A signaling adapter function for alpha6beta4 integrin in the control of HGF-dependent invasive growth

Hepatocyte growth factor promotes melanoma metastasis through ubiquitin-specific peptidase 22-mediated integrins upregulation

Hepatocyte growth factor (HGF) plays a critical role in promoting tumor migration, invasion, and metastasis, partly by upregulating integrins. The molecular mechanisms behind how HGF facilitates integrin-mediated tumorigenesis are not fully understood. In this study, we demonstrate that the ubiquitin-specific peptidase 22 (USP22) is essential for HGF-induced melanoma metastasis. HGF treatment dramatically increased the expression of both USP22 and multiple integrin family members in particular ITGAV, ITGB3, and ITGA1. An unbiased analysis of the TCGA database reveals integrins as common downstream targets of both USP22 and HGF across multiple human cancer types. Notably, CRISPR-mediated deletion of USP22 completely eliminates HGF-induced integrin expression in melanoma cells. At the molecular level, USP22 acts as a bona fide deubiquitinase for Sp1, a transcription factor for the ITGAV, ITGB3, and ITGA1 genes. USP22 interacts with and inhibits Sp1 ubiquitination, protecting against Sp1 proteasomal degradation. Supporting this, immunohistology analysis detects a positive correlation among USP22, Sp1, and integrin αv in human melanoma tissues. This study identifies the death from the signature gene USP22 as a critical positive regulator for HGF-induced integrin expression by deubiquitinating the Sp1 transcription factor during melanoma metastasis.

Comparative transcriptomics of the garden dormouse hypothalamus during hibernation

Torpor or heterothermy is an energy-saving mechanism used by endotherms to overcome harsh environmental conditions. During winter, the garden dormouse (Eliomys quercinus) hibernates with multiday torpor bouts and body temperatures of a few degrees Celsius, interrupted by brief euthermic phases. This study investigates gene expression within the hypothalamus, the key brain area controlling energy balance, adding information on differential gene expression potentially relevant to orchestrate torpor. A de novo assembled transcriptome of the hypothalamus was generated from garden dormice hibernating under constant darkness without food and water at 5 °C. Samples were collected during early torpor, late torpor, and interbout arousal. During early torpor, 765 genes were differentially expressed as compared with interbout arousal. Twenty-seven pathways were over-represented, including pathways related to hemostasis, extracellular matrix organization, and signaling of small molecules. Only 82 genes were found to be differentially expressed between early and late torpor, and no pathways were over-represented. During late torpor, 924 genes were differentially expressed relative to interbout arousal. Despite the high number of differentially expressed genes, only 10 pathways were over-represented. Of these, eight were also observed to be over-represented when comparing early torpor and interbout arousal. Our results are largely consistent with previous findings in other heterotherms. The addition of a transcriptome of a novel species may help to identify species-specific and overarching torpor mechanisms through future species comparisons.

Non B Cell-Derived Immunoglobulins in Lung Epithelial Cells and Lung Cancer

As the locus for air exchange, lung tissue is perpetually exposed to a significant quantity of foreign pathogens. Consequently, lung has developed a refined and intricate immune system. Beyond their physical and chemical barrier roles, lung epithelial cells can contribute to immune defence through the expression of Toll-like receptors (TLRs) and other pattern recognition receptors, along with the secretion of cytokines. Emerging evidence demonstrates that lung epithelial cells can generate and secrete immunoglobulins (Igs), including IgM, IgA, or IgG, thus performing antibody function. Moreover, malignantly transformed lung epithelial cells have been discovered to produce high levels of Ig, predominantly IgG, which do not fulfill the role of antibodies, but instead carries out tumour-promoting activity. Structural analysis has indicated that the biological activity of IgG produced by lung cancer cells differs from that of Igs produced by normal lung epithelial cells due to the unique glycosylation modification. Specifically, the sialylated IgG (SIA-IgG), characterised by a non-traditional N-glycosylation modification at the Asn162 site of Igγ CH1, is highly expressed in tumour stem cells. It has been demonstrated that SIA-IgG relies on this unique sialylation modification to promote tumorigenesis, metastasis, and immune evasion. Current results have proven that the Ig produced by lung epithelial cells has multifaceted biological activities, including immune defence functions under physiological conditions, while acquiring tumour-promoting activity during malignant transformation. These insights possess potential for the diagnosis and treatment of lung cancer as novel biomarkers and targets.

The laminin-keratin link shields the nucleus from mechanical deformation and signalling

The mechanical properties of the extracellular matrix dictate tissue behaviour. In epithelial tissues, laminin is a very abundant extracellular matrix component and a key supporting element. Here we show that laminin hinders the mechanoresponses of breast epithelial cells by shielding the nucleus from mechanical deformation. Coating substrates with laminin-111-unlike fibronectin or collagen I-impairs cell response to substrate rigidity and YAP nuclear localization. Blocking the laminin-specific integrin β4 increases nuclear YAP ratios in a rigidity-dependent manner without affecting the cell forces or focal adhesions. By combining mechanical perturbations and mathematical modelling, we show that β4 integrins establish a mechanical linkage between the substrate and keratin cytoskeleton, which stiffens the network and shields the nucleus from actomyosin-mediated mechanical deformation. In turn, this affects the nuclear YAP mechanoresponses, chromatin methylation and cell invasion in three dimensions. Our results demonstrate a mechanism by which tissues can regulate their sensitivity to mechanical signals.

An Observatory for the MET Oncogene: A Guide for Targeted Therapies

The MET proto-oncogene encodes a pivotal tyrosine kinase receptor, binding the hepatocyte growth factor (HGF, also known as scatter factor, SF) and governing essential biological processes such as organogenesis, tissue repair, and angiogenesis. The pleiotropic physiological functions of MET explain its diverse role in cancer progression in a broad range of tumors; genetic/epigenetic alterations of MET drive tumor cell dissemination, metastasis, and acquired resistance to conventional and targeted therapies. Therefore, targeting MET emerged as a promising strategy, and many efforts were devoted to identifying the optimal way of hampering MET signaling. Despite encouraging results, however, the complexity of MET's functions in oncogenesis yields intriguing observations, fostering a humbler stance on our comprehension. This review explores recent discoveries concerning MET alterations in cancer, elucidating their biological repercussions, discussing therapeutic avenues, and outlining future directions. By contextualizing the research question and articulating the study's purpose, this work navigates MET biology's intricacies in cancer, offering a comprehensive perspective.

Liver-Inspired Polyetherketoneketone Scaffolds Simulate Regenerative Signals and Mobilize Anti-Inflammatory Reserves to Reprogram Macrophage Metabolism for Boosted Osteoporotic Osseointegration

Tissue regeneration is regulated by morphological clues of implants in bone defect repair. Engineered morphology can boost regenerative biocascades that conquer challenges such as material bioinertness and pathological microenvironments. Herein, a correlation between the liver extracellular skeleton morphology and the regenerative signaling, namely hepatocyte growth factor receptor (MET), is found to explain the mystery of rapid liver regeneration. Inspired by this unique structure, a biomimetic morphology is prepared on polyetherketoneketone (PEKK) via femtosecond laser etching and sulfonation. The morphology reproduces MET signaling in macrophages, causing positive immunoregulation and optimized osteogenesis. Moreover, the morphological clue activates an anti-inflammatory reserve (arginase-2) to translocate retrogradely from mitochondria to the cytoplasm due to the difference in spatial binding of heat shock protein 70. This translocation enhances oxidative respiration and complex II activity, reprogramming the metabolism of energy and arginine. The importance of MET signaling and arginase-2 in the anti-inflammatory repair of biomimetic scaffolds is also verified via chemical inhibition and gene knockout. Altogether, this study not only provides a novel biomimetic scaffold for osteoporotic bone defect repair that can simulate regenerative signals, but also reveals the significance and feasibility of strategies to mobilize anti-inflammatory reserves in bone regeneration.

