cell carcinoma, which is the most common form of bladder cancer. General involvement in cancer of key superfamily members, focusing on mechanisms and downstream pathways, was also reviewed through MEDLINE and manual bibliographic searches.

RESULTS

With more than 100 members in humans the Ras superfamily is a diverse group of monomeric G proteins. These proteins regulate many cellular processes, such as cell cycle progression, actin cytoskeletal dynamics and membrane traffic. Members of the Ras and Rho family are also known to be involved in human cancer through mutation, over expression and dysregulation. In this review we focus on bladder cancer. In particular we focus on how H-Ras, RalA/B and RhoGDI2, a regulator of Rho family members, participate in bladder cancer progression and how their participation may be related to other molecules associated with bladder cancer progression, such as epidermal growth factor receptor, p53 and PTEN (phosphatase and tensin homologue deleted on chromosome 10).

CONCLUSIONS

The findings discussed offer the hopeful possibility that signaling pathways mediated by Ras superfamily members may offer new opportunities for diagnostic and therapeutic interventions in bladder cancer.

Oncogenic and invasive potentials of human macrophage-stimulating protein receptor, the RON receptor tyrosine kinase

The product of the RON (recepteur d'origine nantais) gene belongs to the MET proto-oncogene family, a distinct subfamily of receptor tyrosine kinases. The ligand of RON was identified as macrophage-stimulating protein (MSP), a member of the plasminogen-related growth factor family. RON is mainly expressed in cells of epithelial origin and is required for embryonic development. In vitro RON activation results in epithelial cell dissociation, migration and matrix invasion, suggesting that RON might be involved in the pathogenesis of certain epithelial cancers in vivo. Indeed, recent studies have shown that RON expression is significantly altered in several primary human cancers, including those of the breast and colon. Truncation of the RON protein has also been found in primary tumors from the gastrointestinal tract. These alterations lead to constitutive activation of RON that causes cell transformation in vitro, induces neoplasm formation in athymic nude mice, and promotes tumor metastasis into the lung. Studies employing transgenic models further demonstrated that over-expression of RON in lung epithelial cells results in multiple tumor formation with features of large cell undifferentiated carcinoma. The oncogenic activities of RON are mediated by RON-transduced signals that promote unbalanced cell growth and transformation leading to tumor development. Thus, abnormal accumulation and activation of RON could play a critical role in vivo in the progression of certain malignant human epithelial cancers.

Upregulated expression of Ezrin and invasive phenotype in malignantly transformed esophageal epithelial cells

AIM: To investigate the correlation between ezrin expression and invasive phenotype formation in malignantly transformed esophageal epithelial cells.

METHODS: The experimental cell line employed in the present study was originated form the progressive induction of a human embryonic esophageal epithelial cell line (SHEE) by the E6E7 genes of human papillomavirus (HPV) type 18. The cells at the 35^th passage after induction called SHEEIMM were in a state of immortalized phase and used as the control, while that of the 85^th passage denominated as SHEEMT represented the status of cells that were malignantly transformed. The expression changes of ezrin and its mRNA in both cell passages were respectively analyzed by RT-PCR and Western blot. Invasive phenotype was assessed in vivo by inoculating these cells into the severe combined immunodeficient (SCID) mice via subcutaneous and intraperitoneal injection, and in vitro by inoculating them on the surface of the amnion membranes, which then was determined by light microscopy and scanning electron microscopy.

RESULTS: Upregulated expression of ezrin protein and its mRNA was observed in SHEEMT compared with that in SHEEIMM cells. The SHEEMT cells inoculated in SCID mice were observed forming tumor masses in both visceral organs and soft tissues in a period of 40 d with a special propensity to invading mesentery and pancreas, but did not exhibit hepatic metastases. Pathologically, these tumor cells harboring larger nucleus, nucleolus and less cytoplasm could infiltrate and destroy adjacent tissues. In the in vitro study, the inoculated SHEEMT cells could grow in cluster on the amniotic epithelial surface and intrude into the amniotic stroma. In contrast, unrestricted growth and invasiveness were not found in SHEEIMM cells in both in vivo and in vitro experiment.

CONCLUSION: The upregulated ezrin expression is one of the important factors that are possibly associated with the invasive phenotype formation in malignantly transformed esophageal epithelial cells.

