Tetraspanins at a glance

The septate junction protein Tetraspanin 2A is critical to the structure and function of Malpighian tubules in Drosophila melanogaster

Tetraspanin-2A (Tsp2A) is an integral membrane protein of smooth septate junctions in Drosophila melanogaster. To elucidate its structural and functional roles in Malpighian tubules, we used the c42-GAL4/UAS system to selectively knock down Tsp2A in principal cells of the tubule. Tsp2A localizes to smooth septate junctions (sSJ) in Malpighian tubules in a complex shared with partner proteins Snakeskin (Ssk), Mesh, and Discs large (Dlg). Knockdown of Tsp2A led to the intracellular retention of Tsp2A, Ssk, Mesh, and Dlg, gaps and widening spaces in remaining sSJ, and tumorous and cystic tubules. Elevated protein levels together with diminished V-type H⁺-ATPase activity in Tsp2A knockdown tubules are consistent with cell proliferation and reduced transport activity. Indeed, Malpighian tubules isolated from Tsp2A knockdown flies failed to secrete fluid in vitro. The absence of significant transepithelial voltages and resistances manifests an extremely leaky epithelium that allows secreted solutes and water to leak back to the peritubular side. The tubular failure to excrete fluid leads to extracellular volume expansion in the fly and to death within the first week of adult life. Expression of the c42-GAL4 driver begins in Malpighian tubules in the late embryo and progresses upstream to distal tubules in third instar larvae, which can explain why larvae survive Tsp2A knockdown and adults do not. Uncontrolled cell proliferation upon Tsp2A knockdown confirms the role of Tsp2A as tumor suppressor in addition to its role in sSJ structure and transepithelial transport.

CD82-TRPM7-Numb signaling mediates age-related cognitive impairment

Aging is a crucial cause of cognitive decline and a major risk factor for Alzheimer's disease (AD); however, AD's underlying molecular mechanisms remain unclear. Recently, tetraspanins have emerged as important modulators of synaptic function and memory. We demonstrate that the level of tetraspanin CD82 is upregulated in the brains of AD patients and middle-aged mice. In young adult mice, injection of AAV-CD82 to the hippocampus induced AD-like cognitive deficits and impairments in neuronal spine density. CD82 overexpression increased TRPM7 α-kinase cleavage via caspase-3 activation and induced Numb phosphorylation at Thr346 and Ser348 residues. CD82 overexpression promoted beta-amyloid peptide (Aβ) secretion which could be reversed by Numb T346S348 mutants. Importantly, hippocampus-related memory functions were improved in Cd82-/- mice. Taken together, our findings provide the evidence that links the elevated CD82-TRPM7-Numb signaling to age-related cognitive impairment.

Structural insights into tetraspanin CD9 function

Tetraspanins play critical roles in various physiological processes, ranging from cell adhesion to virus infection. The members of the tetraspanin family have four membrane-spanning domains and short and large extracellular loops, and associate with a broad range of other functional proteins to exert cellular functions. Here we report the crystal structure of CD9 and the cryo-electron microscopic structure of CD9 in complex with its single membrane-spanning partner protein, EWI-2. The reversed cone-like molecular shape of CD9 generates membrane curvature in the crystalline lipid layers, which explains the CD9 localization in regions with high membrane curvature and its implications in membrane remodeling. The molecular interaction between CD9 and EWI-2 is mainly mediated through the small residues in the transmembrane region and protein/lipid interactions, whereas the fertilization assay revealed the critical involvement of the LEL region in the sperm-egg fusion, indicating the different dependency of each binding domain for other partner proteins.

The Interplay between Peripherin 2 Complex Formation and Degenerative Retinal Diseases

Peripherin 2 (Prph2) is a photoreceptor-specific tetraspanin protein present in the outer segment (OS) rims of rod and cone photoreceptors. It shares many common features with other tetraspanins, including a large intradiscal loop which contains several cysteines. This loop enables Prph2 to associate with itself to form homo-oligomers or with its homologue, rod outer segment membrane protein 1 (Rom1) to form hetero-tetramers and hetero-octamers. Mutations in PRPH2 cause a multitude of retinal diseases including autosomal dominant retinitis pigmentosa (RP) or cone dominant macular dystrophies. The importance of Prph2 for photoreceptor development, maintenance and function is underscored by the fact that its absence results in a failure to initialize OS formation in rods and formation of severely disorganized OS membranous structures in cones. Although the exact role of Rom1 has not been well studied, it has been concluded that it is not necessary for disc morphogenesis but is required for fine tuning OS disc size and structure. Pathogenic mutations in PRPH2 often result in complex and multifactorial phenotypes, involving not just photoreceptors, as has historically been reasoned, but also secondary effects on the retinal pigment epithelium (RPE) and retinal/choroidal vasculature. The ability of Prph2 to form complexes was identified as a key requirement for the development and maintenance of OS structure and function. Studies using mouse models of pathogenic Prph2 mutations established a connection between changes in complex formation and disease phenotypes. Although progress has been made in the development of therapeutic approaches for retinal diseases in general, the highly complex interplay of functions mediated by Prph2 and the precise regulation of these complexes made it difficult, thus far, to develop a suitable Prph2-specific therapy. Here we describe the latest results obtained in Prph2-associated research and how mouse models provided new insights into the pathogenesis of its related diseases. Furthermore, we give an overview on the current status of the development of therapeutic solutions.

Anatomy of a viral entry platform differentially functionalized by integrins α3 and α6

During cell invasion, human papillomaviruses use large CD151 patches on the cell surface. Here, we studied whether these patches are defined architectures with features for virus binding and/or internalization. Super-resolution microscopy reveals that the patches are assemblies of closely associated nanoclusters of CD151, integrin α3 and integrin α6. Integrin α6 is required for virus attachment and integrin α3 for endocytosis. We propose that CD151 organizes viral entry platforms with different types of integrin clusters for different functionalities. Since numerous viruses use tetraspanin patches, we speculate that this building principle is a blueprint for cell-surface architectures utilized by viral particles.

Tetraspanin-6 negatively regulates exosome production

Exosomes, extracellular vesicles (EVs) of endosomal origin, emerge as master regulators of cell-to-cell signaling in physiology and disease. Exosomes are highly enriched in tetraspanins (TSPNs) and syndecans (SDCs), the latter occurring mainly in proteolytically cleaved form, as membrane-spanning C-terminal fragments of the proteins. While both protein families are membrane scaffolds appreciated for their role in exosome formation, composition, and activity, we currently ignore whether these work together to control exosome biology. Here we show that TSPN6, a poorly characterized tetraspanin, acts as a negative regulator of exosome release, supporting the lysosomal degradation of SDC4 and syntenin. We demonstrate that TSPN6 tightly associates with SDC4, the SDC4-TSPN6 association dictating the association of TSPN6 with syntenin and the TSPN6-dependent lysosomal degradation of SDC4-syntenin. TSPN6 also inhibits the shedding of the SDC4 ectodomain, mimicking the effects of matrix metalloproteinase inhibitors. Taken together, our data identify TSPN6 as a regulator of the trafficking and processing of SDC4 and highlight an important physical and functional interconnection between these membrane scaffolds for the production of exosomes. These findings clarify our understanding of the molecular determinants governing EV formation and have potentially broad impact for EV-related biomedicine.

