Tetraspanins in cell migration

Role of a novel uropod-like cell membrane protrusion in the pathogenesis of the parasite Trichomonas vaginalis

Trichomonas vaginalis causes trichomoniasis, the most common non-viral sexually transmitted disease worldwide. As an extracellular parasite, adhesion to host cells is essential for the development of infection. During attachment, the parasite changes its tear ovoid shape to a flat ameboid form, expanding the contact surface and migrating through tissues. Here, we have identified a novel structure formed at the posterior pole of adherent parasite strains, resembling the previously described uropod, which appears to play a pivotal role as an anchor during the attachment process. Moreover, our research demonstrates that the overexpression of the tetraspanin T. vaginalis TSP5 protein (TvTSP5), which is localized on the cell surface of the parasite, notably enhances the formation of this posterior anchor structure in adherent strains. Finally, we demonstrate that parasites that overexpress TvTSP5 possess an increased ability to adhere to host cells, enhanced aggregation and reduced migration on agar plates. Overall, these findings unveil novel proteins and structures involved in the intricate mechanisms of T. vaginalis interactions with host cells.

Aged fibroblast-derived extracellular vesicles promote angiogenesis in melanoma

Advancing age is a negative prognostic factor for cutaneous melanoma. However, the role of extracellular vesicles (EVs) within the melanoma tumor microenvironment (TME) has remained unexplored in the context of aging. While the size and morphology of the EVs isolated from young vs. aged fibroblasts remained unaltered, the contents of the protein cargo were changed. Aging reduced the expression of the tetraspanin CD9 in both the dermal fibroblasts and released EVs. CD9 is a crucial regulator of EV cargo sorting. Modulating the CD9 expression in fibroblasts was sufficient to alter its levels in EVs. Mass spectrometry analysis of EVs released by CD9 knockdown (KD) vs. control cells revealed a significant increase in angiopoietin-like protein 2 (ANGPTL2), an angiogenesis promoter. Analysis of primary endothelial cells confirmed increased sprouting under CD9 KD conditions. Together, our data indicate that aged EVs play an important role in promoting a tumor-permissive microenvironment.

Genome-wide meta-analysis identifies novel loci conferring risk of acne vulgaris

Acne vulgaris is a common chronic skin disorder presenting with comedones, cystic structures forming within the distal hair follicle, and in most cases additionally with inflammatory skin lesions on the face and upper torso. We performed a genome-wide association study and meta-analysis of data from 34,422 individuals with acne and 364,991 controls from three independent European-ancestry cohorts. We replicated 19 previously implicated genome-wide significant risk loci and identified four novel loci [11q12.2 (FADS2), 12q21.1 (LGR5), 17q25.3 (FASN), and 22q12.1 (ZNRF3-KREMEN1)], bringing the total number of reported acne risk loci to 50. Our meta-analysis results explain 9.4% of the phenotypic variance of acne. A polygenic model of acne risk variants showed that individuals in the top 5% of the risk percentiles had a 1.62-fold (95% CI 1.47-1.78) increased acne risk relative to individuals with average risk (20-80% on the polygenic risk score distribution). Our findings highlight the Wnt and MAPK pathways as key factors in the genetic predisposition to acne vulgaris, together with the effects of genetic variation on the structure and maintenance of the hair follicle and pilosebaceous unit. Two novel loci, 11q12.2 and 17q25.3, contain genes encoding key enzymes involved in lipid biosynthesis pathways.

Prostaglandin F2 Receptor Negative Regulator (PTGFRN) Expression Correlates With a Metastatic-like Phenotype in Epidermoid Carcinoma, Pediatric Medulloblastoma, and Mesothelioma

Prostaglandin F2 receptor negative regulator (PTGFRN) is a transmembrane protein associated with metastatic characteristics of certain cancer types. However, it remains poorly characterized and its direct function in cancer remains unclear. The study presented here aims to further examine whether PTGFRN expression affects a cancer cell's phenotype, as well as metastatic-like characteristics. We used stable shRNA and cDNA transfections to respectively knockdown and overexpress PTGFRN in three different cancer cell lines, two of which are representative of rare and aggressive cancers (Mesothelioma and Pediatric Medulloblastoma). We then examined the characteristics of the resulting clones and showed a decrease in proliferation, migration, colony formation, and spheroid growth capabilities in cells where PTGFRN expression had been inhibited, while cells overexpressing PTGFRN showed the opposite. In addition, we showed that PTGFRN displayed direct binding to two protein partners, Integrin β1 and E. Cadherin, the latter of which is a novel direct binding partner to PTGFRN. Furthermore, silencing PTGFRN expression impacted the cellular process of autophagy, thereby providing another avenue by which PTGFRN potentially contributes to a cancer cell phenotype. Our findings demonstrate the potential role of PTGFRN in cancer metastasis and suggest PTGFRN as a future target for drug development in the treatment of metastatic cancers.

New insights into the role of tetraspanin 6, 7, and 8 in physiology and pathology

BACKGROUND

The tetraspanin (TSPAN) family comprises 33 membrane receptors involved in various physiological processes in humans. Tetrasapanins are surface proteins expressed in cells of various organisms. They are localised to the cell membrane by four transmembrane domains (TM4SF). These domains bind several cell surface receptors and signalling proteins to tetraspanin-enriched lipid microdomains (TERM or TEM). Tetraspanins play a critical role in anchoring many proteins. They also act as a scaffold for cell signalling proteins.

AIM

To summarise how tetraspanins 6, 7 and 8 contribute to the carcinogenesis process in different types of cancer.

METHODS

To provide a comprehensive review of the role of tetraspanins 6, 7 and 8 in cancer biology, we conducted a thorough search in PubMed, Embase and performed manual search of reference list to collect and extract data.

DISCUSSION

The assembly of tetraspanins covers an area of approximately 100-400 nm. Tetraspanins are involved in various biological processes such as membrane fusion, aggregation, proliferation, adhesion, cell migration and differentiation. They can also regulate integrins, cell surface receptors and signalling molecules. Tetraspanins form direct bonds with proteins and other members of the tetraspanin family, forming a hierarchical network of interactions and are thought to be involved in cell and membrane compartmentalisation. Tetraspanins have been implicated in cancer progression and have been shown to have multiple binding partners and to promote cancer progression and metastasis. Clinical studies have documented a correlation between the level of tetraspanin expression and the prediction of cancer progression, including breast and lung cancer.

CONCLUSIONS

Tetraspanins are understudied in almost all cell types and their functions are not clearly defined. Fortunately, it has been possible to identify the basic mechanisms underlying the biological role of these proteins. Therefore, the purpose of this review is to describe the roles of tetraspanins 6, 7 and 8.

Effect of PTFGRN Expression on the Proteomic Profile of A431 Cells and Determination of the PTGFRN Interactome

Prostaglandin F2 receptor negative regulator (PTGFRN) is a transmembrane protein whose expression has been previously implicated in cancer metastasis. However, the exact molecular mechanisms by which PTGFRN influences cancer progression are still unknown. As such, our laboratory set out to investigate how PTGFRN knockdown affected the expression of other proteins. We also carried out coimmunoprecipitation experiments using a monoclonal anti-PTGFRN antibody. We employed mass spectrometry-based proteomics for both experiments to identify proteins that were associated with PTGFRN. Our data show that PTGFRN knockdown increased pathways related to innate immune responses and decreased pathways associated with the synthesis of metabolic precursors and protein processing, among others. Additionally, the coimmunoprecipitation experiments indicated that PTGFRN is associated with proteins involved in processing and metabolism, as well as VEGF signaling molecules. These results highlight the role of PTGFRN as a protein processing regulator, which may be influencing cancer progression.

