Shedding of plasma membrane fragments. Neoplastic and developmental importance

Size-Exclusion Chromatography as a Technique for the Investigation of Novel Extracellular Vesicles in Cancer

Simple Summary

Extracellular vesicles (EVs) are small particles that are released by cancer cells, and they may hold vital information for researchers looking for early markers for diagnosis. Size-exclusion chromatography (SEC) is a classical technique that has become increasingly popular and can be used for rapid isolation and investigation of both their cargo and functionality. This systematic review highlights its main technical aspects, the type of materials involved and by covering the findings of the identified papers hopes to demonstrate the utility of this method in cancer research to date.

Abstract

Cancer cells release extracellular vesicles, which are a rich target for biomarker discovery and provide a promising mechanism for liquid biopsy. Size-exclusion chromatography (SEC) is an increasingly popular technique, which has been rediscovered for the purposes of extracellular vesicle (EV) isolation and purification from diverse biofluids. A systematic review was undertaken to identify all papers that described size exclusion as their primary EV isolation method in cancer research. In all, 37 papers were identified and discussed, which showcases the breadth of applications in which EVs can be utilised, from proteomics, to RNA, and through to functionality. A range of different methods are highlighted, with Sepharose-based techniques predominating. EVs isolated using SEC are able to identify cancer cells, highlight active pathways in tumourigenesis, clinically distinguish cohorts, and remain functionally active for further experiments.

Extracellular Vesicles Mediate B Cell Immune Response and Are a Potential Target for Cancer Therapy

Extracellular vesicles (EVs) are increasingly understood to participate directly in many essential aspects of host antitumor immune response. Tumor- and immune-cell-derived EVs function in local and systemic contexts with roles in immune processes including cancer antigen conveyance, immune cell priming and activation, as well as immune escape. Current practice of cancer immunotherapy has de facto focused on eliciting T-cell-mediated cytotoxic responses. Humoral immunity is also known to exert antitumor effects, and B cells have been demonstrated to have functions that extend beyond antibody production to include antigen presentation and activation and modulation of T cells and innate immune effectors. Evidence of B cell response against tumor-associated antigens (TAAs) is observed in early stages of tumorigenesis and in most solid tumor types. It is known that EVs convey diverse TAAs, express antigenic-peptide-loaded MHCs, and complex with circulating plasma antitumoral autoantibodies. In this review, we will consider the relationships between EVs, B cells, and other antigen-presenting cells, especially in relation to TAAs. Understanding the intersection of EVs and the cancer immunome will enable opportunities for developing tumor antigen targets, antitumor vaccines and harnessing the full potential of multiple immune system components for next-generation cancer immunotherapies.

Insights into the Proteome of Gastrointestinal Stromal Tumors-Derived Exosomes Reveals New Potential Diagnostic Biomarkers

Developing tumors continuously release nano-sized vesicles that represent circulating "fingerprints" of the tumor's identity. In gastrointestinal stromal tumor (GIST), we have previously reported that these tumors release "oncosomes" carrying the constitutively activated tyrosine kinase (TK) receptor KIT. Despite the clinical utility of TK inhibitors, such as imatinib mesylate (IM), recurrence and metastasis are clinical problems that urge the need to identify new tumor-derived molecules. To this aim, we performed the first high quality proteomic study of GIST-derived exosomes (GDEs) and identified 1,060 proteins composing the core GDE proteome (cGDEp). The cGDEp was enriched in diagnostic markers (e.g. KIT, CD34, ANO1, PROM1, PRKCQ, and ENG), as well as proteins encoded by genes previously reported expressed in GIST (e.g. DPP4, FHL1, CDH11, and KCTD12). Many of these proteins were validated using cell lines, patient-derived KIT⁺ exosomes, and GIST tissues. We further show that in vitro and in vivo-derived GDE, carry proteins associated with IM response, such as Sprouty homolog 4 (SPRY4), surfeit 4 (SURF4), ALIX, and the cGMP-dependent 3',5'-cyclic phosphodiesterase 2A (PDE2A). Additionally, we report that the total exosome levels and exosome-associated KIT and SPRY4 protein levels have therapeutic values. In fact, molecular characterization of in vivo-derived KIT⁺ exosomes indicate significant sorting of p-KIT^Tyr719, total KIT, and SPRY4 after IM-treatment of metastatic patients as compared with the pre-IM levels. Our data suggest that analysis of circulating exosomes levels and molecular markers of IM response in GIST patients with primary and metastatic disease is suitable to develop liquid based biopsies for the diagnosis, prognosis, and monitoring of response to treatment of these tumors. In summary, these findings provide the first insight into the proteome of GIST-derived oncosomes and offers a unique opportunity to further understand their oncogenic elements which contribute to tumorigenesis and drug resistance. Data are available via ProteomeXchange with identifier PXD007997.

