Download Exosomes: From biogenesis and secretion to biological function

Immunology Letters 107 (2006) 102–108
Short review
Exosomes: From biogenesis and secretion to biological function
Sascha Keller a , Michael P. Sanderson a , Alexander Stoeck a,b , Peter Altevogt a,∗
a
German Cancer Research Center (DKFZ), Tumor Immunology Program, D010/TP3, Im Neuenheimer Feld 280, D-69120 Heidelberg, Germany
b Departments of Pediatrics and Molecular and Integrative Physiology, University of Michigan, Ann Arbor, MI, United States
Received 13 September 2006; accepted 21 September 2006
Available online 17 October 2006
Abstract
Exosomes are small microvesicles that are released from late endosomal compartments of cultured cells. Recent work has shown that exosomelike vesicles are also found in many body fluids such as blood, urine, ascites and amnionic fluid. Although the biological function of exosomes is
far from being fully understood, exosomes may have general importance in cell biology and immunology. The present review aims to address some
of the facets of exosome research with particular emphasis on the immunologist’s perspective: (i) exosomes as a novel platform for the ectodomain
shedding of membrane proteins by ADAMs and (ii) recent findings on the role of exosomes in tumor biology and immune regulation.
© 2006 Elsevier B.V. All rights reserved.
Keywords: Exosomes; Membrane vesicles
1. Introduction
Exosomes are small microvesicles released from cells, and
have been the subject of intensive research in recent years.
Originally described as a mechanism for the removal of cell
surface molecules in reticulocytes, the pioneering work of
several labs showed the importance of exosomes for general cell biology and in particular for the immune system.
The reader is also encouraged to refer to other excellent
reviews on exosomes biology that have recently been published
[1,2].
1.1. The endosomal pathway, exosome biogenesis and
secretion
Eukaryotic cells stay in contact with the environment by
receiving signals such as cytokines or chemokines, the uptake
of nutrients and the secretion of proteins into the extracellular
space. For uptake and secretion, each cell has a complex network of membranes inside the cell. Using these compartments,
cells not only take up macromolecules from the exterior environment (endocytosis) but also release newly-synthesized proteins
or carbohydrates (exocytosis).
∗
Corresponding author. Tel.: +49 6221 423714; fax: +49 6221 423791.
E-mail address: [email protected] (P. Altevogt).
0165-2478/$ – see front matter © 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.imlet.2006.09.005
1.1.1. Exocytosis
There are different mechanisms by which cells release proteins into the extracellular space. The most common process
is the release of large biomolecules through the plasma membrane by a process called exocytosis. In multicellular organisms,
exocytosis has a regulatory or signaling function. According to
the mechanism of release, exocytosis can be divided into two
different modes: (1) constitutive (non-calcium-triggered) or (2)
regulated (calcium-triggered) exocytosis. Constitutive exocytosis occurs in all cells and functions to either secrete extracellular
matrix components or to incorporate newly-synthesized proteins
into the plasma membrane after fusion with transport vesicles.
Regulated exocytosis is particularly important in neurological
signaling, where synaptic vesicles fuse with the membrane at
the synaptic cleft and induce nerve impulses [3,4].
Fusion of multivesicular bodies (MVBs) with the plasma
membrane and the subsequent release of their cargo represents
another mechanism of exocytosis. Since the development of
these membrane vesicles has an endocytic origin, this mechanism is a secretion process of the endosomal system. Other
components of the endosomal system include endocytic vesicles,
early endosomes, late endosomes and lysosomes. Endocytic
vesicles arise through clathrin- or non-clathrin-mediated endocytosis at the plasma membrane and are transported to early
endosomes. Late endosomes develop from early endosomes by
acidification, changes in their protein content and their tendency
to fuse with vesicles or more generally with other membranes
S. Keller et al. / Immunology Letters 107 (2006) 102–108
[5]. These different vesicles can be distinguished by their physical shape and cellular location. In particular, early endosomes
display a tubular appearance and are located at the outer margin of the cell, whereas late endosomes are spherical in shape
and are located close to the nucleus. The key step in the formation of MVBs from late endosomes is reversed budding. During
this process, the limiting membrane of late endosomes buds into
their lumen, which results in a continuous enrichment of internal
luminal vesicles [6].
