Download The syndapin protein family: linking membrane trafficking with the

Commentary
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The syndapin protein family: linking membrane
trafficking with the cytoskeleton
Michael M. Kessels and Britta Qualmann*
Department of Neurochemistry and Molecular Biology, Leibniz Institute for Neurobiology, Brenneckestr. 6, 39118 Magdeburg, Germany
*Author for correspondence (e-mail: [email protected])
Journal of Cell Science 117, 3077-3086 Published by The Company of Biologists 2004
doi:10.1242/jcs.01290
Summary
Syndapins – also called PACSINs – are highly conserved
Src-homology 3 (SH3)-domain-containing proteins that
seem to exist in all multicellular eukaryotes. They interact
with the large GTPase dynamin and several other proteins
implicated in vesicle trafficking. Syndapin-dynamin
complexes appear to play an important role in vesicle
fission at different donor membranes, including the
plasma membrane (endocytosis) and Golgi membranes. In
addition, syndapins are implicated in later steps of vesicle
cycling in neuronal and non-neuronal cells. Syndapins also
interact with N-WASP, a potent activator of the Arp2/3
complex that forms a critical part of the actin
polymerization machinery. Syndapin oligomers can
Introduction
The formation and movement of vesicles, as well as the
organization of different pools of vesicles within distinct
compartments of cells, are thought to involve cytoskeletal
elements; however, how the different molecular machineries
involved are interconnected is mostly unclear (Qualmann et al.,
2000b; Qualmann and Kessels, 2002; Engqvist-Goldstein and
Drubin, 2003; Gundelfinger et al., 2003; Orth and McNiven,
2003). Recently, a handful of candidates for proteins that can
act at this interface have been identified. Among these are
members of the syndapin family, which are Src-homology 3
(SH3)-domain-containing proteins that exhibit several
isoforms and splice variants. SH3 domains recognize prolinerich motifs of the PXXP type and their specificity relies mainly
on the residues flanking such motifs. Syndapins belong to a
growing class of accessory proteins functioning in membrane
trafficking that interact with the proline-rich domain of the
GTPase dynamin. Because the name ‘syndapins’ (for synaptic
dynamin-associated proteins) currently seems to reflect best
what is known about the functions of these proteins in vivo,
we refer to them as such here – avoiding use of other names
(e.g. FAP52, SH3p14 and PACSIN) to keep the nomenclature
as simple as possible.
Dynamin is an important player in endocytosis, a process
that comprises several distinct steps. First, cell-surface
receptors are bound by intracellular adaptors. A clathrin coat
is then assembled on the underside of the membrane, which
then invaginates. The developing clathrin-coated pits constrict
at the neck, and finally they pinch off from the membrane. The
newly formed vesicle is transported into the cytosol, where it
is uncoated and can undergo further sorting. Dynamin is crucial
thereby couple bursts of actin polymerization with the
vesicle fission step involving dynamins. This allows newly
formed vesicles to move away from the donor membrane
driven by actin polymerization. Syndapins also engage in
additional interactions with molecules involved in several
signal transduction pathways, producing crosstalk at
the interface between membrane trafficking and the
cytoskeleton. Given the distinct expression patterns of the
different syndapins and their splice forms, these proteins
could have isoform-specific functions.
Key words: Syndapin, Actin polymerization, Vesicle trafficking
for the fission step, in liberating newly formed vesicles from
the donor membrane (Hinshaw, 2000; Sever et al., 2000).
All syndapins cloned and/or identified as DNA sequences
show remarkably high conservation of both domain structure
and amino acid sequence in species as diverse as worms,
insects, fish, birds and mammals. Each is composed of an Nterminal region predicted to be almost exclusively α-helical
and to engage in coiled-coil interactions, a flexible stretch that
may contain up to three NPF motifs, and a C-terminal SH3
domain. The SH3 domain is responsible for interactions with
dynamin and N-WASP, a potent activator of the Arp2/3
complex F-actin-nucleation machine. Syndapin complexes
may thus link membrane trafficking and the actin cytoskeleton.
Recent evanescent field-microscopy studies have demonstrated
that actin, the Arp2/3 complex and N-WASP transiently
accumulate at sites of endocytosis and that this is coordinated
with dynamin-mediated vesicle fission (Merrifield et al., 2002;
Merrifield et al., 2004). Here, we focus mainly on the roles of
the actin cytoskeleton in vesicle formation, discuss how
syndapins might work at the interface of actin and membrane
trafficking, and highlight the molecular requirements and
mechanisms involved. We also analyse the phylogenetic
relationship between the different syndapin orthologs, isoforms
and splice variants, which allows them to be organized into
distinct subgroups.
Syndapin interactions and functions
Connecting the cytoskeleton with vesicle formation
Syndapins interact with N-WASP (a protein important for actin
filament formation) as well as several molecules implicated in
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Journal of Cell Science 117 (15)
membrane trafficking: the GTPase dynamin (which controls
endocytic vesicle formation) (Hinshaw, 2000; Sever et al.,
2000), the phosphatidylinositol 5-phosphatase synaptojanin (a
protein that plays a crucial role in the uncoating of clathrincoated vesicles; Cremona et al., 1999) and synapsin I (a protein
associated with the reserve pool of synaptic vesicles) (Hilfiker
et al., 1999) (Fig. 1). These interactions first raised the
possibility that syndapins have roles in both membrane
trafficking and organization of the actin cytoskeleton
(Qualmann et al., 1999), a hypothesis that was followed up by
more-detailed studies of the interactions with dynamin and NWASP.
The relevance of the interaction with dynamin is
strongly supported by coimmunoprecipitation studies of the
endogenous proteins (Qualmann et al., 1999; Qualmann and
Kelly, 2000) and by the fact that a surplus of dynamin-binding
syndapin SH3 domains inhibits receptor-mediated endocytosis
in both permeabilized cell assays (Simpson et al., 1999) and
intact cells (Qualmann and Kelly, 2000). This block of
endocytosis occurs at the transition from invaginated clathrincoated pits to closed endocytic membrane compartments (i.e.
at the step at which dynamin is crucial) (Simpson et al., 1999).
In common with other SH3-domain-containing dynaminbinding proteins, syndapins might influence the subcellular
localization, GTP-binding and/or GTP hydrolysis rate of
dynamin.
All syndapins also interact with the Arp2/3 complex
Vesicle formation
Clathrin-coated
vesicle uncoating
activator N-WASP (Qualmann et al., 1999; Qualmann and
Kelly, 2000; Modregger et al., 2000); they might thus connect
the actin cytoskeleton with dynamin-mediated vesicle fission
(Fig. 1). The in vivo relevance of this interaction is supported
by studies showing coimmunoprecipitation of endogenous
syndapin I and N-WASP (Qualmann et al., 1999) and by the
fact that overexpression of syndapin I or syndapin II induces
formation of numerous actin-rich filopodia. This requires
activation of the Arp2/3 complex at the cell cortex (Qualmann
and Kelly, 2000), and the phenotype is similar to that caused
by activation of overexpressed N-WASP (Miki et al., 1998).
