Lung cancer secreted microvesicles: underappreciated modulators of microenvironment in expanding tumors

Tumor-derived microvesicles induce proangiogenic phenotype in endothelial cells via endocytosis

Background

Increasing evidence indicates that tumor endothelial cells (TEC) differ from normal endothelial cells (NEC). Our previous reports also showed that TEC were different from NEC. For example, TEC have chromosomal abnormality and proangiogenic properties such as high motility and proliferative activity. However, the mechanism by which TEC acquire a specific character remains unclear. To investigate this mechanism, we focused on tumor-derived microvesicles (TMV). Recent studies have shown that TMV contain numerous types of bioactive molecules and affect normal stromal cells in the tumor microenvironment. However, most of the functional mechanisms of TMV remain unclear.

Methodology/Principal Findings

Here we showed that TMV isolated from tumor cells were taken up by NEC through endocytosis. In addition, we found that TMV promoted random motility and tube formation through the activation of the phosphoinositide 3-kinase/Akt pathway in NEC. Moreover, the effects induced by TMV were inhibited by the endocytosis inhibitor dynasore. Our results indicate that TMV could confer proangiogenic properties to NEC partly via endocytosis.

Conclusion

We for the first time showed that endocytosis of TMV contributes to tumor angiogenesis. These findings offer new insights into cancer therapies and the crosstalk between tumor and endothelial cells mediated by TMV in the tumor microenvironment.

Human ether-a-go-go-related gene K+ channels regulate shedding of leukemia cell-derived microvesicles

Microvesicles (MVs) are released by various cancer cells, including leukemia cells. They can "hijack" membrane components from their parental cells and exert pleiotropic effects on tumor progression. Human ether-a-go-go-related gene (hERG1) K(+) channels are highly expressed in cancer cells and appear of exceptional importance in favoring cancer development. Given the attributes of MVs and hERG1 K(+) channels in disease progression, we investigated the putative relationship between hERG1 K(+) channels and MVs in leukemia. The protein content of MVs isolated from K562 cell supernatants was significantly higher than that from HL-60 cells. The molecular profile of these MVs showed that in addition to the myeloid lineage antigen (CD11b), MVs contained hERG1 K(+) channels. Interestingly, inhibition of hERG1 K(+) channels rapidly reduced MV fractions in supernatants. Furthermore, MVs created positive feedback loops to facilitate leukemogenesis. Upon exposure to MVs, the plasma membrane expression of hERG1 protein was in turn up-regulated, the migration of leukemia cells was significantly increased, and the adhesion of leukemia cells to human umbilical vein endothelial cells (HUVECs) was markedly enhanced. Importantly, hERG1 K(+) channel inhibitor E-4031 impaired these effects. We conclude that leukemia cell-derived MVs can "hijack" the plasma membrane hERG1 K(+) channels, which regulate the release of MVs and their biological effects upon leukemia cells.

Microvesicles in health and disease

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

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.

Marrow cell genetic phenotype change induced by human lung cancer cells

Microvesicles have been shown to mediate varieties of intercellular communication. Work in murine species has shown that lung-derived microvesicles can deliver mRNA, transcription factors, and microRNA to marrow cells and alter their phenotype. The present studies evaluated the capacity of excised human lung cancer cells to change the genetic phenotype of human marrow cells. We present the first studies on microvesicle production by excised cancers from human lung and the capacity of these microvesicles to alter the genetic phenotype of normal human marrow cells. We studied 12 cancers involving the lung and assessed nine lung-specific mRNA species (aquaporin, surfactant families, and clara cell-specific protein) in marrow cells exposed to tissue in co-culture, cultured in conditioned media, or exposed to isolated lung cancer-derived microvesicles. We assessed two or seven days of co-culture and marrow which was unseparated, separated by ficoll density gradient centrifugation or ammonium chloride lysis. Under these varying conditions, each cancer derived from lung mediated marrow expression of between one and seven lung-specific genes. Microvesicles were identified in the pellet of ultracentrifuged conditioned media and shown to enter marrow cells and induce lung-specific mRNA expression in marrow. A lung melanoma and a sarcoma also induced lung-specific mRNA in marrow cells. These data indicate that lung cancer cells may alter the genetic phenotype of normal cells and suggest that such perturbations might play a role in tumor progression, tumor recurrence, or metastases. They also suggest that the tissue environment may alter cancer cell gene expression.