1.1.2. Fates of vesicles within MVBs: degradation versus
exosome secretion
The fusion of a MVB with the lysosome results in the degradation of the vesicle-associated proteins and lipids. This process
allows the cell to remove transmembrane proteins as well as
excessive membranes [7,8]. The degradation of transmembrane
proteins plays an important role in the down-regulation of activated cell surface receptors. For example, many activated growth
factor receptors become internalized by ligand-induced endocytosis and are sorted into the luminal vesicles of the MVB
to then undergo further degradation in the lysosome. Normal
internalization without degradation is in some cases insufficient in diminishing signaling by the receptors. As depicted in
Fig. 1A, even following internalization into early endosomes, the
C-terminal phosphorylated docking sites and kinase domain of
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the activated epidermal growth factor receptor (EGFR/ErbB1)
retain access to the cytosol where further signal transduction
can occur. However, sorting into MVBs isolates the activated
receptors from the cytosol and thereby from binding partners.
Interestingly, mice carrying a mutation resulting in defective
sorting of the EGFR into MVBs have a higher risk of developing tumors [9,10].
In dendritic cells (Fig. 1B), MVBs play a critical role as
a storage compartment for MHC class II molecules and their
associated invariant chain [11,12]. In this case, the MVB compartment is called the MHC class II compartment (MIIC). Following internalization of antigen by dendritic cells, the invariant chain is removed and the MHC complex becomes loaded
with the antigen peptide. These internal vesicles of the MIIC
then fuse with the plasma membrane resulting in the presentation of antigen-loaded MHC class II molecules on the cell
surface.
MVBs can also fuse with the plasma membrane leading
to the release of the internal vesicles into the extracellular
space (Fig. 1C). The released vesicles are then called exosomes.
Many cell types release exosomes via this mechanism including hematopoietic cells, reticulocytes, B- and T-lymphocytes,
dendritic cells, mast cells, platelets, intestinal epithelial cells,
astrocytes, neurons and tumor cells [13–21]. Depending on
their origin, exosomes have previously been named dexosomes
Fig. 1. Different fates and functions of internalized vesicles. (A) Lysosomal degradation: some cell surface receptors such as the EGFR are internalized following
ligand binding and activation. Degradation of the receptor following trafficking to lysosomes functions to down-regulate receptor signaling. (B) MHC class II storage
compartment: antigens taken up into vesicles are degraded into shorter peptides which bind to MHC class II molecules in the MHC class II storage compartment
(MCII). After delivery of the loaded MHC complexes to the cell surface, they can be recognized by CD4+ T cells. (C) Release of exosomes: multivesicular bodies
can fuse with the plasma membrane and release internal vesicles (exosomes) into the extracellular environment.
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S. Keller et al. / Immunology Letters 107 (2006) 102–108
(dendritic cell-derived exosomes) or texosomes (T-cell exosomes or tumor exosomes).
1.1.3. Sorting into the MVB and exosomes
Only very little is know about the sorting signals which
are responsible for the sorting of proteins into vesicles within
MVBs, which can be subsequently released as exosomes. As
mentioned earlier, binding of a ligand to cell surface receptors
results in receptor activation and initiation of signal transduction pathways. The fate of different activated receptors can be
highly variable. Some receptors pass multiple cycles of uptake
and recycling to the plasma membrane, whilst others, which
are destined for degradation, are directly transported to lysosomes. In the case of most cellular transport mechanisms, such
as nuclear translocation, proteins intended for a specific compartment display a characteristic amino acid sequence, which
acts as a sorting signal [22]. For the recruitment of proteins into
MVBs, there is currently no common sorting signal known for
all cells. However, as discussed below, in certain cases some signals have been identified, which are necessary for internalization
and trafficking of proteins to MVBs and exosomes.
For the EGF receptor, a point-mutation has been identified
which does not affect receptor trafficking to the outer membrane
of the MVBs, but prevents inward budding which leads to the formation of luminal vesicles containing the EGFR [23]. In Saccharomyces cerevisiae, ubiquitinylation of the G-protein coupled
receptor (GPCR) Ste2 leads to trafficking into MVBs and subsequent degradation in lysosomes [24,25]. The highly conserved
ubiquitin polypeptide is processed by a cascade of enzymes and
becomes ligated to lysine residues of substrate proteins. The
ligation of a single ubiquitin moiety (mono-ubiquitinylation)
acts as a signal for endocytosis and the delivery into MVBs.
