TSPAN7: A new player in excitatory synapse maturation and function

The role of Tetraspanins in digestive system tumor development: update and emerging evidence

Digestive system malignancies, including cancers of the esophagus, pancreas, stomach, liver, and colorectum, are the leading causes of cancer-related deaths worldwide due to their high morbidity and poor prognosis. The lack of effective early diagnosis methods is a significant factor contributing to the poor prognosis for these malignancies. Tetraspanins (Tspans) are a superfamily of 4-transmembrane proteins (TM4SF), classified as low-molecular-weight glycoproteins, with 33 Tspan family members identified in humans to date. They interact with other membrane proteins or TM4SF members to form a functional platform on the cytoplasmic membrane called Tspan-enriched microdomain and serve multiple functions including cell adhesion, migration, propagation and signal transduction. In this review, we summarize the various roles of Tspans in the progression of digestive system tumors and the underlying molecular mechanisms in recent years. Generally, the expression of CD9, CD151, Tspan1, Tspan5, Tspan8, Tspan12, Tspan15, and Tspan31 are upregulated, facilitating the migration and invasion of digestive system cancer cells. Conversely, Tspan7, CD82, CD63, Tspan7, and Tspan9 are downregulated, suppressing digestive system tumor cell metastasis. Furthermore, the connection between Tspans and the metastasis of malignant bone tumors is reviewed. We also summarize the potential role of Tspans as novel immunotherapy targets and as an approach to overcome drug resistance. Finally, we discuss the potential clinical value and therapeutic targets of Tspans in the treatments of digestive system malignancies and provide some guidance for future research.

Disruption of cortical cell type composition and function underlies diabetes-associated cognitive decline

AIMS/HYPOTHESIS

Type 2 diabetes is associated with increased risk of cognitive decline although the pathogenic basis for this remains obscure. Deciphering diabetes-linked molecular mechanisms in cells of the cerebral cortex could uncover novel therapeutic targets.

METHODS

Single-cell transcriptomic sequencing (scRNA-seq) was conducted on the cerebral cortex in a mouse model of type 2 diabetes (db/db mice) and in non-diabetic control mice in order to identify gene expression changes in distinct cell subpopulations and alterations in cell type composition. Immunohistochemistry and metabolic assessment were used to validate the findings from scRNA-seq and to investigate whether these cell-specific dysfunctions impact the neurovascular unit (NVU). Furthermore, the behavioural and cognitive alterations related to these dysfunctions in db/db mice were assessed via Morris water maze and novel object discrimination tests. Finally, results were validated in post-mortem sections and protein isolates from individuals with type 2 diabetes.

RESULTS

Compared with non-diabetic control mice, the db/db mice demonstrated disrupted brain function as revealed by losses in episodic and spatial memory and this occurred concomitantly with dysfunctional NVU, neuronal circuitry and cerebral atrophy. scRNA-seq of db/db mouse cerebral cortex revealed cell population changes in neurons, glia and microglia linked to functional regulatory disruption including neuronal maturation and altered metabolism. These changes were validated through immunohistochemistry and protein expression analysis not just in the db/db mouse cerebral cortex but also in post-mortem sections and protein isolates from individuals with type 2 diabetes (74.3 ± 5.5 years) compared with non-diabetic control individuals (87.0 ± 8.5 years). Furthermore, metabolic and synaptic gene disruptions were evident in cortical NVU cell populations and associated with a decrease in vascular density.

CONCLUSIONS/INTERPRETATION

Taken together, our data reveal disruption in the cellular and molecular architecture of the cerebral cortex induced by diabetes, which can explain, at least in part, the basis for progressive cognitive decline in individuals with type 2 diabetes.

DATA AVAILABILITY

The single-cell sequencing data that supports this study are available at GEO accession GSE217665 ( https://www.ncbi.nlm.nih.gov/geo/query/acc.cgi?acc=GSE217665 ).

Tetraspanin 7 promotes osteosarcoma cell invasion and metastasis by inducing EMT and activating the FAK-Src-Ras-ERK1/2 signaling pathway

Background

Tetraspanins are members of the 4-transmembrane protein superfamily (TM4SF) that function by recruiting many cell surface receptors and signaling proteins into tetraspanin-enriched microdomains (TEMs) that play vital roles in the regulation of key cellular processes including adhesion, motility, and proliferation. Tetraspanin7 (Tspan7) is a member of this superfamily that plays documented roles in hippocampal neurogenesis, synaptic transmission, and malignant transformation in certain tumor types. How Tspan7 influences the onset or progression of osteosarcoma (OS), however, remains to be defined. Herein, this study aimed to explore the relationship between Tspan7 and the malignant progression of OS, and its underlying mechanism of action.

