Four-dimensional organization of protein kinase signaling cascades: the roles of diffusion, endocytosis and molecular motors
Department of Pathology, Anatomy and Cell Biology, Thomas Jefferson University, 1020 Locust Street, Philadelphia, PA 19107, USA
* e-mail: Boris.Kholodenko{at}mail.tju.edu
Accepted 18 February 2003
![]() |
Summary |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Key words: signal transduction, protein kinase, diffusion, endocytosis, molecular motor, mitogen activated protein kinase (MAPK), traveling wave
![]() |
Introduction |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Signaling through a plethora of cell-surface receptors, such as G-protein
coupled receptors (GPCRs), receptor tyrosine kinases (RTKs) and cytokine
receptors, activate mitogen activated protein kinase (MAPK) cascades, which
function as central integration modules in information processing
(Chang and Karin, 2001;
Kholodenko, 2002
;
Lewis et al., 1998
). MAPK
cascades relay extracellular stimuli from the plasma membrane to crucial
cellular targets distant from the membrane, e.g. transcription factors.
Elucidation of the spatiotemporal organization and regulation of MAPK
signaling is becoming increasingly important for understanding signaling
specificity and the diverse nature of cellular responses. We have recently
shown that simple diffusion of activated kinases may be insufficient for the
effective propagation of phosphorylation signals through MAPK cascades
(Kholodenko, 2002
). In this
paper, we analyze the functional implications of membrane targeting of
cytosolic proteins, examine the consequences of the spatial separation of
certain kinases and phosphatases in MAPK pathways and discuss multiple
mechanisms used by a cell to propagate the signals over long distances.
![]() |
Regulation of signaling by membrane recruitment of cytosolic proteins |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
|
This interaction pattern raises a number of questions about the role of the membrane recruitment in signal transfer. For instance, why should SOS relocate to the membrane if its catalytic activity is not activated by RTKs? What prevents direct interaction of cytosolic SOS or Grb2-SOS complexes with the membrane-bound Ras from catalyzing GDP/GTP exchange on Ras? To clarify the effect of membrane localization, we consider two extreme cases. When two signaling molecules form a productive complex, transducing the signal after each diffusive encounter, the signal-transduction process is called `diffusion-limited'. If only a small fraction of the collisions leads to binding that lasts long enough to transfer the information, the signal transduction is called `reaction-limited'. In the latter case, the two protein molecules associate and dissociate a number of times before signal transduction takes place.
Membrane localization does not significantly enhance
diffusion-limited signal transfer
It has earlier been suggested that localization of signaling proteins close
to the cell membrane causes an increase in the first-encounter rate
(Adam and Delbruck, 1968); the
solutes do not `get lost' by wondering off into the bulk phase
(Axelrod and Wang, 1994
;
Berg and Purcell, 1977
).
However, such an increase appears to be too small to account for significantly
enhanced signal transduction (Kholodenko
et al., 2000b
). The diffusion-limited rates in the membrane and in
the cytosol can be compared in terms of the ratio (h) of the
corresponding association rate constants in two dimensions and in three
dimensions. For diffusion-limited association of two proteins located in the
plasma membrane of a spherical cell or delocalized over the cytosol volume,
the ratio h was estimated to be
(0.020.05)x(Dmembr/Dcyt)x(rcell/rprot)
(Kholodenko et al., 2000b
).
For instance, if the cell radius (rcell) is 10 µm and
the sum (rprot) of typical protein radii is approximately
10-2 µm, then
h
(2050)xDmembr/Dcyt.
Because the diffusion coefficients of proteins in the membrane
(Dmembr) are about two orders of magnitude lower than in
the cytosol (Dcyt)
(Cherry, 1979
;
Kusumi et al., 1993
), we
conclude that the function of the membrane recruitment is unlikely to be an
enhancement of the encounter rates. In fact, it has already been suggested
that the fastest route to diffuse is through the cytosol, not through the
membrane, because of two orders of magnitude difference in the diffusion
coefficients (Bray, 1998
).
Gain in the number of signaling complexes is more critical than an
increase in the association rate
In the reaction-limited extreme, the first-encounter rate is much faster
than the signal transduction rate, which can be estimated as the fraction of
molecules in the associated state (as if this step were at equilibrium)
multiplied by the reaction rate constant. An increase in the effective local
concentration of a cytosolic protein due to membrane relocation brings about
an increase in the apparent affinity to a binding partner in the membrane
(Ferrell, 1998). Haugh and
Lauffenburger (1997
) estimated
that an increase in the reaction-limited protein association rate could be as
high as 102103. In the general case, however, the
rate enhancement depends on many kinetic and molecular details including the
probability of success per diffusion encounter, the concentration depletion
zones near the targets, the reversibility of the binding and other factors
(Axelrod and Wang, 1994
). The
binding reversibility suggests that the dissociation rate constant, in
addition to the association rate, may change upon the membrane relocation, as
in fact was observed for affinity enhancement due to `macromolecular crowding'
(Rohwer et al., 1998
).
Therefore, although the speed of signal transduction increases by the
translocation of signaling proteins, it should not be assumed that any such
enhancement is due to an increase in the rate of formation of protein
complexes. Instead, the underlying mechanism can be an increase in the number
(or average lifetime) of signaling complexes, which act as catalysts
activating downstream processes. We submit that membrane localization serves
to enhance the extent of complex formation of signal-transduction proteins,
and hence increase the intensity of the signal that is being transduced.
