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B and Mitogen-Activated Protein Kinase Signaling Pathways in IL-1ß-Mediated Induction of 
-PDGF Receptor Expression in Rat Pulmonary Myofibroblasts
Airway Inflammation Section, Laboratory of Pulmonary Pathobiology, National Institute of Environmental Health Sciences, Research Triangle Park, NC 27709
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Abstract |
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 Top Abstract IntroductionMaterials and MethodsResultsDiscussionReferences |
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-platelet-derived growth factor receptor
(PDGF-R) by IL-1ß in lung myofibroblasts enhances mitogenic and
chemotactic responses to PDGF, and this could be a mechanism of
myofibroblast hyperplasia during lung fibrogenesis. Since the
regulation of many genes by IL-1ß involves activation of NF-
B and
mitogen-activated protein (MAP) kinases, we examined these signaling
pathways in the control of PDGF-R expression by IL-1ß in cultured
rat lung myofibroblasts. Treatment of cells with pyrrolidine
dithiocarbamate (PDTC), an antioxidant that inhibits NF-B
activation, completely blocked PDGF-R up-regulation by IL-1ß as
assayed by [125I]PDGF-AA binding and PDGF-R mRNA
expression, suggesting a role for NF-B. However, while IL-1ß and
TNF- both induced nuclear binding of the Rel proteins p50 and p65 to
an NF-B consensus oligonucleotide in gel shift assays and caused
transient degradation of inhibitor of NF-B- (IB-) in the
cytoplasm of myofibroblasts, only IL-1ß up-regulated PDGF-R. These
results suggest that NF-B activation alone is not sufficient for
up-regulation of PDGF-R. An investigation of MAP kinase signaling
pathways revealed that IL-1ß or PDTC activated extracellular
signal-regulated kinase-2 (ERK-2) and c-jun
NH2 terminal kinase-1 (JNK-1) phosphorylation of
PHAS-1 and c-Jun substrates, respectively. Pretreatment of cells
with the MAP kinase kinase-1 (MEK1) inhibitor PD 98059 blocked
IL-1ß-induced activation of ERK-2 by more than 90% but enhanced
IL-1ß-stimulated induction of PDGF-R expression fourfold. Taken
together, these data suggest that IL-1ß activates both positive and
negative signaling pathways that control the expression of PDGF-R.
IL-1ß appears to mediate its negative effects on PDGF-R expression
via MAP kinase activation, while the factor(s) that mediate induction
of PDGF-R remain to be elucidated. |
Introduction |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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-smooth muscle actin that represent a
myofibroblast phenotype (1, 2, 3). These newly emerging myofibroblasts
appear to be the major source of secreted collagen within the
developing fibrogenic lesion (4). The factors that stimulate
myofibroblast growth responses during fibrogenesis have not been fully
clarified, although several polypeptide growth factors have been
implicated, including insulin-like growth factor (IGF) family members,
TGF-, basic fibroblast growth factor (FGF-2), and platelet-derived
growth factor (PDGF)2 (5).
PDGF exists as a disulfide-linked dimer of two polypeptide chains, A or
B, that form functional PDGF-AA, PDGF-BB, or PDGF-AB isoforms (6). Two
PDGF receptor subtypes bind the three isoforms of PDGF differentially:
ß-PDGF receptor (PDGF-Rß) can interact only with B-chain-containing
isoforms while -PDGF receptor (PDGF-R) can bind all three
isoforms (7). PDGF binding results in receptor dimerization to form
, ß, or ßß combinations, followed by tyrosine kinase
phosphorylation of the intracellular receptor domain and activation of
a vast array of signal transduction molecules including Src family
kinases, Grb2, Shc, PI3 kinase, GAP, Shb, PTP 1D, and PLC-
(reviewed in 8 .
PDGF-R and its ligand, PDGF-AA, are essential to lung development
(9, 10). Induction of the PDGF-R also occurs in adult tissues but
appears to be related to the pathogenesis of certain fibroproliferative
diseases. For example, human fibroblasts isolated from dermal keloids
express elevated PDGF-R (11), and we recently reported that
PDGF-R is up-regulated during the progression of metal-induced lung
fibrogenesis in rats (12). IL-1ß is a potent inducer of the PDGF-R
on rat lung myofibroblasts in vitro, and PDGF-R up-regulation
enhances the mitogenic and chemotactic responses to PDGF isoforms (13, 14). We and others have demonstrated that maximal responses of
mesenchymal cells to PDGF isoforms require PDGF-R in addition to the
normally abundant PDGF-Rß (15, 16), and this could be due to unique
signal transduction events stimulated by -ß receptor dimerization,
as compared with ß-ß receptor dimerization (16, 17).
The signal transduction pathway(s) involved in regulation of PDGF-R
expression by IL-1ß are unknown. IL-1ß mediates a diversity of
biologic effects through the transcription factors NF-B (18, 19, 20) and
AP-1 (21, 22), and binding motifs for these two transcription factors
exist in the PDGF-R promoter region (23). IL-1ß has also been
reported to act by signaling mitogen-activated protein (MAP) kinases,
including the p46 c-Jun NH2-terminal kinase-1 (JNK-1) (24, 25) and the p42 extracellular signal-regulated kinase-2 (ERK-2) (25, 26). In this study we examined the requirement of NF-B and the MAP
kinases, JNK-1 and ERK-2, for up-regulation of PDGF-R by IL-1ß. We
report that IL-1ß activates both positive and negative signaling
pathways that control PDGF-R expression. The MAP kinase pathway
involving ERK is suppressive for PDGF-R expression. The identity of
the positive signaling pathway that mediates induction of the PDGF-R
by IL-1ß remains unknown, although we rule out NF-B and AP-1 in
this report.
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Materials and Methods |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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TRI reagent was from Molecular Research Center (Cincinnati, OH).
The rat cDNA probe for the PDGF-R was the generous gift of Dr.
Yutaka Kitami, Ehime University, Japan. Recombinant rat TNF- was
purchased from Endogen (Woburn, MA). Murine IL-1ß was purchased from
Upstate Biotechnologies (Lake Placid, NY) or R&D Systems (Minneapolis,
MN). [125I]PDGF-AA (specific activity of 125 µCi/µg)
was from Biomedical Technologies (Stoughton, MA). NF-B consensus
double-stranded oligonucleotide and poly(dI-dC)·poly(dI-dC) were
purchased from Promega (Madison, WI). Abs to the Rel family of proteins
(p50, p65, p52, c-Rel, Rel-B), JNK-1, and ERK-2 were purchased from
Santa Cruz Biotechnology (Santa Cruz, CA). Pyrrolidine dithiocarbamate
(PDTC) and N-acetyl-L-cysteine (LNAC) were from
Sigma (St. Louis, MO). The MEK-1 inhibitor PD 98059
([2-(2'-amino-3'-methoxyphenyl)-oxanapthalen-4-one]) was obtained
from New England Biolabs (Beverly, MA). Primary passage rat lung
myofibroblasts were isolated and characterized as described
previously (27).
[125I]PDGF-AA receptor binding assay
Myofibroblasts in 24-well plates were grown to confluence in 10% FBS/DMEM and then rendered quiescent for 24 h in serum-free defined medium (SFDM) consisting of Ham’s F-12 with HEPES, CaCl2, 0.25% BSA supplemented with an insulin/transferrin/selenium mixture (Boehringer Mannheim, Indianapolis, IN). Cells were then treated with an agent of interest for 24 h. Cultures were chilled to 4°C, rinsed in cold binding buffer (Ham’s F-12 with HEPES, CaCl2, and 0.25% BSA), and exposed to 2 ng/ml of [125I]PDGF-AA for 3 to 4 h at 4°C on an oscillating platform. Cells were then rinsed three times in ice-cold binding buffer and solubilized in 1% Triton X-100, 0.1% BSA, and 0.1 M NaOH. Cell-associated radioactivity was measured with a gamma counter.
Northern blotting for PDGF-R
Total RNA was isolated with TRI reagent as described previously
(13). Twenty micrograms of each sample was electrophoresed in 1%
agarose/2 M formaldehyde gels and capillary transferred onto Immobilon
S membranes. A rat cDNA probe for the PDGF- receptor was labeled
with [-32P]dCTP using a Prime-It II Random primer
labeling. The autoradiographic signal was visualized with a
PhosphorImager (Molecular Dynamics, Sunnyvale, CA).
Western blotting for IB-
Confluent cells in 75-cm2 flasks were rendered
quiescent for 24 h in SFDM and exposed to IL-1ß or TNF- for
10, 30, 60, and 120 min. After washing with PBS, 250 µl of lysis
buffer (50 mM Tris-HCl; 1% Triton X-100; 150 mM NaCl; 1 mM EGTA; 1 mM
PMSF, 0.25% Na-deoxycholate; 1 µg/ml each of aprotinin, leupeptin,
pepstatin; 1 mM Na3VO4, 1 mM NaF) was added to
each flask, and extracts were collected with scraping. Twenty
microliters of each sample was mixed with 5 µl reducing SDS-sample
buffer, boiled for 5 min, and resolved by electrophoresis in a 2 to
15% Tris-glycine SDS-polyacrylamide gel. Protein was transferred from
the gel to nitrocellulose membrane (Hybond, Amersham, Arlington
Heights, IL), and the membrane was blocked with 3% milk/PBS for 1
h before addition of a rabbit anti-human IB- Ab overnight
with rocking. A secondary horseradish peroxidase-conjugated
swine anti-rabbit Ab was added for 1.5 h at a dilution of
1:200. After thoroughly washing with PBS-Tween, blots were developed
with an ECL luminol kit (Amersham).
Nuclear extract preparation and electromobility shift assay for
NF-B
Confluent myofibroblasts were pretreated with PDTC or medium
alone for 1 h before exposure to IL-1ß or TNF- for 30 min.
Nuclear extracts were prepared according to Dignam et al. (28) and
Masamune et al. (29) as follows. Cells were washed with PBS,
trypsinized, and centrifuged at 1500 rpm for 10 min at 4°C. Cell
pellets were resuspended in 400 µl of buffer A (10 mM HEPES, pH 7.9,
2 mM MgCl2, 10 mM KCl, and 1.0 mM DTT, 1.0 mM PMSF, 5
µg/ml each of aprotinin, pepstatin, leupeptin, 0.1% Triton X-100),
incubated for 15 min on ice, vortexed for 15 s, and centrifuged
for 10 min at 14,000 rpm. Pelleted nuclei were resuspended in 40 µl
buffer C (20 mM HEPES, pH 7.9, 25% v/v glycerol, 0.42 M NaCl, 1.5 mM
MgCl2, 0.2 mM EDTA, 1.0 mM DTT, 1.0 mM PMSF, 5 µg/ml each
aprotinin and leupeptin), incubated for 30 min on ice, and centrifuged
for 10 min at 14,000 rpm. Supernatants were diluted with 20 µl buffer
D (20 mM HEPES, pH 7.9, 20% v/v glycerol, 50 mM KCl, 0.2 mM EDTA, 0.5
mM DTT, 0.5 mM PMSF) and stored at -80°C. Protein concentrations
were determined by Bradford assay. Three micrograms of nuclear extract
were incubated in binding buffer (4% glycerol, 1 mM MgCl2,
0.5 mM EDTA, 0.5 mM DTT, 50 mM NaCl, 10 mM Tris-Cl, pH 7.5, 0.5 mg/ml
poly(dI-dC)·poly(dI-dC)) with [-32P]ATP-labeled
NF-B oligonucleotide in a total reaction volume of 20 µl for 20
min at room temperature. In competition experiments, 30-fold molar
excess of unlabeled NF-B oligonucleotide or Oct-1 consensus
oligonucleotide was incubated with the extracts for 15 min before
addition of labeled probe. For supershift experiments, Abs to p50, p65,
c-Rel, p52, or Rel-B were added to the reaction mixture after the
addition of labeled probe, and the incubation was continued for 45 min
at room temperature. Samples were electrophoresed in 6% polyacrylamide
gels (0.5x Tris-glycine) with 0.5x Tris-glycine as running buffer,
and the gels were dried before autoradiography.
Immunoprecipitation of ERK and PHAS-1 kinase assay
ERK activity in myofibroblast cell lysates was measured by the
ability of these lysates to phosphorylate PHAS-1, a substrate for ERK
(30). Cells grown to confluence in 75-cm2 tissue culture
flasks were rendered quiescent in SFDM for 24 h. After 30 min of
treatment with the agent of interest, the cells were placed on ice,
washed twice with PBS, and scraped off with 800 µl of lysate buffer
consisting of 50 mM HEPES, 150 mM NaCl, 1% Triton X-100, 1 mM PMSF,
and 20 µg/ml aprotinin, leupeptin, and pepstatin. Lysates were
clarified by centrifugation at 13,000 rpm for 10 min, and protein
concentrations were determined by Bradford assay. Immunoprecipitation
was performed by incubating 200 µl of lysate with 2 µg of
anti-ERK-2 (p42) Ab for 2 h, then adding 20 µl of protein-A
agarose (Santa Cruz). After an overnight incubation at 0 to 4°C with
end-over-end mixing, the immune-complex was recovered by
centrifugation, washed with lysis buffer three times and then one time
with 250 mM HEPES (pH 7.4), 10 mM MgCl2, 200 µM
Na3VO4. Immune-complex kinase assays were
performed using a MAP Kinase Assay Kit (Stratagene, La Jolla, CA)
according to the manufacturer’s instructions. Briefly, the ERK pellets
were resuspended in Stratagene reaction buffer containing 120 µg of
PHAS-1 substrate along with 3 to 5 µCi [-32P]ATP in
a final volume of 180 µl. Kinase reactions took place for 30 min at
room temperature and were stopped by adding 4x SDS-PAGE reducing
sample buffer and boiling for 10 min. ERK-PHAS samples were
resolved on 4 to 20% PAGE gels, dried, and autoradiographed.
JNK assay
Cell lysates were collected as described above for the ERK
assay. JNK was immunoprecipitated from 200 µl of lysate by first
incubating with 2 µg of an anti-JNK-1 (p46) polyclonal IgG (Santa
Cruz) for 3 h, and then adding 20 µl protein-A agarose for an
overnight incubation at 0 to 4°C with end-over-end mixing. The
immune-complex was recovered by centrifugation, washed three times with
lysis buffer (50 mM HEPES, 150 mM NaCl, 1% Triton X-100, 1 mM PMSF,
and 20 µg/ml aprotinin, leupeptin, and pepstatin) and one time with
JNK kinase buffer (20 mM HEPES, pH 7.9, 15 mM MgCl2, 1 mM
DTT, 100 µM Na3VO4, and 25 mM
ß-glycerophosphate). The pellet was resuspended in 180 µl of kinase
buffer containing 30 µg of glutathione S-transferase
(GST)-c-Jun (1–79) (Stratagene), 100 µM ATP, and 3 to 5 µCi
[-32P]ATP. The reaction was allowed to proceed for 30
min at room temperature and was terminated by the addition of
SDS-loading buffer and boiling for 10 min. Phosphorylated GST-c-Jun
(1–79) was resolved on a 12% SDS-polyacrylamide gel and then
autoradiographed.
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Results |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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and NF-B activation
are blocked by PDTC
Since NF-B is involved in the induction of a number of genes by
IL-1ß, we investigated this transcription factor as a signaling
intermediate in IL-1ß-stimulated up-regulation of PDGF-R. The
antioxidant pyrrolidine dithiocarbamate (PDTC) inhibits activation of
NF-B (31). We used PDTC as a tool to investigate the involvement of
NF-B in the induction of PDGF-R expression. PDTC inhibited the
IL-1ß-induced increase in PDGF-R mRNA and protein expression as
assayed by Northern analysis (Fig. 1
A) and
[125I]PDGF-AA binding (Fig. 1B), respectively.
PDTC also inhibited the IL-1ß-induced nuclear protein binding to an
NF-B consensus oligonucleotide (Fig. 1C).
N-acetyl-L-cysteine (LNAC) is a commonly used
antioxidant that is structurally unrelated to PDTC (32). LNAC (20 mM)
had no effect on the IL-1ß-induced increase in
[125I]PDGF-AA binding (data not shown).
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both induce NF-B binding, but differentially
affect PDGF-R expression
Since PDTC completely inhibited IL-1ß-mediated up-regulation of
PDGF-R and NF-B binding activity in electrophoretic mobility
shift assays (Fig. 1
), we investigated whether TNF-, another known
activator of NF-B, would up-regulate the PDGF-R. TNF- did not
up-regulate [125I]PDGF-AA binding (Fig. 2A). However, supershift
assays using Abs to the Rel family of DNA binding proteins showed that
both TNF- and IL-1ß activated the p50 and p65 subunits of NF-B
(Fig. 2B). No supershift was observed with the c-Rel Ab
(Fig. 2) or Abs to the p52 and Rel-B subunits (data not shown). Nuclear
localization of p50/p65 first requires IB- degradation (33). Both
TNF- and IL-1ß caused transient IB- degradation after a
30-min treatment (Fig. 2C). This agreed with the gel shift
assay results, which showed that TNF- and IL-1ß activated p50/p65
binding to the NF-B consensus oligonucleotide.
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Both JNK-1 and ERK-2 were activated by IL-1ß treatment as
measured by the c-Jun kinase assay and the PHAS-1 kinase assay,
respectively (Fig. 3). Activation of both
MAP kinases by IL-1ß was maximal after 30 min of treatment (data not
shown). Since PDTC inhibited IL-1ß-induced up-regulation of the
PDGF-R, we investigated whether PDTC could counteract activation of
JNK or ERK by IL-1ß. Surprisingly, PDTC alone activated JNK-1 and
ERK-2, but PDTC had no effect on IL-1ß-stimulated activation of these
MAP kinases (Fig. 3).
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is enhanced
following inhibition of ERK by the MEK-1 inhibitor, PD 98059
We further investigated the MAP kinase signaling pathway using a
specific inhibitor of MEK-1 termed PD 98059 (34). Pretreatment of
myofibroblasts with PD 98059 blocked IL-1ß-stimulated activation of
ERK-2 by more than 90% in the PHAS-1 kinase assay (Fig. 4A). Blocking MEK-1, the
upstream activator of ERK-2, had the unexpected effect of enhancing
IL-1ß-stimulated up-regulation of PDGF-R fourfold as determined by
[125I]PDGF-AA-binding assays (Fig. 4B).
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Discussion |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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in vivo appears to be a mechanism that
contributes to the hyperplastic growth of these cells during lung
fibrogenesis in rats (12). We have previously reported that IL-1ß is
the major factor secreted by activated rat alveolar macrophages that
stimulates up-regulation of the PDGF-R in rat lung myofibroblasts in
vitro (13, 14). In this study we have investigated the signal
transduction pathways through which IL-1ß regulates expression of the
PDGF-R. IL-1ß activates at least two distinct signaling pathways
that modulate PDGF-R expression: 1) activation of a MAP kinase (ERK)
pathway that suppresses PDGF-R expression, and 2) activation of an
NF-B-independent pathway that causes induction of PDGF-R. These
positive and negative regulatory pathways are illustrated in Figure 5.
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B, and the promoter region of PDGF-R contains
a B-binding consensus sequence (23). Thus, we investigated the
possibility that the signal transduction pathway mediating PDGF-R
up-regulation by IL-1ß requires NF-B. We first determined whether
inhibition of NF-B affects induction of PDGF-R expression. PDTC,
an antioxidant that inhibits the activation of NF-B, completely
blocked the induction of PDGF-R by IL-1ß. NF-B activation by
IL-1ß in rat lung myofibroblasts was confirmed via gel shift assays
and detection of transient IB- degradation. We also studied the
effect of TNF- on PDGF-R expression, since TNF- has been shown
to activate NF-B and share common signal transduction pathways with
IL-1ß (33). Although TNF- activated NF-B in lung
myofibroblasts, it did not increase PDGF-R expression. Thus, NF-B
activation alone is not sufficient for increased expression of
PDGF-R. We cannot rule out the requirement of NF-B in addition to
another transcription factor(s) for maximal PDGF-R expression in
response to IL-1ß.
PDTC appears to have opposite effects on NF-B and AP-1.
Activation of NF-B by IL-1ß was completely blocked by PDTC (Fig. 1), whereas JNK-1 (an upstream activator of AP-1) was activated by PDTC
(Fig. 3). These data are in agreement with other studies by Meyer and
coworkers that report PDTC to be a potent inhibitor of NF-B in HeLa
cells, yet in this same cell line AP-1 is activated by PDTC
(35).While PDTC is an antioxidant, several lines of evidence
suggest that inhibition of IL-1ß-stimulated up-regulation of the
PDGF-R is most likely not due to the antioxidant properties of PDTC.
First, a structurally unrelated antioxidant,
N-acetyl-L-cysteine (LNAC), did not inhibit
PDGF-R up-regulation by IL-1ß. Second, treatment of myofibroblasts
with an oxidant, hydrogen peroxide (H2O2), did
not up-regulate PDGF-R. Finally, asbestos fibers have been reported
to generate oxidants and subsequently activate NF-B in lung
epithelial cells (36). While a previous report from our laboratory
showed that asbestos fibers induced PDGF-R (37), further
investigation showed this effect is likely due to endotoxin (27). Taken
together, these findings strongly suggest that oxidants do not mediate
up-regulation of the PDGF-R.
IL-1ß is known to activate a variety of MAP kinase pathways.
Therefore, we investigated the possibility that IL-1ß could induce
PDGF-R via MAP kinase pathways. We first investigated JNK, which
phosphorylates the c-Jun component of the c-Jun/Fos (AP-1)
transcription factor (24). IL-1ß activated JNK in cultured rat lung
myofibroblasts as determined by phosphorylation of c-Jun. However, LPS
did not activate JNK, and we previously reported that LPS is a potent
inducer of PDGF-R (27). Furthermore, JNK was also activated by PDTC.
Since PDTC did not up-regulate PDGF-R and was a potent inhibitor of
IL-1ß-stimulated up-regulation of PDGF-R, we conclude that JNK and
the downstream transcription factor AP-1 do not play a role in
induction of PDGF-R.
Similar to JNK, the MAP kinase ERK-2 was also activated by both IL-1ß
and PDTC. Again, this finding suggests that the ERK pathway was not
involved in up-regulation of the PDGF-R. However, treatment of cells
with the MEK-1 inhibitor PD 98059 blocked ERK phosphorylation of PHAS-1
yet enhanced IL-1ß-stimulated induction of PDGF-R fourfold. MEK-1
is the upstream activator of ERK (38). Thus, it appears that the
MEK-1/ERK pathway mediates suppression of PDGF-R transcription.
IL-1ß has been reported to either up-regulate or down-regulate the
PDGF-R on mesenchymal cells (39, 40). For example, IL-1ß
suppresses PDGF-R expression on human osteoblasts (40), and these
cells possess high constitutive expression of the PDGF-R. In
contrast, rat osteoblasts (39) and rat lung myofibroblasts (27) possess
a relatively low expression of the PDGF-R, but this receptor is
up-regulated by IL-1ß. This paradox could be explained by our finding
in the present study of both positive and negative signaling pathways
that control expression of the PDGF-R in rat lung myofibroblasts.
While the net effect of IL-1ß causes up-regulation of the PDGF-R
in rat lung myofibroblasts, blocking MAP kinase activation caused a
several-fold induction of PDGF-R by IL-1ß. We postulate that cells
with constitutively high levels of PDGF-R (e.g., human osteoblasts,
40 already have PDGF-R transcription "turned on" in
culture, and, therefore, only the suppressive effects of IL-1ß are
observed, possibly through activation of MAP kinase.
In summary, we report that IL-1ß modulates expression of the
PDGF-R on rat pulmonary myofibroblasts through distinct positive and
negative regulatory pathways. While IL-1ß up-regulates the PDGF-R
on cultured myofibroblasts, maximal induction of this receptor by
IL-1ß requires inhibition of MAP kinase (MEK-1/ERK pathway). Thus,
MAP kinase is a negative regulatory pathway for PDGF-R expression.
IL-1ß mediates up-regulation of the PDGF-R through an unknown
pathway that is NF-B- and AP-1-independent. Further investigation
should focus on the identity of transcription factors that modulate
expression of the PDGF-R.
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Footnotes |
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2 Abbreviations used in this paper: PDGF, platelet-derived growth factor; IB-, inhibitor of NF-B-; MAP, mitogen-activated protein; ERK-2, extracellular signal-regulated kinase-2; JNK-1, c-Jun NH2 terminal kinase-1; MEK, MAP kinase kinase; PDTC, pyrrolidine dithiocarbamate; LNAC, N-acetyl-L-cysteine; SFDM, serum-free defined medium; AP-1, activator protein 1.
Received for publication March 20, 1998. Accepted for publication June 1, 1998.
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References |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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B transcription factor mediates IL-1/TNF- induction of gro in human fibroblasts. J. Immunol. 147:520.[Abstract]
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B activation in intact cells. J. Exp.Med. 175:1181.B: a mechanism for NF-B activation. Mol. Cell. Biol. 13:3301.B and AP-1 in intact cells: AP-1 as a secondary antioxidant-responsive factor. EMBO J. 12:2005.[Medline]
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 M. Hou, S. Moller, L. Edvinsson, and D. Erlinge Cytokines Induce Upregulation of Vascular P2Y2 Receptors and Increased Mitogenic Responses to UTP and ATP Arterioscler Thromb Vasc Biol, September 1, 2000; 20(9): 2064 - 2069. [Abstract] [Full Text] [PDF]
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Y.-Z. Wang and J. C. Bonner Mechanism of Extracellular Signal-Regulated Kinase (ERK)-1 and ERK-2 Activation by Vanadium Pentoxide in Rat Pulmonary Myofibroblasts Am. J. Respir. Cell Mol. Biol., May 1, 2000; 22(5): 590 - 596. [Abstract] [Full Text]
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W. Ma, W. Lim, K. Gee, S. Aucoin, D. Nandan, M. Kozlowski, F. Diaz-Mitoma, and A. Kumar The p38 Mitogen-activated Kinase Pathway Regulates the Human Interleukin-10 Promoter via the Activation of Sp1 Transcription Factor in Lipopolysaccharide-stimulated Human Macrophages J. Biol. Chem., April 20, 2001; 276(17): 13664 - 13674. [Abstract] [Full Text] [PDF]
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Y.-Z. Wang, P. Zhang, A. B. Rice, and J. C. Bonner Regulation of Interleukin-1beta -induced Platelet-derived Growth Factor Receptor-alpha Expression in Rat Pulmonary Myofibroblasts by p38 Mitogen-activated Protein Kinase J. Biol. Chem., July 14, 2000; 275(29): 22550 - 22557. [Abstract] [Full Text] [PDF]
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P. Zhang, Y.-Z. Wang, E. Kagan, and J. C. Bonner Peroxynitrite Targets the Epidermal Growth Factor Receptor, Raf-1, and MEK Independently to Activate MAPK J. Biol. Chem., July 14, 2000; 275(29): 22479 - 22486. [Abstract] [Full Text] [PDF]
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