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Oncogene (2001) 20, 1594 ± 1600
2001 Nature Publishing Group All rights reserved 0950 ± 9232/01 $15.00
www.nature.com/onc
Cell communication networks: epidermal growth factor receptor
transactivation as the paradigm for interreceptor signal transmission
Andreas Gschwind1, Esther Zwick1, Norbert Prenzel1, Michael Leserer1 and Axel Ullrich*,1
1
Max-Planck-Institut fuÈr Biochemie, Martinsried, Germany
Communication between di€erent cellular signaling
systems has emerged as a common principle that enables
cells to integrate a multitude of signals from its
environment. Transactivation of the epidermal growth
factor receptor (EGFR) represents the paradigm for
cross-talk between G protein-coupled receptors (GPCRs)
and receptor tyrosine kinases (RTKs). The recent
identi®cation of Zn2+-dependent metalloproteinases and
transmembrane growth factor precursors as critical
elements in GPCR-induced EGFR transactivation pathways has de®ned new components of a cellular
communication network of rapidly increasing complexity. Further elucidation of the molecular details of the
EGFR transactivation mechanism will provide new
understanding of its relevance for normal physiological
processes and their pathophysiological deviations.
Oncogene (2001) 20, 1594 ± 1600.
Keywords: EGFR; GPCR; transactivation; cross-talk;
ectodomain shedding; ADAMs
Introduction
Cross-communication between diverse signaling networks is a well established concept in the cellular
stimulus-response conversion system that allows the
translation of complex environmental conditions into
appropriate reactions and adaptations. The EGFR
which belongs to a family of four closely related
receptor tyrosine kinases has been recognized as a
convergence point for diverse signal transduction
pathways (reviewed in Hackel et al., 1999; Moghal
and Sternberg, 1999). Depending on the activating
ligand EGFR family members are able to form various
homo- or heterodimers with di€erent biological
signaling capacities (reviewed in Olayioye et al.,
2000). While signaling through the EGFR family
kinases is essential for the development of fruit ¯ies,
nematodes and mice (Moghal and Sternberg, 1999),
their critical importance for the human organism is
underscored by their frequent involvement in cancer
development due to overexpression, activating muta-
*Correspondence: A Ullrich, Max-Planck-Institut fuÈr Biochemie,
Department of Molecular Biology, Am Klopferspitz 18A, 82152
Martinsried, Germany
tions or autocrine stimulation by diverse EGF-like
ligands.
The six known ligands that act as direct agonists for
the EGFR, EGF, heparin-binding EGF-like growth
factor (HB-EGF), transforming growth factor alpha
(TGFa), amphiregulin, betacellulin and epiregulin are
synthesized as transmembrane precursors and must
therefore be proteolytically cleaved by metalloproteases
to release the mature growth factor (reviewed in
Massague and Pandiella, 1993). The agonist occupied
EGFR undergoes autophosphorylation and activates
the Ras/mitogen activated protein (MAP) kinase
pathway through initial tyrosine phosphorylation of
the adaptor protein SHC, subsequent formation of a
SHC-Grb2-Sos complex and Ras-mediated induction
of Raf function. This prototypical signaling pathway
couples EGFR stimulation to gene transcription and
mitogenesis.
In addition to its cognate ligands, the EGFR is
activated by stimuli that do not directly interact with
the EGFR ectodomain including GPCR ligands, other
RTK agonists, cytokines, chemokines and cell adhesion
elements. Furthermore the EGFR signal may also be
released by non-physiological in¯uences such as UV
and gamma radiation, osmotic shock, membrane
depolarization, heavy metal ions and radical-generating
agents such as hydrogenperoxide (King et al., 1989;
reviewed in Carpenter, 1999; Zwick et al., 1999a;
Prenzel et al., 1999a,b; Leserer et al., 2000). Due to
recent advances in the elucidation of the EGFR
transactivation mechanism we now begin to understand the biological and pathophysiological signi®cance
of these complex signaling networks.
Cross-talk between GPCRs and the EGFR
Occurrence of EGFR transactivation in diverse cell types
Following the early observation by Faure et al. (1994)
that agonist stimulation of COS7 cells transiently
expressing Gq-, or Gi-coupled receptors results in
MAPK activation, in 1996, Daub et al. (1996)
described a critical role of the EGFR in GPCRinduced mitogenesis of rat ®broblasts. They demonstrated that the EGFR and its relative HER2 were
rapidly tyrosine phosphorylated after stimulation of
Rat1 cells with the GPCR agonists endothelin-1 (ET1), lysophosphatidic acid (LPA) or thrombin. This
EGFR transactivation
A Gschwind et al
transactivation of a receptor tyrosine kinase coupled
GPCR-ligand engagement to extracellular regulated
kinase (ERK)-activation, induction of fos gene expression and DNA synthesis which were abrogated either
by the selective EGFR inhibitor tyrphostin AG1478 or
by expression of a dominant-negative EGFR mutant.
