1 CNRS-UMR 5539, Université Montpellier 2, Place Eugène Bataillon,
34095 Montpellier Cedex 05, France
2 INSERM U563, CHU Purpan, place du Dr Blayac, 31059 Toulouse Cedex 03,
France
* Author for correspondence (e-mail: bettache{at}univ-montp2.fr)
Accepted 11 February 2003
![]() |
Summary |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Key words: Platelet, Phospholipid, Filopodia, Actin filament, PI 3-kinase, Akt, Fibroblast
![]() |
Introduction |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
![]() |
Materials and Methods |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Preparation of platelets
Blood collected in 0.15 vol. of ACD (85 mM trisodium citrate, 111 mM
dextrose, 71 mM citric acid), was obtained from healthy volunteers. Platelets
were prepared at room temperature using the erythrocyte cushion procedure, as
previously described (Gaffet et al.,
1995; Valone et al.,
1982
). After staining with Plaxan reagent (Sobioda,
Montbonnot-Saint-Martin, France), platelets were resuspended in buffer B (96
mM NaCl, 1 mM CaCl2, 2.7 mM KCl, 2 mM MgCl2, 5 mM
dextrose, 50 mM HEPES, pH 7.4) at 2.2x109 platelets/ml.
Platelets were incubated for 30 minutes at 37°C (pH 7.4) before the
addition of 1 mM Ca2+ (final concentration) and testing. Platelets
were activated at 37°C by adding calcium ionophore A23187 (1 µM final
concentration) in the presence of 1 mM external Ca2+ (pH 6.9).
Incubation of platelets with phospholipid analogues
Platelets at 2.2x109 cells/ml previously pre-treated or
not with different inhibitors (cytochalasin D, calpeptin, wortmannin or
LY294002) were incubated at 37°C without shaking with a short chain
spin-labeled PS or PC analogue at 1% of total PL as indicated
(Suné and Bienvenüe,
1988). At 2 and 30 minutes, this PL incubation was stopped for
further analysis as indicated below.
Incubation of L929 fibroblasts with phospholipid analogues
Fibroblasts treated with nocodazole (2.5 µg/ml) were immediately plated
onto polylysine-treated coverslips coated with human serum fibronectin for 3
hours according to Kaverina et al.
(Kaverina et al., 1998). After
this treatment, fibroblasts were incubated with 50 µM DLPC (corresponding
to
2% of total phospholipids). At 2 minutes of incubation, fibroblasts
were fixed with 2% paraformaldehyde for 30 minutes and observed at light
microscopy.
Actin labeling and wortmannin treatment of L929 fibroblasts
Untreated and nocodazole-treated fiboblasts were incubated, when necessary,
with 100 nM wortmannin for 15 minutes and then incubated with 50 µM DLPC
for 2 minutes. After 30 minutes fixation with 2% paraformaldehyde, cells were
permeabilized with 0.1% Triton X-100 and were stained with phalloidin-TRITC.
The fluorescence microscopy observations were carried out with a LEICA DMRA2
microscope.
Determination of actin filament content in platelets
Platelets were lysed by the addition of an equal volume of buffer
containing 2% Triton X-100, 10 mM EGTA, and 100 mM Tris-HCl, pH 7.4. The actin
filament content was determined by Dnase I inhibition assay as described
previously (Blikstad et al.,
1978; Fox et al.,
1981
).
Scanning electron microscopy (SEM) and confocal microscopy
Platelets were pre-incubated for 30 minutes at 37°C with or without
different inhibitors (5 µM cytochalasin D or 100 nM wortmannin, 100
µg/ml calpeptin), and then incubated with PL analogues [(0.2)PS or (0.2)PC]
or activated by Ca2+-ionophore A23187 (1 µM) or by PMA. For SEM,
the samples were prepared as indicated
(Gaffet et al., 1995). For
confocal microscopy, control platelets, platelets incubated with (0.2)PC or
(0.2)PS, and platelets pre-treated with calpeptin and then activated with
Ca2+-ionophore A23187 were fixed with 2% paraformaldehyde for 30
minutes and allowed to deposit on coverslips. The deposited platelets were
permeabilized with 0.025% saponin and were stained with Dnase 1 Oregon green
and phalloidin-TRITC or with anti-PI-3-kinase (anti-p85, 1:30, Sigma P-8208).
