The HGF/SF-induced phosphorylation of paxillin, matrix adhesion, and invasion of prostate cancer cells were suppressed by NK4, an HGF/SF variant

Boswellia frereana suppresses HGF-mediated breast cancer cell invasion and migration through inhibition of c-Met signalling

BACKGROUND

Hepatocyte growth factor (HGF) plays a pivotal role in breast cancer cell motility, invasion and angiogenesis. These pro-metastatic events are triggered through HGF coupling and activation of the c-Met receptor. Reports have demonstrated that HGF/c-Met signalling plays an important part in breast cancer progression and that their expression is linked to poor patient outcome. In the present study, we investigated the anti-metastatic potential of an extract from traditional Somalian frankincense, Boswellia frereana, on human breast cancer cells. In addition, we also examined the effect of this Boswellia frereana extract (BFE) upon HGF-mediated stimulation of the c-Met receptor.

METHODS

Two triple negative human breast cancer cell lines, BT549 and MDA-MB-231, were utilised in the study to examine the effect of BFE on tumour cell proliferation, migration, matrix-adhesion, angiogenesis and invasion. Cell migration was investigated using a Cell IQ time-lapsed motion analysis system; while tumour cell-matrix adhesion, angiogenesis and invasion were assessed through Matrigel-based in vitro assays. Breast cancer cell growth and spheroid formation was examined through proliferation assay and 3D non-scaffold cell culture techniques. Western Blotting was employed to determine the phosphorylation status of the c-Met receptor tyrosine kinase following BFE treatment and subsequent HGF stimulation.

RESULTS

Following HGF treatment, the breast cancer cells displayed a significant increase in migration, matrix adhesion, vessel/tubule formation, invasion and c-Met activation. HGF did not appear to have any bearing on the proliferation rate or spheroid formation of these breast cancer cells. The addition of the BFE extract quenched the HGF-enhanced migratory, angiogenic and invasive potential of these cells. Further study revealed that BFE inhibited c-Met receptor tyrosine kinase phosphorylation within these breast cancer cells.

CONCLUSIONS

Our findings reveal that BFE was able to significantly suppress the influence of HGF in breast cancer cell motility and invasion in vitro, through the ability of BFE to reduce HGF/c-Met signalling events. Therefore, these results indicate that BFE could play a novel role in the treatment of breast cancer.

HGF/Met Signaling in Cancer Invasion: The Impact on Cytoskeleton Remodeling

The invasion of cancer cells into surrounding tissue and the vasculature is essential for tumor metastasis. Increasing evidence indicates that hepatocyte growth factor (HGF) induces cancer cell migration and invasion. A broad spectrum of mechanisms underlies cancer cell migration and invasion. Cytoskeletal reorganization is of central importance in the development of the phenotype of cancer cells with invasive behavior. Through their roles in cell mechanics, intracellular trafficking, and signaling, cytoskeleton proteins participate in all essential events leading to cell migration. HGF has been involved in cytoskeleton assembly and reorganization, and its role in regulating cytoskeleton dynamics is still expanding. This review summarizes our current understanding of the role of HGF in regulating cytoskeleton remodeling, distribution, and interactions.

Knockdown of WAVE3 impairs HGF induced migration and invasion of prostate cancer cells

Background

The WASP (Wiskott-Aldrich syndrome protein) and WAVE (WASP Verpolin homologous) family of proteins are structurally related and responsible for regulation of actin polymerization through their interaction with actin related proteins 2&3 (ARP 2/3). WAVE-3 has exhibited an association with disease progression and poorer prognosis of certain malignancies. In the current study, we determined the role of WAVE-3 in hepatocyte growth factor induced cellular changes including cell matrix interaction, invasion and cellular motility, and pathways that may be responsible for the changes in prostate cancer cells.

Methods

We used hammer head ribozymes to knock down the expression of WAVE-3 in PC-3 prostate cancer cell line. In vitro cellular functional assays including growth, invasion, adhesion, motility and invasion, were performed to assess the effects of WAVE-3 knock down. Further experimentation was performed to investigate the role of different pathway through expression and phosphorylation status of various intermediate proteins.

Results

WAVE-3 knockdown reduced invasive potential and motility of prostate cancer cells. Following addition of HGF, control cells showed significantly increased invasion and motility (p value <0.5) and marked increase in cellular growth. However, WAVE-3 knockdown cell line failed to show any increase in these trends (p value <0.5) except increased growth compared with control cells. Further experiments revealed that HGF-induced activation of Paxillin was weakened by the knockdown of WAVE-3. Our study also indicated that reduced invasiveness following WAVE-3 knockdown, may be related to reduce activity of MMP-2.

Conclusions

Our studies suggest a vital role of WAVE-3 in HGF induced invasion and migration in which Paxillin and MMP-2 are involved. Further study will shed light on its potential as therapeutic target to suppress local invasion and metastasis of prostate cancer cells.

Electronic supplementary material

The online version of this article (doi:10.1186/s12935-015-0203-3) contains supplementary material, which is available to authorized users.