Further investigations revealed that the GPCREGFR cross-talk mechanism was installed in a variety
of other cell types such as human keratinocytes,
primary mouse astrocytes, PC12 cells and vascular
smooth muscle cells (Daub et al., 1997; Zwick et al.,
1997; Eguchi et al., 1998) and established it as a widely
relevant pathway towards the activation of the MAP
kinase signal. Subsequent work provided evidence for
widespread use of EGFR signal transactivation by
diverse GPCRs and the capacity of di€erent G-proteins
to generate the necessary connections (Table 1).
Interestingly, LPA-induced transactivation of the
EGFR in COS-7 cells was attenuated by pertussis
toxin (PTX), whereas thrombin-stimulated EGFR
tyrosine phosphorylation and downstream signaling
was not a€ected (Daub et al., 1997). Furthermore,
agonist stimulation of ectopically expressed Gq-coupled
bombesin (BombR) or Gi-coupled M2 muscarinic
acetylcholine receptor (M2R) triggered EGFR transactivation followed by tyrosine phosphorylation of SHC
and formation of SHC-Grb2 complexes. These results
demonstrated that EGFR transactivation occurs via
both PTX-insensitive and -sensitive pathways and that
EGFR inhibition strongly impairs MAP kinase activation by Gq- and Gi-coupled receptors in COS-7 cells.
More recent studies showed that EGFR tyrosine
phosphorylation induced by the GPCR agonist substance P is PTX-sensitive in U-373 MG cells
(Castagliuolo et al., 2000) and that Ga13 subunits
mediate LPA-induced actin polymerization and actin
stress ®ber formation in Swiss 3T3 cells and mouse
®broblasts via EGFR transactivation (Gohla et al.,
1998, 1999). In summary, Gi-, Gq- as well as G13-
coupled receptors have been reported to transactivate
the EGFR after agonist stimulation in diverse cell
systems, whereas up to now there is no data available
concerning an analogous function of Gs-coupled
receptors.
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Characteristics of the EGFR transactivation signal
Several studies indicate that the EGFR transactivation
mechanism is subject to di€erent cell type-characteristic
regulatory in¯uences. In neuron-like PC12 cells,
vascular smooth muscle cells and intestinal epithelial
cells intracellular Ca2+ concentration has been demonstrated to be a critical parameter in Gq-coupled
receptor mediated EGFR transactivation upon bradykinin, angiotensin II (AngII), ET-1 or carbachol
stimulation (Zwick et al., 1997; Solto€, 1998; Eguchi
et al., 1998; Murasawa et al., 1998; Iwasaki et al.,
1999). Moreover, in ovarian cancer cells it was shown
that through activation of Gq-coupled heptahelical
receptors the chemokine interleukin-8 (IL-8) induces
EGFR activation in a Ca2+-dependent manner (Venkatakrishnan et al., 2000) and a recent study provides
evidence that the pathogenic dermatonecrotic toxin
produced by Pasteurella multocida (rPMT) exerts its
mitogenic e€ect on HEK 293 cells through a Gqdependent pathway involving EGFR-dependent ERK
activation (Seo et al., 2000).
Activation of the Ser/Thr protein kinase C (PKC)
was shown to be required for Gq-coupled receptors to
induce EGFR transactivation in HEK 293 and PC12
cells (Tsai et al., 1997; Solto€, 1998) as well as in
response to gonadotropin-releasing hormone in a
variety of cell lines such as gonadotropic aT3-1 cells
(Grosse et al., 2000). In rat liver epithelial cells,
however, Li et al. (1998) proposed an AngII-stimulated
EGFR-dependent signaling pathway to Ras only when
PKC activity was inhibited. In contrast, others have
reported that bradykinin-stimulated ERK activation
Table 1 Cross-talk between G protein-coupled receptors and the epidermal growth factor receptor (adapted from Zwick et al., 1999a,b)
GPCR ligand
Endothelin-1, LPA, Thrombin
Bradykinin
Bombesin, Carbachol, LPA
Angiotensin II
Thrombin, LPA
Thrombin
Carbachol
G proteins involved
?
Gq
Gq, Gi
Gq
?
?
Gq
Carbachol
Gq
LPA
LPA
LPA
G13
?
?