MET Receptor Tyrosine Kinase Inhibition Reduces Interferon-Gamma (IFN-γ)-Stimulated PD-L1 Expression through the STAT3 Pathway in Melanoma Cells

Melanoma is the leading cause of death from cutaneous malignancy. While targeted therapy and immunotherapy with checkpoint inhibitors have significantly decreased the mortality rate of this disease, advanced melanoma remains a therapeutic challenge. Here, we confirmed that interferon-gamma (IFN-γ)-induced PD-L1 expression in melanoma cell lines. This increased expression was down-regulated by the reduction in phosphorylated STAT3 signaling via MET tyrosine kinase inhibitor treatment. Furthermore, immunoprecipitation and confocal immunofluorescence microscopy analysis reveals MET and PD-L1 protein-protein interaction and colocalization on the cell surface membrane of melanoma cells. Together, these findings demonstrate that the IFN-γ-induced PD-L1 expression in melanoma cells is negatively regulated by MET inhibition through the JAK/STAT3 signaling pathway and establish the colocalization and interaction between an RTK and a checkpoint protein in melanoma cells.

Inhibition of the SLC35B2-TPST2 Axis of Tyrosine Sulfation Attenuates the Growth and Metastasis of Pancreatic Ductal Adenocarcinom

BACKGROUND & AIMS

Pancreatic ductal adenocarcinoma (PDAC) is the fourth leading cause of cancer deaths in the United States. Tyrosine sulfation, catalyzed by the tyrosylprotein sulfotransferase 2 (TPST2), is a post-translational modification essential for protein-protein interactions and cellular functions. Solute carrier family 35 member B (SLC35B2) is a key transporter that transports the universal sulfate donor 3'-phosphoadenosine 5'-phosphosulfate into the Golgi apparatus where the protein sulfation occurs. The goal of this study was to determine whether and how the SLC35B2-TPST2 axis of tyrosine sulfation plays a role in PDAC.

METHODS

Gene expression was analyzed in PDAC patients and mice. Human PDAC MIA PaCa-2 and PANC-1 cells were used for in vitro studies. TPST2-deficient MIA PaCa-2 cells were generated to assess xenograft tumor growth in vivo. Mouse PDAC cells derived from the KrasLSL-G12D/+;Tp53L/+;Pdx1-Cre (KPC) mice were used to generate Tpst2 knockout KPC cells to evaluate tumor growth and metastasis in vivo.

RESULTS

High expressions of SLC35B2 and TPST2 were correlated with poor PDAC patient survival. Knocking down SLC35B2 or TPST2, or pharmacologicically inhibiting sulfation, resulted in the inhibition of PDAC cell proliferation and migration in vitro. TPST2-deficient MIA PaCa-2 cells showed inhibited xenograft tumor growth. Orthotopic inoculation of Tpst2 knockout KPC cells in mice showed inhibition of primary tumor growth, local invasion, and metastasis. Mechanistically, the integrin β4 was found to be a novel substrate of TPST2. Inhibition of sulfation destabilizes integrin β4 protein, which may have accounted for the suppression of metastasis.

CONCLUSIONS

Targeting the SLC35B2-TPST2 axis of tyrosine sulfation may represent a novel approach for therapeutic intervention of PDAC.

The Role of cMET in Gastric Cancer—A Review of the Literature

Gastric cancer (GC) is an important cause of cancer worldwide with over one million new cases yearly. The vast majority of cases present in stage IV disease, and it still bears a poor prognosis. However, since 2010, progress has been made with the introduction of targeted therapies against HER2 and with checkpoint inhibitors (PDL1). More agents interfering with other targets (FGFR2B, CLDN18.2) are being investigated. cMET is a less frequent molecular target that has been studied for gastric cancer. It is a proto-oncogene that leads to activation of the MAPK pathway and the PI3K pathway, which is responsible for activating the MTOR pathway. The prevalence of cMET is strongly debated as different techniques are being used to detect MET-driven tumors. Because of the difference in diagnostic assays, selecting patients who benefit from cMET inhibitors is difficult. In this review, we discuss the pathway of cMET, its clinical significance and the different diagnostic assays that are currently used, such as immunohistochemy (IHC), fluorescence in situ hybridization (FISH), the H-score and next-generation sequencing (NGS). Next, we discuss all the current data on cMET inhibitors in gastric cancer. Since the data on cMET inhibitors are very heterogenous, it is difficult to provide a general consensus on the outcome, as inclusion criteria differ between trials. Diagnosing cMET-driven gastric tumors is difficult, and potentially the only accurate determination of cMET overexpression/amplification may be next-generation sequencing (NGS).

KCNF1 promotes lung cancer by modulating ITGB4 expression

Lung cancer continues to be the leading cause of cancer death in the United States. Despite recent advances, the five-year survival rate for lung cancer compared to other cancers still remains fairly low. The discovery of molecular targets for lung cancer is key to the development of new approaches and therapies. Electrically silent voltage-gated potassium channel (KvS) subfamilies, which are unable to form functional homotetramers, are implicated in cell-cycle progression, cell proliferation and tumorigenesis. Here, we analyzed the expression of KvS subfamilies in human lung tumors and identified that potassium voltage-gated channel subfamily F member 1 (KCNF1) was up-regulated in non-small cell lung cancer (NSCLC). Silencing of KCNF1 in NSCLC cell lines reduced cell proliferation and tumor progression in mouse xenografts, re-established the integrity of the basement membrane, and enhanced cisplatin sensitivity. KCNF1 was predominately localized in the nucleoplasm and likely mediated its functions in an ion-independent manner. We identified integrin β4 subunit (ITGB4) as a downstream target for KCNF1. Our findings suggest that KCNF1 promotes lung cancer by enhancing ITGB4 signaling and implicate KCNF1 as a novel therapeutic target for lung cancer.

KRAS Mutants Upregulate Integrin β4 to Promote Invasion and Metastasis in Colorectal Cancer

KRAS mutation in colorectal cancer is associated with aggressive tumor behavior through increased invasiveness and higher rates of lung metastases, but the biological mechanisms behind these features are not fully understood. In this study, we show that KRAS-mutant colorectal cancer upregulates integrin α6β4 through ERK/MEK signaling. Knocking-out integrin β4 (ITGB4) specifically depleted the expression of integrin α6β4 and this resulted in a reduction in the invasion and migration ability of the cancer cells. We also observed a reduction in the number and area of lung metastatic foci in mice that were injected with ITGB4 knockout KRAS-mutant colorectal cancer cells compared with the mice injected with ITGB4 wild-type KRAS-mutant colorectal cancer cells, while no difference was observed in liver metastases. Inhibiting integrin α6β4 in KRAS-mutant colorectal cancer could be a potential therapeutic target to diminish the KRAS-invasive phenotype and associated pulmonary metastasis rate.

