Synergistic inhibition of cell migration by tetraspanin CD82 and gangliosides occurs via the EGFR or cMet-activated Pl3K/Akt signalling pathway

The MET Oncogene Network of Interacting Cell Surface Proteins

The MET oncogene, encoding the hepatocyte growth factor (HGF) receptor, plays a key role in tumorigenesis, invasion, and resistance to therapy, yet its full biological functions and activation mechanisms remain incompletely understood. A feature of MET is its extensive interaction network, encompassing the following: (i) receptor tyrosine kinases (RTKs); (ii) co-receptors (e.g., CDCP1, Neuropilin1); (iii) adhesion molecules (e.g., integrins, tetraspanins); (iv) proteases (e.g., ADAM10); and (v) other receptors (e.g., CD44, plexins, GPCRs, and NMDAR). These interactions dynamically modulate MET's activation, signaling, intracellular trafficking, and degradation, enhancing its functional versatility and oncogenic potential. This review offers current knowledge on MET's partnerships, focusing on their functional impact on signaling output, therapeutic resistance, and cellular behavior. Finally, we evaluate emerging combination therapies targeting MET and its interactors, highlighting their potential to overcome resistance and improve clinical outcomes. By exploring the complex interplay within the MET network of interacting cell surface proteins, this review provides insights into advancing anti-cancer strategies and understanding the broader implications of RTK crosstalk in oncology.

Glycan-Lectin interactions between platelets and tumor cells drive hematogenous metastasis

Glycosylation is a ubiquitous cellular or microenvironment-specific post-translational modification that occurs on the surface of normal cells and tumor cells. Tumor cell-associated glycosylation is involved in hematogenous metastasis. A wide variety of tumors undergo aberrant glycosylation to interact with platelets. As platelets have many opportunities to engage circulating tumor cells, they represent an important avenue into understanding the role glycosylation plays in tumor metastasis. Platelet involvement in tumor metastasis is evidenced by observations that platelets protect tumor cells from damaging shear forces and immune system attack, aid metastasis through the endothelium at specific sites, and facilitate tumor survival and colonization. During platelet-tumor-cell interactions, many opportunities for glycan-ligand binding emerge. This review integrates the latest information about glycans, their ligands, and how they mediate platelet-tumor interactions. We also discuss adaptive changes that tumors undergo upon glycan-lectin binding and the impact glycans have on targeted therapeutic strategies for treating tumors in clinical settings.

Impact of Neuron-Derived HGF on c-Met and KAI-1 in CNS Glial Cells: Implications for Multiple Sclerosis Pathology

Demyelination and axonal degeneration are fundamental pathological characteristics of multiple sclerosis (MS), an inflammatory disease of the central nervous system (CNS). Although the molecular mechanisms driving these processes are not fully understood, hepatocyte growth factor (HGF) has emerged as a potential regulator of neuroinflammation and tissue protection in MS. Elevated HGF levels have been reported in MS patients receiving immunomodulatory therapy, indicating its relevance in disease modulation. This study investigated HGF's neuroprotective effects using transgenic mice that overexpressed HGF. The experimental autoimmune encephalomyelitis (EAE) model, which mimics MS pathology, was employed to assess demyelination and axonal damage in the CNS. HGF transgenic mice showed delayed EAE progression, with reduced CNS inflammation, decreased demyelination, and limited axonal degeneration. Scanning electron microscopy confirmed the preservation of myelin and axonal integrity in these mice. In addition, we explored HGF's effects using a cuprizone-induced demyelination model, which operates independently of the immune system. HGF transgenic mice exhibited significant protection against demyelination in this model as well. We also investigated the expression of key HGF receptors, particularly c-Met and KAI-1. While c-Met, which is associated with increased inflammation, was upregulated in EAE, its expression was significantly reduced in HGF transgenic mice, correlating with decreased neuroinflammation. Conversely, KAI-1, which has been linked to axonal protection and stability, showed enhanced expression in HGF transgenic mice, suggesting a protective mechanism against axonal degeneration. These findings underscore HGF's potential in preserving CNS structure and function, suggesting it may be a promising therapeutic target for MS, offering new hope for mitigating disease progression and enhancing neuroprotection.

Metabolomics of Esophageal Squamous Cell Carcinoma Tissues: Potential Biomarkers for Diagnosis and Promising Targets for Therapy

Background

The incidence of esophageal squamous cell carcinoma in China ranks first in the world. The early diagnosis technology is underdeveloped, and the prognosis is poor, which seriously threatens the quality of life of the Chinese people. Epidemiological findings are related to factors such as diet, living habits, and age. The specific mechanism is not clear yet. Metabolomics is a kind of omics that simultaneously and quantitatively analyzes the comprehensive profile of metabolites in living systems. It has unique advantages in the study of the diagnosis and pathogenesis of tumor-related diseases, especially in the search for biomarkers. Therefore, it is desirable to perform metabolic profiling analysis of cancer tissues through metabolomics to find potential biomarkers for the diagnosis and treatment of esophageal squamous cell carcinoma.