N-WASP exists in an autoinhibited state and needs to be
opened up by effector molecules such as phosphatidylinositol
(4,5)-bisphosphate [PtdIns(4,5)P2] and Cdc42 to associate with
and activate the Arp2/3 complex (Kim et al., 2000; Higgs and
Pollard, 2001; Welch and Mullins, 2002). As syndapins can
recruit N-WASP to membranes and trigger local actin
polymerization in vivo in an SH3-domain- and Arp2/3complex-dependent manner (Kessels and Qualmann, 2002),
syndapins seem to belong to the diverse set of N-WASP
effectors that can trigger activation of the Arp2/3 complex and
thereby actin polymerization. The cytoskeletal role of
syndapins is also reflected by the fact that syndapins are
enriched at sites of high actin turnover, such as lamellipodia
(Qualmann and Kelly, 2000) and neuronal growth cones
(Kessels and Qualmann, 2002).
Studies of the syndapin II isoform in chicken (FAP52)
GDP/GTP exchange
(GEF)
GTP
GDP
PtdIns(4,5)P2
Synaptojanin
Dynamin
mSos
Ectodomain shedding
Vesicle recycling
and endocytosis
SH3
ADAM
NPF
EHD
proteins
Syndapin
F-actin crosslinking
Oligomerization
Anchoring of synaptic
vesicles to F-Actin
Filamin
NPF
SH3
Synapsin
N-WASP
Huntingtin
Huntington's disease
CD95L
Apoptosis
F-Actin nucleation
Fig. 1. Interactions of the syndapin protein
family. Depicted are all syndapin
interaction partners described thus far,
irrespective of species, syndapin isoform or
splice variant. Note that the depicted
antiparallel dimers are merely a
hypothetical model for syndapin
oligomerization, which is not yet supported
by a crystal structure. The thickness of the
arrows indicates whether the interactions
are based on in vitro data, supported by in
vivo interaction studies or confirmed by
functional analyses of the respective
cellular functions and corresponding rescue
experiments.
Syndapin interactions and functions
reinforce this connection with the actin cytoskeleton. FAP52
binds to the actin-crosslinking protein filamin/ABP-280 (Nikki
et al., 2002a) (Fig. 1) and localizes to focal adhesions
(Meriläinen et al., 1997). Note, however, that this has not been
found in other mammalian systems or in Xenopus laevis (Ritter
et al., 1999; Cousin et al., 2000) (M.M.K. and B.Q.,
unpublished). Moreover, filamin/ABP-280 is not a focal
adhesion protein, and the distribution of the two proteins only
partially overlaps at sites of contact between stress fibres and
focal adhesions (Nikki et al., 2002a).
A link between the cytoskeletal and endocytic functions
of syndapins was suggested by the observation that
overexpression of N-WASP interferes with receptor-mediated
endocytosis, and this depends solely on the syndapin-binding,
central proline-rich domain of N-WASP. The phenotype can
be rescued by syndapin co-overexpression (Kessels and
Qualmann, 2002). The involvement of N-WASP interactions in
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endocytic vesicle formation is strongly supported by the
observation that endocytosis is inhibited in cells in which
endogenous N-WASP is confined to mitochondria or targeted
by anti-N-WASP antibodies. One can rescue endocytosis by
resupplying the cells with N-WASP (Kessels and Qualmann,
2002). Analysis of lymphocytes from mice lacking WASP also
implicates WASP family members in endocytosis. These cells
exhibit defects in T-cell receptor endocytosis in addition to
defects in actin polymerization (Zhang et al., 1999).
What part might actin play in vesicle formation? The actin
cytoskeleton might spatially organize the endocytic machinery.
It might represent a barrier through which newly formed
vesicles must be transported that needs to be removed by a
local increase in actin turnover. It might also provide structural
support for membrane topologies that facilitate vesicle
formation, such as invaginated tubules, and/or promote vesicle
formation by generating force through motor proteins and/or
Fig. 2. Interconnection of dynamin-mediated
vesicle fission with Arp2/3-complex-dependent
F-actin nucleation triggered by N-WASP and
syndapins. (A) Early in vesicle formation, the
membrane is deeply invaginated and dynamin
starts to concentrate at the vesicle neck, which
is still wide. Syndapin oligomers associated
with dynamin may help recruit and activate the
Arp2/3 complex activator N-WASP (1). In this
way, actin nucleation by the Arp2/3 complex
can be linked to dynamin-mediated fission
control (2). Actin filaments can be generated de
novo (2) and as new branches from already
existing actin fibres that may be part of the
cortical cytoskeleton (3). It remains to be
investigated whether syndapin-dynamin
complexes form first in the cytosol (4), after
dynamin has been recruited to the plasma
membrane (5) or both. (B) Late in vesicle
formation, the vesicle neck is constricted and
the vesicle is subsequently pinched off and
detached from the plasma membrane. Dynamin
oligomers surrounding the neck could be a
spatial and temporal cue for Arp2/3-complexmediated F-actin nucleation. Syndapins and NWASP serve as connecting elements that
ensure that actin polymerization is restricted to
the neck region. Such a restriction of actin
build-up and a polarization of actin fibres in a
manner that orientates the fast-growing plus
ends towards the forming/moving vesicle
provides force and ensures the directionality of
vesicle movement away from the donor
membrane. Growing plus ends of actin
filaments are marked by ATP-loaded actin
monomers, which are depicted in darker blue.
PIP2, phosphatidylinositol (4,5)-bisphosphate.
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Journal of Cell Science 117 (15)
actin polymerization (Qualmann et al., 2000b). The latter could
be achieved by activation of the Arp2/3 complex by N-WASP
and syndapin, if actin polymerization is spatially restricted and
occurs mainly at vesicle membrane areas facing the plasma
membrane (Fig. 2). By contrast, F-actin formation at vesicle
membrane areas facing the cytoplasm or within wide areas of
the cortical cytoskeleton would create a barrier and thus instead
be inhibitory.
The timing of local actin polymerization would need to be
tightly controlled to correlate with the fission reaction (Fig. 2).
Short-lived actin structures at sites of endocytosis whose
appearance coincides with dynamin-mediated vesicle release
can be observed by evanescent field microscopy (Merrifield
et al., 2002). Additionally, both N-WASP and the Arp2/3
complex transiently appear at sites of endocytosis (Merrifield
et al., 2004). The kinetics of Arp2/3 complex recruitment
mirror those of formation of the actin structures – this is
expected because the complex becomes incorporated into
forming F-actin structures. By contrast, the catalytic Arp2/3
complex activator N-WASP appears transiently, being present
at its highest levels during the initial phase of F-actin formation
upon vesicle departure (Merrifield et al., 2004).
An attractive hypothesis is that the coincidence of actin
Deuterostomia
Vertebrates
nucleation and dynamin-mediated fission reflects the use of a
common binding partner for both machineries, such as
syndapin (Fig. 2). Dynamin forms a collar at the neck region
of plasma membrane invaginations in synaptosomes incubated
with GTPγS and in nerve terminals of shibire flies (Hinshaw,
2000). The interaction with the dynamin-associated syndapin
could allow specific recruitment of N-WASP to the neck of
coated pits and thereby produce polarity in the actin
polymerization and directed movement of newly formed
vesicles away from the plasma membrane (Fig. 2). Indeed,
recent studies have revealed that syndapins can recruit NWASP to intracellular membranes (Kessels and Qualmann,
2002). Such mechanisms might not only facilitate the
departure of the vesicle from the donor membrane but might
also create actin structures that have the appropriate
localization, timing and polarity for moving detached vesicles
away from the plasma membrane. Several studies showing
actin tails attached to moving vesicles support this theory
(Taunton, 2001). Interestingly, both dynamin and N-WASP
have been detected in such actin tails, mainly at the actinmembrane interface (Taunton, 2001; Orth et al., 2002; Lee and
De Camilli, 2002).
