A Novel HGF/SF Receptor (MET) Agonist Transiently Delays the Disease Progression in an Amyotrophic Lateral Sclerosis Mouse Model by Promoting Neuronal Survival and Dampening the Immune Dysregulation.

Amyotrophic Lateral Sclerosis (ALS) is a fatal neurodegenerative disease with no effective treatment. The Hepatocyte Growth Factor/Scatter Factor (HGF/SF), through its receptor MET, is one of the most potent survival-promoting factors for motor neurons (MN) and is known as a modulator of immune cell function. We recently developed a novel recombinant MET agonist optimized for therapy, designated K1K1. K1K1 was ten times more potent than HGF/SF in preventing MN loss in an in vitro model of ALS. Treatments with K1K1 delayed the onset of muscular impairment and reduced MN loss and skeletal muscle denervation of superoxide dismutase 1 G93A (SOD1G93A) mice. This effect was associated with increased levels of phospho-extracellular signal-related kinase (pERK) in the spinal cord and sciatic nerves and the activation of non-myelinating Schwann cells. Moreover, reduced activated microglia and astroglia, lower T cells infiltration and increased interleukin 4 (IL4) levels were found in the lumbar spinal cord of K1K1 treated mice. K1K1 treatment also prevented the infiltration of T cells in skeletal muscle of SOD1G93A mice. All these protective effects were lost on long-term treatment suggesting a mechanism of drug tolerance. These data provide a rational justification for further exploring the long-term loss of K1K1 efficacy in the perspective of providing a potential treatment for ALS.

Crystal structure of an engineered YopM-InlB hybrid protein.

BACKGROUND: The multi-domain protein InlB (internalin B) from Listeria monocytogenes is an agonist of the human receptor tyrosine kinase MET. Only the internalin domain directly interacts with MET. The internalin domain consists of seven central leucine-rich repeats (LRRs) flanked by an N-terminal helical cap domain and a C-terminal immunoglobulin-like structure. A potential function of the N-terminal cap in receptor binding could so far not be demonstrated by deleting the cap, since the cap is also implicated in nucleating folding of the LRR domain. RESULTS: We generated an InlB variant (YopM-InlB) in which the InlB cap domain was replaced by the unrelated N-terminal capping structure of the LRR protein YopM from Yersinia enterocolitica. The crystal structure of the engineered protein shows that it folds properly. Because the first LRR is structurally closely linked to the cap domain, we exchanged LRR1 along with the cap domain. This resulted in unexpected structural changes extending to LRR2 and LRR3, which are deeply involved in MET binding. As a consequence, the binding of YopM-InlB to MET was substantially weaker than that of wild type InlB. The engineered protein was about one order of magnitude less active in colony scatter assays than wild type InlB. CONCLUSIONS: We obtained a well-behaved InlB variant with an altered N-terminal capping structure through protein design. The reduced affinity for MET precludes a straightforward interpretation of the results from cell-based assays. Still, the engineered hybrid protein induced cell scatter, suggesting that the cap is required for folding and stability of InlB but is not essential for interactions that assemble the signalling-active receptor complex. The cap swap approach described here is clearly applicable to other L. monocytogenes internalins and other LRR proteins such as YopM and may yield useful structure/function correlates within this protein family.

Protein engineered variants of hepatocyte growth factor/scatter factor promote proliferation of primary human hepatocytes and in rodent liver.