Methods

HPLC-TOF-MS/MS technology and Illumina Hiseq Xten Sequencing was used for the analysis of 210 pairs of matched esophageal squamous cell carcinoma tissues and normal tissues in Zhenjiang City, Jiangsu Province, a high-incidence area of esophageal cancer in China. Bioinformatics analysis was also performed.

Results

Through metabolomic and transcriptomic analysis, this study found that a total of 269 differential metabolites were obtained in esophageal squamous cell carcinoma and normal tissues, and 48 differential metabolic pathways were obtained through KEGG enrichment analysis. After further screening and identification, 12 metabolites with potential biomarkers to differentiate esophageal squamous cell carcinoma from normal tissues were obtained.

Conclusions

From the metabolomic data, 4 unknown compounds were found to be abnormally expressed in esophageal squamous cell carcinoma for the first time, such as 9,10-epoxy-12,15-octadecadienoate; 3 metabolites were found in multiple abnormal expression in another tumor, but upregulation or downregulation was found for the first time in esophageal cancer, such as oleoyl glycine; at the same time, it was further confirmed that five metabolites were abnormally expressed in esophageal squamous cell carcinoma, which was similar to the results of other studies, such as PE.

CD82 and Gangliosides Tune CD81 Membrane Behavior

Tetraspanins are a family of transmembrane proteins that form a network of protein–protein interactions within the plasma membrane. Within this network, tetraspanin are thought to control the lateral segregation of their partners at the plasma membrane through mechanisms involving specific lipids. Here, we used a single molecule tracking approach to study the membrane behavior of tetraspanins in mammary epithelial cells and demonstrate that despite a common overall behavior, each tetraspanin (CD9, CD81 and CD82) has a specific signature in terms of dynamics. Furthermore, we demonstrated that tetraspanin dynamics on the cell surface are dependent on gangliosides. More specifically, we found that CD82 expression increases the dynamics of CD81 and alters its localization at the plasma membrane, this has no effect on the behavior of CD9. Our results provide new information on the ability of CD82 and gangliosides to differentially modulate the dynamics and organization of tetraspanins at the plasma membrane and highlight that its lipid and protein composition is involved in the dynamical architecture of the tetraspanin web. We predict that CD82 may act as a regulator of the lateral segregation of specific tetraspanins at the plasma membrane while gangliosides could play a crucial role in establishing tetraspanin-enriched areas.

Signature of prognostic epithelial-mesenchymal transition related long noncoding RNAs (ERLs) in hepatocellular carcinoma

Reliable biomarkers are of great significance for the treatment and diagnosis of hepatocellular carcinoma (HCC). This study identified potential prognostic epithelial-mesenchymal transition related lncRNAs (ERLs) by the cancer genome atlas (TCGA) database and bioinformatics.The differential expression of long noncoding RNA (lncRNA) was obtained by analyzing the lncRNA data of 370 HCC samples in TCGA. Then, Pearson correlation analysis was carried out with EMT related genes (ERGs) from molecular signatures database. Combined with the univariate Cox expression analysis of the total survival rate of hepatocellular carcinoma (HCC) patients, the prognostic ERLs were obtained. Then use "step" function to select the optimal combination of constructing multivariate Cox expression model. The expression levels of ERLs in HCC samples were verified by real-time quantitative polymerase chain reaction.Finally, we identified 5 prognostic ERLs (AC023157.3, AC099850.3, AL031985.3, AL365203.2, CYTOR). The model showed that these prognostic markers were reliable independent predictors of risk factors (P value <.0001, hazard ratio [HR] = 2.400, 95% confidence interval [CI] = 1.667-3.454 for OS). In the time-dependent receiver operating characteristic analysis, this prognostic marker is a good predictor of HCC survival (area under the curve of 1 year, 2 years, 3 years, and 5 years are 0.754, 0.720, 0.704, and 0.662 respectively). We analyzed the correlation of clinical characteristics of these prognostic markers, and the results show that this prognostic marker is an independent factor that can predict the prognosis of HCC more accurately. In addition, by matching with the Molecular Signatures Database, we obtained 18 ERLs, and then constructed the HCC prognosis model and clinical feature correlation analysis using 5 prognostic ERLs. The results show that these prognostic markers have reliable independent predictive value. Bioinformatics analysis showed that these prognostic markers were involved in the regulation of EMT and related functions of tumor occurrence and migration.Five prognostic types of ERLs identified in this study can be used as potential biomarkers to predict the prognosis of HCC.