Membrane organization by tetraspanins and galectins shapes lymphocyte function

Immune receptors are not randomly distributed at the plasma membrane of lymphocytes but are segregated into specialized domains that function as platforms to initiate signalling, as exemplified by the B cell or T cell receptor complex and the immunological synapse. 'Membrane-organizing proteins' and, in particular, tetraspanins and galectins, are crucial for controlling the spatiotemporal organization of immune receptors and other signalling proteins. Deficiencies in specific tetraspanins and galectins result in impaired immune synapse formation, lymphocyte proliferation, antibody production and migration, which can lead to impaired immunity, tumour development and autoimmunity. In contrast to conventional ligand-receptor interactions, membrane organizers interact in cis (on the same cell) and modulate receptor clustering, receptor dynamics and intracellular signalling. New findings have uncovered their complex and dynamic nature, revealing shared binding partners and collaborative activity in determining the composition of membrane domains. Therefore, immune receptors should not be envisaged as independent entities and instead should be studied in the context of their spatial organization in the lymphocyte membrane. We advocate for a novel approach to study lymphocyte function by globally analysing the role of membrane organizers in the assembly of different membrane complexes and discuss opportunities to develop therapeutic approaches that act via the modulation of membrane organization.

Molecular Regulation and Oncogenic Functions of TSPAN8

Tetraspanins, a superfamily of small integral membrane proteins, are characterized by four transmembrane domains and conserved protein motifs that are configured into a unique molecular topology and structure in the plasma membrane. They act as key organizers of the plasma membrane, orchestrating the formation of specialized microdomains called "tetraspanin-enriched microdomains (TEMs)" or "tetraspanin nanodomains" that are essential for mediating diverse biological processes. TSPAN8 is one of the earliest identified tetraspanin members. It is known to interact with a wide range of molecular partners in different cellular contexts and regulate diverse molecular and cellular events at the plasma membrane, including cell adhesion, migration, invasion, signal transduction, and exosome biogenesis. The functions of cell-surface TSPAN8 are governed by ER targeting, modifications at the Golgi apparatus and dynamic trafficking. Intriguingly, limited evidence shows that TSPAN8 can translocate to the nucleus to act as a transcriptional regulator. The transcription of TSPAN8 is tightly regulated and restricted to defined cell lineages, where it can serve as a molecular marker of stem/progenitor cells in certain normal tissues as well as tumors. Importantly, the oncogenic roles of TSPAN8 in tumor development and cancer metastasis have gained prominence in recent decades. Here, we comprehensively review the current knowledge on the molecular characteristics and regulatory mechanisms defining TSPAN8 functions, and discuss the potential and significance of TSPAN8 as a biomarker and therapeutic target across various epithelial cancers.

A novel prognostic index of stomach adenocarcinoma based on immunogenomic landscape analysis and immunotherapy options

Stomach adenocarcinoma (STAD) is one of the most common malignant tumors worldwide. In this study, we attempted to construct a valid immune-associated gene prognostic index risk model that can predict the survival of patients with STAD and the efficacy of immune checkpoint inhibitors (ICIs) treatment. Transcriptome, clinical, and gene mutational data were obtained from the TCGA database. Immune-related genes were downloaded from the ImmPort and InnateDB databases. A total of 493 immune-related genes were identified to be enriched in functions associated with immune response, as well as in immune and tumor-related pathways. Further, 36 candidate genes related to the overall survival (OS) of STAD were obtained by weighted gene co-expression network analysis (WGCNA). Next, based on a Cox regression analysis, we constructed an immune-associated gene prognostic index (IAGPI) risk model based on eight genes, which was verified using the GEO STAD cohort. The patients were divided into two subsets according to their risk score. Patients in the low-risk group had better OS than those in the high-risk group. In the low-risk group, there were more CD8, activated memory CD4, and follicular helper T cells, and M1 macrophages, whereas monocytes, M2 macrophages, eosinophils, and neutrophils were more abundant in the high-risk group. The patients in the low-risk group were more sensitive to ICIs therapy. The IAGPI risk model can precisely predict the prognosis, reflect the tumor immune microenvironment, and predict the efficacy of ICIs therapy in patients with STAD.

TM4SF1 promotes esophageal squamous cell carcinoma metastasis by interacting with integrin α6

Transmembrane-4 L-six family member-1 (TM4SF1) is a member of the L6 family and functions as a signal transducer to regulate tumor cell behaviors. However, the function and mechanism of TM4SF1 in esophageal squamous cell carcinoma (ESCC) metastasis remains unclear. Here, we find that TM4SF1 expression is increased and positively correlated with clinical TNM stage, N classification, differentiation, tumor size, and poor prognosis in ESCC patients. Interestingly, we demonstrate that TM4SF1 promotes ESCC cell adhesion, spreading, migration, and invasion, but not cell proliferation, in a laminin-dependent manner by interacting with integrin α6. Mechanistically, the TM4SF1/integrin α6/FAK axis signal pathway mediates cell migration under laminin-coating condition. Inhibiting FAK or knocking down TM4SF1 can attenuate TM4SF1-mediated cell migration and lung metastasis. Clinically, the TM4SF1/integrin α6/FAK axis positively correlates with ESCC. Altogether, these findings reveal a new mechanism of TM4SF1 in promoting ESCC metastasis via binding to integrin α6 and suggest that the cross-talk between TM4SF1 and integrin α6 may serve as a therapeutic target for ESCC.

The Tetraspanin CD81 Is a Host Factor for Chikungunya Virus Replication

Chikungunya virus (CHIKV) is an arthritogenic reemerging virus replicating in plasma membrane-derived compartments termed "spherules." Here, we identify the human transmembrane protein CD81 as host factor required for CHIKV replication. Ablation of CD81 results in decreased CHIKV permissiveness, while overexpression enhances infection. CD81 is dispensable for virus uptake but critically required for viral genome replication. Likewise, murine CD81 is crucial for CHIKV permissiveness and is expressed in target cells such as dermal fibroblasts, muscle and liver cells. Whereas related alphaviruses, including Ross River virus (RRV), Semliki Forest virus (SFV), Sindbis virus (SINV) and Venezuelan equine encephalitis virus (VEEV), also depend on CD81 for infection, RNA viruses from other families, such as coronaviruses, replicate independently of CD81. Strikingly, the replication-enhancing function of CD81 is linked to cholesterol binding. These results define a mechanism exploited by alphaviruses to hijack the membrane microdomain-modeling protein CD81 for virus replication through interaction with cholesterol. IMPORTANCE In this study, we discover the tetraspanin CD81 as a host factor for the globally emerging chikungunya virus and related alphaviruses. We show that CD81 promotes replication of viral genomes in human and mouse cells, while virus entry into cells is independent of CD81. This provides novel insights into how alphaviruses hijack host proteins to complete their life cycle. Alphaviruses replicate at distinct sites of the plasma membrane, which are enriched in cholesterol. We found that the cholesterol-binding ability of CD81 is important for its function as an alphavirus host factor. This discovery thus broadens our understanding of the alphavirus replication process and the use of host factors to reprogram cells into virus replication factories.