Tetraspanins TSP-12 and TSP-14 function redundantly to regulate the trafficking of the type II BMP receptor in Caenorhabditis elegans

Tetraspanins are a unique family of 4-pass transmembrane proteins that play important roles in a variety of cell biological processes. We have previously shown that 2 paralogous tetraspanins in Caenorhabditis elegans, TSP-12 and TSP-14, function redundantly to promote bone morphogenetic protein (BMP) signaling. The underlying molecular mechanisms, however, are not fully understood. In this study, we examined the expression and subcellular localization patterns of endogenously tagged TSP-12 and TSP-14 proteins. We found that TSP-12 and TSP-14 share overlapping expression patterns in multiple cell types, and that both proteins are localized on the cell surface and in various types of endosomes, including early, late, and recycling endosomes. Animals lacking both TSP-12 and TSP-14 exhibit reduced cell-surface levels of the BMP type II receptor DAF-4/BMPRII, along with impaired endosome morphology and mislocalization of DAF-4/BMPRII to late endosomes and lysosomes. These findings indicate that TSP-12 and TSP-14 are required for the recycling of DAF-4/BMPRII. Together with previous findings that the type I receptor SMA-6 is recycled via the retromer complex, our work demonstrates the involvement of distinct recycling pathways for the type I and type II BMP receptors and highlights the importance of tetraspanin-mediated intracellular trafficking in the regulation of BMP signaling in vivo. As TSP-12 and TSP-14 are conserved in mammals, our findings suggest that the mammalian TSP-12 and TSP-14 homologs may also function in regulating transmembrane protein recycling and BMP signaling.

Multistep peripherin-2/rds self-assembly drives membrane curvature for outer segment disk architecture and photoreceptor viability

Rod and cone photoreceptor outer segment (OS) structural integrity is essential for normal vision; disruptions contribute to a broad variety of retinal ciliopathies. OSs possess many hundreds of stacked membranous disks, which capture photons and scaffold the phototransduction cascade. Although the molecular basis of OS structure remains unresolved, recent studies suggest that the photoreceptor-specific tetraspanin, peripherin-2/rds (P/rds), may contribute to the highly curved rim domains at disk edges. Here, we demonstrate that tetrameric P/rds self-assembly is required for generating high-curvature membranes in cellulo, implicating the noncovalent tetramer as a minimal unit of function. P/rds activity was promoted by disulfide-mediated tetramer polymerization, which transformed localized regions of curvature into high-curvature tubules of extended lengths. Transmission electron microscopy visualization of P/rds purified from OS membranes revealed disulfide-linked tetramer chains up to 100 nm long, suggesting that chains maintain membrane curvature continuity over extended distances. We tested this idea in Xenopus laevis photoreceptors, and found that transgenic expression of nonchain-forming P/rds generated abundant high-curvature OS membranes, which were improperly but specifically organized as ectopic incisures and disk rims. These striking phenotypes demonstrate the importance of P/rds tetramer chain formation for the continuity of rim formation during disk morphogenesis. Overall, this study advances understanding of the normal structure and function of P/rds for OS architecture and biogenesis, and clarifies how pathogenic loss-of-function mutations in P/rds cause photoreceptor structural defects to trigger progressive retinal degenerations. It also introduces the possibility that other tetraspanins may generate or sense membrane curvature in support of diverse biological functions.

Tetraspanin 33 (TSPAN33) regulates endocytosis and migration of human B lymphocytes by affecting the tension of the plasma membrane

B lymphocytes are a leukocyte subset capable of developing several functions apart from differentiating into antibody-secreting cells. These processes are triggered by external activation signals that induce changes in the plasma membrane properties, regulated by the formation of different lipid-bilayer subdomains that are associated with the underlying cytoskeleton through different linker molecules, thus allowing the functional specialization of regions within the membrane. Among these, there are tetraspanin-enriched domains. Tetraspanins constitute a superfamily of transmembrane proteins that establish lateral associations with other molecules, determining its activity and localization. In this study, we identified TSPAN33 as an active player during B-lymphocyte cytoskeleton and plasma membrane-related phenomena, including protrusion formation, adhesion, phagocytosis, and cell motility. By using an overexpression model of TSPAN33 in human Raji cells, we detected a specific distribution of this protein that includes membrane microvilli, the Golgi apparatus, and extracellular vesicles. Additionally, we identified diminished phagocytic ability and altered cell adhesion properties due to the aberrant expression of integrins. Accordingly, these cells presented an enhanced migratory phenotype, as shown by its augmented chemotaxis and invasion rates. When we evaluated the mechanic response of cells during fibronectin-induced spreading, we found that TSPAN33 expression inhibited changes in roughness and membrane tension. Contrariwise, TSPAN33 knockdown cells displayed opposite phenotypes to those observed in the overexpression model. Altogether, our data indicate that TSPAN33 represents a regulatory element of the adhesion and migration of B lymphocytes, suggesting a novel implication of this tetraspanin in the control of the mechanical properties of their plasma membrane.

Impaired Expression of Tetraspanin 32 (TSPAN32) in Memory T Cells of Patients with Multiple Sclerosis

Tetraspanins are a conserved family of proteins involved in a number of biological processes. We have previously shown that Tetraspanin-32 (TSPAN32) is significantly downregulated upon activation of T helper cells via anti-CD3/CD28 stimulation. On the other hand, TSPAN32 is marginally modulated in activated Treg cells. A role for TSPAN32 in controlling the development of autoimmune responses is consistent with our observation that encephalitogenic T cells from myelin oligodendrocyte glycoprotein (MOG)-induced experimental autoimmune encephalomyelitis (EAE) mice exhibit significantly lower levels of TSPAN32 as compared to naïve T cells. In the present study, by making use of ex vivo and in silico analysis, we aimed to better characterize the pathophysiological and diagnostic/prognostic role of TSPAN32 in T cell immunity and in multiple sclerosis (MS). We first show that TSPAN32 is significantly downregulated in memory T cells as compared to naïve T cells, and that it is further diminished upon ex vivo restimulation. Accordingly, following antigenic stimulation, myelin-specific memory T cells from MS patients showed significantly lower expression of TSPAN32 as compared to memory T cells from healthy donors (HD). The expression levels of TSPAN32 was significantly downregulated in peripheral blood mononuclear cells (PBMCs) from drug-naïve MS patients as compared to HD, irrespective of the disease state. Finally, when comparing patients undergoing early relapses in comparison to patients with longer stable disease, moderate but significantly lower levels of TSPAN32 expression were observed in PBMCs from the former group. Our data suggest a role for TSPAN32 in the immune responses underlying the pathophysiology of MS and represent a proof-of-concept for additional studies aiming at dissecting the eventual contribution of TSPAN32 in other autoimmune diseases and its possible use of TSPAN32 as a diagnostic factor and therapeutic target.

Parallels between wound healing, epimorphic regeneration and solid tumors

Striking similarities between wound healing, epimorphic regeneration and the progression of solid tumors have been uncovered by recent studies. In this Review, we discuss systemic effects of tumorigenesis that are now being appreciated in epimorphic regeneration, including genetic, cellular and metabolic heterogeneity, changes in circulating factors, and the complex roles of immune cells and immune modulation at systemic and local levels. We suggest that certain mechanisms enabling regeneration may be co-opted by cancer to promote growth at primary and metastatic sites. Finally, we advocate that working with a unified approach could complement research in both fields.