Role of Metastasis Suppressor KAI1/CD82 in Different Cancers

Metastasis is one of the characteristics of malignant tumors and the main cause of death worldwide. The process of metastasis is mainly affected by tumor metastasis genes, tumor metastasis suppressor genes, tumor microenvironment, extracellular matrix degradation, and other factors. Thus, it is essential to elucidate the mechanism of metastasis and find the therapeutic targets in order to prevent the development of malignant tumors. KAI1/CD82, a member of tetraspanin superfamily of glycoproteins, has been reported as a tumor metastasis suppressor gene in various types of cancers without affecting the tumor formation. Many studies have demonstrated that low expression of KAI1/CD82 might lead to poor prognosis due to its interactions with other tetraspanins and integrins, resulting in the regulation of cell motility and invasion, cell-cell adhesion, and apoptosis. Considering its pathological and physiological significance, KAI1/CD82 could be a potential strategy for clinical predicting and preventing tumor progression and metastasis. The present review aims to discuss the role of KAI1/CD82 in metastasis for different cancers and examine its prospects as a metastasis biomarker and a therapeutic target.

Gangliosides as Signaling Regulators in Cancer

At the plasma membrane, gangliosides, a group of glycosphingolipids, are expressed along with glycosphingolipids, phospholipids, and cholesterol in so-called lipid rafts that interact with signaling receptors and related molecules. Most cancers present abnormalities in the intracellular signal transduction system involved in tumor growth, invasion, and metastasis. To date, the roles of gangliosides as regulators of signal transduction have been reported in several cancer types. Gangliosides can be expressed by the exogenous ganglioside addition, with their endogenous expression regulated at the enzymatic level by targeting specific glycosyltransferases. Accordingly, the relationship between changes in the composition of cell surface gangliosides and signal transduction has been investigated by controlling ganglioside expression. In cancer cells, several types of signaling molecules are positively or negatively regulated by ganglioside expression levels, promoting malignant properties. Moreover, antibodies against gangliosides have been shown to possess cytotoxic effects on ganglioside-expressing cancer cells. In the present review, we highlight the involvement of gangliosides in the regulation of cancer cell signaling, and we explore possible therapies targeting ganglioside-expressing cancer.

Role of a metastatic suppressor gene KAI1/CD82 in the diagnosis and prognosis of breast cancer

Globally, breast cancer is the most common type of cancer in females and is one of the leading causes of cancer death in women. The advancement in the targeted therapies and the slight understanding of the molecular cascades of the disease have led to small improvement in the rate of survival of breast cancer patients. However, metastasis and resistance to the current drugs still remain as challenges in the management of breast cancer patients. Metastasis, potentially, leads to failure of the available treatment, and thereby, makes the research on metastatic suppressors a high priority. Tumor metastasis suppressors are several genes and their protein products that have the capability of arresting the metastatic process without affecting the tumor formation. The metastasis suppressors KAI1 (also known as CD82) has been found to inhibit tumor metastasis in various types of solid cancers, including breast cancer. KAI1 was identified as a metastasis suppressor that inhibits the process of metastasis by regulating several mechanisms, including cell motility and invasion, induction of cell senescence, cell–cell adhesion and apoptosis. KAI1 is a member of tetraspanin membrane protein family. It interacts with other tetraspanins, chemokines and integrins to control diverse signaling pathways, which are crucial for protein trafficking and intracellular communication. It follows that better understanding of the molecular events of such genes is needed to develop prognostic biomarkers, and to identify specific therapies for breast cancer patients. This review aims to discuss the role of KAI1/CD82 as a prognosticator in breast cancer.

Cooperation and Interplay between EGFR Signalling and Extracellular Vesicle Biogenesis in Cancer

Epidermal growth factor receptor (EGFR) takes centre stage in carcinogenesis throughout its entire cellular trafficking odyssey. When loaded in extracellular vesicles (EVs), EGFR is one of the key proteins involved in the transfer of information between parental cancer and bystander cells in the tumour microenvironment. To hijack EVs, EGFR needs to play multiple signalling roles in the life cycle of EVs. The receptor is involved in the biogenesis of specific EV subpopulations, it signals as an active cargo, and it can influence the uptake of EVs by recipient cells. EGFR regulates its own inclusion in EVs through feedback loops during disease progression and in response to challenges such as hypoxia, epithelial-to-mesenchymal transition and drugs. Here, we highlight how the spatiotemporal rules that regulate EGFR intracellular function intersect with and influence different EV biogenesis pathways and discuss key regulatory features and interactions of this interplay. We also elaborate on outstanding questions relating to EGFR-driven EV biogenesis and available methods to explore them. This mechanistic understanding will be key to unravelling the functional consequences of direct anti-EGFR targeted and indirect EGFR-impacting cancer therapies on the secretion of pro-tumoural EVs and on their effects on drug resistance and microenvironment subversion.