Receptor-mediated membrane recruitment significantly increases the
number of complexes formed by a cytoplasmic protein and a membrane-anchored
protein
A gain in the number of signaling complexes involving a cytosolic protein X
and a membrane-bound protein Y can be brought about by a two-step, `piggyback'
mechanism. The first step is binding of X to an activated membrane receptor R
(`piggy'), which confines X to a membrane shell, where Y is located. The
second step is a `piggyback riding' of X until it meets membrane-anchored Y. X
then forms a complex with Y, while continuing to ride piggyback on R. The
quantitative analysis shows that this piggyback riding leads to a strong
reduction of the apparent dissociation constant, Kd,app,
which can be expressed through the equilibrium dissociation constant
Kd of cytosolic X and membrane-bound Y, as follows
(Kholodenko et al., 2000b):
![]() | (1) |
An alternative mechanism of an enhancement in signal transfer rate may be
an increase in the efficiency of the reaction between cytosolic X and
membrane-bound Y due to a conformational change of X upon binding to a
membrane anchor, such as receptor R. However, for SOS-Ras interactions,
structural and kinetic data on the catalytic mechanism and activity rule out
this possibility (Buday and Downward,
1993; Corbalan-Garcia et al.,
1998
; Lenzen et al.,
1998
).
Recruitment to a scaffold
Our results apply not only to the case of membrane translocation, but to
translocation into any subcellular compartment. Scaffolds of various sorts
should be mentioned here. They act as templates, bringing together signaling
proteins, organizing and coordinating the function of entire signaling
cascades (Bray, 1998).
Importantly, our results suggest that the number of signaling complexes will
increase only if these complexes do not dissociate from a scaffold. Even if
the interacting proteins were brought to close vicinity on a scaffold, the
dissociation of the protein complex from the scaffold will result in further
dissociation of the complex, which will be in thermodynamic equilibrium with
its components.
Specifics of SOS-Ras and GAP-Ras interactions
The calculations demonstrate that activation of Ras by SOS from the cytosol
is two or three orders of magnitude less effective than the catalysis,
mediated by the RTK-bound SOS, for instance, mediated by the EGFR-Grb2-SOS and
EGFR-Shc-Grb2-SOS complexes (Haugh and
Lauffenburger, 1997). After the dissociation of phosphorylated Src
homology and collagen domain protein (Shc) from EGFR, the Shc-Grb-SOS
complexes may bring about an additional route for Ras activation. However,
quasi-equilibrium association of these complexes with Ras may be insignificant
compared to receptor-mediated association unless the Shc-Grb-SOS complexes are
also targeted to the plasma membrane through specific domains, such as
phosphotyrosine-binding and pleckstrin homology domains
(Drugan et al., 2000
;
Ugi et al., 2002
).
Quantification of relative contributions of SOS complexes with the receptor
and with phosphorylated Shc to Ras activation is awaiting experimental
verification.
Signaling of activated Ras is turned off by the activation of
GTPase-activating proteins (GAPs) (Bollag
and McCormick, 1992). Similar to SOS, p120 GAP is a cytoplasmic
protein. As in the case of SOS signals, the membrane recruitment of GAP is
necessary for an appreciable increase in the rate of GTP hydrolysis on
Ras.
A variation on the topic of Ras activation by RTKs has been described for
fibroblast growth factor receptors (FGFRs)
(Kouhara et al., 1997).
Stimulation of FGFRs induces cell proliferation, differentiation and migration
by activation of the Ras/MAPK signaling pathway. However, unlike other RTKs,
activated FGFR cannot bind Grb2 directly. Recently, a novel membrane-anchored
protein, phosphorylated by activated FGFR, has been discovered and is known as
FRS2 (FGFR substrate 2) (Kouhara et al.,
1997
). Tyrosine-phosphorylated FRS2 is able to bind Grb2 and,
therefore, the Grb2-SOS complex. In a familiar twist, the juxtaposition of the
FRS2-Grb2-Sos complex on the membrane may facilitate the Ras activation by
SOS, providing a feasible mechanism for linking FGFRs to the Grb2/SOS/Ras/MAPK
pathway.
![]() |
Signal transduction through MAPK cascades can require endocytic trafficking and/or active molecular transport |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
MAPK activation by RTKs and GPCRs
MAPK cascades are widely involved in eukaryotic signal transduction, and
these pathways are evolutionarily conserved in cells from yeast to mammals
(reviewed in Chang and Karin,
2001; Lewis et al.,
1998
). Mammalian cells express at least four different MAPK
families, including the ERK, the c-Jun N-terminal kinase (JNK) and p38 MAPK
cascades. A three-tiered cascade comprises MAPK, MAPK kinase (MKK) and MKK
kinase (MKKK). A kinase at the first cascade level, MKKK, is activated at the
cell membrane. A kinase at the bottom level, MAPK, is activated in the cytosol
and phosphorylates target proteins both in the cytosol and nucleus. Mitogenic
signaling by RTKs and GPCRs is associated with Ras-dependent stimulation of
the ERK cascade. The classical paradigm for GPCR signaling involves the
agonist-dependent interaction of GPCRs with heterotrimeric G proteins that
stimulates the exchange of bound GDP for GTP, resulting in dissociation of G
proteins into
and ß
subunits. Subsequent interaction of
and ß
subunits with effector enzymes or ion channels
regulates the generation of soluble second messengers or ionic conductance
changes. However, this paradigm should be extended to include the
proliferative and differentiative effects of GPCRs. It is presently known that
in a multitude of cell types, GPCRs stimulate the MAPK cascades, such as the
ERK, JNK and p38 MAPK cascades (Garrington
and Johnson, 1999
; Gutkind,
1998
; van Biesen et al.,
1996
). Interestingly, the pathways of GPCR and RTK-mediated MAPK
activation often converge. Recently, evidence has emerged that the overlap of
GPCR and RTK signaling pathways is accounted for in part by GPCR-mediated
`transactivation' of RTKs, such as EGFR
(Fig.1), platelet-derived
growth factor receptor and insulin-like growth factor-1 receptor. For
instance, EGFR activation by GPCR was shown to be mediated by signaling
pathways involving non-receptor tyrosine kinases, Src and Pyk2, and through
activation of the metalloprotease leading to the release of heparin binding
EGF (Pierce et al., 2001
;
Prenzel et al., 1999
). It is,
however, important to realize that although RTK transactivation is now a
recognized mechanism for GPCR-induced activation of the ERK cascade, other
signaling pathways can also contribute to this link
(Andreev et al., 2001
;
Miller and Lefkowitz,
2001
).