TspanC8 tetraspanins differentially regulate ADAM10 endocytosis and half-life

ADAM10 is a transmembrane metalloprotease that is essential for development and tissue homeostasis. It cleaves the ectodomain of many proteins, including amyloid precursor protein, and plays an essential role in Notch signaling. ADAM10 associates with six members of the tetraspanin superfamily referred to as TspanC8 (Tspan5, Tspan10, Tspan14, Tspan15, Tspan17, and Tspan33), which regulate its exit from the endoplasmic reticulum and its substrate selectivity. We now show that ADAM10, Tspan5, and Tspan15 influence each other's expression level. Notably, ADAM10 undergoes faster endocytosis in the presence of Tspan5 than in the presence of Tspan15, and Tspan15 stabilizes ADAM10 at the cell surface yielding high expression levels. Reciprocally, ADAM10 stabilizes Tspan15 at the cell surface, indicating that it is the Tspan15/ADAM10 complex that is retained at the plasma membrane. Chimeric molecules indicate that the cytoplasmic domains of these tetraspanins contribute to their opposite action on ADAM10 trafficking and Notch signaling. In contrast, an unusual palmitoylation site at the end of Tspan15 C-terminus is dispensable. Together, these findings uncover a new level of ADAM10 regulation by TspanC8 tetraspanins.

The Contrasting Role of Extracellular Vesicles in Vascular Inflammation and Tissue Repair

Extracellular vesicles are a heterogeneous family of vesicles, generated from different subcellular compartments and released into the extracellular space. Composed of a lipid bilayer encompassing both soluble cytosolic material and nuclear components, these organelles have been recently described as novel regulators of intercellular communication between adjacent and remote cells. Due to their diversified composition and biological content, they portray specific signatures of cellular activation and pathological processes, their potential as diagnostic and prognostic biomarkers has raised significant interest in cardiovascular diseases. Circulating vesicles, especially those released from platelets, leukocytes, and endothelial cells are found to play a critical role in activating several fundamental cells within the vasculature, including endothelial cells and vascular smooth muscle cells. Their intrinsic activity and immunomodulatory properties lends them to not only promote vascular inflammation, but also enhance tissue regeneration, vascular repair, and indeed resolution. In this review we aim to recapitulate the recent findings concerning the roles played by EVs that originate from different circulating cells, with particular reference to their action on the endothelium. We focus herein, on the interaction of platelet and leukocyte EVs with the endothelium. In addition, their potential biological function in promoting tissue resolution and vascular repair will also be discussed.

LncRNA KCNQ1OT1 contributes to the progression and chemoresistance in acute myeloid leukemia by modulating Tspan3 through suppressing miR-193a-3p

AIMS

Acute myeloid leukemia (AML) is an aggressive cancer that invariably produces drug resistance after treatment. The aim is to explore the role of lncRNA potassium voltage-gated channel subfamily Q member 1 overlapping transcript 1 (KCNQ1OT1) and associated novel mechanisms in the progression and chemoresistance of AML.

MAIN METHODS

The expression of KCNQ1OT1, miR-193a-3p, and Tspan3 was measured by qRT-PCR. The values of IC50 for adriamycin (ADR) and the ability of proliferation were analyzed by CCK-8 assay. Cell migration and invasion were assessed by transwell assay. Cell apoptosis was monitored by flow cytometry assay. The expression of Tspan3, MRP1, P-gp and LRP at the protein level was quantified by western blot. The relationship between miR-193a-3p and KCNQ1OT1 or Tspan3 was predicted by bioinformatics tool Diana and verified by dual-luciferase reporter assay, RIP assay or RNA pull-down assay.

KEY FINDINGS

KCNQ1OT1 and Tspan3 were up-regulated, while miR-193a-3p was down-regulated in ADR resistant AML samples and cells. KCNQ1OT1 knockdown reduced ADR resistance, inhibited proliferation, migration and invasion but promoted apoptosis of ADR resistant AML cells, miR-193a-3p inhibition reversed these effects. MiR-193a-3p was a target of KCNQ1OT1 and combined with Tspan3 3' untranslated region (3' UTR). Enrichment of miR-193a-3p decreased ADR resistance, inhibited proliferation, migration and invasion and stimulated apoptosis in ADR resistant AML cells, but Tspan3 overexpression overturned these impacts.

SIGNIFICANCE

KCNQ1OT1 aggravates AML progression and chemoresistance to ADR by inducing Tspan3 expression via adsorbing miR-193a-3p in ADR resistant AML cells, providing a theoretical basis for the treatment of AML with chemoresistance.

Tumorigenesis, diagnosis, and therapeutic potential of exosomes in liver cancer

Hepatocellular carcinoma (HCC, also called primary liver cancer) is one of the most fatal cancers in the world. Due to the insidiousness of the onset of HCC and the lack of effective treatment methods, the prognosis of HCC is extremely poor, and the 5-year average survival rate is less than 10%. Exosomes are nano-sized microvesicle and contain various components such as nucleic acids, proteins, and lipids. Exosomes are important carriers for signal transmission or transportation of material from cell to cell or between cells and tissues. In recent years, exosomes have been considered as potential therapeutic targets of HCC. A large number of reports indicate that exosomes play a key role in the establishment of an HCC microenvironment, as well as the development, progression, invasion, metastasis, and even the diagnosis, treatment, and prognosis of HCC. However, the exact molecular mechanisms and roles of exosomes in these processes remain unclear. We believe that elucidation of the regulatory mechanism of HCC-related exosomes and its signaling pathway and analysis of its clinical applications in the diagnosis and treatment of HCC can provide useful clues for future treatment regimens for HCC. This article discusses and summarizes the research progress of HCC-related exosomes and their potential clinical applications.

NADPH oxidase regulates chemotropic growth of the fungal pathogen Fusarium oxysporum towards the host plant

Soil-inhabiting fungal pathogens use chemical signals to locate and colonise the host plant. In the vascular wilt fungus Fusarium oxysporum, hyphal chemotropism towards tomato roots is triggered by secreted plant peroxidases (Prx), which catalyse the reductive cleavage of reactive oxygen species (ROS). Here we show that this chemotropic response requires the regulated synthesis of ROS by the conserved fungal NADPH oxidase B (NoxB) complex, and their transformation into hydrogen peroxide (H₂ O₂ ) by superoxide dismutase (SOD). Deletion of NoxB or the regulatory subunit NoxR, or pharmacological inhibition of SOD, specifically abolished chemotropism of F. oxysporum towards Prx gradients. Addition of isotropic concentrations of H₂ O₂ rescued chemotropic growth in the noxBΔ and noxRΔ mutants, but not in a mutant lacking the G protein-coupled receptor Ste2. Prx-triggered rapid Nox- and Ste2-dependent phosphorylation of the cell wall integrity mitogen-activated protein kinase (CWI MAPK) Mpk1, an essential component of the chemotropic response. These results suggest that Ste2 and the CWI MAPK cascade function downstream of NoxB in Prx chemosensing. Our findings reveal a new role for Nox enzymes in directed hyphal growth of a filamentous pathogen towards its host and might be of broad interest for chemotropic interactions between plants and root-colonising fungi.

Tumorigenesis, diagnosis, and therapeutic potential of exosomes in liver cancer

Hepatocellular carcinoma (HCC, also called primary liver cancer) is one of the most fatal cancers in the world. Due to the insidiousness of the onset of HCC and the lack of effective treatment methods, the prognosis of HCC is extremely poor, and the 5-year average survival rate is less than 10%. Exosomes are nano-sized microvesicle and contain various components such as nucleic acids, proteins, and lipids. Exosomes are important carriers for signal transmission or transportation of material from cell to cell or between cells and tissues. In recent years, exosomes have been considered as potential therapeutic targets of HCC. A large number of reports indicate that exosomes play a key role in the establishment of an HCC microenvironment, as well as the development, progression, invasion, metastasis, and even the diagnosis, treatment, and prognosis of HCC. However, the exact molecular mechanisms and roles of exosomes in these processes remain unclear. We believe that elucidation of the regulatory mechanism of HCC-related exosomes and its signaling pathway and analysis of its clinical applications in the diagnosis and treatment of HCC can provide useful clues for future treatment regimens for HCC. This article discusses and summarizes the research progress of HCC-related exosomes and their potential clinical applications.