BACKGROUND & AIMS: Hepatocyte growth factor/scatter factor (HGF/SF) stimulates hepatocyte DNA synthesis and protects against apoptosis; in vivo it promotes liver regeneration and reduces fibrosis. However, its therapeutic value is limited by its complex domain structure, high cost of production, instability, and poor tissue penetration due to sequestration by heparin sulfate proteoglycans (HSPGs). METHODS: Using protein engineering techniques, we created a full-length form of HGF/SF (called HP21) and a form of the small, naturally occurring HGF/SF fragment, NK1 (called 1K1), which have reduced affinity for HSPG. We characterized the stability and proliferative and anti-apoptotic effects of these variants in primary human hepatocytes and in rodents. RESULTS: Analytical ultracentrifugation showed that 1K1 and NK1 were more stable than the native, full-length protein. All 4 forms of HGF/SF induced similar levels of DNA synthesis in human hepatocytes; 1K1 and NK1 required heparin, an HSPG analogue, for full agonistic activity. All the proteins reduced levels of Fas ligand-mediated apoptosis, reducing the activity of caspase-3/7 and cleavage of poly(adenosine diphosphate-ribose) polymerase. 1K1 was more active than NK1 in rodents; in healthy mice, 1K1 significantly increased hepatocyte DNA synthesis, and in mice receiving carbon tetrachloride, it reduced fibrosis. In rats, after 70% partial hepatectomy, daily administration of 1K1 for 5 days significantly increased liver mass and the bromodeoxyuridine labeling index compared with mice given NK1. CONCLUSIONS: 1K1, an engineered form of the small, naturally occurring HGF/SF fragment NK1, has reduced affinity for HSPG and exerts proliferative and antiapoptotic effects in cultured hepatocytes. In rodents, 1K1 has antifibrotic effects and promotes liver regeneration. The protein has better stability and is easier to produce than HGF/SF and might be developed as a therapeutic for acute and chronic liver disease.

Structural basis for agonism and antagonism of hepatocyte growth factor.

Hepatocyte growth factor (HGF) is an activating ligand of the Met receptor tyrosine kinase, whose activity is essential for normal tissue development and organ regeneration but abnormal activation of Met has been implicated in growth, invasion, and metastasis of many types of solid tumors. HGF has two natural splice variants, NK1 and NK2, which contain the N-terminal domain (N) and the first kringle (K1) or the first two kringle domains of HGF. NK1, which is a Met agonist, forms a head-to-tail dimer complex in crystal structures and mutations in the NK1 dimer interface convert NK1 to a Met antagonist. In contrast, NK2 is a Met antagonist, capable of inhibiting HGF's activity in cell proliferation without clear mechanism. Here we report the crystal structure of NK2, which forms a "closed" monomeric conformation through interdomain interactions between the N- domain and the second kringle domain (K2). Mutations that were designed to open up the NK2 closed conformation by disrupting the N/K2 interface convert NK2 from a Met antagonist to an agonist. Remarkably, this mutated NK2 agonist can be converted back to an antagonist by a mutation that disrupts the NK1/NK1 dimer interface. These results reveal the molecular determinants that regulate the agonist/antagonist properties of HGF NK2 and provide critical insights into the dimerization mechanism that regulates the Met receptor activation by HGF.

Coupling growth-factor engineering with nanotechnology for therapeutic angiogenesis.

Therapeutic angiogenesis is an emerging paradigm for the management of ischemic pathologies. Proangiogenic Therapy is limited, however, by the current inability to deliver angiogenic factors in a sustained manner at the site of pathology. In this study, we investigated a unique nonglycosylated active fragment of hepatocyte growth factor/scatter factor, 1K1, which acts as a potent angiogenic agent in vitro and in a zebrafish embryo and a murine matrigel implant model. Furthermore, we demonstrate that nanoformulating 1K1 for sustained release temporally alters downstream signaling through the mitogen activated protein kinase pathway, and amplifies the angiogenic outcome. Merging protein engineering and nanotechnology offers exciting possibilities for the treatment of ischemic disease, and furthermore allows the selective targeting of downstream signaling pathways, which translates into discrete phenotypes.

Dimerization of kringle 1 domain from hepatocyte growth factor/scatter factor provides a potent MET receptor agonist.

Hepatocyte growth factor/scatter factor (HGF/SF) and its cognate receptor MET play several essential roles in embryogenesis and regeneration in postnatal life of epithelial organs such as the liver, kidney, lung, and pancreas, prompting a strong interest in harnessing HGF/SF-MET signalling for regeneration of epithelial organs after acute or chronic damage. The limited stability and tissue diffusion of native HGF/SF, however, which reflect the tightly controlled, local mechanism of action of the morphogen, have led to a major search of HGF/SF mimics for therapy. In this work, we describe the rational design, production, and characterization of K1K1, a novel minimal MET agonist consisting of two copies of the kringle 1 domain of HGF/SF in tandem orientation. K1K1 is highly stable and displays biological activities equivalent or superior to native HGF/SF in a variety of in vitro assay systems and in a mouse model of liver disease. These data suggest that this engineered ligand may find wide applications in acute and chronic diseases of the liver and other epithelial organs dependent of MET activation.