Graphene Oxide Nanosheets Stimulate Ruffling and Shedding of Mammalian Cell Plasma Membranes

Graphene oxide (GO) has attracted intense interest for use in living systems and environmental applications. GO's compatibility with mammalian cells is sometimes inferred from its low cytotoxicity, but such conclusions ignore non-lethal effects that will influence GO's utility. Here we demonstrate, with rat basophilic leukemia (RBL) cells, profound plasma membrane (PM) ruffling and shedding induced by GO using confocal and live cell fluorescence microscopy, as well as scanning electron microscopy. These membrane structures contain immunoglobulin E receptors, are resistant to detergents, and lack detectable fluorescence labeling of F-actin and fibronectin. The formation of these membrane structures correlates with a loss of contact inhibition between RBL cells. We observe similar cellular responses towards GO for NIH-3T3 fibroblast cells and MDA-MB-231 human breast cancer cells. These findings reveal a previously unreported cellular response towards foreign nanomaterials. Membrane ruffling and shedding raise fundamental questions about how GO interacts with the PM, as well as its potential to modulate cellular mechanosensing for tissue engineering, stem cell differentiation, and other biomedical applications.

The Role of MicroRNAs as Predictors of Response to Tamoxifen Treatment in Breast Cancer Patients

Endocrine therapy is a key treatment strategy to control or eradicate hormone-responsive breast cancer. However, resistance to endocrine therapy leads to breast cancer relapse. The recent extension of adjuvant tamoxifen treatment up to 10 years actualizes the need for identifying biological markers that may be used to monitor predictors of treatment response. MicroRNAs are promising biomarkers that may fill the gap between preclinical knowledge and clinical observations regarding endocrine resistance. MicroRNAs regulate gene expression by posttranscriptional repression or degradation of mRNA, most often leading to gene silencing. MicroRNAs have been identified directly in the primary tumor, but also in the circulation of breast cancer patients. The few available studies investigating microRNA in patients suggest that seven microRNAs (miR-10a, miR-26, miR-30c, miR-126a, miR-210, miR-342 and miR-519a) play a role in tamoxifen resistance. Ingenuity Pathway Analysis (IPA) reveals that these seven microRNAs interact more readily with estrogen receptor (ER)-independent pathways than ER-related signaling pathways. Some of these pathways are targetable (e.g., PIK3CA), suggesting that microRNAs as biomarkers of endocrine resistance may have clinical value. Validation of the role of these candidate microRNAs in large prospective studies is warranted.

Curcumin Modulates Pancreatic Adenocarcinoma Cell-Derived Exosomal Function

Pancreatic cancer has the highest mortality rates of all cancer types. One potential explanation for the aggressiveness of this disease is that cancer cells have been found to communicate with one another using membrane-bound vesicles known as exosomes. These exosomes carry pro-survival molecules and increase the proliferation, survival, and metastatic potential of recipient cells, suggesting that tumor-derived exosomes are powerful drivers of tumor progression. Thus, to successfully address and eradicate pancreatic cancer, it is imperative to develop therapeutic strategies that neutralize cancer cells and exosomes simultaneously. Curcumin, a turmeric root derivative, has been shown to have potent anti-cancer and anti-inflammatory effects in vitro and in vivo. Recent studies have suggested that exosomal curcumin exerts anti-inflammatory properties on recipient cells. However, curcumin's effects on exosomal pro-tumor function have yet to be determined. We hypothesize that curcumin will alter the pro-survival role of exosomes from pancreatic cancer cells toward a pro-death role, resulting in reduced cell viability of recipient pancreatic cancer cells. The main objective of this study was to determine the functional alterations of exosomes released by pancreatic cancer cells exposed to curcumin compared to exosomes from untreated pancreatic cancer cells. We demonstrate, using an in vitro cell culture model involving pancreatic adenocarcinoma cell lines PANC-1 and MIA PaCa-2, that curcumin is incorporated into exosomes isolated from curcumin-treated pancreatic cancer cells as observed by spectral studies and fluorescence microscopy. Furthermore, curcumin is delivered to recipient pancreatic cancer cells via exosomes, promoting cytotoxicity as demonstrated by Hoffman modulation contrast microscopy as well as AlamarBlue and Trypan blue exclusion assays. Collectively, these data suggest that the efficacy of curcumin may be enhanced in pancreatic cancer cells through exosomal facilitation.

Advances in circulating microRNAs as diagnostic and prognostic markers for ovarian cancer

Ovarian cancer is one of the most lethal malignant gynecological tumors. More than 70% of patients with ovarian cancer are diagnosed at advanced stage. The 5-year survival in patients with advanced ovarian cancer is less than 30% because of the lack of effective biomarkers for diagnosis, prognosis, and personalized treatment. MicroRNA (miR) is a class of small noncoding RNAs that negatively regulate gene expression primarily through post-transcriptional repression. Many studies on tissue miR in ovarian cancer have been carried out and show great potential in clinical practice. However, tissue samples are not easily available because sampling causes injury. Researchers have started to focus on plasma/serum miR, assuming that blood samples may replace tissue samples in miR research in the future. Plasma/serum miR research is still in its early stages. Studies on its function in the early diagnosis of ovarian cancer have achieved some progress, but plasma/serum miR profiling for prognosis and personalized treatment of ovarian cancer remains unknown. A thorough understanding of the function of plasma/serum miR in ovarian cancer will facilitate early diagnosis and improve treatment for ovarian cancer.