Proteomic profiling of plasma exosomes reveals CD82 involvement in the development of esophageal squamous cell carcinoma

The Xinjiang Uygur autonomous region has a high incidence of esophageal cancer. For the early diagnosis of patients with esophageal squamous cell carcinoma (ESCC), exosomes were isolated and quantified by liquid chromatography tandem mass spectrometry ((LC-MS/MS) with data independent acquisition (DIA) from the peripheral blood of patients with benign esophageal disease (BED), esophageal intraepithelial neoplasia (EIN) and ESCC. A total of 1117 proteins were identified in the above 9 samples. The proteomic results showed that the quantity of CD82 in exosomes of EIN was significantly higher than that in patients with BED and ESCC. Meanwhile, our ELISA test verified our proteomic results. In addition, the immunohistochemical results showed high CD82 expression in adjacent normal tissues and low expression in ESCC tissues. CD82 expression in ESCC tissues was negatively correlated with tumor stage and the expression of PKM2, and the high expression of CD82 combined with low expression of PKM2 in ESCC tissues suggested a good prognosis. To further clarify the tumor suppressive mechanism of CD82, the TIMER and TISDB databases were analyzed, and CD82 expression in tumor tissues was found to be related to the infiltration of immune cells. CD82 in exosomes is involved in the development of ESCC. SIGNIFICANCE: Xinjiang is a high incidence area of ESCC. When diagnosed in the middle and late stages of the disease, the prognosis of patients is poor. Exosomes provide the possibility of relatively noninvasive and early detection of esophageal carcinogenesis. To the best of our knowledge, this was the first study using the DIA technique to analyze the exosomal proteins of patients with different stages of ESCC. The proteins identified in the exosomes in these three groups could provide insights for understanding how exosomes promote the occurrence of ESCC, the antitumour mechanism of humans and the early diagnosis of ESCC.

Role of Tetraspanins in Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC) is characterized by high prevalence, morbidity, and mortality. Liver cancer is the sixth most common cancer worldwide; and its subtype, HCC, accounts for nearly 80% of cases. HCC progresses rapidly, and to date, there is no efficacious treatment for advanced HCC. Tetraspanins belong to a protein family characterized by four transmembrane domains. Thirty-three known tetraspanins are widely expressed on the surface of most nucleated cells and play important roles in different biological processes. In our review, we summarize the functions of tetraspanins and their underlying mechanism in the life cycle of HCC, from its initiation, progression, and finally to treatment. CD9, TSPAN15, and TSPAN31 can promote HCC cell proliferation or suppress apoptosis. CD63, CD151, and TSPAN8 can also facilitate HCC metastasis, while CD82 serves as a suppressor of metastasis. TSPAN1, TSPAN8, and CD151 act as prognosis indicators and are inversely correlated to the overall survival rate of HCC patients. In addition, we discuss the potential of role of the tetraspanin family proteins as novel therapeutic targets and as an approach to overcome drug resistance, and also provide suggestions for further research.

Nicotine self-administration with menthol and audiovisual cue facilitates differential packaging of CYP2A6 and cytokines/chemokines in rat plasma extracellular vesicles

In this study, we investigated whether intravenously self-administered nicotine with menthol and audiovisual cue modulates nicotine-metabolizing CYP2A6, oxidative stress modulators, and cytokines/chemokines in plasma extracellular vesicles (EVs) in rats. We assigned rats to self-administered nicotine with: (a) audiovisual cue (AV), (b) menthol, and (c) menthol and AV cue. We found increased levels of CD9 in plasma EVs after self-administered nicotine with menthol and AV cue. Moreover, expression of CYP2A6 in plasma EVs was significantly increased after self-administered nicotine in response to menthol and AV cue. However, despite an upward trend on SOD1 and catalase, increase was not found to be statistically significant, while total antioxidant capacity was found to be significantly increased in plasma and plasma EVs obtained after self-administered nicotine with menthol and AV cue. Among cytokine and chemokine profiling, we found a significant increase in the levels of MCP-1 after self-administered nicotine with menthol and AV cue and complete packaging of IL-1β in EVs. Taken together, the study provides evidence that nicotine in response to menthol and AV cues can package altered levels of CYP2A6, and cytokines/chemokines in plasma EVs that may contribute to cell–cell communication, nicotine metabolism, and inflammation upon cigarette smoking.

Multi-layered proteogenomic analysis unravels cancer metastasis directed by MMP-2 and focal adhesion kinase signaling

The role of matrix metalloproteinase-2 (MMP-2) in tumor cell migration has been widely studied, however, the characteristics and effects of MMP-2 in clinical sample of metastatic colorectal cancer (CRC) remain poorly understood. Here, in order to unveil the perturbed proteomic signal during MMP-2 induced cancer progression, we analyzed plasma proteome of CRC patients according to disease progression, HCT116 cancer secretome upon MMP-2 knockdown, and publicly available CRC tissue proteome data. Collectively, the integrative analysis of multi-layered proteomes revealed that a protein cluster containing EMT (Epithelial-to-Mesenchymal Transition)-associated proteins such as CD9-integrin as well as MMP-2. The proteins of the cluster were regulated by MMP-2 perturbation and exhibited significantly increased expressions in tissue and plasma as disease progressed from TNM (Tumor, Node, and Metastasis) stage I to II. Furthermore, we also identified a plausible association between MMP-2 up-regulation and activation of focal adhesion kinase signaling in the proteogenomic analysis of CRC patient tissues. Based on these comparative and integrative analyses, we suggest that the high invasiveness in the metastatic CRC resulted from increased secretion of MMP-2 and CD9-integrin complex mediated by FAK signaling activation.

Expression of CD9 on porcine lymphocytes and its relation to T cell differentiation and cytokine production

In this work, we report on two novel monoclonal antibodies, specific for porcine CD9. CD9 is a tetraspanin that is expressed on a wide variety of cells. We phenotyped porcine immune cell subsets and found that CD9 was expressed on all monocytes as well as a subset of B cells. CD9 was variably expressed on T cells, with CD4 T cells containing the highest frequency of CD9⁺ cells. CD9 expression positively correlated with the frequency of central memory CD4 T cells in ex vivo PBMC. Therefore, we proceeded to explore CD9 as a marker of T cell function. Here we observed that CD9 was expressed on the vast majority of long-lived influenza A virus-specific effector cells that retained the capacity for cytokine production in response to in vitro recall antigen. Therefore, the new antibodies enable the detection of a cell surface molecule with functional relevance to T cells. Considering the importance of CD9 in membrane remodelling across many cell types, they will also benefit the wider field of swine biomedical research.

Fibroblastic reticular cell response to dendritic cells requires coordinated activity of podoplanin, CD44 and CD9

In adaptive immunity, CLEC-2+ dendritic cells (DCs) contact fibroblastic reticular cells (FRCs) inhibiting podoplanin-dependent actomyosin contractility, permitting FRC spreading and lymph node expansion. The molecular mechanisms controlling lymph node remodelling are incompletely understood. We asked how podoplanin is regulated on FRCs in the early phase of lymph node expansion, and which other proteins are required for the FRC response to DCs. We find that podoplanin and its partner proteins CD44 and CD9 are differentially expressed by specific lymph node stromal populations in vivo, and their expression in FRCs is coregulated by CLEC-2 (encoded by CLEC1B). Both CD44 and CD9 suppress podoplanin-dependent contractility. We find that beyond contractility, podoplanin is required for FRC polarity and alignment. Independently of podoplanin, CD44 and CD9 affect FRC-FRC interactions. Furthermore, our data show that remodelling of the FRC cytoskeleton in response to DCs is a two-step process requiring podoplanin partner proteins CD44 and CD9. Firstly, CLEC-2 and podoplanin binding inhibits FRC contractility, and, secondly, FRCs form protrusions and spread, which requires both CD44 and CD9. Together, we show a multi-faceted FRC response to DCs, which requires CD44 and CD9 in addition to podoplanin.