However, the attachment of multiple ubiquitin chains (polyubiquitinylation) directs proteins for degradation in the proteasome. Mutation of lysine residues in Ste2 blocks downregulation
via ubiquitin-triggered internalization. The formation of MVBs
relies on ubiquitin-binding proteins [26,27]. The endosomal
sorting complex required for transport (ESCRT) recognizes the
ubiquitinylated cargo via Vps-27. Vps-27 then recruits another
ESCRT complex and Tsg-101, which activate AIP/Alix. This
complex drives the cargo into the budding vesicles. Although
mono-ubiquitinylation triggers the uptake into MVBs, not all
proteins in exosomes are ubiquitinylated. It appears that there is
also a passive mechanism involved in protein sorting to MVBs.
The responsible signals for this processes are in some cases the
presence of tetraspanin enriched [28] or cholesterol enriched
(=lipid rafts) membrane microdomains [29].
1.2. Exosomal structure and integral constituents
Exosomes are classically defined as membranous vesicles
with a diameter of 30–100 nm. Many groups have performed
proteomic analysis of vesicles derived from cell lines or body
fluids such as urine, blood and ascites. Such analyses have
shown that all mammalian exosomes share some common characteristics such as structure (bilipidic layer), size, density and
overall protein composition. Some proteins are located on the
surface or in the lumen of nearly all exosomes (exosomal markers). Notably, these include cytoplasmic proteins such as tubulin, actin, actin-binding proteins, annexins and Rab proteins as
well as molecules responsible for signal transduction (protein
kinases, heterotrimeric G-proteins) [30–32]. Most exosomes
also contain MHC class I molecules [33,34] and heat-shock proteins such as Hsp70 and Hsp90 [30,35]. The protein family most
commonly associated with exosomes is the tetraspanins including CD9, CD63, CD81 and CD82 [36–38]. Conversely, other
exosomal proteins directly represent the proteome of the source
cells. For example, analysis of urinary vesicles showed a link
between exosomes containing aquaporin-2 and their origin from
the urogenital tract [39]. Meanwhile, urinary vesicles have been
examined for their potential use in the detection of malignancyassociated proteins and from these analysis it was concluded
that exosomes could present novel biomarkers for renal diseases
[39]. As exosomes are also found in serum and ascites fluids of
tumor patients, it is possible that exosome analysis may eventually become important for diagnosis and biomarker analysis. In
some tumors, certain overexpressed markers can also be detected
in exosomes [40]. Consistent with their endosomal origin, there
are typically no proteins of the nucleus, mitochondria, or endoplasmic reticulum detectable in exosomes [41]. In contrast, all
exosomal proteins are typically found in the cell cytosol or at
the plasma membrane.
1.3. Biological functions of exosomes and other secreted
vesicles
In contrast to the fate of proteins trafficked for degradation to
the lysosomal system, secreted exosomes are biologically active
entities which are important for a variety of pathways. Some
examples of roles for exosomes are discussed below.
1.3.1. Morphogen signaling
Exosomes and other cell-derived soluble vesicle compartments can themselves act as biologically active signals. For
example, in developmental biology, morphogens play an essential role in tissue patterning. They are released by donor cells and
spread through the adjacent tissue at different concentrations.
Pattern formation in developing Drosophila tissues occurs in
response to the graded distribution of morphogens such as Wingless and Hedgehog [42–44]. Interestingly, Wingless is tightly
associated with secreted exosome-like vesicles called argosomes
[45,46]. It has been reported that argosomes arise by a mechanism similar to the formation of exosomes from MVBs. The
Wingless morphogen gradient is established by multiple transcytosis events. Thereby, the main contingent of argosomes travels
thorough tissues and is found in endosomes, whilst few argosomes become degraded in lysosomes. The argosomes therefore
function to spread a morphogen gradient of the Wingless protein.
1.3.2. Exosomes as immunological mediators
Exosomes display a wide variety of immunostimulatory
properties. For example, exosomes secreted by Eppstein-Barr
virus (EBV)-transformed B cells are able to stimulate CD4+
T cells in an antigenic-specific manner [15]. Meanwhile,
S. Keller et al. / Immunology Letters 107 (2006) 102–108
exosomes produced by mouse dendritic cells pulsed with tumor
peptide are able to mediate the rejection of established tumors
[13,47]. These antitumor effects were antigen-specific and were
associated with the activity of T cells. Direct stimulation of T
cells by membrane vesicles from antigen-presenting cells has
also been reported [48]. Conversely, it has been suggested that
intestinal epithelial cells, T-cell tumors and melanoma cells
can secrete exosomes capable of inducing antigen-specific
tolerance and FasL-mediated T-cell apoptosis [49,50].