IMPLICATIONS

Knocking-out ITGB4, which is overexpressed in KRAS-mutant colorectal cancer and promotes tumor aggressiveness, diminishes local invasiveness and rates of pulmonary metastasis.

Revising the Role of Integrin Subunit β4 Expression in Colon Cancer Progression and Survival

PURPOSE

Integrin subunit β4 (β4) has been proposed to play an important role in colon cancer progression through its involvement in hemidesmosome disassembly processes and tumor cell migration. However, the association between β4 expression and clinicopathological outcomes in colon cancer remains unclear.

METHODS

Expression of β4 was assessed by immunohistochemistry in a large cohort of 651 colon cancer patients, the largest colon cancer cohort so far. Chi-squared tests were used to study the association between β4 expression and clinicopathological features. Overall and disease-free survival were assessed by Cox proportional hazard models.

RESULTS

Loss of β4 expression was associated with local tumor invasion. Only 17.9% of the pT1 tumors displayed weak β4 expression level versus 28.1% of pT4 tumors, and 25.0% of the pT1 tumors had a high expression level versus 8.6% of the pT4 tumors (p = 0.012). No association between β4 expression and overall (p = 0.845) or disease-free survival (p = 0.767) was encountered, which disputes the role of β4 as a biomarker of malignant behavior in colon cancer.

CONCLUSION

Contradictory reports have suggested opposite roles for β4 expression in (colon) cancer progression. In the present large cohort of colon cancer patients, we found that β4 expression was not associated with worse clinical prognosis, but decreased with advanced pathological tumor stage. Future studies should establish whether loss of β4 expression promotes invasive characteristics of colon cancer cells.

c-Met-integrin cooperation: Mechanisms, tumorigenic effects, and therapeutic relevance

c-Met is a receptor tyrosine kinase which upon activation by its ligand, the hepatocyte growth factor, mediates many important signalling pathways that regulate cellular functions such as survival, proliferation, and migration. Its oncogenic and tumorigenic signalling mechanisms, greatly contributing to cancer development and progression, are well documented. Integrins, heterogeneous adhesion receptors which facilitate cell-extracellular matrix interactions, are important in biomechanically sensitive cell adhesion and motility but also modulate diverse cell behaviour. Here we review the studies which reported cooperation between c-Met and several integrins, particularly β1 and β4, in various cell models including many tumour cell types. From the various experimental models and results analysed, we propose that c-Met-integrin cooperation occurs via inside-out or outside-in signalling. Thus, either c-Met activation triggers integrin activation and cell adhesion or integrin adhesion to its extracellular ligand triggers c-Met activation. These two modes of cooperation require the adhesive function of integrins and mostly lead to cell migration and invasion. In a third, less conventional, mode of cooperation, the integrin plays the role of a signalling adaptor for c-Met, independently from its adhesive property, leading to anchorage independent survival. Recent studies have revealed the influence of endocytic trafficking in c-Met-integrin cooperation including the adaptor function of integrin occurring on endomembranes, triggering an inside-in signalling, believed to promote survival of metastatic cells. We present the evidence of the cooperation in vivo and in human tissues and highlight its therapeutic relevance. A better understanding of the mechanisms regulating c-Met-integrin cooperation in cancer progression could lead to the design of new therapies targeting this cooperation, providing more effective therapeutic approaches than c-Met or integrin inhibitors as monotherapies used in the clinic.

A MET-PTPRK kinase-phosphatase rheostat controls ZNRF3 and Wnt signaling

Zinc and ring finger 3 (ZNRF3) is a transmembrane E3 ubiquitin ligase that targets Wnt receptors for ubiquitination and lysosomal degradation. Previously, we showed that dephosphorylation of an endocytic tyrosine motif (4Y motif) in ZNRF3 by protein tyrosine phosphatase receptor-type kappa (PTPRK) promotes ZNRF3 internalization and Wnt receptor degradation (Chang et al 2020). However, a responsible protein tyrosine kinase(s) (PTK) phosphorylating the 4Y motif remained elusive. Here we identify the proto-oncogene MET (mesenchymal-epithelial transition factor) as a 4Y kinase. MET binds to ZNRF3 and induces 4Y phosphorylation, stimulated by the MET ligand HGF (hepatocyte growth factor, scatter factor). HGF-MET signaling reduces ZNRF3-dependent Wnt receptor degradation thereby enhancing Wnt/β-catenin signaling. Conversely, depletion or pharmacological inhibition of MET promotes the internalization of ZNRF3 and Wnt receptor degradation. We conclude that HGF-MET signaling phosphorylates- and PTPRK dephosphorylates ZNRF3 to regulate ZNRF3 internalization, functioning as a rheostat for Wnt signaling that may offer novel opportunities for therapeutic intervention.

Regulation of hemidesmosome dynamics and cell signaling by integrin α6β4

Hemidesmosomes (HDs) are specialized multiprotein complexes that connect the keratin cytoskeleton of epithelial cells to the extracellular matrix (ECM). In the skin, these complexes provide stable adhesion of basal keratinocytes to the underlying basement membrane. Integrin α6β4 is a receptor for laminins and plays a vital role in mediating cell adhesion by initiating the assembly of HDs. In addition, α6β4 has been implicated in signal transduction events that regulate diverse cellular processes, including proliferation and survival. In this Review, we detail the role of α6β4 in HD assembly and beyond, and we discuss the molecular mechanisms that regulate its function.

C1GALT1 in health and disease

O-linked glycosylation (O-glycosylation) and N-linked glycosylation (N-glycosylation) are the two most important forms of protein glycosylation, which is an important post-translational modification. The regulation of protein function involves numerous mechanisms, among which protein glycosylation is one of the most important. Core 1 synthase glycoprotein-N-acetylgalactosamine 3-β-galactosyltransferase 1 (C1GALT1) serves an important role in the regulation of O-glycosylation and is an essential enzyme for synthesizing the core 1 structure of mucin-type O-glycans. Furthermore, C1GALT1 serves a vital role in a number of biological functions, such as angiogenesis, platelet production and kidney development. Impaired C1GALT1 expression activity has been associated with different types of human diseases, including inflammatory or immune-mediated diseases, and cancer. O-glycosylation exists in normal tissues, as well as in tumor tissues. Previous studies have revealed that changes in the level of glycosyltransferase in different types of cancer may be used as potential therapeutic targets. Currently, numerous studies have reported the dual role of C1GALT1 in tumors (carcinogenesis and cancer suppression). The present review reports the role of C1GALT1 in normal development and human diseases. Since the mechanism and regulation of C1GALT1 and O-glycosylation remain elusive, further studies are required to elucidate their effects on development and disease.