Distinct Signatures in the Receptor Repertoire Discriminate CD56bright and CD56dim Natural Killer Cells

NK cells are phenotypically and functionally diverse lymphocytes due to variegated expression of a large array of receptors. NK-cell activity is tightly regulated through integration of receptor-derived inhibitory and activating signals. Thus, the receptor profile of each NK cell ultimately determines its ability to sense aberrant cells and subsequently mediate anti-viral or anti-tumor responses. However, an in-depth understanding of how different receptor repertoires enable distinct immune functions of NK cells is lacking. Therefore, we investigated the phenotypic diversity of primary human NK cells by performing extensive phenotypic characterization of 338 surface molecules using flow cytometry (n = 18). Our results showed that NK cells express at least 146 receptors on their surface. Of those, 136 (>90%) exhibited considerable inter-donor variability. Moreover, comparative analysis of CD56bright and CD56dim NK cells identified 70 molecules with differential expression between the two major NK-cell subsets and allowed discrimination of these subsets via unsupervised hierarchical clustering. These receptors were associated with a broad range of NK-cell functions and multiple molecules were not previously associated with predominant expression on either subset (e.g. CD82 and CD147). Altogether, our study contributes to an improved understanding of the phenotypic diversity of NK cells and its potential functional implications on a cellular and population level. While the identified distinct signatures in the receptor repertoires provide a molecular basis for the differential immune functions exerted by CD56bright and CD56dim NK cells, the observed inter-individual differences in the receptor repertoire of NK cells may contribute to a diverging ability to control certain diseases.

Designing Enzyme-responsive Biomaterials

Enzymes are a class of protein that catalyze a wide range of chemical reactions, including the cleavage of specific peptide bonds. They are expressed in all cell types, play vital roles in tissue development and homeostasis, and in many diseases, such as cancer. Enzymatic activity is tightly controlled through the use of inactive pro-enzymes, endogenous inhibitors and spatial localization. Since the presence of specific enzymes is often correlated with biological processes, and these proteins can directly modify biomolecules, they are an ideal biological input for cell-responsive biomaterials. These materials include both natural and synthetic polymers, cross-linked hydrogels and self-assembled peptide nanostructures. Within these systems enzymatic activity has been used to induce biodegradation, release therapeutic agents and for disease diagnosis. As technological advancements increase our ability to quantify the expression and nanoscale organization of proteins in cells and tissues, as well as the synthesis of increasingly complex and well-defined biomaterials, enzyme-responsive biomaterials are poised to play vital roles in the future of biomedicine.

Extracellular Vesicles as an Efficient and Versatile System for Drug Delivery

Despite the recent advances in drug development, the majority of novel therapeutics have not been successfully translated into clinical applications. One of the major factors hindering their clinical translation is the lack of a safe, non-immunogenic delivery system with high target specificity upon systemic administration. In this respect, extracellular vesicles (EVs), as natural carriers of bioactive cargo, have emerged as a promising solution and can be further modified to improve their therapeutic efficacy. In this review, we provide an overview of the biogenesis pathways, biochemical features, and isolation methods of EVs with an emphasis on their many intrinsic properties that make them desirable as drug carriers. We then describe in detail the current advances in EV therapeutics, focusing on how EVs can be engineered to achieve improved target specificity, better circulation kinetics, and efficient encapsulation of therapeutic payloads. We also identify the challenges and obstacles ahead for clinical translation and provide an outlook on the future perspective of EV-based therapeutics.

Molecular modeling and in vitro study on pyrocatechol as potential pharmacophore of CD151 inhibitor

CD151 has been recognized as a prognostic marker, the therapeutic target of breast cancers, but less explored for small molecule inhibitors due to lack of a validated model. The 3-D structure of CD151 large extracellular loop (LEL) was modeled using the LOMETS server and validated by the Ramachandran plot. The validated structure was employed for molecular docking and structure-based pharmacophore analysis. Druglikeness was evaluated by the ADMET description protocol. Antiproliferative activity was evaluated by MTT, BrdU incorporation, flow cytometry, and cell death ELISA^PLUS assay. This study predicted the best model for CD151-LEL with 94.1% residues in favored regions and Z score -2.79 kcal/mol using the threading method. The web-based receptor cavity method identified one functional target site, which was suitable for the binding of aromatic and heterocyclic compounds. Molecular docking study identified pyrocatechol (PCL) and 5-fluorouracil (FU) as potential leads of CD151-LEL. The pharmacophore model identified interaction points of modeled CD151-LEL with PCL and FU. Also, the analysis of ADMET properties revealed the drug-likeness of PCL and FU. The viability of MDA-MB 231 cells was significantly reduced with PCL and FU but less affected MCF-12A, normal healthy breast epithelial cell line. With 50% toxic concentration, both PCL and FU significantly inhibited 82.46 and 87.12% proliferation, respectively, of MDA-MB 231 cells by altering morphology and inducing G1 cell cycle arrest and apoptosis. In addition, PCL and FU inhibited the CD151 expression by 4.5-and 4.8-folds, respectively. This study suggests the further assessment of pyrocatechol as a potential lead of CD151 in breast cancer at the molecular level.

Molecular mechanisms of dendritic cell migration in immunity and cancer

Dendritic cells (DCs) are a heterogeneous population of antigen-presenting cells that act to bridge innate and adaptive immunity. DCs are critical in mounting effective immune responses to tissue damage, pathogens and cancer. Immature DCs continuously sample tissues and engulf antigens via endocytic pathways such as phagocytosis or macropinocytosis, which result in DC activation. Activated DCs undergo a maturation process by downregulating endocytosis and upregulating surface proteins controlling migration to lymphoid tissues where DC-mediated antigen presentation initiates adaptive immune responses. To traffic to lymphoid tissues, DCs must adapt their motility mechanisms to migrate within a wide variety of tissue types and cross barriers to enter lymphatics. All steps of DC migration involve cell-cell or cell-substrate interactions. This review discusses DC migration mechanisms in immunity and cancer with a focus on the role of cytoskeletal processes and cell surface proteins, including integrins, lectins and tetraspanins. Understanding the adapting molecular mechanisms controlling DC migration in immunity provides the basis for therapeutic interventions to dampen immune activation in autoimmunity, or to improve anti-tumour immune responses.

Expression and function of transmembrane 4 superfamily proteins in digestive system cancers

Background

Although the medical level is constantly improving, cancer is still a major disease that threatens human health, and very effective treatments have not been found. In recent years, studies have found that four-transmembrane superfamily proteins are involved in multiple stages of tumorigenesis and development, but their expression and function in tumors have not been systematically studied.

Methods

We used the Oncomine database to analyze the mRNA expression levels of TSPAN family in various cancers. Then differentially expressed genes were screened out and verified by liver cancer, colorectal cancer, and gastric cancer cells by q-PCR and Western blot analysis. CCK8 and EDU analysis are used to detect cell proliferation, Cell wound scrape assay and Cell invasion assay are used to analyze cell invasion and metastasis. Nude tumor formation test used to verify the tumor suppressive effect of TSPAN7 in vivo.

Results

Differential analysis of 33 TSPAN proteins revealed that a total of 11 proteins showed differential expression in 10% of independent analyses, namely TSPAN1, TSPAN3, TSPAN5, TSPAN6, TSPAN7, TSPAN8, TSPAN13, TSPAN25, TSPAN26, TSPAN29, TSPAN30. TSPAN7 is the only four-transmembrane protein with reduced expression in three types of digestive tract tumors, so we chose TSPAN7 to be selected for cellular and molecular level verification. We found that compared with normal cells, the expression of TSPAN7 in liver cancer cells was significantly reduced, while the expression of gastric and colon cancer was not significantly different from that of normal cells. In addition, we also found that the high expression of Tspan7 not only inhibited the proliferation of HCC-LM3 cells, but also inhibited its invasion and metastasis.

Conclusions

Our study evaluated the expression and function of the TSPANs family in digestive cancers and explored TSPAN7 in hepatoma cells in detail. We found some members of the TSPAN family show significant expression differences between cancer and normal tissues, of which TSPAN7 may be a potential biomarker for liver cancer.