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.

Sporadic vestibular schwannomas associated with good hearing secrete higher levels of fibroblast growth factor 2 than those associated with poor hearing irrespective of tumor size

HYPOTHESIS

We hypothesize that the severity of hearing loss (HL) associated with sporadic vestibular schwannomas (VS) is correlated with tumor secretion of proteins with ototoxic or otoprotective potential.

BACKGROUND

Because the recognition that HL associated with VS is not solely due to compression of the auditory nerve, elucidating the mechanism by which VS cause HL has been an important task. We previously showed that VS stratified by hearing have differential gene expression. We now focus on identifying differentially expressed proteins in tumor secretions.

METHODS

Fresh surgical specimens of VS were incubated in sterile PBS at 37°C to collect secretions. The specimens were divided into a group associated with good hearing (GH, word recognition ≥ 70% and pure-tone average ≤ 30 dB, n = 11) or poor hearing (PH, n = 10). The groups were compared using a customized cytokine array. Statistically significant results were verified with an enzyme-linked immunosorbent assay on a different set of secretions (n = 8 for GH and n = 10 for PH group).

RESULTS

Of the 37 molecules we studied, 9 were significantly expressed in secretions from VS compared with secretions from control nerves. Secretion of fibroblast growth factor 2 (FGF2) was 3.5-fold higher in VS associated with GH versus PH based on cytokine array analysis (p = 0.02), which was validated with enzyme-linked immunosorbent assay.

CONCLUSION

This study highlights FGF2, a mitogen known to protect the auditory nerve, as a potential tumor-secreted mediator of hearing protection in VS. If FGF2's significant role in hearing protection in patients with VS is validated, then FGF2 could be used as a biomarker for HL in VS, and therapeutic targeting of the FGF2 signaling pathway may reduce HL due to VS.

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.

Lung cancer screening: from imaging to biomarker

Despite several decades of intensive effort to improve the imaging techniques for lung cancer diagnosis and treatment, primary lung cancer is still the number one cause of cancer death in the United States and worldwide. The major causes of this high mortality rate are distant metastasis evident at diagnosis and ineffective treatment for locally advanced disease. Indeed, approximately forty percent of newly diagnosed lung cancer patients have distant metastasis. Currently, the only potential curative therapy is surgical resection of early stage lung cancer. Therefore, early detection of lung cancer could potentially increase the chance of cure by surgery and underlines the importance of screening and detection of lung cancer. In the past fifty years, screening of lung cancer by chest X-Ray (CXR), sputum cytology, computed tomography (CT), fluorescence endoscopy and low-dose spiral CT (LDCT) has not improved survival except for the recent report in 2010 by the National Lung Screening Trial (NLST), which showed a 20 percent mortality reduction in high risk participants screened with LDCT compared to those screened with CXRs. Furthermore, serum biomarkers for detection of lung cancer using free circulating DNA and RNA, exosomal microRNA, circulating tumor cells and various lung cancer specific antigens have been studied extensively and novel screening methods are being developed with encouraging results. The history of lung cancer screening trials using CXR, sputum cytology and LDCT, as well as results of trials involving various serum biomarkers, are reviewed herein.

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.

Analysis of the expression of human tumor antigens in ovarian cancer tissues

Biomarkers for early detection of cancer have great clinical diagnostic potential. Numerous reports have documented the generation of humoral immune responses that are triggered in response to changes in protein expression patterns in tumor tissues and these biomarkers are referred to as tumor associated antigens (TAAs). Using a high-throughput technology, we previously identified 65 proteins as diagnostically useful TAAs by profiling the humoral immune responses in ovarian cancer (OVCA) patients. Here we determined the expression status of some of those TAAs in tissues from OVCA patients. The protein expression patterns of 4 of those 65 antigens, namely NASP, RCAS1, Nijmegen breakage syndrome1 (NBS1) and eIF5A, along with p53 and Her2 (known molecular prognosticators) and two proteins that interact with NBS1, MRE11 and RAD50, were assessed by immunohistochemistry (IHC). NASP and RCAS1 proteins were more frequently expressed in ovarian cancer tissues than with normal ovarian tissue and serous cystadenomas and MRE11 was less frequently expressed. When evaluated simultaneously, only NASP and MRE11 remained statistically significant with sensitivity of 66% and specificity of 89%. None of these proteins' expression levels were prognostic for survival. Together, our results indicate that occurrence of humoral immune responses against some of these TAAs in OVCA patients is triggered by antigen protein overexpression.

