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of March 11, 2013.
This information is current as
Phosphatidylinositol-3 Kinase
ofCells Is Dependent on Transient Activation
Thapsigargin-Induced Degranulation of Mast
Michael Huber, Michael R. Hughes and Gerald Krystal
http://www.jimmunol.org/content/165/1/124
2000; 165:124-133; ;J Immunol
References
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Print ISSN: 0022-1767 Online ISSN: 1550-6606.
Immunologists All rights reserved.
Copyright © 2000 by The American Association of
9650 Rockville Pike, Bethesda, MD 20814-3994.
The American Association of Immunologists, Inc.,
is published twice each month byThe Journal of Immunology
at RWTH Aachen Bibliotheksverwaltung Medizin on March 11, 2013http://jimmunol.org/Downloaded from
Thapsigargin-Induced Degranulation of Mast Cells Is
Dependent on Transient Activation of Phosphatidylinositol-3
Kinase
1
Michael Huber,
2
Michael R. Hughes, and Gerald Krystal
3
Thapsigargin, which elevates cytosolic calcium levels by inhibiting the sarcoplasmic/endoplasmic reticulum calcium-dependent
ATPase, was tested for its ability to degranulate bone marrow-derived mast cells (BMMCs) from src homology 2-containing
inositol phosphatase !/!(SHIP
!/!
) and SHIP
"/"
mice. As was found previously with steel factor, thapsigargin stimulated far
more degranulation in SHIP
"/"
than in SHIP
!/!
BMMCs, and this was blocked with the phosphatidylinositol-3 (PI-3) kinase
inhibitors, LY294002 and wortmannin. In contrast to steel factor, however, this heightened degranulation of SHIP
"/"
BMMCs
was not due to a greater calcium influx into these cells, nor was the thapsigargin-induced calcium influx inhibited by LY294002,
suggesting that the heightened thapsigargin-induced degranulation of SHIP
"/"
BMMCs was due to a PI-3 kinase-regulated step
distinct from that regulating calcium entry. An investigation of thapsigargin-stimulated pathways in both cell types revealed that
MAPK was heavily but equally phosphorylated. Interestingly, the protein kinase C inhibitor, bisindolylmaleimide (compound 3),
totally blocked thapsigargin-induced degranulation in both SHIP
!/!
and SHIP
"/"
BMMCs. As well, thapsigargin stimulated a
PI-3 kinase-dependent, transient activation of protein kinase B, and this activation was far greater in SHIP
"/"
than in SHIP
!/!
BMMCs. Consistent with this, thapsigargin was found to be a potent survival factor, following cytokine withdrawal, for both cell
types and was more potent with SHIP
"/"
cells. These studies have both identified an additional PI-3 kinase-dependent step within
the mast cell degranulation process, possibly involving 3-phosphoinositide-dependent protein kinase-1 and a diacylglycerol-inde-
pendent protein kinase C isoform, and shown that the tumor-promoting activity of thapsigargin may be due to its activation of
protein kinase B and subsequent promotion of cell survival. The Journal of Immunology, 2000, 165: 124 –133.
Mast cells play a crucial role in the initiation of allergic
responses. Upon exposure to multivalent allergens,
they are activated and rapidly secrete preformed me-
diators, such as histamine, from cytoplasmic granules. This pro-
cess is initiated by allergens that cross-link IgE molecules that bind
with high affinity to the Fc
!
R1 on the surface of mast cells (1, 2).
Recently, it has been shown that mast cell degranulation is respon-
sible for the coating of nonimmunogenic surgically implanted bio-
materials (3). Specifically, release of histamine at the site of the
implant appears to act as a chemoattractant for phagocytic cells
that encapsulate the implant and can lead to its failure (3). It is
therefore important to elucidate the intracellular pathways that reg-
ulate mast cell degranulation. Studies to date indicate that this
degranulation process is strictly dependent on the influx of extra-
cellular calcium. The depletion of extracellular calcium by the
chelator EGTA results in the complete inhibition of Ag-induced
degranulation (4). In general, receptors that are capable of stimu-
lating the release of intracellular calcium induce the tyrosine phos-
phorylation of phospholipase C-
"
1 (PLC-
"
1)
4
and PLC-
"
2 (5),
resulting in the generation of the two second messengers inositol-
1,4,5-trisphosphate (IP
3
) and diacylglycerol (DAG) (6). IP
3
binds
to its receptor in the membrane of the endoplasmic reticulum and
induces the release of intracellular calcium, whereas DAG associ-
ates with certain isoforms of the serine/threonine protein kinase C
(PKC), thereby promoting their activation (6). The IP
3
-induced
emptying of intracellular calcium stores then triggers the entry of
extracellular calcium through store-operated calcium channels in
the plasma membrane (7).
We recently generated a mouse containing a targeted disruption
of the gene encoding the hemopoietic specific src homology
2-containing inositol phosphatase, SHIP. Bone marrow-derived
mast cells (BMMCs) from these mice were found to readily de-
granulate with either IgE (4) or steel factor (SF) (8), two proteins
that do not by themselves stimulate degranulation in normal mu-
rine BMMCs. This hyperresponsiveness was due in large part to
markedly elevated levels of PI-3 kinase-generated phosphatidyl-
inositol-3,4,5-trisphosphate (PIP
3
), because SHIP was not present
to hydrolyze PIP
3
to PI-3,4-P
2
. Specifically, in SF-induced degran-
ulation of SHIP
!/!
BMMCs, we found that PI-3 kinase-generated
Terry Fox Laboratory, British Columbia Cancer Agency, Vancouver, British Colum-
bia, Canada
Received for publication May 27, 1999. Accepted for publication April 17, 2000.
The costs of publication of this article were defrayed in part by the payment of page
charges. This article must therefore be hereby marked advertisement in accordance
with 18 U.S.C. Section 1734 solely to indicate this fact.
1
This work was supported by the National Cancer Institute of Canada (NCI-C) and
the Medical Research Council of Canada (MRC-C), with core support from the Brit-
ish Columbia Cancer Foundation and the British Columbia Cancer Agency. M.H. was
supported by the Deutsche Forschungsgemeinschaft. M.R.H. was supported by the
Natural Sciences and Engineering Research Council (NSERC). G.K. is a Terry Fox
Cancer Research Scientist of the NCI-C, supported by funds from the Canadian Can-
cer Society and the Terry Fox Run.
2
Current address: Department of Molecular Immunology, Biology III, University of
Freiburg and Max-Planck-Institute for Immunobiology, 79108 Freiburg, Germany.