Heterogeneous spatial distribution of activated components in MAPK
cascades
Multiple cellular proteins are phosphorylated and dephosphorylated at
distinct cellular locations. In the Ras-ERK pathway, inactive Raf-1 (MKKK)
resides in the cytosol. Upon stimulation of cell-surface receptors, Raf-1 is
translocated from the cytosol to the plasma membrane by a high-affinity
binding to GTP-loaded Ras. At the membrane, Raf-1 undergoes a series of
activation steps involving interaction with 14-3-3 proteins and
phosphorylation on specific tyrosine and serine residues
(Mason et al., 1999). Although
the mechanism of activation is not yet completely understood, the association
of Raf-1 with membranes appears to be essential for its activation. The Raf-1
kinase phosphorylates the cytosolic kinase MEK (MKK) at the plasma membrane,
whereas soluble serine/threonine phosphatases dephosphorylate the activated
MEK in the bulk phase (Kyriakis et al.,
1992
; Strack et al.,
1997
). In the cytosol, active MEK kinase phosphorylates ERK (MAPK)
and specific ERK phosphatases are localized to the cytosol and nucleus.
Spatial separation of protein kinases and phosphatases suggests that there may
be cellular gradients of phosphorylated (active) forms of MEK and ERK, with
high concentrations in the periplasmic region near the phosphorylation
location and low concentrations at a distance from the plasma membrane. Since
activated ERK phosphorylates multiple cytoplasmic and nuclear targets, large
spatial gradients of this kinase may have very important implications for cell
signaling.
Indeed, the quantitative analysis demonstrates that the spatial separation
of kinases and phosphatases potentially results in precipitous gradients of
phospho-proteins, given measured values of protein diffusion coefficients and
phosphatase and kinase activities (Brown
and Kholodenko, 1999;
Kholodenko et al., 2000a
). We
illustrate this analysis by calculating the spatial gradients for a single
level cascade, in which the kinase is located on the plasma membrane and the
phosphatase is distributed homogeneously in the cytoplasm (These calculations
and Fig. 2, which illustrates
them, are reproduced from Kholodenko,
2002
, with permission from Elsevier Science.) For a spherical
cell, the following equation describes radial diffusion of the phospho-protein
(p) from the cell membrane, where p is produced at the rate,
vkin, to the cell interior, where p is
dephosphorylated at the rate, vp,
![]() | (2) |
![]() | (3) |
|
This analysis suggests that unless there is an additional mechanism (besides slow protein diffusion) for signal propagation through the MAPK cascade, the levels of activated MEK and ERK will drop precipitously in the cell interior. At distances larger than several µm from the plasma membrane, the phosphorylation signal should decrease to subthreshold levels, provided that the cytosolic phosphatase activity is sufficiently high. Since eukaryotic cell radii vary from 5 to 50 µm, we conclude that propagating a message from the plasma membrane to the nucleus can require an additional vehicle besides diffusion in the cytoplasm.
A novel role of endocytosis in activation of MAPK signaling
Upon ligand binding and activation, many GPCRs and RTKs internalize
via clathrin-coated pits. For instance, in hepatocytes over 50% of
phosphorylated EGFR is transferred to early endosomes during the first 10 min
after EGF stimulation (Di Guglielmo et
al., 1994). Internalization takes receptorligand complexes
and other signaling proteins from the plasma membrane and brings them inside
the cell. Molecules that were not recycled back to the cell membrane are
degraded in lysosomes. Although internalized GPCRs continuously recycle back
to the cell surface after dephosphorylation in endosomes, a significant
proportion of receptors are located internally
(Koenig and Edwardson, 1997
).
Therefore, traditionally, clathrin-mediated endocytosis has been implicated in
downregulation of signaling by plasma membrane receptors. A novel role of
endocytosis in `turning on' activation of the ERK cascade by cell surface
receptors was first reported for the EGF receptor
(Vieira et al., 1996
). A
conditional defect in endocytosis can be imposed by the regulated expression
of a mutant form of dynamin (Dyn1-K44A), a GTPase that is required for
clathrin-coated vesicle formation. In HeLa cells, this expression led to a
marked decrease in EGF-induced ERK activation, whereas Shc phosphorylation was
enhanced in endocytosis-defective cells. Subsequent studies have demonstrated
that both GPCR- and EGFR-mediated activation of ERK is sensitive to various
distinct inhibitors of clathrin-mediated endocytosis, including
monodansylcadaverine, depletion of intracellular K+ or cholesterol,
cytochalasin D and a mutant dynamin
(Ceresa et al., 1998
;
Daaka et al., 1998
;
Kranenburg et al., 1999
;
Maudsley et al., 2000
;
Rizzo et al., 2001
;
Vieira et al., 1996
).
Therefore, a possible mechanism of control over signal transduction may engage
receptor endocytosis (Clague and Urbe,
2001
; Di Fiore and De Camilli,
2001
; Haugh et al.,
1999
). However, whereas experimental evidence points to an
essential role of receptor endocytosis in the activation of MAPK cascades, the
reason for the involvement of the endocytic machinery remains poorly
understood (Ceresa and Schmid,
2000
; Kranenburg et al.,
1999
; Pierce et al.,
2000
). Interestingly, in some cellular systems endocytosis was not
required to activate ERK (for a review, see
Leof, 2000
).
