Characterisation of the biosynthesis and processing of the neutrophil granule membrane protein CD63 in myeloid cells

Utility of pleural fluid-derived extracellular vesicles as a source of Mycobacterium tuberculosis antigens MPT51 and MPT64 for pleural TB diagnosis: a proof-of-concept study

Extracellular vesicles (EVs) have recently emerged as a source of microbe-specific biomarkers for disease diagnosis. In the present study, we evaluated the utility of pleural fluid-derived extracellular vesicles (pEVs) as a source of Mycobacterium tuberculosis (M. tb.) antigens for pleural TB (pTB) diagnosis. EVs were isolated from pleural fluid (PF) samples and were characterized by scanning electron microscopy, and immunoblotting by targeting CD63 and LAMP2 markers. Antigen-detection ELISAs were developed for 2 M.tb.-specific antigens, MPT51 and MPT64 in pEVs (pEV-ELISA) and direct PF samples (PF-ELISA), and were evaluated on n = 86 samples in a blinded manner. Cut-off values were calculated by ROC-curve analysis to achieve 90 % (95%CI:73.47-97.89) and 86.67 % (95%CI:69.28-96.24) specificity for MPT51 and MPT64 pEV-ELISA respectively. The sensitivity of pEV-ELISA was 71.43 % (95%CI; 29.04-96.33) for MPT51 antigen and 57.14 % (95%CI; 18.41-90.1) for MPT64 antigen in the 'Definite' pTB group, while in the 'Definite and Probable' pTB group, the sensitivity was 62.86 % (95%CI:44.92-78.53) for MPT51 and 65.71 % (95%CI:47.79-80.87) for MPT64. The performance of PF-ELISA was sub-optimal, with 28.57 % (95%CI:3.67-70.96) and 14.29 % (95%CI:0.36-57.87) sensitivity for MPT51 and MPT64 in 'Definite' pTB group respectively. We conclude that M. tb.-antigens are concentrated in the EV-fraction of PF samples and EVs can be utilized for antigen-detection assays for pTB diagnosis.

Tracing the STING exocytosis pathway during herpes viruses infection

The STimulator of INterferon Genes (STING) constitutes a major DNA-sensing pathway that restricts HSV-1 infection in different models by activating type I interferon and pro-inflammatory responses. To counteract STING, HSV-1 has evolved numerous strategies including mechanisms to interfere with its oligomerization, post-translational modifications, and downstream signaling. Previously, we demonstrated that STING is packaged in extracellular vesicles (EVs) produced from HSV-1-infected cells. These EVs activated antiviral responses in uninfected recipient cells and suppressed a subsequent HSV-1 infection in a STING-dependent manner. Here, we provide information on the packaging of STING in EVs and its exocytosis. We found that STING exocytosis did not occur in CD63 knockdown cells supporting that STING follows the CD63 exocytosis pathway. Consistently, we found that STING co-localized with CD63 in cytoplasmic globular structures and exosomal STING and CD63 co-fractionated. Both golgicide A and brefeldin A prevented STING exocytosis during HSV-1 infection suggesting that STING trafficking through the Golgi is required. A STING ligand was insufficient for STING exocytosis, and downstream signaling through TBK1 was not required. However, STING palmitoylation and tethering to the ER by STIM1 were required for STING exocytosis. Finally, we found that HSV-1 replication/late gene expression triggered CD63 exocytosis that was required for STING exocytosis. Surprisingly, HSV-2 strain G did not trigger CD63 or STING exocytosis as opposed to VZV and HCMV. Also, EVs from HSV-1(F)- and HSV-2(G)-infected cells displayed differences in their ability to restrict these viruses. Overall, STING exocytosis is induced by certain viruses and shapes the microenvironment of infection.IMPORTANCEExtracellular vesicles (EVs) are released by all types of cells as they constitute a major mechanism of intercellular communication. The packaging of specific cargo in EVs and the pathway of exocytosis are not fully understood. STING is a sensor of a broad spectrum of pathogens and a key component of innate immunity. STING exocytosis during HSV-1 infection has been an intriguing observation, raising questions of whether this is a virus-induced process, the purpose it serves, and whether it is observed after infection with other viruses. Here, we have provided insights into the pathway of STING exocytosis and determined factors involved. STING exocytosis is a virus-induced process and not a response of the host to the infection. Besides HSV-1, other herpes viruses triggered STING exocytosis, but HSV-2(G) did not. HSV-1 EVs displayed different restriction capabilities compared with HSV-2(G) EVs. Overall, STING exocytosis is triggered by viruses to shape the microenvironment of infection.

Tetraspanin CD63 reduces the progression and metastasis of head and neck squamous cell carcinoma via KRT1-mediated cell cycle arrest

Despite the fact that metastasis is the leading cause of death in patients with head and neck squamous cell carcinoma, fundamental questions about the mechanisms that enable or inhibit metastasis remain unanswered. Tetraspanin CD63 has been linked to tumor progression and metastasis. However, few studies have examined the role of CD63 in HNSCC. In this study, we discovered that CD63 levels were abnormally altered in HNSCC tissue compared to adjacent tissue (n = 69 pairs), and that this was linked to prognosis. Through functional in vitro and in vivo experiments, the roles of CD63 in HNSCC were confirmed. Overexpression of CD63 inhibited the progression and metastasis of HNSCC cells. Using mass spectrometry and co-immunoprecipitation assays, we discovered that KRT1 could be a direct interacting partner of CD63. Furthermore, both CD63 and KRT1 expression was significantly decreased in metastatic tissue compared with primary tumor tissue (n = 13 pairs), suggesting that CD63 and KRT1 play a role in reducing the metastasis of HNSCC. In summary, we reveal a previously unrecognized role of CD63 in regulating KRT1-mediated cell cycle arrest in HNSCC cells, and our findings contribute to defining an important mechanism of HNSCC progression and metastasis.

An in vitro lipid-mixing assay to investigate the fusion between small extracellular vesicles and endosome

Small extracellular vesicles (sEVs) such as exosomes can efficiently deliver nucleic acids into the cytosol of recipient cells. However, the molecular mechanism of the subsequent fusion with an endosome is not well understood. In this study, we developed an in vitro lipid-mixing assay using an endosomal-mimicking anionic liposome to investigate the fusion between sEVs and endosomes. We observed that the particle number ratio between the sEVs and the anionic liposomes, the diameter of the liposomes, and the buffer pH were all important for fusion activity. Furthermore, we optimized the liposomal lipid composition and demonstrated that incorporating the anionic lipid bis(monooleoylglycero) phosphate and cholesterol was important for efficient and reliable fusion. Our in vitro assay suggested that a decrease in pH increased the fusion activity. Additionally, it was suggested that this pH-dependent increase in the fusion activity was predominantly due to a change in the sEVs. sEVs possess a larger fusion activity than artificial liposomes that mimic the physicochemical properties of exosomes. These results are consistent with those of previous in vivo studies, supporting the physiological relevance of our system. This study provides an important platform for further research to clarify the molecular mechanisms of fusion between sEVs and endosomes.

HA-tag CD63 is a novel conditional transgenic approach to track extracellular vesicle interactions with sperm and their transfer at conception

Extracellular vesicles (EVs) are a unique mode of intercellular communication capable of specificity in transmitting signals and cargo to coordinate local and distant cellular functions. A key example of this is the essential role that EVs secreted by epithelial cells lining the lumen of the male reproductive tract play in post-spermatogenic sperm maturation. We recently showed in a preclinical mouse model that this fundamental process had a causal role in somatic-to-germline transmission of biological information regarding prior stress experience capable of altering the rate of fetal development. However, critical mechanistic questions remain unanswered as to the processes by which signaling occurs between EVs and sperm, and whether EVs or their cargo are delivered at conception and are detectable in the early embryo. Unfortunately, notable methodological limitations shared across EV biology, particularly in the isolation and labeling of EVs, complicate efforts to answer these important questions as well as questions on EV targeting specificity and mechanisms. In our current studies, we developed a novel approach to track EVs using a conditional transgenic construct designed to label EVs via conditional Cre-induced hemagglutinin (HA) tagging of the EV endogenous tetraspanin, CD63. In our exhaustive validation steps, this internal small molecular weight tag did not affect EV secretion or functionality, a common problem found in the previous design of EV tags using larger molecular weight proteins, including fluorescent proteins. Utilizing a stably transfected immortalized epididymal epithelial cell line, we first validated key parameters of the conditional HA-tagged protein packaged into secreted EVs. Importantly, we systematically confirmed that expression of the CD63-HA had no impact on the production, size distribution, or surface charge of secreted EVs, nor did it alter the tetraspanin or miRNA composition of these EVs. We also utilized the CD63-HA EVs to verify physical interactions with sperm. Finally, using in vitro fertilization we produced some of the first images confirming sperm delivered EV cargo at conception and still detectable in the early-stage embryo. As such, this construct serves as a methodological advance and as a valuable tool, with applications in the study of EV function across biomedical research areas.

Exosomes are secreted at similar densities by M21 and PC3 human cancer cells and show paclitaxel solubility

Exosomes are cell-secreted vesicles less than ≈150 nm in size that contain gene-encoding and gene-silencing RNA and cytosolic proteins with roles in intercellular communication. Interest in the use of exosomes as targeted drug delivery vehicles has grown since it was shown that they can bind specific cells and deliver intact genetic material to the cytosol of target cells. We isolated extracellular vesicles (EVs), consisting of a mixture of exosomes and microvesicles, from prostate (PC3) and melanoma (M21) cancer cell lines using serial ultracentrifugation. Interrogation via western blot analysis confirmed enrichment of CD63, a widely recognized EV surface protein, in the EV pellet from both cell lines. Nanoparticle tracking analysis (NTA) of EV pellets revealed that the two cell lines produced distinct vesicle size profiles in the ≈30 nm to ≈400 nm range. NTA further showed that the fraction of exosomes to all EVs was constant, suggesting cellular mechanisms that control the fraction of secreted vesicles that are exosomes. Transmission electron microscopy (TEM) images of the unmodified PC3 EVs showed vesicles with cup-like (i.e., nanocapsule) and previously unreported prolate morphologies. The observed non-spherical morphologies for dehydrated exosomal vesicles (size ≈30-100 nm) are most likely related to the dense packing of proteins in exosome membranes. Solubility phase diagram data showed that EVs enhanced the solubility of paclitaxel (PTX) in aqueous solution compared to a water-only control. Combined with their inherent targeting and cytosol delivery properties, these findings highlight the potential advantages of using exosomes as chemotherapeutic drug carriers in vivo.

A pretreatment-free electrical capacitance biosensor for exosome detection in undiluted serum

The exosome is considered a useful biomarker for the early diagnosis of cancer. However, pretreatment of samples used in diagnosis is time-consuming. Herein, we fabricated a capacitance-based electrical biosensor that requires no pretreatment of the sample; it is composed of a DNA aptamer/molybdenum disulfide (MoS₂) heterolayer on an interdigitated micro-gap electrode (IDMGE)/printed circuit board (PCB) system for detecting exosomes in an undiluted serum sample. The DNA aptamer detects the CD63 protein on the exosome as the biomarker, while the MoS₂ nanoparticle enhances electrical sensitivity. In this study, for the first time, the IDMGE system was used to amplify the electrical signal efficiently for exosome detection. The IDMGE amplifies the capacitance signal as the gap between electrodes decreases, making it easy to detect the target by utilizing the heightened sensitivity. Moreover, it is possible to immobilize a bio-probe more efficiently than with an electrical sensitivity-enhancing electrode with the same area. The thiol-modified (SH-) CD63 DNA aptamer was introduced as the bio-probe that selectively binds to the CD63 protein on the exosome surface. The capacitance signal from the IDMGE electrical sensor increased linearly with the increase in the concentration of exosomes in human serum expressed on a logarithmic scale, the detection limit being 2192.6 exosomes/mL. The proposed biosensor can detect exosomes in undiluted human serum with high selectivity and sensitivity. A blind test was also carried out to test the reliability of the biosensor. The capacitance-based electrical biosensor thus offers a new platform for cancer diagnosis in the future.

CD63 is Regulated by Iron via the IRE-IRP System and is Important for Ferritin Secretion by Extracellular Vesicles

CD63 is involved in EV secretion from cells and is shown herein to be regulated by iron via the IRE-IRP system.

Iron-loading increased secretion of CD63⁺ EVs containing iron-loaded ferritin.

Extracellular vesicles (EVs) transfer functional molecules between cells. CD63 is a widely recognized EV marker that contributes to EV secretion from cells. However, the regulation of its expression remains largely unknown. Ferritin is a cellular iron storage protein that can also be secreted by the exosome pathway, and serum ferritin levels classically reflect body iron stores. Iron metabolism–associated proteins such as ferritin are intricately regulated by cellular iron levels via the iron responsive element-iron regulatory protein (IRE-IRP) system. Herein, we present a novel mechanism demonstrating that the expression of the EV-associated protein CD63 is under the regulation of the IRE-IRP system. We discovered a canonical IRE in the 5′ untranslated region of CD63 messenger RNA that is responsible for regulating its expression in response to increased iron. Cellular iron loading caused a marked increase in CD63 expression and the secretion of CD63⁺ EVs from cells, which were shown to contain ferritin-H and ferritin-L. Our results demonstrate that under iron loading, intracellular ferritin is transferred via nuclear receptor coactivator 4 (NCOA4) to CD63⁺ EVs that are then secreted. Such iron-regulated secretion of the major iron storage protein ferritin via CD63⁺ EVs, is significant for understanding the local cell-to-cell exchange of ferritin and iron.

Overexpression of ribophorin II is required for viability of nasopharyngeal cancer cells by regulating JAK1/STAT3 activation

OBJECTIVE

This study aimed to elucidate the role of ribophorin II (RPN2) in nasopharyngeal cancer (NPC) cell survival and death. RPN2 expression was upregulated in 22 human NPC specimens and 5-8F and CNE1 cells compared with that in adjacent normal tissues and normal nasopharyngeal NP69 cells.

MATERIALS AND METHODS

CCK-8 and colony formation assays indicated that the silencing of RPN2 hindered the proliferation and growth of 5-8F and CNE1 cells.

RESULTS

RPN2 expression was upregulated in 22 human NPC specimens as well as in 5-8F and CNE1 cells compared with that in adjacent normal tissues and NP69 cells. CCK-8 and colony formation assays indicated that the silencing of RPN2 reduced the proliferation and growth of 5-8F and CNE1 cells. Annexin V/PI flow cytometry and Bcl-2/Bax analysis showed that RPN2 silencing led to increased apoptosis. Moreover, JAK1 was found to interact with RPN2, and total JAK1, STAT3, and phosphorylated STAT3 levels were dramatically decreased in cells with RPN2 silencing. Furthermore, the nuclear localization of STAT3 was blocked by the silencing of RPN2. The administration of the STAT3 activator colivelin could offset the inhibitory effect of RPN2 silencing on the survival and apoptosis of NPC cells.

CONCLUSION

RPN2 is upregulated in NPC tissues or cells, and RPN2 silencing repressed NPC cell proliferation and elicited apoptosis. RPN2 overexpression is possibly associated with JAK1/STAT3 silencing and activation. Finally, RPN2 represents a promising target for NPC treatment.

Experimental artefacts can lead to misattribution of bioactivity from soluble mesenchymal stem cell paracrine factors to extracellular vesicles

It has been demonstrated that some commonly used Extracellular Vesicle (EV) isolation techniques can lead to substantial contamination with non-EV factors. Whilst it has been established that this impacts the identification of biomarkers, the impact on apparent EV bioactivity has not been explored. Extracellular vesicles have been implicated as critical mediators of therapeutic human mesenchymal stem cell (hMSC) paracrine signalling. Isolated hMSC-EVs have been used to treat multiple in vitro and in vivo models of tissue damage. However, the relative contributions of EVs and non-EV factors have not been directly compared. The dependence of hMSC paracrine signalling on EVs was first established by ultrafiltration of hMSC-conditioned medium to deplete EVs, which led to a loss of signalling activity. Here, we show that this method also causes depletion of non-EV factors, and that when this is prevented proangiogenic signalling activity is fully restored in vitro. Subsequently, we used size-exclusion chromatography (SEC) to separate EVs and soluble proteins to directly and quantitatively compare their relative contributions to signalling. Non-EV factors were found to be necessary and sufficient for the stimulation of angiogenesis and wound healing in vitro. EVs in isolation were found to be capable of potentiating signalling only when isolated by a low-purity method, or when used at comparatively high concentrations. These results indicate a potential for contaminating soluble factors to artefactually increase the apparent bioactivity of EV isolates and could have implications for future studies on the biological roles of EVs.

Supported Membrane Platform to Assess Surface Interactions between Extracellular Vesicles and Stromal Cells

Extracellular vesicles (EVs) are membrane-encapsulated particles secreted by eukaryotic cells that stimulate cell communication and horizontal cargo exchange. EV interactions with stromal cells can result in molecular changes in the recipient cell and, in some cases, lead to disease progression. However, mechanisms leading to these changes are poorly understood. A few model systems are available for studying the outcomes of surface interactions between EV membranes with stromal cells. Here, we created a hybrid supported bilayer incorporating EVs membrane material, called an extracellular vesicle supported bilayer, EVSB. Using EVSBs, we investigated the surface interactions between breast cancer EVs and adipose-derived stem cells (ADSCs) by culturing ADSCs on EVSBs and analyzing cell adhesion, spreading, viability, vascular endothelial growth factor (VEGF) secretion, and myofibroblast differentiation. Results show that cell viability, adhesion, spreading, and proangiogenic activity were enhanced, conditions that promote oncogenic activity, but cell differentiation was not. This model system could be used to develop therapeutic strategies to limit EV-ADSC interactions and proangiogenic conditions. Finally, this model system is not limited to the study of cancer but can be used to study surface interactions between EVs from any origin and any target cell to investigate EV mechanisms leading to cellular changes in other diseases.

Overexpression of RPN2 promotes osteogenic differentiation of hBMSCs through the JAK/STAT3 pathway

Osteoporosis is characterized by decreased bone mass and degenerating bone structure, which cause severe bone fragility and increase the risk for fractures. Human bone mesenchymal stem cells (hBMSCs) differentiate into osteoblasts through osteogenesis, and disturbances in the balance between bone generation and degeneration underlie the pathogenesis of senile osteoporosis. The highly conserved glycoprotein Ribophorin II (RPN2) is involved in multiple biological reactions, but the role of RPN2 in the osteogenic differentiation of hBMSCs and their molecular etiology is incompletely understood. Here, we show that RPN2 expression is up‐regulated in hBMSCs during osteogenic differentiation. In vitro assays revealed that silencing of RPN2 inhibited hBMSC differentiation into osteoblasts. Moreover, RPN2 overexpression enhanced the expression of linked genes and resulted in high alkaline phosphatase activity. Our results suggest that RPN2 targets Janus kinase 1 (JAK1), and RPN2 overexpression was observed to induce JAK1 ubiquitination. Depletion of JAK1 facilitated osteogenic differentiation of RPN2‐silenced hBMSCs. Moreover, western blot analysis revealed that RPN2 silencing suppressed the stimulation and nuclear translocation of the downstream signal transducer and activator of transcription 3 sensor; this could be reversed via RPN2 overexpression. This research sheds light on an innovative molecular mechanism that is associated with hBMSC differentiation into osteoblasts and may facilitate bone anabolism through RPN2.

RPN2 promotes metastasis of hepatocellular carcinoma cell and inhibits autophagy via STAT3 and NF-κB pathways

This study aimed to investigate the function and the molecular mechanism of Ribophorin II (RPN2) in regulating Hepatocellular carcinoma (HCC) cell growth, metastasis, and autophagy. Quantitative real-time PCR (qPCR), western blotting analysis, and immunofluorescence assay were utilized to detect the RPN2 expression in HCC cell lines and specimens of HCC patients. We discovered that RPN2 expression was upregulated in HCC cell lines and tissues of HCC patients, which correlated with the low histological grade and low survival rate. Enhanced RPN2 expression stimulated cell proliferation, metastasis, invasion, and epithelial-mesenchymal transition (EMT), and decreased Microtubule-associated protein light chain 3B (LC3B) synthesis and reduced the expression of p62 protein. Further studies suggested that matrix metalloproteinase 9 (MMP-9) was partially upregulated by RPN2 via Nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) p65. Interestingly, we found that phosphorylated RPN2 activated the signal transducer and activator of transcription 3 (STAT3) in HCC cells. It was also accountable for RPN2-stimulated elevated expression of MMP-9 and for invading HCC cells. It can be concluded that over-expression of RPN2 in HCC aggravated the malignant progression into cancerous cells. This research provided new evidences that RPN2 could facilitate tumor invasion by increasing the expression of MMP-9 in HCC cells.

Polycyclic aromatic hydrocarbons can trigger hepatocyte release of extracellular vesicles by various mechanisms of action depending on their affinity for the aryl hydrocarbon receptor

Extracellular vesicles (EVs) are membrane enclosed nanostructures released by cells into the extracellular environment. As major actors of physiological intercellular communication, they have been shown to be pathogenic mediators of several liver diseases. EVs also appear to be potential actors of drug-induced liver injury, but nothing is known concerning environmental pollutants. We aimed to study the impact of polycyclic aromatic hydrocarbons (PAHs), major contaminants, on hepatocyte-derived EV production, with a special focus on hepatocyte death. Three PAHs were selected, based on their presence in food and their affinity for the aryl hydrocarbon receptor (AhR): benzo(a)pyrene (BP), dibenzo(a,h)anthracene (DBA), and pyrene (PYR). Treatment of primary rat and WIF-B9 hepatocytes by all three PAHs increased the release of EVs, mainly comprised of exosomes, in parallel with modifying exosome protein marker expression and inducing apoptosis. Moreover, PAH treatment of rodents for three months also led to increased EV levels in plasma. The EV release involved CYP metabolism and the activation of the transcription factor, the AhR, for BP and DBA and another transcription factor, the constitutive androstane receptor (CAR), for PYR. Furthermore, all PAHs increased cholesterol levels in EVs but only BP and DBA were able to reduce the cholesterol content of total cell membranes. All cholesterol changes very likely participated in the increase in EV release and cell death. Finally, we studied changes in cell membrane fluidity caused by BP and DBA due to cholesterol depletion. Our data showed increased cell membrane fluidity, which contributed to hepatocyte EV release and cell death.

Cell surface CD63 increased by up-regulated polylactosamine modification sensitizes human melanoma cells to the BRAF inhibitor PLX4032

The BRAF inhibitor PLX4032 is effective in treating BRAF-mutated melanoma; however, because drug resistance develops in most cases, it is critical to develop a new strategy for inhibiting drug-resistant melanoma growth. The melanoma-associated membrane glycoprotein CD63 is involved in cell proliferation and metastasis. Here, we found that cell surface CD63 suppresses the proliferation of human melanoma cells and PLX4032-resistant cells. Endogenous CD63 protein levels were negatively correlated with PLX4032 resistance of human melanoma cell lines. CD63 overexpression in these cells, in which endogenous CD63 levels are low, suppressed cell proliferation under PLX4032 treatment. The cell surface levels and average molecular mass of CD63 were increased with PLX4032 treatment because of the up-regulated polylactosamine modification caused by induced β1,3- N-acetylglucosaminyltransferase 2 expression, which is involved in polylactosamine synthesis. Forced cell surface localization of CD63 led to reduced melanoma cell proliferation without PLX4032 treatment. CD63 overexpression in PLX4032-resistant cells, in which CD63 levels were lower and cell surface polylactosamine levels were higher than those in parental cells, effectively suppressed proliferation. Our study shows the potential of CD63 to sensitize melanoma cells to PLX4032 and to reduce the proliferation of PLX4032-resistant cells.-Kudo, K., Yoneda, A., Sakiyama, D., Kojima, K., Miyaji, T., Yamazaki, M., Yaita, S., Hyodo, T., Satow, R., Fukami, K. Cell surface CD63 increased by up-regulated polylactosamine modification sensitizes human melanoma cells to the BRAF inhibitor PLX4032.

RPN2 promotes colorectal cancer cell proliferation through modulating the glycosylation status of EGFR

Various studies have found that silencing ribophorin II (RPN2) inhibits cell growth in several cancers. However, the underlying mechanism by which RPN2 regulates cancer cell proliferation remains unclear. Herein, we reveal that downregulation of RPN2, which may be a crucial regulator of N-linked glycosylation in cancer cells and drug-resistant cancer cells, promoted the progression of colorectal cancer (CRC) cell cycle and proliferation in vitro and in vivo. We found that RPN2 silencing reduced glycosylation of EGFR, a highly N-link glycosylated cell surface glycoprotein that plays a critical role in majority of human cancers correlating with increased cell growth, proliferation, and differentiation. In addition, RPN2 knockdown decreased EGFR expression and cell surface transport by EGFR deglycosylation. In summary, our findings suggest that RPN2 regulates CRC cell proliferation through mediating the glycosylation of EGFR which affecting the EGFR/ERK signaling pathways. Clinicopathological analysis showed that the overexpression of RPN2 and EGFR was positively correlated with colorectal tumor size. Therefore, RPN2 may be a new therapeutic target and prognostic biomarker for CRC.

Extracellular Vesicle Isolation and Analysis by Western Blotting

Extracellular vesicles (EVs) are released by mammalian cells and are thought to be important mediators of intercellular communication. There are many methods for isolating EVs from cell culture media, but the most popular methods involve purification based on ultracentrifugation . Here, we provide a detailed protocol for isolating EVs by differential ultracentrifugation and analyzing EV proteins (such as the tetraspanins CD9 , CD63 and CD81 ) by western blotting.

The C Isoform of Dictyostelium Tetraspanins Localizes to the Contractile Vacuole and Contributes to Resistance against Osmotic Stress

Tetraspanins (Tsps) are membrane proteins that are widely expressed in eukaryotic organisms. Only recently, Tsps have started to acquire relevance as potential new drug targets as they contribute, via protein-protein interactions, to numerous pathophysiological processes including infectious diseases and cancer. However, due to a high number of isoforms and functional redundancy, knowledge on specific functions of most Tsps is still scarce. We set out to characterize five previously annotated Tsps, TspA-E, from Dictyostelium discoideum, a model for studying proteins that have human orthologues. Using reverse transcriptase PCRs, we found mRNAs for TspA-E in the multicellular slug stage, whereas vegetative cells expressed only TspA, TspC and, to a lesser extent, TspD. We raised antibodies against TspA, TspC and TspD and detected endogenous TspA, as well as heterologously expressed TspA and TspC by Western blot. N-deglycosylation assays and mutational analyses showed glycosylation of TspA and TspC in vivo. GFP-tagged Tsps co-localized with the proton pump on the contractile vacuole network. Deletion strains of TspC and TspD exibited unaltered growth, adhesion, random motility and development. Yet, tspC⁻ cells showed a defect in coping with hypo-osmotic stress, due to accumulation of contractile vacuoles, but heterologous expression of TspC rescued their phenotype. In conclusion, our data fill a gap in Dictyostelium research and open up the possibility that Tsps in contractile vacuoles of e.g. Trypanosoma may one day constitute a valuable drug target for treating sleeping sickness, one of the most threatening tropical diseases.

RPN2-mediated glycosylation of tetraspanin CD63 regulates breast cancer cell malignancy

Background

The tetraspanin CD63 is a highly N-glycosylated protein that is known to regulate cancer malignancy. However, the contribution of glycosylation of CD63 to cancer malignancy remains unclear. Previously, we reported that ribophorin II (RPN2), which is part of an N-oligosaccharyle transferase complex, is responsible for drug resistance in breast cancer cells. In this study, we demonstrate that cancer malignancy associated with the glycosylation of CD63 is regulated by RPN2.

Results

Inhibition of RPN2 expression led to a reduction in CD63 glycosylation. In addition, the localization of CD63 was deregulated by knockdown of RPN2. Interestingly, multidrug resistance protein 1 (MDR1) localization was displaced from the cell surface in CD63-silenced cells. CD63 silencing reduced the chemoresistance and invasion ability of malignant breast cancer cells. Furthermore, the enrichment of CD63/MDR1-double positive cells was associated with lymph node metastasis. Taken together, these results indicated that high glycosylation of CD63 by RPN2 is implicated in clinical outcomes in breast cancer patients.