3
Address correspondence and reprint requests to Dr. Gerald Krystal, Terry Fox Lab-
oratory, 601 West 10th Avenue, Vancouver, BC, Canada V5Z 1L3. E-mail address:
gerryk@terryfox.ubc.ca
4
Abbreviations used in this paper: PLC, phospholipase C; BMMC, bone marrow-
derived mast cell; DAG, diacylglycerol; ERK, extracellular signal-related kinase; IP
3
,
inositol-1,4,5-trisphosphate; MAPK, mitogen-activated protein kinase; P-ERK, phos-
pho-ERK; P-MAPK, T202/Y204-phosphorylated MAPK; P-PKB, S473-phosphory-
lated PKB; PDK, 3-phosphoinositide-dependent protein kinase; PH, pleckstrin ho-
mology; PI, phosphatidylinositol; PIP
3
, phosphatidylinositol-3,4,5-trisphosphate;
PKB, protein kinase B; PKC, protein kinase C; SF, steel factor; SHIP, src homology
2-containing inositol phosphatase.
Copyright © 2000 by The American Association of Immunologists 0022-1767/00/$02.00
at RWTH Aachen Bibliotheksverwaltung Medizin on March 11, 2013http://jimmunol.org/Downloaded from
PIP
3
was critical both for a step upstream of intracellular calcium
release and between intracellular calcium release and extracellular
calcium entry (8). Our working hypothesis based on these results
was that the markedly increased, membrane-anchored PIP
3
in
SHIP
!/!
BMMCs attracted substantially more pleckstrin homol-
ogy (PH) domain-containing proteins, such as PLC-
"
(9) and Btk
(10), to the plasma membrane to mediate these calcium fluxes.
Thus, SHIP appears to function in normal BMMCs to restrict the
entry of extracellular calcium by reducing the level of PI-3 kinase-
generated PIP
3
(4, 8).
One approach to studying the regulation of mast cell degranu-
lation downstream of extracellular calcium entry is by bypassing
the activation of plasma membrane receptors by using calcium
ionophores that transport calcium ions across the plasma mem-
brane or via chemicals that induce the release of calcium from
intracellular stores. In this study, the effect of the tumor promoter
thapsigargin on mast cell degranulation was evaluated in SHIP
"/"
and SHIP
!/!
BMMCs. Thapsigargin is a specific inhibitor of the
sarcoplasmic/endoplasmic reticulum calcium-dependent ATPase,
which pumps calcium that leaks from the endoplasmic reticulum
back into this organelle (11). Adding thapsigargin to mast cells
thus results in the draining of calcium ions from the endo-
plasmic reticulum, capacitative entry of extracellular cal-
cium through store-operated calcium surface channels, and
subsequent degranulation (12).
The results presented in this work demonstrate that although
thapsigargin induces degranulation in a cell surface receptor-inde-
pendent fashion, this process is still dependent on the activation of
PI-3 kinase in normal BMMCs and is strongly enhanced in
SHIP
!/!
BMMCs. In fact, the independence of thapsigargin-me-
diated degranulation from surface receptors as well as PLC-
"
en-
abled us to identify an additional PI-3 kinase-dependent step
within the mast cell degranulation process downstream from in-
tracellular calcium release and influx of extracellular calcium. We
also show that thapsigargin stimulation of BMMCs leads to the
activation of protein kinase B (PKB) and survival of cells in the
absence of cytokines, thereby providing a possible mechanism for
the tumor-promoting ability of this molecule.
Materials and Methods
Mast cell culture
Bone marrow cells from 4- to 8-wk-old SHIP
"/"
and SHIP
!/!
littermates
were plated in methylcellulose (Methocult M3234; StemCell Technolo-
gies, Vancouver, Canada) supplemented with 30 ng/ml murine IL-3, 50
ng/ml murine SF, and 10 ng/ml human IL-6 for 10 –14 days. They were
then harvested and grown in suspension in IMDM containing 15% FCS
(StemCell Technologies), 150
#
M monothioglycerol (Sigma, Oakville,
Canada), and 30 ng/ml IL-3. By 8 wk in culture, greater than 99% of the
cells were c-kit and Fc
!
R1 positive, as assessed by FITC-labeled anti-c-kit
Abs (PharMingen, Mississauga, Canada) and FITC-labeled IgE (anti-
erythropoietin) (26), respectively (4, 8).
Reagents
Polyclonal Abs against S473-phosphorylated PKB (P-PKB), PKB, and
T202/Y204-phosphorylated MAPK (P-MAPK) were obtained from New
England Biolabs (Mississauga, Canada). The polyclonal anti-ERK-1 Ab
was purchased from Upstate Biotechnology (Lake Placid, NY). Compound
3 (bisindolylmaleimide) (catalog no. 203290), thapsigargin (catalog
586005), and LY294002 (catalog no. 440202) were obtained from Calbio-
chem (San Diego, CA). Wortmannin (catalog no. W1628) and PMA (cat-
alog no. P8139) were purchased from Sigma.
Measurement of intracellular calcium
Calcium fluxes were measured according to Huber et al. (8). In brief,
SHIP
"/"
and SHIP
!/!
BMMCs were incubated with 2
#
M fura 2-ace-
toxymethyl ester (Molecular Probes, Eugene, OR) in Tyrode’s buffer (130
mM NaCl, 5 mM KCl, 1.4 mM CaCl
2
, 1 mM MgCl
2
, 5.6 mM glucose, and
0.1% BSA in 10 mM HEPES, pH 7.4) at 23°C for 45 min. The cells were
then washed, resuspended in 1 ml of the same buffer at 5 #10
5
cells/ml in
a stirring cuvette. Following stimulation with thapsigargin or SF, cytosolic
calcium was measured by monitoring fluorescence intensity at 510 nm,
after excitation of the sample with two different wavelengths (340 and 380
nm) using an MC200 monochromator from SLM AMINCO with a 8100
V3.0 software program.
Degranulation assay
For degranulation studies, 5 #10
5
cells/sample were washed with IMDM
and starved overnight in IMDM, containing 10% FCS and 150
#
M mono-
thioglycerol. The cells were then resuspended in Tyrode’s buffer
and treated for 15 min at 37°C with or without 1
#
g/ml thapsigargin.
The degree of degranulation was determined by measuring release of
$
-hexosaminidase (13).