HGF-MET cascade, a key target for inhibiting cancer metastasis: the impact of NK4 discovery on cancer biology and therapeutics

Hepatocyte growth factor (HGF) was discovered in 1984 as a mitogen of rat hepatocytes in a primary culture system. In the mid-1980s, MET was identified as an oncogenic mutant protein that induces malignant phenotypes in a human cell line. In the early 1990s, wild-type MET was shown to be a functional receptor of HGF. Indeed, HGF exerts multiple functions, such as proliferation, morphogenesis and anti-apoptosis, in various cells via MET tyrosine kinase phosphorylation. During the past 20 years, we have accumulated evidence that HGF is an essential conductor for embryogenesis and tissue regeneration in various types of organs. Furthermore, we found in the mid-1990s that stroma-derived HGF is a major contributor to cancer invasion at least in vitro. Based on this background, we prepared NK4 as an antagonist of HGF: NK4 inhibits HGF-mediated MET tyrosine phosphorylation by competing with HGF for binding to MET. In vivo, NK4 treatments produced the anti-tumor outcomes in mice bearing distinct types of malignant cancers, associated with the loss in MET activation. There are now numerous reports showing that HGF-antagonists and MET-inhibitors are logical for inhibiting tumor growth and metastasis. Additionally, NK4 exerts anti-angiogenic effects, partly through perlecan-dependent cascades. This paper focuses on the chronology and significance of HGF-antagonisms in anti-tumor researches, with an interest in NK4 discovery. Tumor HGF–MET axis is now critical for drug resistance and cancer stem cell maintenance. Thus, oncologists cannot ignore this cascade for the future success of anti-metastatic therapy.

Repulsive guidance molecule B (RGMB) plays negative roles in breast cancer by coordinating BMP signaling

Repulsive guidance molecules (RGMs) coordinate axon formation and iron homestasis. These molecules are also known as co-receptors of bone morphogenetic proteins (BMPs). However, the role played by RGMs in breast cancer remains unclear. The present study investigated the impact of RGMB on functions of breast cancer cells and corresponding mechanisms. RGMB was knocked down in breast cancer cells by way of an anti-RGMB ribozyme transgene. Knockdown of RGMB resulted in enhanced capacities of proliferation, adhesion, and migration in breast cancer cells. Further investigations demonstrated RGMB knockdown resulted in a reduced expression and activity of Caspase-3, accompanied with better survival in RGMB knockdown cells under serum starvation, which might be induced by its repression on MAPK JNK pathway. Up-regulations of Snai1, Twist, FAK, and Paxillin via enhanced Smad dependent sigaling led to increased capacities of adhesion and migration. Our current data firstly revealed that RGMB may act as a negative regulator in breast cancer through BMP signaling.

Association of Differentiation-Related Gene-1 (DRG1) with Breast Cancer Survival and in Vitro Impact of DRG1 Suppression

Differentiation-related gene-1, DRG1, is a metastasis suppressor gene whose expression has been shown to be dysregulated in a number of malignancies. The current study examines the expression of DRG1 in a clinical breast cohort and its association with a number of clinical pathological factors using quantitative polymerase chain reaction. Additionally, DRG1 expression is targeted in vitro using ribozyme transgene technology to explore the function of DRG1 in two human breast cancer cell lines. Low levels of DRG1 were found in patients who developed metastasis (p = 0.036) and who died of breast cancer (p = 0.0048) compared to disease free patients. Knockdown of DRG1 also resulted in significantly increased invasion and motility, but decreased matrix-adhesion in MCF7 cells. Knockdown of DRG1 seemed to have minimal impact on the cellular functions of the MDA-MB-231 breast cancer cell line causing no significant differences in cell growth, invasion, motility or matrix-adhesion. Thus, DRG1 appears to be linked to development of metastasis and death in patients who died as a result of breast cancer and may be useful as a prognostic factor as its knockdown appears to be linked with increased invasion and motility and decreased adhesion in MCF7 breast cancer cells.

Multistage carcinogenesis process as molecular targets in cancer chemoprevention by epicatechin-3-gallate

The consumption of green tea has long been associated with a reduced risk of cancer development. (-)-Epicatechin-3-gallate (ECG) or (-)-epigallocatechin-3-gallate (EGCG) are the major antioxidative polyphenolic compounds of green tea. They have been shown to exert growth-inhibitory potential of various cancer cells in culture and antitumor activity in vivo models. ECG or EGCG could interact with various molecules like proteins, transcription factors, and enzymes, which block multiple stages of carcinogenesis via regulating intracellular signaling transduction pathways. Moreover, ECG and EGCG possess pharmacological and physiological properties including induction of phase II enzymes, mediation of anti-inflammation response, regulation of cell proliferation and apoptosis effects and prevention of tumor angiogenesis, invasion and metastasis. Numerous review articles have been focused on EGCG, however none have been focused on ECG despite many studies supporting the cancer preventive potential of ECG. To develop ECG as an anticarcinogenic agent, more clear understanding of the cell signaling pathways and the molecular targets responsible for chemopreventive and chemotherapeutic effects are needed. This review summarizes recent research on the ECG-induced cellular signal transduction events which implicate in cancer management.

Expression patterns of PAX5, c-Met, and paxillin in neuroendocrine tumors of the lung

CONTEXT

c-Met is important in the pathogenesis, invasion, and spread of several forms of lung cancer, and multiple c-Met inhibitors are undergoing clinical trials. PAX5 has been shown to upregulate c-Met in small cell lung carcinoma (SCLC), and coinhibiting PAX5 and c-Met had a synergic effect in killing tumor cells. Paxillin is a downstream target of activated c-Met, and its activation leads to enhanced cell motility and tumor spread. The expression patterns of these functionally related proteins have not, to our knowledge, been systemically studied in neuroendocrine tumors of the lung.