Anti-p85
was detected with FITC-conjugated goat anti-rabbit IgG (1 hour
at room temperature). The confocal microscopy observations were carried out
with a LEICA TCS 4D microscope.
Measurement of [32P]3-phosphoinositides
Platelets were labeled with [32P]orthophosphate (0.4 mCi/ml) for
60 minutes, washed, and resuspended at 1x109 cells/ml. After
incubation of platelets with excess PL or with thrombin (without shaking),
reactions were stopped at the indicated time by addition of
chloroform/methanol (1:1 v/v) containing 0.4 mol/l HCl, and lipids were
immediately extracted and analyzed by high-performance liquid chromatography
(HPLC) as described (Gratarap et al.,
1998).
Miscellaneous
Platelet secretion was quantified as described previously
(Suné and Bienvenüe,
1988) using (3H) 5-HT as a marker for dense granules.
Radioactivity was measured in the supernatant of the platelet suspension
(11,000 g for 3 minutes) and expressed as a percentage of
total radioactivity in the suspension. Platelet lysis, as evaluated by lactate
dehydrogenase activity (Sigma kit No 500) in the supernatant of activated
platelets, did not exceed 4.5%. Platelet activation was carried out either by
the Ca2+-ionophore A23187 (1 µM for 4 minutes) in the presence
of calpeptin (100 µg/ml, 30 minutes pre-incubation time) or by the phorbol
12-myristate 13-acetate (100 nM for 20 minutes). Akt phosphorylation was
assessed by western blot using a specific antibody that recognizes Akt only
when phosphorylated at Ser473 (pSer473Akt, 1:1000, Cell Signaling Technology,
Beverly, MA).
![]() |
Results |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
|
Filopodia are sustained and stabilized by actin filaments
Observations by confocal microscopy of platelets stained with fluorescently
labeled phalloidin and DNase I (labeling F- and G-actin, respectively) showed
that G- and F-actin strongly redistributed after PL addition: long filopodia
contained mainly F-actin while G-actin was concentrated in the cell body. This
demonstrated that actin filaments sustained the filopodia induced by external
addition of PL in a manner similar to that described for platelet activation
by a Ca2+ ionophore (Fig.
2j-l). Finally, similar results were obtained with different short
chain PL (spin labeled-, dilauroyl-, or NBD-PC or -PS) demonstrating that the
fatty acid composition was not responsible for filopodia formation (not
shown).
|
The physical constraint generated by phospholipid excess induces
actin polymerization
In a previous paper (Suné and
Bienvenüe, 1988), where the shape change was first described,
no data were provided to demonstrate the implication of actin cytoskeleton in
response to PL excess. Two hypotheses could explain this actin remodeling
event occurring in response to excess PL: (1) platelet recruitment of
pre-existing actin filaments at some points of the plasma membrane; or (2) de
novo actin polymerization from the monomeric actin pool. To distinguish
between these hypothesis, we measured the G- and F-actin content of platelets
under various conditions. Actually, PL addition clearly triggered actin
polymerization, inhibited by cytochalasin D
(Fig. 3).
|
Addition of PS or PC analogues to resting platelets resulted in a rapid and
marked increase in F-actin concentrations from 50% of the total amount of
cell actin in untreated platelets to
64% in treated platelets
(Fig. 3). When a PS analogue
was added to resting platelets, actin polymerization was reversible: the
F-actin content raised 2 minutes after PS addition (
64%) and
progressively decreased to the control value (
51%) 30 minutes later. This
reversibility correlated with the translocation of aminophospholipids to the
inner leaflet by aminophospholipid translocase
(Suné et al., 1987
). By
contrast, after PC addition, F-actin content remained high (
63%) during
the entire period of the incubation, correlating with the stable insertion of
PC in the outer leaflet. The transient 13% increase in actin polymerization
induced by excess PL in the outer leaflet was highly significant, and
corresponded to about one half of what was observed (21%) in the case of
Ca2+-ionophore activation of platelets. In all cases, addition of 5
µM cytochalasin D, 15 minutes before platelet treatments almost completely
abolished actin polymerization response
(Fig. 3).