Plasma membrane preparation, p85 immunoblotting, and PI-3
kinase assay
SHIP
!/!
and SHIP
"/"
BMMCs were starved as above and incubated
for 1 min at 37°C with control buffer,1
#
g/ml thapsigargin, or 300
ng/ml SF. Plasma membrane-enriched membrane fractions were pre-
pared as described by Miura et al. (14). Briefly, the cells were then
pelleted, resuspended at 1.5 #10
7
cells/ml in 4°C hypotonic lysis
buffer (20 mM Tris-Cl, pH 7.4, 5 mM EDTA, 5 mM EGTA, 5 mM DTT,
5mMNa
3
VO
4
, 0.5 mM PMSF, 2
#
g/ml leupeptin, and 10
#
g/ml apro-
tinin), allowed to swell for 5 min on ice, and sonicated for 15 #1-s
bursts on ice using an ultrasonic cell disruptor (Heat Systems Ultra-
sonics, Faimingdale, NY). After centrifugation at 2000 #gfor 5 min
at 4°C, the supernatant was centrifuged at 100,000 #gfor 10 min at
4°C in an airfuge (Beckman Instruments, Fullerton, CA). The pellet was
resuspended in 400
#
l of hypotonic lysis buffer containing 1% Nonidet
P-40 by repeated vortex mixing. After a 60-min incubation at 4°C, the
suspension was centrifuged at 100,000 #gfor 10 min, and the super-
natant was collected as the membrane fraction. This solubilized mem-
brane fraction was then subjected either to Western blot analysis with
anti-p85 (Upstate Biotechnology), and the blot reprobed with anti-c-kit
as a loading control or to immunoprecipitation by first incubating at 4°C
for 1 h with anti-p85 Ab (Upstate Biotechnology) and then with protein
A-Sepharose beads at 4°C for 1 h. Beads were then washed and PI-3
kinase assays were performed, as described previously (15).
Immunoblotting
SHIP
"/"
and SHIP
!/!
BMMCs were starved as above and incubated for
various times at 37°C with 1
#
g/ml thapsigargin. The cells were then
solubilized with 0.5% Nonidet P-40 in 4°C phosphorylation solubiliza-
tion buffer (16), and subjected to Western blot analysis, as described
previously (16).
Survival studies
SHIP
"/"
and SHIP
!/!
BMMCs were washed with IMDM and incubated
at5#10
5
cells/ml in IMDM containing 10% FCS and vehicle (DMSO) or
various concentrations (0.015– 0.06
#
g/ml) of thapsigargin at 0.4 ml/well
in Falcon 3047 24-well flat-bottom plates. Viability was assessed by trypan
blue exclusion.
Results
Enhanced thapsigargin-induced degranulation in SHIP
!/!
BMMCs
We recently demonstrated that both IgE and SF stimulate a much
more profound calcium influx into SHIP
!/!
than SHIP
"/"
BMMCs, and this leads to a substantially greater degranulation of
the SHIP
!/!
cells (4, 8). Moreover, the enhanced calcium entry
and degranulation of the SHIP
!/!
BMMCs by these two agonists
were shown to be dependent on elevated PIP
3
levels in these cells
(8). This is consistent with our finding that SHIP is the primary
enzyme responsible for hydrolyzing SF-induced PIP
3
in these BM-
MCs and that PIP
3
reaches substantially higher levels in response
to SF or IgE when SHIP is absent (8, 17). To gain some insight
into the regulation of the degranulation process downstream of
calcium release from intracellular stores, we investigated the de-
granulation potential of thapsigargin in SHIP
"/"
and SHIP
!/!
BMMCs. We found that while SHIP
"/"
BMMCs only degranu-
lated to $10% in response to this agent, stimulation of SHIP
!/!
125The Journal of Immunology
at RWTH Aachen Bibliotheksverwaltung Medizin on March 11, 2013http://jimmunol.org/Downloaded from
BMMCs resulted in about 55% degranulation (Fig. 1A). Based on
our previous findings with IgE- and SF-stimulated BMMCs (4, 8),
we anticipated an increased thapsigargin-induced extracellular cal-
cium influx in SHIP
!/!
BMMCs. However, the calcium entry in-
duced by thapsigargin in SHIP
"/"
and SHIP
!/!
BMMCs was
identical (Fig. 1B). For comparison, a SF-induced calcium influx
was conducted with the same cells and, as reported previously (8),
SF stimulated a far greater influx of calcium into SHIP
!/!
than
into SHIP
"/"
BMMCs (Fig. 1B). These results suggested that
there was at least one additional, calcium-independent pathway
present in thapsigargin-stimulated mast cells that contributes to the
enhanced degranulation in SHIP
!/!
BMMCs.
Thapsigargin-induced degranulation is sensitive to PI-3 kinase
inhibitors
Since one characteristic of SHIP
!/!
BMMCs is their aug-
mented, PI-3 kinase-generated PIP
3
levels in response to vari-
ous stimuli (8, 17), we asked whether PI-3 kinase activation
might be involved in the thapsigargin-induced degranulation
process. To address this, SHIP
"/"
and SHIP
!/!
BMMCs were
preincubated with various concentrations of the PI-3 kinase in-
hibitors, LY294002 and wortmannin, and thapsigargin-stimu-
lated degranulation was assessed. As shown in Fig. 2A, thapsi-
gargin-induced degranulation of SHIP
"/"
BMMCs was
significantly inhibited by LY294002, with 10
#
M LY294002
giving a maximal reduction of $75% (Fig. 2A,left panel). In
SHIP
!/!
BMMCs, thapsigargin-induced degranulation was
even more inhibited by LY294002. However, higher concen-
trations of this PI-3 kinase inhibitor were required to achieve
maximal inhibition, i.e., 97% at 100
#
M LY294002 (Fig. 2A,
right panel). Similar results were obtained with wortmannin
(Fig. 2B). Both LY294002 and wortmannin reduced the thap-
sigargin-induced degranulation of the two cell types to $3%,
suggesting that this residual degranulation may be PI-3 kinase
independent. These results suggested that thapsigargin was ca-
pable of stimulating PI-3 kinase activity in both SHIP
"/"
and
SHIP
!/!
BMMCs, and that this activation plays a critical role
within the thapsigargin-mediated degranulation process. Impor-
tantly, as was found previously with IgE- or SF-stimulated
SHIP
"/"
and SHIP
!/!
BMMCs (4, 8), thapsigargin-induced
PI-3 kinase activity in SHIP
"/"
and SHIP
!/!
BMMCs was
similar, as assessed both by the level of p85 associated with
FIGURE 1. Thapsigargin induces greater degranulation in SHIP
!/!
than SHIP
"/"
BMMCs without increasing calcium mobilization. A, SHIP
"/"
and
SHIP
!/!