OBJECTIVE

To investigate the expression patterns of PAX5, paxillin, c-Met, and phosphorylated c-Met in 4 categories of pulmonary neuroendocrine tumors.

DESIGN

Tissue microarrays of 38 typical carcinoids, 6 atypical carcinoids, 34 SCLCs, and 11 large cell neuroendocrine carcinomas were studied with immunohistochemistry.

RESULTS

Most of the 4 tumor types expressed c-Met, phosphorylated c-Met, and paxillin. PAX5 was frequently expressed in atypical carcinoids, SCLCs, and large cell neuroendocrine carcinomas but tended to be negative in typical carcinoids. Coexpression of PAX5 with c-Met or phosphorylated c-Met was present in most of the atypical carcinoids, SCLCs, and large cell neuroendocrine carcinomas. Significant correlation between PAX5 and paxillin was detected in SCLCs and large cell neuroendocrine carcinomas but not in carcinoid tumors.

CONCLUSIONS

The frequent coexpression of PAX5 with c-Met or phosphorylated c-Met in intermediate-grade and high-grade neuroendocrine tumors supports the therapeutic strategy of coinhibiting these proteins. The discrepancy between high-grade and low-grade neuroendocrine tumors in PAX5/paxillin expression correlation may be due to the different underlying molecular genetics of these tumors.

PAK4: a pluripotent kinase that regulates prostate cancer cell adhesion

Hepatocyte growth factor (HGF) is associated with tumour progression and increases the invasiveness of prostate carcinoma cells. Migration and invasion require coordinated reorganisation of the actin cytoskeleton and regulation of cell-adhesion dynamics. Rho-family GTPases orchestrate both of these cellular processes. p21-activated kinase 4 (PAK4), a specific effector of the Rho GTPase Cdc42, is activated by HGF, and we have previously shown that activated PAK4 induces a loss of both actin stress fibres and focal adhesions. We now report that DU145 human prostate cancer cells with reduced levels of PAK4 expression are unable to successfully migrate in response to HGF, have prominent actin stress fibres, and an increase in the size and number of focal adhesions. Moreover, these cells have a concomitant reduction in cell-adhesion turnover rates. We find that PAK4 is localised at focal adhesions, is immunoprecipitated with paxillin and phosphorylates paxillin on serine 272. Furthermore, we demonstrate that PAK4 can regulate RhoA activity via GEF-H1. Our results suggest that PAK4 is a pluripotent kinase that can regulate both actin cytoskeletal rearrangement and focal-adhesion dynamics.

Predictive value of plasma hepatocyte growth factor/scatter factor levels in patients with clinically localized prostate cancer

PURPOSE

Hepatocyte growth factor/scatter factor (HGF/SF) is a multifunctional cytokine that is involved in cancer growth, motility, invasion, and angiogenesis. We assessed whether preoperative plasma levels of HGF can enhance the accuracy of standard models for predicting pathologic features and clinical outcomes.

EXPERIMENTAL DESIGN

The study comprised 421 consecutive patients treated with radical prostatectomy and bilateral lymphadenectomy for clinically localized prostatic adenocarcinoma. HGF/SF was measured using a commercially available immunoassay. Multivariate logistic regression was used to assess the relationship between plasma HGF/SF and pathologic features. Multivariate Cox regression was used to predict disease recurrence. One thousand bootstrap replicates were created for internal validation and predictive accuracies were estimated for each model.

RESULTS

Plasma HGF/SF levels were significantly elevated in patients with lymph node and/or seminal vesicle invasion (P < 0.0001 and P = 0.007, respectively). Preoperative plasma HGF/SF level was an independent predictor of lymph node invasion [odds ratio (OR) for every 100 pg/mL increase in HGF/SF, 1.82; 95% confidence interval (95% CI), 1.33-2.49] and seminal vesicle invasion (OR, 1.18; 95% CI, 1.06-1.3). Addition of HGF/SF increased the accuracy of a base model that included standard preoperative variables for prediction of lymph node invasion by 6.7% (predictive accuracy, 98.4%). HGF/SF also independently predicted disease recurrence after surgery (hazard ratio, 1.07; 95% CI, 1.0-1.15).

CONCLUSIONS

Preoperative plasma level of HGF/SF is an independent predictor of prostate cancer metastasis to lymph nodes and disease recurrence after surgery. Use of HGF may help in therapeutic decision-making and enrollment into clinical trials.

HGF/SF up-regulates the expression of bone morphogenetic protein 7 in prostate cancer cells

Both HGF and BMP-7 have been implicated in the prostate cancer, particularly in bone metastasis. We recently demonstrated an up-regulation of BMP receptors by HGF in prostate cancer cells. Whether HGF has an effect on BMP-7 is still unknown. In the current study, we investigated the effects of HGF on the expression of BMP-7 in prostate cancer cells. Human prostate cancer cells, PC-3 and DU-145, were exposed to HGF at different concentrations for up to 24 hours. The mRNA levels of BMP7 were detected using RT-PCR and Quantitative PCR, and protein levels using Western blotting and immunocytochemistry. The levels of the BMP-7 transcripts in both PC-3 and DU-145 cells were up-regulated by the treatment with HGF in a concentration dependent and time related manner. The rise in BMP-7 mRNA was accompanied by an increase in protein levels, an effect completely blocked by the HGF antagonist, NK4. We further assessed this effect in an in vivo murine tumor model and showed that HGF up-regulated BMP-7 in prostate tumors. The antagonist of HGF, NK4 similarly blocked the induction of BMP-7 by HGF under the in vivo conditions. Taken together, HGF/SF can regulate BMP-7 expression in prostate cancer cells, both in vitro and in vivo. It may have a significant influence on the progression of prostate cancer and/or the development of bone metastasis.