Methods

In this study, the levels of Tspan7 expression in human OS cell lines were evaluated via qRT-PCR and western blotting. The effect of Tspan7 on proliferation was examined using CCK-8 and colony formation assays, while metastatic role of Tspan7 was assessed by functional assays both in vitro and in vivo. In addition, mass spectrometry and co-immunoprecipitation were performed to verify the interaction between Tspan7 and β1 integrin, and western blotting was used to explore the mechanisms of Tspan7 in OS progresses.

Results

We found that Tspan7 is highly expressed in primary OS tumors and OS cell lines. Downregulation of Tspan7 significantly suppressed OS growth, metastasis, and attenuated epithelial-mesenchymal transition (EMT), while its overexpression had the opposite effects in vitro. Furthermore, it exhibited reduced OS pulmonary metastases in Tspan7-deleted mice comparing control mice in vivo. Additionally, we proved that Tspan7 interacted with β1 integrin to facilitate OS metastasis through the activation of integrin-mediated downstream FAK-Src-Ras-ERK1/2 signaling pathway.

Conclusion

In summary, this study demonstrates for the first time that Tspan7 promotes OS metastasis via interacting with β1 integrin and activating the FAK-Src-Ras-ERK1/2 pathway, which could provide rationale for a new therapeutic strategy for OS.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12935-022-02591-1.

Tetraspanins as Potential Modulators of Glutamatergic Synaptic Function

Tetraspanins (Tspans) comprise a membrane protein family structurally defined by four transmembrane domains and intracellular N and C termini that is found in almost all cell types and tissues of eukaryotes. Moreover, they are involved in a bewildering multitude of diverse biological processes such as cell adhesion, motility, protein trafficking, signaling, proliferation, and regulation of the immune system. Beside their physiological roles, they are linked to many pathophysiological phenomena, including tumor progression regulation, HIV-1 replication, diabetes, and hepatitis. Tetraspanins are involved in the formation of extensive protein networks, through interactions not only with themselves but also with numerous other specific proteins, including regulatory proteins in the central nervous system (CNS). Interestingly, recent studies showed that Tspan7 impacts dendritic spine formation, glutamatergic synaptic transmission and plasticity, and that Tspan6 is correlated with epilepsy and intellectual disability (formerly known as mental retardation), highlighting the importance of particular tetraspanins and their involvement in critical processes in the CNS. In this review, we summarize the current knowledge of tetraspanin functions in the brain, with a particular focus on their impact on glutamatergic neurotransmission. In addition, we compare available resolved structures of tetraspanin family members to those of auxiliary proteins of glutamate receptors that are known for their modulatory effects.

PDCD4 regulates axonal growth by translational repression of neurite growth-related genes and is modulated during nerve injury responses

Programmed cell death 4 (PDCD4) protein is a tumor suppressor that inhibits translation through the mTOR-dependent initiation factor EIF4A, but its functional role and mRNA targets in neurons remain largely unknown. Our work identified that PDCD4 is highly expressed in axons and dendrites of CNS and PNS neurons. Using loss- and gain-of-function experiments in cortical and dorsal root ganglia primary neurons, we demonstrated the capacity of PDCD4 to negatively control axonal growth. To explore PDCD4 transcriptome and translatome targets, we used Ribo-seq and uncovered a list of potential targets with known functions as axon/neurite outgrowth regulators. In addition, we observed that PDCD4 can be locally synthesized in adult axons in vivo, and its levels decrease at the site of peripheral nerve injury and before nerve regeneration. Overall, our findings demonstrate that PDCD4 can act as a new regulator of axonal growth via the selective control of translation, providing a target mechanism for axon regeneration and neuronal plasticity processes in neurons.