Mechanistic implications of altered protein expression in rheumatic heart disease

Rheumatic heart disease (RHD) is a major cause of cardiovascular morbidity and mortality in low- and middle-income countries, where living conditions promote spread of group A β-haemolytic streptococcus. Autoimmune reactions due to molecular mimicry of bacterial epitopes by host proteins cause acute rheumatic fever (ARF) and subsequent disease progression to RHD. Despite knowledge of the factors that predispose to ARF and RHD, determinants of the progression to valvular damage and the molecular events involved remain incompletely characterised. This review focuses on altered protein expression in heart valves, myocardial tissue and plasma of patients with RHD and pathogenic consequences on RHD. Proteins mainly involved in structural organization of the valve matrix, blood homeostasis and immune response were altered due to RHD pathogenesis. Study of secreted forms of these proteins may aid the development of non-invasive biomarkers for early diagnosis and monitoring outcomes in RHD. Valve replacement surgery, the single evidence-based strategy to improve outcomes in severe RHD, is costly, largely unavailable in low- and middle-income countries (LMIC) and requires specialised facilities. When diagnosed early, penicillin prophylaxis may be used to delay progression to severe valvular damage. Echocardiography and cardiovascular magnetic resonance and the standard imaging tools recommended to confirm early diagnosis remain largely unavailable and inaccessible in most LMIC and both require expensive equipment and highly skilled persons for manipulation as well as interpretation of results. Changes in protein expression in heart valves and myocardium are associated with progressive valvular deformation in RHD. Understanding these protein changes should shed more light on the mechanisms of pathogenicity, while secreted forms of these proteins may provide leads towards a biomarker for non-invasive early detection of RHD.

New directions in chimeric antigen receptor T cell [CAR-T] therapy and related flow cytometry

Chimeric antigen receptor (CAR) T cells provide a promising approach to the treatment of hematologic malignancies and solid tumors. Flow cytometry is a powerful analytical modality, which plays an expanding role in all stages of CAR T therapy, from lymphocyte collection, to CAR T cell manufacturing, to in vivo monitoring of the infused cells and evaluation of their function in the tumor environment. Therefore, a thorough understanding of the new directions is important for designing and implementing CAR T-related flow cytometry assays in the clinical and investigational settings. However, the speed of new discoveries and the multitude of clinical and preclinical trials make it challenging to keep up to date in this complex field. In this review, we summarize the current state of CAR T therapy, highlight the areas of emergent research, discuss applications of flow cytometry in modern cell therapy, and touch upon several considerations particular to CAR detection and assessing the effectiveness of CAR T therapy.

miR-216a-mediated upregulation of TSPAN1 contributes to pancreatic cancer progression via transcriptional regulation of ITGA2

Pancreatic cancer (PC) is recognized as the most aggressive and deadliest malignancy because it has the highest mortality of all cancers in humans. Mutations in multiple tumor suppressors and oncogenes have been documented to be involved in pancreatic cancer progression and metastasis. The upregulation of tetraspanin 1 (TSPAN1), a transmembrane protein, has been reportedly observed in many human cancers. However, the role of TSPAN1 and its underlying molecular mechanisms in PC progression have not been fully elucidated. In this study, we validated the oncogenic role of TSPAN1 in PC, showing that TSPAN1 reinforces cell proliferation, migration, invasion and tumorigenesis. To investigate the upregulation of TSPAN1 in PC, we showed that miR-216a is the upstream negative regulator of TSPAN1 via direct binding to the TSPAN1 3'-untranslated region. Through RNA-Seq analysis, we for the first time revealed that TSPAN1 expression transcriptionally regulates ITGA2, which is involved in the actin cytoskeleton pathway. The stimulated cell proliferation and invasion initiated by TSPAN1 overexpression could be abolished by knockdown of ITGA2 in PC cells. Furthermore, TSPAN1 epigenetically regulates the expression of ITGA2 by modulating the levels of TET2 DNMT3B and DNMT1, resulting in hypomethylation of the CpG island of the ITGA2 promoter. In conclusion, the newly identified miR-216a/TSPAN1/ITGA2 axis is involved in the modulation of PC progression and represents a novel therapeutic strategy for future pancreatic cancer treatment.

Increased expression of CD81 is associated with poor prognosis of prostate cancer and increases the progression of prostate cancer cells in vitro

CD81, a member of the tetraspanin family, has been revealed to be upregulated and associated with prognosis in several types of cancer; however, this relationship has not been explored in prostate cancer. The present study aimed to investigate the prognostic significance and functional role of CD81 in prostate cancer. The expression of CD81 in prostate cancer tissues and cell lines was evaluated using qRT-PCR analysis. Kaplan-Meier survival analysis and Cox regression analysis were conducted to explore the prognostic significance of CD81. Cell experiments were used to explore the effects of CD81 on cell proliferation, migration, and invasion in prostate cell lines in vitro. The expression of CD81 was increased in both prostate cancer tissues and cell lines. Upregulation of CD81 was significantly associated with lymph node metastasis and TNM stage. Moreover, patients with high CD81 levels had poorer overall survival than those with lower levels. Additionally, tumor cell proliferation, migration, and invasion were inhibited by knockdown of CD81. The present results indicated that CD81 plays an oncogenic role in prostate cancer. Overexpression of CD81 may serve as a prognostic biomarker and therapeutic target and is involved in the progression of prostate cancer.

Genome-Wide Analysis of Known and Potential Tetraspanins in Entamoeba histolytica

Tetraspanins are membrane proteins involved in intra- and/or intercellular signaling, and membrane protein complex formation. In some organisms, their role is associated with virulence and pathogenesis. Here, we investigate known and potential tetraspanins in the human intestinal protozoan parasite Entamoeba histolytica. We conducted sequence similarity searches against the proteome data of E. histolytica and newly identified nine uncharacterized proteins as potential tetraspanins in E. histolytica. We found three subgroups within known and potential tetraspanins, as well as subgroup-associated features in both their amino acid and nucleotide sequences. We also examined the subcellular localization of a few representative tetraspanins that might be potentially related to pathogenicity. The results in this study could be useful resources for further understanding and downstream analyses of tetraspanins in Entamoeba.

Modulation of Tetraspanin 32 (TSPAN32) Expression in T Cell-Mediated Immune Responses and in Multiple Sclerosis

Tetraspanins are a conserved family of proteins involved in a number of biological processes including, cell–cell interactions, fertility, cancer metastasis and immune responses. It has previously been shown that TSPAN32 knockout mice have normal hemopoiesis and B-cell responses, but hyperproliferative T cells. Here, we show that TSPAN32 is expressed at higher levels in the lymphoid lineage as compared to myeloid cells. In vitro activation of T helper cells via anti-CD3/CD28 is associated with a significant downregulation of TSPAN32. Interestingly, engagement of CD3 is sufficient to modulate TSPAN32 expression, and its effect is potentiated by costimulation with anti-CD28, but not anti-CTLA4, -ICOS nor -PD1. Accordingly, we measured the transcriptomic levels of TSPAN32 in polarized T cells under Th1 and Th2 conditions and TSPAN32 resulted significantly reduced as compared with unstimulated cells. On the other hand, in Treg cells, TSPAN32 underwent minor changes upon activation. The in vitro data were finally translated into the context of multiple sclerosis (MS). Encephalitogenic T cells from Myelin Oligodendrocyte Glycoprotein (MOG)-Induced Experimental Autoimmune Encephalomyelitis (EAE) mice showed significantly lower levels of TSPAN32 and increased levels of CD9, CD53, CD82 and CD151. Similarly, in vitro-activated circulating CD4 T cells from MS patients showed lower levels of TSPAN32 as compared with cells from healthy donors. Overall, these data suggest an immunoregulatory role for TSPAN32 in T helper immune response and may represent a target of future immunoregulatory therapies for T cell-mediated autoimmune diseases.