Exosomes and Ectosomes in Intercellular Communication

Exosomes and ectosomes, two distinct types of extracellular vesicles generated by all types of cell, play key roles in intercellular communication. The formation of these vesicles depends on local microdomains assembled in endocytic membranes for exosomes and in the plasma membrane for ectosomes. These microdomains govern the accumulation of proteins and various types of RNA associated with their cytosolic surface, followed by membrane budding inward for exosome precursors and outward for ectosomes. A fraction of endocytic cisternae filled with vesicles - multivesicular bodies - are later destined to undergo regulated exocytosis, leading to the extracellular release of exosomes. In contrast, the regulated release of ectosomes follows promptly after their generation. These two types of vesicle differ in size - 50-150 nm for exosomes and 100-500 nm for ectosomes - and in the mechanisms of assembly, composition, and regulation of release, albeit only partially. For both exosomes and ectosomes, the surface and luminal cargoes are heterogeneous when comparing vesicles released by different cell types or by single cells in different functional states. Upon release, the two types of vesicle navigate through extracellular fluid for varying times and distances. Subsequently, they interact with recognized target cells and undergo fusion with endocytic or plasma membranes, followed by integration of vesicle membranes into their fusion membranes and discharge of luminal cargoes into the cytosol, resulting in changes to cellular physiology. After fusion, exosome/ectosome components can be reassembled in new vesicles that are then recycled to other cells, activating effector networks. Extracellular vesicles also play critical roles in brain and heart diseases and in cancer, and are useful as biomarkers and in the development of innovative therapeutic approaches.

Classes of non-conventional tetraspanins defined by alternative splicing

Tetraspanins emerge as a family of membrane proteins mediating an exceptional broad diversity of functions. The naming refers to their four transmembrane segments, which define the tetraspanins' typical membrane topology. In this study, we analyzed alternative splicing of tetraspanins. Besides isoforms with four transmembrane segments, most mRNA sequences are coding for isoforms with one, two or three transmembrane segments, representing structurally mono-, di- and trispanins. Moreover, alternative splicing may alter transmembrane topology, delete parts of the large extracellular loop, or generate alternative N- or C-termini. As a result, we define structure-based classes of non-conventional tetraspanins. The increase in gene products by alternative splicing is associated with an unexpected high structural variability of tetraspanins. We speculate that non-conventional tetraspanins have roles in regulating ER exit and modulating tetraspanin-enriched microdomain function.

Tspan15 plays a crucial role in metastasis in oral squamous cell carcinoma

Tetraspanin 15 (Tspan15) is a member of the tetraspanin family, which is associated with various biological events and several diseases, however, its role in human oral squamous cell carcinoma (OSCC) remains unknown. The current study aimed to clarify the role of Tspan15 in OSCC. The mRNA and protein expression levels of Tspan15 were up-regulated in OSCC cases and OSCC-derived cell lines. Significant up-regulated Tspan15 expression was found in the advanced OSCC cases; primary tumoral size (P = 0.042), regional lymph node metastasis (P = 0.036) and TNM classification (P = 0.024). The decreased expression of Tspan15 did not significantly affect cellular proliferation, whereas tumoral invasion and migration activities were suppressed in Tspan15-down-regulated cells, suggesting that Tspan15 might activate metastasis-related signaling. Moreover, in the Tspan15-down-regulated cells, the expression of a disintegrin and metalloproteinase (ADAM) 10 was also down-regulated and the cells secreted less soluble N-cadherin compared with control cells. And weak immunoreactivity of β-catenin in the nucleus was detected in Tspan15-down-regulated cells compared with the control cells. These findings suggested that overexpression of Tspan15 positively regulates development of OSCC, and that ADAM10, N-cadherin, β-catenin might be involved in the Tspan15-mediated pathway. These unusual conditions of cell adhesion molecules may lead to high metastasis rate found in Tspan15-overexpressing cases.

Genome-wide association analysis of 95 549 individuals identifies novel loci and genes influencing optic disc morphology

Optic nerve head morphology is affected by several retinal diseases. We measured the vertical optic disc diameter (DD) of the UK Biobank (UKBB) cohort (N = 67 040) and performed the largest genome-wide association study (GWAS) of DD to date. We identified 81 loci (66 novel) for vertical DD. We then replicated the novel loci in International Glaucoma Genetic Consortium (IGGC, N = 22 504) and European Prospective Investigation into Cancer–Norfolk (N = 6005); in general the concordance in effect sizes was very high (correlation in effect size estimates 0.90): 44 of the 66 novel loci were significant at P < 0.05, with 19 remaining significant after Bonferroni correction. We identified another 26 novel loci in the meta-analysis of UKBB and IGGC data. Gene-based analyses identified an additional 57 genes. Human ocular tissue gene expression analysis showed that most of the identified genes are enriched in optic nerve head tissue. Some of the identified loci exhibited pleiotropic effects with vertical cup-to-disc ratio, intraocular pressure, glaucoma and myopia. These results can enhance our understanding of the genetics of optic disc morphology and shed light on the genetic findings for other ophthalmic disorders such as glaucoma and other optic nerve diseases.

Differential tetraspanin genes expression and subcellular localization during mutualistic interactions in Phaseolus vulgaris

Arbuscular mycorrhizal fungi and rhizobia association with plants are two of the most successful plant-microbe associations that allow the assimilation of P and N by plants, respectively. These mutualistic interactions require a molecular dialogue, i.e., legume roots exude flavonoids or strigolactones which induce the Nod factors or Myc factors synthesis and secretion from the rhizobia or fungi, respectively. These Nod or Myc factors trigger several responses in the plant root, including calcium oscillations, and reactive oxygen species (ROS). Furthermore, superoxide and H₂O₂ have emerged as key components that regulate the transitions from proliferation to differentiation in the plant meristems. Similar to the root meristem, the nodule meristem accumulates superoxide and H₂O₂. Tetraspanins are transmembrane proteins that organize into tetraspanin web regions, where they recruit specific proteins into platforms required for signal transduction, membrane fusion, cell trafficking and ROS generation. Plant tetraspanins are scaffolding proteins associated with root radial patterning, biotic and abiotic stress responses, cell fate determination, and hormonal regulation and recently have been reported as a specific marker of exosomes in animal and plant cells and key players at the site of plant fungal infection. In this study, we conducted transcriptional profiling of the tetraspanin family in common bean (Phaseolus vulgaris L. var. Negro Jamapa) to determine the specific expression patterns and subcellular localization of tetraspanins during nodulation or under mycorrhizal association. Our results demonstrate that the tetraspanins are transcriptionally modulated during the mycorrhizal association, but are also expressed in the infection thread and nodule meristem development. Subcellular localization indicates that tetraspanins have a key role in vesicular trafficking, cell division, and root hair polar growth.

JUNO, the receptor of sperm IZUMO1, is expressed by the human oocyte and is essential for human fertilisation

STUDY QUESTION

Is JUNO protein present at the surface membrane of human oocytes and involved in the fertilisation process?

SUMMARY ANSWER

JUNO protein is expressed on the plasma membrane of human oocytes and its inhibition by a monoclonal antibody completely blocks gamete fusion.

WHAT IS KNOWN ALREADY

Fusion of gamete membranes is the culminating event of the fertilisation process, but its molecular mechanisms are poorly understood. Until now, three molecules have been shown to be essential: CD9 tetraspanin in the oocyte, Izumo1 protein on the sperm and Juno, its corresponding receptor on the oocyte. Oocyte CD9 and sperm IZUMO1 have been identified in human gametes and their interaction is also well-conserved among several mammalian species. The presence of JUNO on human oocytes, however, has not yet been reported, nor has its role in fertilisation been investigated.