Tetraspanin 7 and its closest paralog tetraspanin 6: membrane organizers with key functions in brain development, viral infection, innate immunity, diabetes and cancer

Tetraspanin (TSPAN) protein family forms a family of transmembrane proteins that act as organizers/scaffold for other proteins. TSPANs are primarily present on plasma membranes although they are also found in other biological membranes. They are organized in tetraspanin-enriched microdomains (TEMs), which allow spatiotemporal tuning of protein functions through the control of their membrane localization. TSPAN6 and TSPAN7 are close paralogs expressed in different tissues, TSPAN7 being highly expressed in the brain. Their functions only started to be unveiled in the late 2000's and are still poorly understood. Here, we introduce how TSPAN7 was first highlighted has a protein mutated in some forms of X-linked mental retardation, which was later proposed to be caused by defects in neuronal morphogenesis and synaptic transmission. We then discuss the impacts TSPAN7 has on cell morphology of dendritic cells and osteoclasts, through rearrangement of actin cytoskeleton and how TSPAN7 was shown to be a target of autoantibody in patients suffering from type 1 diabetes. Finally, we are addressing the double edge sword that is TSPAN7 in cancer. In the second part of this review, we address the known roles of TSPAN6 and how this protein was shown to participate in synaptic transmission and in amyloid precursor protein secretion, which may contribute to Alzheimer's disease pathology. We conclude this review by discussing the anti-inflammatory effect of TSPAN6.

Palmitoylated Proteins in Dendritic Spine Remodeling

Activity-responsive changes in the actin cytoskeleton are required for the biogenesis, motility, and remodeling of dendritic spines. These changes are governed by proteins that regulate the polymerization, depolymerization, bundling, and branching of actin filaments. Thus, processes that have been extensively characterized in the context of non-neuronal cell shape change and migration are also critical for learning and memory. In this review article, we highlight actin regulatory proteins that associate, at least transiently, with the dendritic plasma membrane. All of these proteins have been shown, either in directed studies or in high-throughput screens, to undergo palmitoylation, a potentially reversible, and stimulus-dependent cysteine modification. Palmitoylation increases the affinity of peripheral proteins for the membrane bilayer and contributes to their subcellular localization and recruitment to cholesterol-rich membrane microdomains.

Assessment of de novo copy-number variations in Italian patients with schizophrenia: Detection of putative mutations involving regulatory enhancer elements

OBJECTIVES

Variants appearing de novo in genes regulating key neurodevelopmental processes and/or in non-coding cis-regulatory elements (CREs), as enhancers, may increase the risk for schizophrenia. However, CREs involvement in schizophrenia needs to be explored more deeply.

METHODS

We investigated de novo copy-number variations (CNVs) in the whole-genomic DNA obtained from 46 family trios of schizophrenia probands by using the Enhancer Chip, a customised array CGH able to investigate the whole genome with a 300-kb resolution, specific disease loci at a ten-fold higher resolution, and which was highly enriched in probes in more than 1,250 enhancer elements selected from Vista Enhancer Browser.

RESULTS

In seven patients, we found de novo CNVs, two of which overlapped VISTA enhancer elements. De novo CNVs encompass genes (CNTNAP2, MAGI1, TSPAN7 and MET) involved in brain development, while that involving the enhancer element hs1043, also includes ZIC1, which plays a role in neural development and is responsible of behavioural abnormalities in Zic mutant mice.

CONCLUSIONS

These findings provide further evidence for the involvement of de novo CNVs in the pathogenesis of schizophrenia and suggest that CNVs affecting regulatory enhancer elements could contribute to the genetic vulnerability to the disorder.

TSPAN7 promotes the migration and proliferation of lung cancer cells via epithelial-to-mesenchymal transition

PURPOSE

To explore the effects and mechanisms of tetraspanin TSPAN7 on the progression of non-small-cell lung cancer (NSCLC) cells.

PATIENTS AND METHODS

All 125 lung cancer specimens and 60 metastatic tissues were obtained from patients diagnosed with NSCLC, and we used immunohistochemistry to detect the expression of TSPAN7 in NSCLC tissues and adjacent normal tissues. Cell proliferation and invasion ability were determined by MTT, colony formation, and cell migration. The relative protein expression level was analyzed by Western blot analysis.

RESULTS

Our clinical data showed that among 125 patients with lung cancer, TSPAN7 was associated with lymph node status, differentiation, tumor size, and poor prognosis. TSPAN7 knockout inhibited cell proliferation and migration. In addition, TSPAN7 increased the expression of N-cadherin in NSCLC cells by reducing the expression of E-cadherin and vimentin and promoting the cell epithelial-mesenchymal transition (EMT) process. Xenograft transplantation model confirmed the role of TSPAN7 in NSCLC metastasis.

