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Receptor I and Stem Cell Factor Receptor Is Differentially Regulated by Phosphatidylinositol 3-Kinase and Calcineurin in Mouse Bone Marrow-Derived Mast Cells1








*
Division of Basic Sciences, Department of Pediatrics,
Program in Molecular Signal Transduction, and
Division of Immunology, Department of Medicine, National Jewish Medical and Research Center, Denver, CO 80206
| Abstract |
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|
|
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RI) on mast cells
activates intracellular signal transduction pathways, including the
activation of protein tyrosine kinases, phosphatidylinositol 3-kinase
(PI3-kinase), and protein kinase C. Binding of stem cell factor (SCF)
to its receptor (SCFR, c-Kit) on mast cells also induces increases in
intrinsic tyrosine kinase activity and activation of PI3-kinase.
Although ligation of both receptors induces Ras and Raf-1 activation,
the downstream consequences of these early activation events are not
well defined, except for the activation of extracellular
signal-regulated kinases (ERK). Addition of Ag (OVA) to mouse bone
marrow-derived mast cells (BMMC) sensitized with anti-OVA IgE
triggers the activation of three members of the mitogen-activated
protein (MAP) kinase family, c-Jun amino-terminal kinase (JNK), p38 MAP
kinase (p38), and extracellular signal-regulated kinases. SCF similarly
activates all three MAP kinases. Wortmannin, an inhibitor of
PI3-kinase, inhibited both Fc
RI- and SCFR-mediated JNK activation
and partially inhibited Fc
RI, but not SCFR-mediated p38 activation.
Cyclosporin A inhibited Fc
RI-mediated JNK and p38 activation, but
did not affect the activation of these kinases when stimulated through
the SCFR. Wortmannin and cyclosporin A inhibited Fc
RI-mediated
production of TNF-
and IL-4 in addition to serotonin release in
BMMC. These results indicate that both PI3-kinase and calcineurin may
contribute to the regulation of cytokine gene transcription and the
degranulation response by modulating JNK activity in
BMMC. | Introduction |
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RI)
triggers the activation of different signal transduction pathways.
Activation of protein tyrosine kinases
(PTKs),3 including Syk, Lyn,
Btk, and Itk, is one of the earliest signaling events induced by
aggregation of the Fc
RI on mast cells 1, 2, 3, 4, 5 . PTK activation is
thought to be proximal to the activation of phospholipase C
and
protein kinase C, and appears to be essential for mast cell
degranulation 6 since PTK inhibitors prevent the liberation of
inositol trisphosphate and histamine release 7, 8 . In addition to the
release of mast cell granule contents, these pathways lead to later
responses, such as the modulation of cytokine gene expression. However,
the downstream consequences of these early activation events are not
well defined. We have shown recently that three members of the
mitogen-activated protein (MAP) kinase family, designated c-Jun
amino-terminal kinase (JNK), p38 MAP kinase (p38), and extracellular
signal-regulated kinase (ERK), are activated following Fc
RI
aggregation in a mouse mast cell line, MC/9 9, 10 . Stem cell factor
(SCF), the ligand for the Kit tyrosine kinase receptor (SCFR) encoded
by the c-Kit proto-oncogene, also plays an important role in the
development of mast cells and hemopoiesis 11, 12, 13 . In this study, we
show that the same three MAP kinase family members are activated
through both Fc