Gangliosides and CD82 inhibit the motility of colon cancer by downregulating the phosphorylation of EGFR at different tyrosine sites and signaling pathways

Previous studies have shown that (GM3), a ganglioside, suppresses hepatoma cell motility and migration by inhibiting phosphorylation of EGFR and the activity of the PI3K/AKT signaling pathway. Therefore, the aim of the present study was to investigate whether the combined treatment of CD82 with gangliosides can exert a synergistic inhibitory effect on cell motility and migration. Epidermal growth factor receptor (EGFR) signaling was studied for its role in the mechanism through which CD82 and gangliosides synergistically inhibit the motility and migration of SW620 human colon adenocarcinoma cells. GM3 and/or GM2 treatment, and/or overexpression of CD82 was performed in SW620 cells. High-performance thin layer chromatography, reverse transcription-quantitative PCR, western blotting and flow cytometry assays were used to confirm the content changes of GM2, GM3 and CD82. In addition, the phosphorylation of EGFR, MAPK and Akt were evaluated by western blot analysis. SW620 cell motility was investigated using wound healing analysis and chemotaxis migration assay. The combination of GM3 and GM2 with CD82 was found to markedly suppress EGF-stimulated SW620 cell motility compared with the individual factors or combination of GM2 or GM3 with CD82 by inhibiting the phosphorylation of EGFR. The results suggested that CD82 in combination with either GM2 or GM3 can exert a synergistic inhibitory effect on cell motility and migration; however, the synergistic mechanisms elicited by GM2 or GM3 with CD82 differ.

Tetraspanin CD82 interaction with cholesterol promotes extracellular vesicle-mediated release of ezrin to inhibit tumour cell movement

Tumour metastasis suppressor KAI1/CD82 inhibits tumour cell movement. As a transmembrane protein, tetraspanin CD82 bridges the interactions between membrane microdomains of lipid rafts and tetraspanin-enriched microdomains (TEMs). In this study, we found that CD82 and other tetraspanins contain cholesterol recognition/interaction amino-acid consensus (CRAC) sequences in their transmembrane domains and revealed that cholesterol binding of CD82 determines its interaction with lipid rafts but not with TEMs. Functionally, CD82 needs cholesterol binding to inhibit solitary migration, collective migration, invasion and infiltrative outgrowth of tumour cells. Importantly, CD82–cholesterol/–lipid raft interaction not only promotes extracellular release of lipid raft components such as cholesterol and gangliosides but also facilitates extracellular vesicle (EV)–mediated release of ezrin–radixin–moesin (ERM) protein Ezrin. Since ERM proteins link actin cytoskeleton to the plasma membrane, we show for the first time that cell movement can be regulated by EV-mediated releases, which disengage the plasma membrane from cytoskeleton and then impair cell movement. Our findings also conceptualize that interactions between membrane domains, in this case converge of lipid rafts and TEMs by CD82, can change cell movement. Moreover, CD82 coalescences with both lipid rafts and TEMs are essential for its inhibition of tumour cell movement and for its enhancement of EV release. Finally, our study underpins that tetraspanins as a superfamily of functionally versatile molecules are cholesterol-binding proteins.

Abbreviations:Ab: antibody; CBM: cholesterol-binding motif; CCM: cholesterol consensus motif; CRAC/CARC: cholesterol recognition or interaction amino-acid consensus; CTxB: cholera toxin B subunit; ECM: extracellular matrix; ERM: ezrin, radixin and moesin; EV: extracellular vesicles; FBS: foetal bovine serum; mAb: monoclonal antibody; MST: microscale thermophoresis; pAb: polyclonal antibody; and TEM: tetraspanin-enriched microdomain

Akt-ing Up Just About Everywhere: Compartment-Specific Akt Activation and Function in Receptor Tyrosine Kinase Signaling

The serine/threonine kinase Akt is a master regulator of many diverse cellular functions, including survival, growth, metabolism, migration, and differentiation. Receptor tyrosine kinases are critical regulators of Akt, as a result of activation of phosphatidylinositol-3-kinase (PI3K) signaling leading to Akt activation upon receptor stimulation. The signaling axis formed by receptor tyrosine kinases, PI3K and Akt, as well as the vast range of downstream substrates is thus central to control of cell physiology in many different contexts and tissues. This axis must be tightly regulated, as disruption of PI3K-Akt signaling underlies the pathology of many diseases such as cancer and diabetes. This sophisticated regulation of PI3K-Akt signaling is due in part to the spatial and temporal compartmentalization of Akt activation and function, including in specific nanoscale domains of the plasma membrane as well as in specific intracellular membrane compartments. Here, we review the evidence for localized activation of PI3K-Akt signaling by receptor tyrosine kinases in various specific cellular compartments, as well as that of compartment-specific functions of Akt leading to control of several fundamental cellular processes. This spatial and temporal control of Akt activation and function occurs by a large number of parallel molecular mechanisms that are central to regulation of cell physiology.