The relationship between receptor internalization and ERK activation allows
us to suggest that trafficking of signaling intermediates within endocytic
vesicles may be an efficient way of propagating the signal
(Kholodenko, 2002). Indeed, it
was reported that the engagement of the endocytic machinery is essential for
ERK activation by MEK, but not for activation of Ras
(Kranenburg et al., 1999
).
Interestingly, the data on the subcellular distribution of activated MEK
demonstrated that biphosphorylated MEK is detectable only at the plasma
membrane and in intracellular vesicles, whereas the total MEK pool is
cytosolic (Kranenburg et al.,
1999
). Endocytic trafficking of active MEK can help to avoid the
formation of steep spatial gradients of phosphorylated MEK and ERK, since this
mechanism overcomes the spatial separation of kinases and phosphatases within
the MAPK cascade. Therefore, the endocytosis of phosphorylated MEK (or a
protein complex containing activated MEK) rather than of activated receptors
appears to be critical for ERK activation.
Scaffolding, cytoplasmic streaming and active transport as mechanisms
facilitating signal propagation
Other mechanisms besides endocytosis can help to spread the phosphorylation
signals from the plasma membrane further into the cell by preventing the
formation of steep spatial gradients of phosphorylated ERK. For instance,
cytoplasmic streaming, i.e. solvent fluxes brought about by the movement of
cytoplasmic organelles along actin cables, can contribute to intracellular
transport of activated MAPK kinases
(Agutter et al., 1995). Recent
evidence indicates that the MAPK cascade components can bind to scaffolding
proteins, e.g. MP1 and JIP-1 in mammalian cells (for a review, see
Garrington and Johnson, 1999
).
Dephosphorylation of the MAP kinases in scaffold complexes may be decreased or
even precluded because of sterical obstructions, as was suggested by Levchenko
et al. (2000
).
Scaffolding may also help to deliver an entire signaling complex containing
the MAP kinases to endocytic vesicles. Novel mechanisms have been discovered
that link GPCRs to MAPK activation through use of ß-arrestin as a
scaffold for the ERK and JNK cascades
(Miller and Lefkowitz, 2001;
Pierce et al., 2001
). Besides
its role in GPCR desensitization, ß-arrestin has been shown to promote
the targeting of the receptor to clathrin-coated pits. As ß-arrestins can
also recruit and activate Src, it is likely that the entire ERK and JNK
cascades can be activated and recruited for clathrin-mediated
internalization.
Recent data suggest that molecular motors can be involved in transport of
signaling complexes. In fact, in nerve cells, a cargo for the molecular motor
kinesin has been identified as scaffolding proteins for the JNK pathway, known
as JIPs (Verhey and Rapoport,
2001). Endocytic vesicles and signaling complexes, loaded on
molecular motors, can be transported along microtubules to remote cellular
locations.
![]() |
Long-range signaling |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Several models were suggested to explain the retrograde transduction of
neuronal survival signals (for a review, see
Ginty and Segal, 2002).
According to a widely accepted model, shortly after NGF binding to TrkA at
nerve terminals, the NGF-TrkA complexes are internalized into endosomes by
means of clathrin-mediated endocytosis. Signaling endosomes containing
activated TrkA with associated ligand are retrogradely transported to the cell
bodies. Data on blocking the NGF-TrkA transport by the dynein ATPase inhibitor
(EHNA) suggest that vesicular transport can be carried out by molecular motors
(Reynolds et al., 1998
). In
fact, Trk neurotrophin receptors were found to bind directly to a dynein light
chain (Yano et al., 2001
). The
retrograde axonal transport was also shown to be inhibited by the
phosphatidylinositol 3-kinase (PI3K) inhibitor wortmannin, by cytochalasin D,
a disruptor of actin filaments, and by the microtubule inhibitor colchicine
(Reynolds et al., 1998
). Taken
together, these studies support a model where the retrograde transport of the
NGF-TrkA complexes along axon structural elements (e.g. microtubules) can
provide survival signals to neurons.
Ligand-independent waves of receptor activation
Cells have developed multiple mechanisms to overcome the problem of
long-distance signaling. It was recently discovered that survival signals
might not depend on retrograde transport of NGF
(MacInnis and Campenot, 2002).
Application of NGF, which was covalently cross-linked to beads to prevent
internalization, showed that survival signals were able to reach the cell
bodies unaccompanied by the ligand that initiated TrkA activation. One
possibility is that activated TrkA can be internalized and retrogradely
transported without NGF, implying that the active state of TrkA can be
maintained in the absence of the ligand. Another possibility is that
downstream TrkA targets, such as PI3K or Akt, can mediate the retrograde
signal. An intriguing possibility is that activation of TrkA receptors in
nerve terminals brings about an NGF-independent wave of TrkA activation, which
rapidly propagates through the neuronal axon
(Ginty and Segal, 2002
).
Indeed, ligand-independent waves of receptor (EGFR) activation, emanated from
a point EGF source, were recently reported
(Verveer et al., 2000
).
How can waves of receptor activation emerge? A possible scenario is that an
activated receptor, monomer or dimer, is capable of transphosphorylating and
activating an inactive receptor molecule upon diffusive encounter, potentially
resulting in lateral spread of receptor activation. In fact, spontaneous
activation and signaling by overexpressed EGFR has been reported recently
(Thomas et al., 2003). Let us
sketch the functional implications of this local amplification assumption for
the dynamics of the receptor system on the cell surface. For simplicity, a
one-dimensional diffusion is analyzed, and only monomer or dimer forms of the
receptor are taken into account (the model can be generalized to include
monomer-dimer association/dissociation).