Bombesin
Substance P
Interleukin-8
?
Gi
Gq
Cell type or tissue
Cellular response
Reference
Rat-1
ERK activation, FOS transcription
Daub et al., 1996
PC-12
ERK activation
Zwick et al., 1997
COS-7
ERK activation
Daub et al., 1997
vascular smooth muscle
ERK activation
Eguchi et al., 1998
HaCaT
ERK activation
Daub et al., 1997
primary astrocytes
ERK activation
Daub et al., 1997
HEK 293
Modulation of Kv1.2 ion
Tsai et al., 1997
channel activity
T84
ERK activation, inhibition
Keely et al., 1998
of Cl7 secretion
Swiss 3T3
stress fiber formation
Gohla et al., 1998
HeLa
ERK activation
Cunnick et al., 1998
NIH3T3
MKK1/2 activation,
Cunnick et al., 1998
DNA synthesis
PC3
EGFR tyrosine phosphorylation
Prenzel et al., 1999
U-373 MG
ERK activation, DNA synthesis
Castagliuolo et al., 2000
SK-OV-3
ERK activation, morphology
Venkatakrishnan et al., 2000
changes
Abbreviations: extracellular regulated kinase (ERK), lysophosphatidic acid (LPA), mitogen-activated protein kinase kinase 1 and 2 (MKK1/2)
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EGFR transactivation
A Gschwind et al
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requires simultaneous signaling via both PKC and
EGFR in COS-7 cells that are transiently expressing
the bradykinin B2 receptor (Adomeit et al., 1999). In
this study Adomeit et al. (1999) report that inhibition
of phosphoinositide 3-kinase g (PI3Kg) failed to
diminish bradykinin-induced ERK activation, whereas
in the same cell system Daub et al. (1997) demonstrated that the PI3K inhibitors wortmannin and
LY294002 signi®cantly reduced ERK activity stimulated through M2R, BombR or in response to LPA or
EGF. The latter result was con®rmed in a more recent
study where accumulation of PI3K lipid products was
directly measured after LPA stimulated EGFR transactivation in COS-7 cells (La€argue et al., 1999).
Interestingly, in vascular smooth muscle cells AngIIinduced p70S6K activation is mediated via both ERK
and PI3K/Akt cascades that bifurcate at the point of
EGFR-dependent Ras activation (Eguchi et al., 1999).
In agreement with these results Iwasaki et al. (1999)
reported that ET-1-mediated vascular growth requires
ERK and p70S6K signaling through transactivation of
the EGFR.
Besides the function of PKC in GPCR-mediated
EGFR transactivation Matsubara and coworkers
reported Ca2+/calmodulin-dependent receptor activation in Ang II-stimulated cardiac ®broblasts (Murasawa et al., 1998). Similarly in PC12 cells Zwick et al.
(1999a,b) demonstrated the involvement of a Ca2+calmodulin-dependent kinase II (CaMK II) activity in
K+-but not bradykinin-induced EGFR signal transactivation (reviewed in Prenzel et al., 2000). The role of
another Ca2+-dependent kinase, PYK2, in the transmission of mitogenic signals is somewhat controversial.
While Solto€ (1998) and Keely et al. (2000) suggested a
role of this tyrosine kinase in Gq-mediated EGFR
tyrosine phosphorylation in PC12 (Solto€, 1998) and
intestinal epithelial cells (Keely et al., 2000) respectively, Zwick et al. (1999a,b) reported Ca2+-dependent,
but PYK2-independent EGFR transactivation in
response to bradykinin in PC12 cells. Furthermore,
tyrosine phosphorylated Src is often found in association with the EGFR (Luttrell et al., 1999) or with
PYK2 (Solto€, 1998; Keely et al., 2000) upon
stimulation of Gq-coupled receptors and has therefore
been proposed to function as a mediator of EGFR
transactivation. Since other reports have demonstrated
Src-independent EGFR transactivation, but Src-dependent SHC tyrosine phosphorylation and ERK activation (Daub et al., 1997; Adomeit et al., 1999; Slack,
2000) it seems likely that Src is recruited by the
transactivated EGFR and thereby contributes to
activation of the Ras signaling pathway.