Exosomal protein CD82 as a diagnostic biomarker for precision medicine for breast cancer

CD82, a member of the tetraspanin superfamily, has been proposed to exert its activity via tetra-transmembrane protein enriched microdomains (TEMs) in exosomes. The present study aimed to explore the potential of the exosome protein CD82 in diagnosing breast cancers of all stages and various histological subtypes in patients. The results strongly suggest that CD82 expression in breast cancer tissue was significantly lower than that in healthy and benign breast disease tissues. There was a significant negative correlation between CD82 expression in tissues and CD82 content in exosomes, which indicated that CD82 expression was redistributed from tissues to the blood with the development and metastasis of breast cancer.

GD3 ganglioside-enriched extracellular vesicles stimulate melanocyte migration

Melanomas often accumulate gangliosides, sialic acid-containing glycosphingolipids found in the outer leaflet of plasma membranes, as disialoganglioside G_D3 and its derivatives. Here, we have transfected the G_D3 synthase gene (ST8Sia I) in a normal melanocyte cell line in order to evaluate changes in the biological behavior of non-transformed cells. G_D3-synthase expressing cells converted G_M3 into G_D3 and accumulated both G_D3 and its acetylated form, 9-O-acetyl-G_D3. Melanocytes were rendered more migratory on laminin-1 surfaces. Cell migration studies using the different transfectants, either treated or not with the glucosylceramide synthase inhibitor d-1-threo-1-phenyl-2-palmitoylamino-3-pyrrolidino-1-propanol (PPPP), allowed us to show that while G_M3 is a negative regulator of melanocyte migration, G_D3 increases it. We showed that gangliosides were shed to the matrix by migrating cells and that G_D3 synthase transfected cells shed extracellular vesicles (EVs) enriched in G_D3. EVs enriched in G_D3 stimulated cell migration of G_D3 negative cells, as observed in time lapse microscopy studies. Otherwise, EVs shed by G_M3^+veG_D3^-ve cells impaired migration and diminished cell velocity in cells overexpressing G_D3. The balance of antimigratory G_M3 and promigratory G_D3 gangliosides in melanocytes could be altered not only by the overexpression of enzymes such as ST8Sia I, but also by the horizontal transfer of ganglioside enriched extracellular vesicles. This study highlights that extracellular vesicles transfer biological information also through their membrane components, which include a variety of glycosphingolipids remodeled in disease states such as cancer.

A viral microRNA downregulates metastasis suppressor CD82 and induces cell invasion and angiogenesis by activating the c-Met signaling

Kaposi’s sarcoma (KS) is the most common AIDS-associated malignancy etiologically caused by Kaposi’s sarcoma-associated herpesvirus (KSHV). KS is a highly disseminated and vascularized tumor comprised of poorly differentiated spindle-shaped endothelial cells. KSHV encodes 12 pre-microRNAs (pre-miRNAs) that yield 25 mature miRNAs, but their roles in KSHV-induced tumor dissemination and angiogenesis remain largely unknown. KSHV-encoded miR-K12-6 (miR-K6) can produce two mature miRNAs, miR-K6-3p and miR-K6-5p. Recently, we have shown that miR-K6-3p promoted cell migration and angiogenesis by directly targeting SH3 domain binding glutamate-rich protein (SH3BGR) (PLoS Pathog. 2016;12(4):e1005605). Here, by using mass spectrometry, bioinformatics analysis and luciferase reporter assay, we showed that miR-K6-5p directly targeted the coding sequence (CDS) of CD82 molecule (CD82), a metastasis suppressor. Ectopic expression of miR-K6-5p specifically inhibited the expression of endogenous CD82 and strongly promoted endothelial cells invasion in vitro and angiogenesis in vivo. Overexpression of CD82 significantly inhibited cell invasion and angiogenesis induced by miR-K6-5p. Mechanistically, CD82 directly interacted with c-Met to inhibit its activation. MiR-K6-5p directly repressed CD82, relieving its inhibition on c-Met activation and inducing cell invasion and angiogenesis. Deletion of miR-K6 from KSHV genome abrogated KSHV suppression of CD82 resulting in compromised KSHV activation of c-Met pathway, and KSHV-induced invasion and angiogenesis. In conclusion, these results show that by inhibiting CD82, KSHV miR-K6-5p promotes cell invasion and angiogenesis by activating the c-Met pathway. Our findings illustrate that KSHV miRNAs may play an essential role in the dissemination and angiogenesis of KSHV-induced malignancies.