Role of exosomes released by chronic myelogenous leukemia cells in angiogenesis

Our study is designed to assess if exosomes released from chronic myelogenous leukemia (CML) cells may modulate angiogenesis. We have isolated and characterized the exosomes generated from LAMA84 CML cells and demonstrated that addition of exosomes to human vascular endothelial cells (HUVEC) induces an increase of both ICAM-1 and VCAM-1 cell adhesion molecules and interleukin-8 expression. The stimulation of cell-cell adhesion molecules was paralleled by a dose-dependent increase of adhesion of CML cells to a HUVEC monolayer. We further showed that the treatment with exosomes from CML cells caused an increase in endothelial cell motility accompanied by a loss of VE-cadherin and β-catenin from the endothelial cell surface. Functional characterization of exosomes isolated from CML patients confirmed the data obtained with exosomes derived from CML cell line. CML exosomes caused reorganization into tubes of HUVEC cells cultured on Matrigel. When added to Matrigel plugs in vivo, exosomes induced ingrowth of murine endothelial cells and vascularization of the Matrigel plugs. Our results suggest for the first time that exosomes released from CML cells directly affect endothelial cells modulating the process of neovascularization.

Leukocyte-mediated cell dissemination and metastasis: findings from multiple types of human tumors

Our previous studies revealed that leukocyte infiltration could trigger human breast and prostate tumor invasion through focal disruptions of the tumor capsule, which selectively favors monoclonal proliferation of tumor progenitors or a biologically more aggressive cell clone overlying the focal disruptions. Our current study, involving multiple types of human tumors, further shows that leukocyte infiltration could also trigger tumor metastasis through the following pathways: [1] more leukocytes migrate to focally disrupted tumor capsules, which forms leukocyte aggregates surrounding newly formed tumor cell clusters, [2] the physical movement of leukocytes into proliferating tumor cells disrupts the intercellular junctions and cell-surface adhesion molecules, causing the disassociation of tumor cells from the tumor core, [3] leukocytes are conjoined with some of these tumor cells through plasma membrane fusion, creating tumor cell-leukocyte chimeras (TLCs), and [4] the leukocyte of TLCs impart migratory capacity to associated tumor cell partners, physically dragging them to different tissue sites. Our findings suggest a novel pathway for tumor cell dissemination from the primary sites and the subsequent journey to new sites. Our findings also provide a unique explanation for the cellular mechanism of leukocytes on tumor invasion and metastasis. If confirmed, our hypothesis and technical approach may significantly facilitate early detection and intervention of tumor invasion and metastasis.

Tumor exploits alternative strategies to achieve vascularization

Neoangiogenesis is crucial for solid tumor growth and invasion, as the vasculature provides metabolic support and access to the circulation. Current antiangiogenic therapies have been designed on the assumption that endothelial cells forming the tumor vasculature exhibit genetic stability. Recent studies demonstrate that this is not the case. Tumor endothelial cells possess a distinct phenotype, differing from normal endothelial cells at both molecular and functional levels. This challenges the concept that tumor angiogenesis exclusively depends on normal endothelial cell recruitment from the surrounding vascular network. Indeed, recent data suggest alternative strategies for tumor vascularization. It has been reported that tumor vessels may derive from an intratumor embryonic-like vasculogenesis. This condition might be due to differentiation of normal stem and progenitor cells of hematopoietic origin or resident in tissues. Cancer stem cells may also participate in tumor vasculogenesis by virtue of their stem and progenitor cell properties. Finally, normal endothelial cells might be reprogrammed to a proangiogenic or dedifferentiated phenotype by genetic information transmitted from the tumor trough apoptotic bodies, or following mRNA and microRNA transfer by exosomes and microvesicles. In this review, we discuss the different aspects of intratumor angiogenesis and vasculogenesis, the known mechanisms involved, and the possible implications for the response to antiangiogenic therapy.