Role of laminin and cognate receptors in cholangiocarcinoma cell migration

Extensive desmoplasia in cholangiocarcinoma (CCA) is associated with tumor aggressiveness, indicating a need for further understanding of CCA cell-matrix interaction. This study demonstrated laminin as the most potent attractant for CCA cell migration and the vast elevation of its receptor integrin β4 (ITGB4) in CCA cell lines. Besides, their high expressions in CCA tissues were correlated with lymphatic invasion and the presence of ITGB4 was also associated with short survival time. ITGB4 silencing revealed it as the receptor for laminin-induced HuCCA-1 migration, but KKU-213 utilized 37/67-kDa laminin receptor (LAMR) instead. These findings highlight the role of ITGB4 and LAMR in transducing laminin induction of CCA cell migration and the potential of ITGB4 as diagnostic and prognostic biomarkers for CCA.

The roles of integrins in cancer

Integrin-mediated adhesion of cells to the extracellular matrix (ECM) is crucial for the physiological development and functioning of tissues but is pathologically disrupted in cancer. Indeed, abnormal regulation of integrin receptors and ECM ligands allows cancer cells to break down tissue borders, breach into blood and lymphatic vessels, and survive traveling in suspension through body fluids or residing in metabolically or pharmacologically hostile environments. Different molecular and cellular mechanisms responsible for the modulation of integrin adhesive function or mechanochemical signaling are altered and participate in cancer. Cancer development and progression are also bolstered by dysfunctionalities of integrin-mediated ECM adhesion occurring both in tumor cells and in elements of the surrounding tumor microenvironment, such as vascular cells, cancer-associated fibroblasts, and immune cells. Mounting evidence suggests that integrin inhibitors may be effectively exploited to overcome resistance to standard-of-care anti-cancer therapies.

EGFR-dependent tyrosine phosphorylation of integrin β4 is not required for downstream signaling events in cancer cell lines

In epithelial cancers, the epidermal growth factor receptor (EGFR) and integrin α6β4 are frequently overexpressed and found to synergistically activate intracellular signaling pathways that promote cell proliferation and migration. In cancer cells, the β4 subunit is phosphorylated at tyrosine residues not normally recognized as kinase substrates; however, the function of these phosphotyrosine residues in cancer cells is a subject of much debate. In EGFR-overexpressing carcinoma cells, we found that the Src family kinase (SFK) inhibitor PP2 reduces β4 tyrosine phosphorylation following the activation of EGFR. However, siRNA mediated knockdown of the SFKs Src, Fyn, Yes and Lyn, individually or in combination, did not affect the EGF-induced phosphorylation of β4. Using phospho-peptide affinity chromatography and mass spectrometry, we found that PLCγ1 binds β4 at the phosphorylated residues Y1422/Y1440, but were unable to verify this interaction in A431 carcinoma cells that overexpress the EGFR. Furthermore, using A431 cells devoid of β4 or reconstituted with phenylalanine specific mutants of β4, the activation of several downstream signaling pathways, including PLCγ/PKC, MAPK and PI3K/Akt, were not substantially affected. We conclude that tyrosine-phosphorylated β4 does not enhance EGFR-mediated signaling in EGFR-overexpressing cells, despite the fact that this integrin subunit is highly tyrosine phosphorylated in these cells.

State of the structure address on MET receptor activation by HGF

The MET receptor tyrosine kinase (RTK) and its cognate ligand hepatocyte growth factor (HGF) comprise a signaling axis essential for development, wound healing and tissue homeostasis. Aberrant HGF/MET signaling is a driver of many cancers and contributes to drug resistance to several approved therapeutics targeting other RTKs, making MET itself an important drug target. In RTKs, homeostatic receptor signaling is dependent on autoinhibition in the absence of ligand binding and orchestrated set of conformational changes induced by ligand-mediated receptor dimerization that result in activation of the intracellular kinase domains. A fundamental understanding of these mechanisms in the MET receptor remains incomplete, despite decades of research. This is due in part to the complex structure of the HGF ligand, which remains unknown in its full-length form, and a lack of high-resolution structures of the complete MET extracellular portion in an apo or ligand-bound state. A current view of HGF-dependent MET activation has evolved from biochemical and structural studies of HGF and MET fragments and here we review what these findings have thus far revealed.

Phenotypic Plasticity of Cancer Cells Based on Remodeling of the Actin Cytoskeleton and Adhesive Structures

There is ample evidence that, instead of a binary switch, epithelial-mesenchymal transition (EMT) in cancer results in a flexible array of phenotypes, each one uniquely suited to a stage in the invasion-metastasis cascade. The phenotypic plasticity of epithelium-derived cancer cells gives them an edge in surviving and thriving in alien environments. This review describes in detail the actin cytoskeleton and E-cadherin-based adherens junction rearrangements that cancer cells need to implement in order to achieve the advantageous epithelial/mesenchymal phenotype and plasticity of migratory phenotypes that can arise from partial EMT.

A receptor-antibody hybrid hampering MET-driven metastatic spread

Background

The receptor encoded by the MET oncogene and its ligand Hepatocyte Growth Factor (HGF) are at the core of the invasive-metastatic behavior. In a number of instances genetic alterations result in ligand-independent onset of malignancy (MET addiction). More frequently, ligand stimulation of wild-type MET contributes to progression toward metastasis (MET expedience). Thus, while MET inhibitors alone are effective in the first case, combination therapy with ligand inhibitors is required in the second condition.

Methods

In this paper, we generated hybrid molecules gathering HGF and MET inhibitory properties. This has been achieved by ‘head-to-tail’ or ‘tail-to-head’ fusion of a single chain Fab derived from the DN30 MET antibody with a recombinant ‘ad-hoc’ engineered MET extracellular domain (decoyMET), encompassing the HGF binding site but lacking the DN30 epitope.

Results

The hybrid molecules correctly bind MET and HGF, inhibit HGF-induced MET downstream signaling, and quench HGF-driven biological responses, such as growth, motility and invasion, in cancer cells of different origin. Two metastatic models were generated in mice knocked-in by the human HGF gene: (i) orthotopic transplantation of pancreatic cancer cells; (ii) subcutaneous injection of primary cells derived from a cancer of unknown primary. Treatment with hybrid molecules strongly affects time of onset, number, and size of metastatic lesions.

Conclusion

These results provide a strategy to treat metastatic dissemination driven by the HGF/MET axis.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13046-020-01822-5.

Forcing a growth factor response - tissue-stiffness modulation of integrin signaling and crosstalk with growth factor receptors

Research throughout the 90s established that integrin crosstalk with growth factor receptors stimulates robust growth factor signaling. These insights were derived chiefly from comparing adherent versus suspension cell cultures. Considering the new understanding that mechanosensory inputs tune adhesion signaling, it is now timely to revisit this crosstalk in different mechanical environments. Here, we present a brief historical perspective on integrin signaling against the backdrop of the mechanically diverse extracellular microenvironment, then review the evidence supporting the mechanical regulation of integrin crosstalk with growth factor signaling. We discuss early studies revealing distinct signaling consequences for integrin occupancy (binding to matrix) and aggregation (binding to immobile ligand). We consider how the mechanical environments encountered in vivo intersect with this diverse signaling, focusing on receptor endocytosis. We discuss the implications of mechanically tuned integrin signaling for growth factor signaling, using the epidermal growth factor receptor (EGFR) as an illustrative example. We discuss how the use of rigid tissue culture plastic for cancer drug screening may select agents that lack efficacy in the soft in vivo tissue environment. Tuning of integrin signaling via external mechanical forces in vivo and subsequent effects on growth factor signaling thus has implications for normal cellular physiology and anti-cancer therapies.