Role of endocytosis in signaling of the
GPCR-transactivated EGFR
In HEK293 and COS-7 cells stimulation of the Gicoupled b2 adrenergic receptor (b2AR) results in its
association with activated Src and b-arrestin (Luttrell
et al., 1999). The formation of this complex is thought
to be an essential step in Src-dependent activation of
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the Ras signaling pathway. Recently, however, it was
suggested that mitogenic signaling through the b2AR
and a2AAR requires transactivation of the EGFR
which for ecient ERK activation needs to be linked
to the endocytotic machinery (Maudsley et al., 2000;
Pierce et al., 2000). Hence, clathrin-mediated endocytosis has been attributed a critical role in GPCRmediated ERK activation (Figure 1). Interestingly,
receptor internalization appears to be di€erentially
regulated since upon AR stimulation and EGFR
transactivation the b 2 subtype is internalized together
with the EGFR while the a2AAR remains on the
surface of transfected COS-7 cells (Pierce et al., 2000).
Remarkably, concanavalin A (ConA)-treatment of
vascular smooth muscle cells blocked AT1R internalization, AngII-induced EGFR transactivation and
MAP kinase activation demonstrating the necessity of
an intact cytoskeleton for receptor downregulation and
signal transmission (Tang et al., 2000).
Ligand-independent pathways of GPCR-induced EGFR
transactivation
While the overall role of Ca2+, PKC and Src as
mediators of EGFR transactivation is established, little
is known about the detailed mechanism whereby
agonist-occupied GPCRs cause tyrosine phosphorylation of the EGFR. In time-course experiments GPCRinduced EGFR tyrosine phosphorylation was detectable after 2 min of stimulation (Daub et al., 1996;
Iwasaki et al., 1999). This rapid response and the fact
that soluble EGF-like growth factors could not be
detected in the culture medium (Daub et al., 1996; Tsai
et al., 1997; Eguchi et al., 1998) suggested that EGFR
transactivation is exclusively mediated through intracellular mechanisms and did not involve the interaction
of the EGFR with a ligand. This notion gained further
support by the observation that transient overexpression of Gb1g2 subunits was sucient to trigger tyrosine
phosphorylation of SHC suggesting that a physical
interaction with Gbg subunits played a role in EGFR
transactivation (Luttrell et al., 1997).
Metalloprotease-mediated shedding of EGF-like ligands
as a key step in GPCR-induced EGFR transactivation
Critical reexamination of the `ligand-independent'
EGFR transactivation hypothesis resulted in an
unexpected explanation of the ®ndings by Daub et al.
(1996) and led to the establishment of a `Triple
Membrane Passing Signal' (TMPS) mechanism that
involves a metalloprotease activity and the processing
of transmembrane EGF-like growth factor precursors.
Prenzel et al. (1999) ®rst showed that a chimeric RTK
consisting of the EGFR ectodomain and the transmembrane and intracellular portion of the PDGFR
was transactivated upon treatment of Rat1 ®broblasts
with GPCR ligands while endogenous PDGFR was
not. Hence, GPCR-induced transactivation of the
arti®cial RTK did not involve an intracellular pathway
and was dependent on the extracellular ligand-binding
EGFR transactivation
A Gschwind et al
domain of the EGFR. In addition, using the diphtheria
toxin mutant CRM197 that speci®cally blocks HBEGF function or the metalloprotease inhibitor batimastat (BB94), LPA-, carbachol- or tetra-decanoylphorbol-13-acetate (TPA)-induced transactivation of
the EGFR and tyrosine phosphorylation of SHC was
completely abrogated in COS-7 and HEK 293 cells.
Flow cytometric analysis directly con®rmed cell surface
ectodomain shedding of proHB-EGF upon treatment
with GPCR agonists or TPA. Together, these experimental data yield the novel triple membrane-passing
signal (TMPS) mechanism of EGFR transactivation
(Prenzel et al., 2000), (Figure 2) which provides new
insights towards the understanding of interreceptor
communication and helps to interpret previously
reported physiological and pathophysiological phenomena (reviewed in Carpenter, 2000; Leserer et al.,
2000). Therein, GPCR stimulation induces a metallo-
1597
Figure 1 Role of clathrin-mediated endocytosis in signaling of the GPCR-transactivated EGFR: Stimulation of GPCRs as
exempli®ed by the b2AR and the a2AAR leads to complex formation of the activated heptahelical receptor with Src and b-arrestin.
Subsequent activation of the Ras/MAP-kinase pathway is based on transactivation of the EGFR that needs to be linked to the
endocytotic machinery for ecient downstream signaling
Figure 2 Triple-membrane-passing signal mechanism of the EGFR transactivation: GPCR-induced and metalloprotease-mediated
proteolytic cleavage of EGF-like growth factor precursors leads to transactivation of the EGFR. This new mechanistic signaling
model for ligand-dependent interreceptor communication encloses three membrane passages and couples receptor activation to the
Ras/MAP kinase pathway
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EGFR transactivation
A Gschwind et al
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protease activity which cleaves the HB-EGF precursor
and allows the released growth factor to bind to the
extracellular receptor domain thereby transactivating
the EGFR signaling potential. This process also allows
the transactivation of EGFRs on neighboring cells but
only over short distances and under participation of
the heparan sulfate proteoglycan matrix which in
retrospect explains the failure of Daub et al. (1996)
to detect EGF-like activity in conditioned medium of
GPCR-ligand-stimulated Rat1 cell cultures.