CONCLUSION

TSPAN7-mediated EMT is the key to NSCLC migration. TSPAN7 is a potential target for NSCLC therapy.

Impact of energy restriction during late gestation on the muscle and blood transcriptome of beef calves after preconditioning

Background

Maternal nutrition has been highlighted as one of the main factors affecting intra-uterine environment. The increase in nutritional requirements by beef cows during late gestation can cause nutritional deficiency in the fetus and impact the fetal regulation of genes associated with myogenesis and immune response.

Methods

Forty days before the expected calving date, cows were assigned to one of two diets: 100% (control) or 70% (restricted group) of the daily energy requirement. Muscle samples were collected from 12 heifers and 12 steers, and blood samples were collected from 12 steers. The objective of this work was to identify and to assess the biological relevance of differentially expressed genes (DEG) in the skeletal muscle and blood of beef calves born from cows that experienced [or not] a 30% energy restriction during the last 40 days of gestation.

Results

A total of 160, 164, and 346 DEG (q-value< 0.05) were identified in the skeletal muscle for the effects of diet, sex, and diet-by-sex interaction, respectively. For blood, 452, 1392, and 155 DEG were identified for the effects of diet, time, and diet-by-time interaction, respectively. For skeletal muscle, results based on diet identified genes involved in muscle metabolism. In muscle, from the 10 most DEG down-regulated in the energy-restricted group (REST), we identified 5 genes associated with muscle metabolism and development: SLCO3A1, ATP6V0D1, SLC2A1, GPC4, and RASD2. In blood, among the 10 most DEG, we found genes related to response to stress up-regulated in the REST after weaning, such as SOD3 and INO80D, and to immune response down-regulated in the REST after vaccination, such as OASL, KLRF1, and LOC104968634.

Conclusion

In conclusion, maternal energy restriction during late gestation may limit the expression of genes in the muscle and increase expression in the blood of calves. In addition, enrichment analysis showed that a short-term maternal energy restriction during pregnancy affects the expression of genes related to energy metabolism and muscle contraction, and immunity and stress response in the blood. Therefore, alterations in the intra-uterine environment can modify prenatal development with lasting consequences to adult life.

Electronic supplementary material

The online version of this article (10.1186/s12864-018-5089-8) contains supplementary material, which is available to authorized users.

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.

Membrane lipid rafts and neurobiology: age-related changes in membrane lipids and loss of neuronal function

A better understanding of the cellular physiological role that plasma membrane lipids, fatty acids and sterols play in various cellular systems may yield more insight into how cellular and whole organ function is altered during the ageing process. Membrane lipid rafts (MLRs) within the plasma membrane of most cells serve as key organizers of intracellular signalling and tethering points of cytoskeletal components. MLRs are plasmalemmal microdomains enriched in sphingolipids, cholesterol and scaffolding proteins; they serve as a platform for signal transduction, cytoskeletal organization and vesicular trafficking. Within MLRs are the scaffolding and cholesterol binding proteins named caveolin (Cav). Cavs not only organize a multitude of receptors including neurotransmitter receptors (NMDA and AMPA receptors), signalling proteins that regulate the production of cAMP (G protein-coupled receptors, adenylyl cyclases, phosphodiesterases (PDEs)), and receptor tyrosine kinases involved in growth (Trk), but also interact with components that modulate actin and tubulin cytoskeletal dynamics (e.g. RhoGTPases and actin binding proteins). MLRs are essential for the regulation of the physiology of organs such as the brain, and age-related loss of cholesterol from the plasma membrane leads to loss of MLRs, decreased presynaptic vesicle fusion, and changes in neurotransmitter release, all of which contribute to different forms of neurodegeneration. Thus, MLRs provide an active membrane domain that tethers and reorganizes the cytoskeletal machinery necessary for membrane and cellular repair, and genetic interventions that restore MLRs to normal cellular levels may be exploited as potential therapeutic means to reverse the ageing and neurodegenerative processes.

Tetraspanin 7 (TSPAN7) expression is upregulated in multiple myeloma patients and inhibits myeloma tumour development in vivo

BACKGROUND

Increased expression of the tetraspanin TSPAN7 has been observed in a number of cancers; however, it is unclear how TSPAN7 plays a role in cancer progression.

