Matrix-degrading proteinases are shed in membrane vesicles by ovarian cancer cells in vivo and in vitro

Techniques to improve detection and analysis of extracellular vesicles using flow cytometry

Extracellular vesicles (EVs) range in size from 50 nm to 1 µm. Flow cytometry (FCM) is the most commonly used method for analyzing EVs; however, accurate characterization of EVs remains challenging due to their small size and lack of discrete positive populations. Here we report the use of optimization techniques that are especially well-suited for analyzing EVs from a high volume of clinical samples. Utilizing a two pronged approach that included 1) pre-filtration of antibodies to remove aggregates, followed by 2) detergent lysis of a replicate sample to account for remaining false positive events, we were able to effectively limit false positive non-EV events. In addition, we show that lysed samples are a useful alternative to isotypes for setting gates to exclude background fluorescence. To reduce background, we developed an approach using filters to "wash" samples post-staining thus providing a faster alternative to ultracentrifugation and sucrose gradient fractionation. In conclusion, use of these optimized techniques enhances the accuracy and efficiency of EV detection using FCM.

Proteome characterization of melanoma exosomes reveals a specific signature for metastatic cell lines

Exosomes are important mediators in cell-to-cell communication and, recently, their role in melanoma progression has been brought to light. Here, we characterized exosomes secreted by seven melanoma cell lines with varying degrees of aggressivity. Extensive proteomic analysis of their exosomes confirmed the presence of characteristic exosomal markers as well as melanoma-specific antigens and oncogenic proteins. Importantly, the protein composition differed among exosomes from different lines. Exosomes from aggressive cells contained specific proteins involved in cell motility, angiogenesis, and immune response, while these proteins were less abundant or absent in exosomes from less aggressive cells. Interestingly, when exposed to exosomes from metastatic lines, less aggressive cells increased their migratory capacities, likely due to transfer of pro-migratory exosomal proteins to recipient cells. Hence, this study shows that the specific protein composition of melanoma exosomes depends on the cells' aggressivity and suggests that exosomes influence the behavior of other tumor cells and their microenvironment.

Exosome platform for diagnosis and monitoring of traumatic brain injury

We have previously demonstrated the release of membranous structures by cells into their extracellular environment, which are termed exosomes, microvesicles or extracellular vesicles depending on specific characteristics, including size, composition and biogenesis pathway. With activation, injury, stress, transformation or infection, cells express proteins and RNAs associated with the cellular responses to these events. The exosomes released by these cells can exhibit an array of proteins, lipids and nucleic acids linked to these physiologic events. This review focuses on exosomes associated with traumatic brain injury, which may be both diagnostic and a causative factor in the progression of the injury. Based on current data, exosomes play essential roles as conveyers of intercellular communication and mediators of many of the pathological conditions associated with development, progression and therapeutic failures and cellular stress in a variety of pathologic conditions. These extracellular vesicles express components responsible for angiogenesis promotion, stromal remodelling, signal pathway activation through growth factor/receptor transfer, chemoresistance, immunologic activation and genetic exchange. These circulating exosomes not only represent a central mediator of the pro-inflammatory microenvironment linked with secondary brain injury, but their presence in the peripheral circulation may serve as a surrogate for biopsies, enabling real-time diagnosis and monitoring of neurodegenerative progression.

Hyaluronan-coated extracellular vesicles--a novel link between hyaluronan and cancer

The synthesis of hyaluronan (HA) on the plasma membrane is a unique and still partly mysterious way of macromolecular biosynthesis. HA forms pericellular coats around many cell types and accumulates in the extracellular matrix (ECM) of growing and renewing tissues. It is secreted to high concentrations in body fluids with antifriction properties like pleural, peritoneal, and synovial fluids, but is also detectable in plasma, saliva, and urine. In pathological states, like cancer and inflammation, the amount of HA is increased around cells, in the ECM, and in the body fluids. HA is an indicator of poor prognosis for cancer patients and creates a favorable environment for cellular growth and motility. The recent finding that HA-coated extracellular vesicles act both as a product of HA synthase activity and as special vehicles for HA, and perhaps carry signals important for malignant growth, provides a novel link between HA and cancer. HA could be carried on the surface of these vesicles in tissues and body fluids, creating beneficial environments by itself, or by associated molecules, for the invasion and metastasis of cancer cells. The HA-coated plasma membrane protrusions and vesicles shed from them are potential biomarkers in cancer and other HA-associated disease states.

Microparticles in cancer: A review of recent developments and the potential for clinical application

Once thought of as inert remnants of cellular processes, the significance of membrane vesicles is now expanding as their capacity to package and transfer bioactive molecules during intercellular communication is established. This ability to serve as vectors in the trafficking of cellular cargo is of mounting interest in the context of cancer, particularly in the dissemination of deleterious cancer traits from donor cells to recipient cells. Although microparticles (MPs) contribute to the pathogenesis of cancer, their unique characteristics can also be exploited in the context of cancer management. The detection of MPs in body fluids has the potential to provide an effective means for the diagnosis, prognosis and surveillance of cancer patients. The use of these readily accessible systemic biomarkers has the potential to circumvent the need for invasive biopsy procedures. In addition, the autologous nature of MPs may allow them to be used as novel drug delivery carriers. Consequently, the modulation of MP vesiculation to treat disease, the detection of MPs in disease monitoring, and the application of MPs as therapeutic delivery vehicles present prospective clinical interventions in the treatment of cancer.

Moving targets: Emerging roles for MMPs in cancer progression and metastasis

Matrix metalloproteinases have long been associated with cancer. Clinical trials of small molecule inhibitors for this family of enzymes however, were spectacularly unsuccessful in a variety of tumor types. Here, we discuss some of the newer roles that have been uncovered for MMPs in cancer that would not have been targeted with those initial inhibitors or in the patient populations analyzed. We also consider novel ways of using cancer-associated MMP activity for clinical benefit.

Cellular communication via microparticles: role in transfer of multidrug resistance in cancer

Multidrug resistance (MDR) continues to be a major impediment to the successful treatment of cancer. The two efflux transporters, P-glycoprotein (P-gp) and MRP1 are major contributors to cancer MDR clinically. The upregulation of P-gp leading to MDR was initially understood to occur via pre- and post-transcriptional mechanisms only. However, we demonstrated that microparticles mediate the intercellular exchange and trafficking of bioactive material, including functional P-gp and selected modulatory miRNAs. This exchange of P-gp leads to the dissemination of MDR within a cancer cell population. These findings have significant implications in understanding the cellular basis governing the intercellular acquisition of deleterious traits in cancers, serving to substantially advance our understanding of the molecular basis of the emergence of MDR in cancer clinically.

Small but mighty: microparticles as mediators of tumor progression

A wide spectrum of both normal and diseased cell types shed extracellular vesicles that facilitate intercellular communication without direct cell-to-cell contact. Microparticles (MPs) are a subtype of extracellular vesicles that participate in multiple biological processes. They carry abundant bioactive molecules including different forms of nucleic acids and proteins that can markedly modulate cellular behavior. MPs are involved in several hallmarks of cancer such as drug resistance, thrombosis, immune evasion, angiogenesis, tumor invasion and metastasis. Such MPs originate from either cancer or other host cells. As MPs are secreted and can be detected in various body fluids, they can be used as potential diagnostic and prognostic biomarkers as well as vehicles for delivery of cytotoxic drugs. This review summarizes accumulating evidence on the biological properties of MPs in cancer, with reference to their potential usage in clinical settings.