Distinct Origin of Claudin7 in Early Tumor Endosomes Affects Exosome Assembly

Microvesicles are the body's most powerful intercellular communication system and cancer-initiating cell microvesicles (CIC-TEX) reprogram Non-CIC towards fortified malignancy. Claudin7, a CIC-biomarker in gastrointestinal tumors, is recovered in TEX. Recent evidence suggesting individual cells delivering distinct microvesicles became of particular interest for claudin7, which is part of tight junctions (TJ) and glycolipid-enriched membrane domains (GEM), GEM-located claudin7 is palmitoylated. This offered the unique possibility of exploring the contribution of a CIC marker and its origin from distinct membrane domains on CIC-TEX biogenesis and activities. Proteome and miRNA analysis of wild-type, claudin7-knockdown and a rescue with claudin7 harboring a mutated palmitoylation site (mP) of a rat pancreatic and a human colon cancer line uncovered significant, only partly overlapping contributions of palmitoylated and non-palmitoylated claudin7 to TEX composition. Palmitoylated claudin7 facilitates GEM-integrated plasma membrane and associated signaling molecule recruitment; non-palmitoylated claudin7 supports recruitment of trafficking components, proteins engaged in fatty acid metabolism and TJ proteins into TEX. Claudin7mP also assists TEX recovery of selected miRNA. Thus, distinctly located claudin7 affects CIC-TEX composition and TJ-derived cld7 might play a unique role in equipping CIC-TEX with transporters and lipid metabolism-regulating molecules, awareness of distinct TEX populations being crucial facing therapeutic translation.

Extracellular vesicles isolated from porcine seminal plasma exhibit different tetraspanin expression profiles

Seminal extracellular vesicles (EVs) include exosomes (ø 40–120 nm) and microvesicles (MVs, ø 120–1000 nm), which would be involved in multiple functional reproductive roles. The study aimed to establish which EV subtypes are present in pig semen, using a high-resolution flow cytometer to explore differences in their tetraspanin expression profile. The EVs were isolated from 12 pig ejaculates using serial ultracentrifugation and characterized by dynamic light scattering and electron microscopy for size and morphology as well as for tetraspanin expression using flow cytometry with Carboxyfluorescein succinimidyl ester (CFSE) and antibodies against CD9, CD63 and CD81. Pig semen contained a heterogeneous EV-population regarding size and morphology. Flow cytometric analysis demonstrated that the proportion of EVs expressing CD63 and CD9 was higher in MVs (P < 0.001 and P < 0.05, respectively) than in exosomes, while the opposite was true for CD81; higher (P < 0.001) in exosomes than in MVs. In conclusion, (1) the new generation of flow cytometers are able to accurately identify EVs and to gate them in two size-different populations named exosomes and MVs. (2) Tetraspanins CD9, CD63 and CD81 are present in both seminal EVs, albeit with exosomes and MVs differing in expression profiles, suggesting dissimilar cargo and binding affinity.

Transcriptomic analysis of the impacts of ethinylestradiol (EE2) and its consequences for proliferative kidney disease outcome in rainbow trout (Oncorhynchus mykiss)

Freshwater fish are threatened by the cumulative impact of multiple stressors. The purpose of this study was to unravel the molecular and organism level reactions of rainbow trout, Oncorhynchus mykiss, to the combined impact of two such stressors that occur in the natural habitat of salmonids. Fish were infected with either the myxozoan parasite, Tetracapsuloides bryosalmonae, which causes proliferative kidney disease (PKD), or exposed to ethinylestradiol (EE2) an estrogenic endocrine disrupting compound, or to a combination of both (PKD × EE2). PKD is a slow progressive chronic disease here we focused on a later time point (130-day post-infection (d.p.i.)) when parasite intensity in the fish kidney has already started to decrease. At 130 d.p.i., RNA-seq technology was applied to the posterior kidney, the main target organ for parasite development. This resulted with 280 (PKD), 14 (EE2) and 444 (PKD × EE2) differentially expressed genes (DEGs) observed in the experimental groups. In fish exposed to the combination of stressors (PKD × EE2), a number of pathways were regulated that were neither observed in the single stressor groups. Parasite infection, alone and in combination with EE2, only resulted in a low intensity immune response that negatively correlated with an upregulation of genes involved in a variety of metabolic and inflammation resolution processes. This could indicate a trade-off whereby the host increases investment in recovery/resolution processes over immune responses at a later stage of disease. When PKD infection took place under simultaneous exposure to EE2 (PKD × EE2), parasite intensity decreased and pathological alterations in the posterior kidney were reduced in comparison to the PKD only condition. These findings suggest that EE2 modulated these response profiles in PKD infected fish, attenuating the disease impact on the fish.

The tetraspanin CD9 controls migration and proliferation of parietal epithelial cells and glomerular disease progression

The mechanisms driving the development of extracapillary lesions in focal segmental glomerulosclerosis (FSGS) and crescentic glomerulonephritis (CGN) remain poorly understood. A key question is how parietal epithelial cells (PECs) invade glomerular capillaries, thereby promoting injury and kidney failure. Here we show that expression of the tetraspanin CD9 increases markedly in PECs in mouse models of CGN and FSGS, and in kidneys from individuals diagnosed with these diseases. Cd9 gene targeting in PECs prevents glomerular damage in CGN and FSGS mouse models. Mechanistically, CD9 deficiency prevents the oriented migration of PECs into the glomerular tuft and their acquisition of CD44 and β1 integrin expression. These findings highlight a critical role for de novo expression of CD9 as a common pathogenic switch driving the PEC phenotype in CGN and FSGS, while offering a potential therapeutic avenue to treat these conditions.

In both focal segmental glomerulosclerosis (FSGS) and crescentic glomerulonephritis (CGN), kidney injury is characterised by the invasion of glomerular tufts by parietal epithelial cells (PECs). Here Lazareth et al. identify the tetraspanin CD9 as a key regulator of PEC migration, and find its upregulation in FSGS and CGN contributes to kidney injury in both diseases.

Unique arrangement of bone matrix orthogonal to osteoblast alignment controlled by Tspan11-mediated focal adhesion assembly

During tissue construction, cells coordinate extracellular matrix (ECM) assembly depending on the cellular arrangement. The traditional understanding of the relationship between the ECM and cells is limited to the orientation-matched interaction between them. Indeed, it is commonly accepted that the bone matrix (collagen/apatite) is formed along osteoblast orientation. Nonetheless, our recent findings are contrary to the above theory; osteoblasts on nanogrooves organize formation of the bone matrix perpendicular to cell orientation. However, the precise molecular mechanisms underlying the orthogonal organization of bone matrix are still unknown. Here, we show that mature fibrillar focal adhesions (FAs) facilitate the perpendicular arrangement between cells and bone matrix. The osteoblasts aligned along nanogrooves expressed highly mature fibrillar FAs mediated by integrin clustering. Microarray analysis revealed that Tspan11, a member of the transmembrane tetraspanin protein family, was upregulated in cells on the nanogrooved surface compared with that in cells on isotropic, flat, or rough surfaces. Tspan11 silencing significantly disrupted osteoblast alignment and further construction of aligned bone matrix orthogonal to cell orientation. Our results demonstrate that the unique bone matrix formation orthogonal to cell alignment is facilitated by FA maturation. To the best of our knowledge, this report is the first to show that FA assembly mediated by Tspan11 determines the direction of bone matrix organization.

Mass Spectrometry-based Label-free Quantitative Proteomics To Study the Effect of 3PO Drug at Cellular Level

Human endothelial cells (ECs) have been employed to monitor the protein changes induced by [3-(3-pyridinyl)-1-(4-pyridinyl)-2-propen-1-one] (3PO), a compound able to inhibit the glycolytic flux partially and transiently and to reduce pathological angiogenesis in a variety of disease models. Normal and TNFα induced inflamed ECs were incubated with and without 3PO at a concentration (20 μM) able to inhibit cell proliferation without cell death. At the end of the incubation period, samples were submitted to the following steps: (a) whole protein extraction, reduction, alkylation, and digestion by trypsin; (b) peptide separation by nano-LC-MS/MS analysis using a high-resolution mass spectrometer; (c) data analysis including protein identification, quantification, and statistical analysis. An altered protein expression profiling in combination with protein network analysis was employed by using a mass spectrometry-based label-free quantification approach to explore the underlying mechanisms of 3PO at cellular level.