METHODS

We investigated the expression of TSPAN7 in the haematological malignancy multiple myleoma (MM) and assessed the consequences of TSPAN7 expression in the adhesion, migration and growth of MM plasma cells (PC) in vitro and in bone marrow (BM) homing and tumour growth in vivo. Finally, we characterised the association of TSPAN7 with cell surface partner molecules in vitro.

RESULTS

TSPAN7 was found to be highly expressed at the RNA and protein level in CD138(+) MM PC from approximately 50% of MM patients. TSPAN7 overexpression in the murine myeloma cell line 5TGM1 significantly reduced tumour burden in 5TGM1/KaLwRij mice 4 weeks after intravenous adminstration of 5TGM1 cells. While TSPAN7 overexpression did not affect cell proliferation in vitro, TSPAN7 increased 5TGM1 cell adhesion to BM stromal cells and transendothelial migration. In addition, TSPAN7 was found to associate with the molecular chaperone calnexin on the cell surface.

CONCLUSION

These results suggest that elevated TSPAN7 may be associated with better outcomes for up to 50% of MM patients.

Tetraspanin-3 is an organizer of the multi-subunit Nogo-A signaling complex

To ensure precision and specificity of ligand – receptor induced signaling, co-receptors and modulatory factors play important roles. The membrane bound ligand Nogo-A induces inhibition of neurite outgrowth, cell spreading, adhesion and migration via multi-subunit receptor complexes. Here, we identified the 4-transmembrane-spanning protein tetraspanin-3 (TSPAN3) as a new modulatory co-receptor for the Nogo-A inhibitory domain Nogo-A-Δ20. Single-molecule-tracking showed that TSPAN3 molecules in the cell membrane reacted with elevated mobility to Nogo-A binding, followed by association with the signal transducing Nogo-A receptor sphingosine-1-phosphate receptor 2 (S1PR2). Subsequently, TSPAN3 was co-internalized as part of the Nogo-A ligand – receptor complex into early endosomes, where it subsequently separated from Nogo-A and S1PR2 to be recycled to the cell surface. The functional importance of the Nogo-A – TSPAN3 interaction is shown by the fact that knockdown of TSPAN3 strongly reduced the Nogo-A-induced S1PR2 clustering, RhoA activation and cell spreading and neurite outgrowth inhibition. In addition to the modulatory functions of TSPAN3 on Nogo-A-S1PR2 signaling, these results illustrate the very dynamic spatiotemporal reorganizations of membrane proteins during ligand-induced receptor complex organizations.

Interaction of membrane/lipid rafts with the cytoskeleton: impact on signaling and function: membrane/lipid rafts, mediators of cytoskeletal arrangement and cell signaling

The plasma membrane in eukaryotic cells contains microdomains that are enriched in certain glycosphingolipids, gangliosides, and sterols (such as cholesterol) to form membrane/lipid rafts (MLR). These regions exist as caveolae, morphologically observable flask-like invaginations, or as a less easily detectable planar form. MLR are scaffolds for many molecular entities, including signaling receptors and ion channels that communicate extracellular stimuli to the intracellular milieu. Much evidence indicates that this organization and/or the clustering of MLR into more active signaling platforms depends upon interactions with and dynamic rearrangement of the cytoskeleton. Several cytoskeletal components and binding partners, as well as enzymes that regulate the cytoskeleton, localize to MLR and help regulate lateral diffusion of membrane proteins and lipids in response to extracellular events (e.g., receptor activation, shear stress, electrical conductance, and nutrient demand). MLR regulate cellular polarity, adherence to the extracellular matrix, signaling events (including ones that affect growth and migration), and are sites of cellular entry of certain pathogens, toxins and nanoparticles. The dynamic interaction between MLR and the underlying cytoskeleton thus regulates many facets of the function of eukaryotic cells and their adaptation to changing environments. Here, we review general features of MLR and caveolae and their role in several aspects of cellular function, including polarity of endothelial and epithelial cells, cell migration, mechanotransduction, lymphocyte activation, neuronal growth and signaling, and a variety of disease settings. This article is part of a Special Issue entitled: Reciprocal influences between cell cytoskeleton and membrane channels, receptors and transporters. Guest Editor: Jean Claude Hervé.