Filopodia formation and actin polymerization were significantly
reduced by two unrelated inhibitors of PI 3-kinase
If actin polymerization is essential for membrane extension, the original
cause in this study is obviously physical, being strictly dependent on
transient PL excess on the external leaflet. However, PL insertion and
translocation per se can hardly explain the overall increase in actin
polymerization. Therefore, we next aimed to characterize how a physical
constraint and/or curvature could activate some signals (such as protein or PL
kinase activation) that lead to actin polymerization. A comparable example of
physical force is the fluid shear stress, which plays determinant roles in
maintaining cardiovascular homeostasis. During this mechanical stimulation,
focal adhesion kinase (FAK) (Li et al.,
1997) and the mitogen-activated protein kinases, such as
extracellular signal-regulated kinase (ERK) and c-Jun N-terminal kinase (JNK)
are activated (Jo et al.,
1997
; Li et al.,
1996
; Tseng et al.,
1995
). In addition, it has been recently reported that the
phosphoinositide 3-kinase (PI 3-kinase) mediates shear stress-dependent
activation of JNK in endothelial cells (Go
et al., 1998
). Furthermore, PI 3-kinase activity is strongly
dependent on membrane curvature
(Hübner et al., 1998
).
Interestingly, it was demonstrated that the enzymatic products of PI 3-kinase
mediate platelet actin assembly and filopodial extension after PMA stimulation
(Hartwig et al., 1996a
).
During phagocytosis, PI 3-kinase activity is also reported to be involved in
pseudopodial extension (Cox et al.,
1999
). Since we observed changes in platelet shape with a strong
membrane curvature in filopodia emerging in response to excess PL, we tested
the possible involvement of PI 3-kinase in this mechanism by using two
unrelated and potent PI 3-kinase inhibitors wortmannin and LY294002.
Pre-treatment of platelets with wortmannin significantly reduced the number of
filopodia induced by excess PL (Fig.
4c). We also tested the effect of wortmannin and LY294002 on actin
polymerization. Fig. 4d shows
that the increase in F-actin content induced by PL addition was significantly
reduced by these two inhibitors. Wortmannin also inhibited actin
polymerization of platelets activated by PMA
(Fig. 4d) in agreement with
results obtained by Hartwig et al.
(Hartwig et al., 1996b
). Among
the various PI 3-kinase products,
[32P]PtdIns(3,4)P2 was the only one whose
content was found to be significantly increased when excess PL was added to
the outer leaflet (Fig. 4e). In
the same conditions, [32P]PtdIns(4)P and
[32P]PtdIns(4,5)P2 did not change significantly
(not shown). Pre-incubation of platelets with wortmannin or LY294002, prior to
adding PL, completely inhibited the increase of
PtdIns(3,4)P2.
|
Phospholipid excess induces the recruitment of PI 3-kinase to plasma
membrane and Akt phosphorylation
PI 3-kinase involvement in actin polymerization and filopodia formation was
further assessed by (1) the membrane recruitment of PI 3-kinase in response to
the PL excess; and (2) the phosphorylation of Akt, a downstream protein kinase
target of activated PI 3-kinase (Franke et
al., 1997). During the physical constraint applied by PL excess,
PI 3-kinase was translocated from punctuate sites in the cytoplasm to the
plasma membrane (Fig. 5A). As
far as the constraint persisted, PI 3-kinase remained localized to the plasma
membrane (Fig. 5A, PC 1min, PC
30min, PS 1min). PI 3-kinase translocation from the cytoplasm to the plasma
membrane was already also observed in various cells in response to growth
factor receptor signaling (Gillham et al.,
1999
). However, when the PL excess disappeared, the distribution
of PI 3-kinase reversed to a cytoplasmic localization indistinguishable to
that observed in control platelets (Fig.
5A, PS 30min, Control). Concomitantly, the PL excess induced a net
increase in Akt phosphorylation that was abolished by the presence of PI
3-kinase inhibitors and reversed when PL excess was nullified
(Fig. 5B,C). Akt was previously
demonstrated to be a required intermediate between PI 3-kinase activation and
filopodia extension in Dictyostelium discoideum
(Meili et al., 1999
) and in
the formation of stress fibers in endothelial cells
(Morales-Ruiz et al.,
2000
).
|
Effect of phospholipid excess on membrane extension is also observed
in fibroblasts
We next sought to determine how much of the membrane-cytoskeleton
reactivity that observed in platelets following a mechanical constraint was
generalized to other cellular systems, notably nucleated cells. Addition of
DLPC to untreated L929 fibroblasts induced no gross morphological change (not
shown). However, when L929 cells were pre-treated with nocodazole in order to
disrupt the microtubule cytoskeleton (Fig.
6b), subsequent addition of 50 µM DLPC resulted in drastic
membrane extensions (lamellipodia and short filopodia)
(Fig. 6c). Therefore, under
these specific conditions, as observed with platelets, a similar membrane
reorganization was induced by phospholipid imbalance in nucleated cells.
|
Membrane extensions in fibroblasts are actin- and
PI-3-kinase-dependent
Microscopic observations of L929 fibroblasts stained with fluorescently
labeled phalloidin showed that F-actin was enriched in membrane extensions
when nocodazole-treated cells were incubated with a phospholipid excess
(Fig. 7c). This drastic
enrichment in actin was not observed in untreated cells
(Fig. 7a) or in cells uniquely
treated with nocodazole (Fig.
7b). As in platelets, pre-incubation of nocodazole-treated cells
by wortmannin abrogated the effect of phospholipid addition on F-actin
recruitment (Fig. 7d).
|
![]() |
Discussion |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
The emergence of filopodia extension and actin polymerization may be
rationalized by a generalization of the stochastic theory
(van Oudenaarden and Theriot,
1999). According to this theory, owing to the actin network
dynamics, a bead symmetrically surrounded by actin can move in one direction
when the symmetry of the system is broken by some random process, leading to a
polarization of the actin mantle and formation of an actin tail, a biological
driving force capable of pushing the bead ahead. In this context, the shape of
a resting state platelet would be the result of the dynamic equilibrium
between actin polymerization (controlled by actin and accessory protein
concentrations) and the applied physical constraint. When the transverse
phospholipid content is unbalanced by external addition of a minimal amount of
PL, some small exvaginations occurred that could become nucleation points for
fast actin polymerization by elongation of initially small filaments at their
barbed end, known to be in proximity of the membrane surface
(Wilkins and Lin, 1981
). At
these points, the equilibrium between the two forces is displaced, leading to
elongation until the external excess in PL is accommodated by these highly
curved structures.
Although the precise mechanism governing the changes in cell shape and
actin polymerization that are induced by membrane curvature is not known, our
results indicate that biochemical signaling pathways are triggered by this
initial physical event. Through direct binding to specific protein domains the
products of PI 3-kinase may recruit and modulate the activity of several
proteins involved in the control of cell shape and actin cytoskeleton
reorganization. Many PI 3-kinase products as well as
PtdIns(4,5)P2 act as regulators of actin polymerization
(1) by uncapping the barbed end of microfilaments from gelsolin
(Janmey and Stossel, 1987),
(2) by dissociating the profilactin complex providing a fresh pool of
monomeric actin (Lassing and Lindberg,
1985
), (3) by associating with
-actinin
(Fukami et al., 1992
) and (4)
by strengthening the cytoskeleton-membrane interactions
(Raucher et al., 2000
).
In the case of platelets, a striking observation is that this process is
fully reversible, since filopodia formation, increased actin polymerization,
translocation of PI 3-kinase to the plasma membrane, and Akt phosphorylation
disappeared when the imbalance was neutralized by specific aminophospholipid
transport. PL imbalance creates a curvature in the plasma membrane and induces
actin polymerization. Actin polymerization pushes forwards to form long
filopodia until a new equilibrium occurs between F-actin pressure and membrane
tension induced by transverse phospholipid imbalance. The change in F-/G-actin
ratio appears to be modulated by PI 3-kinase activation, known to be related
to membrane curvature (Hübner et al.,
1998). Subsequently, the aminophospholipid translocase in
platelets can equilibrate the two membrane leaflets, allowing filopodia to
retract and actin to depolymerize. Similar dynamic changes in shape are known
to be induced by upstream signals involving rac and cdc42 activation
(Nobes and Hall, 1995
).