BMMCs were starved overnight and stimulated for 15 min at 37°C with 1
#
g/ml thapsigargin or vehicle (DMSO), and the percentage of
degranulation is determined by assaying supernatants and cell pellets for
$
-hexosaminidase activity. Basal levels of degranulation were subtracted (6.15%
and 5.85% in SHIP
"/"
and SHIP
!/!
BMMCs, respectively). Each bar is the mean %SD of duplicates. Comparable results were obtained in three separate
experiments using mast cells derived from different mice. B, Intracellular calcium concentrations were measured in SHIP
"/"
(left panel) and SHIP
!/!
BMMCs (right panel) in response to 1
#
g/ml thapsigargin or 400 ng/ml SF. The arrows indicate the time when the stimulus was added. Similar results
were obtained in four separate experiments.
126 THAPSIGARGIN ACTIVATES PI-3 KINASE-DEPENDENT PATHWAYS
at RWTH Aachen Bibliotheksverwaltung Medizin on March 11, 2013http://jimmunol.org/Downloaded from
plasma membrane-enriched membrane preparations (Fig. 3A)
and by PI-3 kinase assays with p85 immunoprecipitates from
these membrane preparations (Fig. 3B). Densitometric analysis
of our Western blots (Fig. 3A) revealed that unstimulated levels
of p85 were similar in the two cell types and that thapsigargin
recruited p85 to a similar degree in SHIP
"/"
and SHIP
!/!
cells
($1.4-fold over unstimulated levels). Moreover, this p85 re-
cruitment was substantially less than that recruited by SF
($2.9-fold over unstimulated levels), consistent with the
greater effect of SF on PKB activation in SHIP
"/"
BMMCs (see
below, Fig. 4). Because of the modest PI-3 kinase activation
induced by thapsigargin and the many washing steps involved
in the PI-3 kinase assay (15), we obtained some variation in our
assay results (e.g., in the top panel of Fig. 3B, there appears to
be more PI-3 kinase activity in thapsigargin-stimulated
SHIP
"/"
cells, while in the bottom panel the activation levels
look similar in the two cell types). Averaging the densitometric
results of five separate experiments revealed no significant dif-
ference in thapsigargin-induced PI-3 kinase activity. We also
conducted PI-3 kinase assays with anti-phosphotyrosine (4G10)
(four separate experiments) and anti-p85 (Upstate Biotechnol-
ogy) (four separate experiments) immunoprecipitates from
whole cell lysates and obtained a similar degree of variation and
no significant difference in the SHIP
"/"
and SHIP
!/!
BMMCs
(data not shown). Thus, our finding that higher concentrations
of LY294002 and wortmannin are required to inhibit thapsigar-
gin-induced degranulation in SHIP
!/!
BMMCs is consistent
with there being higher levels of PIP
3
in SHIP
!/!
BMMCs
following thapsigargin exposure due to the loss of SHIP rather
than higher PI-3 kinase activity.
Since we had shown previously that PI-3 kinase activation was
essential for SF-mediated calcium mobilization (8), we investi-
gated whether PI-3 kinase inhibition reduced thapsigargin-induced
calcium influx. As shown in Fig. 3C(left panel), preincubation of
SHIP
!/!
BMMCs with 50
#
M LY294002 had no effect on the
initiation of calcium mobilization by thapsigargin and only a minor
effect on the overall intracellular calcium level after stimulation.
The same concentration of this inhibitor, however, was capable of
almost completely abolishing SF-stimulated calcium entry into the
same cells (Fig. 3C,right panel). The same result was obtained in
SHIP
"/"
BMMCs (data not shown). These data suggested that in
thapsigargin-treated mast cells, PI-3 kinase plays a role in medi-
ating the degranulation process. However, unlike in SF-stimulated
mast cells, this enzyme appears to be acting downstream of cal-
cium entry into thapsigargin-treated cells.
Transient PKB activation occurs in thapsigargin-stimulated
BMMCs
One of the major targets of PI-3 kinase activation is PKB (18, 19).
Because optimal thapsigargin-induced degranulation was depen-
dent on PI-3 kinase (Fig. 2), we asked whether thapsigargin stim-
ulated PKB activation. To study this, SHIP
"/"
BMMCs were
stimulated with thapsigargin for different times, and the activation
FIGURE 2. Thapsigargin-induced degranulation is reduced by PI-3 kinase inhibitors. A, SHIP
"/"
and SHIP
!/!
BMMCs were preincubated with 10, 50,
or 100
#
M LY294002 or vehicle (DMSO) for 25 min at 37°C, then stimulated with 1
#
g/ml thapsigargin for 15 min, and the percentage of degranulation
was determined. Basal levels of degranulation were subtracted (9.80% and 5.50% in SHIP
"/"
and SHIP
!/!
BMMCs, respectively). Each bar is the mean %
SD of duplicates. Similar results were obtained in three separate experiments. In the presence of 100
#
M LY294002, both cell types show a residual
degranulation of $3%. B, A separate batch of SHIP
"/"
and SHIP
!/!
BMMCs was preincubated with 10, 50, or 100 nM wortmannin or vehicle (DMSO)
for 25 min at 37°C, then stimulated with 1
#
g/ml thapsigargin for 15 min, and the percentage of degranulation was determined. Basal levels of degranulation
were subtracted (2.90% and 3.59% in SHIP
"/"
and SHIP
!/!
BMMCs, respectively). Each bar is the mean %SD of duplicates. Similar results were obtained
in three separate experiments.
127The Journal of Immunology
at RWTH Aachen Bibliotheksverwaltung Medizin on March 11, 2013http://jimmunol.org/Downloaded from
of PKB was assessed in total cell lysates using a phospho-specific
Ab recognizing PKB phosphorylated at Ser
473
(P-PKB). Intrigu-
ingly, a very transient phosphorylation of PKB was detected only
at 1 and 2 min after stimulation (Fig. 4A,upper panel), a PKB
activation pattern totally distinct from that elicited by SF with
these cells (Fig. 4B,upper panel). To verify equal loading, the
blots were reprobed with anti-PKB Abs (Fig. 4, Aand B,lower
panels). Because thapsigargin has been shown previously to acti-
vate MAPK in the rat hippocampal cell line, H19-7 (20), we asked
whether MAPK was also activated by thapsigargin in murine
BMMCs and whether this activation followed the same transient
pattern. Total cell lysates from thapsigargin-treated SHIP
"/"
BMMCs were assessed by Western blot analysis with a phospho-
specific Ab recognizing doubly phosphorylated (Thr
202
/Tyr
204
)
ERK-1 and ERK-2 (P-ERK-1 and P-ERK-2). Interestingly, a sus-
tained MAPK phosphorylation/activation was observed in thapsi-
gargin-stimulated SHIP
"/"
BMMCs (Fig. 4C), paralleling the pro-
longed calcium mobilization induced by this drug (Fig. 1B,left
FIGURE 3. Thapsigargin activates PI-3 kinase to the same extent in SHIP
"/"
and SHIP
!/!