RI and SCFR in mouse bone marrow-derived mast cells
(BMMC), that the activation of these kinases is differentially
regulated by upstream proteins such as PI3-kinase and calcineurin, and
both PI3-kinase- and calcineurin-dependent pathways play an important
role in the regulation of cytokine production and the degranulation
response. | Materials and Methods |
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Bone marrow was obtained from the femurs of female BALB/c mice
(The Jackson Laboratory, Bar Harbor, ME) and cultured in Iscoves
modified Dulbeccos medium (IMDM; Life Technologies, Grand Island, NY)
supplemented with 5% FBS (Summit Biotechnology, Ft. Collins, CO), 50
µM 2-ME (Life Technologies), 2 mM glutamine, 100 µg/ml
streptomycin, 100 U/ml penicillin, 0.5 µg/ml amphotericin B, and IL-3
obtained from medium conditioned by X63 AG8-653 myeloma cells
transfected with a vector expressing IL-3 14 . After 4 wk of culture,
more than 95% of nonadherent cells contained granules that stained
positively with toluidine blue. Wortmannin and rapamycin were purchased
from Calbiochem (San Diego, CA). Cyclosporin A (CsA) and cyclosporin H
(CsH) were provided by Sandoz Pharma (Basel, Switzerland), and FK506
was provided by Fujisawa Pharmaceutical (Osaka, Japan). The MEK1
inhibitor, PD98059, was purchased from New England Biolabs (Beverly,
MA). Bovine myelin basic protein was obtained from Upstate
Biotechnology (Lake Placid, NY). Goat polyclonal anti-ERK2 (C-14)
Ab and anti-Akt1 (C-20) Ab were purchased from Santa Cruz
Biotechnology (Santa Cruz, CA). Recombinant protein G agarose was
purchased from Zymed Laboratories (San Francisco, CA). Kit ligand (SCF)
was obtained from medium conditioned by CHO cells transfected with a
kit ligand expression vector (kindly provided by Genetics Institute,
Cambridge, MA). Medium conditioned by nontransfected CHO cells was used
as a control and showed no activity in inducing kinase activation.
Mouse rTNF-
, mouse rIL-4, purified rat anti-mouse TNF-
mAb,
purified rat anti-mouse IL-4 mAb (ELISA capture), biotinylated
rabbit anti-mouse TNF-
polyclonal Ab, and biotinylated rat
anti-mouse IL-4 mAb (ELISA detection) were purchased from
PharMingen (San Diego, CA). The PKA inhibitor (TTYADFIASGRTGRRNAIHD)
and Crosstide (GRPRTSSFAEG) were made in the Molecular Resource Center,
National Jewish Medical and Research Center (Denver, CO).
Passive sensitization and stimulation of BMMC
BMMC (5 x 106/ml) were cultured with 500 ng/ml anti-OVA IgE 15 for 2 h. This concentration of IgE was shown in initial experiments to be optimal in stimulation of JNK in BMMC. The cells were washed with medium three times and cultured with fresh medium for an additional 2 h. OVA dissolved in PBS was added to the passively sensitized cells or PBS was used as a control. In some experiments, BMMC (3 x 106/ml) were incubated with fresh medium for 2 h and SCF was added to the medium in a final volume of 1%. This concentration of conditioned medium was shown in initial studies to lead to optimal activation of JNK and was comparable with 100 ng/ml rSCF 9 .
Activity of JNK
Glutathione S-transferase-c-Jun 179(179) fusion protein was prepared as described previously 16 , and kinase activity was measured as described 9, 10 .
Kinase assay of p38 MAP kinase
p38 kinase activity was assayed as described using ATF-2 as substrate and quantified with a PhosphorImager (Molecular Dynamics, Sunnyvale, CA) 10 .
Kinase assay of ERK2
In vitro kinase assay of ERK2 was conducted as described previously 17 using myelin basic protein as substrate.