Given that the total receptor concentration (or surface density) is
c and the concentration of activated receptors at a distance
x from a ligand source is a(x), the amount of newly
activated receptors per unit time and volume/area will be
kxa(x)x[ca(x)],
where the constant k is proportional to the probability of
phosphorylation per diffusive encounter. Active receptors are dephosphorylated
by the phosphatases at the rate vp(a). Under
these assumptions, the spatial propagation of activated receptor (from a
source at x=0) is described by the following equation:
![]() | (4) |
Traveling waves of activated protein kinases
Another possible scenario of how a survival signal can spread over the axon
includes traveling waves that may arise in a bistable protein kinase cascade.
Bistability is a common theme in cell signaling cascades that contain a
positive feedback loop, or a double-negative feedback loop
(Bhalla and Iyengar, 1999;
Ferrell and Machleder, 1998
;
Gardner et al., 2000
; Thron,
1997
,
1999
;
Tyson and Novak, 2001
). A
bistable protein kinase cascade can switch between two different stable
states, one corresponding to a low and another to a high activity, but cannot
exist in an intermediate unstable state. When the signal strength is below a
given threshold, a kinase cascade, such as the Mos-MEK-p42 MAPK cascade and
the JNK cascade in Xenopus oocytes
(Bagowski and Ferrell, 2001
;
Ferrell, 1999
), and the ERK
cascade in mouse NIH-3T3 cells (Bhalla et
al., 2002
), remains in a low activity state. An increase in the
signal above the threshold switches the cascade to a high activity state.
Importantly, the cascade will remain in this high activity state even when the
initial signal decreases to subthreshold values.
It was proposed that cells utilize bistable signaling circuits that would
enable them to be capable of `all-or-none' switching and to `remember' a
transient differentiation stimulus long after the stimulus was removed
(Ferrell, 2002). Here we
suggest that yet another role for bistable protein kinase cascades may be to
support traveling waves of activated phospho-proteins, propagating signals to
remote cellular locations. Bistability produces local amplification of the
spreading signal, and the combination of local amplification and diffusion may
generate traveling waves. In fact, traveling waves in bistable systems have
been extensively studied in physics, chemistry and biology
(Castiglione et al., 2002
;
Christoph et al., 1999
;
Keener and Sneyd, 1998
;
Shvartsman et al., 2002
;
Zhabotinsky and Zaikin, 1973
).
MAPK cascades and the PI3K/PDK1/Akt cascade coupled with the PIP3 synthesis
pathway might be candidates for bistable protein kinase cascades that are
capable of propagating traveling waves.
Importantly, all of the models of long-range signaling considered are not mutually exclusive. We hypothesize that multiple mechanisms of information transfer have evolved in neurons to transmit signals over long distances. Future experimental work will show if waves of activated kinases emerge in cells.
![]() |
Concluding remarks |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
![]() |
Abbreviations |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
EGFR, EGF receptor
ERK, extracellular signal regulated kinase
GAP, GTPase-activating protein
GDP/GTP, guanosine di/triphosphate
GPCR, G-protein coupled receptor
Grb2, growth factor receptor binding protein 2
JNK, c-Jun N-terminal kinase
MAPK, mitogen activated protein kinase
MKK, MAPK kinase
MKKK, MKK kinase
NGF, nerve growth factor
PI3K, phosphatidylinositol 3-kinase
RTK, receptor tyrosine kinase
SH, Src homology domain
Shc, Src homology and collagen domain protein
SOS, Son of Sevenless homolog protein
TrkA, the NGF receptor
![]() |
Acknowledgments |
---|
![]() |
References |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Adam, G. and Delbruck, M. (1968). Reduction of dimensionality in biological diffusion processes. In Structural Chemistry and Molecular Biology (ed. A. Rich and N. Davidson), pp. 198-215.San Francisco: W. H. Freeman and Co.
Agutter, P. S., Malone, P. C. and Wheatley, D. N. (1995). Intracellular transport mechanisms: a critique of diffusion theory. J. Theor. Biol. 176,261 -272.[CrossRef][Medline]
Andreev, J., Galisteo, M. L., Kranenburg, O., Logan, S. K.,
Chiu, E. S., Okigaki, M., Cary, L. A., Moolenaar, W. H. and
Schlessinger, J. (2001). Src and Pyk2 mediate
G-protein-coupled receptor activation of epidermal growth factor receptor
(EGFR) but are not required for coupling to the mitogen-activated protein
(MAP) kinase signaling cascade. J. Biol. Chem.
276,20130
-20135.
Arrio-Dupont, M., Foucault, G., Vacher, M., Devaux, P. F. and
Cribier, S. (2000). Translational diffusion of
globular proteins in the cytoplasm of cultured muscle cells.
Biophys. J. 78,901
-907.
Axelrod, D. and Wang, M. D. (1994). Reduction-of-dimensionality kinetics at reaction-limited cell surface receptors. Biophys. J. 66,588 -600.[Abstract]
Bagowski, C. P. and Ferrell, J. E., Jr (2001). Bistability in the JNK cascade. Curr. Biol. 11,1176 -1182.[CrossRef][Medline]
Berg, H. C. and Purcell, E. M. (1977). Physics of chemoreception. Biophys. J. 20,193 -219.[Abstract]
Bhalla, U. S. and Iyengar, R. (1999). Emergent
properties of networks of biological signaling pathways [see comments].
Science 283,381
-387.
Bhalla, U. S., Ram, P. T. and Iyengar, R.
(2002). MAP kinase phosphatase as a locus of flexibility in a
mitogen-activated protein kinase signaling network.
Science 297,1018
-10123.
Bollag, G. and McCormick, F. (1992). GTPase activating proteins. Sem. Cancer Biol. 3, 199-208.
Bray, D. (1998). Signaling complexes: biophysical constraints on intracellular communication. Annu. Rev. Biophys. Biomol. Struct. 27,59 -75.[CrossRef][Medline]
Brown, G. C. and Kholodenko, B. N. (1999). Spatial gradients of cellular phospho-proteins. FEBS Lett. 457,452 -454.[CrossRef][Medline]
Buday, L. and Downward, J. (1993). Epidermal growth factor regulates p21ras through the formation of a complex of receptor, Grb2 adapter protein, and Sos nucleotide exchange factor. Cell 73,611 -620.[Medline]
Castiglione, F., Bernaschi, M., Succi, S., Heinrich, R. and Kirschner, M. W. (2002). Intracellular signal propagation in a two-dimensional autocatalytic reaction model. Phys. Rev. E Stat. Nonlin. Soft Matter Phys. 66,1 -031905-10.
Ceresa, B. P., Kao, A. W., Santeler, S. R. and Pessin, J. E.
(1998). Inhibition of clathrin-mediated endocytosis selectively
attenuates specific insulin receptor signal transduction pathways.
Mol. Cell. Biol. 18,3862
-3870.
Ceresa, B. P. and Schmid, S. L. (2000). Regulation of signal transduction by endocytosis. Curr. Opin. Cell Biol. 12,204 -210.[CrossRef][Medline]
Chang, L. and Karin, M. (2001). Mammalian MAP kinase signalling cascades. Nature 410, 37-40.[CrossRef][Medline]
Cherry, R. J. (1979). Rotational and lateral diffusion of membrane proteins. Biochim. Biophys. Acta 559,289 -327.[Medline]
Christoph, J., Strasser, P., Eiswirth, M. and Ertl, G.
(1999). Remote triggering of waves in an electrochemical system.
Science 284,291
-293.
Clague, M. J. and Urbe, S. (2001). The
interface of receptor trafficking and signalling. J. Cell
Sci. 114,3075
-3081.
Corbalan-Garcia, S., Margarit, S. M., Galron, D., Yang, S. S.
and Bar- Sagi, D. (1998). Regulation of Sos activity
by intramolecular interactions. Mol. Cell Biol.
18,880
-886.
Daaka, Y., Luttrell, L. M., Ahn, S., Della Rocca, G. J.,
Ferguson, S. S., Caron, M. G. and Lefkowitz, R. J.
(1998). Essential role for G protein-coupled receptor endocytosis
in the activation of mitogen-activated protein kinase. J. Biol.
Chem. 273,685
-688.
Dayel, M. J., Hom, E. F. and Verkman, A. S.
(1999). Diffusion of green fluorescent protein in the
aqueous-phase lumen of endoplasmic reticulum. Biophys.
J. 76,2843
-2851.
Di Fiore, P. P. and De Camilli, P. (2001). Endocytosis and signaling. an inseparable partnership. Cell 106,1 -4.[Medline]
Di Guglielmo, G. M., Baass, P. C., Ou, W. J., Posner, B. I. and Bergeron, J. J. (1994). Compartmentalization of SHC, GRB2 and mSOS, and hyperphosphorylation of Raf-1 by EGF but not insulin in liver parenchyma. EMBO J. 13,4269 -4277.[Abstract]
Drugan, J. K., Rogers-Graham, K., Gilmer, T., Campbell, S. and
Clark, G. J. (2000). The Ras/p120 GTPase-activating
protein (GAP) interaction is regulated by the p120 GAP pleckstrin homology
domain. J. Biol. Chem.
275,35021
-35027.
Egan, S. E., Giddings, B. W., Brooks, M. W., Buday, L., Sizeland, A. M. and Weinberg, R. A. (1993). Association of Sos Ras exchange protein with Grb2 is implicated in tyrosine kinase signal transduction and transformation. Nature 363, 45-51.[CrossRef][Medline]
Ferrell, J. E., Jr (1998). How regulated protein translocation can produce switch-like responses. Trends Biochem. Sci. 23,461 -465.[CrossRef][Medline]
Ferrell, J. E., Jr (1999). Building a cellular switch: more lessons from a good egg. BioEssays 21,866 -870.[CrossRef][Medline]
Ferrell, J. E., Jr (2002). Self-perpetuating states in signal transduction: positive feedback, double-negative feedback and bistability. Curr. Opin. Cell Biol. 14,140 -148.[CrossRef][Medline]
Ferrell, J. E., Jr and Machleder, E. M. (1998).
The biochemical basis of an all-or-none cell fate switch in Xenopus oocytes.
Science 280,895
-898.
Gardner, T. S., Cantor, C. R. and Collins, J. J. (2000). Construction of a genetic toggle switch in Escherichia coli. Nature 403, 339-342.[CrossRef][Medline]
Garrington, T. P. and Johnson, G. L. (1999). Organization and regulation of mitogen-activated protein kinase signaling pathways. Curr. Opin. Cell Biol. 11,211 -218.[CrossRef][Medline]
Gershon, N. D., Porter, K. R. and Trus, B. L. (1985). The cytoplasmic matrix: its volume and surface area and the diffusion of molecules through it. Proc. Natl. Acad. Sci. USA 82,5030 -5034.[Abstract]
Ginty, D. D. and Segal, R. A. (2002). Retrograde neurotrophin signaling: Trking along the axon. Curr. Opin. Neurobiol. 12,268 -274.[CrossRef][Medline]
Gutkind, J. S. (1998). The pathways connecting
G protein-coupled receptors to the nucleus through divergent mitogen-activated
protein kinase cascades. J. Biol. Chem.
273,1839
-1842.
Haugh, J. M., Huang, A. C., Wiley, H. S., Wells, A. and
Lauffenburger, D. A. (1999). Internalized epidermal
growth factor receptors participate in the activation of p21(ras) in
fibroblasts. J. Biol. Chem.
274,34350
-34360.
Haugh, J. M. and Lauffenburger, D. A. (1997). Physical modulation of intracellular signaling processes by locational regulation. Biophys. J. 72,2014 -20131.[Abstract]
Haugh, J. M. and Lauffenburger, D. A. (1998). Analysis of receptor internalization as a mechanism for modulating signal transduction. J. Theor. Biol. 195,187 -218.[CrossRef][Medline]
Hochachka, P. W. (1999). The metabolic
implications of intracellular circulation. Proc. Natl. Acad. Sci.
USA 96,12233
-12239.
Hollenbeck, P. (2001). Cytoskeleton: Microtubules get the signal. Curr. Biol. 11,R820 -R823.[CrossRef][Medline]
Jacobson, K. and Wojcieszyn, J. (1984). The translational mobility of substances within the cytoplasmic matrix. Proc. Natl. Acad. Sci. USA 81,6747 -6751.[Abstract]
Keener, J. and Sneyd, J. (1998). Mathematical Physiology. New York, Berlin, Heidelberg: Springer.
Kholodenko, B. N. (2002). MAP kinase cascade signaling and endocytic trafficking: a marriage of convenience? Trends Cell Biol. 12,173 -177.[CrossRef][Medline]
Kholodenko, B. N., Brown, G. C. and Hoek, J. B. (2000a). Diffusion control of protein phosphorylation in signal transduction pathways. Biochem. J. 350,901 -907.[CrossRef][Medline]
Kholodenko, B. N., Demin, O. V., Moehren, G. and Hoek, J. B.
(1999). Quantification of short term signaling by the epidermal
growth factor receptor. J. Biol. Chem.
274,30169
-30181.
Kholodenko, B. N., Hoek, J. B. and Westerhoff, H. V. (2000b). Why cytoplasmic signalling proteins should be recruited to cell membranes. Trends Cell Biol. 10,173 -178.[CrossRef][Medline]
Koenig, J. A. and Edwardson, J. M. (1997). Endocytosis and recycling of G protein-coupled receptors. Trends Pharmacol. Sci. 18,276 -287.[CrossRef][Medline]
Kouhara, H., Hadari, Y. R., Spivak-Kroizman, T., Schilling, J., Bar-Sagi, D., Lax, I. and Schlessinger, J. (1997). A lipid-anchored Grb2-binding protein that links FGF-receptor activation to the Ras/MAPK signaling pathway. Cell 89,693 -702.[Medline]
Kranenburg, O., Verlaan, I. and Moolenaar, W. H.
(1999). Dynamin is required for the activation of
mitogen-activated protein (MAP) kinase by MAP kinase kinase. J.
Biol. Chem. 274,35301
-35304.
Kusumi, A., Sako, Y. and Yamamoto, M. (1993). Confined lateral diffusion of membrane receptors as studied by single particle tracking (nanovid microscopy). Effects of calcium-induced differentiation in cultured epithelial cells. Biophys. J. 65,2021 -2040.[Abstract]
Kyriakis, J. M., App, H., Zhang, X. F., Banerjee, P., Brautigan, D. L., Rapp, U. R. and Avruch, J. (1992). Raf-1 activates MAP kinase-kinase. Nature 358,417 -421.[CrossRef][Medline]
Lenzen, C., Cool, R. H., Prinz, H., Kuhlmann, J. and Wittinghofer, A. (1998). Kinetic analysis by fluorescence of the interaction between Ras and the catalytic domain of the guanine nucleotide exchange factor Cdc25Mm. Biochemistry 37,7420 -7430.[CrossRef][Medline]
Leof, E. B. (2000). Growth factor receptor signalling: location, location, location. Trends Cell Biol. 10,343 -348.[CrossRef][Medline]
Levchenko, A., Bruck, J. and Sternberg, P. W.
(2000). Scaffold proteins may biphasically affect the levels of
mitogen-activated protein kinase signaling and reduce its threshold
properties. Proc. Natl. Acad. Sci. USA
97,5818
-5823.
Lewis, T. S., Shapiro, P. S. and Ahn, N. G. (1998). Signal transduction through MAP kinase cascades. Adv. Cancer Res. 74,49 -139.[Medline]
MacInnis, B. L. and Campenot, R. B. (2002).
Retrograde support of neuronal survival without retrograde transport of nerve
growth factor. Science
295,1536
-1539.
Mason, C. S., Springer, C. J., Cooper, R. G., Superti-Furga,
G., Marshall, C. J. and Marais, R. (1999). Serine and
tyrosine phosphorylations cooperate in Raf-1, but not B-Raf activation.
EMBO J. 18,2137
-2148.
Maudsley, S., Pierce, K. L., Zamah, A. M., Miller, W. E., Ahn,
S., Daaka, Y., Lefkowitz, R. J. and Luttrell, L. M.
(2000). The beta(2)-adrenergic receptor mediates extracellular
signal-regulated kinase activation via assembly of a multi-receptor complex
with the epidermal growth factor receptor. J. Biol.
Chem. 275,9572
-9580.
Miller, W. E. and Lefkowitz, R. J. (2001). Expanding roles for beta-arrestins as scaffolds and adapters in GPCR signaling and trafficking. Curr. Opin. Cell Biol. 13,139 -145.[CrossRef][Medline]
Mochly-Rosen, D. (1995). Localization of protein kinases by anchoring proteins: a theme in signal transduction. Science 268,247 -251.[Medline]
Moehren, G., Markevich, N., Demin, O., Kiyatkin, A., Goryanin, I., Hoek, J. B. and Kholodenko, B. N. (2002). Temperature Dependence of the epidermal growth factor receptor signaling network can be accounted for by a kinetic model. Biochemistry 41,306 -320.[CrossRef][Medline]
Murray, J. D. (1993). Mathematical Biology. Berlin, Heidelberg: Springer.
Pierce, K. L., Luttrell, L. M. and Lefkowitz, R. J. (2001). New mechanisms in heptahelical receptor signaling to mitogen activated protein kinase cascades. Oncogene 20,1532 -1539.[CrossRef][Medline]
Pierce, K. L., Maudsley, S., Daaka, Y., Luttrell, L. M. and
Lefkowitz, R. J. (2000). Role of endocytosis in the
activation of the extracellular signal-regulated kinase cascade by
sequestering and nonsequestering G protein-coupled receptors. Proc.
Natl. Acad. Sci. USA 97,1489
-1494.
Prenzel, N., Zwick, E., Daub, H., Leserer, M., Abraham, R., Wallasch, C. and Ullrich, A. (1999). EGF receptor transactivation by G-protein-coupled receptors requires metalloproteinase cleavage of proHB-EGF. Nature 402,884 -888.[CrossRef][Medline]
Reynolds, A. J., Bartlett, S. E. and Hendry, I. A. (1998). Signalling events regulating the retrograde axonal transport of 125I-beta nerve growth factor in vivo. Brain Res. 798,67 -74.[CrossRef][Medline]
Rizzo, M. A., Kraft, C. A., Watkins, S. C., Levitan, E. S. and
Romero, G. (2001). Agonist-dependent traffic of
raft-associated Ras and Raf-1 is required for activation of the
mitogen-activated protein kinase cascade. J. Biol.
Chem. 276,34928
-34933.
Rohwer, J. M., Postma, P. W., Kholodenko, B. N. and Westerhoff,
H. V. (1998). Implications of macromolecular crowding for
signal transduction and metabolite channeling. Proc. Natl. Acad.
Sci. USA 95,10547
-10552.
Sastry, L., Lin, W., Wong, W. T., Di Fiore, P. P., Scoppa, C. A. and King, C. R. (1995). Quantitative analysis of Grb2-Sos1 interaction: the N-terminal SH3 domain of Grb2 mediates affinity. Oncogene 11,1107 -1112.[Medline]
Sawano, A., Takayama, S., Matsuda, M. and Miyawaki, A. (2002). Lateral propagation of EGF signaling after local stimulation is dependent on receptor density. Dev. Cell 3,245 -257.[Medline]
Schlessinger, J. (2000). Cell signaling by receptor tyrosine kinases. Cell 103,211 -225.[Medline]
Schlessinger, J. and Bar-Sagi, D. (1994). Activation of Ras and other signaling pathways by receptor tyrosine kinases. Cold Spring Harbor Symp. Quant. Biol. 59,173 -179.[Medline]
Shvartsman, S. Y., Hagan, M. P., Yacoub, A., Dent, P., Wiley, H.
S. and Lauffenburger, D. A. (2002). Autocrine loops
with positive feedback enable context-dependent cell signaling. Am.
J. Physiol. Cell Physiol. 282,C545
-C559.
Strack, S., Westphal, R. S., Colbran, R. J., Ebner, F. F. and Wadzinski, B. E. (1997). Protein serine/threonine phosphatase 1 and 2A associate with and dephosphorylate neurofilaments. Brain Res. Mol. Brain Res. 49, 15-28.[CrossRef][Medline]
Thomas, C. Y., Chouinard, M., Cox, M., Parsons, S., Stallings-Mann, M., Garcia, R., Jove, R. and Wharen, R. (2003). Spontaneous activation and signaling by overexpressed epidermal growth factor receptors in glioblastoma cells. Int. J. Cancer 104,19 -27.[CrossRef][Medline]
Thron, C. D. (1997). Bistable biochemical switching and the control of the events of the cell cycle. Oncogene 15,317 -325.[CrossRef][Medline]
Thron, C. D. (1999). Mathematical analysis of binary activation of a cell cycle kinase which down-regulates its own inhibitor. Biophys. Chem. 79, 95-106.[CrossRef][Medline]
Tyson, J. J. and Novak, B. (2001). Regulation of the eukaryotic cell cycle: molecular antagonism, hysteresis, and irreversible transitions. J. Theor. Biol. 210,249 -263.[CrossRef][Medline]
Ugi, S., Sharma, P. M., Ricketts, W., Imamura, T. and Olefsky,
J. M. (2002). Phosphatidylinositol 3-kinase is required for
insulin-stimulated tyrosine phosphorylation of Shc in 3T3-L1 adipocytes.
J. Biol. Chem. 277,18592
-18597.
van Biesen, T., Luttrell, L. M., Hawes, B. E. and Lefkowitz, R. J. (1996). Mitogenic signaling via G protein-coupled receptors. Endocrinol. Rev. 17,698 -714.[Medline]
Verhey, K. J. and Rapoport, T. A. (2001). Kinesin carries the signal. Trends Biochem. Sci. 26,545 -550.[CrossRef][Medline]
Verveer, P. J., Wouters, F. S., Reynolds, A. R. and Bastiaens,
P. I. (2000). Quantitative imaging of lateral ErbB1 receptor
signal propagation in the plasma membrane. Science
290,1567
-1570.
Vieira, A. V., Lamaze, C. and Schmid, S. L.
(1996). Control of EGF receptor signaling by clathrin-mediated
endocytosis. Science
274,2086
-2089.
Yano, H., Lee, F. S., Kong, H., Chuang, J., Arevalo, J., Perez, P., Sung, C. and Chao, M. V. (2001). Association of Trk neurotrophin receptors with components of the cytoplasmic dynein motor. J. Neurosci. 21,RC125 .[Medline]
Zhabotinsky, A. M. and Zaikin, A. N. (1973). Autowave processes in a distributed chemical system. J. Theor. Biol. 40,45 -61.[Medline]
Zhao, Y. and Zhang, Z. Y. (2001). The mechanism
of dephosphorylation of extracellular signal-regulated kinase 2 by
mitogen-activated protein kinase phosphatase 3. J. Biol.
Chem. 276,32382
-32391.