STUDY DESIGN, SIZE, DURATION

We selected an anti-human JUNO antibody in order to investigate the presence of JUNO on the oocyte membrane surface and studied its potential involvement in gamete membrane interaction during fertilisation.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Monoclonal antibodies against human JUNO (anti-hJUNO mAb) were produced by immunisation of mice with HEK cells transfected with the putative human JUNO sequence (HEK-hJUNO). These antibodies were used for immunostaining experiments and in vitro fertilisation assays with human gametes (GERMETHEQUE Biobank).

MAIN RESULTS AND THE ROLE OF CHANCE

Three hybridoma supernatants, verified by immunostaining, revealed specifically HEK-hJUNO cells. The three purified monoclonal antibodies, FJ2E4 (IgG1), FJ8E8 (IgG1) and FJ4F5 (IgG2a), recognised the soluble recombinant human JUNO protein and, in a western blot of HEK-hJUNO extracts, a protein with an expected MW of 25 kDa. In addition, soluble recombinant human IZUMO protein inhibited the binding of anti-hJUNO mAbs to cells expressing hJUNO. Using these anti-hJUNO mAbs in immunostaining, we identified the presence of JUNO protein at the plasma membrane of human oocytes. Furthermore, we revealed a progressive expression of JUNO according to oocyte maturity. Finally, we showed that human zona-free oocytes, inseminated in the presence of anti-hJUNO mAb, were not fertilised by human sperm. These results suggest that, as seen in the mouse, JUNO is indeed involved in human gamete membrane fusion during fertilisation.

LARGE-SCALE DATA

N/A.

LIMITATIONS, REASONS FOR CAUTION

In accordance with French bioethics laws, functional tests were performed using zona-free oocytes, which of course does not fully encompass all normal in vivo physiological conditions. However, these in vitro tests do provide direct information regarding sperm-oocyte membrane interactions.

WIDER IMPLICATIONS OF THE FINDINGS

Mechanisms of gamete fusion appear to be homologous between mice and humans. However, some differences do exist and analysing the human mechanisms is essential. In fact, this is the first report describing the presence of JUNO on human oocytes and its involvement in human fertilisation. This discovery allows further examination of the understanding of molecular mechanisms that drive gamete fusion: a crucial challenge at a time when infertility affects 16% of reproductively active couples.

STUDY FUNDING/COMPETING INTERESTS

This work was supported by the Agence Nationale pour la Recherche, Grant no. ANR-13-BVS5-0004, and by Association Institut du Cancer et d'Immunogénétique (ICIG). There are no competing interests.

Tumour infiltrating lymphocytes and immune-related genes as predictors of outcome in pancreatic adenocarcinoma

BACKGROUND

We investigated the correlation between pancreatic ductal adenocarcinoma patient prognosis and the presence of tumour infiltrating lymphocytes and expression of 521 immune system genes.

METHODS

Intratumoural CD3+, CD8+, and CD20+ lymphocytes were examined by immunohistochemistry in 12 PDAC patients with different outcomes who underwent pancreaticoduodenectomy. The results were correlated with gene expression profile using the digital multiplexed NanoString nCounter analysis system (NanoString Technologies, Seattle, WA, USA).

RESULTS

Twenty immune system genes were significantly differentially expressed in patients with a good prognosis relative to patients with a worse prognosis: TLR2 and TLR7 (Toll-like receptor superfamily); CD4, CD37, FOXP3, PTPRC (B cell and T cell signalling); IRF5, IRF8, STAT1, TFE3 (transcription factors); ANP32B, CCND3 (cell cycle); BTK (B cell development); TNF, TNFRF1A (TNF superfamily); HCK (leukocyte function); C1QA (complement system); BAX, PNMA1 (apoptosis); IKBKE (NFκB pathway). Differential expression was more than twice log 2 for TLR7, TNF, C1QA, FOXP3, and CD37.

DISCUSSION

Tumour infiltrating lymphocytes were present at higher levels in samples from patients with better prognosis. Our findings indicate that tumour infiltrating lymphocyte levels and expression level of the immune system genes listed above influence pancreatic ductal adenocarcinoma prognosis. This information could be used to improve selection of best responders to immune inhibitors.

Endothelial Cell-Specific Inactivation of TSPAN12 (Tetraspanin 12) Reveals Pathological Consequences of Barrier Defects in an Otherwise Intact Vasculature

Supplemental Digital Content is available in the text.

Objective—

Blood-CNS (central nervous system) barrier defects are implicated in retinopathies, neurodegenerative diseases, stroke, and epilepsy, yet, the pathological mechanisms downstream of barrier defects remain incompletely understood. Blood-retina barrier (BRB) formation and retinal angiogenesis require β-catenin signaling induced by the ligand norrin (NDP [Norrie disease protein]), the receptor FZD4 (frizzled 4), coreceptor LRP5 (low-density lipoprotein receptor-like protein 5), and the tetraspanin TSPAN12 (tetraspanin 12). Impaired NDP/FZD4 signaling causes familial exudative vitreoretinopathy, which may lead to blindness. This study seeked to define cell type-specific functions of TSPAN12 in the retina.

Approach and Results—

A loxP-flanked Tspan12 allele was generated and recombined in endothelial cells using a tamoxifen-inducible Cdh5-CreERT2 driver. Resulting phenotypes were documented using confocal microscopy. RNA-Seq, histopathologic analysis, and electroretinogram were performed on retinas of aged mice. We show that TSPAN12 functions in endothelial cells to promote vascular morphogenesis and BRB formation in developing mice and BRB maintenance in adult mice. Early loss of TSPAN12 in endothelial cells causes lack of intraretinal capillaries and increased VE-cadherin (CDH5 [cadherin5 aka VE-cadherin]) expression, consistent with premature vascular quiescence. Late loss of TSPAN12 strongly impairs BRB maintenance without affecting vascular morphogenesis, pericyte coverage, or perfusion. Long-term BRB defects are associated with immunoglobulin extravasation, complement deposition, cystoid edema, and impaired b-wave in electroretinograms. RNA-sequencing reveals transcriptional responses to the perturbation of the BRB, including genes involved in vascular basement membrane alterations in diabetic retinopathy.

Conclusions—

This study establishes mice with late endothelial cell–specific loss of Tspan12 as a model to study pathological consequences of BRB impairment in an otherwise intact vasculature.

Migrasomes provide regional cues for organ morphogenesis during zebrafish gastrulation

Migrasomes are recently identified vesicular organelles that form on retraction fibres behind migrating cells. Whether migrasomes are present in vivo and, if so, the function of migrasomes in living organisms is unknown. Here, we show that migrasomes are formed during zebrafish gastrulation and signalling molecules, such as chemokines, are enriched in migrasomes. We further demonstrate that Tspan4 and Tspan7 are required for migrasome formation. Organ morphogenesis is impaired in zebrafish MZtspan4a and MZtspan7 mutants. Mechanistically, migrasomes are enriched on a cavity underneath the embryonic shield where they serve as chemoattractants to ensure the correct positioning of dorsal forerunner cells vegetally next to the embryonic shield, thereby affecting organ morphogenesis. Our study shows that migrasomes are signalling organelles that provide specific biochemical information to coordinate organ morphogenesis.

