Met overexpression confers HGF-dependent invasive phenotype to human thyroid carcinoma cells in vitro

MET∆14 promotes a ligand-dependent, AKT-driven invasive growth

MET is an oncogene encoding the tyrosine kinase receptor for hepatocyte growth factor (HGF). Upon ligand binding, MET activates multiple signal transducers, including PI3K/AKT, STAT3, and MAPK. When mutated or amplified, MET becomes a "driver" for the onset and progression of cancer. The most frequent mutations in the MET gene affect the splicing sites of exon 14, leading to the deletion of the receptor's juxtamembrane domain (MET∆14). It is currently believed that, as in gene amplification, MET∆14 kinase is constitutively active. Our analysis of MET in carcinoma cell lines showed that MET∆14 strictly depends on HGF for kinase activation. Compared with wt MET, ∆14 is sensitive to lower HGF concentrations, with more sustained kinase response. Using three different models, we have demonstrated that MET∆14 activation leads to robust phosphorylation of AKT, leading to a distinctive transcriptomic signature. Functional studies revealed that ∆14 activation is predominantly responsible for enhanced protection from apoptosis and cellular migration. Thus, the unique HGF-dependent ∆14 oncogenic activity suggests consideration of HGF in the tumour microenvironment to select patients for clinical trials.

Acquired resistance to BRAF inhibition induces epithelial-to-mesenchymal transition in BRAF (V600E) mutant thyroid cancer by c-Met-mediated AKT activation

Previously, the authors have identified that c-Met mediates reactivation of the PI3K/AKT pathway following BRAF inhibitor treatment in BRAF (V600E) mutant anaplastic thyroid cancer, thereby contributing to the acquired drug resistance. Therefore dual inhibition of BRAF and c-Met led to sustained treatment response, thereby maximizing the specific anti-tumor effect of targeted therapy. The present study goes one step further and aims to investigate the effect of acquired resistance of BRAF inhibitor on epithelial-to-mesenchymal transition (EMT) in BRAF mutant thyroid cancer cells and the effect of dual inhibition from combinatorial therapy. Two thyroid cancer cell lines, 8505C and BCPAP were selected and treated with BRAF inhibitor, PLX4032 and its effect on EMT were examined and compared. Further investigation was carried out in orthotopic xenograft mouse models. Unlike BCPAP cells, the BRAF inhibitor resistant 8505C cells showed increased expressions of EMT related markers such as vimentin, β-catenin, and CD44. The combinatorial treatment of PLX4032 and PHA665752, a c-Met inhibitor reversed EMT. Similar results were confirmed in vivo. c-Met-mediated reactivation of the PI3K/AKT pathway contributes to the drug resistance to PLX4032 in BRAF (V600E) mutant anaplastic thyroid cancer cells and further promotes tumor cell migration and invasion by upregulated EMT mechanism. Dual inhibition of BRAF and c-Met leads to reversal of EMT, suggesting a maximal therapeutic response.

Coherent modelling switch between pointwise and distributed representations of cell aggregates

Biological systems are typically formed by different cell phenotypes, characterized by specific biophysical properties and behaviors. Moreover, cells are able to undergo differentiation or phenotypic transitions upon internal or external stimuli. In order to take these phenomena into account, we here propose a modelling framework in which cells can be described either as pointwise/concentrated particles or as distributed masses, according to their biological determinants. A set of suitable rules then defines a coherent procedure to switch between the two mathematical representations. The theoretical environment describing cell transition is then enriched by including cell migratory dynamics and duplication/apoptotic processes, as well as the kinetics of selected diffusing chemicals influencing the system evolution. Finally, biologically relevant numerical realizations are presented: in particular, they deal with the growth of a tumor spheroid and with the initial differentiation stages of the formation of the zebrafish posterior lateral line. Both phenomena mainly rely on cell phenotypic transition and differentiated behaviour, thereby constituting biological systems particularly suitable to assess the advantages of the proposed model.