Key signaling pathways and targets in lung cancer therapy

Despite the use of chemotherapy, radiation therapy, and surgery, the overall outcome for lung cancer continues to be disappointing. In order to make a difference in the treatment of lung cancer, novel therapeutics need to be developed. The molecular mechanisms of carcinogenesis in lung cancer are complex and involve multiple oncogenes, tumor suppressor genes, receptor tyrosine kinases, cytoplasmic enzymes, and tumor interstitial elements, among other cellular proteins. In this review, the authors discuss key signaling pathways and molecular targets in the treatment of lung cancer. Through understanding molecular targets and the utilization of specific inhibitors, hopefully, a dramatic impact will be made in the biology and therapy of lung cancer.

Hepatocyte growth factor activation inhibitors (HAI-1 and HAI-2) regulate HGF-induced invasion of human breast cancer cells

Hepatocyte growth factor (HGF) plays a plethora of roles in cancer metastasis and tumour growth. The interaction between tumour cells and their surrounding stromal environment is a crucial factor regulating tumour invasion and metastasis. Stromal fibroblasts are the main source of HGF in the body, and release HGF as an inactive precursor (pro-HGF). HGF activator (HGFA), matriptase, urokinase-type plasminogen activator and hepsin are the main factors responsible for converting pro-HGF into active HGF. HAI-1 and HAI-2 are 2 novel Kunitz-type serine protease inhibitors that regulate HGF activity through inhibition of HGFA, matriptase and hepsin action. Recent studies demonstrate that HAI-1 and HAI-2 may also potently inhibit a number of other pro-metastatic serine proteases and therefore have direct bearing on the spread of tumours. Our study examined the potential of these HAI's to suppress the influence of HGF and regulate cancer metastasis. We generated a retroviral expression system that induced HAI expression in a human fibroblast cell line. Forced expression of either HAI-1 or HAI-2 in these fibroblasts resulted in a dramatic decrease in the production of bioactive hepatocyte growth factor (HGF). This reduction in HGF activity subsequently suppressed HGF's metastatic influence on breast cancer cells. To further assess the anti-cancer properties of HAI-1 and HAI-2 we generated recombinant HAI proteins. These recombinant HAI proteins possessed the ability to potently quench HGF activity. We also demonstrate that these recombinant HAI's suppressed fibroblast-mediated breast cancer invasion. An additional ribozyme transgenes study revealed that elimination of HAI-1 and HAI-2 expression, in an MDA-MB-231 breast cancer cell line, significantly enhanced the migratory, proliferative and invasive nature of these breast cancer cells. Overall, our data demonstrates the important roles of HAI-1 and HAI-2 in cancer metastasis, and reveals that these serine protease inhibitors display strong therapeutic potential.

The polycystin 1-C-terminal fragment stimulates ERK-dependent spreading of renal epithelial cells

Polycystin 1, the product of the PKD1 gene, is mutated in autosomal dominant polycystic kidney disease, a disease characterized by renal cyst formation and progressive renal failure. We show that expression of the C-terminal domain of human polycystin-1 (PKD1-CT) triggers spreading of isolated inner medullary collecting duct cells, a process mediated by Erk. As inner medullary collecting duct cells spread, PKD1-CT localizes to cell-extracellular matrix contacts, interacts with focal adhesion proteins Fak and paxillin, and stimulates Fak phosphorylation, paxillin phosphorylation, Fak-paxillin association, and formation of small focal complexes. PKD1-CT-mediated spreading requires membrane localization and the integrity of the C-terminal protein binding sites. We additionally show that Pkd1 null proximal tubule cells generated from Pkd1(flox/-):TSLargeT mice by in vitro Cre recombinase transfection demonstrate diminished spreading when compared with Pkd(flox/-) heterozygous parental cells. These findings suggest that membrane-bound PC1 has a central role in regulating morphogenic protein signaling at cell-matrix interfaces in non-confluent cells.

Rho family GTPases are activated during HGF-stimulated prostate cancer-cell scattering

An important process in embryogenesis and cancer-cell metastasis is the conversion of epithelial cells to a migratory phenotype, a phenomenon known as epithelial-mesenchymal transition (E-MT). To achieve E-MT, cells dissociate from neighbouring cells and adopt a migratory morphology. This transition requires remodelling of their cell shape and substratum adhesions; activities that require extensive reorganisation of the actin cytoskeleton. Hepatocyte growth factor (HGF)-induced scattering of Madin Darby canine kidney (MDCK) cells is a routinely used model of E-MT, in which actin cytoskeletal rearrangement is known to be dependent on Rho family GTPases. We have developed a novel model of HGF-induced E-MT using the human prostate cancer cell line, DU145. This model overcomes the limitation of using a canine cell line and facilitates the study of E-MT in human cancer. We demonstrate for the first time the scattering response of individual DU145 cells to HGF in real time and have characterised changes in actin cytoskeletal organisation and cell adhesions as these cells respond to HGF. HGF-induced scattering of DU145 cells is dependent on the activity of Rho family GTPases, and using this model, we are able to demonstrate for the first time that endogenous Cdc42 is activated downstream of HGF. Furthermore we have also shown that the response of DU145 cells to HGF is dependent on a phosphatidylinositide 3-kinase pathway.