CD81 Promotes a Migratory Phenotype in Neuronal-Like Cells

Tetraspanins, such as CD81, can form lateral associations with each other and with other transmembrane proteins. These interactions may underlie CD81 functions in multiple cellular processes, such as adhesion, morphology, migration, and differentiation. Since CD81's role in neuronal cells' migration has not been established, we here evaluated effects of CD81 on the migratory phenotype of SH-SY5Y neuroblastoma cells. CD81 was found enriched at SH-SY5Y cell's membrane, co-localizing with its interactor filamentous-actin (F-actin) in migratory relevant structures of the leading edge (filopodia, stress fibers, and adhesion sites). CD81 overexpression increased the number of cells with a migratory phenotype, in a potentially phosphatidylinositol 3 kinase (PI3K)-Ak strain transforming (AKT) mediated manner. Indeed, CD81 also co-localized with AKT, a CD81-interactor and actin remodeling agent, at the inner leaflet of the plasma membrane. Pharmacologic inhibition of PI3K, the canonical AKT activator, led both to a decrease in the acquisition of a migratory phenotype and to a redistribution of intracellular CD81 and F-actin into cytoplasmic agglomerates. These findings suggest that in neuronal-like cells CD81 bridges active AKT and actin, promoting the actin remodeling that leads to a motile cell morphology. Further studies on this CD81-mediated mechanism will improve our knowledge on important physiological and pathological processes such as cell migration and differentiation, and tumor metastasis.

The Many and Varied Roles of Tetraspanins in Immune Cell Recruitment and Migration

Immune cell recruitment and migration is central to the normal functioning of the immune system in health and disease. Numerous adhesion molecules on immune cells and the parenchymal cells they interact with are well recognized for their roles in facilitating the movements of immune cells throughout the body. A growing body of evidence now indicates that tetraspanins, proteins known for their capacity to organize partner molecules within the cell membrane, also have significant impacts on the ability of immune cells to migrate around the body. In this review, we examine the tetraspanins expressed by immune cells and endothelial cells that influence leukocyte recruitment and motility and describe their impacts on the function of adhesion molecules and other partner molecules that modulate the movements of leukocytes. In particular, we examine the functional roles of CD9, CD37, CD63, CD81, CD82, and CD151. This reveals the diversity of the functions of the tetraspanin family in this setting, both in the nature of adhesive and migratory interactions that they regulate, and the positive or inhibitory effects mediated by the individual tetraspanin proteins.

Pharmacological Modulation of AMPAR Rescues Intellectual Disability-Like Phenotype in Tm4sf2-/y Mice

Intellectual disability affects 2–3% of the world's population and typically begins during childhood, causing impairments in social skills and cognitive abilities. Mutations in the TM4SF2 gene, which encodes the TSPAN7 protein, cause a severe form of intellectual disability, and currently, no therapy is able to ameliorate this cognitive impairment. We previously reported that, in cultured neurons, shRNA-mediated down-regulation of TSPAN7 affects AMPAR trafficking by enhancing PICK1–GluA2 interaction, thereby increasing the intracellular retention of AMPAR. Here, we found that loss of TSPAN7 function in mice causes alterations in hippocampal excitatory synapse structure and functionality as well as cognitive impairment. These changes occurred along with alterations in AMPAR expression levels. We also found that interfering with PICK1–GluA2 binding restored synaptic function in Tm4sf2^−/y mice. Moreover, potentiation of AMPAR activity via the administration of the ampakine CX516 reverted the neurological phenotype observed in Tm4sf2^−/y mice, suggesting that pharmacological modulation of AMPAR may represent a new approach for treating patients affected by TM4SF2 mutations and intellectual disability.

Antitumor Immunity Is Controlled by Tetraspanin Proteins

Antitumor immunity is shaped by the different types of immune cells that are present in the tumor microenvironment (TME). In particular, environmental signals (for instance, soluble factors or cell–cell contact) transmitted through the plasma membrane determine whether immune cells are activated or inhibited. Tetraspanin proteins are emerging as central building blocks of the plasma membrane by their capacity to cluster immune receptors, enzymes, and signaling molecules into the tetraspanin web. Whereas some tetraspanins (CD81, CD151, CD9) are widely and broadly expressed, others (CD53, CD37, Tssc6) have an expression pattern restricted to hematopoietic cells. Studies using genetic mouse models have identified important immunological functions of these tetraspanins on different leukocyte subsets, and as such, may be involved in the immune response against tumors. While multiple studies have been performed with regards to deciphering the function of tetraspanins on cancer cells, the effect of tetraspanins on immune cells in the antitumor response remains understudied. In this review, we will focus on tetraspanins expressed by immune cells and discuss their potential role in antitumor immunity. New insights in tetraspanin function in the TME and possible prognostic and therapeutic roles of tetraspanins will be discussed.

Tetraspanins as Organizers of Antigen-Presenting Cell Function

Professional antigen-presenting cells (APCs) include dendritic cells, monocytes, and B cells. APCs internalize and process antigens, producing immunogenic peptides that enable antigen presentation to T lymphocytes, which provide the signals that trigger T-cell activation, proliferation, and differentiation, and lead to adaptive immune responses. After detection of microbial antigens through pattern recognition receptors (PRRs), APCs migrate to secondary lymphoid organs where antigen presentation to T lymphocytes takes place. Tetraspanins are membrane proteins that organize specialized membrane platforms, called tetraspanin-enriched microdomains, which integrate membrane receptors, like PRR and major histocompatibility complex class II (MHC-II), adhesion proteins, and signaling molecules. Importantly, through the modulation of the function of their associated membrane partners, tetraspanins regulate different steps of the immune response. Several tetraspanins can positively or negatively regulate the activation threshold of immune receptors. They also play a role during migration of APCs by controlling the surface levels and spatial arrangement of adhesion molecules and their subsequent intracellular signaling. Finally, tetraspanins participate in antigen processing and are important for priming of naïve T cells through the control of T-cell co-stimulation and MHC-II-dependent antigen presentation. In this review, we discuss the role of tetraspanins in APC biology and their involvement in effective immune responses.

A novel role for sox7 in Xenopus early primordial germ cell development: mining the PGC transcriptome

Xenopus primordial germ cells (PGCs) are determined by the presence of maternally derived germ plasm. Germ plasm components both protect PGCs from somatic differentiation and begin a unique gene expression program. Segregation of the germline from the endodermal lineage occurs during gastrulation, and PGCs subsequently initiate zygotic transcription. However, the gene network(s) that operate to both preserve and promote germline differentiation are poorly understood. Here, we utilized RNA-sequencing analysis to comprehensively interrogate PGC and neighboring endoderm cell mRNAs after lineage segregation. We identified 1865 transcripts enriched in PGCs compared with endoderm cells. We next compared the PGC-enriched transcripts with previously identified maternal, vegetally enriched transcripts and found that ∼38% of maternal transcripts were enriched in PGCs, including sox7 PGC-directed sox7 knockdown and overexpression studies revealed an early requirement for sox7 in germ plasm localization, zygotic transcription and PGC number. We identified pou5f3.3 as the most highly expressed and enriched POU5F1 homolog in PGCs. We compared the Xenopus PGC transcriptome with human PGC transcripts and showed that 80% of genes are conserved, underscoring the potential usefulness of Xenopus for understanding human germline specification.