A tetraspanin gene regulating auxin response and affecting orchid perianth size and various plant developmental processes

The competition between L (lip) and SP (sepal/petal) complexes in P-code model determines the identity of complex perianth patterns in orchids. Orchid tetraspanin gene Auxin Activation Factor (AAF) orthologs, whose expression strongly correlated with the expansion and size of the perianth after P code established, were identified. Virus-induced gene silencing (VIGS) of OAGL6-2 in L complex resulted in smaller lips and the down-regulation of Oncidium OnAAF. VIGS of PeMADS9 in L complex resulted in the enlarged lips and up-regulation of Phalaenopsis PaAAF. Furthermore, the larger size of Phalaenopsis variety flowers was associated with higher PaAAF expression, larger and more cells in the perianth. Thus, a rule is established that whenever bigger perianth organs are made in orchids, higher OnAAF/PaAAF expression is observed after their identities are determined by P-code complexes. Ectopic expression Arabidopsis AtAAF significantly increased the size of flower organs by promoting cell expansion in transgenic Arabidopsis due to the enhancement of the efficiency of the auxin response and the subsequent suppression of the jasmonic acid (JA) biosynthesis genes (DAD1/OPR3) and BIGPETAL gene during late flower development. In addition, auxin-controlled phenotypes, such as indehiscent anthers, enhanced drought tolerance, and increased lateral root formation, were also observed in 35S::AtAAF plants. Furthermore, 35S::AtAAF root tips maintained gravitropism during auxin treatment. In contrast, the opposite phenotype was observed in palmitoylation-deficient AtAAF mutants. Our data demonstrate an interaction between the tetraspanin AAF and auxin/JA that regulates the size of flower organs and impacts various developmental processes.

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.

TSPAN8 promotes cancer cell stemness via activation of sonic Hedgehog signaling

Cancer stem cells (CSCs) represent a major source of treatment resistance and tumor progression. However, regulation of CSCs stemness is not entirely understood. Here, we report that TSPAN8 expression is upregulated in breast CSCs, promotes the expression of the stemness gene NANOG, OCT4, and ALDHA1, and correlates with therapeutic resistance. Mechanistically, TSPAN8 interacts with PTCH1 and inhibits the degradation of the SHH/PTCH1 complex through recruitment of deubiquitinating enzyme ATXN3. This results in the translocation of SMO to cilia, downstream gene expression, resistance of CSCs to chemotherapeutic agents, and enhances tumor formation in mice. Accordingly, expression levels of TSPAN8, PTCH1, SHH, and ATXN3 are positively correlated in human breast cancer specimens, and high TSPAN8 and ATXN3 expression levels correlate with poor prognosis. These findings reveal a molecular basis of TSPAN8-enhanced Sonic Hedgehog signaling and highlight a role for TSPAN8 in promoting cancer stemness.

Tetraspanin 8 (TSPAN8) has been implicated in a number of different tumours, but the underlying mechanisms remain unclear. Here, in breast cancer the authors highlight a role for TSPAN8 in promoting tumorigenesis through the activation of Hedgehog signalling.

Tspan8 is expressed in breast cancer and regulates E-cadherin/catenin signalling and metastasis accompanied by increased circulating extracellular vesicles

Tspan8 exhibits a functional role in many cancer types including pancreatic, colorectal, oesophagus carcinoma, and melanoma. We present a first study on the expression and function of Tspan8 in breast cancer. Tspan8 protein was present in the majority of human primary breast cancer lesions and metastases in the brain, bone, lung, and liver. In a syngeneic rat breast cancer model, Tspan8⁺ tumours formed multiple liver and spleen metastases, while Tspan8⁻ tumours exhibited a significantly diminished ability to metastasise, indicating a role of Tspan8 in metastases. Addressing the underlying molecular mechanisms, we discovered that Tspan8 can mediate up‐regulation of E‐cadherin and down‐regulation of Twist, p120‐catenin, and β‐catenin target genes accompanied by the change of cell phenotype, resembling the mesenchymal–epithelial transition. Furthermore, Tspan8⁺ cells exhibited enhanced cell–cell adhesion, diminished motility, and decreased sensitivity to irradiation. As a regulator of the content and function of extracellular vesicles (EVs), Tspan8 mediated a several‐fold increase in EV number in cell culture and the circulation of tumour‐bearing animals. We observed increased protein levels of E‐cadherin and p120‐catenin in these EVs; furthermore, Tspan8 and p120‐catenin were co‐immunoprecipitated, indicating that they may interact with each other. Altogether, our findings show the presence of Tspan8 in breast cancer primary lesion and metastases and indicate its role as a regulator of cell behaviour and EV release in breast cancer. © 2019 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of Pathological Society of Great Britain and Ireland.

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.

Tetraspanin CD82 Organizes Dectin-1 into Signaling Domains to Mediate Cellular Responses to Candida albicans

Tetraspanins are a family of proteins possessing four transmembrane domains that help in lateral organization of plasma membrane proteins. These proteins interact with each other as well as other receptors and signaling proteins, resulting in functional complexes called "tetraspanin microdomains." Tetraspanins, including CD82, play an essential role in the pathogenesis of fungal infections. Dectin-1, a receptor for the fungal cell wall carbohydrate β-1,3-glucan, is vital to host defense against fungal infections. The current study identifies a novel association between tetraspanin CD82 and Dectin-1 on the plasma membrane of Candida albicans-containing phagosomes independent of phagocytic ability. Deletion of CD82 in mice resulted in diminished fungicidal activity, increased C. albicans viability within macrophages, and decreased cytokine production (TNF-α, IL-1β) at both mRNA and protein level in macrophages. Additionally, CD82 organized Dectin-1 clustering in the phagocytic cup. Deletion of CD82 modulates Dectin-1 signaling, resulting in a reduction of Src and Syk phosphorylation and reactive oxygen species production. CD82 knockout mice were more susceptible to C. albicans as compared with wild-type mice. Furthermore, patient C. albicans-induced cytokine production was influenced by two human CD82 single nucleotide polymorphisms, whereas an additional CD82 single nucleotide polymorphism increased the risk for candidemia independent of cytokine production. Together, these data demonstrate that CD82 organizes the proper assembly of Dectin-1 signaling machinery in response to C. albicans.

Expression of tetraspanins NET-6 and CD151 in breast cancer as a potential tumor biomarker

Tetraspanins have been implicated in multiple biological functions including protein networking and cell signaling. NET-6 (TSPAN 13) has been demonstrated to be a tumor suppressor gene in breast cancer, while CD151 is more likely to act as an oncogene. However, the biological function of both proteins is still inconclusive. Immunohistochemistry was used to analyze the expression of NET-6 and CD151 proteins in breast tumors and benign epithelial cells. The cellular expression of both markers was correlated with HER2, ER, and PR status as well as tumor grade, Ki-67 scores, invasion, and metastasis. Expression of NET-6 and CD151 was variable both in tumors and in benign epithelial cells. Expression of NET-6 and CD151 was stronger in tumors than in benign epithelial cells. The expression of NET-6 was also stronger in HER2-negative, low-grade, lymphovascular invasion-negative, and non-metastatic breast tumors. There was no correlation between NET-6 expression and ER, or PR, or triple-negative status. There was no correlation between CD151 expression and HER2, ER, PR, or triple-negative status, tumor grade, or Ki-67 scores, invasion, and metastasis. The expression of tetraspanins NET-6 and CD151 may indicate an alteration of their biological function during neoplastic transformation. NET-6 expression in tumors might be a potential marker indicating the outcome of breast cancer.

Crystallization of the human tetraspanin protein CD9

The tetraspanin family of proteins with four membrane-spanning proteins function in a wide range of physiological processes in higher organisms, including cell migration and proliferation, cell fusion, fertilization and virus infection. Although the recently reported structure of CD81 unveiled the basic architecture of this family for the first time, further structural and functional studies are required in order to understand the mechanistic details of the complicated functions of the tetraspanin-family proteins. In this study, attempts were made to crystallize human CD9, a representative member of the tetraspanin family, and it was demonstrated that the truncation of a variable region in the second long extracellular loop significantly improved crystal growth.