Human Nonalcoholic Steatohepatitis on a Chip.

Nonalcoholic steatohepatitis (NASH), an advanced stage of nonalcoholic fatty liver disease (NAFLD), is a rapidly growing and global health problem compounded by the current absence of specific treatments. A major limiting factor in the development of new NASH therapies is the absence of models that capture the unique cellular structure of the liver microenvironment and recapitulate the complexities of NAFLD progression to NASH. Organ-on-a-chip platforms have emerged as a powerful approach to dynamically model diseases and test drugs. Herein, we describe a NASH-on-a-chip platform. Four main types of human primary liver cells (hepatocytes [HCs], Kupffer cells, liver sinusoidal endothelial cells, and hepatic stellate cells [HSCs]) were cocultured under microfluidic dynamics. Our chip-based model successfully recapitulated a functional liver cellular microenvironment with stable albumin and urea secretion for at least 2 weeks. Exposing liver chips to a lipotoxic environment led to gradual development of NASH phenotypic characteristics, including intracellular lipid accumulation, hepatocellular ballooning, HSC activation, and elevation of inflammatory and profibrotic markers. Further, exposure of the chip to elafibranor, a drug under study for the therapy of NASH, inhibited the development of NASH-specific hallmarks, causing an ~8-fold decrease in intracellular lipids, a 3-fold reduction in number of ballooned HCs, a significant reduction in HSC activation, and a significant decrease in the levels of inflammatory and profibrotic markers compared with controls. Conclusion: We have successfully developed a microfluidic NASH-on-a-chip platform that recapitulates the main NASH histologic endpoints in a single chip and that can emerge as a powerful noninvasive, human-relevant, in vitro platform to study disease pathogenesis and develop novel anti-NASH drugs.

Inhibition of the MET Kinase Activity and Cell Growth in MET-Addicted Cancer Cells by Bi-Paratopic Linking.

MET, the product of the c-MET proto-oncogene, and its ligand hepatocyte growth factor/scatter factor (HGF/SF) control survival, proliferation and migration during development and tissue regeneration. HGF/SF-MET signaling is equally crucial for growth and metastasis of a variety of human tumors, but resistance to small-molecule inhibitors of MET kinase develops rapidly and therapeutic antibody targeting remains challenging. We made use of the designed ankyrin repeat protein (DARPin) technology to develop an alternative approach for inhibiting MET. We generated a collection of MET-binding DARPins covering epitopes in the extracellular MET domains and created comprehensive sets of bi-paratopic fusion proteins. This new class of molecules efficiently inhibited MET kinase activity and downstream signaling, caused receptor downregulation and strongly inhibited the proliferation of MET-dependent gastric carcinoma cells carrying MET locus amplifications. MET-specific bi-paratopic DARPins may represent a novel and potent strategy for therapeutic targeting of MET and other receptors, and this study has elucidated their mode of action.

Generation and characterization of novel recombinant anti-hERG1 scFv antibodies for cancer molecular imaging.