Promotion of cell growth and adhesion of a peptide hydrogel scaffold via mTOR/cadherin signaling

Understanding neurite outgrowth, orientation, and migration is important for the design of biomaterials that interface with the neural tissue. However, the molecular signaling alternations have not been well elucidated to explain the impact of hydrogels on cell morphology. In our previous studies, a silk fibroin peptide (SF16) hydrogel was found to be an effective matrix for the viability, morphology, and proliferation of PC12 rat pheocrhomocytoma cells. We found that PC12 cells in the peptide hydrogel exhibited adhesive morphology compared to those cultured in agarose or collagen. Moreover, we identified that cell adhesion molecules (E- and N-cadherin) controlled by mTOR signaling were highly induced in PC12 cells cultured in the SF16 peptide hydrogel. Our findings suggest that the SF16 peptide might be suitable to be a cell-adhesion material in cell culture or tissue engineering, and mTOR/cadherin signaling is required for the cell adhesion in the SF16-peptide hydrogel.

Tetraspanins Function as Regulators of Cellular Signaling

Tetraspanins are molecular scaffolds that distribute proteins into highly organized microdomains consisting of adhesion, signaling, and adaptor proteins. Many reports have identified interactions between tetraspanins and signaling molecules, finding unique downstream cellular consequences. In this review, we will explore these interactions as well as the specific cellular responses to signal activation, focusing on tetraspanin regulation of adhesion-mediated (integrins/FAK), receptor-mediated (EGFR, TNF-α, c-Met, c-Kit), and intracellular signaling (PKC, PI4K, β-catenin). Additionally, we will summarize our current understanding for how tetraspanin post-translational modifications (palmitoylation, N-linked glycosylation, and ubiquitination) can regulate signal propagation. Many of the studies outlined in this review suggest that tetraspanins offer a potential therapeutic target to modulate aberrant signal transduction pathways that directly impact a host of cellular behaviors and disease states.

Nuclear Drosha enhances cell invasion via an EGFR-ERK1/2-MMP7 signaling pathway induced by dysregulated miRNA-622/197 and their targets LAMC2 and CD82 in gastric cancer

Drosha is an RNA III-like enzyme that has an aberrant expression in some tumors. Our previous studies showed the aberrant Drosha in gastric tumors. However, the roles of nuclear Drosha, the main regulator of microRNA (miRNA) biogenesis, in gastric cancer (GC) progression remain poorly understood. In this study, we demonstrated that nuclear Drosha is significantly associated with cell invasion of GC and that Drosha silence impedes the tumor invasion. Knockdown of Drosha led to a set of dysregulated miRNAs in GC cells. Multiple targets of these miRNAs were the members in cell migration, invasion and metastasis-associated signaling (e.g. ECM-receptor interaction, focal adhesion, p53 signaling and MAPK signaling pathway) revealed by bioinformatics analysis. LAMC2 (a key element of ECM-receptor signaling) and CD82 (a suppressor of p53 signaling) are the targets of miR-622 and miR-197, respectively. High levels of LAMC2 and low levels of CD82 were significantly related to the worse outcome for GC patients. Furthermore, overexpression of LAMC2 and knockdown of CD82 markedly promoted GC cell invasion and activated EGFR/ERK1/2-MMP7 signaling via upregulation of the expression of phosphorylated (p)-EGFR, p-ERK1/2 and MMP7. Our findings suggest that nuclear Drosha potentially has a role in the development of GC.

Exploiting receptor tyrosine kinase co-activation for cancer therapy

Studies over the past decade have shown that many cancers have evolved receptor tyrosine kinase (RTK) co-activation as a mechanism to drive tumour progression and limit the lethal effects of therapy. This review summarises the general principles of RTK co-activation and discusses approaches to exploit this phenomenon in cancer therapy and drug discovery. Computational strategies to predict kinase co-dependencies by integrating drug screening data and kinase inhibitor selectivity profiles will also be described. We offer a perspective on the implications of RTK co-activation on tumour heterogeneity and cancer evolution and conclude by surveying emerging computational and experimental approaches that will provide insights into RTK co-activation biology and deliver new developments in effective cancer therapies.