A recent study has shown a role for exosomes in the modulation of T-cell signaling in pregnancy [51]. Exosomes from
the serum of pregnant women could suppress the expression
of important T-cell signaling components including CD3-␰ and
JAK3. This suppression was correlated with exosome-associated
FasL and a striking difference was noted between women delivering at term and those delivering pre-term. Marker analysis
suggested that the exosomes were derived from the placenta and
the release of FasL-containing exosomes may be one mechanism
by which the placenta promotes a state of immune privilege.
Exosomes were also shown to play a role in the control
of tumor growth [52]. Pretreatment of mice with exosomes
derived from murine mammary carcinomas augmented subsequent tumor growth by inhibiting the cytolytic activity of NK
cells. On the molecular level, tumor exosomes diminished levels of perforin in NK cells, a molecule that is essential for target
cell lysis. It was shown that exosomes are taken up and remain
stable in NK cells. Meanwhile, mRNA levels of perforin were
not affected by exosomes, suggesting a post-translational regulatory mechanism. One possibility could be that perforin, stored
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in granula, becomes degraded by exosomes that have entered
the NK cell.
As stated above, exosomes from tumor cells or dendritic cells
pulsed with tumor-specific peptides can active the immune system and are a valuable source of material for immunotherapy.
Clinical trials are currently being conducted to assess the safety
and efficacy of anti-tumor vaccines using exosomes [53]. However, the finding that exosomes mediate positive and negative
immune regulatory functions suggests that the application of
exosomes in immunotherapy must be careful examined prior to
onset of further clinical applications.
1.3.3. Ectodomain shedding of proteins in the MVB and
exosomes
Transmembrane proteins in many cases can undergo cell
surface cleavage to generate a soluble form of the molecule
(Fig. 2A). This has been demonstrated for a large number of
molecules including growth factors and receptors, adhesion
molecules and other heterologous proteins [54] and the resulting
soluble forms often exhibit alternate roles to the transmembrane form. For example, the transmembrane form of heparinbinding epidermal-like growth factor (HB-EGF) binds via its
extracellular ectodomain to diphtheria toxin and the diphtheria toxin receptor-associated protein (DRAP27/CD9) [55]. In
addition, the intracellular C-terminus of transmembrane HBEGF binds the anti-apoptotic protein BAG-1 and this affects
cell morphology, adhesion and resistance to apoptosis [56].
Meanwhile, following proteolytic ectodomain shedding, the soluble form of HB-EGF binds the EGFR to mediate a variety of
Fig. 2. Exosomes as a novel platform for ADAM-mediated cleavage. (A) Cleavage of cell surface proteins such as L1 and CD44 can occur at the cell surface. A
second pathway of cleavage is initiated by the endocytosis of both ADAM proteases and cell surface substrates. During vesicles maturation, additional cargo is
derived from the golgi and the trans golgi network (TGN). (B) Proteolysis of substrate transmembrane molecules by ADAMs can also occur in MVBs. The resulting
cleaved/soluble forms are secreted by fusion with the plasma membrane.
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S. Keller et al. / Immunology Letters 107 (2006) 102–108
biological effects including proliferation [57]. Ectodomain shedding events are predominantly mediated by various subclasses of
zinc-binding metalloproteases such as the ADAM (a disintegrin
and metalloprotease), MMP (matrix metalloprotease) and MTMMP (membrane-type matrix metalloprotease) families [58].
ADAMs and MT-MMPs are themselves transmembrane proteins
and we have demonstrated that the two most widely characterized ectodomain sheddases ADAM10 and ADAM17 (TACE)
are also present in secreted exosomes along with substrate transmembrane molecules [59].
The majority of ectodomain shedding reports have suggested that proteolysis of transmembrane molecules occurs at
the cell surface. However, in the case of several molecules,
proteolytic processing can also occur inside the cell within vesicular compartments in MVBs and within secreted exosomes. For
example, we have shown that the L1 adhesion molecule and
CD44 undergo proteolytic ectodomain shedding in MVBs by
ADAM10 [59–61]. The cleaved/soluble ectodomains of L1 and
CD44 can then be directly released from the cell via exocytosis.
Concurrently, full-length transmembrane forms of L1 and CD44
are released from the cell within exosomes and can undergo further ADAM10-mediated cleavage to generate soluble forms of
each molecule (Fig. 2B). The notion for a role of exosomes
in ectodomain shedding and protein secretion is supported by
similar findings for the transmembrane proteins CD46 and the
tumor necrosis factor receptor 1 (TNFR1). Ovarian adenocarcinoma cell lines release full-length transmembrane CD46 in
vesicles [62]. Vesicle-associated CD46 can then become further processed by metalloproteases to generate a soluble form.