Mechanisms and significance of bifunctional NK4 in cancer treatment

Based on the background that hepatocyte growth factor (HGF) and c-Met/HGF receptor tyrosine kinase play a definite role in tumor invasion and metastasis, NK4, four-kringles containing intramolecular fragment of HGF, was isolated as a competitive antagonist for the HGF-c-Met system. Independent of its HGF-antagonist action, NK4 inhibited angiogenesis induced by vascular endothelial cell growth factor and basic fibroblast growth factor, as well as HGF, indicating that NK4 is a bifunctional molecule that acts as an HGF-antagonist and angiogenesis inhibitor. Interestingly, kringle domains in distinct types of proteins, e.g., plasminogen, prothrombin, plasminogen activators, apolipoprotein(a), and HGF, share angioinhibitory actions. In experimental models of distinct types of cancers, NK4 protein administration or NK4 gene therapy inhibited tumor invasion, metastasis, and angiogenesis-dependent tumor growth. Cancer treatment with NK4 may prove to suppress malignant tumors to be 'static' in both tumor growth and spreading, as based on biological characteristics of malignant tumors.

Therapeutic targeting of receptor tyrosine kinases in lung cancer

Lung cancer is a difficult illness with a poor overall survival. Even though combination strategies with chemotherapy, radiation therapy and surgery have all been utilised, the overall outcome for this disease continues to be relatively disappointing. In order to make a difference in the treatment of lung cancer, novel therapeutics will have to be developed. Through basic biological studies, a number of receptor tyrosine kinases have been implicated in the pathogenesis and progression of lung cancer. In this review, the authors summarise the mechanisms of several major receptor tyrosine kinases in lung cancer, especially epidermal growth factor receptor, Her2/neu, MET, vascular endothelial growth factor and KIT. The biology associated with these receptors is described, and the various novel therapeutic inhibitory strategies that are ongoing in preclinical and clinical studies for lung cancer are detailed. Through understanding of receptor tyrosine kinases and the utilisation of specific inhibitors, it is hopeful that a dramatic impact will be made on the biology and therapy for lung cancer.

Hepatocyte growth factor, its receptor, and their potential value in cancer therapies

Hepatocyte growth factor plays multiple roles in cancer, by acting as a motility and invasion stimulating factor, promoting metastasis and tumour growth. Furthermore, it acts as a powerful angiogenic factor. The pivotal role of this factor in cancer has indicated HGF as being a potential target in cancer therapies. The past few years have seen rapid progress in developing tools in targeting HGF, in the context of cancer therapies, including development of antagonists, small compounds, antibodies and genetic approaches. The current article discusses the potential value of HGF and its receptor as targets in cancer therapies, the current development in anti-HGF research, and the clinical value of HGF in prognosis and treatment.

Activation of the c-Met receptor complex in fibroblasts drives invasive cell behavior by signaling through transcription factor STAT3

c-Met is the receptor for hepatocyte growth factor/scatter factor (HGF/SF). It mediates multiple cellular responses in development and adult life, and c-Met hyperactivity is associated with malignant transformation of cells and the acquisition of metastatic properties. Signal transducer and activator of transcription 3 (STAT3) has been shown to contribute to c-Met-mediated cell motility and is, thus, potentially involved in the control of invasive cell behavior. We have functionally reconstituted c-Met-dependent signal transduction in fibroblasts with the aim of studying Met-driven cell invasiveness and the role of STAT3 in this phenomenon. Activation of the system was achieved by means of a hybrid receptor comprising the extracellular domain of the nerve growth factor (NGF) receptor TrkA, the cytoplasmic part of c-Met and a C-terminally fused blue fluorescent protein (BFP). In addition, a GFP-tagged derivative of adaptor protein Gab1 was expressed. NGF-stimulation of mouse fibroblasts expressing tagged versions of both Trk-Met and Gab1 with NGF resulted in anchorage-independent growth and enhanced invasiveness. By freeze-fracture cytochemistry and electron microscopy, we were able to visualize the ligand-induced formation of multivalent receptor complex assemblies within the cell membrane. NGF-stimulation of the heterologous receptor system evoked activation of STAT3 as evidenced by tyrosine phosphorylation and the formation of STAT3 clusters at the cell membrane. siRNA-mediated ablation of STAT3 expression resulted in a drastic reduction of c-Met-driven invasiveness, indicating an important role of STAT3 in the control of this particularly relevant property of transformed cells.

c-Met as a target for human cancer and characterization of inhibitors for therapeutic intervention