Proteins such as Abp1 and cortactin could have functions
Gallus gallus FAP52
Fugu rubripes Syndapin IV
Bos taurus Syndapin II
Sus scrofa Syndapin II
Rattus norvegicus Syndapin II
Homo sapiens PACSIN 2
Mus musculus PACSIN 2
Xenopus laevis X-PACSIN II
Ictalurus punctatus Syndapin II
Danio rerio Syndapin II
Fugu rubripes Syndapin II
II
Sus scrofa Syndapin III
Rattus norvegicus Syndapin III
Homo sapiens PACSIN 3
Mus musculus PACSIN 3
Gallus gallus Syndapin III
Rattus norvegicus Syndapin I
Mus musculus
PACSIN 1
Homo sapiens PACSIN 1
Xenopus laevis Syndapin III
Danio rerio Syndapin IV
III
Ictalurus punctatus Syndapin III
Danio rerio Syndapin I
I
Danio rerio Syndapin III
Fugu rubripes Syndapin III
Fugu rubripes Syndapin I
Xenopus laevis Syndapin I
Insects
Drosophila
melanogaster
Syndapin
Anopheles
gambiae
Syndapin
Fugu rubripes
Syndapin V
Confidence level > 95%
Danio rerio
Syndapin V
Cyprinus carpio
Syndapin V
Confidence level > 90%
Confidence level > 80%
Oncorhynchus
mykiss
Syndapin V
Caenorhabditis
elegans
Syndapin
Confidence level > 70%
Confidence level > 60%
Worms
0.10
Echinococcus
granulosus
EG13
Echinococcus
multilocularis
EM13
Protostomia
V
Syndapin interactions and functions
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similar to those of syndapins in connecting vesicle fission with
the cytoskeleton (Kessels and Qualmann, 2002; Orth and
McNiven, 2003). Both bind to actin and dynamin through
independent domains (Kessels et al., 2001; McNiven et al.,
2000). By contrast, syndapins use their single SH3 domain for
associations with both N-WASP and dynamin. They must
therefore either switch between interacting with N-WASP and
dynamin, or use bridging molecules or oligomerize to interact
with the two simultaneously (see below).
In common with the plasma membrane, Golgi membranes
are associated with a specialized actin-spectrin cytoskeleton
(Beck and Nelson, 1998; De Matteis and Morrow, 2000;
Stamnes, 2002) that seems to support membrane topology and
organelle organization (Valderrama et al., 1998; di Campli et
al., 1999) and might also be involved in membrane trafficking
(Müsch et al., 2001; Valderrama et al., 2001; Fucini et al.,
2002). Both dynamin and N-WASP localize to the trans-Golgi
network (TGN) and play a role in vesicle budding at Golgi
membranes (Jones et al., 1998; Luna et al., 2002), and the Factin-binding Abp1 (Kessels and Qualmann, 2002) has also
been reported to play a role in Golgi trafficking (Fucini et al.,
2002). Recent data suggest that syndapins also associate with
Golgi membranes. Interference with complexes of syndapin II
and dynamin II by antibodies or dominant-negative constructs
strongly inhibits budding from Golgi membranes (Kessels et
al., 2003) (M.M.K. and B.Q., unpublished). The involvement
of actin polymerization in vesicle formation might thus not be
a speciality of the plasma membrane but a more general
mechanism within the cell.
Fig. 3. Unrooted phylogenetic tree of syndapins produced from a
ClustalW alignment of 36 syndapin sequences by the TreeTop
phylogenetic tree reconstruction software (http://www.genebee.msu.
su/services/phtree_reduced.html). Published syndapin sequences or
consensus sequences from as many expressed sequence tag (EST)
clones as could be identified in the NCBI databases were used. More
than 150 syndapin-related DNA sequences were analysed. Few of
those have been described at the protein level (only some vertebrate
syndapins and the antigens EG13 and EM13 from band worms). The
tree is based on an alignment of the first 120 residues of rat syndapin
I with corresponding regions of all syndapin proteins and predicted
proteins from DNA sequences in the databases. Parallel phylogenetic
tree constructions were performed with the first 210 residues (32
sequences) and 305 residues (28 sequences), respectively. These gave
very similar results. The same is true for alignments with blunted Ntermini. Note that the confidence levels of the branch points that have
scores of 63-73% in the above analysis are enhanced to 82-99% in
analyses using longer sequences. Protostomia: parasitic band worms,
Echinococcus granulosus (EG13, GI:158845) and Echinococcus
multilocularis (EM13, GI:158849); roundworms, Caenorhabditis
elegans (GI:17567724, gene XI608); identified but not included (due
to degenerated DNA sequence or lack of N-terminus) were,
Caenorhabditis briggsae (genome contig FPC4044) and a sequence
from the most primitive plathelminthes, the turbellaria (Schmidtea
mediterranea; GI:21308965). Insects: Drosophila melanogaster,
GI:28571784; Anopheles gambiae, overlapping ESTs (GI:31224233
and GI:31224240) and new entry for assembled gene GI:21300122;
Bombyx mori (domestic silk worm), GI:37662803, not included.
Deuterostomia: there are extremely few sequence data for all
organisms originating from the basis of this line (hemichordata and
echinodermata, such as starfish) and for the most primitive chordata
(the tunicata, the copelata and the acrania). Fish and higher
vertebrates, however, were analysed. Fish: Fugu rubripes (fugu fish):
syndapin I (SINFRUP00000064571 and FuguGenscan_5227),
syndapin II (SINFRUP00000062952 and FuguGenscan_1173),
syndapin III (SINFRUP00000059173), syndapin IV
(FuguGenscan_14767) and syndapin V (FuguGenscan_30629);
Danio rerio (zebra fish), syndapin I (GI:156355 and GI:17239474),
syndapin II (GI:31063171, GI:39660160, GI:6949740 and
GI:16098827), syndapin III (GI:28279267), syndapin IV
(GI:38647966 and GI:13104055) and syndapin V (GI:38554082,
GI:38540910 and GI:23193087); Ictalurus punctatus (channel cat
fish), syndapin II (GI:40583787) and III (GI:40581408, GI:18646500
and GI:33607133); Cyprinus carpio (carp), syndapin V
(GI:37560134, GI:37557575 and GI:27491180) and Oncorhynchus
mykiss (rainbow trout), syndapin V (GI:39964270, GI:29590006,
GI:24697026 and GI:24681637). Syndapins from other fish, such as
Oryzias latipes (Japanese rice fish) were identified (GI:17373342 and
17368378) but not included in the above analysis. Birds and frogs:
Gallus gallus (chicken), syndapin I (GI:25737679 and GI:15085432,
not included), syndapin II/FAP52 (GI:2217963); syndapin III
(GI:25904662 and GI:25953223) and Xenopus laevis (African
clawed frog), syndapin I (GI:31090847), X-PACSIN2/syndapin II
(GI:11558503) and syndapin III, GI:27469860). Mammalia: Sus
scrofa (pig), syndapin II (GI:37854627), syndapin III (GI:40437003,
GI:11075716 and GI:40437003), Bos taurus (cow), syndapin II
(GI:9747526, GI:24332175 and GI:9601216), Canis familiaris (dog),
syndapin II (GI:23699945 and GI:23699935, not included), syndapin
III (GI:34413292 and 23707795, not included). The sequences of the
three isoforms from rat, mouse and human included in the
phylogenetic analyses have mostly been published, and these have in
part been studied at the protein level: Rattus norvegicus (rat),
syndapin I (GI:4324451), syndapin II consensus sequence of
syndapin IIaa, IIbb, IIab and IIba (GI:6651162, GI:6651168,
GI:6651164, GI:6651166), syndapin III (GI:27702145 and M.M.K.