This novel mechanistic concept is reinforced by
recently reported experimental data that show thrombin-induced EGFR transactivation and cell migration
of rat and baboon smooth muscle cells to be dependent
on HB-EGF shedding by a metalloprotease (Kalmes et
al., 2000).
Still, the identity of the metalloprotease and the way
it is activated upon GPCR stimulation remains to be
de®ned. A growing body of evidence, however,
suggests the involvement of members of the ADAM
(a disintegrin and metalloprotease) family of zincdependent proteases in the processing of EGF-like
precursors (Werb and Yan, 1998). Knock out of the
gene coding for ADAM17, also called tumor necrosis
factor alpha-converting enzyme (TACE), was embryonic lethal in mice and was similar to that obtained after
homozygous inactivation of the EGFR gene suggesting
a role of TACE in cleavage of EGFR ligands in mouse
development (Peschon et al., 1998). Further analysis of
embryonic ®broblasts derived from TACE knock-out
mice also displayed a de®ciency in release of soluble
TGFa compared to wild-type cells, strongly suggesting
that TACE is responsible for the cleavage of certain
EGF-like precursors (Peschon et al., 1998).
One of the unsolved problems in the TMPS pathway
is the question of metalloprotease activation through a
GPCR-mediated signal. In this regard using a reconstitution system with TACE7/7 ®broblasts Black's
group has now reported that the cytoplasmic domain
of TACE is dispensable at least for phorbolesterstimulated shedding of TNFa and other substrates
(Reddy et al., 2000) although this domain has been
observed to be phosphorylated after TPA treatment of
cells (Black et al., 1997). Similarly, TPA-induced
phosphorylation of the cytoplasmic domain of MDC9
(ADAM9) which was implicated in shedding of
proHB-EGF in Vero cells (Izumi et al., 1998) involved
protein kinase C delta (PKCd) but was not shown to
be related to MDC9 activation. Therefore, much
remains to be learned about domain requirements of
metalloproteases for cell surface ectodomain cleavage
especially in response to physiological stimuli such as
growth factors in order to understand the complex
regulatory mechanisms governing TMPS-mediated
EGFR transactivation and cellular responses such as
cell proliferation, migration and survival. Studies by
Fan and Derynck (1999) provide evidence for the
involvement of MAP kinase pathways in the regulation
of shedding events upon growth factor stimulation.
Treatment of CHO cells with platelet-derived growth
factor (PDGF), ®broblast growth factor (FGF) or
EGF induced cleavage of proTGFa through the ERK
MAP kinase pathway whereas basal proTGFa cleavage
in the absence of growth factors was dependent on p38
MAP kinase signaling.
EGFR transactivation in cancer cells
Upregulated EGFR signaling has often been correlated
with the formation and progression of human cancers
and there is growing evidence for the signi®cance of
metalloprotease-mediated release of EGF-like precursors in oncogenesis and progression. As a ®rst example
the metalloprotease inhibitor BB94 was shown to
inhibit bombesin and TPA-induced transactivation of
the EGFR in PC3 human prostate cancer cells and to
reduce high constitutive levels of EGFR tyrosine
phosphorylation in unstarved cells (Prenzel et al.,
1999). Furthermore, Dong et al. (1999) reported that
BB94 reduced cell proliferation and cell migration of a
human mammary epithelial cell line by interfering with
the release of EGFR ligands. BB94 also inhibited
proliferation of colon and breast cancer cell lines which
were known to depend on autocrine signaling through
the EGFR. In addition, EGFR function was reported
to be critical for GPCR-stimulated mitogenic signaling
in several other cancer cell lines including U-373 MG
astroglioma cells (Castagliuolo et al., 2000) and SKOV-3 ovarian cancer cells (Venkatakrishnan et al.,
2000). Together, these data strongly suggest an
important and broad role for GPCR-EGFR cross-talk
in the pathophysiology of cancer which exceeds by far
that already predicted by the early discovery of the verbB/EGFR oncogene/protooncogene relationship
(Ullrich et al., 1984). In addition to being a member
of a promiscuous family of RTKs that forms
functionally diverse heterodimers in combination with
a variety of directly binding ligands, the EGFR and its
relatives are now subject to activation through many
members of the very large GPCR family and the
di€erential use of di€erent G-proteins by these
receptors expands the physiological and pathophysiological potential of this network even further.