Easy and low-cost stable positioning of suspension cells during live-cell imaging

Dynamic processes of cells can be best monitored when living cells are analyzed by imaging. While it is easy to observe adherent living cells it has been extremely challenging to analyze suspension cells. This cell type floats freely in the culture dish, and it is only a question of time when the focus or the observation field is lost. In order to keep the cells in focus, an easy and inexpensive method allowing the observation of living suspension cells during confocal laser scanning microscope imaging was developed.

Rab3a-Bound CD63 Is Degraded and Rab3a-Free CD63 Is Incorporated into HIV-1 Particles

CD63, a member of the tetraspanin family, is involved in virion production by human immunodeficiency virus type 1 (HIV-1), but its mechanism is unknown. In this study, we showed that a small GTP-binding protein, Rab3a, interacts with CD63. When Rab3a was exogenously expressed, the amounts of CD63 decreased in cells. The Rab3a-mediated reduction of CD63 was suppressed by lysosomal and proteasomal inhibitors. The amount of CD63 was increased by reducing the endogenous Rab3a level using a specific shRNA. These results indicate that Rab3a binds to CD63 to induce the degradation of CD63. Rab3a is thought to be involved in exocytosis, but we found that another function of Rab3a affects the fate of CD63 in lysosomes. CD63 interacted with Rab3a and was incorporated into HIV-1 particles. However, Rab3a was not detected in HIV-1 virions, thereby indicating that Rab3a-free CD63, but not Rab3a-bound CD63, is incorporated into HIV-1 particles. Overexpression or silencing of Rab3a moderately reduced HIV-1 virion formation. Overexpression of Rab3a decreased CD63 levels, but did not affect the incorporation of CD63 into HIV-1 particles. This study showed that Rab3a binds to CD63 to induce the degradation of CD63, and only Rab3a-free CD63 is incorporated into HIV-1 particles.

The cancer-associated cell migration protein TSPAN1 is under control of androgens and its upregulation increases prostate cancer cell migration

Cell migration drives cell invasion and metastatic progression in prostate cancer and is a major cause of mortality and morbidity. However the mechanisms driving cell migration in prostate cancer patients are not fully understood. We previously identified the cancer-associated cell migration protein Tetraspanin 1 (TSPAN1) as a clinically relevant androgen regulated target in prostate cancer. Here we find that TSPAN1 is acutely induced by androgens, and is significantly upregulated in prostate cancer relative to both normal prostate tissue and benign prostate hyperplasia (BPH). We also show for the first time, that TSPAN1 expression in prostate cancer cells controls the expression of key proteins involved in cell migration. Stable upregulation of TSPAN1 in both DU145 and PC3 cells significantly increased cell migration and induced the expression of the mesenchymal markers SLUG and ARF6. Our data suggest TSPAN1 is an androgen-driven contributor to cell survival and motility in prostate cancer.

Expression of Tspan-1 gene in patients with advanced gastric cancer

The present study investigated the correlations of the Tspan-1 gene expression with the clinical characteristics and survival prognoses of patients with advanced gastric cancer. A total of 150 patients with advanced gastric cancer were enrolled in the present study, of whom 84 were at stage II and 66 were at stage III according to the tumor node metastasis (TNM) staging; the immunohistochemical staining method and the semi-quantitative PCR method were used to detect the positive expression rates and mRNA relative expression levels of Tspan-1, vascular endothelial growth factor (VEGF), E-cadherin and N-cadherin. The positive expression rates of Tspan-1, VEGF, E-cadherin and N-cadherin were 58.0% (87 patients), 50.0% (75 patients), 28.0% (42 patients) and 53.3% (80 patients), respectively. The positive expressions and mRNA levels of Tspan-1, VEGF, E-cadherin and N-cadherin were not correlated with sex or age (P>0.05), but associated with the cancer state (stage II or stage III) and maximum tumor diameter (P<0.05). With the increase of stage and tumor diameter, the positive rates and mRNA levels of Tspan-1, VEGF and N-cadherin were increased, while those of E-cadherin were decreased. Among patients with stage II/III advanced gastric cancer, those with positive expression of Tspan-1, VEGF and N-cadherin had lower median survival time and survival rates than patients with negative expressions, while patients with positive expression of E-cadherin had higher median survival time and survival rate than those with negative expression (P<0.05). The high expression of Tspan-1 gene is associated with the TNM staging of advanced gastric cancer and the tumor diameter, influences the survival prognosis, and may involve the processes of angiogenesis and epithelial-mesenchymal transition.

Joint features and complementarities of Tspan8 and CD151 revealed in knockdown and knockout models

Tetraspanins are highly conserved 4-transmembrane proteins which form molecular clusters with a large variety of transmembrane and cytosolic proteins. By these associations tetraspanins are engaged in a multitude of biological processes. Furthermore, tetraspanin complexes are located in specialized microdomains, called tetraspanin-enriched microdomains (TEMs). TEMs provide a signaling platform and are poised for invagination and vesicle formation. These vesicles can be released as exosomes (Exo) and are important in cell contact-independent intercellular communication. Here, we summarize emphasizing knockdown and knockout models' pathophysiological joint and selective activities of CD151 and Tspan8, and discuss the TEM-related engagement of CD151 and Tspan8 in Exo activities.

TETRASPANINs in Plants

Tetraspanins are small transmembrane proteins that laterally associate with each other and cluster with numerous partner proteins as well as lipids. These interactions result in the formation of a distinct class of membrane domains, the tetraspanin-enriched microdomains (TEMs), which influence numerous cellular processes such as cell adhesion and fusion, intracellular membrane trafficking, signaling, morphogenesis, motility as well as interaction with pathogens and cancer development. The majority of information available about tetraspanins is based on studies using animal models or cell lines, but tetraspanins are also present in fungi and plants. Recent studies indicate that tetraspanins have important functions in plant development, reproduction and stress responses. Here we provide a brief summary of the current state of tetraspanin research in plants.

Downregulation of coding transmembrane protein 35 gene inhibits cell proliferation, migration and cell cycle arrest in osteosarcoma cells

Osteosarcoma (OSA) is the most common primary tumor of the bone. Resistance to chemotherapy and the fast rapid development of metastatic lesions are major issues responsible for treatment failure and poor survival rates in OSA patients. Tetraspanins comprise a family of transmembrane receptor glycoproteins that affect tumor cell migration through tetraspanin-integrin interaction. The present study focused on a four-pass transmembrane protein gene, transmembrane protein 35 (TMEM35) gene, and examined its role in the growth, migration and cell cycle progression of OSA cells. In addition, the study discussed whether the TMEM35 gene, which encodes the TMEM35 protein, may be a potential therapeutic target for OSA. In the current study, reverse transcription-quantitative polymerase chain reaction was performed to examine TMEM35 expression in OSA and matched healthy tissues. Small interfering RNAs (siRNAs) were transfected into SaOS2 and U2OS cells to knockdown the TMEM35 expression. Soft-agar colony formation assay was performed to evaluate cell growth, and cell cycle progression was analyzed by flow cytometry. Wound-healing and Boyden chamber assays were also performed to investigate cell invasion and migration by the SaOS2 and U2OS cells. TMEM35 protein was analyzed in a functional protein interaction networks database (STRING database) to predict the functional interaction partner proteins of TMEM35. The results indicated that TMEM35 was abnormally expressed in OSA tissues. Of the 37 examined patients, TMEM35 expression was significantly increased in the OSA tissues of 24 patients (64.86%; P<0.05), when compared with the expression in normal tissues. Furthermore, TMEM35 knockdown following transfection with siRNAs inhibited the colony formation ability of SaOS2 and U2OS cells in soft agar. Flow cytometric analysis also revealed that TMEM35 knockdown by RNA interference may result in G1 phase arrest and a decreased cell population at the S phase. TMEM35 knockdown inhibited cell migration in SaOS2 and U2OS cells in wound-healing assays. In conclusion, TMEM35, a member of the tetraspanin family, serves an important role in the growth of OSA cells.