Modern molecular imaging techniques have greatly improved tumor detection and post-treatment follow-up of cancer patients. In this context, antibody-based imaging is rapidly becoming the gold standard, since it combines the unique specificity of antibodies with the sensitivity of the different imaging technologies. The aim of this study was to generate and characterize antibodies in single chain Fragment variable (scFv) format directed to an emerging cancer biomarker, the human ether-à-go-go-related gene-1 (hERG1) potassium channel, and to obtain a proof of concept for their potential use for in vivo molecular imaging. The anti-hERG1scFv was generated from a full length monoclonal antibody and then mutagenized, substituting a Phenylalanine residue in the third framework of the VH domain with a Cysteine residue. The resulting scFv-hERG1-Cys showed much higher stability and protein yield, increased affinity and more advantageous binding kinetics, compared to the "native" anti-hERG1scFv. The scFv-hERG1-Cys was hence chosen and characterized: it showed a good binding to the native hERG1 antigen expressed on cells, was stable in serum and displayed a fast pharmacokinetic profile once injected intravenously in nude mice. The calculated half-life was 3.1 hours and no general toxicity or cardiac toxic effects were detected. Finally, the in vivo distribution of an Alexa Fluor 750 conjugated scFv-hERG1-Cys was evaluated both in healthy and tumor-bearing nude mice, showing a good tumor-to-organ ratio, ideal for visualizing hERG1-expressing tumor masses in vivo. In conclusion, the scFv-hERG1-Cys possesses features which make it a suitable tool for application in cancer molecular imaging.

Structural basis of affinity maturation of the TEPC15/Vkappa45.1 anti-2-phenyl-5-oxazolone antibodies.

Affinity maturation is a process that leads to the emergence of more efficient antibodies following initial antigen encounter and represents a key strategy of the adaptive immunity of vertebrate organisms. Earlier and detailed sequence studies of the antibody response to a model antigen, the hapten 2-phenyl-5-oxazolone (phOx), define three different classes of antibodies. Class I antibodies use the V(H)Ox1/V(kappa)Ox1 gene pair and dominate the early stages of the anti-phOx response, class II antibodies use the V(kappa)Ox1 gene but a different V(H) segment and are common in the intermediate stages, and class III antibodies use the TEPC15/V(kappa)45.1 genes and play the greatest role in the late stages. Only the crystal structure of one anti-phOx antibody, the class II NQ10/12.5 Fab fragment, has been described. Here we report the crystal structures of the scFv form of the low and high affinity anti-phOx class III antibodies NQ10/1.12 and NQ16/113.8 complexed with the hapten. The two antibodies differ by nine amino acid substitutions, all located in the V(H) domain. Analysis of the two structures shows that affinity maturation results from an increase in surface complementarity, as a consequence of a finely tuned and highly concerted process chaperoned by the somatic mutations, and implies a more efficient hapten-induced fit in the mature antibody. The data also demonstrate that class III antibodies respond in a completely different way to the architectural problem of binding phOx compared to the class II antibody NQ10/12.5.

The sema domain.

The sema domain was first defined from sequence by Kolodkin and colleagues in the early 1990s, and constitutes the distinctive structural and functional element of semaphorins, their plexin receptors and the receptor tyrosine kinases MET and RON, three protein families with major roles in development, tissue regeneration and cancer. Recently determined crystal structures of two semaphorins (SEMA3A and SEMA4D) and the MET receptor have shown that the sema domain consists of a highly conserved variant form of the seven-blade beta-propeller fold. The structures, however, also suggest differences between these families with respect to the mode of dimerisation and the regions of the domain involved in ligand-receptor interactions. This reflects the considerable plasticity and adaptation of the sema domain in order to meet different binding requirements, properties that may underlie the vast array of ligand-receptor specificities and functions of the semaphorin superfamily.

Characterization and structural determination of a new anti-MET function-blocking antibody with binding epitope distinct from the ligand binding domain.

The growth and motility factor Hepatocyte Growth Factor/Scatter Factor (HGF/SF) and its receptor, the product of the MET proto-oncogene, promote invasion and metastasis of tumor cells and have been considered potential targets for cancer therapy. We generated a new Met-blocking antibody which binds outside the ligand-binding site, and determined the crystal structure of the Fab in complex with its target, which identifies the binding site as the Met Ig1 domain. The antibody, 107_A07, inhibited HGF/SF-induced cell migration and proliferation in vitro and inhibited growth of tumor xenografts in vivo. In biochemical assays, 107_A07 competes with both HGF/SF and its truncated splice variant NK1 for MET binding, despite the location of the antibody epitope on a domain (Ig1) not reported to bind NK1 or HGF/SF. Overlay of the Fab-MET crystal structure with the InternalinB-MET crystal structure shows that the 107_A07 Fab comes into close proximity with the HGF/SF-binding SEMA domain when MET is in the "compact", InternalinB-bound conformation, but not when MET is in the "open" conformation. These findings provide further support for the importance of the "compact" conformation of the MET extracellular domain, and the relevance of this conformation to HGF/SF binding and signaling.

