© 1997 American Heart Association, Inc.
Articles |
Platelet-Derived Growth Factor ß-Receptors Can Both Promote and Inhibit Chemotaxis in Human Vascular Smooth Muscle Cells
From the Department of Clinical Pharmacology, Imperial College School of Medicine at St Mary's, London, UK.
Correspondence to Dr Gerard Clunn, Department of Clinical Pharmacology, Imperial College School of Medicine at St Mary's, South Wharf Rd, Paddington, London, W2 1NY, UK. E-mail g.clunn{at}ic.ac.uk
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Abstract |
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Abstract The effect of the three platelet-derived growth factor (PDGF) isoforms AA, AB, and BB on migration was investigated in cultured human saphenous vein smooth muscle cells. The modified Boyden chamber technique yielded efficacies BB>>AB, AA=0. However, the BB concentration-response relationship displayed a pronounced peak, occurring between 1 and 10 ng/mL, with no response above this range. Checkerboard analysis showed that the promotion of migration at low concentrations was chemotactic in nature but that the downturn was independent of gradient. Furthermore, at high concentrations BB was able to prevent chemotaxis induced by fetal calf serum and epidermal growth factor (EGF). Experiments using low concentrations of BB in combination with high concentrations of AA to saturate PDGF
-receptors in the presence and absence of a neutralizing antibody to
-receptors revealed that -receptor activation induced partial
inhibition of chemotaxis but this did not account for the inhibition of
migration by high concentrations of BB. Despite possessing no
significant chemotactic action itself, high concentrations of the AB
isoform completely inhibited BB induced chemotaxis. Taken together
these results suggest that the chemotactic signal induced by PDGF is
dominated by PDGF ß-receptors and switches from positive at low
concentrations to negative at higher concentrations. Stimulation of DNA
synthesis by the three isoforms (as measured by [3H]
thymidine incorporation) yielded saturable responses for the AB and BB
isoforms, with similar efficacy and weak or no response for the AA
isoform. Concentration-dependent patterns of tyrosine
phosphorylation of certain proteins mirrored the form
of the chemotactic response and suggest one possible underlying
regulatory mechanism to account for the disparity between PDGF-induced
chemotaxis and DNA synthesis.
Key Words: vascular smooth muscle • platelet-derived growth factor • chemotaxis • tyrosine phosphorylation
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Introduction |
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Platelet-derived growth factor (PDGF) acts as a mitogen and chemoattractant for vascular smooth muscle cells (SMCs).1 The active growth factor exists as a disulfide-linked dimer composed of two types of peptide chains termed A and B, which give rise to three isoforms denoted PDGF-AA, -AB, and -BB. In addition, there are two types of PDGF receptors termed PDGF-R
and PDGF-Rß, which dimerize and become
active on binding the growth factor to initiate an intracellular
signaling cascade via tyrosine
phosphorylation.2 The A chain can bind
only to PDGF-R but the B chain can bind both receptor subtypes. This
means that PDGF-AA activates only -dimers, PDGF-AB
activates - and ß- dimers (See Reference 33 ), and
PDGF-BB activates -, ß-, and ßß-dimers. Thus the
three isoforms of PDGF can elicit a diverse range of signals in
SMCs.4 5
Although PDGF is one among many molecules involved in normal and
pathological processes such as wound healing, angiogenesis,
atherosclerosis, and restenosis, there is
evidence that it does have particularly important roles to play,
especially with regard to SMC migration. Studies using animal injury
models showed that infusion of PDGF-BB promoted intimal thickening and
promoted SMC migration from the media to intima.6
Furthermore, an antibody against PDGF reduced myointimal hyperplasia in
response to injury.7 Similarly, PDGF-BB production
has been associated with intimally directed SMC migration and
proliferation in organ cultured human saphenous vein.8 The
actions of PDGF on saphenous vein cells is of particular interest
because it is the most widely used conduit for coronary artery
and infrainguinal bypasses, and myointimal hyperplasia as a result of
SMC migration and proliferation accounts for 
80% of failures of
saphenous vein grafts.9
Knowledge of the actions of PDGF on saphenous vein–derived SMC proliferation and migration would be useful in interpreting the events observed in these more complex in vivo situations. In this study we have therefore investigated the effect of PDGF-AA, -AB, and -BB on SMC derived from human saphenous vein. These studies show marked differences between the chemotactic and early proliferative responses to a given isoform and major differences between the isoforms themselves. We further show that the chemotactic signal switches from a positive signal at low concentrations of PDGF-BB to a negative signal at higher concentrations. The dominant signals at all concentrations and to all isoforms appear to be mediated by ß-receptors, indicating a dual role for these receptors in saphenous vein SMC chemotaxis. Regulation of tyrosine phosphorylation of certain key signaling molecules may underlie some of the observed behavior.
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Methods |
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Cell Culture
Human vascular smooth muscle was obtained from saphenous vein from patients undergoing cardiovascular surgery. Tissues were surplus to requirements, and their use conformed to the guidelines of our local Ethics Committee. SMCs were cultured using an explant technique described previously10 in a culture medium consisting of Dulbecco's modified Eagle's medium (DMEM) supplemented with fetal calf serum (FCS, 15% vol/vol), l-alanyl-l-glutamine (4 mmol/L), penicillin (100 U/mL), streptomycin (100 µg/mL), gentamicin (25 µg/mL), and buffered with HEPES (25 mmol/L). Cultures were maintained in a humidified atmosphere of 5% CO2 at 37°C. When confluence was reached, the cells were subcultured under the same conditions described above and were used for experiments when they reached confluence at passage 2. The identity of the cells as SMCs was regularly confirmed by immunocytochemistry in which positive staining for
-actin (a marker for smooth muscle11 ) was
demonstrated. All repeat experiments were carried out on cells derived
from different individuals.
Migration Assays
Confluent monolayers of SMCs were washed twice in PBS and
briefly exposed to a trypsin solution. Neutralization of the trypsin
was achieved by addition of 8 mL of culture medium. The resultant cell
suspension was then centrifuged (1000 rpm, 10 minutes) and
resuspended in serum-free medium (SFM) supplemented with bovine serum
albumin (1 mg/mL) at a density of 2.25x105
cells/mL.
Migration assays were carried out in blind well chemotaxis chambers. The upper and lower compartments were separated by 13-mm-diameter, gelatin-coated polycarbonate filters with 8-µm pores; 0.4 mL of cell suspension was added to the upper compartment and 0.3 mL of the relevant control or chemoattractant (in SFM) was added to the lower compartment unless otherwise stated. Separate control experiments were performed for each cell line in each experiment. Migration was allowed to proceed for 5 hours in a humidified atmosphere of 5% CO2 at 37°C. Cells were then fixed in absolute alcohol and stained for 15 minutes with toluidine blue (65 mmol/L). Cells on the upper side of the filters were removed, leaving the cells on the underside of the filters for counting. Cells in four fields of view (x200 magnification) on duplicate filters were counted.
Measurement of DNA Synthesis
Stimulation of DNA synthesis was measured by using the
incorporation of [methyl 3H]-thymidine.12
SMCs were seeded at a density of 9x104 cells/mL, 200
µL/well in 96 well plates and allowed to attach overnight. The 15%
FCS containing medium was removed and the cells were washed twice with
phosphate-buffered saline (PBS, without calcium and magnesium). The
cells were maintained in DMEM supplemented with bovine serum
albumin (1 mg/mL), insulin (1 µmol/L),
transferrin (5 mg/mL), sodium selenite (0.1
µmol/L), and ascorbic acid (0.5 mmol/L) for 72
hours to growth arrest the cells in the G0 phase of the
cell cycle. Growth stimulation was then commenced with medium
containing the different PDGF isoforms. After 24 hours of incubation,
[methyl 3H]-thymidine was added (1 µCi/well, 40
µCi/mL) for a further 6 hours (determined from time course
experiments13 ). The experiment was terminated by washing
the cells twice with trichloroacetic acid (10%, wt/vol) and then
solubilizing the cells with 200 µL NaOH (1 mol/L) at 37°C
for 12 hours. To precipitate solubilized DNA, the pH was neutralized
with 50 µL hydrochloric acid (4 mol/L). Precipitated DNA was
harvested onto glass fiber filter mats and the radioactivity counted
using a Matrix 96 direct beta counter (Canberra Packard).
Measurement of Tyrosine Phosphorylation
Cells were plated onto Petri dishes (1x106 per
dish) in FCS and allowed to attach overnight, then growth arrested in
SFM for 3 to 4 days. Cells were then stimulated with PDGF-BB (0.1 to
100 ng/mL) for 60 minutes, washed twice in ice-cold PBS, and
lysed with 1 mL lysis buffer Tris-HCl (50 mmol/L, pH 7.4),
NaCl (150 mmol/L), EGTA (100 nmol/L), NP-40 (1%),
and Na deoxycholate (0.25%) containing PMSF, NaF,
Na3VO4 (all 1 mmol/L) and
aprotinin, pepstatin, and leupeptin (1 µg mL). Samples containing 15
µg cell protein were then run on a 10% polyacrylamide gel,
transferred to nitrocellulose, and probed with an antiphosphotyrosine
antibody (PY20).
Materials
Recombinant human PDGF-AB was obtained from Boehringer
Mannheim. Recombinant human PDGF-AA, -BB, and all cell culture
materials were from Gibco Life Technologies. Anti-PDGF-R antibody
was purchased from Genzyme. PY20 was obtained from Affiniti Research
Products. Polycarbonate filters were from Poretics. All other
chemicals were purchased from Sigma.
Statistics and Data Analysis
Data are presented as mean±SEM, and results were
analyzed using Friedman's nonparametric test for
repeated-measures ANOVA followed by Conover's multiple-range test for
individual differences if the results of ANOVA were significant. A
value of P<.05 was considered significant. EC50
values for DNA synthesis were calculated by nonlinear regression on
Excel (Microsoft) using a macro (written by A.D. Hughes).
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Results |
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Chemotaxis
The three PDGF isoforms had markedly distinct effects on human SMC migration. The concentration-response relationships to each isoform are shown in Fig 1
. PDGF-AA failed to
elicit migration over the range 0.1 to 100 ng/mL in four cell
lines and surprisingly, the AB isoform produced only a small increase
that did not reach overall statistical significance. In these
experiments the response to 15% FCS and SFM were used as positive and
negative controls, respectively. Peak cell counts were SFM, 29±11;
PDGF-AA, 20±6; PDGF-AB, 68±37; PDGF-BB, 225±65; and FCS, 213±24
(mean±SEM, n=4 to 11). All the cell lines used in this study responded
to FCS, indicating that the lack of migration in response to PDGF-AA
and PDGF-AB was not due to a lack of viability of the cells.
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In contrast, PDGF-BB was able to potently stimulate migration to a peak
level comparable to FCS. However, the response to this isoform
consisted of a biphasic curve with a peak that reached a maximum value
between 1 and 10 ng/mL (Fig 1
). The responses at 0.1 and 1
ng/mL were 29±11% and 76±17% (mean±SEM) of the peak
response for a given cell line, which means that the concentration of
PDGF-BB required to stimulate half maximal migration was in the range
0.1 to 1 ng/mL. Concentrations of PDGF-BB >10 ng/mL
produced responses comparable to or less than that to SFM, indicating
that there was little or no migration occurring across 90% of the
experimentally tested range. For cells incubated in 100 ng/mL
PDGF-BB, trypan blue exclusion levels at t=0 and 5 hours were not
significantly different (data not shown), which was used as a
verification of cell viability. In addition, thymidine incorporation at
this concentration was not impaired (see below).
To test the nature of the induced migration to PDGF-BB and to
investigate the downturn, an extended checkerboard analysis was
performed for both low and high concentrations of this isoform (Fig 2). Again, BB (2 ng/mL)
strongly induced migration relative to SFM but only when the cells were
exposed to an appropriately directed gradient. When there was no
gradient or a reverse gradient, present migration was abolished
(Fig 2 [III and IV]). Thus the migration was chemotactic in nature.
However, at the high BB concentration (100 ng/mL), all
combinations failed to elicit migration (Fig 2 [V, VI, and VII]).
Migration to high BB was in fact reduced to levels significantly below
that of unstimulated cells.
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The next step therefore was to establish whether the high
concentrations of BB were simply nonstimulatory or actively
inhibitory for chemotaxis. To test this, cells were
stimulated to migrate by FCS (15%) with or without added PDGF-BB (100
ng/mL). Fig 3 shows that this concentration of PDGF-BB was able
to severely inhibit FCS-induced
migration. A similar experiment was
performed (Fig 4a) in which cells were stimulated by epidermal growth
factor (EGF, 0.1 ng/mL), another member of the family of
receptor tyrosine kinase–linked growth factors that potently
stimulates migration in these cells (mean cell count, 324±134,
n=8). In this experiment, PDGF-BB
(100 ng/mL) was added to the upper and lower chambers to remove
the effect of any PDGF gradient. The presence of a high
concentration of BB also abolished the stimulatory effect of EGF.
A similar effect was observed using the AB isoform (Fig 4b).
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Having established the presence of a negative influence on chemotaxis
at high concentrations of PDGF-BB and -AB, the next step was to
determine which receptor subtype was responsible. The BB isoform binds
to both - and ß-receptors.2 There is evidence that
activation of -receptors inhibits migration in some SMC
types.14 15 It was therefore appropriate to investigate
whether activation of PDGF-R could account for the downturn in the
PDGF-BB concentration-response curve. In these experiments, cells
stimulated by PDGF-BB (2 ng/mL) were also exposed to PDGF-AA (1
and 100 ng/mL) in both the upper and lower compartments,
following the protocol of Koyama et al15 to separate
chemotactic from chemokinetic effects. The results are summarized in
Fig 5. PDGF-AA at a concentration of
1 ng/mL had no effect on PDGF-BB–induced chemotaxis. At a
concentration of 100 ng/mL PDGF-AA, the mean response to PDGF-BB
was reduced by 35±17% (n=4) and 26±14% (n=4) when the AA isoform
was in the lower and upper compartment, respectively. PDGF-BB alone,
however, at a concentration of 100 ng/mL, produced a response
significantly lower than unstimulated cells (n=4). These results
suggest that active PDGF-R may display some inhibitory
properties in these cells, but they do not account for the abolition of
the chemotactic response at higher concentrations of PDGF-BB.
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The data above receive further support from studies conducted with an
anti–PDGF-R neutralizing antibody (which is specific for primate
-receptors and does not recognize ß-receptors).16 Fig 6a shows that the antibody had no effect on chemotaxis induced by
PDGF-BB at 2 ng/mL (n=4), indicating that -receptors played
no role in the chemotactic response to low concentrations of
PDGF-BB. However, application of the
antibody did recover the inhibition of chemotaxis by PDGF-AA (100
ng/mL). This result specifically confirmed the data in Fig 5 in
establishing a minor inhibitory role for PDGF-R in
PDGF-BB–induced chemotaxis via -receptor activation at high
concentrations of PDGF-BB. Fig 6b shows the effect of the same antibody
on the high BB concentration. Clearly, the antibody had no effect on
the inhibition of chemotaxis at high concentrations of BB (n=4). This
indicates that activation of PDGF-R by high concentrations of BB was
not necessary for the observed reduction in chemotaxis and suggests
that the downturn could be wholly accounted for by activation of
PDGF-Rß.
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A final piece of supportive evidence for the above proposal could be
demonstrated by testing the effect of the AB isoform on the ability of
the BB isoform to induce chemotaxis. PDGF-AB had no significant
chemotactic stimulatory effect on these cells (Fig 1). Cells stimulated
by PDGF-BB (2 ng/mL) were incubated with or without PDGF-AB (100
ng/mL). As can be seen from Fig 7, PDGF-AB completely inhibited
PDGF-BB–induced chemotaxis. Since
PDGF-AB is thought to cause activation of - and ß-dimers,
this inhibitory effect of PDGF-AB on PDGF-BB–induced
chemotaxis was presumably due to activation of ß-dimers, since
activation of -dimers alone by PDGF-AA (Figs 5 and 6) produced
only a modest inhibition.
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DNA Synthesis
To complement the migration data, the effect of the PDGF isoforms
on DNA synthesis was determined by [3H]-thymidine
incorporation. The results agree well with our previously reported
results on the cellular uptake of thymidine in cultured saphenous vein
cells exposed to PDGF.17 Representative
incorporation data (Fig 8) show that both the AB and BB isoforms of
PDGF were able to concentration-dependently stimulate DNA synthesis in
a saturable manner, but there was no significant response to the AA
isoform. The AB and BB isoforms were
approximately equally efficacious and also had similar EC50
values of 7±1 and 11±1 ng/mL, respectively.
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Tyrosine Phosphorylation
To explore possible mechanisms to account for the downturn in the
chemotactic response, the pattern of tyrosine
phosphorylation elicited by a range of concentrations
of PDGF-BB was measured using the Western blotting technique. Fig 9
shows that PDGF-BB induced tyrosine phosphorylation of
a number of cellular proteins at concentrations as low as 0.1
ng/mL. However, certain bands
(notably at approximately 75 to 85 kD and 100 to 120 kD) become more
intense at intermediate concentrations (1 to 10 ng/mL) but then
markedly decline at the concentrations of PDGF-BB that become
inhibitory with respect to chemotaxis but remain maximally
stimulatory with regard to DNA synthesis. Control of tyrosine
phosphorylation and dephosphorylation
represents a possible route of further investigation into
negative chemotactic signals evoked by PDGF-Rß.
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Discussion |
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This study reports the complexity and heterogeneity of control of chemotaxis and DNA synthesis in human saphenous vein SMC by PDGF isoforms and extends the previously proposed models. The main focus is on the regulation of migration by PDGF-BB. This isoform produced a biphasic response with migration occurring only in the 1 to 10 ng/mL range. A peak in the migratory response has been observed in a number of cell types including neutrophils,18 19 monocytes,20 21 and fibroblasts22 23 and in some SMC types but not others.14 24 The downturn in human saphenous vein SMC was complete (the response returned to unstimulated levels or below) and particularly sharp. Fig 2
confirms the chemotactic nature of the
response and is useful in addressing a few technical issues that may be
raised in interpreting the results from a double well chamber. Fig 2
(I-IV) shows that a gradient was required to induce migration in
response to PDGF-BB. Thus it could be argued that one reason for the
observed downturn in migration at high concentrations of BB is that
partial dissipation of the gradient over the time course of the
experiments led to a high background level of BB in both chambers. This
would saturate the PDGF receptors, thereby effectively masking the
presence of the gradient and leading to a loss of polarity.
However, subsequent data show that the downturn is not simply a passive
response to increasing concentration, that is, the downturn is not an
artifact of the experimental protocol. Fig 3, 4, and 7 show that
PDGF-BB and PDGF-AB at high concentrations were able to negate the
migration induced in response to other stimulants, which indicates that
a net negative signal was generated under these conditions. Such a
result cannot be accounted for by a simple receptor saturation model
such as that described above because that model contains no active
antagonistic component. A model has been proposed in which
PDGF ß-receptors positively regulate and -receptors negatively
regulate SMC chemotaxis. Therefore it was determined whether activation
of -receptors could explain the downturn in the BB
concentration-response curve. Figs 5 and 6 together demonstrate that
activation of -receptors had a small inhibitory effect
that could be overcome by their specific blockade using a neutralizing
antibody. However the effect of -receptors could not explain the
complete abolition of chemotaxis by 100 ng/mL BB alone.
Furthermore, blockade of -receptors with 100 ng/mL BB
produced no recovery whatsoever, indicating that the negative signal
originating from the ß-receptors was sufficient to completely account
for the abolition of chemotaxis. In further support of this argument it
was observed that the AB isoform, which could not itself induce
significant migration, completely inhibited BB-induced chemotaxis. The
difference between application of AA and AB is the activation of
ß-receptors by the AB isoform. Thus it appears that the biphasic
chemotactic response in these cells is predominantly under the control
of PDGF-Rß alone as opposed to a model in which PDGF-R and
PDGF-Rß act in an antagonistic manner to produce the
overall observed effect. These findings also imply that ßß-dimer
activation is necessary for significant chemotaxis to occur, but the
strong inhibitory effect can arise from either ßß or
ß combinations.
The degree of tyrosine phosphorylation is often used as
a marker for the level of activity of many signaling molecules,
including the PDGF receptors. It has recently been observed in Swiss
3T3 cells that stimulation with high levels of PDGF results in a
reduction in the level of tyrosine phosphorylation of
certain molecules, including focal adhesion kinase (FAK, Reference 2525 ),
a protein thought to be intimately involved in the promotion of cell
migration. High concentrations of PDGF also produced a downturn in the
migratory response.24 However, in rabbit aortic SMC that
did not exhibit a downturn, the level of FAK tyrosine
phosphorylation was sustained at high PDGF
concentrations.24 The cells used in this study displayed
peak PDGF-BB–induced tyrosine phosphorylation of
several bands at concentrations of growth factor that parallel those
that produce peak chemotactic responses and reduced tyrosine
phosphorylation at high concentrations of BB (Fig 9).
Most prominent among these were bands at 80 to 90 kD and 100 to 120
kD. Other bands (including a band at 180 kD, presumably the PDGF
ß-receptor) displayed consistently elevated levels of
tyrosine phosphorylation at high concentrations of
PDGF-BB, similar to the sustained DNA synthesis response. These
patterns of phosphorylation could provide clues as to
which tyrosine-phosphorylated proteins are crucial in
the control of SMC migration. Work is currently under way aimed at
identifying these molecules and the mechanisms underlying the reduction
in tyrosine phosphorylation.
The DNA synthesis profiles indicated that the AB and BB isoforms were
very effective in terms of eliciting DNA synthesis, but the AA isoform
was nonstimulatory. These data suggest that -receptors play little
or no role in PDGF-induced entry into the S-phase and therefore the
early proliferative signals are also derived predominantly from
ß-receptors. The DNA synthesis concentration-response curves were
saturable and required a 10-fold higher concentration of growth factor
to achieve half-maximal stimulation than did the chemotactic response.
The concentration range in which the downturn in chemotaxis began
coincided with the range in which DNA synthesis was induced. This
indicates a possible means by which these cells could utilize a
gradient of PDGF to coordinate movement and subsequent proliferation,
as illustrated in Fig 10. Such a
scheme could effectively encode a local sense of position that would be
important in the complex and highly variable situations encountered
in the wound healing process.
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In summary, control of migration and DNA synthesis by PDGF in human
saphenous vein SMC is dominated by ß-receptors. A strong positive
chemotactic signal arising from low levels of ß-receptor activation
becomes a net negative signal at higher levels of activation. The
overall negative signal cannot be accounted for by activation of
-receptors (although they do play some role). Therefore, the
ß-receptors themselves exhibit a biphasic influence that is mirrored
in the whole cell response. It is postulated that tyrosine
phosphorylation and subsequent
dephosphorylation of certain key signaling molecules is
one mechanism by which this complex behavior may be regulated. Work is
currently under way to elucidate the identity and functional importance
of several such candidate molecules.
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Acknowledgments |
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This work was supported by the British Heart Foundation and Pfizer International. We thank the surgeons and theater staff of St Mary's Hospital for supplying samples of saphenous vein. We also gratefully acknowledge the expertise of K. Gallagher in the maintenance of cultured cells.
Received August 7, 1996; accepted April 3, 1997.
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  D. Faraone, M. S. Aguzzi, G. Ragone, K. Russo, M. C. Capogrossi, and A. Facchiano Heterodimerization of FGF-receptor 1 and PDGF-receptor-{alpha}: a novel mechanism underlying the inhibitory effect of PDGF-BB on FGF-2 in human cells Blood, March 1, 2006; 107(5): 1896 - 1902. [Abstract] [Full Text] [PDF]
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 E. Koutsouki, C. A. Beeching, S. C. Slater, O. W. Blaschuk, G. B. Sala-Newby, and S. J. George N-Cadherin-Dependent Cell-Cell Contacts Promote Human Saphenous Vein Smooth Muscle Cell Survival Arterioscler. Thromb. Vasc. Biol., May 1, 2005; 25(5): 982 - 988. [Abstract] [Full Text] [PDF]
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 J. S. Garanich, M. Pahakis, and J. M. Tarbell Shear stress inhibits smooth muscle cell migration via nitric oxide-mediated downregulation of matrix metalloproteinase-2 activity Am J Physiol Heart Circ Physiol, May 1, 2005; 288(5): H2244 - H2252. [Abstract] [Full Text] [PDF]
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 D. L. Hunton, W. G. Barnes, J. Kim, X.-R. Ren, J. D. Violin, E. Reiter, G. Milligan, D. D. Patel, and R. J. Lefkowitz {beta}-Arrestin 2-Dependent Angiotensin II Type 1A Receptor-Mediated Pathway of Chemotaxis Mol. Pharmacol., April 1, 2005; 67(4): 1229 - 1236. [Abstract] [Full Text] [PDF]
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 J. S. Lymn, M. K. Patel, G. F. Clunn, S. J. Rao, K. L. Gallagher, and A. D. Hughes Thrombospondin-1 differentially induces chemotaxis and DNA synthesis of human venous smooth muscle cells at the receptor-binding level J. Cell Sci., November 15, 2002; 115(22): 4353 - 4360. [Abstract] [Full Text] [PDF]
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F. De Marchis, D. Ribatti, C. Giampietri, A. Lentini, D. Faraone, M. Scoccianti, M. C. Capogrossi, and A. Facchiano Platelet-derived growth factor inhibits basic fibroblast growth factor angiogenic properties in vitro and in vivo through its alpha receptor Blood, March 15, 2002; 99(6): 2045 - 2053. [Abstract] [Full Text] [PDF]
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 B. S. Buetow, J. R. Crosby, W. E. Kaminski, R. K. Ramachandran, P. Lindahl, P. Martin, C. Betsholtz, R. A. Seifert, E. W. Raines, and D. F. Bowen-Pope Platelet-Derived Growth Factor B-Chain of Hematopoietic Origin Is Not Necessary for Granulation Tissue Formation and Its Absence Enhances Vascularization Am. J. Pathol., November 1, 2001; 159(5): 1869 - 1876. [Abstract] [Full Text] [PDF]
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 G. Ma, D. P. Mason, and D. B. Young Inhibition of Vascular Smooth Muscle Cell Migration by Elevation of Extracellular Potassium Concentration Hypertension, April 1, 2000; 35(4): 948 - 951. [Abstract] [Full Text] [PDF]
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A Facchiano, F De Marchis, E Turchetti, F Facchiano, M Guglielmi, A Denaro, R Palumbo, M Scoccianti, and M. Capogrossi The chemotactic and mitogenic effects of platelet-derived growth factor-BB on rat aorta smooth muscle cells are inhibited by basic fibroblast growth factor J. Cell Sci., January 8, 2000; 113(16): 2855 - 2863. [Abstract] [PDF]
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J. S. Lymn, S. J. Rao, G. F. Clunn, K. L. Gallagher, C. O'Neil, N. T. Thompson, and A. D. Hughes Phosphatidylinositol 3-Kinase and Focal Adhesion Kinase Are Early Signals in the Growth Factor–Like Responses to Thrombospondin-1 Seen in Human Vascular Smooth Muscle Arterioscler. Thromb. Vasc. Biol., September 1, 1999; 19(9): 2133 - 2140. [Abstract] [Full Text] [PDF]
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H. Zhang, C. S. Facemire, A. J. Banes, and J. E. Faber Different alpha -adrenoceptors mediate migration of vascular smooth muscle cells and adventitial fibroblasts in vitro Am J Physiol Heart Circ Physiol, June 1, 2002; 282(6): H2364 - H2370. [Abstract] [Full Text] [PDF]
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