Meanwhile, TNFR1 is released from vascular endothelial cells
within exosomes and also undergoes ectodomain shedding [63].
Most fascinatingly, both CD46 and TNFR1 maintain their biological activity on the exosome surface with regards to ligand
binding. These findings suggest a crucial role for exosomes in
the biological function and ectodomain shedding of a variety of
transmembrane molecules.
Interestingly, exosome secretion and ADAM-mediated
ectodomain shedding may be tightly related processes. Stimuli
which activate ectodomain shedding such as calcium flux, metalloprotease activators (e.g. 4-aminophenylmercuric acetate) and
agents which stimulate cholesterol extraction from the plasma
membrane (e.g. methyl-␤-cyclodextrin) are also stimulators
of exosome release [59]. In addition, inhibitors of ADAMmetalloproteases block exosome formation [63]. This raises
the possibility that metalloproteases such as ADAM10 and
ADAM17, which are present in endosomes and exosomes, may
play a direct role in exosome formation.
2. Conclusions
In the present review we have focused on some recent aspects
of exosome biology. Whilst much information on the biosynthesis of exosomes has been demonstrated using in vitro cell lines,
many questions regarding the biological role of exosomes in
complex cellular systems remain to be addressed. It is clear that
exosome-like microvesicles are present in body fluids such as
blood, urine, amnionic fluid ascites and pleural effusions under
healthy and disease conditions. However, the origin of these
exosomes and their destination for stimulation of distal cells
remains unclear. It has been demonstrated that exosomes can
be taken up by other cells. However, whether this establishes a
novel mechanism of cell–cell communication is an intriguing yet
unanswered question. The release and subsequent cleavage of
transmembrane protein in microvesicles may be a novel mechanism of secretion that is distinct from the classical exocytosis
pathway. It is presently unclear how exosomal secretion is regulated; however, recent work has shown that the p53 protein
and the p53 regulated protein TSAP6 may be involved in this
process [64]. Meanwhile, it is worth mentioning that in certain
disease conditions, exosomes may play regulatory functions.
This is highlighted by the recent finding that ␤-amyloid peptides, associated with Alzheimer’s disease (AD), are release
in association with exosomes and that exosomal proteins were
found to accumulate in the plaques of AD patients brains [65].
In addition, prions are released from cells in association with
exosomes and trafficking within the body functions as an infectious route for propagation of disease [66,67]. The release of
exosomes from tumor cells may also be a novel mechanism
for chemoresistance. For example, enhanced exosomal export
of cisplatin was observed in drug-resistant human ovarian carcinoma cells [68], whilst exosome-based secretion of doxorubicin
mediates resistance in other cancer cell lines [69]. In conclusion,
the studies mentioned in this review highlight multiple roles for
secreted exosomes in a range of biological settings including
development, immunology and cancer. Whilst functional roles
of exosomes are only recently becoming clear, future investigations are likely to indicate the importance of these mediators in
biological processes.
References
[1] Li XB, Zhang ZR, Schluesener HJ, Xu SQ. Role of exosomes in immune
regulation. J Cell Mol Med 2006;10:364–75.
[2] Johnstone RM. Exosomes biological significance: a concise review. Blood
Cells Mol Dis 2006;36:315–21.
[3] Mellman I. Membranes and sorting. Curr Opin Cell Biol 1996;8:497–8.
[4] Mellman I. Endocytosis and molecular sorting. Annu Rev Cell Dev Biol
1996;12:575–625.
[5] Stoorvogel W, Strous GJ, Geuze HJ, Oorschot V, Schwartz AL. Late endosomes derive from early endosomes by maturation. Cell 1991;65:417–27.
[6] Novikoff AB, Essner E, Quintana N. Golgi apparatus and lysosomes. Fed
Proc 1964;23:1010–22.
[7] Futter CE, Pearse A, Hewlett LJ, Hopkins CR. Multivesicular endosomes
containing internalized EGF–EGF receptor complexes mature and then
fuse directly with lysosomes. J Cell Biol 1996;132:1011–23.
[8] Mullock BM, Bright NA, Fearon CW, Gray SR, Luzio JP. Fusion of lysosomes with late endosomes produces a hybrid organelle of intermediate
density and is NSF dependent. J Cell Biol 1998;140:591–601.
[9] Ceresa BP, Schmid SL. Regulation of signal transduction by endocytosis.
Curr Opin Cell Biol 2000;12:204–10.