A Non-genetic Mechanism Involving the Integrin β4/Paxillin Axis Contributes to Chemoresistance in Lung Cancer

Tumor heterogeneity and cisplatin resistance are major causes of tumor relapse and poor survival. Here, we show that in lung cancer, interaction between paxillin (PXN) and integrin β4 (ITGB4), components of the focal adhesion (FA) complex, contributes to cisplatin resistance. Knocking down PXN and ITGB4 attenuated cell growth and improved cisplatin sensitivity, both in 2D and 3D cultures. PXN and ITGB4 independently regulated expression of several genes. In addition, they also regulated expression of common genes including USP1 and VDAC1, which are required for maintaining genomic stability and mitochondrial function, respectively. Mathematical modeling suggested that bistability could lead to stochastic phenotypic switching between cisplatin-sensitive and resistant states in these cells. Consistently, purified subpopulations of sensitive and resistant cells re-created the mixed parental population when cultured separately. Altogether, these data point to an unexpected role of the FA complex in cisplatin resistance and highlight a novel non-genetic mechanism.

Interplay between Cell-Surface Receptors and Extracellular Matrix in Skin

Skin consists of the epidermis and dermis, which are connected by a specialized basement membrane-the epidermal basement membrane. Both the epidermal basement membrane and the underlying interstitial extracellular matrix (ECM) created by dermal fibroblasts contain distinct network-forming macromolecules. These matrices play various roles in order to maintain skin homeostasis and integrity. Within this complex interplay of cells and matrices, cell surface receptors play essential roles not only for inside-out and outside-in signaling, but also for establishing mechanical and biochemical properties of skin. Already minor modulations of this multifactorial cross-talk can lead to severe and systemic diseases. In this review, major epidermal and dermal cell surface receptors will be addressed with respect to their interactions with matrix components as well as their roles in fibrotic, inflammatory or tumorigenic skin diseases.

In vivo modeling of the EGFR family in breast cancer progression and therapeutic approaches

Modeling breast cancer through the generation of genetically engineered mouse models (GEMMs) has become the gold standard in the study of human breast cancer. Notably, the in vivo modeling of the epidermal growth factor receptor (EGFR) family has been key to the development of therapeutics and has helped better understand the signaling pathways involved in cancer initiation, progression and metastasis. The HER2/ErbB2 receptor is a member of the EGFR family and 20% of breast cancers are found to belong in the HER2-positive histological subtype. Historical and more recent advances in the field have shaped our understanding of HER2-positive breast cancer signaling and therapeutic approaches.

FAM83A exerts tumor‑suppressive roles in cervical cancer by regulating integrins

Family with sequence similarity 83 member A (FAM83A) has been recently observed to be upregulated in various types of cancer and hypothesized to be serve as an oncogene. The present study aimed to determine the functional roles and the underlying molecular mechanism of FAM83A in cervical cancer. The results demonstrated that although FAM83A expression was increased in cervical cancer compared with normal tissues, the expression levels of FAM83A were decreased in patients with advanced FIGO stage, deep stromal invasion, poor differentiation and/or lymph node metastasis and negatively associated with short survival time of patients with cervical cancer. FAM83A knockdown promoted cell proliferative, migratory and invasive abilities of CaSki and HeLa cells. A mouse xenograft model demonstrated that FAM83A knockdown promoted tumor growth in vivo. Mechanistically, RNA sequencing results revealed that knockdown of FAM83A increased the transcription of genes mainly associated with oncogenesis-associated pathways. In addition, FAM83A knockdown increased the protein levels of α1, α3, α5, β4 and β5 integrins in vitro and in vivo, and the expression of FAM83A was also negatively associated with the levels of these proteins in human cervical cancer tissue samples. In conclusion, the results of the present study suggested that FAM83A may exert a tumor-suppressive role in cervical cancer by suppressing the expression of integrins, which may offer new insight into the biological basis of cervical cancer.

The c-Met inhibitor capmatinib alleviates acetaminophen-induced hepatotoxicity

Acetaminophen (APAP)-induced hepatotoxicity comes among the most frequent humans' toxicities caused by drugs. So far, therapeutic interventions for such type of drug-induced toxicity are still limited. In the current study, we examined the influence of capmatinib (Cap), a novel c-Met inhibitor, on APAP-induced hepatotoxicity in mice when administered 2 h prior, 2 h post and 4 h post APAP-challenge. The results revealed that Cap administration significantly attenuated APAP-induced liver injury when administered only 2 h prior and post APAP-administration. Cap hepatoprotective effect was mediated by lowering the excessive formation of lipid peroxidation and nitrosative stress products caused by APAP. Besides, Cap attenuated APAP-induced overproduction and release of proinflammatory mediators like TNF-α, IL-1β, IL-17A, IL-6, and MCP-1. Cap treatment also led to avoidance of APAP-subsequent repair by abating APAP-induced elevation of hepatic IL-22 and PCNA expressions. In conclusion, c-Met receptor inhibition may be a potential strategy for alleviating APAP-hepatotoxicity, especially when administered in the early phase of intoxication.

MET targeting: time for a rematch

MET, the receptor tyrosine kinase (RTK) for hepatocyte growth factor, is a proto-oncogene involved in embryonic development and throughout life in homeostasis and tissue regeneration. Deregulation of MET signaling has been reported in numerous malignancies, prompting great interest in MET targeting for cancer therapy. The present review offers a summary of the biology of MET and its known functions in normal physiology and carcinogenesis, followed by an overview of the most relevant MET-targeting strategies and corresponding clinical trials, highlighting both past setbacks and promising future prospects. By placing their efforts on a more precise stratification strategy through the genetic analysis of tumors, modern trials such as the NCI-MATCH trial could revive the past enthusiasm for MET-targeted therapy.

The Role of MET in Melanoma and Melanocytic Lesions

Melanoma is the leading cause of death due to cutaneous malignancy and its incidence is on the rise. Several signaling pathways, including receptor tyrosine kinases, have been recognized to have an etiopathogenetic role in the development and progression of precursor melanocytic lesions and malignant melanoma. Among those, the hepatocyte growth factor/MET (HGF/MET) axis is emerging as a critical player not only in the tumor itself but also in the immune microenvironment in which the tumor grows and advances in its development. Moreover, the activation of this pathway has emerged as a paradigm of tumor resistance to modern targeted therapies, and the assessment of its expression in patients' samples may be a valuable biomarker of tumor progression and response to targeted therapy. Here we summarize our current understanding of this important receptor tyrosine kinase in normal melanocyte proliferation/motility, in tumor progression and metastasis, its genetic alterations in certain subtype of melanocytic lesions, and how its pathway has been explored for the development of selective inhibitors.