Computer-assisted mass spectrometric analysis of naturally occurring and artificially introduced cross-links in proteins and protein complexes.

A versatile software tool, VIRTUALMSLAB, is presented that can perform advanced complex virtual proteomic experiments with mass spectrometric analyses to assist in the characterization of proteins. The virtual experimental results allow rapid, flexible and convenient exploration of sample preparation strategies and are used to generate MS reference databases that can be matched with the real MS data obtained from the equivalent real experiments. Matches between virtual and acquired data reveal the identity and nature of reaction products that may lead to characterization of post-translational modification patterns, disulfide bond structures, and cross-linking in proteins or protein complexes. The most important unique feature of this program is the ability to perform multistage experiments in any user-defined order, thus allowing the researcher to vary experimental approaches that can be conducted in the laboratory. Several features of VIRTUALMSLAB are demonstrated by mapping both disulfide bonds and artificially introduced protein cross-links. It is shown that chemical cleavage at aspartate residues in the protease resistant RNase A, followed by tryptic digestion can be optimized so that the rigid protein breaks up into MALDI-MS detectable fragments, leaving the disulfide bonds intact. We also show the mapping of a number of chemically introduced cross-links in the NK1 domain of hepatocyte growth factor/scatter factor. The VIRTUALMSLAB program was used to explore the limitation and potential of mass spectrometry for cross-link studies of more complex biological assemblies, showing the value of high performance instruments such as a Fourier transform mass spectrometer. The program is freely available upon request.

Cyclooxygenase-2-selective nonsteroidal anti-inflammatory drugs inhibit hepatocyte growth factor/scatter factor-induced angiogenesis.

Epidemiological studies have indicated a reduced risk of malignancies with the use of nonsteroidal anti-inflammatory drugs (NSAIDs), although the exact mechanisms are debated. NSAIDs inhibit angiogenesis, which is a key step for tumor growth. Hepatocyte growth factor/scatter factor (HGF/SF), a potent and independent angiogenic factor, has been implicated in tumorigenesis, but limited knowledge exists on the potential targets for inhibiting HGF/SF-induced pathological angiogenesis. The current study was designed to elucidate the possible role of cyclooxygenase (COX) downstream of HGF/SF during angiogenesis and to evaluate the potential for harnessing NSAIDs as a therapeutic strategy. Known NSAIDs were classified as COX-1 or COX-2 selective based on their activity in a platelet aggregation experiment. The inhibitors were administered into a polyether polyurethane scaffold implant in mice at the selected doses, and the total neovascularization after the administration of HGF/SF was quantified using a (133)Xenon clearance technique, vessel counts, and immunohistochemistry. Angiogenesis was also quantized into chemoinvasion, migration, proliferation, and tube formation events in vitro, and the effects of the NSAIDs were evaluated on HGF/SF-induced activity of human umbilical vein endothelial cells (HUVECs). HGF/SF accelerated the angiogenic process in the murine implant, and this activity was inhibited by COX-2-selective meloxicam and NS398. The COX-1 inhibitors ketoprofen and SC560 failed to inhibit the HGF/SF-induced angiogenic events in vitro and in vivo. A COX-2 blockade inhibited the HGF/SF-induced chemoinvasion and migration of human umbilical vein endothelial cells, without affecting the proliferative or tubulogenic responses. Western blots revealed the induction COX-2 expression after HGF/SF treatment, and the pharmacological inhibition of COX-2 executed a temporal inhibition of phosphorylation of the mitogen-activated protein kinases. The current study, for the first time, implicates COX-2 as a downstream signal during HGF/SF-induced angiogenesis, temporally impinging on the mitogen-activated protein kinase signaling. However, the mediation is restricted to only the early events of the angiogenic process, emphasizing the chemopreventive role for NSAIDs. Few therapeutic options currently exist for HGF/SF-induced pathological angiogenesis, and the vast knowledge on COX-2 inhibitors can be harnessed to design a newer therapeutic approach.