MicroRNA expression profiling reveals the potential function of microRNA-31 in chordomas

Chordomas are rare bone tumors arising from remnants of the notochord. Molecular studies to determine the pathways involved in their pathogenesis and develop better treatments are limited. Alterations in microRNAs (miRNAs) play important roles in cancer. miRNAs are small RNA sequences that affect transcriptional and post-transcriptional regulation of gene expression in most eukaryotic organisms. Studies show that miRNA dysregulation is important for tumor initiation and progression. We compared the expression profile of miRNAs in chordomas to that of healthy nucleus pulposus samples to gain insight into the molecular pathogenesis of chordomas. Results of functional studies on one of the altered miRNAs, miR-31, are presented. The comparison between the miRNA profile of chordoma samples and the profile of normal nucleus pulposus samples suggests dysregulation of 53 miRNAs. Thirty miRNAs were upregulated in our tumor samples, while 23 were downregulated. Notably, hsa-miR-140-3p and hsa-miR-148a were upregulated in most chordomas relative to levels in nucleus pulposus cells. Two other miRNAs, hsa-miR-31 and hsa-miR-222, were downregulated in chordomas compared with the control group. Quantification with real-time polymerase chain reaction confirmed up or downregulation of these miRNAs among all samples. Functional analyses showed that hsa-miR-31 has an apoptotic effect on chordoma cells and downregulates the expression of c-MET and radixin. miRNA profiling showed that hsa-miR-31, hsa-miR-222, hsa-miR-140-3p and hsa-miR-148a are differentially expressed in chordomas compared with healthy nucleus pulposus. Our profiling may be the first step toward delineating the differential regulation of cancer-related genes in chordomas, helping to reveal the mechanisms of initiation and progression.

Regulation of cell proliferation and migration in glioblastoma: new therapeutic approach

Glioblastoma is the most aggressive brain cancer with the poor survival rate. A microRNA, miR-451, and its downstream molecules, CAB39/LKB1/STRAD/AMPK, are known to play a critical role in regulating a biochemical balance between rapid proliferation and invasion in the presence of metabolic stress in microenvironment. We develop a novel multi-scale mathematical model where cell migration and proliferation are controlled through a core intracellular control system (miR-451-AMPK complex) in response to glucose availability and physical constraints in the microenvironment. Tumor cells are modeled individually and proliferation and migration of those cells are regulated by the intracellular dynamics and reaction-diffusion equations of concentrations of glucose, chemoattractant, extracellular matrix, and MMPs. The model predicts that invasion patterns and rapid growth of tumor cells after conventional surgery depend on biophysical properties of cells, dynamics of the core control system, and microenvironment as well as glucose injection methods. We developed a new type of therapeutic approach: effective injection of chemoattractant to bring invasive cells back to the surgical site after initial surgery, followed by glucose injection at the same location. The model suggests that a good combination of chemoattractant and glucose injection at appropriate time frames may lead to an effective therapeutic strategy of eradicating tumor cells.

RET/PTC1-driven neoplastic transformation and proinvasive phenotype of human thyrocytes involve Met induction and beta-catenin nuclear translocation

Activation of the RET gene by chromosomal rearrangements generating RET/PTC oncogenes is a frequent, early, and causative event in papillary thyroid carcinoma (PTC). We have previously shown that, in human primary thyrocytes, RET/PTC1 induces a transcriptional program including the MET proto-oncogene. In PTCs, beta-catenin is frequently mislocated to the cytoplasm nucleus. We investigated the interplay between Ret/ptc1 signaling and Met in regulating the proinvasive phenotype and beta-catenin localization in cellular models of human PTC. Here, we show that Met protein is expressed and is constitutively active in human thyrocytes exogenously expressing RET/PTC1 as well as a mutant (Y451F) devoid of the main Ret/ptc1 multidocking site. Both in transformed thyrocytes and in the human PTC cell line TPC-1, Ret/ptc1-Y451-dependent signaling and Met cooperated to promote a proinvasive phenotype. Accordingly, gene/functional silencing of either RET/PTC1 or MET abrogated early branching morphogenesis in TPC-1 cells. The same effect was obtained by blocking the common downstream effector Akt. Y451 of Ret/ptc1 was required to promote proliferation and nuclear translocation of beta-catenin, suggesting that these oncogene-driven effects are Met-independent. Pharmacologic inhibition of Ret/ptc1 and Met tyrosine kinases by the multitarget small molecule RPI-1 blocked cell proliferation and invasive ability and dislocated beta-catenin from the nucleus. Altogether, these results support that Ret/ptc1 cross talks with Met at transcriptional and signaling levels and promotes beta-catenin transcriptional activity to drive thyrocyte neoplastic transformation. Such molecular network, promoting disease initiation and acquisition of a proinvasive phenotype, highlights new options to design multitarget therapeutic strategies for PTCs.