and B.Q., unpublished, respectively); Mus musculus (mouse),
syndapin isoform I called h74 or PACSIN (GI:2632077), PACSIN2
(GI:19483912) and PACSIN3 (GI:13539689); Homo sapiens (man),
PACSIN1 (GI:25955520), a consensus of the long PACSIN2 version
and a shorter syndapin II splice variant (GI:6005825 and
GI:12053194) and PACSIN3 (GI:11127645). Note that the database
entries for so-called syndapin-II-related proteins in Dictyostelium
discoideum rather represent a homologue of PSTPIP (GI:28828180)
and a formin-binding protein 17 homologue (GI:21240669),
respectively.
Syndapin oligomerization might physically link different
syndapin interaction partners
All syndapin isoforms contain stretches of amino acids that
are predicted to engage in coiled-coil interactions (Qualmann
et al., 1999). Indeed, both homo-oligomers and heterooligomers composed of different syndapin isoforms can be
observed, and the coiled-coil-domain-containing N-terminus
is sufficient for syndapin-syndapin interactions in vitro and
in vivo (Qualmann et al., 2000a) (M.M.K. and B.Q.,
unpublished). The hypothesis that syndapins oligomerize is
furthermore supported by yeast two-hybrid studies showing
that all isoforms can interact with each other (Modregger et
al., 2000) and by in vitro work including gel filtration and
surface plasmon resonance analyses of the syndapin-related
chicken focal adhesion protein FAP52 (Nikki et al., 2002b).
As the SH3 domain of syndapins is not involved, such
oligomerization could create a multivalent platform to which
different interaction partners of the syndapin SH3 domain are
connected (Figs 1 and 2).
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Journal of Cell Science 117 (15)
Crosstalk between syndapins and signalling pathways
Syndapins interact with several signalling molecules
downstream of activated membrane receptors. These include
the mammalian Sos (for ‘son-of-sevenless’) protein
(Qualmann et al., 2000a; Wasiak et al., 2001), which acts as a
guanine nucleotide exchange factor (GEF) for the small
GTPases Ras and Rac (Scita et al., 1999) (Fig. 1). Ras is
involved in growth factor signalling, whereas the most
prominent role of Rac is the regulation of actin cytoskeleton
dynamics. The interaction between mSos and syndapin
is direct and relies on an intact SH3 domain.
Coimmunoprecipitation and colocalization studies indicate
that syndapin and Sos interact in vivo (Qualmann et al., 2000a;
Wasiak et al., 2001).
Syndapins also bind to the cytoplasmic tails of members of
the ADAM family of metalloprotease disintegrins in vitro
(Cousin et al., 2000; Howard et al., 1999; Mori et al., 2003).
ADAM proteins are transmembrane proteins involved in cellcell communication and proteolytic ectodomain shedding,
which is required for a variety of developmental and
maturation processes (Schlöndorff and Blobel, 1999;
McFarlane, 2003) (Fig. 1). Developmental alterations induced
by overexpression of ADAM13 can be rescued by cooverexpression of the syndapin II isoform X-PACSIN2 in
Xenopus (Cousin et al., 2000). This suggests some form of
negative regulation of ADAMs by syndapins. However, Mori
et al. have shown that syndapin III overexpression increases the
ectodomain shedding of heparin-binding epidermal growth
factor-like growth factor (HB-EGF) and that knocking down
syndapin III by RNA interference partially attenuates this
proteolysis, which is thought to involve ADAM12 (Mori et al.,
2003).
Much less is known about the interaction of the SH3 domain
of syndapins with the proline-rich cytoplasmic portion of the
CD95/Fas/Apo-1 ligand CD95L (Ghadimi et al., 2002).
CD95L is a 40 kDa type II transmembrane receptor that
belongs to the tumour necrosis factor (TNF) family of death
factors and induces apoptosis through the cell death receptor
CD95 but has also been described as costimulatory receptor for
T-cell activation in mice in vivo (Janssen et al., 2003).
It is tempting to speculate not only that syndapins do interact
with proteins involved in different signal transduction
processes but also that syndapin function is controlled
by signalling cascades, because syndapins contain
phosphorylation sites for protein kinase C and casein kinase 2.
Recombinant mouse syndapin I can be phosphorylated by these
kinases in vitro (Plomann et al., 1998). Furthermore, an as-yetuncharacterized signalling pathway regulated by inositol
hexakisphosphate (InsP6) leads to the phosphorylation of
syndapin I – a modification that seems to increase the
association of glutathione-S-transferase (GST)-syndapin I with
dynamin by a factor of 2-3 in vitro (Hilton et al., 2001).
The above observations represent promising starting points
for studying the crosstalk of syndapins with different
signalling pathways. It will be exciting to examine whether
and to what extent the interaction of syndapins with mSos
correlates with the endocytic and cytoskeletal functions of
syndapins and to unravel the molecular details and the
physiological relevance of their interactions with the
signalling molecules mentioned.
Syndapin isoforms and their evolution
Database analyses reveal that syndapins only exist in
multicellular animals. Plants do not seem to contain syndapins;
neither do single-celled eukaryotes such as Dictyostelium
discoideum and the different yeasts. On the basis of all
currently available sequence information, it seems that the
appearance of syndapins correlates with the arrival of
coelomata, which are characterized by the presence of a body
cavity (coelom) and a gut system that spans the body from one
pole (mouth) to the other (anus). Other new structures that
appeared at this stage were blood vessels, nephridiae and the
brain. It remains unclear whether porifera, cnidaria and/or
ctenophora contain syndapins because sequence data for these
animals are generally not available; however, lower worms are
known to possess a syndapin gene (Fig. 3). We have identified
(partial) syndapin-related sequences in the most primitive
plathelminthes, the turbellaria (not included in Fig. 3), as well
as parasitic band worms (Echinococcus). We have also
identified syndapins in roundworms, such as the nematode
Caenorhabditis elegans (Fig. 3). Because the genomes of C.
elegans and Drosophila melanogaster contain a single
syndapin gene, this seems a general property of protostomia.
By contrast, deuterostomia, which ultimately gave rise to the
vertebrates, possess several syndapin isoforms. The gene
duplications must have occurred as much as 400-440 million
years ago because lower vertebrates contain all three syndapin
genes known in mammalia. Our phylogenetic analyses suggest
the following evolutionary sequence: first, a syndapin I/II
ancestor duplicated to give rise to syndapin III; then the former
duplicated again (Fig. 3). In line with this, we have found asyet-undescribed syndapin I, II and III sequences not only in
mammals but also in the segregated branch of higher
vertebrates formed by birds and reptiles. We have identified all
three isoforms in Gallus gallus as well as in Xenopus laevis
(Fig. 3).