Mechanistically detailed systems biology modeling of the HGF/Met pathway in hepatocellular carcinoma

Hepatocyte growth factor (HGF) signaling through its receptor Met has been implicated in hepatocellular carcinoma tumorigenesis and progression. Met interaction with integrins is shown to modulate the downstream signaling to Akt and ERK (extracellular-regulated kinase). In this study, we developed a mechanistically detailed systems biology model of HGF/Met signaling pathway that incorporated specific interactions with integrins to investigate the efficacy of integrin-binding peptide, AXT050, as monotherapy and in combination with other therapeutics targeting this pathway. Here we report that the modeled dynamics of the response to AXT050 revealed that receptor trafficking is sufficient to explain the effect of Met-integrin interactions on HGF signaling. Furthermore, the model predicted patient-specific synergy and antagonism of efficacy and potency for combination of AXT050 with sorafenib, cabozantinib, and rilotumumab. Overall, the model provides a valuable framework for studying the efficacy of drugs targeting receptor tyrosine kinase interaction with integrins, and identification of synergistic drug combinations for the patients.

Are Integrins Still Practicable Targets for Anti-Cancer Therapy?

Correlative clinical evidence and experimental observations indicate that integrin adhesion receptors, in particular those of the αV family, are relevant to cancer cell features, including proliferation, survival, migration, invasion, and metastasis. In addition, integrins promote events in the tumor microenvironment that are critical for tumor progression and metastasis, including tumor angiogenesis, matrix remodeling, and the recruitment of immune and inflammatory cells. In spite of compelling preclinical results demonstrating that the inhibition of integrin αVβ3/αVβ5 and α5β1 has therapeutic potential, clinical trials with integrin inhibitors targeting those integrins have repeatedly failed to demonstrate therapeutic benefits in cancer patients. Here, we review emerging integrin functions and their proposed contribution to tumor progression, discuss preclinical evidence of therapeutic significance, revisit clinical trial results, and consider alternative approaches for their therapeutic targeting in oncology, including targeting integrins in the other cells of the tumor microenvironment, e.g., cancer-associated fibroblasts and immune/inflammatory cells. We conclude that integrins remain a valid target for cancer therapy; however, agents with better pharmacological properties, alternative models for their preclinical evaluation, and innovative combination strategies for clinical testing (e.g., together with immuno-oncology agents) are needed.

Role of Integrins in Resistance to Therapies Targeting Growth Factor Receptors in Cancer

Integrins contribute to cancer progression and aggressiveness by activating intracellular signal transduction pathways and transducing mechanical tension forces. Remarkably, these adhesion receptors share common signaling networks with receptor tyrosine kinases (RTKs) and support their oncogenic activity, thereby promoting cancer cell proliferation, survival and invasion. During the last decade, preclinical studies have revealed that integrins play an important role in resistance to therapies targeting RTKs and their downstream pathways. A remarkable feature of integrins is their wide-ranging interconnection with RTKs, which helps cancer cells to adapt and better survive therapeutic treatments. In this context, we should consider not only the integrins expressed in cancer cells but also those expressed in stromal cells, since these can mechanically increase the rigidity of the tumor microenvironment and confer resistance to treatment. This review presents some of these mechanisms and outlines new treatment options for improving the efficacy of therapies targeting RTK signaling.

Integrin Signaling in Cancer: Mechanotransduction, Stemness, Epithelial Plasticity, and Therapeutic Resistance

Integrins mediate cell adhesion and transmit mechanical and chemical signals to the cell interior. Various mechanisms deregulate integrin signaling in cancer, empowering tumor cells with the ability to proliferate without restraint, to invade through tissue boundaries, and to survive in foreign microenvironments. Recent studies have revealed that integrin signaling drives multiple stem cell functions, including tumor initiation, epithelial plasticity, metastatic reactivation, and resistance to oncogene- and immune-targeted therapies. Here, we discuss the mechanisms leading to the deregulation of integrin signaling in cancer and its various consequences. We place emphasis on novel functions, determinants of context dependency, and mechanism-based therapeutic opportunities.

Extracellular Matrix Influencing HGF/c-MET Signaling Pathway: Impact on Cancer Progression

The extracellular matrix (ECM) is a crucial component of the tumor microenvironment involved in numerous cellular processes that contribute to cancer progression. It is acknowledged that tumor–stromal cell communication is driven by a complex and dynamic network of cytokines, growth factors and proteases. Thus, the ECM works as a reservoir for bioactive molecules that modulate tumor cell behavior. The hepatocyte growth factor (HGF) produced by tumor and stromal cells acts as a multifunctional cytokine and activates the c-MET receptor, which is expressed in different tumor cell types. The HGF/c-MET signaling pathway is associated with several cellular processes, such as proliferation, survival, motility, angiogenesis, invasion and metastasis. Moreover, c-MET activation can be promoted by several ECM components, including proteoglycans and glycoproteins that act as bridging molecules and/or signal co-receptors. In contrast, c-MET activation can be inhibited by proteoglycans, matricellular proteins and/or proteases that bind and sequester HGF away from the cell surface. Therefore, understanding the effects of ECM components on HGF and c-MET may provide opportunities for novel therapeutic strategies. Here, we give a short overview of how certain ECM components regulate the distribution and activation of HGF and c-MET.

Updates on the hepatocyte growth factor/c-Met axis in hepatocellular carcinoma and its therapeutic implications

Hepatocellular carcinoma (HCC) is the fifth most common cancer and is the second leading cause of cancer death. Since the diagnosis of HCC is difficult, in many cases patients with HCC are diagnosed advanced stage of development. Hepatocyte growth factor (HGF)/c-mesenchymal-epithelial transition receptor (c-Met) axis is a key signaling pathway in HCC, either via canonical or non-canonical pathways. Available treatments against HCC based upon HGF/c-Met inhibition can increase patient lifespan, but do not reach the expected therapeutic benefits. In HCC, c-Met monomers can bind other receptor monomers, activating several noncanonical signaling pathways, leading to increased cell proliferation, invasion, motility, and drug resistance. All of these processes are enhanced by the tumor microenvironment, with stromal cells contributing to boost tumor progression through oxidative stress, angiogenesis, lymphangiogenesis, inflammation, and fibrosis. Novel treatments against HCC are being explored to modulate other targets such as microRNAs, methyltransferases, and acetyltransferases, which are all involved in the regulation of gene expression in cancer. This review compiles basic knowledge regarding signaling pathways in HCC, and compounds already used or showing potential to be used in clinical trials.

Every step of the way: integrins in cancer progression and metastasis

Cell adhesion to the extracellular matrix is fundamental to tissue integrity and human health. Integrins are the main cellular adhesion receptors that through multifaceted roles as signalling molecules, mechanotransducers and key components of the cell migration machinery are implicated in nearly every step of cancer progression from primary tumour development to metastasis. Altered integrin expression is frequently detected in tumours, where integrins have roles in supporting oncogenic growth factor receptor (GFR) signalling and GFR-dependent cancer cell migration and invasion. In addition, integrins determine colonization of metastatic sites and facilitate anchorage-independent survival of circulating tumour cells. Investigations describing integrin engagement with a growing number of versatile cell surface molecules, including channels, receptors and secreted proteins, continue to lead to the identification of novel tumour-promoting pathways. Integrin-mediated sensing, stiffening and remodelling of the tumour stroma are key steps in cancer progression supporting invasion, acquisition of cancer stem cell characteristics and drug resistance. Given the complexity of integrins and their adaptable and sometimes antagonistic roles in cancer cells and the tumour microenvironment, therapeutic targeting of these receptors has been a challenge. However, novel approaches to target integrins and antagonism of specific integrin subunits in stringently stratified patient cohorts are emerging as potential ways forward.

Known and novel roles of the MET oncogene in cancer: a coherent approach to targeted therapy

The MET oncogene encodes an unconventional receptor tyrosine kinase with pleiotropic functions: it initiates and sustains neoplastic transformation when genetically altered ('oncogene addiction') and fosters cancer cell survival and tumour dissemination when transcriptionally activated in the context of an adaptive response to adverse microenvironmental conditions ('oncogene expedience'). Moreover, MET is an intrinsic modulator of the self-renewal and clonogenic ability of cancer stem cells ('oncogene inherence'). Here, we provide the latest findings on MET function in cancer by focusing on newly identified genetic abnormalities in tumour cells and recently described non-mutational MET activities in stromal cells and cancer stem cells. We discuss how MET drives cancer clonal evolution and progression towards metastasis, both ab initio and under therapeutic pressure. We then elaborate on the use of MET inhibitors in the clinic with a critical appraisal of failures and successes. Ultimately, we advocate a rationale to improve the outcome of anti-MET therapies on the basis of thorough consideration of the entire spectrum of MET-mediated biological responses, which implicates adequate patient stratification, meaningful biomarkers and appropriate clinical end points.

The Impact of the Epithelial-Mesenchymal Transition Regulator Hepatocyte Growth Factor Receptor/Met on Skin Immunity by Modulating Langerhans Cell Migration

Langerhans cells (LCs), the epidermal dendritic cell (DC) subset, express the transmembrane tyrosine kinase receptor Met also known as hepatocyte growth factor (HGF) receptor. HGF is the exclusive ligand of Met and upon binding executes mitogenic, morphogenic, and motogenic activities to various cells. HGF exerts anti-inflammatory activities via Met signaling and was found to regulate various functions of immune cells, including differentiation and maturation, cytokine production, cellular migration and adhesion, and T cell effector function. It has only recently become evident that a number of HGF-regulated functions in inflammatory processes and immune responses are imparted via DCs. However, the mechanisms by which Met signaling in DCs conveys its immunoregulatory effects have not yet been fully understood. In this review, we focus on the current knowledge of Met signaling in DCs with particular attention on the morphogenic and motogenic activities. Met signaling was shown to promote DC mobility by regulating matrix metalloproteinase activities and adhesion. This is a striking resemblance to the role of Met in regulating a cell fate program during embryonic development, wound healing, and in tumor invasion known as epithelial–mesenchymal transition (EMT). Hence, we propose the concept that an EMT program is executed by Met signaling in LCs.

Integrin α6 promotes esophageal cancer metastasis and is targeted by miR-92b

Tumor invasion and metastasis is responsible for the poor prognosis of esophageal squamous cell carcinoma (ESCC); therefore, exploring the mechanisms by which malignant cells disseminate, spread and flourish in secondary sites, as well as translating the bench results to clinical practice are in urgent need. Previous reports showed that integrin α6 increases in ESCC specimens and its dysregulated spatial localization correlates positively with the unfavorable outcome of ESCC patients. Here, we clarify that integrin α6 promotes invasion and metastasis of ESCC cells In vitro and in vivo. Mechanistically, decreased integrin α6 attenuates motility of malignant cells partially through deactivating Akt pathway, which is essential for ESCC cells motility. Moreover, integrin α6 serves as a genuine target of miR-92b in suppressing ESCC motility. Our results for the first time describe that miR-92b/integrin α6/Akt axis controls the motility of ESCC, thereby providing a promising diagnosis or therapeutic option.

HGF potentiates extracellular matrix-driven migration of human myoblasts: involvement of matrix metalloproteinases and MAPK/ERK pathway

Background

The hepatocyte growth factor (HGF) is required for the activation of muscle progenitor cells called satellite cells (SC), plays a role in the migration of proliferating SC (myoblasts), and is present as a soluble factor during muscle regeneration, along with extracellular matrix (ECM) molecules. In this study, we aimed at determining whether HGF is able to interact with ECM proteins, particularly laminin 111 and fibronectin, and to modulate human myoblast migration.

Methods

We evaluated the expression of the HGF-receptor c-Met, laminin, and fibronectin receptors by immunoblotting, flow cytometry, or immunofluorescence and used Transwell assays to analyze myoblast migration on laminin 111 and fibronectin in the absence or presence of HGF. Zymography was used to check whether HGF could modulate the production of matrix metalloproteinases by human myoblasts, and the activation of MAPK/ERK pathways was evaluated by immunoblotting.

Results

We demonstrated that human myoblasts express c-Met, together with laminin and fibronectin receptors. We observed that human laminin 111 and fibronectin have a chemotactic effect on myoblast migration, and this was synergistically increased when low doses of HGF were added. We detected an increase in MMP-2 activity in myoblasts treated with HGF. Conversely, MMP-2 inhibition decreased the HGF-associated stimulation of cell migration triggered by laminin or fibronectin. HGF treatment also induced in human myoblasts activation of MAPK/ERK pathways, whose specific inhibition decreased the HGF-associated stimulus of cell migration triggered by laminin 111 or fibronectin.

Conclusions

We demonstrate that HGF induces ERK phosphorylation and MMP production, thus stimulating human myoblast migration on ECM molecules. Conceptually, these data state that the mechanisms involved in the migration of human myoblasts comprise both soluble and insoluble moieties. This should be taken into account to optimize the design of therapeutic cell transplantation strategies by improving the migration of donor cells within the host tissue, a main issue regarding this approach.

Electronic supplementary material

The online version of this article (10.1186/s13395-017-0138-6) contains supplementary material, which is available to authorized users.

A Review of Anti-Angiogenic Targets for Monoclonal Antibody Cancer Therapy

Tumor angiogenesis is a key event that governs tumor progression and metastasis. It is controlled by the complicated and coordinated actions of pro-angiogenic factors and their receptors that become upregulated during tumorigenesis. Over the past several decades, vascular endothelial growth factor (VEGF) signaling has been identified as a central axis in tumor angiogenesis. The remarkable advent of recombinant antibody technology has led to the development of bevacizumab, a humanized antibody that targets VEGF and is a leading clinical therapy to suppress tumor angiogenesis. However, despite the clinical efficacy of bevacizumab, its significant side effects and drug resistance have raised concerns necessitating the identification of novel drug targets and development of novel therapeutics to combat tumor angiogenesis. This review will highlight the role and relevance of VEGF and other potential therapeutic targets and their receptors in angiogenesis. Simultaneously, we will also cover the current status of monoclonal antibodies being developed to target these candidates for cancer therapy.