Kinase assay of Akt1
Cells (3 x 106) were lysed in a buffer (10 mM
KPO4 (pH 7.4), 0.1% Nonidet P-40, 1 mM EDTA, 5 mM EGTA, 10
mM MgCl2, 20 mM ß-glycerophosphate, 0.5 mM
Na3VO4, 2 mM DTT, 1 mM PMSF, 10 µg/ml
aprotinin, and 5 mg/ml leupeptin). The lysates were incubated with 0.8
µg goat anti-Akt1 Ab for 2 h at 4°C. Recombinant protein G
agarose was added to the lysates and incubated for an additional 1
h at 4°C. The immunoprecipitates were washed twice with lysis buffer,
and once with kinase buffer (20 mM Tris-HCl (pH 7.5), 10 mM
MgCl2, 0.1 mg/ml BSA, and 1 mM DTT). After the final wash,
50 ml of a kinase assay buffer containing 5 µCi of
[
-32P]ATP (DuPont, Wilmington, DE), 100 µM cold ATP,
1 µg/ml PKA inhibitor, and 5 µg Crosstide 18 was added per
sample. The samples were incubated for 15 min at 30°C and the
reaction was stopped by adding 10 µl of 0.5 M EDTA. A total of 25
µl of each sample was loaded on phosphocellulose paper (Whatman,
Clifton, NJ), and phosphorylation of Crosstide was determined by liquid
scintillation counting. The phosphocellulose paper was washed five
times with 0.425% (v/v) phosphoric acid.
Assay for serotonin release
BMMC (2 x 106/ml) were cultured in medium containing 1 µCi/ml 5-[1,2-3H](N)-hydroxytryptamine creatinine sulfate (DuPont) and cultured for 15 h. After washing, cells (5 x 106/ml) were cultured with 500 ng/ml anti-OVA IgE for 2 h and washed three times with culture medium. BMMC (1 x 106/ml) were incubated in medium for 2 h and stimulated by addition of OVA. The reaction was stopped by adding ice-cold medium and centrifugation. After centrifugation, supernatants and cell pellets were loaded in the scintillation counter. The percentage of release was calculated by dividing the net supernatant counts by the total counts.
ELISA for TNF-
and IL-4
Purified rat anti-mouse TNF-
mAb or purified rat
anti-mouse IL-4 mAb was diluted to 2 µg/ml or 1 µg/ml in
coating solution (0.1 M NaHCO3, pH 8.2), and 50 µl was added to wells
of an ELISA plate (Dynatech Laboratories, Chantilly, VA). After
overnight incubation at 4°C, wells were washed twice with washing
solution (0.05% Tween-20/PBS) and blocked with PBS containing 10% FCS
at room temperature for 2 h. After washing two times, standards
(30 pg/ml-2 ng/ml mouse rTNF-
or 40 pg/ml-2.5 ng/ml mouse rIL-4) and
samples were added at 100 µl/well and incubated overnight at 4°C.
After washing four times, biotinylated rabbit anti-mouse TNF-
polyclonal Ab (1 µg/ml) or biotinylated rat anti-mouse IL-4 mAb
(0.5 µg/ml) was added to the wells and incubated at room temperature
for 45 min, and the wells were washed six times. Avidin-peroxidase (2
µg/ml) was added to the wells and incubated at room temperature for
30 min, and the wells were washed eight times.
2,2'-Azino-bis(3-ethylbenzthiazoline-6-sulfonic acid) (ABTS, 30 mg/ml
0.1 M citric acid, pH 4.35) containing 0.03%
H2O2 was added at 100 µl/well, and the color
reaction was allowed to develop at room temperature for 30 min. The
plates were read at OD 410 nm and analyzed by Microplate Manager
(Bio-Rad, Hercules, CA).
Statistical analysis
Values were compared by Students t test or Welchs t test.
| Results |
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RI and ligation of SCFR on BMMC stimulate JNK,
p38, and ERK2 activation
BMMC previously sensitized with anti-OVA IgE were challenged
in the presence or absence of OVA. Fig. 1
, AC, shows that
addition of 10 µg/ml OVA induced the activation of three members of
the MAP kinase family, JNK, p38, and ERK2. Similarly, addition of SCF
(1%) to BMMC induced the activation of JNK, p38, and ERK2 (Fig. 1
, DF). JNK activity reached maximum levels at 15
min, p38 activity at 5 min, and ERK2 activity at 515 min after the
addition of either OVA or SCF. These data indicate that aggregation of
Fc
RI receptors or signaling through the SCFR rapidly activates all
three MAP kinases in BMMC.
|
RI and ligation of SCFR in
BMMC
The Akt proto-oncogene encodes a serine/threonine kinase, Akt1
19 , which is rapidly and specifically activated by growth factors
such as platelet-derived growth factor (PDGF) 20 . It is well
known that Akt1 activation is mediated through PI3-kinase signaling
21 and Akt1 activation is predicted to parallel PI3-kinase activity.