Transactivation of IGF1R and PDGR by GPCRs
Cross-talk between GPCRs and other RTKs besides
the EGFR has been reported to contribute to GPCRmediated mitogenic pathways in a variety of cell
systems. One of the ®rst such demonstrations involved
thrombin-induced IGF1R transactivation in primary
rat smooth muscle cells (Linseman et al., 1995; Rao et
al., 1995). Recently, Roudabush et al. (2000) showed
that ERK1/2 activation after IGF1R stimulation is
mediated by the EGFR in COS-7 cells. Interestingly,
they proposed an IGF1R-EGFR cross-talk pathway
based on metalloprotease-induced shedding of proHBEGF. Another study suggested the release of pertussis
toxin-sensitive heterotrimeric Gi proteins from agonistoccupied IGF1R (Hallak et al., 2000) which is critical
for ERK activation in certain rat neurons. Together,
EGFR transactivation
A Gschwind et al
one could envision a pathway connecting IGF1
signaling with the activation of the EGFR by release
of a population of Gbg subunits by agonist occupied
IGF1R that by an unknown mechanism activate a
metalloprotease resulting in the release of EGF-like
ligands from the cell surface.
In L cells LPA was shown to induce transactivation
of the PDGF-b-R and subsequent signaling steps
analogous to EGFR transactivation in COS-7 cells
(Herrlich et al., 1998). Furthermore, several studies
have demonstrated AngII-stimulated transactivation of
the PDGF-b-R in vascular smooth muscle cells (Linseman et al., 1995; Heeneman et al., 2000) and reported
the involvement of PTX-sensitive G-proteins in PDGFstimulated ERK activation in airway smooth muscle
cells (Conway et al., 1999). In addition, there is
evidence that in the same cell system activation of
the MAP kinase pathway is dependent on both Src and
complex formation of Grb2 with PI3K. Very recently,
a new ligand for the PDGF-a-R, PDGF-C, has been
identi®ed that is activated by proteolysis (Li et al.,
2000). When overexpressed PDGF-C causes hyperproliferation of cardiac ®broblasts in transgenic mice.
PDGF-C displays a two-domain structure consisting of
N-terminal complement proteins C1r/C1s, Uegf, and
BMP-1 like (CUB) domain and a C-terminal PDGF/
VEGF core domain connected by a hinge region. Only
the core domain functions as a high-anity ligand for
the PDGF-a-R, which is released from the CUB
domain by an unknown protease presumably at the
cell surface. These ®ndings suggest that PDGF-C could
be another growth factor that is released in its active
form the cell surface after limited proteolysis similar to
the members of the EGF-family of ligands.
1599
Conclusion
Progress in understanding the communication
mechanism between GPCRs and RTKs has revolutionized the classical view of signal transmission from
the cell surface to the nucleus which so far appeared
to be composed of largely parallel linear pathways.
In the new scenario the EGFR and HER2 as well as
the PDGFR and IGF1R can be transactivated by
agonist-occupied GPCRs and the number of RTKs
that are downstream signaling elements of haptahelical receptors is likely to increase in the future.
Although the mechanistic details of EGFR transactivation are still not fully understood it has become
obvious that metalloproteases play an important role
in signaling through GPCRs in both physiological
and pathophysiological processes. Questions that
remain to be answered include the identity of
additional elements of the TMPS pathway, the tissueand substrate speci®city of participating metalloproteases and the signi®cance of auto- and transregulatory in¯uences by other signaling circuits.
Furthermore, the elucidation of the pathophysiological signi®cance of EGFR signal transactivation can
be expected to yield novel intervention targets for the
treatment of diseases such as cancer and other
hyperproliferative disorders.
References
Adomeit A, Graness A, Gross S, Seedorf K, Wetzker R and
Liebmann C. (1999). Mol. Cell. Biol., 19, 5289 ± 5297.
Black RA, Rauch CT, Kozlosky CJ, Peschon JJ, Slack JL,
Wolfson MF, Castner BJ, Stocking KL, Reddy P,
Srinivasan S, Nelson N, Boiani N, Schooley KA, Gerhart
M, Davis R, Fitzner JN, Johnson RS, Paxton RJ, March
CJ and Cerretti DP. (1997). Nature, 385, 729 ± 733.
Carpenter G. (1999). J. Cell. Biol., 146, 697 ± 702.