Exosomes as a tumor immune escape mechanism: possible therapeutic implications

Advances in cancer therapy have been substantial in terms of molecular understanding of disease mechanisms, however these advances have not translated into increased survival in the majority of cancer types. One unsolved problem in current cancer therapeutics is the substantial immune suppression seen in patients. Conventionally, investigations in this area have focused on antigen-nonspecific immune suppressive molecules such as cytokines and T cell apoptosis inducing molecules such as Fas ligand. More recently, studies have demonstrated nanovesicle particles termed exosomes are involved not only in stimulation but also inhibition of immunity in physiological conditions. Interestingly, exosomes secreted by cancer cells have been demonstrated to express tumor antigens, as well as immune suppressive molecules such as PD-1L and FasL. Concentrations of exosomes from plasma of cancer patients have been associated with spontaneous T cell apoptosis, which is associated in some situations with shortened survival. In this paper we place the "exosome-immune suppression" concept in perspective of other tumor immune evasion mechanisms. We conclude by discussing a novel therapeutic approach to cancer immune suppression by extracorporeal removal of exosomes using hollow fiber filtration technology

Tissue factor activity is increased in a combined platelet and microparticle sample from cancer patients

BACKGROUND

Cancer patients have an increased risk of thrombosis. Tissue factor (TF) antigen and TF activity associated with microparticles in plasma are elevated in patients with various types of cancer. Of these two measurements, TF activity is considered superior to TF antigen levels because the activity more closely reflects the ability of TF to initiate coagulation. Recent studies showed that platelets also express TF.

OBJECTIVE

To determine the level of TF activity associated with a combined platelet and microparticle sample from cancer patients (n = 20) and healthy individuals (n = 23).

METHODS

TF activity was measured using a two step chromogenic assay and soluble P-selectin was measured by ELISA in healthy controls and metastatic cancer patients.

RESULTS

We determined the composition of a combined platelet and microparticle sample. The sample consisted of platelets, large microparticles (30-200 nm) and membrane debris. We compared the TF activity of a combined platelet and microparticle sample from cancer patients with that from healthy individuals. We found that TF activity in a combined platelet and microparticle sample from cancer patients was higher than in samples from healthy individuals (21.5+/-12.3 pM (n = 20) versus 8.6+/-6.8 pM (n = 23), mean+/-SD, p < 0.001). Cancer patients also had a higher level of soluble P-selectin compared with controls (18.9+/-5.5 ng/mL versus 13.2+/-2.3 ng/mL, p < 0.001).

CONCLUSION

This study indicates that measurement of TF activity in a combined platelet and microparticle sample can be used as a simple assay to determine the level of circulating TF.

C4.4A as a candidate marker in the diagnosis of colorectal cancer

C4.4A is a member of the Ly-6 family with restricted expression in non-transformed tissues. C4.4A expression in human cancer has rarely been evaluated. Thus, it became important to explore C4.4A protein expression in human tumour tissue to obtain an estimate on the frequency of expression and the correlation with tumour progression, the study focusing on colorectal cancer. The analysis of C4.4A in human tumour lines by western blot and immunoprecipitation using polyclonal rabbit antibodies that recognize different C4.4A epitopes revealed C4.4A oligomer and heavily glycosylated C4.4A isoform expression that, in some instances, inhibited antibody binding and interaction with the C4.4A ligand galectin-3. In addition, tumour cell lines released C4.4A by vesicle shedding and proteolytic cleavage. C4.4A was expressed in over 80% of primary colorectal cancer and liver metastasis with negligible expression in adjacent colonic mucosa, inflamed colonic tissue and liver. This compares well with EpCAM and CO-029 expression in over 90% of colorectal cancer. C4.4A expression was only observed in about 50% of pancreatic cancer and renal cell carcinoma. By de novo expression in colonic cancer tissue, we consider C4.4A as a candidate diagnostic marker in colorectal cancer, which possibly can be detected in body fluids.

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.

Human tumor-derived vs dendritic cell-derived exosomes have distinct biologic roles and molecular profiles

Microvesicles (MV) or exosomes are produced and secreted by tumor and normal cells. The molecular profile and functions of tumor-derived vs dendritic cell (DC)-derived MV are distinct. The former express death ligands and mediate apoptosis of activated T cells. The latter promote CD4+ T cell proliferation and may play a role in regulating T cell responses. Serving as intercellular communication networks, tumor-derived MV contribute to tumor escape, while DC-derived MV drive and regulate immune response.

Human tumor-released microvesicles promote the differentiation of myeloid cells with transforming growth factor-beta-mediated suppressive activity on T lymphocytes