Tumor-derived exosomes: A message delivery system for tumor progression

Intercellular communication is a key process in the development and progression of cancer. The dynamic and reciprocal interplays between the tumor and its microenvironment orchestrate events critical to the establishment of primary and metastatic niches and maintenance of a permissive environment at the tumor−stroma interface. Atay and colleagues found that gastrointestinal stromal tumor cells secrete vesicles known as exosomes. These exosomes contain oncogenic KIT and their transfer and uptake by surrounding smooth muscle cells lead to enhanced AKT and MAPK signaling and phenotypic modulation of several cellular processes, including morphological changes, expression of tumor-associated markers, secretion of matrix metalloproteinases, and enhanced tumor cell invasion. This provocative study emphasizes that exosome-mediated signaling within the tumor microenvironment acts as a positive feedback loop that contributes to invasiveness and that interfering with this message delivery system may represent promising therapeutic approaches, not only for GIST, but for other types of cancer.

Neutrophil extracellular traps induce endothelial dysfunction in systemic lupus erythematosus through the activation of matrix metalloproteinase-2

RATIONALE

The structural and functional integrity of the endothelium is crucial in maintaining vascular homeostasis and preventing atherosclerosis. Patients with systemic lupus erythematosus (SLE) have an increased risk of developing endothelial dysfunction and premature cardiovascular disease. Neutrophil extracellular trap (NET) formation is increased in SLE and has been proposed to contribute to endothelial damage, but the mechanism remains unclear.

OBJECTIVE

To determine the mechanism by which enhanced NET formation by low-density granulocytes (LDGs) in SLE contributes to endothelial damage and disrupts the endothelium.

RESULTS

The putative role of NET-externalised matrix metalloproteinases (MMPs) in altering the functional integrity of the endothelium was examined. MMP-9 externalised by lupus LDGs during NET formation specifically impaired murine aortic endothelium-dependent vasorelaxation and induced endothelial cell apoptosis. Endothelial dysfunction correlated with the activation of endothelial MMP-2 by MMP-9 present in NETs, while inhibition of MMP-2 activation restored endothelium-dependent function and decreased NET-induced vascular cytotoxicity. Moreover, immunogenic complexes composed of MMP-9 and anti-MMP-9 were identified in SLE sera. These complexes, as well as anti-MMP-9 autoantibodies, induced NETosis and enhanced MMP-9 activity.

CONCLUSIONS

These observations implicate activation of endothelial MMP-2 by MMP-9 contained in NETs as an important player in endothelial dysfunction, and MMP-9 as a novel self-antigen in SLE. These results further support that aberrant NET formation plays pathogenic roles in SLE.

Exosomes are involved in mediating radiation induced bystander signaling in human keratinocyte cells

There is much evidence supporting the existence of bystander effects in cells that were never exposed to radiation. Directly irradiated cells and bystander cells can communicate with each other using gap junctional intercellular communication or by releasing soluble factors into the surrounding medium. Exosomes and microvesicles are also known to mediate communication between cells. The main aim of this study is to establish whether exosomes and microvesicles are involved in radiation induced bystander signaling. Human keratinocytes, HaCaT cells, were irradiated (0.005, 0.05 and 0.5 Gy) using γ rays produced from a cobalt 60 teletherapy unit. After irradiation, the cells were incubated for 1 h and the irradiated cell conditioned medium (ICCM) was harvested. Exosomes were isolated from the ICCM using ultracentrifugation. Exosomes were characterized using light scattering analysis (LSA) and scanning transmission electron microscopy (STEM). Cytotoxicity and reactive oxygen species assays and real time calcium imaging were performed either with ICCM from which exosomes and microvesicles were removed or with the exosome fraction resuspended in cell culture media. The characterization data showed a particle size distribution indicative of both exosomes (30-100 nm) and microvesicles (>100 nm) and the light scattering analysis showed increased concentration of both exosomes and microvesicles with increasing dose. Western blotting confirmed the presence of an exosomal protein marker, TSG 101. Treatment of unirradiated cells with ICCM in which exosomes and microvesicles were removed resulted in abrogation of ICCM induced effects such as reduction in viability, calcium influx and production of reactive oxygen species. Addition of exosomes to fresh media produced similar effects to complete ICCM. These results suggest a role for exosomes and microvesicles in radiation induced bystander signaling.

Inhibition of the multidrug resistance P-glycoprotein: time for a change of strategy?

P-glycoprotein (P-gp) is a key player in the multidrug-resistant phenotype in cancer. The protein confers resistance by mediating the ATP-dependent efflux of an astonishing array of anticancer drugs. Its broad specificity has been the subject of numerous attempts to inhibit the protein and restore the efficacy of anticancer drugs. The general strategy has been to develop compounds that either compete with anticancer drugs for transport or act as direct inhibitors of P-gp. Despite considerable in vitro success, there are no compounds currently available to "block" P-gp-mediated resistance in the clinic. The failure may be attributed to toxicity, adverse drug interaction, and numerous pharmacokinetic issues. This review provides a description of several alternative approaches to overcome the activity of P-gp in drug-resistant cells. These include 1) drugs that specifically target resistant cells, 2) novel nanotechnologies to provide high-dose, targeted delivery of anticancer drugs, 3) compounds that interfere with nongenomic transfer of resistance, and 4) approaches to reduce the expression of P-gp within tumors. Such approaches have been developed through the pursuit of greater understanding of resistance mediators such as P-gp, and they show considerable potential for further application.

Molecular characterization of exosome-like vesicles from breast cancer cells

Background

Membrane vesicles released by neoplastic cells into extracellular medium contain potential of carrying arrays of oncogenic molecules including proteins and microRNAs (miRNA). Extracellular (exosome-like) vesicles play a major role in cell-to-cell communication. Thus, the characterization of proteins and miRNAs of exosome-like vesicles is imperative in clarifying intercellular signaling as well as identifying disease markers.

Methods

Exosome-like vesicles were isolated using gradient centrifugation from MCF-7 and MDA-MB 231 cultures. Proteomic profiling of vesicles using liquid chromatography-mass spectrometry (LC-MS/MS) revealed different protein profiles of exosome-like vesicles derived from MCF-7 cells (MCF-Exo) than those from MDA-MB 231 cells (MDA-Exo).

Results

The protein database search has identified 88 proteins in MDA-Exo and 59 proteins from MCF-Exo. Analysis showed that among all, 27 proteins were common between the two exosome-like vesicle types. Additionally, MDA-Exo contains a higher amount of matrix-metalloproteinases, which might be linked to the enhanced metastatic property of MDA-MB 231 cells. In addition, microarray analysis identified several oncogenic miRNA between the two types vesicles.

Conclusions

Identification of the oncogenic factors in exosome-like vesicles is important since such vesicles could convey signals to non-malignant cells and could have an implication in tumor progression and metastasis.