Receptor tyrosine kinase (RTK) targeted agents such as trastuzumab, imatinib, bevacizumab, and gefitinib inhibitors have illustrated the utility of targeting this protein class for treatment of selected cancers. A unique member of the RTK family, c-Met, also represents an intriguing target for cancer therapy that is yet to be explored in a clinical setting. The proto-oncogene, c-Met, encodes the high-affinity receptor for hepatocyte growth factor (HGF) or scatter factor (SF). c-Met and HGF are each required for normal mammalian development and have been shown to be particularly important in cell migration, morphogenic differentiation, and organization of three-dimensional tubular structures (e.g. renal tubular cells, gland formation, etc.) as well as cell growth and angiogenesis. Both c-Met and HGF have been shown to be deregulated in and to correlate with poor prognosis in a number of major human cancers. New data describing the constitutive phosphorylation of c-Met in a number of human tumors is presented here along with a variety of mechanisms by which c-Met can become activated, including mutation and gene amplification. In support of the clinical data implicating c-Met activation in the pathogenesis of human cancers, introduction of c-Met and HGF (or mutant c-Met) into cells conferred the properties of motility, invasiveness, and tumorgenicity to the transformed cells. Conversely, the inhibition of c-Met with a variety of receptor antagonists inhibited the motility, invasiveness, and tumorgenicity of human tumor cell lines. Consistent with this observation, small-molecule inhibitors of c-Met were developed that antagonized c-Met/HGF-dependent phenotypes and tumor growth in mouse models. This review will address the potential for development of c-Met inhibitors for treatment of human cancers with particular emphasis on recent findings with small-molecule inhibitors.

Epithelial cell spreading induced by hepatocyte growth factor influences paxillin protein synthesis and posttranslational modification

Superficial wounds in the gastrointestinal tract rapidly reseal by coordinated epithelial cell migration facilitated by cytokines such as hepatocyte growth factor (HGF)/scatter factor released in the wound vicinity. However, the mechanisms by which HGF promotes physiological and pathophysiologic epithelial migration are incompletely understood. Using in vitro models of polarized T84 and Caco-2 intestinal epithelia, we report that HGF promoted epithelial spreading and RhoA GTPase activation in a time-dependent manner. Inducible expression of enhanced green fluorescent protein-tagged dominant-negative RhoA significantly attenuated HGF-induced spreading. HGF expanded a zone of partially flattened cells behind the wound edge containing basal F-actin fibers aligned in the direction of spreading. Concomitantly, plaques positive for the focal adhesion protein paxillin were enhanced. HGF induced an increase in the translation of paxillin and, to a lesser extent, beta1-integrin. This was independent of cell-matrix adhesion through beta1-integrin. Subcellular fractionation revealed increased cosedimentation of paxillin with plasma membrane-containing fractions following HGF stimulation, without corresponding enhancements in paxillin coassociation with beta1 integrin or actin. Tyrosine phosphorylation of paxillin was reduced by HGF and was sensitive to the Src kinase inhibitor PP2. With these taken together, we propose that HGF upregulates a free cytosolic pool of paxillin that is unaffiliated with either the cytoskeleton or focal cell-matrix contacts. Thus early spreading responses to HGF may partly relate to increased paxillin availability for incorporation into, and turnover within, dynamic cytoskeletal/membrane complexes whose rapid and transient adhesion to the matrix drives migration.

Inhibition by Copper(II) Binding of Hepatocyte Growth Factor (HGF) Interaction with Its Receptor Met and Blockade of HGF/Met Function

Overexpression of hepatocyte growth factor (HGF) and its receptor Met often occurs in carcinoma cells, leading to establishment of an HGF/Met autocrine loop. Therefore, disruption of the HGF/Met autocrine loop may lead to down-regulation of tumorigenesis. To study the HGF/Met interaction, we have developed a cell-free system to detect HGF binding to a Met fusion protein, Met-IgG, using a modified enzyme-linked immunosorbent assay methodology. Since we previously showed that HGF can be purified by copper(II) affinity chromatography, we further explored the effect of copper(II) on the HGF/Met interaction. The divalent metal cations copper(II) and zinc(II) significantly inhibited HGF binding to immobilized Met-IgG with IC(50) values of 230-270 microM, respectively, whereas manganese(II) and magnesium(II) were less inhibitory with 20-60-fold higher IC(50) values. Incubation of 1 mM copper(II) with HGF resulted in nondenaturing and denaturing gel-mobility shifts, indicating that copper(II) binds directly to HGF. This interaction occurs at the N terminus of HGF, as incubation of 1 mM copper(II) with both HGF and the HGF derivative NK1 yielded similar results on SDS-PAGE. HGF-induced activation of Met and cell scattering were inhibited upon addition of HGF in the presence of 1 mM and 500 microM copper(II), respectively. Chemical protonation with diethyl pyrocarbonate of HGF histidine residues impeded the ability of 500 microM copper(II) to inhibit the binding of HGF to immobilized Met-IgG. Based on the NK1 domain structure, we propose that copper(II) may interact with HGF via the histidine residues in either N-terminal or kringle domains. The inhibition of HGF/Met interaction and subsequent downstream cellular functions may be through direct interference by copper(II), such as a change in charge or an induced local conformational change. This putative copper(II) binding domain may be the basis for developing potential inhibitors of HGF/Met binding and downstream functions and could lead to novel strategies for anti-cancer treatment.