[10] DiFiore PP, Gill GN. Endocytosis and mitogenic signaling. Curr Opin Cell
Biol 1999;11:483–8.
[11] Kleijmeer M, Ramm G, Schuurhuis D, Griffith J, Rescigno M, RicciardiCastagnoli P, et al. Reorganization of multivesicular bodies regulates MHC
class II antigen presentation by dendritic cells. J Cell Biol 2001;155:53–63.
[12] Kleijmeer MJ, Escola JM, UytdeHaag FG, Jakobson E, Griffith JM, Osterhaus AD, et al. Antigen loading of MHC class I molecules in the endocytic
tract. Traffic 2001;2:124–37.
S. Keller et al. / Immunology Letters 107 (2006) 102–108
[13] Zitvogel L, Angevin E, Tursz T. Dendritic cell-based immunotherapy of
cancer. Ann Oncol 2000;11:199–205.
[14] Johnstone RM, Bianchini A, Teng K. Reticulocyte maturation and exosome
release: transferrin receptor containing exosomes shows multiple plasma
membrane functions. Blood 1989;74:1844–51.
[15] Raposo G, Nijman HW, Stoorvogel W, Liejendekker R, Harding CV, Melief
CJ, et al. B lymphocytes secrete antigen-presenting vesicles. J Exp Med
1996;183:1161–72.
[16] Clayton A, Turkes A, Navabi H, Mason MD, Tabi Z. Induction of heat
shock proteins in B-cell exosomes. J Cell Sci 2005;118:3631–8.
[17] Skokos D, Goubran-Botros H, Roa M, Mecheri S. Immunoregulatory properties of mast cell-derived exosomes. Mol Immunol 2002;38:
1359–62.
[18] Amigorena S. Anti-tumour immunotherapy using dendritic-cell-derived
exosomes. Res Immunol 1998;149:661–2.
[19] Heijnen HF, Schiel AE, Fijnheer R, Geuze HJ, Sixma JJ. Activated platelets
release two types of membrane vesicles: microvesicles by surface shedding
and exosomes derived from exocytosis of multivesicular bodies and alphagranules. Blood 1999;94:3791–9.
[20] van GN, Raposo G, Candalh C, Boussac M, Hershberg R, Cerf-Bensussan
N, et al. Intestinal epithelial cells secrete exosome-like vesicles. Gastroenterology 2001;121:337–49.
[21] Faure J, Lachenal G, Court M, Hirrlinger J, Chatellard-Causse C, Blot B, et
al. Exosomes are released by cultured cortical neurones. Mol Cell Neurosci
2006;31:642–8.
[22] Schwoebel ED, Moore MS. The control of gene expression by regulated
nuclear transport. Essays Biochem 2000;36:105–13.
[23] Felder S, Miller K, Moehren G, Ullrich A, Schlessinger J, Hopkins CR.
Kinase activity controls the sorting of the epidermal growth factor receptor
within the multivesicular body. Cell 1990;61:623–34.
[24] Odorizzi G, Babst M, Emr SD. Fab1p PtdIns(3)P 5-kinase function essential
for protein sorting in the multivesicular body. Cell 1998;95:847–58.
[25] Sprague Jr GF. Signal transduction in yeast mating: receptors, transcription
factors, and the kinase connection. Trends Genet 1991;7:393–8.
[26] Fisher RD, Wang B, Alam SL, Higginson DS, Robinson H, Sundquist WI,
et al. Structure and ubiquitin binding of the ubiquitin-interacting motif. J
Biol Chem 2003;278:28976–84.
[27] vonSchwedler UK, Stuchell M, Muller B, Ward DM, Chung HY,
Morita E, et al. The protein network of HIV budding. Cell 2003;114:
701–13.
[28] Wubbolts R, Leckie RS, Veenhuizen PT, Schwarzmann G, Mobius W,
Hoernschemeyer J, et al. Proteomic and biochemical analyses of human B
cell-derived exosomes. Potential implications for their function and multivesicular body formation. J Biol Chem 2003;278:10963–72.
[29] deGassart A, Geminard C, Fevrier B, Raposo G, Vidal M. Lipid raftassociated protein sorting in exosomes. Blood 2003;102:4336–44.
[30] Thery C, Boussac M, Veron P, Ricciardi-Castagnoli P, Raposo G, Garin J,
et al. Proteomic analysis of dendritic cell-derived exosomes: a secreted
subcellular compartment distinct from apoptotic vesicles. J Immunol
2001;166:7309–18.
[31] Skokos D, Le PS, Villa I, Rousselle JC, Peronet R, Namane A, et al. Nonspecific B and T cell-stimulatory activity mediated by mast cells is associated
with exosomes. Int Arch Allergy Immunol 2001;124:133–6.
[32] Skokos D, Le PS, Villa I, Rousselle JC, Peronet R, David B, et al. Mast
cell-dependent B and T lymphocyte activation is mediated by the secretion
of immunologically active exosomes. J Immunol 2001;166:868–76.
[33] Blanchard N, Lankar D, Faure F, Regnault A, Dumont C, Raposo G, et
al. TCR activation of human T cells induces the production of exosomes
bearing the TCR/CD3/zeta complex. J Immunol 2002;168:3235–41.
[34] Wolfers J, Lozier A, Raposo G, Regnault A, Thery C, Masurier C, et al.
Tumor-derived exosomes are a source of shared tumor rejection antigens
for CTL cross-priming. Nat Med 2001;7:297–303.
[35] Thery C, Zitvogel L, Amigorena S. Exosomes: composition, biogenesis
and function. Nat Rev Immunol 2002;2:569–79.
[36] Escola JM, Kleijmeer MJ, Stoorvogel W, Griffith JM, Yoshie O, Geuze HJ.
Selective enrichment of tetraspan proteins on the internal vesicles of multivesicular endosomes and on exosomes secreted by human B-lymphocytes.
J Biol Chem 1998;273:20121–7.
107
[37] Bard MP, Hegmans JP, Hemmes A, Luider TM, Willemsen R, Severijnen
LA, et al. Proteomic analysis of exosomes isolated from human malignant
pleural effusions. Am J Respir Cell Mol Biol 2004;31:114–21.
[38] Chaput N, Taieb J, Andre F, Zitvogel L. The potential of exosomes in
immunotherapy. Expert Opin Biol Ther 2005;5:737–47.
[39] Pisitkun T, Shen RF, Knepper MA. Identification and proteomic profiling of exosomes in human urine. Proc Natl Acad Sci USA 2004;101:
13368–73.
[40] Koga K, Matsumoto K, Akiyoshi T, Kubo M, Yamanaka N, Tasaki A, et al.
Purification, characterization and biological significance of tumor-derived
exosomes. Anticancer Res 2005;25:3703–7.
[41] Mears R, Craven RA, Hanrahan S, Totty N, Upton C, Young SL, et al.
Proteomic analysis of melanoma-derived exosomes by two-dimensional
polyacrylamide gel electrophoresis and mass spectrometry. Proteomics
2004;4:4019–31.
[42] Lawrence PA, Struhl G. Morphogens, compartments, and pattern: lessons
from Drosophila? Cell 1996;85:951–61.
[43] Neumann C, Cohen S. Morphogens and pattern formation. Bioessays
1997;19:721–9.
[44] Christian JL. BMP, Wnt and Hedgehog signals: how far can they go? Curr
Opin Cell Biol 2000;12:244–9.
[45] Greco V, Hannus M, Eaton S. Argosomes: a potential vehicle for the spread
of morphogens through epithelia. Cell 2001;106:633–45.
[46] Cadigan KM. Regulating morphogen gradients in the Drosophila wing.
Semin Cell Dev Biol 2002;13:83–90.
[47] Zitvogel L, Regnault A, Lozier A, Wolfers J, Flament C, Tenza D, et al.
Eradication of established murine tumors using a novel cell-free vaccine:
dendritic cell-derived exosomes. Nat Med 1998;4:594–600.
[48] Kovar M, Boyman O, Shen X, Hwang I, Kohler R, Sprent J. Direct stimulation of T cells by membrane vesicles from antigen-presenting cells. Proc
Natl Acad Sci USA 2006;103:11671–6.
[49] Andreola G, Rivoltini L, Castelli C, Huber V, Perego P, Deho P, et al.
Induction of lymphocyte apoptosis by tumor cell secretion of FasL-bearing
microvesicles. J Exp Med 2002;195:1303–16.
[50] Abusamra AJ, Zhong Z, Zheng X, Li M, Ichim TE, Chin JL, et al. Tumor
exosomes expressing Fas ligand mediate CD8+ T-cell apoptosis. Blood
Cells Mol Dis 2005;35:169–73.
[51] Taylor DD, Akyol S, Gercel-Taylor C. Pregnancy-associated exosomes and
their modulation of T cell signaling. J Immunol 2006;176:1534–42.