The physical and mechanical constraint exerted on membrane through
experimental phospholipid excess is not limited to the sole platelet model,
where it is sometimes difficult to assess the actual state of activation of
the cellular model. Here, it is important to point out that the PL excess
provided by aminophospholipid addition induced a reversible phenotypic change
in shape that cannot be explained by standard platelet activation. It was,
however, very important to reproduce these phenotypic changes in a different
cell model, notably within nucleated cells. In order to do so, we have had to
simplify the nucleated cell model by slowing down the intense membrane
dynamics that are normally recorded at the surface of dynamic fibroblasts.
This was performed by disrupting the microtubule network in L929 cells with
nocodazole, leaving the actin cytoskeleton functional. Under those
experimental conditions, we were able to trigger major membrane extensions
(lamellipodia together with short filopodia) induced by PL imbalance in L929
fibroblasts. As previously observed in platelets, the membrane extensions in
fibroblasts were also actin- and PI 3-kinase-dependent, supporting a
generalized concept linking physical membrane constraint with a signaling
pathway leading to actin polymerization via PI 3-kinase activation. How the
physical signal (i.e. the introduction of a few phospholipids to the outer
phospholipid leaflet of the membrane) triggers the signaling cascade remains
unknown. When growth factors activate their receptors, phosphorylated tyrosine
residues on the latter are sites of PI 3-kinase recruitment
(Bjorge et al., 1990). What
kind of receptors are activated when excess phospholipids are inserted in the
outer leaflet of the membrane remains to be determined.
Recent work (Funamoto et al.,
2002; Iijima and Devreotes,
2002
) has demonstrated that PI 3-kinase is recruited and activated
in the leading edge of cells exposed to chemoattractants gradients. The
localization of PI 3-kinase could explain the generation of
3-phosphoinositides in the leading edge and the reversibility of these events
may be achieved by PTEN (3-phosphoinositide phosphatase), the antagonist of PI
3-kinase.
The effect of lipid addition was also observed in NIH 3T3 fibroblasts. In
these cells, the lipid excess modulates cell spreading and lamellipodial
extension (Raucher and Sheetz,
2000). In that study (Raucher
and Sheetz, 2000
), the concentration of the lipid added (2 mM) was
much higher than the one used in the experiments reported here (8 µM for
platelets and 50 µM for fibroblasts). However, both studies clearly show
that physical constraint and/or membrane tension modulates cellular dynamics.
Nevertheless, one should keep in mind that the mechanism induced by lipid
addition may be subtly different depending on the cell type
characteristics.
In conclusion, although the effect of tension could not be completely excluded, the data presented here indicate that cells may respond to physical forces exerted by membrane curvature, a form of mechanical stress, by activation of the PI 3-kinase/Akt signaling pathway, followed by actin polymerization and change in cell shape.
![]() |
Acknowledgments |
---|
![]() |
References |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Bettache, N., Gaffet, P., Allegre, N., Maurin, L., Toti, F., Freyssinet, J. M. and Bienvenüe, A. (1998). Impaired redistribution of aminophospholipids with distinctive cell shape change during Ca2+-induced activation of platelets from a patient with Scott syndrome. Br. J. Haematol. 101,50 -58.[CrossRef][Medline]
Bjorge, J., Chan, T., Antczak, M., Kung, H. and Fujita, D. (1990). Activated Type I Phosphatidylinositol Kinase is Associated with the Epidermal Growth Factor (EGF) Receptor Following EGF Stimulation. Proc. Natl. Acad. Sci. USA 87,3816 -3820.[Abstract]
Blikstad, I., Markey, F., Carlsson, L., Persson, T. and Lindberg, U. (1978). Selective assay of monomeric and filamentous actin in cell extracts, using inhibition of deoxyribonuclease I. Cell 15,935 -943.[Medline]
Bretscher, M. S. (1972). Phosphatidyl-ethanolamine: differential labelling in intact cells and cell ghosts of human erythrocytes by a membrane-impermeable reagent. J. Mol. Biol. 71,523 -528.[Medline]
Chap, H. J., Zwaal, R. F. A. and van Deenen, L. L. M. (1977). Action of highly purified phospholipases on blood platelets. Evidence for an asymetric distribution of phospholipids in the surface membrane. Biochim. Biophys. Acta 467,146 -164.[Medline]
Connor, J., Pak, C. C. and Schroit, A. J.