Akt1 was activated both by aggregation of Fc
RI and ligation of the
SCFR (Fig. 2
). SCFR-induced Akt1
activation was stronger than Fc
RI-mediated activation in BMMC.
Activation was maximal 15 min after addition of the ligand (Fig. 2
A). Under both conditions, Akt1 activation was inhibited by
wortmannin, a PI3-kinase inhibitor 22 , in a dose-dependent manner
(Fig. 2
B). These results confirm that PI3-kinase is
activated following aggregation of Fc
RI and ligation of the SCFR in
mast cells 23 .
|
Addition of wortmannin demonstrated the sensitivity of JNK
activation via Fc
RI in BMMC; inhibition of JNK was dose dependent,
and in the presence of 100 nM wortmannin, JNK activation was inhibited
by 90% (Fig. 3
A). Wortmannin
also inhibited p38 activation via Fc
RI in BMMC in a dose-dependent
manner, although the degree of inhibition in p38 activity was less
(50%) than observed for JNK activation (Fig. 3
B).
Wortmannin failed to inhibit ERK2 activation via Fc
RI in BMMC (Fig. 3
C). These results indicate that Fc
RI-mediated PI3-kinase
activation is involved in JNK activation, and to some extent, p38
activation in BMMC, whereas ERK activation is independent. Virtually
identical results were obtained previously in MC/9 cells 9, 10 .
Preincubation of BMMC with wortmannin before the addition of SCF
revealed that JNK activation was inhibited in a dose-dependent manner,
similar to activation of JNK through Fc
RI, but SCF-induced
activation of p38 and ERK2 was insensitive in these mast cells (Fig. 3
, DF).
|
CsA is known to affect mast cell function, particularly the
degranulation response and cytokine production 24, 25, 26, 27 . Addition of
CsA (1 µg/ml) strongly inhibited JNK activation (80% inhibition) and
partially inhibited p38 activation (40% inhibition) through Fc
RI;
ERK2 activation via Fc
RI was not affected. CsH, a derivative of CsA
that does not bind cyclophilin A or B and is not immunosuppressive
28, 29, 30, 31 , did not affect JNK activation (Fig. 4
A). FK506 and RAP similarly
did not affect JNK activation. It is known that BMMC lack FKBP12 32 ,
and since binding to FKBP12 is required for FK506 to inhibit
calcineurin 33 , the absence of the protein accounts for the lack of
FK506-inhibitory activity. By contrast, CsA did not affect SCF-induced
JNK, p38, or ERK2 activation (Fig. 4
, DF).
|
It has been shown that wortmannin inhibits mast cell degranulation
at the same concentration in which inhibition of PI3-kinase is observed
34, 35 . Wortmannin inhibited Fc
RI-mediated serotonin release from
BMMC in a dose-dependent manner; at a concentration of 100 nM
wortmannin, serotonin release was inhibited by more than 75% (Fig. 5
A). CsA also inhibits
Fc
RI-mediated degranulation in rat basophilic leukemia cells and
basophils 24, 25, 26 , and a role for calcineurin in the degranulation
process has been proposed 36 . CsA (1 µg/ml) partially (56%) but
significantly inhibited Fc
RI-mediated serotonin release in these
BMMC. In concert with the data on kinase activation, FK506 and RAP did
not affect mast cell degranulation in BMMC (Fig. 5
B). The
MEK1 inhibitor PD98059 37, 38 also inhibited serotonin release and
ERK2 activation in Ag-stimulated BMMC in a dose-dependent fashion (Fig. 5
, C and D). These data imply that MEK1 and ERK2
activation may be involved in mast cell degranulation; however, the
exact mechanism whereby PD98059 inhibits mast cell degranulation is not
defined.
|
and IL-4
production following the aggregation of Fc
RI on BMMC
BMMC sensitized with anti-OVA IgE were incubated with 10
µg/ml OVA for 3 h, and cytokine secretion in the medium was
measured by ELISA. Aggregation of Fc
RI on BMMC induced both TNF-
and IL-4 production (TNF-
, 1.44 ± 0.44 ng/106
cells; IL-4, 1.14 ± 0.80 ng/106 cells). As shown in
Fig. 6
A, wortmannin inhibited
both TNF-
and IL-4 production in a dose-dependent manner; the
production of IL-4 appeared to be more sensitive to the drug. CsA, but
not FK506 and RAP, inhibited both TNF-
and IL-4 production in a
similar manner (Fig. 6
, B and C). The inhibition
by CsA was complete at 1 µg/ml, suggesting that inhibition of
calcineurin completely blocks cytokine production in BMMC. In contrast,
addition of the MEK1 inhibitor failed to alter TNF-
or IL-4
production (Fig. 6
D), although it significantly inhibited
ERK2 activation (Fig. 5
D). These data not only indicate the
role of calcineurin in BMMC cytokine production, but also imply the
absence of a role for ERK or MEK1 activation in TNF-
or IL-4
production in these cells. Addition of SCF to BMMC did not trigger any
release of IL-4 or TNF-
.
|
| Discussion |
|---|
|
|
|---|
RI, and that release
of a number of cytokines, including TNF-
and IL-4, may play major
roles in triggering and sustaining the allergic inflammatory response
39 . However, little is known about the signal transduction pathways,
other than the role of calcineurin/NF-AT, that regulate cytokine gene
expression in mast cells. Clues are evident from the promoters for the
TNF-
and IL-4 genes, which contain nuclear factor-
B-, AP-1-,
AP-2-, NF-AT-, Ets-, AP-1/ATF-, NF-AT/AP-1, and c-Maf-related elements,
implicating additional signal transduction pathways that regulate
cytokine gene expression 40, 41, 42, 43, 44, 45, 46, 47, 48, 49 .
In our previous studies, we demonstrated aggregation of Fc
RI
resulted in the rapid activation of JNK, p38, and ERK2 in the mouse
mast cell line, MC/9 9, 10 . In MC/9 cells, wortmannin, at
concentrations that inhibit PI3-kinase activity 19, 50, 51, 52, 53, 54 , strongly
inhibited JNK and partially inhibited p38 activation, but not ERK2
activation 9, 10 . As shown in this study, these three members of the
MAP kinase family were also activated following aggregation of Fc
RI
of BMMC. The effects of wortmannin on Fc
RI-mediated JNK, p38, and
ERK2 activation in BMMC were virtually identical to those observed in
MC/9 cells 9, 10 . Mechanistically, these results indicate that there
is an early separation in the signaling pathways activated through
Fc
RI to differentially regulate the ERK, p38, and JNK sequential
protein kinase pathways.
Signaling through the tyrosine kinase receptor, SCFR, also
resulted in activation of these three MAP kinase family members in
BMMC. Wortmannin inhibited SCFR-induced JNK activation, but did not
affect p38 or ERK2 activation in BMMC (Figs. 2
and 7
). The effects of wortmannin on
SCFR-induced JNK activation in BMMC contrast with the resistance
demonstrated in MC/9 cells 55 . These results suggest that in BMMC,
PI3-kinase activation is required for JNK activation through either
Fc
RI or SCFR, and that, at least in MC/9 cells, the SCFR can utilize
a wortmannin-insensitive pathway to activate JNK. One of the downstream
events following PI3-kinase is the activation of Akt1 20, 21 . As
shown in this study, addition of Ag to passively sensitized cells or
SCF stimulated Akt1 activity, and this activity was completely blocked
in the presence of wortmannin in BMMC.
|
RI-mediated JNK
activation and partially inhibited p38 activation without affecting
ERK2 activation. Another inhibitor of calcineurin activation, FK506,
did not affect Fc
RI-mediated JNK activation in BMMC, almost
certainly due to our demonstration that BMMC do not express the binding
protein FKBP12 (data not shown). In T cells, CsA has been demonstrated
to inhibit cytokine production by inhibiting calcineurin activity and
the nuclear translocation of NF-AT 56 . However, based on the data
presented in this work and our studies of MC/9 cells 55 , CsA can also
inhibit the Fc
RI-mediated induction of JNK activation and
JNK-activated transcription factors. These results indicate an
additional mechanism whereby CsA can regulate cytokine production in
mast cells. In contrast to Fc
RI signaling, SCFR-induced activation
of JNK and p38 was insensitive to CsA, further indicating that
signaling through Fc
RI and SCFR can utilize different upstream
pathways for the activation of JNK and p38.
CsA inhibits the Fc
RI-mediated degranulation of rat basophilic
leukemia cells and human basophils without affecting
phosphatidylinositol hydrolysis or Ca2+ fluxes 30 .
Similarly, CsA, but not FK506, inhibited serotonin release in BMMC. CsA
did not affect Fc
RI-mediated Ca2+ fluxes in these BMMC
(data not shown). Although the mechanism underlying the inhibition of
the degranulation response remains to be defined, the inhibition of
calcineurin is suspected to play a role 36 . The inhibitor PD98059
also abolished Fc
RI-mediated degranulation, suggesting that MEK1 and
ERK activation are involved in the degranulation response. PD98059, on
the other hand, had no effect on cytokine production, indicating that
MEK1 or ERK2 activation is not required for this response. These data
clearly distinguish the downstream signaling requirements for the
degranulation response and cytokine production following Fc
RI
aggregation.
We previously showed that the wortmannin-sensitive pathways play an
important role in TNF-
production in MC/9 cells 10 . It appears
that calcineurin and NF-AT, the MEK kinase/JNK kinase/JNK pathway, and
PI3-kinase may play a role in the synthesis and secretion of cytokines
such as TNF-
and IL-4 in response to the activation through Fc
RI
in BMMC. In addition to cytokine production, wortmannin also inhibited
Fc
RI-mediated degranulation, as previously reported 34, 35 . Thus,
the activation of PI3-kinase is important for both the secretion of
preformed mediators and the induction of cytokine synthesis. However,
neither activation of PI3-kinase alone nor JNK alone is sufficient to
induce cytokine production, since addition of SCF, which can trigger
both of these responses, cannot induce TNF-
or IL-4 production (data
not shown). SCF induced little serotonin release (2% net release) or
consistent arachidonic acid release (6% net release) at the
concentrations used to activate JNK. Our findings define the importance
of the calcineurin and PI3-kinase pathways in IgE-mediated signaling
through Fc
RI in BMMC.
| Acknowledgments |
|---|
| Footnotes |
|---|
2 Address correspondence and reprint requests to Dr. Erwin W. Gelfand, Department of Pediatrics, National Jewish Medical and Research Center, 1400 Jackson Street, Denver, CO 80206. E-mail address: ![]()
3 Abbreviations used in this paper: PTK, protein tyrosine kinase; BMMC, bone marrow-derived mast cell; CsA, cyclosporin A; CsH, cyclosporin H; ERK, extracellular signal-regulated kinase; JNK, c-Jun amino-terminal kinase; MAP, mitogen-activated protein; MEK, MAP/ERK kinase; NF-AT, NF of activated T cells; PI3, phosphatidylinositol 3; RAP, rapamycin; SCF, stem cell factor. ![]()
Received for publication July 9, 1998. Accepted for publication November 11, 1998.
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