Interestingly, in fugu and zebra fish, we have identified five
syndapin genes. Sequences from other fish support the
existence of the two additional groups of syndapin isoforms.
The syndapin V group is clearly at the basis of all vertebrate
syndapins. The data from our phylogenetic analysis could be
interpreted as indicating loss of these most ancient syndapins
during the evolution of higher chordata and of life on land (Fig.
3). The group of syndapin IV genes currently contains only two
sequences suitable for phylogenetic analysis. We have termed
the partial Danio rerio syndapin sequence put in isoform group
I (shown in grey in Fig. 3) syndapin IV because alignments and
phylogenetic analyses with the entire sequence suggest it to be
a member of this subgroup. Further sequence data will be
required for a firmer analysis of the nature and phylogenetic
relationships between syndapin IV isoforms.
The picture is further complicated by the fact that not
only do different syndapin isoforms exist but also they are
alternatively spliced. As in the case of the rat syndapin II
isoforms (Qualmann and Kelly, 2000), alternative splicing is
also evident from database sequences of the other isoforms in
all vertebrates. (Because this predominantly affects the flexible
region preceding the SH3 domain, this region was excluded
from the sequence alignments used to generate the
phylogenetic analysis shown in Fig. 3.)
The evolution of different isoforms and splice variants might
Syndapin interactions and functions
reflect a need for differential regulation and/or differential
affinities for interacting molecules, but none of this has been
studied in detail yet. Our current knowledge is therefore largely
restricted to the differential distribution of syndapins in
mammalian tissues (Table 1).
The syndapin III isoform is the least characterized and seems
mainly to occur in skeletal muscle and heart (Table 1). In
differentiated C2F3 myotubes, syndapin III has a cytosolic
immunolabelling pattern (Modregger et al., 2000) (Fig. 4).
The syndapin II isoforms are expressed more ubiquitously
(Table 1). Interestingly, the short and long splice variants
display different tissue distributions (Qualmann and Kelly,
2000). Xenopus syndapin II proteins are observed as early
as the two-cell stage of development. Immunostaining of
sectioned embryos reveals expression in all cells of the three
germ layers with varying intensities (Cousin et al., 2000).
Syndapin I is mainly restricted to the brain (Table 1). In
common with other proteins involved in membrane trafficking,
such as clathrin and dynamin, which are present at 10-50-fold
higher concentrations in neuronal cells compared with non-
3083
neuronal cells (Morris and Schmid, 1995), syndapin I is
detectable at high levels in the (adult) brain and accumulates
in synaptic compartments (Plomann et al., 1998; Qualmann et
al., 1999; Kessels and Qualmann, 2002; Modregger et al.,
2002) (Fig. 4). This might reflect the need for high-capacity
and high-speed recycling of synaptic vesicles in neurons,
which might be facilitated by the coupling of membrane
trafficking to the cytoskeleton by syndapins (Gundelfinger et
al., 2003).
Such coupling might also be highly important in nonneuronal, regulated secretory cells. Lacrimal acini cells, for
example, are the principal source of tear proteins that are
released into nascent tear fluid at the apical plasma membrane.
These cells perform massive exocytosis and compensatory
endocytosis. Membrane trafficking processes in polarized cells
like these must be tightly controlled in order to generate and
maintain polarity. Endocytosis and exocytosis at the apical
surface of many epithelial cells has to occur within an elaborate
cortical actin network. Interference with syndapin interactions
by introduction of the syndapin I or syndapin II SH3 domain
Table 1. Differential expression of syndapin isoforms
I
Isoform
Amino
acids RNA expression
Protein expression
References
Mouse PACSIN 1
441
4.1 kb transcript in total adult brain; absent
in total brain P10, thymus, liver, spleen,
kidney and heart
50 kDa signal in total brain; absent in thymus,
liver, spleen, kidney, heart and lung
Plomann et al., 1998
Rat syndapin I
441
n.d.*
52 kDa signal in brain and low levels in PC12
cells. Not detectable in liver, kidney, spleen, lung,
heart and skeletal muscle
Qualmann et al., 1999
4.4 kb transcript in brain; lower in heart
and pancreas; absent in placenta, lung,
liver, skeletal muscle and kidney
n.d.
Sumoy et al., 2001
Two transcripts of 3.7 and 7.2 kb in all
tissues tested (gizzard, liver, cardiac muscle,
skeletal muscle, brain, lung, intestine, kidney,
skin, eye, chicken embryonic heart fibroblast
cells)
63 kDa signal in all tissues tested (cardiac muscle,
brain, lung, intestine and chicken embryonic
heart fibroblast cells)
Meriläinen et al.,
1997
Mouse PACSIN 2 486
3.5 kb transcript; ubiquitous (brain, thymus,
liver, spleen, kidney, heart, lung, muscle,
testis, ovaries); highest levels in brain, heart,
skeletal muscle and ovaries
65 kDa signal in brain, thymus, liver, spleen,
kidney, heart, lung, muscle, testis and uterus
Ritter et al., 1999
Human PACSIN 2 486
3.4 kb transcript, ubiquitous (brain, heart,
pancreas, placenta, lung, liver, skeletal
muscle, kidney)
n.d.
Ritter et al., 1999
Rat syndapin II
IIbb
IIab
IIba
Iiaa
n.d.
Ubiquitously expressed with a different tissue
Qualmann and Kelly,
distribution for the short and long splice variants.
2000
65 kDa signal preferentially in PC12 cells and heart;
52 kDa signal in most tissues examined (brain, liver,
kidney, spleen, heart, testis and skeletal muscle)
n.d.
Doublet of 65/72 kDa as early as two-cell stage
In all three germ layers (with varying intensities);
high levels in neural crest cells, lens, pronephros
tissue and neural tube
Cousin et al., 2000
2.0 kb transcript in skeletal muscle and heart
48 kDa signal in skeletal muscle, heart and lung
(weak in kidney, uterus and brain); no signal in
liver, spleen, testis and thymus
Modregger et al.,
2000; Sumoy et al.,
2001
2.0 kb transcript, enhanced in heart and
skeletal muscle; low levels rather ubiquitous
(brain, heart, pancreas, placenta, lung, liver
skeletal muscle and kidney)
n.d.
Modregger et al.,
2000; Sumoy et al.,
2001
Human PACSIN 1 444
II Chicken FAP52
448
445
447
486
488
Frog X-PACSIN 2 477
III Mouse PACSIN 3 424
Human PACSIN 3 424
*n.d., not determined.
3084
Journal of Cell Science 117 (15)
Fig. 4. Immunofluorescence microscopy images of syndapin
isoforms I, II and III in different cell types. (A) Rat hippocampal
neurons in culture immunostained for syndapin I (green) and for the
synaptic vesicle marker synaptophysin (red); merged confocal image,
colocalization appears yellow. Reproduced with permission from The
American Society for Cell Biology (Qualmann et al., 1999).
(B,C) Isolated rabbit lacrimal acini (lumen marked by asterisks)
treated with the cytoskeletal toxin cytochalasin D display an
accumulation of syndapin II (B) close to the actin-rich (C) apical
membrane; confocal images. Reproduced with permission from The
American Society for Cell Biology (da Costa et al., 2003).