BMMCs. SHIP
!/!
and SHIP
"/"
BMMCs were starved
overnight and incubated for 1 min at 37°C with control buffer, 1
#
g/ml thapsigargin, or 300 ng/ml SF, and plasma membrane-enriched membrane fractions
were prepared as described in Materials and Methods. The Nonidet P-40-solubilized membrane fraction was then subjected either to A, Western blot
analysis (800,000 cell equivalents/lane) with anti-p85 (upper panel) and reprobing with anti-c-kit (lower panel) to show equal loading, or B,upper panel,
anti-p85 immunoprecipitation and PI-3 kinase assay (8 #10
6
cell equivalents/sample), as described previously (15). The lower panel in Bis an independent
experiment to show the variation in thapsigargin-induced PI-3 kinase activity. C, Intracellular calcium concentrations were measured in SHIP
!/!
BMMCs
in response to 1
#
g/ml thapsigargin (left panel) or 400 ng/ml SF (right panel) in the presence or absence of 50
#
M LY294002. The arrows indicate the
time when the stimulus was added. Similar results were obtained in three separate experiments.
128 THAPSIGARGIN ACTIVATES PI-3 KINASE-DEPENDENT PATHWAYS
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panel). To verify equal loading, the blot was reprobed with anti-
ERK-1 Abs (Fig. 4C,lower panel).
Thapsigargin induces PKB activation via PI-3 kinase
Recently, Yano et al. identified a calcium-triggered signaling cas-
cade in which calcium/calmodulin-dependent kinase kinase acti-
vates PKB in a PI-3 kinase-independent fashion (21). We therefore
investigated whether the transient PKB activation observed in
BMMCs in response to thapsigargin was dependent on PI-3 kinase
activation. Specifically, SHIP
"/"
BMMCs were stimulated with 1
#
g/ml thapsigargin for 1 or 5 min in the presence or absence of the
two PI-3 kinase inhibitors, LY294002 (50
#
M) and wortmannin
(50 nM), and cell lysates were examined for P-PKB expression. As
shown in Fig. 5 (upper panel), both inhibitors were capable of
inhibiting thapsigargin-induced PKB phosphorylation, indicating
PI-3 kinase dependence. Equal loading was verified by reprobing
with anti-PKB Abs (Fig. 5, lower panel). Interestingly, thapsigar-
gin stimulation in the presence of the PI-3 kinase inhibitors had no
effect on the activation of MAPK (data not shown).
Augmented activation of PKB in SHIP
!/!
BMMCs in response
to thapsigargin
In previous reports, we demonstrated that SHIP deficiency in mu-
rine BMMCs results in the potentiation of PI-3 kinase-mediated
effects, such as IgE- and SF-stimulated calcium mobilization and
degranulation (4, 8). Since we have shown in this study that PI-3
kinase-dependent PKB activation takes place in SHIP
"/"
BMMCs
in response to thapsigargin (Figs. 4Aand 5), we asked whether
thapsigargin treatment of SHIP
!/!
BMMCs might result in a more
pronounced activation of PKB. To investigate this, SHIP
"/"
and
SHIP
!/!
BMMCs were stimulated with 1
#
g/ml thapsigargin for
various times and cell lysates subjected to Western blot analysis
using anti-P-PKB Abs. As shown in Fig. 6A, PKB phosphorylation
in SHIP
!/!
BMMCs was easily detected after a 5-s exposure (up-
per panel), whereas 3 min of exposure was required to barely see
phosphorylation of PKB in SHIP
"/"
BMMCs (middle panel). This
demonstrates that PKB is much more activated in SHIP
!/!
FIGURE 4. Thapsigargin stimulates an early, transient activation of
PKB in BMMCs. A, SHIP
"/"
BMMCs were stimulated for the indicated
times (in min) with 1
#
g/ml thapsigargin, and cell lysates were subjected
to Western analysis using anti-phospho (Ser
473
)-PKB (anti-P-PKB) Abs
(upper panel). The lower panel is a reblot with anti-PKB Abs. Phospho-
PKB (P-PKB) and PKB are indicated with arrows. Identical results were
obtained in three separate experiments. B, SHIP
"/"
BMMCs were stimu-
lated for the same times as in Awith 100 ng/ml murine SF, and lysates were
subjected to Western analysis using anti-P-PKB Abs (upper panel). Equal
loading was assessed by reprobing the blot with anti-PKB Abs (lower
panel). Results are representative of three separate experiments. C, Cell
lysates prepared as in Awere analyzed by anti-phospho-MAPK (anti-P-
MAPK) immunoblotting (upper panel). The blot was reprobed with anti-
ERK-1 Abs (lower panel). P-ERK-1 and P-ERK-2 as well as ERK-1 and
ERK-2 are indicated with arrows.
FIGURE 5. Thapsigargin activates PKB via PI-3 kinase. SHIP
"/"
BM-
MCs were preincubated with 50
#
M LY294002, 50 nM wortmannin, or
vehicle (DMSO) for 25 min at 37°C. Cells were then stimulated with 1
#
g/ml thapsigargin for 1 or 5 min, and cell lysates were examined for PKB
activation using anti-P-PKB Abs (upper panel). To verify equal loading,
the membrane was reprobed with anti-PKB Abs (lower panel). P-PKB and
PKB are indicated with arrows. con, Control; LY, LY294002; and WM,
wortmannin. Identical results were obtained in three separate experiments.
FIGURE 6. Thapsigargin activates PKB to a much greater extent in
SHIP
!/!
BMMCs. A, SHIP
"/"
and SHIP
!/!
BMMCs were stimulated
with 1
#
g/ml thapsigargin for the indicated times (in min), and cell lysates
were analyzed by anti-P-PKB Western blotting. The blot was exposed 5 s
to detect P-PKB in SHIP
!/!