Microvesicles as mediators of intercellular communication in cancer

The discovery that cancer cells generate large membrane-enclosed packets of epigenetic information, known as microvesicles (MVs), that can be transferred to other cells and influence their behavior (Antonyak et al., Small GTPases 3:219-224, 2012; Cocucci et al., Trends Cell Biol 19:43-51, 2009; Rak, Semin Thromb Hemost 36:888-906, 2010; Skog et al., Nat Cell Biol 10:1470-1476, 2008) has added a unique perspective to the classical paracrine signaling paradigm. This is largely because, in addition to growth factors and cytokines, MVs contain a variety of components that are not usually thought to be released into the extracellular environment by viable cells including plasma membrane-associated proteins, cytosolic- and nuclear-localized proteins, as well as nucleic acids, particularly RNA transcripts and micro-RNAs (Skog et al., Nat Cell Biol 10:1470-1476, 2008; Al-Nedawi et al., Nat Cell Biol 10:619-624, 2008; Antonyak et al., Proc Natl Acad Sci U S A 108:4852-4857, 2011; Balaj et al., Nat Commun 2:180, 2011; Choi et al., J Proteome Res 6:4646-4655, 2007; Del Conde et al., Blood 106:1604-1611, 2005; Gallo et al., PLoS One 7:e30679, 2012; Graner et al., FASEB J 23:1541-1557, 2009; Grange et al., Cancer Res 71:5346-5356, 2011; Hosseini-Beheshti et al., Mol Cell Proteomics 11:863-885, 2012; Martins et al., Curr Opin Oncol 25:66-75, 2013; Noerholm et al., BMC Cancer 12:22, 2012; Zhuang et al., EMBO J 31:3513-3523, 2012). When transferred between cancer cells, MVs have been shown to stimulate signaling events that promote cell growth and survival (Al-Nedawi et al., Nat Cell Biol 10:619-624, 2008). Cancer cell-derived MVs can also be taken up by normal cell types that surround the tumor, an outcome that helps shape the tumor microenvironment, trigger tumor vascularization, and even confer upon normal recipient cells the transformed characteristics of a cancer cell (Antonyak et al., Proc Natl Acad Sci U S A 108:4852-4857, 2011; Martins et al., Curr Opin Oncol 25:66-75, 2013; Al-Nedawi et al., Proc Natl Acad Sci U S A 106:3794-3799, 2009; Ge et al., Cancer Microenviron 5:323-332, 2012). Thus, the production of MVs by cancer cells plays crucial roles in driving the expansion of the primary tumor. However, it is now becoming increasingly clear that MVs are also stable in the circulation of cancer patients, where they can mediate long-range effects and contribute to the formation of the pre-metastatic niche, an essential step in metastasis (Skog et al., Nat Cell Biol 10:1470-1476, 2008; Noerholm et al., BMC Cancer 12:22, 2012; Peinado et al., Nat Med 18:883-891, 2012; Piccin et al., Blood Rev 21:157-171, 2007; van der Vos et al., Cell Mol Neurobiol 31:949-959, 2011). These findings, when taken together with the fact that MVs are being aggressively pursued as diagnostic markers, as well as being considered as potential targets for intervention against cancer (Antonyak et al., Small GTPases 3:219-224, 2012; Hosseini-Beheshti et al., Mol Cell Proteomics 11:863-885, 2012; Martins et al., Curr Opin Oncol 25:66-75, 2013; Ge et al., Cancer Microenviron 5:323-332, 2012; Peinado et al., Nat Med 18:883-891, 2012; Piccin et al., Blood Rev 21:157-171, 2007; Al-Nedawi et al., Cell Cycle 8:2014-2018, 2009; Cocucci and Meldolesi, Curr Biol 21:R940-R941, 2011; D'Souza-Schorey and Clancy, Genes Dev 26:1287-1299, 2012; Shao et al., Nat Med 18:1835-1840, 2012), point to critically important roles for MVs in human cancer progression that can potentially be exploited to develop new targeted approaches for treating this disease.

Cell-derived vesicles as a bioplatform for the encapsulation of theranostic nanomaterials

There is a great deal of interest in the development of nanoplatforms gathering versatility and multifunctionality. The strategy reported herein meets these requirements and further integrates a cell-friendly shell in a bio-inspired approach. By taking advantage of a cell mechanism of biomolecule transport using vesicles, we engineered a hybrid biogenic nanoplatform able to encapsulate a set of nanoparticles regardless of their chemistry or shape. As a proof of versatility, different types of hybrid nanovesicles were produced: magnetic, magnetic-metallic and magnetic-fluorescent vesicles, either a single component or multiple components, combining the advantageous properties of each integrant nanoparticle. These nanoparticle-loaded vesicles can be manipulated, monitored by MRI and/or fluorescence imaging methods, while acting as efficient nano-heaters. The resulting assets for targeting, imaging and therapy converge for the outline of a new generation of nanosystems merging versatility and multifunctionality into a bio-camouflaged and bio-inspired approach.

ARF1 regulates the Rho/MLC pathway to control EGF-dependent breast cancer cell invasion

The small GTPase ARF1 is overexpressed in invasive breast cancer cells. This ARF isoform controls MMP-9 activity to degrade the extracellular matrix by regulating invadopodia maturation and microvesicle shedding. The molecular mechanisms by which ARF1 controls invasiveness involve regulation of the Rho/MLC pathway.

Invasion of tumor cells is a key step in metastasis that depends largely on the ability of these cells to degrade the extracellular matrix. Although we have showed that the GTPase ADP-ribosylation factor 1 (ARF1) is overexpressed in highly invasive breast cancer cell lines and that epidermal growth factor stimulation can activate this ARF isoform to regulate migration as well as proliferation, the role of this small GTP-binding protein has not been addressed in the context of invasiveness. Here we report that modulation of ARF1 expression and activity markedly impaired the ability of M.D. Anderson-metastatic breast-231 cells, a prototypical highly invasive breast cancer cell line, to degrade the extracellular matrix by controlling metalloproteinase-9 activity. In addition, we demonstrate that this occurs through inhibition of invadopodia maturation and shedding of membrane-derived microvesicles, the two key structures involved in invasion. To further define the molecular mechanisms by which ARF1 controls invasiveness, we show that ARF1 acts to modulate RhoA and RhoC activity, which in turn affects myosin light-chain (MLC) phosphorylation. Together our findings underscore for the first time a key role for ARF1 in invasion of breast cancer cells and suggest that targeting the ARF/Rho/MLC signaling axis might be a promising strategy to inhibit invasiveness and metastasis.

Proteolysis during tumor cell extravasation in vitro: metalloproteinase involvement across tumor cell types

To test if proteolysis is involved in tumor cell extravasation, we developed an in vitro model where tumor cells cross an endothelial monolayer cultured on a basement membrane. Using this model we classified the ability of the cells to transmigrate through the endothelial cell barrier onto the underlying matrix, and scored this invasion according to the stage of passage through the endothelium. Metalloproteinase inhibitors reduced tumor cell extravasation by at least 35%. Visualization of protease and cell adhesion molecules by confocal microscopy demonstrated the cell surface localization of MMP-2, MMP-9, MT1-MMP, furin, CD44 and αvβ3, during the process of transendothelial migration. By the addition of inhibitors and bio-modulators we assessed the functional requirement of the aforementioned molecules for efficient migration. Proteolytic digestion occurred at the cell-matrix interface and was most evident during the migratory stage. All of the inhibitors and biomodulators affected the transition of the tumor cells into the migratory stage, highlighting the most prevalent use of proteolysis at this particular step of tumor cell extravasation. These data suggest that a proteolytic interface operates at the tumor cell surface within the tumor-endothelial cell microenvironment.