Carpenter G. (2000). Science's stke (www.stke.org) January
18, 2000.
Castagliuolo I, Valenick L, Liu J and Pothoulakis C. (2000).
J. Biol. Chem., 275, 26545 ± 26550.
Conway AM, Rahkit S, Pyne S and Pyne NJ. (1999).
Biochem. J., 337, 171 ± 177.
Cunnick J, Dorsey J, Standley T, Turkson J, Kraker A, Fry
D, Jove R and Wu J. (1998). J. Biol. Chem., 273, 14468 ±
14475.
Daub H, Wallasch C, Lankenau A, Herrlich A and Ullrich
A. (1997). EMBO J., 16, 7032 ± 7044.
Daub H, Weiss FU, Wallasch C and Ullrich A. (1996).
Nature, 379, 557 ± 560.
Dong J, Opresko LK, Dempsey PJ, Lau€enburger DA,
Co€ey RJ and Wiley HS. (1999). Proc. Natl. Acad. Sci.
USA, 96, 6235 ± 6240.
Eguchi S, Iwasaki H, Ueno H, Frank GD, Motley ED,
Eguchi K, Marumo F, Hirata Y and Inagami T. (1999). J.
Biol. Chem., 274, 36843 ± 36851.
Eguchi S, Numaguchi K, Iwasaki H, Matsumoto T,
Yamakawa T, Utsunomiya H, Motley ED, Kawakatsu
H, Owada KM, Hirata Y, Marumo F and Inagami TJ.
(1998). J. Biol. Chem., 273, 8890 ± 8896.
Fan H and Derynck R. (1999). EMBO J., 18, 6962 ± 6972.
Faure M, Voyno-Yasenetskaya TA and Bourne HR. (1994).
J. Biol. Chem., 269, 7851 ± 7854.
Gohla A, Harhammer R and Schultz G. (1998). J. Biol.
Chem., 273, 4653 ± 4659.
Gohla A, O€ermanns S, Wilkie TM and Schultz G. (1999). J.
Biol. Chem., 274, 17901 ± 17907.
Grosse R, Roelle S, Herrlich A, Hohn J and Gudermann T.
(2000). J. Biol. Chem., 275, 12251 ± 12260.
Hackel PO, Zwick E, Prenzel N and Ullrich A. (1999). Curr.
Opin. Cell. Biol., 11, 184 ± 189.
Hallak H, Seiler AE, Green JS, Ross BN and Rubin R.
(2000). J. Biol. Chem., 275, 2255 ± 2258.
Heeneman S, Haendeler J, Saito Y, Ishida M and Berk BC.
(2000). J. Biol. Chem., 275, 15926 ± 15932.
Herrlich A, Daub H, Knebel A, Herrlich P, Ullrich A,
Schultz G and Gudermann T. (1998). Proc. Natl. Acad.
Sci. USA, 95, 8985 ± 8990.
Iwasaki H, Eguchi S, Ueno H, Marumo F and Hirata Y.
(1999). Endocrinology, 140, 4659 ± 4668.
Izumi Y, Hirata M, Hasuwa H, Iwamoto R, Umata T,
Miyado K, Tamai Y, Kurisaki T, Sehara-Fujisawa A,
Ohno S and Mekada E. (1998). EMBO J., 17, 7260 ± 7272.
Oncogene
EGFR transactivation
A Gschwind et al
1600
Oncogene
Kalmes A, Vesti BR, Daum G, Abraham JA and Clowes
AW. (2000). Circ. Res., 87, 92 ± 98.
Keely S, Uribe J and Barrett K. (1998). J. Biol. Chem., 273,
27111 ± 27117.
Keely SJ, Calandrella SO and Barrett KE. (2000). J. Biol.
Chem., 275, 12619 ± 12625.
King CR, Borello I, Porter L, Comoglio P and Schlessinger J.
(1989). Oncogene, 4, 13 ± 18.
La€argue M, Raynal P, Yart A, Peres C, Wetzker R, Roche
S, Payrastre B and Chap H. (1999). J. Biol. Chem., 274,
32835 ± 32841.
Leserer M, Gschwind A and Ullrich A. (2000). IUBMB Life,
49, 405 ± 409.
Li X, Ponten A, Aase K, Karlsson L, Abramsson A, Uutela
M, Backstrom G, Hellstrom M, Bostrom H, Li H, Soriano
P, Betsholtz C, Heldin CH, Alitalo K, Ostman A and
Eriksson U. (2000). Nat. Cell. Biol., 2, 302 ± 309.
Li X, Lee JW, Graves LM and Earp HS. (1998). EMBO J.,
17, 2574 ± 2583.
Linseman DA, Benjamin CW and Jones DA. (1995). J. Biol.
Chem., 270, 12563 ± 12568.
Luttrell LM, Della Rocca GJ, van Biesen T, Luttrell DK and
Lefkowitz RJ. (1997). J. Biol. Chem., 272, 4637 ± 4644.
Luttrell LM, Ferguson SS, Daaka Y, Miller WE, Maudsley
S, Della Rocca GJ, Lin F, Kawakatsu H, Owada K,
Luttrell DK, Caron MG and Lefkowitz R. (1999). Science,
283, 655 ± 661.
Maudsley S, Pierce KL, Zamah AM, Miller WE, Ahn S,
Daaka Y, Lefkowitz RJ and Luttrell LM. (2000). J. Biol.
Chem., 275, 9572 ± 9580.
Massague J and Pandiella A. (1993). Annu. Rev. Biochem.,
62, 515 ± 554.
Moghal N and Sternberg PW. (1999). Curr. Opin. Cell. Biol.,
11, 190 ± 196.
Murasawa S, Mori Y, Nozawa Y, Gotoh N, Shibuya M,
Masaki H, Maruyama K, Tsutsumi Y, Moriguchi Y,
Shibazaki Y, Tanaka Y, Iwasaka T, Inada M and
Matsubara H. (1998). Circ. Res., 82, 1338 ± 1348.
Olayioye MA, Neve RM, Lane HA and Hynes NE. (2000).
EMBO J., 19, 3159 ± 3167.
Peschon JJ, Slack JL, Reddy P, Stocking KL, Sunnarborg
SW, Lee DC, Russell WE, Castner BJ, Johnson RS,
Fitzner JN, Boyce RW, Nelson N, Kozlosky CJ, Wolfson
MF, Rauch CT, Cerretti DP, Paxton RJ, March CJ and
Black RA. (1998). Science, 282, 1281 ± 1284.
Pierce KL, Maudsley S, Daaka Y, Luttrell LM and
Lefkowitz RJ. (2000). Proc. Natl. Acad. Sci. USA, 97,
1489 ± 1494.
Prenzel N, Zwick E, Leserer M and Ullrich A. (2000). Breast
Cancer Res., 2, 184 ± 190.
Prenzel N, Zwick E, Daub H, Leserer M, Abraham R,
Wallasch C and Ullrich A. (1999). Nature, 402, 884 ± 888.
Rao GN, Delafontaine P and Runge MS. (1995). J. Biol.
Chem., 270, 2781 ± 2785.
Reddy P, Slack JL, Davis R, Cerretti DP, Kozlosky CJ,
Blanton RA, Shows D, Peschon JJ and Black RA. (2000).
J. Biol. Chem., 275, 14608 ± 14614.
Roudabush FL, Pierce KL, Maudsley S, Khan KD and
Luttrell LM. (2000). J. Biol. Chem., 275, 22583 ± 22589.
Seo B, Choy EW, Maudsley S, Miller WE, Wilson BA and
Luttrell LM. (2000). J. Biol. Chem., 275, 2239 ± 2245.
Slack BE. (2000). Biochem. J., 348, 381 ± 387.
Solto€ SP. (1998). J. Biol. Chem., 273, 23110 ± 23117.
Tang H, Nishishita T, Fitzgerald T, Landon EJ and Inagami
T. (2000). J. Biol. Chem., 275, 13420 ± 13426.
Tsai W, Morielli AD and Peralta EG. (1997). EMBO J., 16,
4597 ± 4605.
Ullrich A, Coussens L, Hay¯ick JS, Dull TJ, Gray A, Tam
AW, Lee J, Yarden Y, Libermann TA, Schlessinger J,
Downward J, Mayes ELV, Whittle N, Water®eld MD and
Seeburg PH. (1984). Nature, 309, 418 ± 425.
Venkatakrishnan G, Salgia R and Groopman JE. (2000). J.
Biol. Chem., 275, 6868 ± 6875.
Werb Z and Yan Y. (1998). Science, 282, 1279 ± 1280.
Zwick E, Daub H, Aoki N, Yamaguchi-Aoki Y, Tinhofer I,
Maly K and Ullrich A. (1997). J. Biol. Chem., 272, 24767 ±
24770.
Zwick E, Hackel PO, Prenzel N and Ullrich A. (1999a).
Trends Pharmac. Sci., 20, 408 ± 412.
Zwick E, Wallasch C, Daub H and Ullrich A. (1999b). J.
Biol. Chem., 274, 20989 ± 20996.