(D) Differentiated C2F3 myotubes immunostained for the syndapin
III isoform (image kindly provided by M. Plomann).
significantly increases the F-actin content of these cells (da
Costa et al., 2003) and blocks endocytosis at the stage of
clathrin-coated pit formation. The result is a remarkable
accumulation of components of the endocytic machinery at the
apical plasma membrane and an increase in the number of
clathrin-coated structures. Both phenotypes depend on the
Arp2/3 complex, which suggests that the endocytosis block is
caused by extensive actin polymerization elicited by the
syndapin SH3 domains (da Costa et al., 2003). The syndapin
isoform expressed in these specialized secretory cells is mainly
the long version of syndapin II. Syndapin II but not syndapin
I accumulates together with other endocytic components, such
as clathrin and AP2, at the apical plasma membrane when these
cells are stimulated by secretagogues, such as carbachol, or
incubated with cytoskeletal toxins (da Costa et al., 2003) (Fig.
4). This suggests that the syndapin II isoform preferentially
participates in apical endocytosis.
A further isoform-specific function might exist for the SH3domain-mediated interaction with the huntingtin protein. This
protein, which contains extended polyglutamine stretches in
patients with Huntington’s disease, binds directly to the brainspecific syndapin I isoform in vitro but not to the other two
isoforms (Modregger et al., 2002). If this occurs in vivo,
huntingtin would be the first SH3-domain-binding partner of
syndapins that is specific for one isoform. Interestingly, the
presence of an extended polyglutamine stretch in the huntingtin
protein seems to enhance the binding of syndapin I in
yeast two-hybrid analyses. Biochemical fractionation and
immunocytochemical analysis has suggested that syndapin is
relocalized in tissue from one Huntington’s disease patient
(Modregger et al., 2002). Huntingtin can associate with a
plethora of factors involved in clathrin-mediated endocytosis,
including α-adaptin, huntingtin-interacting protein 1 (HIP1),
HIP1-related protein (HIP1R), endophilin and syndapin. All
of these interactions are modulated by the length of the
polyglutamine repeat (Harjes and Wanker, 2003). It thus seems
possible that defects in membrane trafficking triggered by
extended polyglutamine stretches participate in the pathology
of Huntington’s disease.
Finally, syndapins have very recently been shown to interact
with EHD (eps15-homology domain) proteins (Braun et al.,
2004), which are implicated in endocytic vesicle formation
and/or recycling (Grant et al., 2001; Lin et al., 2001; Guilherme
et al., 2004). The interaction is mediated by the syndapin NPF
motifs and the highly conserved EH domain present in all four
EHD isoforms (Braun et al., 2004). All syndapin III proteins
known thus far (Fig. 3) lack NPFs; the interaction is therefore
specific for the phylogenetically younger syndapin I and II
isoforms.
Perspectives
Coordination of the cytoskeleton with membrane trafficking
processes at various sites within cells is a complex task that is
probably very important for cellular organization and for the
function of individual cells within the context of complex
tissues and organs. Studying syndapins as molecular
components that can link the actin cytoskeleton with vesicle
formation processes at the plasma membrane and at the Golgi
apparatus will continue to provide us with a valuable research
avenue that leads to a deeper understanding of the individual
processes, their interconnection and the physiological
processes within multicellular organisms that rely on them.
Syndapin functions are probably similar to those of other
molecular links between actin and membrane trafficking, such
as the F-actin-binding proteins Abp1 and cortactin. In common
with syndapins, Abp1 and cortactin associate with dynamin
and thus appear to play a role in endocytosis (Kessels et al.,
2001; Mise-Omata et al., 2003; Cao et al., 2003). A plausible
Syndapin interactions and functions
hypothesis is that the three proteins work together in sequential
steps of a self-accelerating process of actin polymerization at
sites of endocytosis. Syndapins seem to couple de novo actin
nucleation at the vesicle membrane to the dynamin-mediated
vesicle fission step by activating the Arp2/3 complex activator
N-WASP, which has been localized to actin-membrane
interfaces. By contrast, cortactin has the ability to activate the
Arp2/3 complex directly (Olazabal and Machesky, 2001). As
a starting point for filament polymerization, cortactin might use
existing actin fibres, such as those created by syndapin, NWASP and the Arp2/3 complex at the vesicle surface. This
would create branched dynamic actin structures that could be
coupled to the vesicle fission machinery by both cortactin and
Abp1 (Orth and McNiven, 2003). Indeed, the endocytic role of
Abp1 depends on its ability to bind to F-actin (Kessels et al.,
2001). Furthermore, Abp1 and cortactin might help organize
actin tails to propel vesicles.
To identify how syndapins coordinate actin nucleation with
the fission event, it will be important to dissect syndapin
regulation and to study the interactions with the signalling
components in more detail. Furthermore, studies comparing
various syndapins in terms of (different) sets of interacting
proteins, their means of regulation and their functions in
different cell systems should shed light on the functions of
individual syndapin isoforms and splice variants. This might
reveal how the cellular functions of syndapins can be finetuned and adapted to cope with the different needs of various
cell types. Comparing the specialized roles of the individual
syndapins in different cell types and studying gene-knockout
models, particularly in worms and insects, which posses only
a single syndapin gene, will also highlight common principles
in vesicle trafficking from different cellular membranes such
as the plasma membrane and Golgi membranes.
We thank Sarah Hamm-Alvarez and Markus Plomann for their
immunofluorescence images, and we apologize to those whose work
could not be cited and covered in more detail because of space
limitations. This work was supported by fellowships from the
Deutsche Forschungsgemeinschaft (Qu116/2-3; Qu116/3-1) and the
Kultusministerium Land Sachsen-Anhalt (LSA 3451A/0502M).
References
Beck, K. A. and Nelson, W. J. (1998). A spectrin membrane skeleton of the
Golgi complex. Biochim. Biophys. Acta. Mol. Cell Res. 1404, 153-160.
Braun, A., Pinyol i Agelet, R., Dahlhaus, R., Grant, B. D., Kessels, M. M.
and Qualmann, B. (2004). Interaction of EHD proteins with syndapin I and
II, a basis for functional connections between membrane trafficking and the
actin cytoskeleton. Eur. J. Cell Biol. 83 Suppl. 54, 81 (Abstract MS10-3).
Cao, H., Orth, J. D., Chen, J., Weller, S. G., Heuser, J. E. and McNiven,
M. A. (2003). Cortactin is a component of clathrin-coated pits and
participates in receptor-mediated endocytosis. Mol. Biol. Cell 23, 21622170.
Cousin, H., Gaultier, A., Bleux, C., Darribère, T. and Alfandari, D. (2000).
PACSIN2 is a regulator of the metalloprotease/disintegrin ADAM13. Dev.
Biol. 227, 197-210.
Cremona, O., di Paolo, G., Wenk, M. R., Lüthi, A., Kim, W. T., Takei, K.,
Daniell, L., Nemoto, Y., Shears, S. B., Flavell, R. A. et al. (1999). Essential
role of phosphoinositide metabolism in synaptic vesicle recycling. Cell 99,
179-188.
da Costa, S. R., Sou, E., Xie, J., Yarber, F. A., Okamoto, C. T., Pidgeon,
M., Kessels, M. M., Mircheff, A. K., Schechter, J. E., Qualmann, B. et
al. (2003). Impairing actin filament or syndapin functions promotes
accumulation of clathrin-coated vesicles at the apical plasma membrane of
acinar epithelial cells. Mol. Biol. Cell 14, 4397-4413.