The origin, function, and diagnostic potential of RNA within extracellular vesicles present in human biological fluids

We have previously demonstrated that tumor cells release membranous structures into their extracellular environment, which are termed exosomes, microvesicles or extracellular vesicles depending on specific characteristics, including size, composition and biogenesis pathway. These cell-derived vesicles can exhibit an array of proteins, lipids and nucleic acids derived from the originating tumor. This review focuses of the transcriptome (RNA) of these extracellular vesicles. Based on current data, these vesicular components play essential roles as conveyers of intercellular communication and mediators of many of the pathological conditions associated with cancer development, progression and therapeutic failures. These extracellular vesicles express components responsible for angiogenesis promotion, stromal remodeling, signal pathway activation through growth factor/receptor transfer, chemoresistance, and genetic exchange. These tumor-derived extracellular vesicles not only to represent a central mediator of the tumor microenvironment, but their presence in the peripheral circulation may serve as a surrogate for tumor biopsies, enabling real-time diagnosis and disease monitoring.

Magnetic and photoresponsive theranosomes: translating cell-released vesicles into smart nanovectors for cancer therapy

Cell-released vesicles are natural carriers that circulate in body fluids and transport biological agents to distal cells. As nature uses vesicles in cell communication to promote tumor progression, we propose to harness their unique properties and exploit these biogenic carriers as Trojan horses to deliver therapeutic payloads to cancer cells. In a theranostic approach, cell-released vesicles were engineered by a top-down procedure from precursor cells, previously loaded with a photosensitizer and magnetic nanoparticles. The double exogenous cargo provided vesicles with magnetic and optical responsiveness allowing therapeutic and imaging functions. This new class of cell-derived smart nanovectors was named "theranosomes". Theranosomes enabled efficient photodynamic tumor therapy in a murine cancer model in vivo. Moreover the distribution of this biogenic vector could be monitored by dual-mode imaging, combining fluorescence and MRI. This study reports the first success in translating a cell communication mediator into a smart theranostic nanovector.

Revisited role of microparticles in arterial and venous thrombosis

Microparticles (MPs) represent a heterogeneous population of submicronic vesicles that are released in response to cell activation or apoptosis. MPs harbor a large repertoire of cell surface receptors and mRNA and biological activities representative of their parent cells and related to their involvement in many biological functions. Although MP generation is a physiological response, a dramatic increase in circulating MPs is detectable in a variety of thrombosis-associated disorders compared with healthy individuals. In this review, we will discuss a new vision of MPs as complex and ambivalent structures that express both activators and inhibitors of coagulation but also convey fibrinolytic properties. After summarizing our current knowledge about the role of MPs in venous and arterial thrombosis, this review will explore how this new vision of MPs influences their definition as emergent biomarkers in thrombotic diseases. Among the studies that have aimed to establish a link between thrombosis and MPs, a few studies have demonstrated a predictive value of MPs. So far, it is unclear whether this limited causative association is the result of current technical concerns and limited standardization or has to be integrated into a more complex vision of the role of MPs as key systems for regulating the balance between coagulation and fibrinolysis.

Tumor-cell-derived microvesicles as carriers of molecular information in cancer

PURPOSE OF REVIEW

Exosomes and microvesicles are secreted particles of 30-200  nm in diameter, delimited by a lipid bilayer and containing a wide range of membrane-bound or free proteins and nucleic acids (in particular mRNA and miRNA). Here, we review the properties of tumor-cell-derived microvesicles as carriers of molecular information in relation to cancer progression and promotion of metastasis.

RECENT FINDINGS

Microvesicles from tumor cells operate as signaling platforms that diffuse in the extracellular space to target cells in the microenvironment, modulating the interactions of tumor cells with stromal, inflammatory, dendritic, immune or vascular cells and priming the formation of the metastatic niche.

SUMMARY

Because of their stability, exosomes and microvesicles can be retrieved in bodily fluids as biomarkers for cancer detection and monitoring. They offer a range of molecular targets for controlling cell-cell interactions during invasion and metastasis.

CSE1L, a novel microvesicle membrane protein, mediates Ras-triggered microvesicle generation and metastasis of tumor cells

Tumor-derived microvesicles are rich in metastasis-related proteases and play a role in the interactions between tumor cells and tumor microenvironment in tumor metastasis. Because shed microvesicles may remain in the extracellular environment around tumor cells, the microvesicle membrane protein may be the potential target for cancer therapy. Here we report that chromosome segregation 1-like (CSE1L) protein is a microvesicle membrane protein and is a potential target for cancer therapy. v-H-Ras expression induced extracellular signal-regulated kinase (ERK)-dependent CSE1L phosphorylation and microvesicle biogenesis in various cancer cells. CSE1L overexpression also triggered microvesicle generation, and CSE1L knockdown diminished v-H-Ras-induced microvesicle generation, matrix metalloproteinase (MMP)-2 and MMP-9 secretion and metastasis of B16F10 melanoma cells. CSE1L was preferentially accumulated in microvesicles and was located in the microvesicle membrane. Furthermore, anti-CSE1L antibody-conjugated quantum dots could target tumors in animal models. Our findings highlight a novel role of Ras-ERK signaling in tumor progression and suggest that CSE1L may be involved in the "early" and "late" metastasis of tumor cells in tumorigenesis. Furthermore, the novel microvesicle membrane protein, CSE1L, may have clinical utility in cancer diagnosis and targeted cancer therapy.

Targeted destruction of the orchestration of the pancreatic stroma and tumor cells in pancreatic cancer cases: molecular basis for therapeutic implications

Pancreatic cancer is one of the most lethal malignancies, with a prominent desmoplastic reaction as its defining hallmark. The past several decades have seen dramatic progress in understanding of pancreatic cancer pathogenesis, including identification of precursor lesions, sequential transformation from normal pancreatic tissue to invasive pancreatic cancer and corresponding signature genetic events, and the biological impact of these events on malignant behavior. However, the currently used therapeutic strategies for epithelial tumor cells, which have exhibited potent antitumor activity in cell culture and animal models, have failed to produce significant effects in the clinic. The desmoplastic stroma surrounding pancreatic cancer cells, which accounts for about 90% of a tumor's mass, clearly is not a passive scaffold for cancer cells but an active contributor to carcinogenesis. Improved understanding of the dynamic interaction between cancer cells and the stroma will be important to designing effective therapeutic strategies for pancreatic cancer. This review focuses on the origin of stromal molecular and cellular components in pancreatic tumors, their biological effects on pancreatic cancer cells, and the orchestration of these two components.