BMMCs (upper panel) and 3 min to show
PKB phosphorylation in SHIP
"/"
BMMCs (middle panel). To verify equal
loading, the blot was reprobed with anti-PKB Abs (lower panel). P-PKB
and PKB are indicated with arrows. Comparable results were obtained in
three separate experiments. B, The lysates described under Awere sub-
jected to Western blotting using anti-P-MAPK Abs (upper panel). To show
equal loading, the blot was reprobed with anti-ERK-1 Abs (lower panel).
P-ERK-1, P-ERK-2, ERK-1, and ERK-2 are marked with arrows.
129The Journal of Immunology
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BMMCs in response to thapsigargin. Interestingly, even in the ab-
sence of thapsigargin, the level of PKB phosphorylation was sig-
nificantly higher in SHIP
!/!
BMMCs (see Fig. 6A,middle panel),
most likely because the cells were starved in the presence of 10%
FCS, which contains substantial levels of SF (22). Also of interest,
PKB phosphorylation was lower following 30 and 60 min of thap-
sigargin treatment than in unstimulated SHIP
!/!
BMMCs (see
Fig. 6A,middle panel), and this could be due to activation of the
serine/threonine phosphatase, PP2A, which has been implicated in
the in vivo dephosphorylation/inactivation of PKB (23). Equal
loading of the gels shown in the upper and middle panels of Fig.
6Awas confirmed by reprobing with anti-PKB Abs (Fig. 6A,lower
panel). Thapsigargin stimulation in the presence of the PI-3 kinase
inhibitor LY294002 resulted in the inhibition of PKB phosphory-
lation in SHIP
"/"
(Fig. 5) as well as in SHIP
!/!
BMMCs (data
not shown). To determine whether all signaling pathways were
activated more strongly in SHIP
!/!
BMMCs, the same cell lysates
were analyzed by Western blotting with anti-P-MAPK Abs. As
shown in Fig. 6B(upper panel), phosphorylation of the MAPKs,
ERK-1 and ERK-2, was the same in the two cell types, consistent
with the notion that the loss of SHIP primarily enhances PIP
3
-
mediated pathways. The membrane was reprobed with anti-ERK-1
Abs to demonstrate equal loading (Fig. 6B,lower panel).
PKC is involved in thapsigargin-induced degranulation
Having established, using thapsigargin as a probe, that a PI-3 ki-
nase-regulated step in degranulation is present downstream of ex-
tracellular calcium entry, we asked what PIP
3
-binding protein(s)
could be mediating this process. Recently, certain conventional
(PKC
%
and
$
II), novel (PKC
&
), and atypical (PKC
'
) PKC iso-
types have been reported to be regulated by PI-3 kinase via the
downstream 3-phosphoinositide-dependent protein kinase, PDK-1,
which binds PIP
3
in the plasma membrane (24 –28). Because
PDK-1 is involved in the phosphorylation/activation of PKB (26,
29) and because we found that thapsigargin increased PKB phos-
phorylation more in SHIP
!/!
than in SHIP
"/"
BMMCs, we in-
vestigated whether a pan-specific PKC inhibitor, compound 3,
could inhibit thapsigargin-induced degranulation. As shown in Fig.
7A, compound 3 markedly inhibited thapsigargin-induced degran-
ulation in both SHIP
"/"
and SHIP
!/!
BMMCs. To gain some
insight into which PKC might be involved in this process, we
assessed degranulation in the presence of the phorbol ester, PMA,
which specifically activates DAG-dependent PKC isoforms. Al-
though 50 nM PMA had no statistically significant effect on de-
granulation by itself in SHIP
"/"
or in SHIP
!/!
BMMCs, it
slightly enhanced thapsigargin-induced degranulation (Fig. 7B). It
did not, however, increase thapsigargin-induced degranulation in
SHIP
"/"
cells to the same level observed in SHIP
!/!
BMMCs.
This suggests that a PDK-1-dependent DAG-independent PKC,
such as PKC
'
(28), might be important in this step.
Thapsigargin is a survival factor for BMMCs
Because we found that thapsigargin stimulated PKB, a kinase
shown to enhance survival of many cell types (29), we asked
FIGURE 7. PKC mediates thapsigargin-induced degranulation. A, SHIP
"/"
(left panel) and SHIP
!/!
(right panel) BMMCs were preincubated with 10
or 25
#
M compound 3 or vehicle (DMSO) for 25 min at 37°C, then stimulated with 1
#
g/ml thapsigargin for 15 min, and the percentage of degranulation
was determined. Basal levels of degranulation were subtracted (7.50% and 5.50% in SHIP
"/"
and SHIP
!/!
BMMCs, respectively). Each bar is the mean %
SD of duplicates. Similar results were obtained in three separate experiments. B, SHIP
"/"
and SHIP
!/!
BMMCs were stimulated with 1
#
g/ml thapsi-
gargin, 50 nM PMA, or a combination of both for 15 min at 37°C, and the percentage of degranulation was measured. Basal levels of degranulation were
subtracted (7.50% and 5.50% in SHIP
"/"
and SHIP
!/!
BMMCs, respectively). Each bar is the mean %SD of duplicates. Similar results were obtained
in three separate experiments.
130 THAPSIGARGIN ACTIVATES PI-3 KINASE-DEPENDENT PATHWAYS
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whether thapsigargin might promote the survival of our SHIP
"/"
and SHIP
!/!
BMMCs following withdrawal of IL-3. As can be
seen in Fig. 8A, thapsigargin at concentrations between 0.02 and
0.06
#
g/ml dramatically enhanced the survival of both SHIP
"/"
and SHIP
!/!
BMMCs in the absence of IL-3. Also, as predicted
based on the greater activation of PKB in SHIP
!/!
BMMCs, thap-
sigargin was more effective at promoting survival of SHIP
!/!
BMMCs at low concentrations of the tumor promoter. This is also
shown in a time course study with SHIP
"/"
and SHIP
!/!
BMMCs
using 0.02
#
g/ml thapsigargin (Fig. 8B).
Discussion
The present study was aimed at evaluating the effect of thapsigar-
gin, a non-phorbol ester-type tumor promoter originally isolated
from the plant Thapsia garganica L. (Apiaceae) (11), on mast cell
degranulation using SHIP
"/"
and SHIP
!/!
BMMCs. Interest-
ingly, as was found previously with IgE and SF (4, 8), thapsigargin
induced a more profound degranulation in SHIP
!/!
BMMCs (Fig.
1A). However, unlike IgE and SF, this thaspigargin-induced in-
creased degranulation did not correlate with an elevated calcium
influx into SHIP
!/!
BMMCs (Fig. 1B), suggesting that calcium
entry is a crucial trigger, but not the only factor responsible for
degranulation. Consistent with this observation, Ludowyke et al.
(30) reported that the calcium ionophore, A23187, caused degran-
ulation of the rat mast cell line RBL-2H3, but far less than that
elicited with IgE plus cross-linking Ag. However, they found that
A23187 plus the phorbol ester PMA (which did not stimulate de-
granulation by itself) induced degranulation to the same extent as
IgE plus cross-linking Ag (30) and proposed that in addition to
calcium, other signals have to be generated for optimal degranu-
lation. Related to this, we found in the present study that
LY294002 and wortmannin inhibited thapsigargin-induced de-
granulation in both SHIP
"/"
and SHIP
!/!
BMMCs (Fig. 2), sug-
gesting that activation of PI-3 kinase by thapsigargin provides a
signal in addition to calcium mobilization to attain maximal de-
granulation. This is consistent with a report by Marquardt et al.
(31), who showed that A23187-induced degranulation of BMMCs
could be attenuated using the PI-3 kinase inhibitor, wortmannin.
Intriguingly, we found that LY294002 had no significant effect on
the calcium influx induced by thapsigargin (Fig. 3B), suggesting a
PI-3 kinase-dependent step downstream of calcium mobilization.
This downstream step could not be detected with PI-3 kinase in-
hibitors in our earlier studies employing IgE or SF to trigger mast
cell degranulation because the degranulation pathway initiated by
these two agonists was blocked by PI-3 kinase inhibitors at two
much earlier steps (intracellular calcium release and extracellular
calcium entry) (4, 8). Thus, thapsigargin has proven extremely
useful, by bypassing PLC-
"
-induced calcium release and PI-3 ki-
nase-mediated extracellular calcium entry, in revealing this third
PI-3 kinase-regulated step in degranulation.
PI-3 kinase phosphorylates PI-4,5-P
2
at the 3&position of the
inositol ring to generate PIP
3
, which then serves as a substrate for
SHIP, yielding PI-3,4-P
2
(32). We demonstrated recently that the
loss of SHIP enhances PI-3 kinase-induced cellular responses by
elevating PIP
3
levels (4, 8). Because several signaling proteins
containing PH domains, such as PLC-
"
(9), the tyrosine kinase Btk
(10), and the serine/threonine kinase PKB (33, 34), are capable of
binding to and becoming activated by PI-3 kinase-generated phos-
phoinositides, PI-3 kinase is an important switch for the initiation
of various pathways. Related to this, we observed transient PI-3
kinase-mediated activation of PKB in response to thapsigargin.
This is especially interesting given that PKB activation requires
colocalization of the PH-containing kinase PDK-1 (which phos-
phorylates PKB at Thr
308
) at the plasma membrane. PDK-1 has
been shown to phosphorylate/activate various PKC isoforms (24 –
28). This, coupled with our data showing that the pan-specific PKC
inhibitor, compound 3, prevents thapsigargin-induced degranula-
tion and that PMA doesn’t bring thapsigargin-induced degranula-
tion in SHIP
"/"
BMMCs to levels obtained with SHIP
!/!
BM-
MCs suggests that a PIP
3
-binding DAG-independent PKC isotype,
such as PKC
'
, might be connecting the activation of PI-3 kinase
with the degranulation machinery (Fig. 7). Consistent with this
model, Cissel et al. (35) have demonstrated in the rat RBL-2H3
mast cell line, using a variety of pharmacological activators and
inhibitors of signaling molecules, that thapsigargin-induced de-
granulation is regulated by both phospholipase D and PKC in a
PI-3 kinase-dependent manner. As well, it has been known for
some time that activation of PKC is a critical event for effective
degranulation to occur (30). Moreover, as mentioned earlier, the
combination of calcium-mobilizing probes and pharmacological
PKC activators has been shown to lead to a synergistic increase in
mast cell degranulation (30).
With respect to thapsigargin being a tumor promoter, the acti-
vation of PKB and the enhanced survival in the absence of exog-
enous cytokines offer an interesting new possibility for the tumor-
igenicity of thapsigargin. PKB is known to be a key survival kinase
required for the inhibition of apoptosis in both hemopoietic cells
and other cell types (36, 37). Seven targets of PKB have been
identified to date, and they are the Bcl-2 family member, Bad (38),
FIGURE 8. Thapsigargin enhances the survival of BMMCs. A,
SHIP
"/"
(F) and SHIP
!/!
(E) BMMCs were incubated at 5 #10
5
cells/ml with the indicated concentrations of thapsigargin, in the absence of
IL-3, and viable cells were counted on day 3. B, SHIP
"/"
(F) and SHIP
!/!
(E) BMMCs were incubated in the absence of IL-3 at 5 #10
5
cells/ml in
the presence (——) or absence (---) of 0.02
#
g/ml ($30 nM) thapsigargin,
and viable cells were counted each day. Each point represents the mean %
SD of four separate experiments.
131The Journal of Immunology
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glycogen synthase kinase-3 (39), caspase-9 (40), a forkhead tran-
scription factor (FKHRL1) (41), I
((%
(42), endothelial NO syn-
thase (eNOS) (43, 44), and Raf (45). Phosphorylation of these
proteins by PKB inactivates them, thus promoting survival in cer-
tain cell types. Because we also found that thapsigargin activates
MAPK (Fig. 4), which has been shown to promote survival in
some cell types and proliferation in others (46, 47), the initiation of
antiapoptotic (and/or cell proliferation) pathways might be the
main mechanism(s) by which thapsigargin mediates its tumor-pro-
moting activity. However, it is worth noting that thapsigargin has
been reported to activate both a tyrosine as well as a serine/thre-
onine kinase, leading to transcriptional activation of the glucose-
regulated protein GRP78 promoter (48). Consistent with this, Chao
et al. (20, 49, 50) have reported the activation of Src tyrosine
kinase as well as Raf-1 and MAPK serine/threonine kinases in
response to thapsigargin in H19-7 cells. Thus, we cannot rule out
at this time that activation of a tyrosine kinase such as Src is also
involved in the tumor-promoting activity of thapsigargin. In con-
trast to our studies, Conus et al., who assessed the role of calcium
in the regulation of PKB and p70
S6K
in BALB/c-3T3 fibroblasts,
found that thapsigargin stimulated full activation of p70
S6K
,
whereas little or no activation of PKB was observed (51). How-
ever, because a different source of cells was used and the time
point assessed was 5 min (51), a time in which PKB activation is
almost back to baseline in BMMCs (Figs. 4 and 5), their results do
not necessarily contradict ours.
In summary, we have shown that the tumor promoter thapsigar-
gin activates a PI-3 kinase-dependent survival pathway, thereby
providing a new model for its tumor promotion. Moreover, we
have identified a PI-3 kinase-dependent pathway important for pri-
mary mast cell degranulation that is downstream of intracellular
calcium release and extracellular calcium entry. This pathway
might involve PDK-1 and a DAG-independent PKC isoform. Fur-
ther studies are currently underway to identify the PKC isoform(s)
involved in this pathway.
Acknowledgments
We thank Vivian Lam for excellent technical support and Christine Kelly
for typing the manuscript.
References
1. Beaven, M. A., and H. Metzger. 1993. Signal transduction by Fc receptors: the
Fc
!
R1 case. Immunol. Today 14:222.
2. Turner, H., and J.-P. Kinet. 1999. Signalling through the high-affinity IgE recep-
tor Fc
!
R1. Nature 402:B24.
3. Tang, L., T. A. Jennings, and J. W. Eaton. 1998. Mast cells mediate acute in-
flammatory responses to implanted biomaterials. Proc. Natl. Acad. Sci. USA 95:
8841.
4. Huber, M., C. D. Helgason, J. E. Damen, L. Liu, R. K. Humphries, and
G. Krystal. 1998. The src homology 2-containing inositol phosphatase (SHIP) is
the gatekeeper of mast cell degranulation. Proc. Natl. Acad. Sci. USA 95:11330.
5. Zhang, J., E. H. Berenstein, R. L. Evans, and R. P. Siraganian. 1996. Transfection
of Syk protein tyrosine kinase reconstitutes high affinity IgE receptor-mediated
degranulation in a Syk-negative variant of rat basophilic leukemia RBL-2H3
cells. J. Exp. Med. 184:71.
6. Berridge, M. J., and R. F. Irvine. 1989. Inositol phosphates and cell signalling.
Nature 341:197.
7. Hoth, M., and R. Penner. 1992. Depletion of intracellular calcium stores activates
a calcium current in mast cells. Nature 355:353.
8. Huber, M., C. D. Helgason, M. P. Scheid, V. Duronio, R. K. Humphries, and
G. Krystal. 1998. Targeted disruption of SHIP leads to steel factor-induced de-
granulation of mast cells. EMBO J. 17:7311.
9. Falasca, M., S. K. Logan, V. P. Lehto, G. Baccante, M. A. Lemmon, and
J. Schlessinger. 1998. Activation of phospholipase C
"
by PI 3-kinase-induced PH
domain-mediated membrane targeting. EMBO J. 17:414.
10. Salim, K., M. J. Bottomley, E. Querfurth, M. J. Zvelebil, I. Gout, R. Scaife,
R. L. Margolis, R. Gigg, C. I. Smith, P. C. Driscoll, et al. 1996. Distinct speci-
ficity in the recognition of phosphoinositides by the pleckstrin homology domains
of dynamin and Bruton’s tyrosine kinase. EMBO J. 15:6241.
11. Thastrup, O., A. P. Dawson, O. Scharff, B. Foder, P. J. Cullen, B. K. Drobak,
P. J. Bjerrum, S. B. Christensen, and M. R. Hanley. 1994. Thapsigargin, a novel
molecular probe for studying intracellular calcium release and storage. Agents
Actions 43:187.
12. Putney, J. W. Jr., and G. S. Bird. 1993. The signal for capacitative calcium entry.
Cell 75:199.
13. Nishizumi, H., and T. Yamamoto. 1997. Impaired tyrosine phosphorylation and
Ca
2"
mobilization, but not degranulation, in lyn-deficient bone marrow-derived
mast cells. J. Immunol. 158:2350.
14. Miura, K., and D.W. MacGlashan Jr. 1998. Expression of protein kinase C
isozymes in human basophils: regulation by physiological and nonphysiological
stimuli. Blood 92:1206.
15. Liu, L., A. B. Jefferson, X. Zhang, F. A. Norris, P. W. Majerus, and G. Krystal.
1996. A novel phosphatidylinositol-3,4,5-trisphosphate 5-phosphatase associates
with the interleukein-3 receptor. J. Biol. Chem. 271:29729.
16. Liu, L., J. E. Damen, R. L. Cutler, and G. Krystal. 1994. Multiple cytokines
stimulate the binding of a common 145-kilodalton protein to Shc at the Grb2
recognition site. Mol. Cell. Biol. 14:6926.
17. Huber, M., C. D. Helgason, J. E. Damen, M. P. Scheid, V. Duronio, V. Lam,
R. K. Humphries, and G. Krystal. 1999. The role of SHIP in FceR1-induced
signalling. Curr. Top. Microbiol. Immunol. 244:29.
18. Franke, T. F., S.-I. Yang, T. O. Chan, K. Datta, A. Kazlauskas, D. K. Morrison,
D. R. Kaplan, and P. N. Tsichlis. 1995. The protein kinase encoded by Akt
proto-oncogene is a target of the PDGF-activated phosphatidylinositol 3-kinase.
Cell 81:727.
19. Burgering, B. M. T., and P. J. Coffer. 1995. Protein kinase B (c-Akt) in phos-
phatidylinositol-3-OH kinase signal transduction. Nature 376:599.
20. Chao, T.-S. O., M. Abe, M. B. Hershenson, I. Gomes, and M. R. Rosner. 1997.
Src tyrosine kinase mediates stimulation of Raf-1 and mitogen-activated protein
kinase by the tumor promoter thapsigargin. Cancer Res. 57:3168.
21. Yano, S., H. Tokumitsu, and T. R. Soderling. 1998. Calcium promotes cell sur-
vival through CaM-K kinase activation of the protein-kinase-B pathway. Nature
396:584.
22. Hsu, Y. R., G. M. Wu, E. A. Mendiaz, R. Syed, J. Wypych, R. Toso, M. B. Mann,
T. C. Boone, L. O. Narhi, H. S. Lu, and K. E. Langley. 1997. The majority of
stem cell factor exists as monomer under physiological conditions: implications
for dimerization mediating biological activity. J. Biol. Chem. 272:6406.
23. Meier, R., M. Thelen, and B. A. Hemmings. 1998. Inactivation and dephosphor-
ylation of protein kinase B
%
(PKB
%
) promoted by hyperosmotic stress. EMBO J.
17:7294.
24. Le Good, J. A., W. H. