A Coxsackievirus B1-mediated nonlytic Extracellular Vesicle-to-cell mechanism of virus transmission and its possible control through modulation of EV release.

Like most non-enveloped viruses, CVB1 mainly uses cell lysis to spread. Details of a nonlytic virus transmission remain unclear. Extracellular Vesicles (EVs) transfer biomolecules between cells. We show that CVB1 entry into HeLa cells results in apoptosis and release of CVB1-induced 'medium-sized' EVs (CVB1i-mEVs). These mEVs (100-300 nm) harbour CVB1 as shown by immunoblotting with anti-CVB1-antibody; viral capsids were detected by transmission electron microscopy and RT-PCR revealed CVB1 RNA. The percentage of mEVs released from CVB1-infected HeLa cells harbouring virus was estimated from TEM at 34 %. Inhibition of CVB1i-mEV production, with calpeptin or siRNA knockdown of CAPNS1 in HeLa cells limited spread of CVB1 suggesting these vesicles disseminate CVB1 virions to new host cells by a nonlytic EV-to-cell mechanism. This was confirmed by detecting CVB1 virions inside HeLa cells after co-culture with CVB1i-mEVs; EV release may also prevent apoptosis of infected cells whilst spreading apoptosis to secondary sites of infection.

Label-free real-time acoustic sensing of microvesicle release from prostate cancer (PC3) cells using a Quartz Crystal Microbalance.

Using a Quartz Crystal Microbalance with dissipation monitoring, QCM-D (label-free system) measuring changes in resonant frequency (Δf) that equate to mass deposited on a sensor, we showed the attachment, over a 60min period, of a monolayer of PC3 cells to the gold electrodes of the quartz crystal sensor, which had been rendered hydrophilic. That MVs were released upon BzATP stimulation of cells was confirmed by NTA analysis (average 250nm diameter), flow cytometry, showing high phosphatidylserine exposition and by fluorescent (Annexin V Alexa Fluor® 488-positive) and electron microscopy. Over a period of 1000s (16.7min) during which early apoptosis increased from 4% plateauing at 10% and late apoptosis rose to 2%, the Δf increased 20Hz, thereupon remaining constant for the last 1000s of the experiment. Using the Sauerbrey equation, the loss in mass, which corresponded to the release of 2.36×10(6)MVs, was calculated to be 23ng. We therefore estimated the mass of an MV to be 0.24pg. With the deposition on the QCM-D of 3.5×10(7)MVs over 200s, the decrease in Δf (Hz) gave an estimate of 0.235pg per MV.

The role of microvesicles in cancer progression and drug resistance.

Microvesicles are shed constitutively, or upon activation, from both normal and malignant cells. The process is dependent on an increase in cytosolic Ca2+, which activates different enzymes, resulting in depolymerization of the actin cytoskeleton and release of the vesicles. Drug resistance can be defined as the ability of cancer cells to survive exposure to a wide range of anti-cancer drugs, and anti-tumour chemotherapeutic treatments are often impaired by innate or acquired MDR (multidrug resistance). Microvesicles released upon chemotherapeutic agents prevent the drugs from reaching their targets and also mediate intercellular transport of MDR proteins.

Coxsackievirus B transmission and possible new roles for extracellular vesicles.

Coxsackievirus B1, a member of the Picornaviridae family is a non-enveloped single-stranded RNA virus associated with human diseases including myocarditis and pancreatitis. Infection of the intestinal mucosa, lined by polarized epithelial cells, requires interaction of coxsackievirus with apically located DAF (decay-accelerating factor) before transport to the basolaterally located CAR (coxsackie and adenovirus receptor), where entry is mediated by endocytosis. As with many other non-enveloped viruses, coxsackievirus has to induce lysis of host cells in order to perpetuate infection. However, recent evidence indicates that virus spread to secondary sites is not only achieved by a lytic mechanism and a non-lytic cell-cell strategy has been suggested for coxsackievirus B3. A physical interaction between infected and non-infected cells has been shown to be an efficient mechanism for retroviral transmission and one type of extracellular vesicle, the exosome, has been implicated in HIV-1 transmission. HIV-1 also takes advantage of depolymerization of actin for spread between T-cells. Calpain-mediated depolymerization of the actin cytoskeleton, as a result of increases in intracellular calcium concentration during coxsackievirus infection, would result in a release of host cell-derived microvesicles. If so, we speculate that maybe such microvesicles, increasingly recognized as major vehicles mediating intercellular communication, could play a role in the intercellular transmission of non-enveloped viruses.

Plasma mEV levels in Ghanain malaria patients with low parasitaemia are higher than those of healthy controls, raising the potential for parasite markers in mEVs as diagnostic targets.

This study sought to measure medium-sized extracellular vesicles (mEVs) in plasma, when patients have low Plasmodium falciparum early in infection. We aimed to define the relationship between plasma mEVs and: (i) parasitaemia, (ii) period from onset of malaria symptoms until seeking medical care (patient delay, PD), (iii) age and (iv) gender. In this cross-sectional study, n = 434 patients were analysed and Nanosight Tracking Analysis (NTA) used to quantify mEVs (vesicles of 150-500 nm diameter, isolated at 15,000 × g, ß-tubulin-positive and staining for annexin V, but weak or negative for CD81). Overall plasma mEV levels (1.69 × 1010 mEVs mL-1) were 2.3-fold higher than for uninfected controls (0.51 × 1010 mEVs mL-1). Divided into four age groups, we found a bimodal distribution with 2.5- and 2.1-fold higher mEVs in infected children (<11 years old [yo]) (median:2.11 × 1010 mEVs mL-1) and the elderly (>45 yo) (median:1.92 × 1010 mEVs mL-1), respectively, compared to uninfected controls; parasite density varied similarly with age groups. There was a positive association between mEVs and parasite density (r = 0.587, p < 0.0001) and mEVs were strongly associated with PD (r = 0.919, p < 0.0001), but gender had no effect on plasma mEV levels (p = 0.667). Parasite density was also exponentially related to patient delay. Gender (p = 0.667) had no effect on plasma mEV levels. During periods of low parasitaemia (PD = 72h), mEVs were 0.93-fold greater than in uninfected controls. As 75% (49/65) of patients had low parasitaemia levels (20-500 parasites µL-1), close to the detection limits of microscopy of Giemsa-stained thick blood films (5-150 parasites µL-1), mEV quantification by NTA could potentially have early diagnostic value, and raises the potential of Pf markers in mEVs as early diagnostic targets.

Inhibition of microvesiculation sensitizes prostate cancer cells to chemotherapy and reduces docetaxel dose required to limit tumor growth in vivo.

Microvesicles shed from cells carry constituents of the cell cytoplasm, including, of importance in multidrug resistance to cancer chemotherapy, drugs that the tumor cell attempts to efflux. To see whether such drugs could be used at lower concentrations with the same efficacy, it was first shown that microvesiculation of prostate cancer (PCa) cells, PC3, could be inhibited pharmacologically with calpeptin (calpain inhibitor) and by siRNA (CAPNS1). In cells treated with docetaxel (DTX), this inhibition resulted in a third-fold increase in intracellular concentrations of DTX. As a result, 20-fold lower concentrations of DTX (5 nM) could be used, in the presence of calpeptin (20 µM) inducing the same degree of apoptosis after 48 h in PC3 cells, as 100 nM of DTX alone. Inhibition of microvesiculation similarly improved combination chemotherapy (DTX and methotrexate). In a mouse xenograft model of PCa, DTX (0.1 mg/kg) together with calpeptin (10 mg/kg), administered i.p., significantly reduced tumor volumes compared to DTX alone (0.1 mg/kg) and brought about the same reductions in tumor growth as 10 mg/kg of DTX alone. As well as further reducing vascularization, it also increased apoptosis and reduced proliferation of PC3 cells in tumor xenografts.

A novel role for peptidylarginine deiminases in microvesicle release reveals therapeutic potential of PAD inhibition in sensitizing prostate cancer cells to chemotherapy.

INTRODUCTION: Protein deimination, defined as the post-translational conversion of protein-bound arginine to citrulline, is carried out by a family of 5 calcium-dependent enzymes, the peptidylarginine deiminases (PADs) and has been linked to various cancers. Cellular microvesicle (MV) release, which is involved in cancer progression, and deimination have not been associated before. We hypothesize that elevated PAD expression, observed in cancers, causes increased MV release in cancer cells and contributes to cancer progression. BACKGROUND: We have previously reported that inhibition of MV release sensitizes cancer cells to chemotherapeutic drugs. PAD2 and PAD4, the isozymes expressed in patients with malignant tumours, can be inhibited with the pan-PAD-inhibitor chloramidine (Cl-am). We sought to investigate whether Cl-am can inhibit MV release and whether this pathway could be utilized to further increase the sensitivity of cancer cells to drug-directed treatment. METHODS: Prostate cancer cells (PC3) were induced to release high levels of MVs upon BzATP stimulation of P2X7 receptors. Western blotting with the pan-protein deimination antibody F95 was used to detect a range of deiminated proteins in cells stimulated to microvesiculate. Changes in deiminated proteins during microvesiculation were revealed by immunoprecipitation and immunoblotting, and mass spectrometry identified deiminated target proteins with putative roles in microvesiculation. CONCLUSION: We report for the first time a novel function of PADs in the biogenesis of MVs in cancer cells. Our results reveal that during the stimulation of prostate cancer cells (PC3) to microvesiculate, PAD2 and PAD4 expression levels and the deimination of cytoskeletal actin are increased. Pharmacological inhibition of PAD enzyme activity using Cl-am significantly reduced MV release and abrogated the deimination of cytoskeletal actin. We demonstrated that combined Cl-am and methotrexate (MTX) treatment of prostate cancer cells increased the cytotoxic effect of MTX synergistically. Refined PAD inhibitors may form part of a novel combination therapy in cancer treatment.

Microvesicles in health and disease.

Microvesicles (or MVs) are plasma membrane-derived vesicles released from most eukaryotic cells constitutively during early apoptosis or at higher levels after chemical or physical stress conditions. This review looks at some of the functions of MVs in terms of intercellular communication and ensuant signal transduction, including the transport of proteins (unconventional protein export) as well as of mRNA and microRNA. MVs also have roles in membrane repair, the removal of misfolded proteins, and in the control of apoptosis. We also discuss the role MVs have been shown to have in invasive growth and metastasis as well as in hypoxia in tumours and cerebral ischaemia. The association of MVs in infectious and autoimmune disease is also summarised together with their possible use as therapeutic agents.

A filtration-based protocol to isolate human plasma membrane-derived vesicles and exosomes from blood plasma.

The methods of Plasma Membrane-derived Vesicle (PMV) isolation and quantification vary considerably in the literature and a new standard needs to be defined. This study describes a novel filtration method to isolate PMVs in plasma, which avoids high speed centrifugation, and to quantify them using a Becton Dickinson (BD) FACS Calibur™ flow cytometer, as annexin V-positive vesicles, larger than 0.2 µm in diameter. Essentially microvesicles (which comprise a mixture of PMVs and exosomes) from citrate plasma were sonicated to break up clumped exosomes, and filtered using Millipore 0.1 µm pore size Hydrophilic Durapore membranes in Swinnex 13 mm filter holders. Phosphatidylserine-positive PMVs detected with annexin V-PE were quantified using combined labelling and gating strategies in conjunction with Polysciences Polybead Microspheres (0.2 µm) and BDTrucount tubes. The PMV absolute count was calculated on the analysis template using the Trucount tube lot number information and expressed in PMV count/ml. Having estimated a normal reference range (0.51×10(5)-2.82×10(5) PMVs/ml) from a small sample of human donors, using the developed method, the effect of certain variables was investigated. Variations such as freezing of samples and gender status did not significantly alter the PMV absolute count, and with age plasma PMV levels were only marginally reduced. Smokers appeared to have reduced PMV levels. Nicotine, as for calpeptin was shown to dose-dependently (from 10 up to 50 µM) reduce levels of early apoptosis in THP-1 monocytes and to decrease the level of PMV release. Fasting individuals had 2-3 fold higher PMV absolute counts compared to non-fasting subjects.