A method to assess the migration properties of cell-derived microparticles within a living tissue

BACKGROUND

Cells undergoing activation or apoptosis exhibit plasma membrane changes, leading to the formation of shed vesicles (microparticles, MP). Although their effects on recipient cells in vitro, and their ability to support inflammatory or thrombotic events in the circulation have been studied, the spreading of such vesicles in tissues is still elusive. Our aim was to set up a method to examine the behavior of these vesicles in vivo.

METHODS

We examined the persistence of green-fluorescent microparticles (fMP), prepared after Ca2+ ionophore activation (iono-fMP) or apoptogenic treatment (eto-fMP) of human Jurkat T lymphoblastic or non-hematopoietic embryonic kidney (HEK) cell lines, following injection in zebrafish embryos 2h after egg fertilization.

RESULTS

One hour post-injection, iono-fMP issued from both cell types formed a fluorescent dispersal in the intercellular space of embryos. In contrast, eto-fMP or MP deprived of sialic acid at their membrane, gathered together at the site of injection.

CONCLUSIONS

We propose a method characterizing the abilities of MP to spread in the intercellular space. We showed that MP produced by apoptosis of T cells and those deprived of sialic acid at their membrane do not diffuse within the living cells. On the contrary, MP shed upon calcium induced activation of T and HEK cells, diffuse at a distance and spread in the intercellular space.

GENERAL SIGNIFICANCE

The fate of injected MP relies on the type of induction rather than the cell species and results provide a model to test the ability of vesicles to interact locally or to spread outside of the site of production.

The role of microvesicles in malignancies

Microvesicles are membrane-covered cell fragments whose size varies between 30 and 1,000 nm. They are generated by all cell types, constituvely and in response to activation signals. Their importance in intercellular communication has been only recently discovered. They seem to enhance the potential of information transfer between cells, displaying a large number of proteins and lipids as membrane constituents and as components of the inner vesicular content. The content reflects the phenotype of the donor cell and allows the identification of the microvesicular origine as well. Complex "packets" of molecules are transmitted to the target cells this way, modifying their cellular physiology. Additionally, epigenetic changes may be induced by transmitted DNA and RNAs, that have also been identified in these vesicles. The vesicles can act in close and far distances as well. Microvesicles have been implicated in several physiological and pathological processes. There is an increasing evidence, that they play a pivotal role in tumorigenesis. Vesicles shedding from tumor cells reflect the special potential of the tumor for survival and expansion, independently from cell-to-cell contact. Tumor derived vesicles are fully equipped to facilitate the escape of tumor cells from immune surveillance through their protein and RNA content, at the same time they are involved in the establishment of an optimal environment for newly formed and metastatic tumor cells, influencing angiogenesis and the reorganization of the extracellular matrix. As immune cells, endothels, platelets and stem cells also release microvesicles, a multilevel communication network draws up, allowing a complex interplay between the cells. The concentration of tumor derived vesicles increases in blood plasma and other body fluids with the progression of the disease; therefor they may serve as prognostic markers. The microvesicular approach can offer new perspectives: interfering with the formation, release and propagation of these vesicles, they can be considered as new targets in tumor therapy.