Radiation to stromal fibroblasts increases invasiveness of pancreatic cancer cells through tumor-stromal interactions

Radiotherapy represents a major treatment option for patients with pancreatic cancer, but recent evidence suggests that radiation can promote invasion and metastasis of cancer cells. Interactions between cancer cells and surrounding stromal cells may play an important role in aggressive tumor progression. In the present study, we investigated the invasive phenotype of pancreatic cancer cells in response to coculture with irradiated fibroblasts. Using in vitro invasion assay, we demonstrated that coculture with nonirradiated fibroblasts significantly increased the invasive ability of pancreatic cancer cells and, surprisingly, the increased invasiveness was further accelerated when they were cocultured with irradiated fibroblasts. The hepatocyte growth factor (HGF) secretion from fibroblasts remained unchanged after irradiation, whereas exposure of pancreatic cancer cells to supernatant from irradiated fibroblasts resulted in increased phosphorylation of c-Met (HGF receptor) and mitogen-activated protein kinase activity, possibly or partially via increased expression of c-Met. We also demonstrated that scattering of pancreatic cancer cells was accelerated by the supernatant from irradiated fibroblasts. The enhanced invasiveness of pancreatic cancer cells induced by coculture with irradiated fibroblasts was completely blocked by NK4, a specific antagonist of HGF. These data suggest that invasive potential of certain pancreatic cancer cells is enhanced by soluble mediator(s) released from irradiated fibroblasts possibly through up-regulation of c-Met expression/phosphorylation and mitogen-activated protein kinase activity in pancreatic cancer cells. Our present findings further support the potential use of NK4 during radiotherapy for patients with pancreatic cancer.

Enhanced invasion of hormone refractory prostate cancer cells through hepatocyte growth factor (HGF) induction of urokinase-type plasminogen activator (u-PA)

BACKGROUND

Increased expression of the hepatocyte growth factor (HGF) receptor (MET) is associated with high-grade prostatic adenocarcinoma and metastasis. However, the mechanism through which MET signaling contributes to prostate cancer (CaP) metastasis remains unclear.

METHODS

Human PC-3 CaP cells and in vivo selected, isogeneic variant cells of increasing metastatic potential (PC-3M, PC-3M-Pro4, and PC-3M-LN4) were used to investigate the effect of HGF on CaP cell growth, protease production, and invasion. Cell-free urokinase-type plasminogen activator (u-PA) expression and function following HGF treatment were analyzed by Western blot, ELISA, and casein/plasminogen zymography. In vitro invasion stimulated by HGF was measured using Matrigel-coated invasion chambers.

RESULTS

Both mRNA and functional protein for MET were detected in each of the CaP cell lines. HGF treatment (0-40 ng/ml) weakly increase proliferation, however, HGF induced soluble u-PA protein and activity 3-fold in the metastatic variant cells. HGF significantly stimulated the invasion of highly metastatic PC-3M-LN4 cells through Matrigel and treatment with specific urokinase receptor inhibitors diminished the HGF-stimulated invasion in a dose-dependent manner.

CONCLUSIONS

These results demonstrate the biological significance of u-PA up-regulation in response to HGF in highly metastatic hormone refractory CaP cells.

Phosphorylation-dependent paxillin-ERK association mediates hepatocyte growth factor-stimulated epithelial morphogenesis

Activation of the hepatocyte growth factor (HGF) receptor c-met results in the regulation of cell-matrix interactions, including the MAPK-dependent stimulation of epithelial cell morphogenesis. In the present study we demonstrate that HGF stimulates the localization of ERK to sites of cell-matrix interactions and that this is mediated by the tyrosine phosphorylation-dependent association of inactive ERK and the focal adhesion complex protein paxillin. In addition, paxillin was found to associate with the upstream MAP kinases Raf and MEK, resulting in a complex that can mediate localized ERK activation. Mutation of the ERK binding site in paxillin prevented HGF-stimulated ERK-paxillin association and eliminated HGF-induced cell spreading and branching process formation. These experiments reveal that paxillin-dependent ERK activation at sites of cell-matrix interaction is critical for HGF-stimulated epithelial morphogenesis.

The HGF/SF antagonist NK4 reverses fibroblast- and HGF-induced prostate tumor growth and angiogenesis in vivo

Our study examined the in vitro and in vivo responses of a newly discovered HGF/SF antagonist, NK4, on HGF/SF-promoted growth of human prostate cancer cells (PC-3). Nude mice were s.c. injected with either PC-3- and/or HGF/SF-producing fibroblasts (MRC5), and tumor size was measured over a 4-week period. rh-HGF/SF and/or NK4 were introduced by osmotic minipumps. An in vitro study found that NK4 significantly suppressed HGF/SF-induced invasion (HGF/SF; p < 0.01 vs. HGF/SF+NK4) and migration (HGF/SF; p < 0.05 vs. HGF/SF+NK4). Similarly, NK4 also suppressed the invasion (MRC5; p < 0.01 vs. MRC5+NK4) and migration (MRC5; p < 0.05 vs. MRC5+NK4) induced by MRC5 cells. NK4 also suppressed HGF/SF- and MRC5-induced tyrosine phosphorylation of the HGF/SF receptor Met as assessed by immunoprecipitation. Using a nude mouse model, prostate tumor volume (mm(3)) was significantly increased in both HGF/SF- (HGF/SF; p < 0.05 vs. control) and MRC5- (MRC5; p < 0.01 vs. control) treated groups compared to the control. In contrast, NK4 alone significantly reduced the growth of prostate tumors (NK4; p < 0.01 vs. control). In addition, NK4 also suppressed both HGF/SF- (HGF/SF; p < 0.01 vs. HGF/SF+NK4) and MRC5- (MRC5; p < 0.05 vs. MRC5+NK4) induced tumor growth in vivo by significantly reducing (p < 0.05) the degree of tumor angiogenesis using a recently discovered family of tumor endothelial markers (TEMs) by Q-RT-PCR analysis. In conclusion, NK4 suppresses both HGF/SF- and MRC5-induced invasion/migration of PC-3 cells in vitro. Furthermore, the HGF/SF antagonist NK4 significantly reduces prostate tumor growth in vivo by inhibiting the degree of tumor angiogenesis as determined by TEM-1 and TEM-8. Finally, our study provides evidence of the therapeutic potential of NK4 in prostate cancer development by antagonising HGF/SF-mediated events.