[52] Liu C, Yu S, Zinn K, Wang J, Zhang L, Jia Y, et al. Murine mammary
carcinoma exosomes promote tumor growth by suppression of NK cell
function. J Immunol 2006;176:1375–85.
[53] Mignot G, Roux S, Thery C, Segura E, Zitvogel L. Prospects for exosomes
in immunotherapy of cancer. J Cell Mol Med 2006;10:376–88.
[54] Dello Sbarba P, Rovida E. Transmodulation of cell surface regulatory molecules via ectodomain shedding. Biol Chem 2002;383:69–
83.
[55] Iwamoto R, Higashiyama S, Mitamura T, Taniguchi N, Klagsbrun M,
Mekada E. Heparin-binding EGF-like growth factor, which acts as the
diphtheria toxin receptor, forms a complex with membrane protein
DRAP27/CD9, which up-regulates functional receptors and diphtheria
toxin sensitivity. EMBO J 1994;13:2322–30.
[56] Lin J, Hutchinson L, Gaston SM, Raab G, Freeman MR. BAG-1 is a novel
cytoplasmic binding partner of the membrane form of heparin-binding
EGF-like growth factor: a unique role for proHB-EGF in cell survival regulation. J Biol Chem 2001;276:30127–32.
[57] Nishi E, Klagsbrun M. Heparin-binding epidermal growth factor-like
growth factor (HB-EGF) is a mediator of multiple physiological and pathological pathways. Growth Factors 2004;22:253–60.
[58] Sanderson MP, Dempsey PJ, Dunbar AJ. Control of ErbB signaling
through metalloprotease mediated ectodomain shedding of EGF-like factors. Growth Factors 2006;24:121–36.
[59] Stoeck A, Keller S, Riedle S, Sanderson MP, Runz S, LeNaour F, et al.
A role for exosomes in the constitutive and stimulus-induced ectodomain
cleavage of L1 and CD44. Biochem J 2006;393:609–18.
[60] Gutwein P, Mechtersheimer S, Riedle S, Stoeck A, Gast D, Joumaa S, et al.
ADAM10-mediated cleavage of L1 adhesion molecule at the cell surface
and in released membrane vesicles. FASEB J 2003;17:292–4.
108
S. Keller et al. / Immunology Letters 107 (2006) 102–108
[61] Gutwein P, Stoeck A, Riedle S, Gast D, Runz S, Condon TP, et al. Cleavage
of L1 in exosomes and apoptotic membrane vesicles released from ovarian
carcinoma cells. Clin Cancer Res 2005;11:2492–501.
[62] Hakulinen J, Junnikkala S, Sorsa T, Meri S. Complement inhibitor membrane cofactor protein (MCP; CD46) is constitutively shed from cancer cell
membranes in vesicles and converted by a metalloproteinase to a functionally active soluble form. Eur J Immunol 2004;34:2620–9.
[63] Hawari FI, Rouhani FN, Cui X, Yu ZX, Buckley C, Kaler M, et al. Release of
full-length 55-kDa TNF receptor 1 in exosome-like vesicles: a mechanism
for generation of soluble cytokine receptors. Proc Natl Acad Sci USA
2004;101:1297–302.
[64] Yu X, Harris SL, Levine AJ. The regulation of exosome secretion: a novel
function of the p53 protein. Cancer Res 2006;66:4795–801.
[65] Rajendran L, Honsho M, Zahn TR, Keller P, Geiger KD, Verkade P, et al.
Alzheimer’s disease beta-amyloid peptides are released in association with
exosomes. Proc Natl Acad Sci USA 2006;103:11172–7.
[66] Porto-Carreiro I, Fevrier B, Paquet S, Vilette D, Raposo G. Prions and
exosomes: from PrPc trafficking to PrPsc propagation. Blood Cells Mol
Dis 2005;35:143–8.
[67] Fevrier B, Vilette D, Archer F, Loew D, Faigle W, Vidal M, et al. Cells
release prions in association with exosomes. Proc Natl Acad Sci USA
2004;101:9683–8.
[68] Safaei R, Larson BJ, Cheng TC, Gibson MA, Otani S, Naerdemann W.
Abnormal lysosomal trafficking and enhanced exosomal export of cisplatin in drug-resistant human ovarian carcinoma cells. Mol Cancer Ther
2005;4:1595–604.
[69] Shedden K, Xie XT, Chandaroy P, Chang YT, Rosania GR. Expulsion of small molecules in vesicles shed by cancer cells: association
with gene expression and chemosensitivity profiles. Cancer Res 2003;63:
4331–7.