Genome-wide association analyses identify 139 loci associated with macular thickness in the UK Biobank cohort

The macula, located near the center of the retina in the human eye, is responsible for providing critical functions, such as central, sharp vision. Structural changes in the macula are associated with many ocular diseases, including age-related macular degeneration (AMD) and glaucoma. Although macular thickness is a highly heritable trait, there are no prior reported genome-wide association studies (GWASs) of it. Here we describe the first GWAS of macular thickness, which was measured by spectral-domain optical coherence tomography using 68 423 participants from the UK Biobank cohort. We identified 139 genetic loci associated with macular thickness at genome-wide significance (P < 5 × 10-8). The most significant loci were LINC00461 (P = 5.1 × 10-120), TSPAN10 (P = 1.2 × 10-118), RDH5 (P = 9.2 × 10-105) and SLC6A20 (P = 1.4 × 10-71). Results from gene expression demonstrated that these genes are highly expressed in the retina. Other hits included many previously reported AMD genes, such as NPLOC4 (P = 1.7 × 10-103), RAD51B (P = 9.1 × 10-14) and SLC16A8 (P = 1.7 × 10-8), further providing functional significance of the identified loci. Through cross-phenotype analysis, these genetic loci also exhibited pleiotropic effects with myopia, neurodegenerative diseases (e.g. Parkinson's disease, schizophrenia and Alzheimer's disease), cancer (e.g. breast, ovarian and lung cancers) and metabolic traits (e.g. body mass index, waist circumference and type 2 diabetes). Our findings provide the first insight into the genetic architecture of macular thickness and may further elucidate the pathogenesis of related ocular diseases, such as AMD.

Nanoscale organization of tetraspanins during HIV-1 budding by correlative dSTORM/AFM

Membrane partition and remodeling play a key role in numerous cell mechanisms, especially in viral replication cycles where viruses subvert the plasma membrane to enter and escape from the host cell. Specifically assembly and release of HIV-1 particles require specific cellular components, which are recruited to the egress site by the viral protein Gag. We previously demonstrated that HIV-1 assembly alters both partitioning and dynamics of the tetraspanins CD9 and CD81, which are key players in many infectious processes, forming enriched areas where the virus buds. In this study we correlated super resolution microscopy mapping of tetraspanins with membrane topography delineated by atomic force microscopy (AFM) in Gag-expressing cells. We revealed that CD9 is specifically trapped within the nascent viral particles, especially at buds tips, suggesting that Gag mediates CD9 and CD81 depletion from the plasma membrane. In addition, we showed that CD9 is organized as small membrane assemblies of few tens of nanometers that can coalesce upon Gag expression.

Exosomes in Allergic Airway Diseases

PURPOSE OF REVIEW

This review will cover what is known regarding exosomes and allergy, and furthermore discuss novel mechanism of exosome-mediated immune modulation and metabolic regulation via the transfer of mitochondria.

RECENT FINDINGS

Exosomes are nano-sized extracellular vesicles (EVs) derived from the endosome that play a direct role in governing physiological and pathological conditions by transferring bioactive cargo such as proteins, enzymes, nucleic acids (miRNA, mRNA, DNA), and metabolites. Recent evidence suggest that exosomes may signal in autocrine but, most importantly, in paracrine and endocrine manner, being taken up by neighboring cells or carried to distant sites. Exosomes also mediate immunogenic responses, such as antigen presentation and inflammation. In asthma and allergy, exosomes facilitate cross-talk between immune and epithelial cells, and drive site-specific inflammation through the generation of pro-inflammatory mediators like leukotrienes. Recent studies suggest that myeloid cell-generated exosomes transfer mitochondria to lymphocytes. Exosomes are nano-sized mediators of the immune system which can modulate responses through antigen presentation, and the transfer of pro- and anti-inflammatory mediators. In addition to conventional mechanisms of immune modulation, exosomes may act as a novel courier of functional mitochondria that is capable of modulating the recipient cells bioenergetics, resulting in altered cellular responses. The transfer of mitochondria and modulation of bioenergetics may result in immune activation or dampening depending on the context.

The Late Endosomal Pathway Regulates the Ciliary Targeting of Tetraspanin Protein Peripherin 2

Peripherin 2 (PRPH2) is a tetraspanin protein concentrated in the light-sensing cilium (called the outer segment) of the vertebrate photoreceptor. The mechanism underlying the ciliary targeting of PRPH2 and the etiology of cone dystrophy caused by PRPH2 mutations remain elusive. Here we show that the late endosome (LE) is the main waystation that critically sorts newly synthesized PRPH2 to the cilium. PRPH2 is expressed in the luminal membrane of the LE. We delineate multiple C-terminal motifs of PRPH2 that distinctively regulate its LE and ciliary targeting through ubiquitination and binding to ESCRT (Endosomal Sorting Complexes Required for Transport) component Hrs. Using the newly developed TetOn-inducible system in transfected male and female mouse cones in vivo, we show that the entry of nascent PRPH2 into the cone outer segment can be blocked by either cone dystrophy-causing C-terminal mutations of PRPH2, or by short-term perturbation of the LE or recycling endosomal traffic. These findings open new avenues of research to explore the biological role of the LE in the biosynthetic pathway and the etiology of cone dystrophy caused by PRPH2 mutations and/or malfunctions of the LE.SIGNIFICANCE STATEMENT Peripherin 2 (PRPH2) is a tetraspanin protein abundantly expressed in the light-sensing cilium, the outer segment, of the vertebrate photoreceptor. The mechanism underlying the ciliary transport of PRPH2 is unclear. The present study reveals a novel ciliary targeting pathway, in which the newly synthesized PRPH2 is first targeted to the lumen of the late endosome (LE) en route to the cilia. We deciphered the protein motifs and the machinery that regulates the LE trafficking of PRPH2. Using a novel TetOn-inducible system in transfected mouse cones, we showed that the LE pathway of PRPH2 is critical for its outer segment expression. A cone dystrophy-causing mutation impairs the LE and ciliary targeting of PRPH2, implicating the relevance of LE to cone/macular degenerative diseases.

Molecular Players in Hematologic Tumor Cell Trafficking

The trafficking of neoplastic cells represents a key process that contributes to progression of hematologic malignancies. Diapedesis of neoplastic cells across endothelium and perivascular cells is facilitated by adhesion molecules and chemokines, which act in concert to tightly regulate directional motility. Intravital microscopy provides spatio-temporal views of neoplastic cell trafficking, and is crucial for testing and developing therapies against hematologic cancers. Multiple myeloma (MM), chronic lymphocytic leukemia (CLL), and acute lymphoblastic leukemia (ALL) are hematologic malignancies characterized by continuous neoplastic cell trafficking during disease progression. A common feature of these neoplasias is the homing and infiltration of blood cancer cells into the bone marrow (BM), which favors growth and survival of the malignant cells. MM cells traffic between different BM niches and egress from BM at late disease stages. Besides the BM, CLL cells commonly home to lymph nodes (LNs) and spleen. Likewise, ALL cells also infiltrate extramedullary organs, such as the central nervous system, spleen, liver, and testicles. The α4β1 integrin and the chemokine receptor CXCR4 are key molecules for MM, ALL, and CLL cell trafficking into and out of the BM. In addition, the chemokine receptor CCR7 controls CLL cell homing to LNs, and CXCR4, CCR7, and CXCR3 contribute to ALL cell migration across endothelia and the blood brain barrier. Some of these receptors are used as diagnostic markers for relapse and survival in ALL patients, and their level of expression allows clinicians to choose the appropriate treatments. In CLL, elevated α4β1 expression is an established adverse prognostic marker, reinforcing its role in the disease expansion. Combining current chemotherapies with inhibitors of malignant cell trafficking could represent a useful therapy against these neoplasias. Moreover, immunotherapy using humanized antibodies, CAR-T cells, or immune check-point inhibitors together with agents targeting the migration of tumor cells could also restrict their survival. In this review, we provide a view of the molecular players that regulate the trafficking of neoplastic cells during development and progression of MM, CLL, and ALL, together with current therapies that target the malignant cells.