(1994). Exposure of phosphatidylserine in the outer leaflet of
human red blood cells. J. Biol. Chem.
269,2399
-2404.
Cox, D., Tseng, C., Bjekic, G. and Grennberg, S.
(1999). A requirement for phosphatidylinositol 3-kinase in
pseudopod extension. J. Biol. Chem.
274,1240
-1247.
Fadok, V. A., Voelker, D. R. and Campbell, P. A. (1992). Exposure of phosphatidylserine on the surface of apoptotic lymphocytes triggers specific recognition and removal by macrophages. J. Immunol. 142,2207 -2216.
Farge, E. (1995). Increased vesicle endocytosis due to an increase in the plasma membrane phosphatidylserine concentration. Biophys. J. 69,2501 -2506.[Abstract]
Farge, E. and Devaux, P. F. (1992). Shape changes of giant liposomes induced by an asymmetric transmembrane distribution of phospholipids. Biophys. J. 61,347 -357.[Abstract]
Farge, E., Ojcius, D. M., Subtil, A. and Dautry-Varsat, A. (1999). Enhancement of endocytosis due to aminophospholipid transport across the plasma membrane of living cells. Am. J. Physiol. 276,C725 -C733.[Medline]
Fox, J. E. B., Dockter, M. E. and Phillips, D. R. (1981). An improved method for determining the actin filament content of nonmuscle cells by the DNAase I inhibition assay. Anal. Biochem. 117,170 -177.[Medline]
Franck, P. F., Bevers, E. M., Lubin, B. H., Comfurius, P., Chiu, D. T., Op den Kamp, J. A., Zwaal, R. F., van Deenen, L. L. and Roelofsen, B. (1985). Uncoupling of the membrane skeleton from the lipid bilayer. The cause of accelerated phospholipid flip-flop leading to an enhanced procoagulant activity of sickled cells. J. Clin. Invest. 75,183 -190.[Medline]
Franke, T. F., Kaplan, D. R., Cantley, L. C. and Toker, A.
(1997). Direct regulation of the Akt proto-oncogene product by
phosphatidylinositol-3,4-bisphosphate. Science
275,665
-668.
Fujii, T. and Tamura, A. (1984). Shape change of human erythrocytes induced by phosphatidylcholine and lysophosphatidylcholine species with various acyl chain lengths. Cell. Biochem. Funct. 2,171 -176.[Medline]
Fukami, K., Furuhashi, K., Inagaki, M., Endo, T., Hatano, S. and Takenawa, T. (1992). Requirement of phosphatidylinositol 4,5-bisphosphate for alpha-actinin function. Nature 359,150 -152.[CrossRef][Medline]
Funamoto, S., Meili, R., Lee, S., Parry, L. and Firtel, R. A. (2002). Spatial and temporal regulation of 3-phosphoinositides by PI 3-kinase and PTEN mediates chemotaxis. Cell 109,611 -623.[Medline]
Gaffet, P., Bassé, F. and Bienvenüe, A. (1994). Loss of phospholipid asymmetry in human platelet plasma membrane after 1-12 days of storage an ESR study. Eur. J. Biochem. 222,1033 -1040.[Abstract]
Gaffet, P., Bettache, N. and Bienvenüe, A. (1995). Phosphatidylserine exposure on the platelet plasma membrane during A23187-induced activation is independent of cytoskeleton reorganization. Eur. J. Cell Biol. 67,336 -345.[Medline]
Gillham, H., Golding, M. C., Pepperkok, R. and Gullick, W.
J. (1999). Intracellular movement of green fluorescent
protein-tagged phosphatidylinositol 3-kinase in response to growth factor
receptor signaling. J. Cell Biol.
146,869
-880.
Go, Y. M., Park, H., Maland, M. C., Darley-Usmar, V. M., Stoyanov, B., Wetzker, R. and Jo, H. (1998). Phosphatidylinositol 3-kinase gamma mediates shear stress-dependent activation of JNK in endothelial cells. Am. J. Physiol. 275,H1898 -H1904.[Medline]
Gratarap, M., Payrastre, B., Viala, C., Mauco, G., Plantavid, M.
and Chap, H. (1998). Phosphatidylinositol
3,4,5-triphosphate-dependent stimulation of phospholipase C-2 is an
early key event in Fc
RIIA-mediated activation of human platelets.
J. Biol. Chem. 273,24314
-24321.
Hamill, O. P. and Martinac, B. (2001).
Molecular basis of mechanotransduction in living cells. Physiol.
Rev. 81,685
-740.
Hartwig, J., Kung, S., Kovacsovics, T., Janmey, P., Cantley, L.,
Stossel, T. and Toker, A. (1996a). D3phosphoinositides and
outside-in integrin signaling by glycoprotein IIb-IIIa mediate platelet actin
assembly and filopodial extension induced by porbol 12-myristate 13-acetate.
J. Biol. Chem. 271,32986
-32993.
Hartwig, J. H., Kung, S., Kovacsovics, T., Janmey, P. A.,
Cantley, L. C., Stossel, T. P. and Toker, A. (1996b). D3
phosphoinositides and outside-in integrin signaling by glycoprotein IIb-IIIa
mediate platelet actin assembly and filopodial extension induced by phorbol
12-myristate 13-acetate. J. Biol. Chem.
271,32986
-32993.
Hauser, H. (2000). Short-chain phospholipids as detergents. Biochim. Biophys. Acta 1508,164 -181.[Medline]
Hübner, S., Couvillon, A., Käs, J., Bankaitis, V., Vegners, R., Carpenter, C. and Janmey, P. (1998). Enhancement of phosphoinositide 3-kinase (PI3-Kinase) activity by membrane curvate and inositol-phospholipids-binding peptides. Eur. J. Biochem. 258,846 -853.[Abstract]
Iijima, M. and Devreotes, P. (2002). Tumor suppressor PTEN mediates sensing of chemoattractant gradients. Cell 109,599 -610.[Medline]
Janmey, P. A. and Stossel, T. P. (1987). Modulation of gelsolin function by phosphatidylinositol 4,5-bisphosphate. Nature 325,362 -364.[CrossRef][Medline]
Jo, H., Sipos, K., Go, Y.-M., Law, R., Rong, J. and McDonald, J.
M. (1997). Differential effect of shear stress on
extracellular signal-regulated kinase and N-terminal Jun kinase in endothelial
cells. Gi2- and Gbeta/gamma-dependent signaling pathways. J. Biol.
Chem. 272,1395
-1401.
Kaverina, I., Rottner, K. and Small, J. V.
(1998). Targeting, capture, and stabilization of microtubules at
early focal adhesions. J. Cell Biol.
142,181
-190.
Lassing, I. and Lindberg, U. (1985). Specific interaction between phosphatidylinositol 4,5-bisphosphate and profilactin. Nature 314,472 -474.[Medline]
Li, S., Kim, M., Hu, Y. L., Jalali, S., Schlaepfer, D. D.,
Hunter, T., Chien, S. and Shyy, J. Y. (1997). Fluid shear
stress activation of focal adhesion kinase. Linking to mitogen-activated
protein kinases. J. Biol. Chem.
272,30455
-30462.
Li, Y. S., Shyy, J. Y., Li, S., Lee, J., Su, B., Karin, M. and Chien, S. (1996). The Ras-JNK pathway is involved in shear-induced gene expression. Mol. Cell Biol. 16,5947 -5954.[Abstract]
Meili, R., Ellsworth, C., Lee, S., Reddy, T. B., Ma, H. and
Firtel, R. A. (1999). Chemoattractant-mediated transient
activation and membrane localization of Akt/PKB is required for efficient
chemotaxis to cAMP in Dictyostelium. EMBO J.
18,2092
-2105.
Morales-Ruiz, M., Fulton, D., Sowa, G., Languino, L. R., Fujio,
Y., Walsh, K. and Sessa, W. C. (2000). Vascular endothelial
growth factor-stimulated actin reorganization and migration of endothelial
cells is regulated via the serine/threonine kinase Akt. Circ.
Res. 86,892
-896.
Nobes, C. D. and Hall, A. (1995). Rho, rac, and cdc42 GTPases regulate the assembly of multimolecular focal complexes associated with actin stress fibers, lamellipodia, and filopodia. Cell 81,53 -62.[Medline]
Raucher, D. and Sheetz, M. P. (2000). Cell
spreading and lamellipodial extension rate is regulated by membrane tension.
J. Cell Biol. 148,127
-136.
Raucher, D., Stauffer, T., Chen, W., Shen, K., Guo, S., York, J. D., Sheetz, M. P. and Meyer, T. (2000). Phosphatidylinositol 4,5-bisphosphate functions as a second messenger that regulates cytoskeleton-plasma membrane adhesion. Cell 100,221 -228.[Medline]
Seigneuret, M. and Devaux, P. F. (1984). ATP-dependent asymmetric distribution of spin-labeled phospholipids in the erythrocyte membrane: relation to shape changes. Proc. Natl. Acad. Sci. USA 81,3751 -3755.[Abstract]
Sheetz, M. P. and Singer, S. J. (1974). Biological membranes as bilayer couples. A molecular mechanism of drug-erythrocyte interactions. Proc. Natl. Acad. Sci. USA 71,4457 -4461.[Abstract]
Siess, W. (2002). Athero- and thrombogenic actions of lysophosphatidic acid and sphingosine-1-phosphate. Biochim. Biophys. Acta 1582,204 -215.[Medline]
Suné, A. and Bienvenüe, A. (1988). Relationship between the transverse distribution of phospholipids in plasma membrane and shape change of human platelets. Biochemistry 27,6794 -6800.[Medline]
Suné, A., Bette-Bobillo, P., Bienvenüe, A., Fellmann, P. and Devaux, P. F. (1987). Selective outside-inside translocation of aminophospholipids in human platelets. Biochem. 26,2972 -2978.[Medline]
Tseng, H., Peterson, T. E. and Berk, B. C.
(1995). Fluid shear stress stimulates mitogen-activated protein
kinase in endothelial cells. Circ. Res.
77,869
-878.
Valone, F. H., Coles, E., Vernon, R. R. and Goetzl, E. J.
(1982). Specific binding of phospholipid platelet-activating
factor by human platelets. J. Immunol.
129,1637
-1641.
van Oudenaarden, A. and Theriot, J. A. (1999). Cooperative symmetry-breaking by actin polymerization in a model for cell motility. Nat. Cell Biol. 1, 493-499.[CrossRef][Medline]
Wilkins, J. A. and Lin, S. (1981). Association of actin with chromaffin granule membranes and the effect of cytochalasin B on the polarity of actin filament elongation. Biochim. Biophys. Acta 642,55 -66.[Medline]
Zachowski, A. (1993). Phospholipids in animal eukaryotic membranes: transverse asymmetry and movement. Biochem. J. 294,1 -14.[Medline]
Zwaal, R. F. A., Bevers, E. M., Comfurius, P., Rosing, J., Tilly, R. H. J. and Verhallen, P. F. J. (1989). Loss of membrane phospholipid asymmetry during activation of blood platelets and sickled red cells; mechanisms and physiological significance. Mol. Cell Biochem. 91,23 -31.[Medline]
Zwaal, R. F. A., Comfurius, P. and Bevers, E. M. (1993). Mechanism and function of changes in membrane-phospholipid asymmetry in platelets and erythrocytes. Biochem. Soc. Trans. 21,248 -253.[Medline]