Exosome/microvesicle-mediated epigenetic reprogramming of cells

Microvesicles (MVs) are released by different cell types and may remain in the extracellular space in proximity of the cell of origin or may enter the biological fluids. MVs released by tumor cells are detectable in patients with cancer and their number in the circulation correlates with poor prognosis. Recent studies demonstrated that MVs may act as mediator of cell-to-cell communication thus ensuring short- and long-range exchange of information. Due to their pleyotropic effects, MVs may play a role in the prothrombotic state associated with cancer as well as in cancer development and progression. It has been recently shown that MVs may induce epigenetic changes in target cells by transferring genetic information. This finding suggests that tumor and stromal cells may talk each other via MVs to establish a favorable tumor niche and to promote tumor growth, invasiveness and progression. Moreover, MVs contain genetic material under the form of mRNA and microRNA, that may allow an easy screening for cancer genetic markers and offer new diagnostic and prognostic information. This review presents an overview of the many biological actions of MVs and of the potential role of MV-mediated exchange of genetic information among cells in tumor biology.

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.

Microvesicle induction of prostate specific gene expression in normal human bone marrow cells

PURPOSE

Transfer of genetic material from cancer cells to normal cells occurs via microvesicles. Cell specific phenotypes can be induced in normal cells by the transfer of material in microvesicles, leading to genetic changes. We report the identification and expression of prostate specific genes in normal human marrow cells co-cultured with human prostate cancer cells.

MATERIALS AND METHODS

We harvested prostate tissue from 11 patients with prostate cancer. In 4 cases prostate tissue was co-cultured across from human marrow for 2 or 7 days but separated from it by a 0.4 μM polystyrene membrane. In 5 cases conditioned medium from patient cancer tissue was collected and ultracentrifuged, and microvesicles were collected for co-culture (3) and vesicle characterization (3). Explanted human marrow was harvested from cultures and RNA extracted. Real-time reverse transcriptase-polymerase chain reaction was done for select prostate specific genes.

RESULTS

Marrow exposed to human prostate tumor or isolated microvesicles in culture in 4 and 3 cases, respectively, showed at least 2-fold or greater prostate gene expression than control marrow. In 1 case in which normal prostate was co-cultured there were no prostate gene increases in normal marrow.

CONCLUSIONS

Prostate cancer tumor cells co-cultured with human bone marrow cells induce prostate specific gene expression. The proposed mechanism of transfer of genetic material is via microvesicles. This represents an opportunity for novel therapeutic agents, such as antibodies, to block microvesicle release from cancer cells or for agents that may block cells from accepting microvesicles.

Microvesicles derived from adult human bone marrow and tissue specific mesenchymal stem cells shuttle selected pattern of miRNAs

BACKGROUND

Cell-derived microvesicles (MVs) have been described as a new mechanism of cell-to-cell communication. MVs after internalization within target cells may deliver genetic information. Human bone marrow derived mesenchymal stem cells (MSCs) and liver resident stem cells (HLSCs) were shown to release MVs shuttling functional mRNAs. The aim of the present study was to evaluate whether MVs derived from MSCs and HLSCs contained selected micro-RNAs (miRNAs).

METHODOLOGY/PRINCIPAL FINDINGS

MVs were isolated from MSCs and HLSCs. The presence in MVs of selected ribonucleoproteins involved in the traffic and stabilization of RNA was evaluated. We observed that MVs contained TIA, TIAR and HuR multifunctional proteins expressed in nuclei and stress granules, Stau1 and 2 implicated in the transport and stability of mRNA and Ago2 involved in miRNA transport and processing. RNA extracted from MVs and cells of origin was profiled for 365 known human mature miRNAs by real time PCR. Hierarchical clustering and similarity analysis of miRNAs showed 41 co-expressed miRNAs in MVs and cells. Some miRNAs were accumulated within MVs and absent in the cells after MV release; others were retained within the cells and not secreted in MVs. Gene ontology analysis of predicted and validated targets showed that the high expressed miRNAs in cells and MVs could be involved in multi-organ development, cell survival and differentiation. Few selected miRNAs shuttled by MVs were also associated with the immune system regulation. The highly expressed miRNAs in MVs were transferred to target cells after MV incorporation.