3085
De Matteis, M. A. and Morrow, J. S. (2000). Spectrin tethers and mesh in
the biosynthetic pathway. J. Cell Sci. 113, 2331-2343.
di Campli, A., Valderrama, F., Babià, T., de Matteis, M. A., Luini, A. and
Egea, G. (1999). Morphological changes in the Golgi complex correlate
with actin cytoskeleton rearrangements. Cell Motil. Cytoskeleton 43, 334348.
Engqvist-Goldstein, Å. E. Y. and Drubin, D. G. (2003). Actin assembly and
endocytosis: from yeast to mammals. Annu. Rev. Cell Dev. Biol. 19, 287332.
Fucini, R. V., Chen, J. L., Sharma, C., Kessels, M. M. and Stamnes, M.
(2002). Golgi vesicle proteins are linked to the assembly of an actin complex
defined by mAbp1. Mol. Biol. Cell 13, 621-631.
Ghadimi, M. P., Sanzenbacher, R., Thiede, B., Wenzel, J., Jing, Q.,
Plomann, M., Borkhardt, A., Kabelitz, D. and Janssen, O. (2002).
Identification of interaction partners of the cytosolic polyproline region of
CD95 ligand (CD178). FEBS Lett. 519, 50-58.
Grant, B., Zhang, Y., Paupard, M. C., Lin, S. X., Hall, D. H. and Hirsh,
D. (2001). Evidence that RME-1, a conserved C. elegans EH-domain
protein, functions in endocytic recycling. Nat. Cell Biol. 3, 573-579.
Guilherme, A., Soriano, N. A., Bose, S., Holik, J., Bose, A., Pomerleau, D.
P., Furcinitti, P., Leszyk, J., Corvera, S. and Czech, M. P. (2004). EHD2
and the novel EH-domain binding protein EHBP1 couple endocytosis to the
actin cytoskeleton. J. Biol. Chem. 279, 10593-10605.
Gundelfinger, E. D., Kessels, M. M. and Qualmann, B. (2003). Temporal
and spatial coordination of exocytosis and endocytosis. Nat. Rev. Mol. Cell.
Biol. 4, 127-139.
Harjes, P. and Wanker, E. E. (2003). The hunt for huntingtin function:
interaction partners tell many different stories. Trends Biochem. Sci. 28, 425433.
Higgs, H. N. and Pollard, T. D. (2001). Regulation of actin filament network
formation through Arp2/3 complex: activation by a diverse array of proteins.
Annu. Rev. Biochem. 70, 649-676.
Hilfiker, S., Pieribone, V. A., Czernik, A. J., Kao, H. T., Augustine, G. J.
and Greengard, P. (1999). Synapsins as regulators of neurotransmitter
release. Philos. Trans. R. Soc. London B. Biol. Sci. 354, 269-279.
Hilton, J. M., Plomann, M., Ritter, B., Modregger, J., Freeman, H. N.,
Falck, J. R., Krishna, U. M. and Tobin, A. B. (2001). Phosphorylation of
a synaptic vesicle-associated protein by an inositol hexakisphosphateregulated protein kinase. J. Biol. Chem. 276, 16341-16347.
Hinshaw, J. E. (2000). Dynamin and its role in membrane fission. Annu. Rev.
Cell Dev. Biol. 16, 483-519.
Howard, L., Nelson, K. K., Maciewicz, R. A. and Blobel, C. P. (1999).
Interaction of the metalloprotease disintegrins MDC9 and MDC15 with two
SH3 domain-containing proteins, endophilin I and SH3PX1. J. Biol. Chem.
274, 31693-31699.
Janssen, O., Qian, J., Linkermann, A. and Kabelitz, D. (2003). CD95
ligand-death factor and costimulatory molecule? Cell Death Differ. 10,
1215-1225.
Jones, S. M., Howell, K. E., Henley, J. R., Cao, H. and McNiven, M. A.
(1998). Role of dynamin in the formation of transport vesicles from the
trans-Golgi network. Science 279, 573-577.
Kessels, M. M., Engqvist-Goldstein, Å. E. Y., Drubin, D. G. and
Qualmann, B. (2001). Mammalian Abp1, a signal-responsive F-actinbinding protein, links the actin cytoskeleton to endocytosis via the GTPase
dynamin. J. Cell Biol. 153, 351-366.
Kessels, M. M. and Qualmann, B. (2002). Syndapins integrate N-WASP in
receptor-mediated endocytosis. EMBO J. 21, 6083-6094.
Kessels, M. M., Dong, J., Westermann, P. and Qualmann, B. (2003).
Dynamin II and syndapin II form heterodimeric complexes promoting
vesicle formation at the trans-Golgi network. Mol. Biol. Cell 14 Suppl.,
377a (Abstract 2111).
Kim, A. S., Kakalis, L. T., Abdul-Manan, N., Liu, G. A. and Rosen, M. K.
(2000). Autoinhibition and activation mechanisms of the Wiskott-Aldrich
syndrome protein. Nature 404, 151-158.
Lee, E. and de Camilli, P. (2002). Dynamin at actin tails. Proc. Natl. Acad.
Sci. USA 99, 161-166.
Lin, S. X., Grant, B., Hirsh, D. and Maxfield, F. R. (2001). Rme-1 regulates
the distribution and function of the endocytic recycling compartment in
mammalian cells. Nat. Cell Biol. 3, 567-572.
Luna, A., Matas, O. B., Martínez-Menárguez, J. A., Mato, E., Durán, J.
M., Ballesta, J., Way, M. and Egea, G. (2002). Regulation of protein
transport from the Golgi complex to the endoplasmic reticulum by CDC42
and N-WASP. Mol. Biol. Cell 13, 866-879.
3086
Journal of Cell Science 117 (15)
McFarlane, S. (2003). Metalloproteases: carving out a role in axon guidance.
Neuron 37, 559-562.
McNiven, M. A., Kim, L., Krueger, E. W., Orth, J. D., Cao, H. and Wong,
T. W. (2000). Regulated interactions between dynamin and the actin-binding
protein cortactin modulate cell shape. J. Cell Biol. 151, 187-198.
Meriläinen, J., Lehto, V. P. and Wasenius, V. M. (1997). FAP52, a novel,
SH3 domain-containing focal adhesion protein. J. Biol. Chem. 272, 2327823284.
Merrifield, C. J., Feldman, M. E., Wan, L. and Almers, W. (2002). Imaging
actin and dynamin recruitment during invagination of single clathrin-coated
pits. Nat. Cell Biol. 4, 691-698.
Merrifield, C. J., Qualmann, B., Kessels, M. M. and Almers, W. (2004).
Neural Wiskott Aldrich Syndrome Protein (N-WASP) and the Arp2/3
complex are recruited to sites of clathrin-mediated endocytosis in cultured
fibroblasts. Eur. J. Cell Biol. 83, 13-18.
Miki, H., Sasaki, T., Takai, Y. and Takenawa, T. (1998). Induction of
filopodium formation by a WASP-related actin-depolymerizing protein NWASP. Nature 391, 93-96.