Conclusions

These findings describe a novel and important function of RPN2-mediated CD63 glycosylation, which regulates MDR1 localization and cancer malignancy, including drug resistance and invasion.

Biochemical and physical characterisation of urinary nanovesicles following CHAPS treatment

Urinary exosomes represent a precious source of potential biomarkers for disease biology. Currently, the methods for vesicle isolation are severely restricted by the tendency of vesicle entrapment, e.g. by the abundant Tamm-Horsfall protein (THP) polymers. Treatment by reducing agents such as dithiothreitol (DTT) releases entrapped vesicles, thus increasing the final yield. However, this harsh treatment can cause remodelling of all those proteins which feature extra-vesicular domains stabilized by internal disulfide bridges and have detrimental effects on their biological activity. In order to optimize exosomal yield, we explore two vesicle treatment protocols - dithiothreitol (DTT) and 3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonic (CHAPS) - applied to the differential centrifugation protocol for exosomal vesicle isolation. The results show that CHAPS treatment does not affect vesicle morphology or exosomal marker distribution, thus eliminating most of THP interference. Moreover, the recovery and preservation of catalytic activity of two trans-membrane proteases, dipeptidyl peptidase IV and nephrilysin, was examined and found to be clearly superior after CHAPS treatment compared to DTT. Finally, proteomic profiling by mass spectrometry (MS) revealed that 76.2% of proteins recovered by CHAPS are common to those seen for DTT treatment, which illustrates underlining similarities between the two approaches. In conclusion, we provide a major improvement to currently-utilized urinary vesicle isolation strategies to allow recovery of urinary vesicles without the deleterious interference of abundant urinary proteins, while preserving typical protein folding and, consequently, the precious biological activity of urinary proteins which serve as valuable biomarkers.

Regulation of zebrafish hatching by tetraspanin cd63

Tetraspanins cause the clustering of membrane proteins into a level of organisation essential for cellular function. Given the importance and complicated nature of this mechanism, we attempted a novel approach to identify the function of a single component in a biologically relevant context. A morpholino knockdown strategy was used to investigate the role of cd63, a membrane protein associated with intracellular transport and a melanoma marker, in embryonic zebrafish. By using three separate morpholinos targeting cd63, we were able to identify a specific phenotype. Strikingly, morphant fish failed to hatch due to the lack of secreted proteolytic enzymes required for chorion-softening. The morphology of the hatching gland at both the cellular and intracellular levels was disorganised, suggesting a role for cd63 in the functioning of this organ. This work identifies a specific role for cd63 in the zebrafish embryo and provides evidence for the suitability of zebrafish as a model system for the investigation of tetraspanin enriched microdomains.

Inefficient targeting to the endoplasmic reticulum by the signal recognition particle elicits selective defects in post-ER membrane trafficking

The signal recognition particle (SRP) is required for protein translocation into the endoplasmic reticulum (ER). With RNA interference we reduced its level about ten-fold in mammalian cells to study its cellular functions. Such low levels proved insufficient for efficient ER-targeting, since the accumulation of several proteins in the secretory pathway was specifically diminished. Although the cells looked unaffected, they displayed noticeable and selective defects in post-ER membrane trafficking. Specifically, the anterograde transport of VSV-G and the retrograde transport of the Shiga toxin B-subunit were stalled at the level of the Golgi whereas the endocytosed transferrin receptor failed to recycle to the plasma membrane. Endocytic membrane trafficking from the plasma membrane to lysosomes or Golgi was undisturbed and major morphological changes in the ER and the Golgi were undetectable at low resolution. Selective membrane trafficking defects were specifically suppressed under conditions when low levels of SRP became sufficient for efficient ER-targeting and are therefore a direct consequence of the lower targeting capacity of cells with reduced SRP levels. Selective post-ER membrane trafficking defects occur at SRP levels sufficient for survival suggesting that changes in SRP levels and their effects on post-ER membrane trafficking might serve as a mechanism to alter temporarily the localization of selected proteins.