Microparticles from ovarian carcinomas are shed into ascites and promote cell migration

OBJECTIVE

Microparticles are cellular-derived vesicles (0.5-1.0 μm) composed of cell membrane components, which are actively shed from the surface of various cells, including epithelial cells. We compared microparticles in ascites between women with ovarian carcinoma and women with benign ovarian pathology, and isolated tumor-derived (epithelial cell adhesion molecule [EpCAM]-positive) microparticles for functional analysis and proteomics.

MATERIALS AND METHODS

Cases included 8 patients with benign ovarian neoplasms and 41 with ovarian carcinoma. Ascites from a high-grade stage III serous carcinoma was used for functional and proteomic analysis. Cancer cells were isolated using EpCAM-coated beads, microparticles were isolated by ultracentrifugation/flow cytometry, and sorting was achieved using markers (eg, EpCAM). Binding and migrations assays were performed with 3 ovarian cancer cell lines. Proteomic analysis of EpCAM-positive microparticles and ascites cancer cells was performed by mass spectrometry.

RESULTS

Microparticles in benign pelvic fluid were similar to early and advanced-stage ascites (2.4 vs 2.8 vs 2.0 × 10⁶ microparticles/mL). Advanced stage had a greater proportion of EpCAM-positive microparticles than early or benign disease (13.3% vs 2.5% vs 2.1%; P = 0.001), and serous histology had more than endometrioid (13.2% vs 1.8%; P = 0.01). Microparticles bound to the surface of 3 cultured cell lines, and were internalized into the EpCAM-positive microparticles, resulting in more cell migration than buffer alone or EpCAM-negative microparticles (P = 0.007). A dose-dependent increase was seen with increasing numbers of EpCAM-positive microparticles. Proteomics revealed that most proteins in EPCAM-positive microparticles were shared with cancer cells, and many are associated with cell motility and invasion, such as fibronectin, filamin A, vimentin, myosin-9, and fibrinogen.

CONCLUSIONS

Ascites from advanced-stage and serous ovarian carcinomas contain large numbers of tumor-derived microparticles. In vitro, these microparticles bind to cancer cells and stimulate migration. Tumor-derived microparticles in ascites could mediate the predilection for peritoneal spread in serous ovarian carcinomas.

Leukocyte- and endothelial-derived microparticles: a circulating source for fibrinolysis

BACKGROUND

We recently assigned a new fibrinolytic function to cell-derived microparticles in vitro. In this study we explored the relevance of this novel property of microparticles to the in vivo situation.

DESIGN AND METHODS

Circulating microparticles were isolated from the plasma of patients with thrombotic thrombocytopenic purpura or cardiovascular disease and from healthy subjects. Microparticles were also obtained from purified human blood cell subpopulations. The plasminogen activators on microparticles were identified by flow cytometry and enzyme-linked immunosorbent assays; their capacity to generate plasmin was quantified with a chromogenic assay and their fibrinolytic activity was determined by zymography.

RESULTS

Circulating microparticles isolated from patients generate a range of plasmin activity at their surface. This property was related to a variable content of urokinase-type plasminogen activator and/or tissue plasminogen activator. Using distinct microparticle subpopulations, we demonstrated that plasmin is generated on endothelial and leukocyte microparticles, but not on microparticles of platelet or erythrocyte origin. Leukocyte-derived microparticles bear urokinase-type plasminogen activator and its receptor whereas endothelial microparticles carry tissue plasminogen activator and tissue plasminogen activator/inhibitor complexes.

CONCLUSIONS

Endothelial and leukocyte microparticles, bearing respectively tissue plasminogen activator or urokinase-type plasminogen activator, support a part of the fibrinolytic activity in the circulation which is modulated in pathological settings. Awareness of this blood-borne fibrinolytic activity conveyed by microparticles provides a more comprehensive view of the role of microparticles in the hemostatic equilibrium.

Exosomes in Cancer Microenvironment and Beyond: have we Overlooked these Extracellular Messengers?

Cancer is a complex organ whose behavior is not only influenced by genetic and epigenetic changes in cancer cells but also by stromal cells, local extracellular matrix and specific tissue architecture. Intercellular communications within the cancer microenvironment are critical to coordinate the assembly of multiple cell types for an amalgamated form and function of a cancer. Exosomes are small membrane vesicles with an endosome origin that are released by cells into the extracellular environment. They carry a cargo of proteins, lipids, and nucleic acids and transfer their cargo to recipient cells and altering the recipient cells' biochemical composition, signaling pathways, and gene regulation. Exosomes can thus serve as extracellular messengers mediating cell-cell communication. Both cancer cells and stromal cells release exosomes not only into the cancer microenvironment but also into the circulation. In this review, we summarize the research done so far on cancer-derived exosomes and assess their roles as extracellular messengers facilitating cancer progression and metastasis.

The roles of tumor-derived exosomes in cancer pathogenesis

Exosomes are endosome-derived, 30–100 nm small membrane vesicles released by most cell types including tumor cells. They are enriched in a selective repertoire of proteins and nucleic acids from parental cells and are thought to be actively involved in conferring intercellular signals. Tumor-derived exosomes have been viewed as a source of tumor antigens that can be used to induce antitumor immune responses. However, tumor-derived exosomes also have been found to possess immunosuppressive properties and are able to facilitate tumor growth, metastasis, and the development of drug resistance. These different effects of tumor-derived exosomes contribute to the pathogenesis of cancer. This review will discuss the roles of tumor-derived exosomes in cancer pathogenesis, therapy, and diagnostics.

Paracrine SLPI secretion upregulates MMP-9 transcription and secretion in ovarian cancer cells

OBJECTIVES

Secretory leukocyte protease inhibitor (SLPI) is amplified in serous ovarian cancer. We have dissected its function, showing it is a survival factor for ovarian cancer and promotes tumorigenesis and paclitaxel-resistance. We hypothesized that the protease inhibitory function was responsible for modulating SLPI's invasive capacity.

METHODS

Stable HEYA8 ovarian cancer transfectants expressing vector, wild type SLPI, and protease inhibitor null (F-)SLPI were examined in vitro and in xenografts. Invasion, enzyme activity, and MMP production and function assays were applied. SLPI and MMP immunoexpression was graded on tissue microarray and clinical samples. Statistical comparisons used unpaired t test and ANOVA, where appropriate.

RESULTS

SLPI and F-SLPI cells caused greater parenchymal and peritoneal dissemination over control cells in xenografts and invasion assays (p<0.001). MMP-9 protease activity was increased in SLPI and F-SLPI cells over control. SLPI, but not F-SLPI, inhibited plasmin activity, necessary for MMP-9 activation and release, and inhibited activation of MMP-9. However, paradoxically, both induced quantitative MMP-9 transcription (p<0.05) and protein (p<0.008), yielding an increased net MMP-9 activity in the face of plasmin inhibition. SLPI and MMP-9 expression were strongly correlated in serous ovarian cancers (r(2)=0.986) and a set of ovarian cancers (p<0.02). SLPI expression was greater in serous than endometrioid ovarian cancers (p=0.04).

CONCLUSIONS

SLPI stimulates ovarian cancer invasion, modulated in part by its serine protease inhibitory activity attenuating MMP-9 release. However, SLPI induction of MMP-9, independent of protease inhibition activity, is greater yielding a net pro-invasive behavior. These findings further support SLPI as a molecular target for ovarian cancer.