Identification of a novel population of highly cytotoxic c-Met-expressing CD8+ T lymphocytes

CD8⁺ cytotoxic T lymphocytes (CTLs) are critical mediators of anti-tumor immunity, and controlling the mechanisms that govern CTL functions could be crucial for enhancing patient outcome. Previously, we reported that hepatocyte growth factor (HGF) limits effective murine CTL responses via antigen-presenting cells. Here, we show that a fraction of murine effector CTLs expresses the HGF receptor c-Met (c-Met⁺ CTLs). Phenotypic and functional analysis of c-Met⁺ CTLs reveals that they display enhanced cytolytic capacities compared to their c-Met^- CTL counterparts. Furthermore, HGF directly restrains the cytolytic function of c-Met⁺ CTLs in cell-mediated cytotoxicity reactions in vitro and in vivo and abrogates T-cell responses against metastatic melanoma in vivo Finally, we establish in three murine tumor settings and in human melanoma tissues that c-Met⁺ CTLs are a naturally occurring CD8⁺ T-cell population. Together, our findings suggest that the HGF/c-Met pathway could be exploited to control CD8⁺ T-cell-mediated anti-tumor immunity.

Roles of Integrin α6β4 Glycosylation in Cancer

Malignant transformation is accompanied with aberrant glycosylation of proteins. Such changes in glycan structure also occur in the integrins, which are a large family of cell surface receptors for the extracellular matrix and play key roles in tumor progression. There is now increasing evidence that glycosylation of integrins affects cellular signaling and interaction with the extracellular matrix, receptor tyrosine kinases, and galectins, thereby regulating cell adhesion, motility, growth, and survival. Integrin α6β4 is a receptor for laminin-332 and the increased expression level is correlated with malignant progression and poor survival in various types of cancers. Recent studies have revealed that integrin α6β4 plays central roles in tumorigenesis and the metastatic process. In this review, we summarize our current understanding of the molecular mechanisms of tumor progression driven by integrin α6β4 and also discuss the modification of glycans on integrin β4 subunit to address the important roles of glycan in integrin-mediated tumor progression.

Targeting c-MET in gastrointestinal tumours: rationale, opportunities and challenges

Data from many preclinical studies, including those using cellular models of colorectal, gastric, gastro-oesophageal and gastro-oesophageal junction cancers, indicate that the hepatocyte growth factor (HGF)-hepatocyte growth factor receptor (c-MET) pathway is vital for the growth, survival and invasive potential of gastrointestinal cancers. Following the availability of data from these various studies, and data on c-MET expression as a biomarker that indicates a poor prognosis in patients with gastrointestinal cancer and increased c-MET expression, inhibitors targeting this pathway have entered the clinic in the past decade. However, the design of clinical trials that incorporate the use of HGF/c-MET inhibitors in their most appropriate genetic and molecular context remains crucial. Recognizing and responding to this challenge, the European Commission funded Framework 7 MErCuRIC programme is running a biomarker-enriched clinical trial investigating the efficacy of combined c-MET/MEK inhibition in patients with RAS-mutant or RAS-wild-type metastatic colorectal cancer with aberrant c-MET expression. The design of this trial enables the continued refinement of the predictive biomarker and co-development of companion diagnostics. In this Review, we focus on advances in our understanding of inhibition of the HGF/c-MET pathway in patients with gastro-intestinal cancers, the prominent challenges facing the clinical translation and implementation of agents targeting HGF/c-MET, and discuss the various efforts, and associated obstacles to the discovery and validation of biomarkers that will enable patient stratification in this context.

Crosstalk between insulin-like growth factor (IGF) receptor and integrins through direct integrin binding to IGF1

It has been generally accepted that integrin cell adhesion receptors are involved in growth factor signaling (integrin-growth factor crosstalk), since antagonists to integrins often suppress growth factor signaling. Partly because integrins have been originally identified as cell adhesion receptors to extracellular matrix (ECM) proteins, current models of the crosstalk between IGF1 and integrins propose that ECM ligands (e.g., vitronectin) bind to integrins and IGF1 binds to IGF receptor type 1 (IGF1R), and two separate signals merge inside the cells. Our research proves otherwise. We discovered that IGF1 interacts directly with integrins, and induces integrin-IGF-IGF1R complex formation on the cell surface. IGF1 signaling can be detected in the absence of ECM (anchorage-independent conditions). Integrin antagonists block both ECM-integrin interaction and IGF-integrin interaction, and do not distinguish the two. This is one possible reason why integrin-IGF1 interaction has not been detected. With these new discoveries, we believe that the direct IGF-integrin interaction should be incorporated into models of IGF1 signaling. The integrin-binding defective mutant of IGF1 is defective in inducing IGF signaling, although the mutant still binds to IGF1R. Notably, the IGF1 mutant is dominant-negative and suppresses cell proliferation induced by wt IGF1, and suppresses tumorigenesis in vivo, and thus the IGF1 mutant has potential as a therapeutic.

Integrin β4 promotes cell invasion and epithelial-mesenchymal transition through the modulation of Slug expression in hepatocellular carcinoma

Integrin β4 (ITGB4) is a transmembrane receptor involved in tumorigenesis and the invasiveness of many cancers. However, its role in hepatocellular carcinoma (HCC), one of the most prevalent human cancers worldwide, remains unclear. Here, we examined the involvement of ITGB4 in HCC and explored the underlying mechanisms. Real-time PCR and immunohistochemical analyses of tissues from 82 patients with HCC and four HCC cell lines showed higher ITGB4 levels in tumor than in adjacent non-tumor tissues and in HCC than in normal hepatic cells. Silencing of ITGB4 repressed cell proliferation, colony forming ability and cell invasiveness, whereas ectopic expression of ITGB4 promoted the proliferation and invasion of HCC cells and induced epithelial to mesenchymal transition (EMT) in parallel with the upregulation of Slug, as shown by transwell assays, WB and immunocytochemistry. Knockdown of Slug reduced cell viability inhibited invasion and reversed the effects of ITBG4 overexpression on promoting EMT, and AKT/Sox2-Nanog may also be involved. In a xenograft tumor model induced by injection of ITGB4-overexpressing cells into nude mice, ITGB4 promoted tumor growth and metastasis to the lungs. Taken together, our results indicate that ITGB4 plays a tumorigenic and pro-metastatic role mediated by Slug and suggest IGTB4 could be a prognostic indicator or a therapeutic target in patients with HCC.

The role of the HGF/Met axis in mesothelioma

Malignant mesothelioma is an asbestos-related cancer that occurs most commonly in the pleural space and is incurable. Increasing evidence suggests that aberrant receptor tyrosine kinase (RTK)-directed signalling plays a key role in the pathogenesis of this cancer. In the majority of mesotheliomas, up-regulated expression or signalling by Met, the receptor for hepatocyte growth factor (HGF) can be demonstrated. Following binding of ligand, Met relays signals that promote cell survival, proliferation, movement, invasiveness, branching morphogenesis and angiogenesis. Here we describe the HGF/Met axis and review the mechanisms that lead to the aberrant activation of this signalling system in mesothelioma. We also describe the cross-talk that occurs between HGF/Met and a number of other receptors, ligands and co-receptor systems. The prevalent occurrence of HGF/Met dysregulation in patients with mesothelioma sets the scene for the investigation of pharmaceutical inhibitors of this axis. In light of the inter-relationship between HGF/Met and other ligand receptor, combinatorial targeting strategies may provide opportunities for therapeutic advancement in this challenging tumour.