Human tumors constitutively release endosome-derived microvesicles, transporting a broad array of biologically active molecules with potential modulatory effects on different immune cells. Here, we report the first evidence that tumor-released microvesicles alter myeloid cell function by impairing monocyte differentiation into dendritic cells and promoting the generation of a myeloid immunosuppressive cell subset. CD14+ monocytes isolated from healthy donors and differentiated with interleukin (IL)-4 and granulocyte macrophage colony-stimulating factor in the presence of tumor-derived microvesicles turned into HLA-DR(-/low) cells, retaining CD14 expression and failing to up-regulate costimulatory molecules, such as CD80 and CD86. These phenotypic changes were paralleled by a significant release of different cytokines, including IL-6, tumor necrosis factor-alpha, and transforming growth factor-beta (TGF-beta), and a dose-dependent suppressive activity on activated T-cell-proliferation and cytolytic functions, which could be reversed by anti-TGF-beta-neutralizing antibodies. Microvesicles isolated from plasma of advanced melanoma patients, but not from healthy donors, mediated comparable effects on CD14+ monocytes, skewing their differentiation toward CD14+HLA-DR-/low cells with TGF-beta-mediated suppressive activity on T-cell-functions. Interestingly, a subset of TGF-beta-secreting CD14+HLA-DR- cells mediating suppressive activity on T lymphocytes was found to be significantly expanded in peripheral blood of melanoma patients compared with healthy donors. These data suggest the development in cancer patients of an immunosuppressive circuit by which tumors promote the generation of suppressive myeloid cells through the release of circulating microvesicles and without the need for cell-to-cell contact. Therapeutic interventions on the crucial steps of this pathway may contribute to restore tumor/immune system interactions favoring T-cell-mediated control of tumor growth in cancer patients.

Bioavailability of VEGF in tumor-shed vesicles depends on vesicle burst induced by acidic pH

Tumor angiogenesis is regulated by a dynamic cross-talk between tumor cells and the host microenvironment. Because membrane vesicles shed by tumor cells are known to mediate several tumor-host interactions, we determined whether vesicles might also stimulate angiogenesis. Vesicles shed by human ovarian carcinoma cell lines CABA I and A2780 stimulated the motility and invasiveness of endothelial cells in vitro. Enzyme-linked immunosorbent assay and Western blot analysis revealed relevant amounts of vascular endothelial growth factor (VEGF) and the two matrix metalloproteinases MMP-2 and MMP-9, but not fibroblast growth factor-2, contained in shed vesicles. An A2780 cell-derived clone transfected to overexpress VEGF shed the same amount of vesicles as did a control clone, but contained significantly more VEGF within the vesicles. Despite a greater amount of VEGF in vesicles of the overexpressing clone, vesicles of both clones stimulated endothelial cell motility to comparable levels, suggesting that VEGF was stored within the vesicle and was unavailable. Only following vesicle burst induced by acidic pH (a characteristic of the tumor microenvironment) was VEGF released, leading to significantly higher stimulation of cell motility. Thus, tumor-shed membrane vesicles carry VEGF and release it in a bioactive form in conditions typical of the tumor microenvironment.

Cleavage of L1 in exosomes and apoptotic membrane vesicles released from ovarian carcinoma cells

PURPOSE

The L1 adhesion molecule (CD171) is overexpressed in human ovarian and endometrial carcinomas and is associated with bad prognosis. Although expressed as a transmembrane molecule, L1 is released from carcinoma cells in a soluble form. Soluble L1 is present in serum and ascites of ovarian carcinoma patients. We investigated the mode of L1 cleavage and the function of soluble L1.

EXPERIMENTAL DESIGN

We used ovarian carcinoma cell lines and ascites from ovarian carcinoma patients to analyze soluble L1 and L1 cleavage by Western blot analysis and ELISA.

RESULTS

We find that in ovarian carcinoma cells the constitutive cleavage of L1 proceeds in secretory vesicles. We show that apoptotic stimuli like C2-ceramide, staurosporine, UV irradiation, and hypoxic conditions enhance L1-vesicle release resulting in elevated levels of soluble L1. Constitutive cleavage of L1 is mediated by a disintegrin and metalloproteinase 10, but under apoptotic conditions multiple metalloproteinases are involved. L1 cleavage occurs in two types of vesicles with distinct density features: constitutively released vesicles with similarity to exosomes and apoptotic vesicles. Both types of L1-containing vesicles are present in the ascites fluids of ovarian carcinoma patients. Soluble L1 from ascites is a potent inducer of cell migration and can trigger extracellular signal-regulated kinase phosphorylation.

CONCLUSIONS

We suggest that tumor-derived vesicles may be an important source for soluble L1 that could regulate tumor cell function in an autocrine/paracrine fashion.

Tumour-derived exosomes and their role in cancer-associated T-cell signalling defects

Dendritic and lymphoid ‘exosomes’ regulate immune activation. Tumours release membranous material mimicking these ‘exosomes,’ resulting in deletion of reactive lymphocytes. Tumour-derived ‘exosomes’ have recently been explored as vaccines, without analysis of their immunologic consequences. This investigation examines the composition of tumour-derived ‘exosomes’ and their effects on T lymphocytes. Membranous materials were isolated from ascites of ovarian cancer patients (n=6) and Western immunoblotting was performed for markers associated with ‘exosomes.’ Using cultured T cells, ‘exosomes’ were evaluated for suppression of CD3-ζ and JAK 3 expressions and induction of apoptosis, measured by DNA fragmentation. ‘Exosome’ components mediating suppression of CD3-ζ were isolated by continuous eluting electrophoresis and examined by Western immunoblotting. ‘Exosomes’ were shown to be identical with previously characterised shed membrane vesicles by protein staining and TSG101 expression. ‘Exosomes’ expressed class I MHC, placental alkaline phosphatase, B23/nucleophosmin, and FasL. ‘Exosomes’ suppressed expression of T-cell activation signalling components, CD3-ζ and JAK 3 and induced apoptosis. CD3-ζ suppression was mediated by two components: 26 and 42 kDa. Only the 42 kDa component reacted with anti-FasL antibody. These results indicate that, while ‘exosomes’ express tumour antigens, leading to their proposed utility as tumour vaccines, they also can suppress T-cell signalling molecules and induce apoptosis.