Mise-Omata, S., Montagne, B., Deckert, M., Wienands, J. and Acuto, O.
(2003). Mammalian actin binding protein 1 is essential for endocytosis but
not lamellipodia formation: functional analysis by RNA interference.
Biochem. Biophys. Res. Commun. 301, 704-710.
Modregger, J., Ritter, B., Witter, B., Paulsson, M. and Plomann, M. (2000).
All three PACSIN isoforms bind to endocytic proteins and inhibit
endocytosis. J. Cell Sci. 113, 4511-4521.
Modregger, J., DiProspero, N. A., Charles, V., Tagle, D. A. and Plomann,
M. (2002). PACSIN 1 interacts with huntingtin and is absent from synaptic
varicosities in presymptomatic Huntington’s disease brains. Hum. Mol.
Genet. 11, 2547-2558.
Mori, S., Tanaka, M., Nanba, D., Nishiwaki, E., Ishiguro, H.,
Higashiyama, S. and Matsuura, N. (2003). PACSIN3 binds
ADAM12/meltrin α and up-regulates ectodomain shedding of heparinbinding epidermal growth factor-like growth factor. J. Biol. Chem. 278,
46029-46034.
Morris, S. A. and Schmid, S. L. (1995). Synaptic vesicle recycling. The
Ferrari of endocytosis? Curr. Biol. 5, 113-115.
Müsch, A., Cohen, D., Kreitzer, G. and Rodriguez-Boulan, E. (2001). cdc42
regulates the exit of apical and basolateral proteins from the trans-Golgi
network. EMBO J. 20, 2171-2179.
Nikki, M., Meriläinen, J. and Lehto, V. P. (2002a). FAP52 regulates actin
organization via binding to filamin. J. Biol. Chem. 277, 11432-11440.
Nikki, M., Meriläinen, J. and Lehto, V. P. (2002b). Focal adhesion protein
FAP52 self-associates through a sequence conserved among the members
of the PCH family proteins. Biochemistry 41, 6320-6329.
Olazabal, I. M. and Machesky, L. M. (2001). Abp1p and cortactin, new
‘hand-holds’ for actin. J. Cell Biol. 154, 679-682.
Orth, J. D. and McNiven, M. A. (2003). Dynamin at the actin-membrane
interface. Curr. Opin. Cell Biol. 15, 31-39.
Orth, J. D., Krueger, E. W., Cao, H. and McNiven, M. A. (2002). The large
GTPase dynamin regulates actin comet formation and movement in living
cells. Proc. Natl. Acad. Sci. USA 99, 167-172.
Plomann, M., Lange, R., Vopper, G., Cremer, H., Heinlein, U. A. O.,
Scheff, S., Baldwin, S. A., Leitges, M., Cramer, M., Paulsson, M. et al.
(1998). PACSIN, a brain protein that is upregulated upon differentiation into
neuronal cells. Eur. J. Biochem. 256, 201-211.
Qualmann, B. and Kelly, R. B. (2000). Syndapin isoforms participate in
receptor-mediated endocytosis and actin organization. J. Cell Biol. 148,
1047-1061.
Qualmann, B. and Kessels, M. M. (2002). Endocytosis and the cytoskeleton.
Int. Rev. Cytol. 220, 93-144.
Qualmann, B., Roos, J., DiGregorio, P. J. and Kelly, R. B. (1999). Syndapin
I, a synaptic dynamin-binding protein that associates with the neural
Wiskott-Aldrich syndrome protein. Mol. Biol. Cell 10, 501-513.
Qualmann, B., Gundelfinger, E. D. and Kessels, M. M. (2000a). Regulated
function of syndapins at the interconnection of endocytosis, cytoskeletal
dynamics and signal transduction. Mol. Biol. Cell 11, 216a (Abstr.).
Qualmann, B., Kessels, M. M. and Kelly, R. B. (2000b). Molecular links
between endocytosis and the actin cytoskeleton. J. Cell Biol. 150, F111F116.
Ritter, B., Modregger, J., Paulsson, M. and Plomann, M. (1999). PACSIN
2, a novel member of the PACSIN family of cytoplasmic adapter proteins.
FEBS Lett. 454, 356-362.
Schlöndorff, J. and Blobel, C. P. (1999). Metalloprotease-disintegrins:
modular proteins capable of promoting cell-cell interactions and triggering
signals by protein-ectodomain shedding. J. Cell Sci. 112, 3603-3617.
Scita, G., Nordstrom, J., Carbone, R., Tenca, P., Giardina, G., Gutkind,
S., Bjarnegård, M., Betsholtz, C. and di Fiore, P. P. (1999). EPS8 and
E3B1 transduce signals from Ras to Rac. Nature 401, 290-293.
Sever, S., Damke, H. and Schmid, S. L. (2000). Garrotes, springs, ratchets,
and whips: putting dynamin models to the test. Traffic 1, 385-392.
Simpson, F., Hussain, N. K., Qualmann, B., Kelly, R. B., Kay, B. K.,
McPherson, P. S. and Schmid, S. L. (1999). SH3-domain-containing
proteins function at distinct steps in clathrin-coated vesicle formation. Nat.
Cell Biol. 1, 119-124.
Stamnes, M. (2002). Regulating the actin cytoskeleton during vesicular
transport. Curr. Opin. Cell Biol. 14, 428-433.
Sumoy, L., Pluvinet, R., Andreu, N., Estivill, X. and Escarceller, M. (2001).
PACSIN 3 is a novel SH3 domain cytoplasmic adapter protein of the pacsinsyndapin-FAP52 gene family. Gene 262, 199-205.
Taunton, J. (2001). Actin filament nucleation by endosomes, lysosomes and
secretory vesicles. Curr. Opin. Cell Biol. 13, 85-91.
Valderrama, F., Babià, T., Ayala, I., Kok, J. W., Renau-Piqueras, J. and
Egea, G. (1998). Actin microfilaments are essential for the cytological
positioning and morphology of the Golgi complex. Eur. J. Cell Biol. 76, 917.
Valderrama, F., Durán, J. M., Babià, T., Barth, H., Renau-Piqueras, J. and
Egea, G. (2001). Actin microfilaments facilitate the retrograde transport
from the Golgi complex to the endoplasmic reticulum in mammalian cells.
Traffic 2, 717-726.
Wasiak, S., Quinn, C. C., Ritter, B., de Heuvel, E., Baranes, D., Plomann,
M. and McPherson, P. S. (2001). The Ras/Rac guanine nucleotide
exchange factor mSos interacts with PACSIN 1/syndapin I, a regulator of
endocytosis and the actin cytoskeleton. J. Biol. Chem. 276, 26622-26628.
Welch, M. D. and Mullins, R. D. (2002). Cellular control of actin nucleation.
Annu. Rev. Cell Dev. Biol. 18, 247-288.
Zhang, J., Shehabeldin, A., da Cruz, L. A. G., Butler, J., Somani, A. K.,
McGavin, M., Kozieradzki, I., dos Santos, A. O., Nagy, A., Grinstein, S.
et al. (1999). Antigen receptor-induced activation and cytoskeletal
rearrangement are impaired in Wiskott-Aldrich syndrome protein-deficient
lymphocytes. J. Exp. Med. 190, 1329-1342.