Osteopontin promotes integrin activation through outside-in and inside-out mechanisms: OPN-CD44V interaction enhances survival in gastrointestinal cancer cells

Osteopontin (OPN) and splice variants of CD44 (CD44(V)) have independently been identified as markers for tumor progression. In this study, we show that both OPN and CD44(V) are frequently overexpressed in human gastric cancer and that OPN-engaged CD44(V) ligation confers cells an increased survival mediated through integrin activation. First, we show that OPN treatment confers cells an increased resistance to UV-induced apoptosis. The OPN-mediated antiapoptosis is dependent on the expression of the variant exon 6 (V6)- or V7-containing CD44 as shown by overexpression of individual CD44(V) in gastric AZ521 cells that express no or very low level of endogenous CD44 and by knockdown of the constitutively expressed V6-containing CD44 isoforms in colon HT29 cells. Although OPN also interacts with RGD integrins, OPN-RGD sequence is dispensable for OPN-mediated antiapoptosis. OPN-induced antiapoptosis is mainly attributed to the engagement of CD44(V) isoforms and the relay of an inside-out signaling via Src activity, leading to robust integrin activation. Furthermore, OPN-elicited antiapoptosis was observed when cells were plated on fibronectin but not on poly-D-lysin, and preincubation of cells with anti-integrin beta(1) antibody to block integrin-extracellular matrix (ECM) interaction or ectopic expression of the dominant-negative forms of focal adhesion kinase to block ECM-derived signal abolished OPN-induced survival, suggesting that OPN-elicited antiapoptotic function is propagated from matrix transduced by integrin. Taken together, we showed that OPN-CD44(V) interaction promotes ECM-derived survival signal mediated through integrin activation, which may play an important role in the pathogenic development and progression of gastric cancer.

Molecular mechanisms involved in differentiated thyroid cancer invasion and metastasis

PURPOSE OF REVIEW

The majority of patients with thyroid cancer have an excellent prognosis, however patients with extensive local invasion and distant metastasis frequently do not respond to standard treatments and have worsened prognosis. Understanding the specific mechanisms involved in thyroid cancer invasion and metastasis is critical in order to develop new treatments specifically targeted for these patients.

RECENT FINDINGS

The genetic basis for thyroid cancer initiation and development is well characterized, with the majority of studies implicating activation of the RAS-RAF-ERK and PI3K/PDK1/Akt signaling pathways. Over the last several years, data from a concerted effort to define the pathways involved in invasion and metastasis suggest that reactivation of embryonic pathways involved in cell movement, to include epithelial to mesenchymal transition and collective cell migration, may be involved in cancer cell migration and invasion. The previously identified thyroid oncogenes, BRAF, RET/PTC and Ras, appear to be important regulators of this process.

SUMMARY

The molecular mechanisms that control cell migration during embryological development, such as epithelial to mesenchymal transition, appear to be reactivated in invading thyroid cancer cells. Elucidation of the signal-transduction networks and molecules that are involved in thyroid cancer invasion may lead to novel therapeutic targets.

Mitogen-inducible gene 6 is an endogenous inhibitor of HGF/Met-induced cell migration and neurite growth

Hepatocyte growth factor (HGF)/Met signaling controls cell migration, growth and differentiation in several embryonic organs and is implicated in human cancer. The physiologic mechanisms that attenuate Met signaling are not well understood. Here we report a mechanism by which mitogen-inducible gene 6 (Mig6; also called Gene 33 and receptor-associated late transducer) negatively regulates HGF/Met-induced cell migration. The effect is observed by Mig6 overexpression and is reversed by Mig6 small interfering RNA knock-down experiments; this indicates that endogenous Mig6 is part of a mechanism that inhibits Met signaling. Mig6 functions in cells of hepatic origin and in neurons, which suggests a role for Mig6 in different cell lineages. Mechanistically, Mig6 requires an intact Cdc42/Rac interactive binding site to exert its inhibitory action, which suggests that Mig6 acts, at least in part, distally from Met, possibly by inhibiting Rho-like GTPases. Because Mig6 also is induced by HGF stimulation, our results suggest that Mig6 is part of a negative feedback loop that attenuates Met functions in different contexts and cell types.

Des-gamma-carboxy prothrombin is a potential autologous growth factor for hepatocellular carcinoma

Des-gamma-carboxyl prothrombin (DCP) is a well recognized tumor marker for hepatocellular carcinoma (HCC). In the present study, we demonstrate that DCP has a mitogenic effect on HCC cell lines. Purified DCP stimulated DNA synthesis of Hep3B and SK-Hep-1 cells in a dose-dependent manner. DCP was found to bind with cell surface receptor Met causing Met autophosphorylation and also to activate STAT3 signaling pathway through Janus kinase 1. Luciferase gene reporter analysis showed that DCP induced STAT3-related transcription. Small interfering RNAs against both STAT3 and Met abrogated DCP-induced cell proliferation. DCP did not affect the mitogen-activated protein kinase pathway, Myc signaling pathway, or phosphoinositide 3-kinase/Akt pathway. Based on these results, we believe that DCP acts as an autologous mitogen for HCC cell lines. The Met-Janus kinase 1-STAT3 signaling pathway may be a major signaling pathway for DCP-induced cell proliferation.

Angiogenesis in endocrine tumors

Angiogenesis is the process of new blood vessel development from preexisting vasculature. Although vascular endothelium is usually quiescent in the adult, active angiogenesis has been shown to be an important process for new vessel formation, tumor growth, progression, and spread. The angiogenic phenotype depends on the balance of proangiogenic growth factors such as vascular endothelial growth factor (VEGF) and inhibitors, as well as interactions with the extracellular matrix, allowing for endothelial migration. Endocrine glands are typically vascular organs, and their blood supply is essential for normal function and tight control of hormone feedback loops. In addition to metabolic factors such as hypoxia, the process of angiogenesis is also regulated by hormonal changes such as increased estrogen, IGF-I, and TSH levels. By measuring microvascular density, differences in angiogenesis have been related to differences in tumor behavior, and similar techniques have been applied to both benign and malignant endocrine tumors with the aim of identification of tumors that subsequently behave in an aggressive fashion. In contrast to other tumor types, pituitary tumors are less vascular than normal pituitary tissue, although the mechanism for this observation is not known. A relationship between angiogenesis and tumor size, tumor invasiveness, and aggressiveness has been shown in some pituitary tumor types, but not in others. There are few reports on the role of microvascular density or angiogenic factors in adrenal tumors. The mechanism of the vascular tumors, which include adrenomedullary tumors, found in patients with Von Hippel Lindau disease has been well characterized, and clinical trials of antiangiogenic therapy are currently being performed in patients with Von Hippel Lindau disease. Thyroid tumors are more vascular than normal thyroid tissue, and there is a clear correlation between increased VEGF expression and more aggressive thyroid tumor behavior and metastasis. Although parathyroid tissue induces angiogenesis when autotransplanted and PTH regulates both VEGF and MMP expression, there are few studies of angiogenesis and angiogenic factors in parathyroid tumors. An understanding of the balance of angiogenesis in these vascular tumors and mechanisms of vascular control may assist in therapeutic decisions and allow appropriately targeted treatment.

c-Met expression in tall cell variant papillary carcinoma of the thyroid

BACKGROUND

Tall cell variant papillary carcinoma of the thyroid demonstrates unusually aggressive clinical behavior compared with the usual form of papillary thyroid carcinoma. The proto-oncogene c-met encodes a tyrosine kinase receptor known to influence cell invasion. This current study examined c-Met expression in tall cell variant tumors compared with other types of papillary thyroid carcinoma and benign thyroid disease.