Targeting the Tetraspanins with Monoclonal Antibodies in Oncology: Focus on Tspan8/Co-029

Tetraspanins are exposed at the surface of cellular membranes, which allows for the fixation of cognate antibodies. Developing specific antibodies in conjunction with genetic data would largely contribute to deciphering their biological behavior. In this short review, we summarize the main functions of Tspan8/Co-029 and its role in the biology of tumor cells. Based on data collected from recently reported studies, the possibilities of using antibodies to target Tspan8 in immunotherapy or radioimmunotherapy approaches are also discussed.

The Septate Junction Protein Tsp2A Restricts Intestinal Stem Cell Activity via Endocytic Regulation of aPKC and Hippo Signaling

Hippo signaling and the activity of its transcriptional coactivator, Yorkie (Yki), are conserved and crucial regulators of tissue homeostasis. In the Drosophila midgut, after tissue damage, Yki activity increases to stimulate stem cell proliferation, but how Yki activity is turned off once the tissue is repaired is unknown. From an RNAi screen, we identified the septate junction (SJ) protein tetraspanin 2A (Tsp2A) as a tumor suppressor. Tsp2A undergoes internalization to facilitate the endocytic degradation of atypical protein kinase C (aPKC), a negative regulator of Hippo signaling. In the Drosophila midgut epithelium, adherens junctions (AJs) and SJs are prominent in intestinal stem cells or enteroblasts (ISCs or EBs) and enterocytes (ECs), respectively. We show that when ISCs differentiate toward ECs, Tsp2A is produced, participates in SJ assembly, and turns off aPKC and Yki-JAK-Stat activity. Altogether, our study uncovers a mechanism allowing the midgut to restore Hippo signaling and restrict proliferation once tissue repair is accomplished.

Tumor-derived exosomes: Potential biomarkers and therapeutic target in the treatment of colorectal cancer

Colorectal cancer (CRC) is the third most common cause of cancer-related death in men and women in many countries. Early detection of CRC helps to prevent the advanced stages of the disease, and may thereby improve the survival of these patients. A noninvasive test with high specificity and sensitivity is required for this. Exosomes are lipid bilayer membrane nanovesicles that are released into most body fluids and especially in the microenvironment of cancer. They carry various proteins, lipids, and nucleic materials such as DNA, RNA, messenger RNA (mRNA), and microRNA (miRNA), and may also alter the function of target cells. In this review, we aimed to describe the biogenesis, composition, function, and the role of tumor-derived exosomes in cancer progression. Moreover, their applications in tumor diagnosis and treatment are described, with a particular focus on CRC.

Biogenesis of Extracellular Vesicles during Herpes Simplex Virus 1 Infection: Role of the CD63 Tetraspanin

Herpes simplex virus 1 (HSV-1) infections afflict more than 80% of the population worldwide. The virus primarily infects mucoepithelial cells and establishes latent reservoirs in neurons in sensory ganglia. Frequent reactivation has been linked to severe diseases, especially in immunocompromised individuals. Earlier, we reported that viral and host factors are packaged in extracellular vesicles (EVs) and delivered to uninfected cells, where they activate antiviral responses and restrict virus infection. Here, we interrogated the effect of HSV-1 infection on EV biogenesis. We found that HSV-1 infection causes a decrease in the amount of intracellular CD63 protein with a concomitant increase in extracellular CD63. This observation correlates with our previous finding that infected cells release more CD63-positive EVs than uninfected cells. The stimulation of CD63 exocytosis requires virus replication. CD63 is a member of the tetraspanin family of proteins that traffics between the plasma membrane and endosomal compartments and has a role in sorting cargo into the EVs. Previously, we reported that in cells depleted of CD63, HSV-1 virus yields increased, and here we provide data showing that in cells overexpressing CD63, HSV-1 virus yields decreased. Taken together, our data indicate that CD63 negatively impacts HSV-1 infection and that the CD63-positive EVs could control the dissemination of the virus in the host. Perhaps EV release by HSV-1-infected cells is a mechanism that controls virus dissemination.IMPORTANCE Intercellular communication, especially in neurons, largely relies on EVs, and modulation of EVs is known to impact physiological processes. Here, we present evidence that HSV-1 infection causes major alterations in the biogenesis of EVs, including an increase in their number and an increase in the CD63-positive population of EVs. These alterations result in an enrichment of the milieu of infection with EVs carrying signatures from infected cells. In addition to changes in the origin and type, EVs released by infected cells have differences in cargo, as they carry viral and host factors determined by the virus. The tetraspanin CD63 negatively impacts the infection, as demonstrated by CD63-knockdown and overexpression assays. A proposed mechanism involves the activation of antiviral responses in cells receiving CD63-positive EVs released by infected cells. Overall, HSV-1 causes major alterations in EVs that could contribute to HSV-1 persistence and pathogenesis.

Exosomes: fighting cancer with cancer

Exosomes are nanovesicles secreted by many cells, including cancer cells. Extensive research has been carried out to validate potential applications of exosomes and to evaluate their efficiency in a wide range of diseases, including cancer. The current knowledge on the origin, biogenesis and composition of exosomes is described. This review then focuses on the use of exosomes in cancer diagnostics and therapeutics.

Emerging roles of tetraspanins in plant inter-cellular and inter-kingdom communication

Inter-cellular and inter-kingdom signaling systems of various levels of complexity regulate pathogenic and mutualistic interactions between bacteria, parasites, and fungi and animal and plant hosts. Inter-kingdom interactions between mutualistic bacteria such as rhizobia and legumes during nodulation and between fungi and plants during mycorrhizal associations, are characterized by the extensive exchange of molecular signals, which allow nitrogen and phosphate assimilation, respectively. A novel aspect of this signaling exchange is the existence of specific structures, the exosomes, that carry important molecules that shape the plant-pathogen interactions. Exosomes contain a wide array of molecules, such as lipids, proteins, messenger RNA, and microRNAs, that play important roles in cell-to-cell communication in animal and plant cells by affecting gene expression and other physiological activity in distant cells within the same organism (e.g., during cancer metastases and neuron injuries). In plant cells, it has been recently reported that exosomes go beyond organism boundaries and inhibit a pathogenic interaction in plants. Plant produce and send exosomes loaded with specific small miRNA which inhibit the pathogen infection, but the pathogen can also produce exosomes carrying pro-pathogenic proteins and microRNAs. Therefore, exosomes are the important bridge regulating the signal exchange. Exosomes are small membrane-bound vesicles derived from multivesicular bodies (MVBs), which carries selected cargos from the cytoplasm (protein, lipids, and microRNAs) and under certain circumstances, they fuse with the plasma membrane, releasing the small vesicles as cargo-carrying exosomes into the extracellular space during intercellular and inter-kingdom communication. Animal and plant proteomic studies have demonstrated that tetraspanin proteins are an integral part of exosome membranes, positioning tetraspanins as essential components for endosome organization, with key roles in membrane fusion, cell trafficking, and membrane recognition. We discuss the similarities and differences between animal tetraspanins and plant tetraspanins formed during plant-microbe interactions and their potential role in mutualistic communication.