Fas Ligand–Positive Membranous Vesicles Isolated from Sera of Patients with Oral Cancer Induce Apoptosis of Activated T Lymphocytes

Objective: In patients with oral squamous cell carcinoma, a high proportion of T cells in the tumor undergo apoptosis, which correlates with Fas ligand (FasL) expression on tumor cells. The present study was done to identify mechanisms responsible for apoptosis of T cells seen in the peripheral circulation of these patients.

Methods: Sera of 27 patients, normal donor sera, and supernatants of cultured normal or tumor cells were fractionated by size exclusion chromatography and ultracentrifugation to isolate microvesicles. The presence of microvesicle-associated FasL was studied by Western blots, blocking with anti-Fas reagents, and immunoelectron microscopy. Biological activities of microvesicles were tested including the ability to induce apoptosis of Jurkat and T-cell blasts. Semiquantitative analysis of FasL in microvesicles was correlated with caspase-3 activity, DNA fragmentation, cytochrome c release, loss of mitochondrial membrane potential, and TCR-ζ chain expression in lymphocytes.

Results: FasL-positive (FasL+) microvesicles were detected in sera of 21 of 27 patients. Microvesicles contained 42 kDa FasL. These microvesicles induced caspase-3 cleavage, cytochrome c release, loss of mitochondrial membrane potential, and reduced TCR-ζ chain expression in target lymphocytes. Biological activity of the FasL+ microvesicles was partially blocked by ZB4 anti-Fas monoclonal antibody. Microvesicle-associated FasL levels correlated with the patients' tumor burden and nodal involvement.

Conclusion: Sera of patients with active oral squamous cell carcinoma contain FasL+ microvesicles, which induce the receptor and mitochondrial apoptotic pathways in Jurkat and activated T cells.

Apical cell membranes are shed into urine from injured podocytes: a novel phenomenon of podocyte injury

Previously it was shown that urine from patients with nephritis contains podocytes and their fragments (podocalyxin [PCX]-positive granular structures [PPGS]), reflecting the degree of podocyte injury. The present study was designed to trace PPGS to their origin. Urine samples and renal biopsy specimens from 53 children with nephrotic syndrome and nephritis were examined immunohistochemically. Immunofluorescence studies of kidney sections using an anti-PCX antibody demonstrated that PPGS originated from the glomerulus and flowed into the tubular lumen. Electron microscopic examination revealed that PPGS originated from microvillous or vesicle-like structures on injured podocytes in the glomerulus. For examining the origin of the PPGS, apical, slit-diaphragmatic, and basal portions of the podocytes were specifically stained, revealing that PPGS are composed primarily of apical podocyte membranes. Several newly developed antibodies that are reactive with various segments of the PCX molecule were used to analyze more detailed membrane structures, and it was found that PPGS contained intact PCX molecules, indicating that cell membrane structures are excreted in urine. The quantification of PCX content and podocyte numbers revealed that urinary sediment PCX (u-sed-PCX) content per urinary podocyte was much higher than PCX content per podocyte from isolated glomeruli of normal controls, suggesting that u-sed-PCX are derived from sources other than just the cell debris of detached podocytes. Analysis of the correlation between u-sed-PCX and renal histology revealed that the presence of PPGS reflects acute glomerular injury. In conclusion, podocyte apical cell membranes are shed into the urine from injured podocytes, indicating a previously unrecognized manifestation of podocyte injury.

The microvesicle as a vehicle for EMMPRIN in tumor-stromal interactions

EMMPRIN is a transmembrane glycoprotein expressed at high levels by tumor cells. It has been identified as a tumor-derived factor that can stimulate matrix metalloproteinase expression in fibroblasts and hence facilitate tumor invasion and metastasis. Recent studies have shown that full-length EMMPRIN is released by tumor cells, but the mechanism of release remains unclear. Here, we show that EMMPRIN is released from the surface of NCI-H460 cells via microvesicle shedding. However, these vesicles are unstable and rapidly break down to release bioactive EMMPRIN. Although microvesicle shedding has been considered a constitutive process in tumor cells, our data show that it can be amplified upon cell exposure to PMA, elucidating at least one signalling cascade responsible for EMMPRIN release. This pathway is dependent on protein kinase C, calcium mobilization and mitogen-activated protein kinase kinase (MEK 1/2). Thus, the results outline a novel form of tumor-stromal interaction in which extracellular matrix degradation by fibroblasts is controlled through the microvesicular release of EMMPRIN from tumor cells.