Developing Antagonists for the Met-HGF/SF Protein-Protein Interaction Using a Fragment-Based Approach.

In many cancers, aberrant activation of the Met receptor tyrosine kinase leads to dissociation of cells from the primary tumor, causing metastasis. Accordingly, Met is a high-profile target for the development of cancer therapies, and progress has been made through development of small molecule kinase inhibitors and antibodies. However, both approaches pose significant challenges with respect to either target specificity (kinase inhibitors) or the cost involved in treating large patient cohorts (antibodies). Here, we use a fragment-based approach in order to target the protein-protein interaction (PPI) between the α-chain of hepatocyte growth factor/scatter factor (HGF/SF; the NK1 fragment) and its high-affinity binding site located on the Met Sema domain. Surface plasmon resonance was used for initial fragment library screening and hits were developed into larger compounds using substructure (similarity) searches. We identified compounds able to interfere with NK1 binding to Met, disrupt Met signaling, and inhibit tumorsphere generation and cell migration. Using molecular docking, we concluded that some of these compounds inhibit the PPI directly, whereas others act indirectly. Our results indicate that chemical fragments can efficiently target the HGF/SF-Met interface and may be used as building blocks for generating biologically active lead compounds. This strategy may have broad application for the development of a new class of Met inhibitors, namely receptor antagonists, and in general for the development of small molecule PPI inhibitors of key therapeutic targets when structural information is not available.

Targeting of mitogen-activated protein kinases and phosphatidylinositol 3 kinase inhibits hepatocyte growth factor/scatter factor-induced angiogenesis.

BACKGROUND: Hepatocyte growth factor/scatter factor (HGF/SF) can sufficiently and independently induce pathophysiological angiogenesis. However, the treatment strategies have mostly been unsuccessful. The present study is the first to evaluate the possible targeting of downstream signals for the inhibition of HGF/SF-induced angiogenesis. METHODS AND RESULTS: In a multichannel scratch assay with human endothelial cells (ECs), HGF/SF induced a strong and prolonged activation of MAPK and cell proliferation that was inhibited by PD98059 and LY294002/wortmannin, selective inhibitors of MAPK and PI3K signaling modules, respectively. Western blotting demonstrated a temporal relation between the activation of the two pathways. Chemical inhibition of the PI3K and MAPK signals inhibited HGF/SF-induced chemoinvasion of ECs in vitro and blocked the HGF/SF-induced neovascularization into a polymer scaffold in vivo, as quantified by vessel counts and the clearance of radioactive 133Xe. CONCLUSIONS: These data indicate that MEK and PI3K inhibitors represent a promising approach to the clinical management of pathological conditions characterized by overt HGF/SF-induced angiogenesis.

Crystal structure of the beta-chain of human hepatocyte growth factor-like/macrophage stimulating protein.

Hepatocyte growth factor like/macrophage stimulating protein (HGFl/MSP) and hepatocyte growth factor/scatter factor (HGF/SF) define a distinct family of vertebrate-specific growth factors structurally related to the blood proteinase precursor plasminogen and with important roles in development and cancer. Although the two proteins share a similar domain structure and mechanism of activation, there are differences between HGFl/MSP and HGF/SF in terms of the contribution of individual domains to receptor binding. Here we present a crystal structure of the 30 kDa beta-chain of human HGFl/MSP, a serine proteinase homology domain containing the high-affinity binding site for the RON receptor. The structure describes at 1.85 Angstrom resolution the region of the domain corresponding to the receptor binding site recently defined in the HGF/SF beta-chain, namely the central cleft harboring the three residues corresponding to the catalytic ones of active proteinases (numbers in brackets define the sequence position according to the standard chymotrypsinogen numbering system) [Gln522 (c57), Gln568 (c102) and Tyr661 (c195)] and an adjacent loop flanking the S1 specificity pocket and containing residues Asn682 (c217) and Arg683 (c218) previously shown to be essential for binding of HGFl/MSP to the RON receptor. The study confirms the concept that the serine proteinase homology domains of HGFl/MSP and HGF/SF bind their receptors in an 'enzyme-substrate' mode, reflecting the common evolutionary origin of the plasminogen-related growth factors and the proteinases of the clotting and fibrinolytic pathways. However, analysis of the intermolecular interactions in the crystal lattice of beta-chain HGFl/MSP fails to show the same contacts seen in the HGF/SF structures and does not support a conserved mode of dimerization of the serine proteinase homology domains of HGFl/MSP and HGF/SF responsible for receptor activation.