Growth and angiogenesis of human breast cancer in a nude mouse tumour model is reduced by NK4, a HGF/SF antagonist

Hepatocyte growth factor/scatter factor (HGF/SF) is a cytokine primarily produced by stromal fibroblasts and is a known angiogenic and invasion-inducing factor. It is increased in patients with breast cancer. This study examined the effect of NK4, a newly described HGF/SF antagonist, on HGF/SF-promoted growth of a human breast cancer. Both in vitro (invasion and migration assays) and in vivo (murine tumour model) methods were used to ascertain the effect of NK4 on HGF/SF from two sources: human fibroblast-derived HGF/SF and recombinant HGF/SF. In the in vitro invasion assay and migration assay, both HGF/SF and human fibroblasts, which secrete bioactive HGF/SF, increased the invasiveness and migration of the breast cancer cells (MDA MB 231). NK4 significantly reduced this invasiveness and motility. In the animal model, tumour volume and weight was significantly reduced with addition of NK4. It also suppressed HGF/SF-induced growth and markedly retarded tumour growth induced by fibroblasts (MRC5), secreting bioactive HGF/SF. Tumour angiogenesis was assessed by immunohistochemical staining of primary tissue sections using VE-cadherin (an endothelial cell specific cell-cell adhesion molecule). Again, NK4 reduced the effects of both HGF/SF and fibroblasts. We conclude that NK4 has a significant effect on the growth of human breast tumours in nude mice, particularly when stimulated by HGF/SF or fibroblasts. This may occur by decreasing angiogenesis. This gives a clear indication of the therapeutic worth of NK4.

Epithelial cell differentiation in the human prostate epithelium: implications for the pathogenesis and therapy of prostate cancer

Within the human prostate epithelium four cell populations are discriminated by their expression of keratins (K). While basal cells co-localize K5 and K14 combined with low levels of K18 (K5(++)/14(++)/18(+)), luminal cells highly express K18 (K18(++)). In addition, two intermediate subpopulations are characterized either by basal K5(++)/18(+)- or luminal K5(+)/18(++)- expression. The entire prostate epithelium is putatively derived from a basal stem cell population. They give rise to intermediate cells that transiently proliferate and mature towards differentiated luminal epithelium. Within prostate carcinoma luminal exocrine, neuro-endocrine and intermediate cells are distinguished. Intermediate cells have been postulated as progenitors for prostate carcinogenesis and targets for androgen-independent tumor progression. Androgen-independency is associated with an enrichment of intermediate cells and over-expression of peptide growth factor receptors. Targeting intermediate cells by inhibition of their peptide growth factor receptors, therefore, offers novel treatment modalities for prostate cancer.

Antagonistic effect of NK4 on HGF/SF induced changes in the transendothelial resistance (TER) and paracellular permeability of human vascular endothelial cells

Hepatocyte growth factor/scatter factor (HGF/SF) is a multi-function cytokine that has been shown to regulate the expression of cell adhesion molecules in human endothelial cells. It is also a key cytokine in the development and progression of cancer, particularly during metastasis. NK4 is a variant of HGF/SF that has already been shown to be antagonistic to HGF/SF. This study shows that HGF/SF decreased transendothelial resistance (TER) and increased paracellular permeability in human vascular endothelial cells can that such effects can be inhibited by addition of the NK4 variant. In addition, HGF/SF-stimulated invasion of endothelium by breast cancer cells was inhibited by the addition of NK4. Western blotting revealed that HGF/SF decreased the protein level, and increased tyrosine phosphorylation of ZO-1, but did not cause a change in level of occludin or claudin-1, both molecules involved in tight junction function. RT-PCR revealed that addition of HGF/SF caused no change in signal for claudin-5 or junctional adhesion molecule (JAM), but there was a decrease in the signal for claudin-1. NK4 was able to prevent the decrease in levels of ZO-1 protein by HGF/SF.

Tumor suppression effect using NK4, a molecule acting as an antagonist of HGF, on human gastric carcinomas

Hepatocyte growth factor (HGF) is involved in malignant behavior of cancers as a mediator of tumor-stromal interactions, facilitating tumor invasion and metastasis. We have investigated whether a blockade of HGF using recombinant NK4, an HGF antagonist, would lead to growth inhibition of the human gastric carcinoma cell line, TMK1. To evaluate the function of endogenous NK4 and investigate its potential inhibitory effect, TMK1 cells were transfected with NK4 plasmid. After selection, NK4-expressing cells (T11) were obtained, and cell growth was evaluated. Significant growth inhibition was observed in the T11-group compared to the control both in vitro and in vivo. Moreover, we investigated the effect of exogenous NK4 transferred by an adenovirus vector (AdCMV.NK4). Cell proliferation of AdCMV.NK4 infected TMK1 cells was significantly inhibited compared with the control group. We also assessed the in vivo tumor suppression effect of AdCMV.NK4. The tumor volume following treatment with AdCMV.NK4 was significantly inhibited compared to that of the control group. These findings indicate that NK4 gene expression has a potential role in controlling proliferation of cancer cells. In conclusion, NK4 is a promising therapeutic agent and its gene delivery may be a new approach to treating patients with advanced gastric cancer.

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.