METHODS

c-Met expression in 60 archived thyroid specimens was evaluated by immunohistochemical staining.

RESULTS

Tall cell variant specimens expressed significantly greater levels of c-Met than other forms of papillary thyroid carcinoma and benign thyroid disease (P < 0.0001). c-Met expression was significantly different for the following pairs of histologies: tall cell variant versus usual papillary carcinoma of the thyroid (P < 0.0001), tall cell variant versus follicular variant papillary thyroid carcinoma (P < 0.0001), tall cell variant versus benign thyroid (P < 0.0001), and usual papillary carcinoma of the thyroid versus benign thyroid (P = 0.005). In addition, for all types of papillary carcinomas evaluated, c-Met expression was significantly higher in specimens with extracapsular spread (P = 0.01) and skeletal muscle invasion (P = 0.02), and approached significance for specimens with lymphatic invasion (P = 0.06). After adjusting for extracapsular spread, c-Met expression was still found to be associated significantly with tall cell histology (P < 0.0001).

CONCLUSIONS

c-Met expression is a significant marker for tall cell variant papillary carcinoma of the thyroid and its invasive behavior. This finding may explain the unusually aggressive behavior of this tumor and suggests a role for c-Met in the early identification of patients with tall cell variant thyroid disease.

Concurrent overexpression of Ets-1 and c-Met correlates with a phenotype of high cellular motility in human esophageal cancer

Hepatocyte growth factor (HGF) stimulates cell motility as well as mitotic activity of cells. High concentrations of HGF or overexpression of its cellular receptor c-Met in cancer have been reported. We analyzed the expression status of c-Met immunohistochemically in 76 cases of human esophageal cancer. Overexpression of c-Met was noted at a considerably high frequency. Intriguingly, c-Met overexpression was frequent in a specific type of cell nest formation in tumors, i.e., the small nest type, in which tumors form small, dispersed cell nests. Further immunohistochemical analyses using serial sections revealed a striking coincidence between overexpression of c-Met and its transcriptional factor, Ets-1. Overexpression of c-Met and Ets-1 was statistically more frequent in small nest type tumors. The close correlation in expression status between Ets-1 and c-Met was also confirmed using 6 established human esophageal cancer cell lines. In addition, cells that expressed high levels of Ets-1 and c-Met exhibited an extremely motile phenotype by HGF stimulation in vitro. The presence of HGF in tissue sections was confirmed using similar immunohistochemical approaches. These observations suggest that in human esophageal cancer cells the transcriptional factor Ets-1 upregulates the expression of c-Met and, consequently, confers on cells a highly motile phenotype leading to a specific form of tumor development.

Expression and localization of HGF and met in Wilms' tumours

A number of growth factors and cognate receptors that contribute to normal kidney development have been shown to play roles in the pathogenesis of Wilms' tumours. Expression of both hepatocyte growth factor (HGF) and its tyrosine kinase receptor met has been demonstrated in normal tissues and their neoplastic counterparts, implicating these factors in normal development and tumour progression. HGF and met expression has not been studied in Wilms' tumour. Since HGF and met function in a paracrine fashion by regulating tubulogenesis in normal kidney development, they could be involved in the pathogenesis of Wilms' tumour, in which tubular formation is dysplastic. In the present study, a series of ten homotypic (consisting of blastemal, epithelial, and stromal elements) and ten heterotypic (consisting of triphasic histology and a muscle component) Wilms' tumour cases were examined for expression of HGF and met, using in situ hybridization, immunohistochemistry, and western blot analysis. Relatively high met message and protein expression, compared with normal kidney, were evident in homotypic and heterotypic tumour blastemal, epithelial, and rhabdomyoblastic cells and a 145 kD met polypeptide was found in all tumours, with a few cases also expressing the 170 kD precursor form. No apparent alterations of the met receptor were observed. Similarly, HGF protein was also abundantly expressed in blastemal, epithelial, and rhabdomyoblastic cells of the homotypic and heterotypic Wilms' tumours and a 69 kD HGF polypeptide was demonstrated by western blot analysis. Immunohistochemistry for the Ki-67 proliferation marker indicated that the pattern of Ki-67 expression correlated with the HGF and met pattern of expression in both homotypic and heterotypic tumours. These results reveal, for the first time, significant co-expression of met/HGF in Wilms' tumours, with a correspondingly high proliferative index in the same cell groups.

Met protein and hepatocyte growth factor (HGF) in papillary carcinoma of the thyroid: evidence for a pathogenetic role in tumourigenesis

In the last 10 years, evidence has accumulated that overexpression of Met protein is a distinguishing feature of almost every case of well-differentiated papillary carcinoma. Increased expression of the protein is probably due to enhanced transcription of the MET gene and/or to post-transcriptional mechanisms. So far, alterations of the MET gene have not been recognized, but evidence has been provided that activated RAS and RET can cause accumulation of MET RNA. Thus, the possibility exists that dysregulation of MET is the final result of different molecular pathways capable of inducing thyroid cell transformation; RET rearrangements might account for some of the cases, but the demonstration that the majority of papillary carcinomas do not have recognized alterations of the RET gene strongly suggests that MET gene dysregulation can also be achieved through other molecular pathways. Dysregulation of MET causes marked accumulation of Met protein in tumour cells that is promptly detected by immunohistochemistry. Thus, overexpression of Met protein might represent an immunohistochemical marker of papillary carcinoma, potentially helpful in problematic cases, but caution is required; moderate expression of Met protein is observed in non-neoplastic thyroid diseases, such as Graves' and Hashimoto's thyroiditis, and reagents active on paraffin sections may have a low affinity and/or low specificity for Met protein, leading to artifactual staining. Met protein-positive papillary carcinoma cells may produce hepatocyte growth factor (HGF) and may activate HGF through the urokinase-type plasminogen activator (uPA) bound to urokinase-type plasminogen activator receptor (uPA-R). Thus, papillary carcinoma cells possess the molecular machinery necessary for a productive HGF/Met interaction. In vitro studies have demonstrated that HGF enhances the motility and invasiveness of tumour cells and induces the synthesis and release of chemokines active in the recruitment of dendritic cells. These observations provide a rational basis for the understanding of two distinguishing features of papillary carcinoma. First, the tumour is often characterized by early metastatic spread to regional lymph nodes and by multifocal involvement of the gland, which suggests highly invasive behaviour. Second, a prominent peritumoural inflammatory reaction is often observed, which suggests cross-talk between tumour cells and the immune system.

Molecular pathogenesis of thyroid nodules and cancer

Tumours derived from the thyroid follicular epithelium represent an informative model for understanding the molecular pathogenesis of multistage tumourigenesis, which is the prevailing theory on cancer development and progression nowadays. The early stages of thyroid tumour development appear to be the consequence of the activation or 'de novo' expression of several proto-oncogenes or growth factor receptors, such as ras, ret, NTRK, met, gsp and the thyrotropin (TSH) receptor. Alterations in the expression pattern of these genes are associated with the development of differentiated neoplasms, ranging from benign toxic adenomas (gsp and TSH receptor), to follicular (ras) and papillary (ret/PTC, NTRK, met) carcinomas. They may all be considered to be early events of thyroid cell transformation and, for some, experimental evidence derived from gene transfer studies supports this hypothesis. Alterations in tumour suppressor genes (p53, Rb) are associated instead with the most aggressive and poorly differentiated forms of thyroid cancer, indicating that, in the thyroid tumourigenic process, they represent late genetic events. Specific environmental factors (iodine deficiency, ionizing radiations) have been shown to play a crucial role in promoting the development of thyroid cancer, influencing both its genotypic and phenotypic features. Interestingly, a high percentage of genetic lesions causing thyroid cancer originate from gene rearrangements and chromosomal translocations (ret/PTC, NTRK, Pax-8/PPARgamma) a finding which, being a rare event in most epithelial tumours, makes the molecular pathogenesis of thyroid cancer unique. The uninterrupted flow of information on the molecular genetics of thyroid nodules and cancer will broaden the correlation between genotype and phenotype and will also provide important information for the development of more accurate preoperative diagnostic tools and more efficient treatment choices for the different forms of thyroid cancer.