A new crystal form of the NK1 splice variant of HGF/SF demonstrates extensive hinge movement and suggests that the NK1 dimer originates by domain swapping.

NK1 is a splice variant of the polypeptide growth factor HGF/SF that consists of the N terminal (N) and first kringle (K) domains and retains receptor binding and signalling. While NK1 behaves as a monomer in solution, two independent crystallographic structures have previously shown an identical, tightly packed dimer. Here we report a novel orthorhombic crystal form of NK1 at 2.5 A resolution in which four NK1 protomers are packed in two distinct dimers in the asymmetric unit. Although the basic architecture of the new NK1 dimers is similar to the two described earlier, the new crystal form demonstrates extensive hinge movement between the N and K domain that leads to re-orientation of the receptor-binding sites. The hinge bending is evidence of the paucity of strong interactions between domains within the protomer, in contrast to the extensive interactions between protomers in the dimer. These observations are consistent with domain swapping in the dimer, such that the interdomain interactions of the monomer are replaced by equivalent interprotomer interactions in the dimer and offer a route for protein engineering of NK1 variants which may act as receptor antagonists.

Hepatocyte growth factor/scatter factor can induce angiogenesis independently of vascular endothelial growth factor.

OBJECTIVE: Hepatocyte growth factor/scatter factor (HGF/SF) promotes vascular endothelial growth factor (VEGF) expression and induces angiogenesis in multiple pathological conditions. The present study was designed to delineate the HGF/SF and VEGF signaling cascades during angiogenesis by using PTK787, a selective VEGF receptor antagonist. METHODS AND RESULTS: PTK787 produced a concentration-dependent (10(-8) to 10(-6) mol/L) inhibition of VEGF-induced angiogenesis, without altering the basal or HGF/SF-induced response in vitro. In contrast, the nonspecific kinase inhibitor genistein blocked the HGF/SF-induced effect. Both VEGF and HGF/SF induced a rapid phosphorylation of extracellular receptor kinases-1 and -2 (ERKs) and Akt. PTK787 inhibited the VEGF-induced activation of Akt and ERKs, without affecting the HGF/SF-induced phosphorylation. Treatment with VEGF and HGF/SF increased total neovascularization in a murine scaffold granuloma model, but no additive or synergistic interactions were observed. PTK787 (50 mg/kg) blocked the VEGF-induced response without altering the basal or HGF/SF-induced neovascularization. CONCLUSIONS: We demonstrate that HGF/SF can induce angiogenesis independently of VEGF, possibly through the direct activation of the Akt and ERKs. These results demonstrate the necessity of a multitargeted approach for the rational design of newer therapies to inhibit pathophysiological angiogenesis.

A G2/M cell cycle block in transformed cells by contact with normal neighbors.

Neighbour suppression of growth of tumour cells by stationary normal cells might be important in early stages of cancer. We have studied this using suppressor and non-suppressor lines of 3T3 fibroblasts and SV40 transformed derivatives. Growth suppression of transformed cells depended on direct contact with stationary confluent cultures of 3T3 cells but not on gap junction communication. It was not caused by apoptosis nor through the normal G0/G1 block present in the confluent normal cells. Instead, there was a progressive elongation of the cell cycle leading to arrest in G2/M in the transformed cells. This indicates an unusual type of growth arrest not previously involved in social control of cell growth.