Role of Cytokine-Induced Glycosylation Changes in Regulating Cell Interactions and Cell Signaling in Inflammatory Diseases and Cancer

Glycosylation is one of the most important modifications of proteins and lipids, and cell surface glycoconjugates are thought to play important roles in a variety of biological functions including cell-cell and cell-substrate interactions, bacterial adhesion, cell immunogenicity and cell signaling. Alterations of glycosylation are observed in number of diseases such as cancer and chronic inflammation. In that context, pro-inflammatory cytokines have been shown to modulate cell surface glycosylation by regulating the expression of glycosyltransferases involved in the biosynthesis of carbohydrate chains. These changes in cell surface glycosylation are also known to regulate cell signaling and could contribute to disease pathogenesis. This review summarizes our current knowledge of the glycosylation changes induced by pro-inflammatory cytokines, with a particular focus on cancer and cystic fibrosis, and their consequences on cell interactions and signaling.

Tetraspanin CD82: a suppressor of solid tumors and a modulator of membrane heterogeneity

Tetraspanin CD82 suppresses the progression and metastasis of a wide range of solid malignant tumors. However, its roles in tumorigenesis and hematopoietic malignancy remain unclear. Ubiquitously expressed CD82 restrains cell migration and cell invasion by modulating both cell-matrix and cell-cell adhesiveness and confining outside-in pro-motility signaling. This restraint at least contributes to, if not determines, the metastasis-suppressive activity and, also likely, the physiological functions of CD82. As a modulator of cell membrane heterogeneity, CD82 alters microdomains, trafficking, and topography of the membrane by changing the membrane molecular landscape. The functional activities of membrane molecules and the cytoskeletal interaction of the cell membrane are subsequently altered, followed by changes in cellular functions. Given its pathological and physiological importance, CD82 is a promising candidate for clinically predicting and blocking tumor progression and metastasis and also an emerging model protein for mechanistically understanding cell membrane organization and heterogeneity.

Distinct intracellular signaling mediates C-MET regulation of dendritic growth and synaptogenesis

Hepatocyte growth factor (HGF) activation of the MET receptor tyrosine kinase influences multiple neurodevelopmental processes. Evidence from human imaging and mouse models shows that, in the forebrain, disruptions in MET signaling alter circuit formation and function. One likely means of modulation is by controlling neuron maturation. Here, we examined the signaling mechanisms through which MET exerts developmental effects in the neocortex. In situ hybridization revealed that hgf is located near MET-expressing neurons, including deep neocortical layers and periventricular zones. Western blot analyses of neocortical crude membranes demonstrated that HGF-induced MET autophosphorylation peaks during synaptogenesis, with a striking reduction in activation between P14 and P17 just before pruning. In vitro analysis of postnatal neocortical neurons assessed the roles of intracellular signaling following MET activation. There is rapid, HGF-induced phosphorylation of MET, ERK1/2, and Akt that is accompanied by two major morphological changes: increases in total dendritic growth and synapse density. Selective inhibition of each signaling pathway altered only one of the two distinct events. MAPK/ERK pathway inhibition significantly reduced the HGF-induced increase in dendritic length, but had no effect on synapse density. In contrast, inhibition of the PI3K/Akt pathway reduced HGF-induced increases in synapse density, with no effect on dendritic length. The data reveal a key role for MET activation during the period of neocortical neuron growth and synaptogenesis, with distinct biological outcomes mediated via discrete MET-linked intracellular signaling pathways in the same neurons. © 2016 Wiley Periodicals, Inc. Develop Neurobiol 76: 1160-1181, 2016.

Charming neighborhoods on the cell surface: plasma membrane microdomains regulate receptor tyrosine kinase signaling

Receptor tyrosine kinases (RTK) are an important family of growth factor and hormone receptors that regulate many aspects of cellular physiology. Ligand binding by RTKs at the plasma membrane elicits activation of many signaling intermediates. The spatial and temporal regulation of RTK signaling within cells is an important determinant of receptor signaling outcome. In particular, the compartmentalization of the plasma membrane into a number of microdomains allows context-specific control of RTK signaling. Indeed various RTKs are recruited to and enriched within specific plasma membrane microdomains under various conditions, including lipid-ordered domains such as caveolae and lipid rafts, clathrin-coated structures, tetraspanin-enriched microdomains, and actin-dependent protrusive membrane microdomains such as dorsal ruffles and invadosomes. We examine the evidence for control of RTK signaling by each of these plasma membrane microdomains, as well as molecular mechanisms for how this spatial organization controls receptor signaling.

Tetraspanins in cell migration

Tetraspanins are a superfamily of small transmembrane proteins that are expressed in almost all eukaryotic cells. Through interacting with one another and with other membrane and intracellular proteins, tetraspanins regulate a wide range of proteins such as integrins, cell surface receptors, and signaling molecules, and thereby engage in diverse cellular processes ranging from cell adhesion and migration to proliferation and differentiation. In particular, tetraspanins modulate the function of proteins involved in all determining factors of cell migration including cell-cell adhesion, cell-ECM adhesion, cytoskeletal protrusion/contraction, and proteolytic ECM remodeling. We herein provide a brief overview of collective in vitro and in vivo studies of tetraspanins to illustrate their regulatory functions in the migration and trafficking of cancer cells, vascular endothelial cells, skin cells (keratinocytes and fibroblasts), and leukocytes. We also discuss the involvement of tetraspanins in various pathologic and remedial processes that rely on cell migration and their potential value as targets for therapeutic intervention.

A role for Galgt1 in skeletal muscle regeneration

BACKGROUND

Cell surface glycans are known to play vital roles in muscle membrane stability and muscle disease, but to date, roles for glycans in muscle regeneration have been less well understood. Here, we describe a role for complex gangliosides synthesized by the Galgt1 gene in muscle regeneration.

METHODS

Cardiotoxin-injected wild type (WT) and Galgt1 (-/-) muscles, and mdx and Galgt1 (-/-) mdx muscles, were used to study regeneration in response to acute and chronic injury, respectively. Muscle tissue was analyzed at various time points for morphometric measurements and for gene expression changes in satellite cell and muscle differentiation markers by quantitative real-time polymerase chain reaction (qRT-PCR). Primary cell cultures were used to measure growth rate and myotube formation and to identify Galgt1 expression changes after cardiotoxin by fluorescence-activated cell sorting (FACS). Primary cell culture and tissue sections were also used to quantify satellite cell apoptosis.

RESULTS

A query of a microarray data set of cardiotoxin-induced mouse muscle gene expression changes identified Galgt1 as the most upregulated glycosylation gene immediately after muscle injury. This was validated by qRT-PCR as a 23-fold upregulation in Galgt1 expression 1 day after cardiotoxin administration and a 16-fold upregulation in 6-week-old mdx muscles. These changes correlated with increased expression of Galgt1 protein and GM1 ganglioside in mononuclear muscle cells. In the absence of Galgt1, cardiotoxin-induced injury led to significantly reduced myofiber diameters after 14 and 28 days of regeneration. Myofiber diameters were also significantly reduced in Galgt1-deficient mdx mice compared to age-matched mdx controls, and this was coupled with a significant increase in the loss of muscle tissue. Cardiotoxin-injected Galgt1 (-/-) muscles showed reduced gene expression of the satellite cell marker Pax7 and increased expression of myoblast markers MyoD, Myf5, and Myogenin after injury along with a tenfold increase in apoptosis of Pax7-positive muscle cells. Cultured primary Galgt1 (-/-) muscle cells showed a normal growth rate but demonstrated premature fusion into myofibers, resulting in an overall impairment of myofiber formation coupled with a threefold increase in muscle cell apoptosis.

CONCLUSIONS

These experiments demonstrate a role for Galgt1 in skeletal muscle regeneration and suggest that complex gangliosides made by Galgt1 modulate the survival and differentiation of satellite cells.

c-Met and Other Cell Surface Molecules: Interaction, Activation and Functional Consequences

The c-Met receptor, also known as the HGF receptor, is one of the most studied tyrosine kinase receptors, yet its biological functions and activation mechanisms are still not fully understood. c-Met has been implicated in embryonic development and organogenesis, in tissue remodelling homeostasis and repair and in cancer metastasis. These functions are indicative of the many cellular processes in which the receptor plays a role, including cell motility, scattering, survival and proliferation. In the context of malignancy, sustained activation of c-Met leads to a signalling cascade involving a multitude of kinases that initiate an invasive and metastatic program. Many proteins can affect the activation of c-Met, including a variety of other cell surface and membrane-spanning molecules or receptors. Some cell surface molecules share structural homology with the c-Met extracellular domain and can activate c-Met via clustering through this domain (e.g., plexins), whereas other receptor tyrosine kinases can enhance c-Met activation and signalling through intracellular signalling cascades (e.g., EGFR). In this review, we provide an overview of c-Met interactions and crosstalk with partner molecules and the functional consequences of these interactions on c-Met activation and downstream signalling, c-Met intracellular localization/recycling and c-Met degradation.

How Do Gangliosides Regulate RTKs Signaling?

Gangliosides, the glycosphingolipids carrying one or several sialic acid residues, are located on the outer leaflet of the plasma membrane in glycolipid-enriched microdomains, where they interact with molecules of signal transduction pathways including receptors tyrosine kinases (RTKs). The role of gangliosides in the regulation of signal transduction has been reported in many cases and in a large number of cell types. In this review, we summarize the current knowledge on the biosynthesis of gangliosides and the mechanism by which they regulate RTKs signaling.