Dynamic physical properties of dissociated tumor cells revealed by dielectrophoretic field-flow fractionation

Metastatic disease results from the shedding of cancer cells from a solid primary tumor, their transport through the cardiovascular system as circulating tumor cells (CTCs) and their engraftment and growth at distant sites. Little is known about the properties and fate of tumor cells as they leave their growth site and travel as single cells. We applied analytical dielectrophoretic field-flow fractionation (dFFF) to study the membrane capacitance, density and hydrodynamic properties together with the size and morphology of cultured tumor cells after they were harvested and placed into single cell suspensions. After detachment, the tumor cells exhibited biophysical properties that changed with time through a process of cytoplasmic shedding whereby membrane and cytoplasm were lost. This process appeared to be distinct from the cell death mechanisms of apoptosis, anoikis and necrosis and it may explain why multiple phenotypes are seen among CTCs isolated from patients and among the tumor cells obtained from ascitic fluid of patients. The implications of dynamic biophysical properties and cytoplasmic loss for CTC migration into small blood vessels in the circulatory system, survival and gene expression are discussed. Because the total capacitance of tumor cells remained higher than blood cells even after they had shed cytoplasm, dFFF offers a compelling, antibody-independent technology for isolating viable CTCs from blood even when they are no larger than peripheral blood mononuclear cells.

Exosomes/microvesicles: mediators of cancer-associated immunosuppressive microenvironments

Cancer cells, both in vivo and in vitro, have been demonstrated to release membranous structures, defined as microvesicles or exosomes, consisting of an array of macromolecules derived from the originating cells, including proteins, lipids, and nucleic acids. While only recently have the roles of these vesicular components in intercellular communication become elucidated, significant evidence has demonstrated that tumor exosomes can exert a broad array of detrimental effects on the immune system-ranging from apoptosis of activated cytotoxic T cells to impairment of monocyte differentiation into dendritic cells, to induction of myeloid-suppressive cells and T regulatory cells. Immunosuppressive exosomes of tumor origin can be found within neoplastic lesions and in biologic fluids from cancer patients, implying a potential role of these pathways in in vivo tumor progression and systemic paraneoplastic syndromes. Through the expression of molecules involved in angiogenesis promotion, stromal remodeling, signaling pathway activation through growth factor/receptor transfer, chemoresistance, and genetic intercellular exchange, tumor exosomes could represent a central mediator of the tumor microenvironment. By understanding the nature of these tumor-derived exosomes/microvesicles and their roles in mediating cancer progression and modulating the host immune response will significantly impact therapeutic approaches targeting exosomes.

Plasmin on adherent cells: from microvesiculation to apoptosis

Cell activation by stressors is characterized by a sequence of detectable phenotypic cell changes. A given stimulus, depending on its strength, induces modifications in the activity of membrane phospholipid transporters and calpains, which lead to phosphatidylserine exposure, membrane blebbing and the release of microparticles (nanoscale membrane vesicles). This vesiculation could be considered as a warning signal that may be followed, if the stimulus is maintained, by cell detachment-induced apoptosis. In the present study, plasminogen incubated with adherent cells is converted into plasmin by constitutively expressed tPA (tissue-type plasminogen activator) or uPA (urokinase-type plasminogen activator). Plasmin formed on the cell membrane then induces a unique response characterized by membrane blebbing and vesiculation. Hitherto unknown for plasmin, these membrane changes are similar to those induced by thrombin on platelets. If plasmin formation persists, matrix proteins are then degraded, cells lose their attachments and enter the apoptotic process, characterized by DNA fragmentation and specific ultrastructural features. Since other proteolytic or inflammatory stimuli may evoke similar responses in different types of adherent cells, the proposed experimental procedure can be used to distinguish activated adherent cells from cells entering the apoptotic process. Such a distinction is crucial for evaluating the effects of mediators, inhibitors and potential therapeutic agents.

Localization of uPAR and MMP-9 in lipid rafts is critical for migration, invasion and angiogenesis in human breast cancer cells

Background

uPAR and MMP-9, which play critical roles in tumor cell invasion, migration and angiogenesis, have been shown to be associated with lipid rafts.

Methods

To investigate whether cholesterol could regulate uPAR and MMP-9 in breast carcinoma, we used MβCD (methyl beta cyclodextrin, which extracts cholesterol from lipid rafts) to disrupt lipid rafts and studied its effect on breast cancer cell migration, invasion, angiogenesis and signaling.

Results

Morphological evidence showed the association of uPAR with lipid rafts in breast carcinoma cells. MβCD treatment significantly reduced the colocalization of uPAR and MMP-9 with lipid raft markers and also significantly reduced uPAR and MMP-9 at both the protein and mRNA levels. Spheroid migration and invasion assays showed inhibition of breast carcinoma cell migration and invasion after MβCD treatment. In vitro angiogenesis studies showed a significant decrease in the angiogenic potential of cells pretreated with MβCD. MβCD treatment significantly reduced the levels of MMP-9 and uPAR in raft fractions of MDA-MB-231 and ZR 751 cells. Phosphorylated forms of Src, FAK, Cav, Akt and ERK were significantly inhibited upon MβCD treatment. Increased levels of soluble uPAR were observed upon MβCD treatment. Cholesterol supplementation restored uPAR expression to basal levels in breast carcinoma cell lines. Increased colocalization of uPAR with the lysosomal marker LAMP1 was observed in MβCD-treated cells when compared with untreated cells.

Conclusion

Taken together, our results suggest that cholesterol levels in lipid rafts are critical for the migration, invasion, and angiogenesis of breast carcinoma cells and could be a critical regulatory factor in these cancer cell processes mediated by uPAR and MMP-9.

Role of extracellular membrane vesicles in the pathogenesis of various diseases, including cancer, renal diseases, atherosclerosis, and arthritis

Extracellular membrane vesicles (MVs) 30-1000 nm in diameter and of varying cellular origins are increasingly recognized for their participation in a range of processes, including the pathogenesis of various diseases, such as: (1) atherosclerosis, (2) thromboembolism, (3) osteoarthritis (OA), (4) chronic renal disease and pulmonary hypertension, (5) tissue invasion and metastasis by cancer cells, (6) gastric ulcers and bacterial infections, and (7) periodontitis. MVs are derived from many different cell types and intracellular mechanisms, and perform different metabolic functions or roles, depending on the cell of origin.The presence of a metabolically active, outer membrane is a distinguishing feature of all MVs, regardless of their cell type of origin and irrespective of terminologies applied to them such as exosomes, microparticles, or matrix vesicles. The MV membrane provides one of the few protected and controlled internal microenvironments outside cells in which specific metabolic objectives of the host cell may be pursued vigorously at a distance from the host cell. MVs are also involved in various forms of normal and abnormal intercellular communication. Evidence is emerging that circulating MVs are good predictors of the severity of several diseases. In addition, recently, the role of MVs in inducing immunity against cancer cells and bacterial infections has become a topic of interest to researchers in the area of therapeutics. The main objective of this review is to list and briefly describe the increasingly well-defined roles of MVs in selected diseases in which they seem to have a significant role in pathogenesis.