Cis-acting elements in the hepatocyte growth factor-like protein gene regulate kidney and liver-specific expression in mice

Previous studies from our laboratory demonstrated that the hepatocyte-specific transcriptional activity of the hepatocyte growth factor-like protein/macrophage stimulating protein (HGFL) promoter is modulated in HepG2 cells by the first 135 base pairs (bp) upstream of the HGFL transcriptional start site. Gel mobility shift and transactivation assays demonstrated that hepatocyte nuclear factor-4 (HNF-4) binds to this region and is responsible, in part, for the liver-specific expression of this gene in HepG2 cells. In an attempt to understand the in vivo mechanism regulating the expression of HGFL, a series of transgenic mice were generated that contained four different regions upstream of the HGFL promoter attached to the coding sequences for chloramphenicol acetyltransferase (CAT). Interestingly, upstream promoter sequences, containing as little as 104 bp upstream of the translational start site, were able to drive reporter expression and protein production specifically in kidney and liver tissue. Strikingly, when the first exon and intron of the HGFL gene was inserted downstream of the 135 bp promoter element, only liver-specific expression was observed. These studies indicate that short sequences upstream of HGFL can drive efficient expression in kidney and liver tissue, and that sequences in the first intron of the HGFL gene contain regulatory elements that direct kidney-specific transcriptional repression in vivo and aid in the proper recapitulation of HGFL expression in mice.

Differential regulation of thalamic and cortical axonal growth by hepatocyte growth factor/scatter factor

The initial axonal projections between the cerebral cortex and thalamus are established during embryogenesis. Chemoattractants and repellents are thought to provide specific guidance cues for directional growth of these pathways. Hepatocyte growth factor/scatter factor (HGF/SF) serves as an attractant for developing motor neurons, and its distribution in embryonic pallidum, pallium and thalamus suggests a similar role in forebrain development. We examined the effectiveness of HGF/SF in regulating thalamic and cortical neuronal growth using in vitro assays. HGF/SF increased neurite outgrowth of thalamic, but not cortical neurons, grown in dissociated cultures or as explants. HGF/SF also exhibited a chemoattractant property for thalamic axons, promoting the extension of neurites towards an HGF/SF source. These experiments demonstrate HGF/SF has the capacity to selectively direct thalamocortical projections into an intermediate target, the pallidum, and eventually to their final cortical destination.

Altered expression of the RON receptor tyrosine kinase in primary human colorectal adenocarcinomas: generation of different splicing RON variants and their oncogenic potential

The RON receptor tyrosine kinase is a member of the MET proto-oncogene family that has been implicated in regulating motile-invasive phenotypes in certain types of epithelial cancers. The purpose of this study was to determine if RON expression is altered in primary human colorectal adenocarcinomas. Results from immunohistochemical staining showed that RON is highly expressed in the majority of colorectal adenocarcinomas (29/49 cases). Accumulated RON is also constitutively active with autophosphorylation in tyrosine residues. Moreover, three splicing variants of RON, namely RONdelta165, RONdelta160, and RONdelta155 were detected and cloned from two primary colon cancer samples. These RON variants were generated by deletions in different regions in extracellular domains of the RON beta chain. Functional studies showed that expression of RONdelta160 or RONdelta155 in Martin-Darby canine kidney cells resulted in increased cell dissociation (scatter-like activity). RON variants, RONdelta160 and RONdelta155, also exerted the ability to induce multiple focus formation and sustain anchorage-independent growth of transfected NIH3T3 cells. Moreover, NIH3T3 cells expressing RONdelta160 or RONdelta155 formed tumors in athymic nude mice and colonized in the lungs. These data suggest that RON expression is altered in certain primary colon cancers. Abnormal accumulation of RON variants may play a role in the progression of certain colorectal cancers in vivo.

Urokinase, a constitutive component of the inflamed synovial fluid, induces arthritis

Urokinase plasminogen activator (uPA) is an important regulator of fibrinolysis in synovial fluid. An increase of uPA activity and expression of its receptor have been reported in joints of patients with rheumatoid arthritis (RA). The aim of the present study was to assess the arthritogenic capacity of uPA and the mechanisms by which this effect is mediated. uPA was injected into the knee joints of healthy mice, and morphological signs of arthritis were assessed 4 days after the injection. The prerequisite of different leukocyte populations for the development of uPA-triggered arthritis was assessed by selective cell depletion. The inflammatory capacity of uPA was assessed in vitro. Finally, levels of uPA were measured in 67 paired blood and synovial fluid samples from RA patients. The synovial fluid from RA patients displayed higher levels of uPA compared with blood samples. Morphological signs of arthritis were found in 72% of uPA-injected joints compared with in only 18% of joints injected with PBS (P < 0.05). Synovitis was characterised by infiltration of CD4-Mac-1+ mononuclear cells, by the formation of pannus and by occasional cartilage destruction. The absence of monocytes and lymphocytes diminished the frequency of synovitis (P < 0.01), indicating an arthritogenic role of both these leukocyte populations. Synthetic uPA inhibitor downregulated the incidence of uPA-triggered arthritis by 50%. uPA induced arthritis, stimulating the release of proinflammatory cytokines IL-6, IL-1beta and tumour necrosis factor alpha. Accumulation of uPA locally in the joint cavity is a typical finding in erosive RA. uPA exerts potent arthritogenic properties and thus may be viewed as one of the essential mediators of joint inflammation.

Prostate tumor-stroma interaction: molecular mechanisms and opportunities for therapeutic targeting

Maintenance of cell and tissue homeostasis is dependent upon the dynamic balance of cell proliferation, differentiation, and apoptosis through interactions between cells and their microenvironment. The unique prostatic cellular phenotypes are induced and maintained by interaction between epithelium and adjacent stroma through intimate intercellular signaling pathways. In this article, we summarize current advances in the tumor-stroma interaction and its biologic and therapeutic implications. We specifically emphasize current studies of the possible factors driving the "vicious cycle" between stroma and emerging prostate tumor epithelial cells that may be responsible for carcinogenesis and metastasis to bone. Stroma responds both genotypically and phenotypically to tumor epithelium upon co-culture under 3-D conditions. Likewise, the emerging carcinoma responds to stromal signals that drive progression to malignancy. A vicious cycle mediated by soluble and insoluble molecules secreted by tumor cells and stroma appear be the critical factors supporting and sustaining tumor colonization in bone. Co-targeting tumor and stroma with therapeutic agents has yielded promising results both in pre-clinical models of prostate cancer and bony metastasis and in clinical trials of patients treated with a dual tumor and stroma targeting strategies. In conclusion, understanding and targeting the interaction of the tumor and its stromal microenvironmant may improve the prognosis, reduce the suffering and increase the survival of patients with advanced cancer metastasis.

Elevated levels of IGF-1 receptor convey invasive and metastatic capability in a mouse model of pancreatic islet tumorigenesis

In a prototypical model of multistage tumorigenesis involving pancreatic islets in RIP1-Tag2 transgenic mice, activation of insulin-like growth factor II (IGF-II) was previously shown to serve as a survival factor that inhibited apoptosis. Now IGF-1R, the receptor tyrosine kinase for IGF-II, has been found to be variably upregulated, first uniformly in dysplastic and angiogenic progenitors and then focally at the margins and in invasive regions of carcinomas. When the levels of IGF-1R were forcibly elevated throughout islet tumorigenesis, progression was accelerated at all stages in the pathway, although apoptosis was not differentially suppressed. Notably, encapsulated tumors were absent; instead, invasive carcinomas with downregulated E-cadherin were prevalent, and the majority of mice had local lymph node metastasis.

Role of the hepatocyte growth factor receptor, c-Met, in oncogenesis and potential for therapeutic inhibition

Receptor tyrosine kinases have become important therapeutic targets for anti-neoplastic molecularly targeted therapies. c-Met is a receptor tyrosine kinase shown to be over-expressed and mutated in a variety of malignancies. Stimulation of c-Met via its ligand hepatocyte growth factor also known as scatter factor (HGF/SF), leads to a plethora of biological and biochemical effects in the cell. There has been considerable knowledge gained on the role of c-Met-HGF/SF axis in normal and malignant cells. This review summarizes the structure of c-Met and HGF/SF and their family members. Since there are known mutations of c-Met in solid tumors, particularly in papillary renal cell carcinoma, we have summarized the various mutations and over-expression of c-Met known thus far. Stimulation of c-Met can lead to scattering, angiogenesis, proliferation, enhanced cell motility, invasion, and eventual metastasis. The biological functions altered by c-Met are quite unique and described in detail. Along with biological functions, various signal transduction pathways, including the cytoskeleton are altered with the activation of c-Met-HGF/SF loop. We have recently shown the phosphorylation of focal adhesion proteins, such as paxillin and p125FAK in response to c-Met stimulation in lung cancer cells, and this is detailed here. Finally, c-Met when mutated or over-expressed in malignant cells serves as an important therapeutic target and the most recent data in terms of inhibition of c-Met and downstream signal transduction pathways is summarized.

A mechanism of cell survival: sequestration of Fas by the HGF receptor Met

Death receptors such as Fas are present in a variety of organs including liver and play an important role in homeostasis. What prevents these harmful receptors from forming homooligomers, clustering, and initiating the apoptotic pathway is not known. Here, we report the discovery of a cell survival mechanism by which Met, a growth factor receptor tyrosine kinase, directly binds to and sequesters the death receptor Fas in hepatocytes. This interaction prevents Fas self-aggregation and Fas ligand binding, thus inhibiting Fas activation and apoptosis. Our results describe a direct link between growth factor tyrosine kinase receptors and death receptors to establish a novel paradigm in growth regulation.

Role of myofibroblasts at the invasion front

Tumor progression occurs within a microecosystem, where cancer cells and myofibroblasts exchange proteinases and cytokines that promote growth directly through stimulation of proliferation and survival, as well as invasion through local proteolysis of the extracellular matrix and stimulation of motility. Myofibroblasts maintain the capacity of fibroblasts to induce differentiation. Fibroblasts are the main source of tumor-associated myofibroblasts. The transition to myofibroblasts also occurs in noncancerous situations. This transition is modulated by mechanical stress and cytokines, amongst which transforming growth factor-beta. The cross-talk between cancer cells and myofibroblasts illustrates the microecosystem of tumor invasion. In order to consider myofibroblasts as a possibly new target for cancer therapy, further characterization of the molecular cross-talk between myofibroblasts and cancer cells is required.

Inhibition of lung cancer cell growth and induction of apoptosis after reexpression of 3p21.3 candidate tumor suppressor gene SEMA3B

Semaphorins SEMA3B and its homologue SEMA3F are 3p21.3 candidate tumor suppressor genes (TSGs), the expression of which is frequently lost in lung cancers. To test the TSG candidacy of SEMA3B and SEMA3F, we transfected them into lung cancer NCI-H1299 cells, which do not express either gene. Colony formation of H1299 cells was reduced 90% after transfection with wild-type SEMA3B compared with the control vector. By contrast, only 30-40% reduction in colony formation was seen after the transfection of SEMA3F or SEMA3B variants carrying lung cancer-associated single amino acid missense mutations. H1299 cells transfected with wild-type but not mutant SEMA3B underwent apoptosis. We found that lung cancers (n = 34) always express the neuropilin-1 receptor for secreted semaphorins, whereas 82% expressed the neuropilin-2 receptor. Because SEMA3B and SEMA3F are secreted proteins, we tested conditioned medium from COS-7 cells transfected with SEMA3B and SEMA3F and found that medium from wild-type SEMA3B transfectants reduced the growth of several lung cancer lines 30-90%, whereas SEMA3B mutants or SEMA3F had little effect in the same assay. Sequencing of sodium bisulfite-treated DNA showed dense methylation of CpG sites in the SEMA3B 5' region of lung cancers not expressing SEMA3B but no methylation in SEMA3B-expressing tumors. These results are consistent with SEMA3B functioning as a TSG, the expression of which is inactivated frequently in lung cancers by allele loss and promoter region methylation.

The Role of Semaphorins in Lung Cancer

The semaphorins are a family of secreted, transmembrane, and membrane-associated proteins initially identified as causing the repulsion of nerve growth cone guidance. However, subsequent experiments have demonstrated that they can induce retraction in non-neural cells and affect the development of non-neural organs. Two related secreted semaphorins, SEMA3F and SEMA3B, were isolated from a recurrent 3p21.3 homozygous deletion region in small-cell lung cancer (SCLC) cell lines. Moreover, a functionally related molecule, Roundabout/DUTT1, was identified as the target of a more proximal chromosome 3p deletion also involving SCLCs. Based on current data, it is likely that the loss of these semaphorins or Roundabout may affect cell migration, metastasis, and apoptosis. In addition, receptors for the secreted semaphorins, neuropilin-1 and neuropilin-2, have been shown to function as coreceptors for a subset of vascular endothelial growth factor (VEGF) isoforms and related growth factors. Since semaphorins and VEGF bind antagonistically to neuropilins, their loss is likely to facilitate angiogenesis. In lung cancer specimens, antibody staining against SEMA3F has been shown to correlate with stage and histologic subtypes with more aggressive tumors showing increased VEGF and decreased SEMA3F staining. This review is focused on a basic understanding of these pathways with an emphasis on their role in lung cancer.

Differential requirement of the last C-terminal tail of Met receptor for cell transformation and invasiveness

Biological responses to Hepatocyte Growth Factor are mediated by the tyrosine kinase receptor encoded by the Met oncogene. Under physiological conditions, Met triggers a multi-step genetic program called 'invasive growth' including cell-dissociation, invasion of extracellular matrices and growth. When constitutively activated, Met can induce cell transformation and metastasis. Phosphorylation of two docking tyrosines in the receptor tail is essential for all biological responses. To investigate the role of the C-terminal part of Met, we have generated mutants lacking either the last 26 or 47 amino acids. As expected, mutants lacking the docking sites fail to mediate cell transformation and invasion. Interestingly, while Met Delta26 can mediate invasion, its transforming ability is severely impaired. Moreover, the lack of the last 26 amino acids strongly reduces Met ability to phosphorylate substrates in vitro and in vivo. These data indicate that the last 26 amino acids are required to confer the kinase its full enzymatic activity, which is critical for cell transformation but dispensable for invasive properties. Finally, we also show that up-regulation of Met enzymatic activity by insertion of a point mutation in the kinase domain (M1250T) overcomes the regulatory role played by the last 26 amino acids of the tail. It is concluded that the C-terminal domain of Met is crucial not only for recruitment of transducers but also for regulation of receptor enzymatic activity.

Scatter factors and invasive growth

Scatter factors are unequivocal signals governing a genetic program that includes cell detachment, repulsion, protection from apoptosis, invasiveness of extracellular matrices and proliferation. This pleiomorphic response is defined as 'invasive growth'. Under physiological conditions, it leads to morphogenic cell movements through the matrix, and--primarily--to ordered building of epithelial tubules. Dysfunctions in invasive growth cause enhanced proliferation, uncontrolled migration into surrounding tissues, and failure to differentiate, events that foster tumour growth and invasiveness. Scatter factors act through tyrosine kinase receptors that belong to the Met oncogene family. Here we discuss how alterations of these receptors or of their signal transduction pathways are responsible for cancer onset and progression towards metastasis.

The transcriptional signature of dioxin in human hepatoma HepG2 cells

We have used a high density microarray hybridization approach to characterize the transcriptional response of human hepatoma HepG2 cells to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). We find that exposure to 10 nM TCDD for 8 hr alters by at least a factor of 2.1 the expression of 310 known genes and of an equivalent number of expressed sequence tags. Treatment with TCDD in the presence of 20 microg/mL of cycloheximide blocked the effect on 202 of these genes, allowing us to distinguish between primary effects of TCDD exposure, which take place whether cycloheximide is present or not, and secondary effects, which are blocked by inhibition of protein synthesis. Of the 310 known genes affected by TCDD, 30 are up-regulated and 78 are down-regulated regardless of cycloheximide treatment, and 84 are up-regulated and 118 are down-regulated only when protein synthesis is not inhibited. Functional clustering of genes regulated by TCDD reveals many potential physiological interactions that might shed light on the multiple biological effects of this compound. Our results, however, suggest that arriving at a sound understanding of the molecular mechanisms governing the biological outcome of TCDD exposure promises to be orders of magnitude more complicated than might have been previously imagined.