Shedding of the matrix metalloproteinases MMP-2, MMP-9, and MT1-MMP as membrane vesicle-associated components by endothelial cells

Production of matrix-degrading proteases, particularly matrix metalloproteinases (MMPs), by endothelial cells is a critical event during angiogenesis, the process of vessel neoformation that occurs in normal and pathological conditions. MMPs are known to be highly regulated at the level of synthesis and activation, however, little is known about the regulation of MMP secretion by endothelial cells. We found that cultured human umbilical vein endothelial cells shed vesicles (300 to 600 nm) originating from localized areas of the cell plasma membrane, as revealed by ultrastructural analysis. Normal and reverse zymography, Western blot, and immunogold analyses of the vesicles showed two gelatinases, MMP-2 and MMP-9, in both the active and proenzyme forms, the MT1-MMP proenzyme located on the external side of the vesicle membrane and the two inhibitors TIMP-1 and TIMP-2. Serum and the angiogenic factors, fibroblast growth factor-2 and vascular endothelial growth factor, stimulated the shedding of MMPs as vesicle components. Shedding the vesicle was rapid, as it was already completed after 4 hours. Addition of shed vesicles to human umbilical vein endothelial cells resulted in autocrine stimulation of invasion through a layer of reconstituted basement membrane (Matrigel) and cord formation on Matrigel. We conclude that endothelial cells shed MMP-containing vesicles and this may be a mechanism for regulating focalized proteolytic activity vital to invasive and morphogenic events during angiogenesis.

Vesicle-associated urokinase plasminogen activator promotes invasion in prostate cancer cell lines

The ability of a cell to modify the extracellular matrix is important in several pathophysiological alterations including tumorigenesis. Cell transformation is accompanied by changes in the surrounding stroma as a result of the action of specific proteases such as the urokinase plasminogen activator (uPA), which has been associated with invasive potential in many tumor types. In this study, we analyzed the release of vesicle-associated uPA by the aggressive prostatic carcinoma cell line PC3 and the implications of this release for the invasive behaviour of prostatic tumor cells. Zymography and Western blot analysis revealed the presence of vesicle-associated uPA in the high-molecular weight form. Vesicles adhered to and degraded both collagen IV and reconstituted basal membrane (Matrigel), and plasminogen enhanced the degradation in a dose-dependent manner. Addition of membrane vesicles shed by PC3 cells to cultures of the poorly invasive prostate cancer cell line LnCaP enhanced the adhesive and invasive capabilities of the latter, suggesting a mechanism involving substrate recognition and degradation. Together, these findings indicate that membrane vesicles can promote tumor invasion and point to the important role of vesicle-associated uPA in the extracellular compartment.

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

The in vitro release of matrix-degrading proteinases from breast cancer cells is associated in part with shed membrane vesicles. To determine whether shed vesicles might play a similar role in ovarian cancer cells, we analyzed the shedding phenomenon in vivo and in vitro as well as the enzymatic content of their vesicles. This is the first time that an immunoelectron microscopical analysis revealed membrane vesicles carrying tumor-associated antigen alpha-Folate Receptor (alpha-FR), circulating in biological fluids (ascites and serum) of an ovarian carcinoma patient. These vesicles were trapped in a fiber network with characteristic fibrin periodicity. An ovarian cancer cell line (CABA I) established from ascitic fluid cells of this patient, grew in Matrigel and formed tubular structures suggesting invasive capability. Immunofluorescence analysis demonstrated strong cytoplasmic staining of CABA I cells with anti-matrix metalloproteinase-9 (MMP-9) and anti-urokinase-type plasminogen activator (uPA) antibodies. CABA I cells shed membrane vesicles, which were morphologically similar to those identified in vivo, as determined by electron microscopy. Gelatin zymography of vesicles isolated both in vivo and in vitro revealed major gelatinolytic bands of the MMP family, identified as the zymogen and active forms of gelatinase B (MMP-9) and gelatinase A (MMP-2). By casein-plasminogen zymography we observed high-molecular weight (HMW)-uPA and plasmin bands. Incubation of purified vesicles from CABA I cells with Matrigel led to cleavage of Matrigel components. Taken together, our results point to a possible role of shed vesicles, both in vivo and in vitro, in proteolysis that mediates invasion and spread of ovarian epithelial carcinoma cells.