CONCLUSIONS

This study demonstrated that MVs contained ribonucleoproteins involved in the intracellular traffic of RNA and selected pattern of miRNAs, suggesting a dynamic regulation of RNA compartmentalization in MVs. The observation that MV-highly expressed miRNAs were transferred to target cells, rises the possibility that the biological effect of stem cells may, at least in part, depend on MV-shuttled miRNAs. Data generated from this study, stimulate further functional investigations on the predicted target genes and pathways involved in the biological effect of human adult stem cells.

Microvesicle entry into marrow cells mediates tissue-specific changes in mRNA by direct delivery of mRNA and induction of transcription

OBJECTIVE

Microvesicles have been shown to mediate intercellular communication. Previously, we have correlated entry of murine lung-derived microvesicles into murine bone marrow cells with expression of pulmonary epithelial cell-specific messenger RNA (mRNA) in these marrow cells. The present studies establish that entry of lung-derived microvesicles into marrow cells is a prerequisite for marrow expression of pulmonary epithelial cell-derived mRNA.

MATERIALS AND METHODS

Murine bone marrow cells cocultured with rat lung, but separated from them using a cell-impermeable membrane (0.4-microm pore size), were analyzed using species-specific primers (for rat or mouse).

RESULTS

These studies revealed that surfactant B and C mRNA produced by murine marrow cells were of both rat and mouse origin. Similar results were obtained using murine lung cocultured with rat bone marrow cells or when bone marrow cells were analyzed for the presence of species-specific albumin mRNA after coculture with rat or murine liver. These studies show that microvesicles both deliver mRNA to marrow cells and mediate marrow cell transcription of tissue-specific mRNA. The latter likely underlies the longer-term stable change in genetic phenotype that has been observed. We have also observed microRNA in lung-derived microvesicles, and studies with RNase-treated microvesicles indicate that microRNA negatively modulates pulmonary epithelial cell-specific mRNA levels in cocultured marrow cells. In addition, we have also observed tissue-specific expression of brain, heart, and liver mRNA in cocultured marrow cells, suggesting that microvesicle-mediated cellular phenotype change is a universal phenomena.

CONCLUSION

These studies suggest that cellular systems are more phenotypically labile than previously considered.

Future directions in the field of endometrial cancer research: the need to investigate the tumor microenvironment

Endometrial cancer is the most commonly diagnosed gynecologic malignancy in the United States. In 2008, approximately 40,000 cases were newly diagnosed. Although the majority of these cancers are curable by means of hysterectomy and radiotherapy, a subset of endometrial tumors exhibits an aggressive phenotype characterized by lymphovascular invasion, high histological grade, and myometrial invasion, leading to poor prognosis. The mechanisms involved in this aggressive transformation are largely unknown, however, interactions between the primary tumor mass and the surrounding stroma likely play a role in this transformation. Despite the fact that research in other common malignancies has elucidated important associations between stromal protein expression and invasion, these mechanisms have been poorly explored in the area of endometrial cancer. In fact, few investigations have been conducted in the area of tumor microenvironment for endometrial tumors. Invasion and metastasis are two primary reasons for treatment failure related to endometrial cancer. Expression of stromal-derived proteins can potentially serve as biomarkers of aggressive disease as well as biomarkers for remission monitoring. In order to study how expression of these proteins relates to the prognosis of endometrial cancer, these proteins need to be explored in large sets of existing data and/or tissue banks. In this paper, we briefly review the role of three stromal related pathways, SDF-1alpha/CXCR4, HGF/c-Met, and VEGF-A in endometrial cancer prognosis as an overview of the literature. We report that the role of SDF-1alpha/CXCR4 and HGF/c-Met in endometrial cancer prognosis remains unclear, whereas the evidence pertaining to VEGF indicates that overexpression is involved in tumor growth and metastasis. Finally, we would like to highlight the need to explore stromal proteins as a potential tool for the detection of aggressive endometrial tumors and explore some of the molecular approaches that can be utilized in the exploration of the tumor environment.