Microvesicles: mediators of extracellular communication during cancer progression

Microvesicles are generated by the outward budding and fission of membrane vesicles from the cell surface. Recent studies suggest that microvesicle shedding is a highly regulated process that occurs in a spectrum of cell types and, more frequently, in tumor cells. Microvesicles have been widely detected in various biological fluids including peripheral blood, urine and ascitic fluids, and their function and composition depend on the cells from which they originate. By facilitating the horizontal transfer of bioactive molecules such as proteins, RNAs and microRNAs, they are now thought to have vital roles in tumor invasion and metastases, inflammation, coagulation, and stem-cell renewal and expansion. This Commentary summarizes recent literature on the properties and biogenesis of microvesicles and their potential role in cancer progression.

Characterization of the liver tissue interstitial fluid (TIF) proteome indicates potential for application in liver disease biomarker discovery

Tissue interstitial fluid (TIF) forms the interface between circulating body fluids and intracellular fluid. Pathological alterations of liver cells could be reflected in TIF, making it a promising source of liver disease biomarkers. Mouse liver TIF was extracted, separated by SDS-PAGE, analyzed by linear ion trap mass spectrometer, and 1450 proteins were identified. These proteins may be secreted, shed from membrane vesicles, or represent cellular breakdown products. They show different profiling patterns, quantities, and possibly modification/cleavage of intracellular proteins. The high solubility and even distribution of liver TIF supports its suitability for proteome analysis. Comparison of mouse liver TIF data with liver tissue and plasma proteome data identified major proteins that might be released from liver to plasma and serve as blood biomarkers of liver origin. This result was partially supported by comparison of human liver TIF data with human liver and plasma proteome data. Paired TIFs from tumor and nontumor liver tissues of a hepatocellular carcinoma patient were analyzed and the profile of subtracted differential proteins supports the potential for biomarker discovery in TIF. This study is the first analysis of the liver TIF proteome and provides a foundation for further application of TIF in liver disease biomarker discovery.

Development of a multimarker assay for early detection of ovarian cancer

PURPOSE

Early detection of ovarian cancer has great promise to improve clinical outcome.

PATIENTS AND METHODS

Ninety-six serum biomarkers were analyzed in sera from healthy women and from patients with ovarian cancer, benign pelvic tumors, and breast, colorectal, and lung cancers, using multiplex xMAP bead-based immunoassays. A Metropolis algorithm with Monte Carlo simulation (MMC) was used for analysis of the data.

RESULTS

A training set, including sera from 139 patients with early-stage ovarian cancer, 149 patients with late-stage ovarian cancer, and 1,102 healthy women, was analyzed with MMC algorithm and cross validation to identify an optimal biomarker panel discriminating early-stage cancer from healthy controls. The four-biomarker panel providing the highest diagnostic power of 86% sensitivity (SN) for early-stage and 93% SN for late-stage ovarian cancer at 98% specificity (SP) was comprised of CA-125, HE4, CEA, and VCAM-1. This model was applied to an independent blinded validation set consisting of sera from 44 patients with early-stage ovarian cancer, 124 patients with late-stage ovarian cancer, and 929 healthy women, providing unbiased estimates of 86% SN for stage I and II and 95% SN for stage III and IV disease at 98% SP. This panel was selective for ovarian cancer showing SN of 33% for benign pelvic disease, SN of 6% for breast cancer, SN of 0% for colorectal cancer, and SN of 36% for lung cancer.

CONCLUSION

A panel of CA-125, HE4, CEA, and VCAM-1, after additional validation, could serve as an initial stage in a screening strategy for epithelial ovarian cancer.

Soluble adhesion molecules in human cancers: sources and fates

Adhesion molecules endow tumor cells with the necessary cell-cell contacts and cell-matrix interactions. As such, adhesion molecules are involved in cell signalling, proliferation and tumor growth. Rearrangements in the adhesion repertoire allow tumor cells to migrate, invade and form metastases. Besides these membrane-bound adhesion molecules several soluble adhesion molecules are detected in the supernatant of tumor cell lines and patient body fluids. Truncated soluble adhesion molecules can be generated by several conventional mechanisms, including alternative splicing of mRNA transcripts, chromosomal translocation, and extracellular proteolytic ectodomain shedding. Secretion of vesicles (ectosomes and exosomes) is an alternative mechanism mediating the release of full-length adhesion molecules. Soluble adhesion molecules function as modulators of cell adhesion, induce proteolytic activity and facilitate cell signalling. Additionally, adhesion molecules present on secreted vesicles might be involved in the vesicle-target cell interaction. Based on currently available data, released soluble adhesion molecules contribute to cancer progression and therefore should not be regarded as unrelated and non-functional side products of tumor progression.

ARF6-regulated shedding of tumor cell-derived plasma membrane microvesicles

BACKGROUND

Increased mitogen-activated protein kinase (MAPK) signaling, small GTPase activation, cytoskeletal rearrangements, and the directed targeting of proteases to sites of extracellular matrix degradation all accompany the process of tumor cell invasion. Several studies have implicated the small GTP-binding protein ARF6 in tumor cell invasion, although the molecular basis by which ARF6 facilitates this process is unclear.

RESULTS

We show that the ARF6 GTP/GDP cycle regulates the release of protease-loaded plasma membrane-derived microvesicles from tumor cells into the surrounding environment. To enable microvesicle shedding, ARF6-GTP-dependent activation of phospholipase D promotes the recruitment of the extracellular signal-regulated kinase (ERK) to the plasma membrane where, in turn, ERK phosphorylates and activates myosin light-chain kinase (MLCK). MLCK-mediated MLC phosphorylation is required for microvesicle release. Inhibition of ARF6 activation is accompanied by PKC-mediated phosphorylation of MLC, which blocks microvesicle shedding. Protein cargo appears to be selectively sorted into microvesicles, and adhesion to the extracellular matrix (ECM) is facilitated by microvesicle-associated integrin receptors.

CONCLUSIONS

Microvesicle shedding in tumor cells occurs via an actomyosin-based membrane abscission mechanism that is regulated by nucleotide cycling on ARF6. Microvesicle shedding appears to release selected cellular components, particularly those involved in cell adhesion and motility, into the surrounding environment. These findings suggest that ARF6 activation and the proteolytic activities of microvesicles, both of which are thought to correlate directly with tumor progression, could potentially serve as biomarkers for disease.

MMP-2 expression precedes the final ripening process of the bovine cervix

Collagen is denatured in the gradual cervical ripening process during late pregnancy, already before the onset of final cervical ripening at parturition. Matrix Metallo Proteinases (MMPs) might be responsible for this process. To investigate the presence and potential function of MMPs at the different stages of the ripening process, serial cervical biopsies were obtained from 10 cows at Days 185 and 275 of pregnancy (approximately 5 days before calving), at parturition and at 30 days after parturition. The mRNA and protein expression of MMP-1, MMP-2, and MMP-9 and of the tissue inhibitors of MMPs (TIMP)-1 and TIMP-2 were semi-quantitatively determined using RT-PCR, respectively, zymography, Westernblot, and ELISA techniques and the localization of MMP-2 protein and presence of granulocytes by immunohistochemistry and Luna staining. At parturition compared to 185 days pregnancy the MMP-1 protein expression and the numbers of granulocytes were significantly increased by 3 and 26-fold respectively. MMP-2 mRNA and protein expression had already increased 2.5 (P < 0.05) and twofold (P < 0.05) at 5 days before parturition, prior to final ripening. At that time, MMP-2 was present in smooth muscle cells and extra cellular matrix. TIMP-1 mRNA expression was significantly increased at parturition and TIMP-2 mRNA expression peaked at 5 days before parturition. The increased expression of MMP-2 at 5 days before parturition, suggests that in the cow MMP-2 is responsible for collagen denaturation in the last part of gradual cervical ripening, while MMP-1 and MMP-9 are only active during the final cervical ripening process at parturition.

The Tumor Microenvironment: Key to Early Detection

The tumor microenvironment plays an important role equal to the tumor cell population in the progression of cancer. Consisting of stromal fibroblasts, inflammatory cells, components of the vasculature, normal epithelia, and extracellular matrix, the surrounding environment interacts or "cross-talks" with tumor cells through the release of growth factors, cytokines, proteases, and other bioactive molecules. Tumor growth, formation of new vascular networks, evasion of the host immune system, and invasion and metastasis are processes that co-evolve and become finely optimized and regulated within the tumor microenvironment. However, relatively recent reports on three areas of study have come together to add new levels of complexity to the tumor microenvironment. These include ectodomain shedding of proteins, shedding of membrane-derived vesicles, and novel roles for phospholipids. These dynamic changes that take place in the tumor microenvironment provide new avenues for study and for the early detection of cancer, whereas proteomic technologies provide the means to detect these unique proteins and lipids. Here we review the evolving concepts of the tumor microenvironment that, together with advances in proteomic technologies, hold the promise to facilitate the detection of early-stage cancer.

Cathepsin B mediates the pH-dependent proinvasive activity of tumor-shed microvesicles

Vesicles shed by cancer cells are known to mediate several tumor-host interactions. Tumor microenvironment may, in turn, influence the release and the activity of tumor-shed microvesicles. In this study, we investigated the molecular mediators of the pH-dependent proinvasive activity of tumor-shed vesicles. Gelatinase zymography showed increased microvesicle activity of matrix metalloproteinases 9 and 2 as a result of acid exposure (pH 5.6) compared to pH 7.4. Thus, we reasoned that the cysteine protease cathepsin B might play a role in mediating the pH-dependent activation of gelatinases. Cathepsin B expression in tumor-shed microvesicles was confirmed by Western blot analysis and zymography. The activity of vesicle-associated cathepsin B measured using Z-Arg-Arg-pNA as substrate was significantly increased at acidic pH values. Inhibition of protease activity by the cysteine protease inhibitor, E-64, and treatment of ovarian cancer cells with small interfering RNA against cathepsin B suppressed the ability of tumor-shed microvesicles to stimulate both gelatinase activation and the invasiveness of endothelial cells observed at low pH values. We conclude that microvesicle shedding is a major secretory pathway for cathepsin B release from tumor cells. Hence, the acidic microenvironment found in most solid tumors may contribute to cathepsin B-mediated proinvasive capabilities of tumor-shed vesicles.

Dissecting lipid raft facilitated cell signaling pathways in cancer

Cancer is one of the most devastating disorders in our lives. Higher rate of proliferation than death of cells is one of the essential factors for development of cancer. The dynamicity of cell membrane plays some vital roles in cell survival and cell death, including protection, endocytosis, signaling, and increases in mechanical stability during cell division, as well as decrease of shear forces during separation of two cells after division, and cell separation from tissues for cancer metastasis. Within the membrane, there are specialized domains, known as lipid rafts. A raft can coordinate various signaling pathways. Recent data on the proteomics of lipid rafts/caveolae have highlighted the enigmatic role of various signaling proteins in cancer development. Analysis of these data of raft proteome from various tumors, cancer tissues, and cell lines cultured without and with therapeutic agents, as well as from model rafts revealed that there may be two subsets of raft assemblage in cell membrane. One subset of raft is enriched with cholesterol-sphingomyeline-ganglioside-cav-1/Src/EGFR (hereafter, "chol-raft") that is involved in normal cell signaling, and when dysregulated promotes cell transformation and tumor progression; another subset of raft is enriched with ceramide-sphingomyeline-ganglioside-FAS/Ezrin (hereafter, "cer-raft") that generally promotes apoptosis. In view of this, and to focus insight into the cancer cell physiology caused by the lipid rafts mediated signals and their receptors, and the downstream transmitters, either proliferative (for example, EGF and EGFR) or death-inducing (for example, FASL and FAS), and the precise roles of some therapeutic drugs and endogenous acid sphingomylenase in this scenario in in situ transformation of "chol-raft" into "cer-raft" are summarized and discussed in this contribution.

Tumor vesicle-associated CD147 modulates the angiogenic capability of endothelial cells

Matrix metalloproteinase (MMP) degradation of extracellular matrix is thought to play an important role in invasion, angiogenesis, tumor growth, and metastasis. Several studies have demonstrated that CD147/extracellular MMP inducer, a membrane-spanning molecule highly expressed in tumor cells, may be involved in the progression of malignancies by regulating expression of MMP in peritumoral stromal cells. In the present study we show that CD147 is expressed in microvesicles derived from epithelial ovarian cancer cells and that CD147-positive vesicles may promote an angiogenic phenotype in endothelial cells in vitro. Vesicles shed by human ovarian carcinoma cell lines OVCAR3, SKOV3, and A2780 expressed different levels of CD147 and stimulated proangiogenic activities of human umbilical vein endothelial cells (HUVECs) in a CD147-dependent fashion (OVCAR3 > SKOV3 > A2780). Moreover, vesicles shed by ovarian carcinoma cell line CABA I with low CD147 expression had no significant effect on the development of angiogenic phenotype in HUVECs. The treatment of OVCAR3 cells with small interfering RNA against CD147 suppressed the angiogenic potential of OVCAR3-derived microvesicles. However, transfection of CD147 cDNA into the CABA I cell line enabled CABA I-derived vesicles to induce angiogenesis and to promote MMP genes expression in HUVECs. We therefore conclude that vesicles shed by ovarian cancer cells may induce proangiogenic activities of HUVECs by a CD147-mediated mechanism.

Microvesicles in the venom of Crotalus durissus terrificus (Serpentes, Viperidae)

Microvesicles with electron-dense content are consistently observed by transmission electron microscopy on the luminal face of secretory cells of venom glands of viperid snakes. In this work, we evaluated their presence in Crotalus durissus terrificus venom glands and also in freshly collected venom. Microvesicles were found in the venom glands mainly in regions of exocytosis. They ranged from 40 to 80 nm in diameter. Freeze-fracture replicas of the glands revealed particles on the cytoplasmic leaflet (P-face) of these vesicles, suggesting that they carry transmembrane proteins. Vesicles separated by ultracentrifugation from cell-free venom were similar in size and structure to the microvesicles observed in the glands. A fine fuzzy coat surrounded each microvesicle. The function of these venom vesicles is still unknown, but they may contribute to inactivation of stored venom components, or their activation after the venom is released.