Membrane vesicles shed into the extracellular medium by human breast carcinoma cells carry tumor-associated surface antigens

We have compared the pattern of surface antigen expression, as detected by monoclonal antibodies (mAbs), in plasma membranes vs shed membrane vesicles of two human breast carcinoma cell lines, MCF-7 and 8701-BC. Antigen expression was detected on cells by immunofluorescence (IF) analysis, whilst, due to their small dimensions, the same technique was not applicable to vesicles. For these structures dot-blot analysis and immunoelectron microscopy (IEM) were employed. When applicable, both cell membranes and membrane vesicles were immunoprecipitated and the precipitate (IP) was analyzed by SDS-PAGE. Cells of both lines expressed HLA class I antigens, epithelial cytokeratins, beta 1 integrins, CEA and the glycoprotein detected by mAb 19.9, but only MCF-7 cells expressed Lewis Y, episialin and globo-H antigens and only 8701-BC cells expressed folate receptor. Membrane vesicles of both cell lines appeared to be rich in beta 1, alpha 3 and alpha 5 integrin chains, expressed HLA class I antigens and carried most of the plasma membrane antigens found in the cell membranes. Overall we have analyzed 17 antigens on the two cell lines and on their vesicles. The results obtained for cells (IF and IP) and those for vesicles (dot-blot and IP) were generally concordantly positive or concordantly negative. We obtained a total of 26 clearly concordant combinations on 34 analyses. In three cases we found discordant results, whereas in the remaining combinations we observed slight reactivity and we found difficulties in determining concordance. Discordant results concerned the expression of the following antigens: folate receptors, which were clearly expressed in 8701-BC cells but not detected by dot-blot analysis or IEM on their shed membrane vesicles; neu (c-erb-B2) receptor found in MCF-7 cell membranes but not in their vesicles; and the globo-H antigen recognized by mAb MBr1, detected at low levels on 8701-BC plasma membranes but undetectable on their membrane vesicles. Like vesicles shed in vitro by cultured cells, the vesicles shed in vivo by human breast carcinoma cells could be tagged with several antibodies against tumor-associated antigens. The vesicles shed in vivo were found in association with a fiber network. Some of the fibers had the characteristic fibrin periodicity. These data suggest that tumor markers detected in the circulation of carcinoma patients, at least in part, are carried by shed membrane vesicles. Moreover the observation that membrane vesicles carry both tumor-associated antigens and HLA class I molecules indicate that these structures could in principle present antigens to the immune system.(ABSTRACT TRUNCATED AT 400 WORDS)

Streptolysin-O induces release of glycosylphosphatidylinositol-anchored alkaline phosphatase from ROS cells by vesiculation independently of phospholipase action

Streptolysin-O (SLO), a cholesterol-binding agent, was used for studies on the release of glycosylphosphatidylinositol (GPI)-anchored alkaline phosphatase (AP) from ROS cells. Treatment of cells with SLO resulted in a time- and concentration-dependent release of AP into the extracellular medium. This release was potentiated by Ca2+ and bovine serum, but not by GPI-specific phospholipase D (GPI-PLD) purified from bovine serum. The released AP distributed to the detergent phase after Triton X-114 phase separation. This result suggested that the released AP contained an intact GPI anchor, and thus both proteolysis and anchor degradation by anchor-specific hydrolases, including GPI-PLD, as the potential mechanisms for SLO-mediated AP release were ruled out. The released AP sedimented at 100,000 g. A substantial amount of lipids was detected in the 100,000 g pellet. Cholesterol and sphingomyelin were enriched in SLO-released material, compared with intact cells. These results were consistent with vesiculation as the mechanism for SLO induction of AP release. Two other cholesterol-binding agents, saponin and digitonin, were also able to release AP, possibly by a similar vesiculation mechanism, whereas others, including nystatin, filipin and beta-escin, failed to elicit any AP release. Eight GPI-anchored proteins were identified in ROS cells, and all were substantially enriched in the vesicles released by SLO. Taken together, these results do not provide any support for the hypothesis that the clustering of GPI-anchored proteins in the plasma membrane is responsible for their resistance to GPI-PLD cleavage.

Intracellular regulation of the production and release of human erythroid-directed lymphokines

Erythroid burst-promoting activity (BPA) is released from B lymphocytes in soluble (sBPA) and membrane-bound (mBPA) forms. To study intracellular processes involved in production of these physically separable factors, we measured their time course release into serum-free medium from B cells that were pulse-exposed for 5-240 min to nonmitogenic base medium or inhibitors of energy-dependent metabolism (2,4-dinitrophenol, sodium azide, and 2-deoxy-D-glucose), transcription and translation (actinomycin D and cycloheximide), replicative DNA synthesis (cytosine arabinoside), or posttranslational processing (monensin). mBPA and sBPA were initially detectable after 1 and 2 h, respectively. Maximum cumulative levels of 8 +/- 0.6 and 9 +/- 1.0 U/ml, respectively, were reached after 8 h. In contrast, cumulative mBPA and sBPA levels in medium prepared from cells treated with metabolic inhibitors were reduced by up to 90%. Both surface exfoliation and mBPA expression by intact plasma membranes were diminished. Whereas pulse-exposure to cytosine arabinoside had no effect, treatment with actinomycin D or cycloheximide abolished BPA expression. Exposure to monensin reduced mBPA and sBPA levels to zero in a concentration-and time-dependent fashion. We conclude that production and release of BPA is an energy-dependent process, requiring mRNA synthesis and translation and posttranslational remodeling of the protein but not replicative DNA synthesis.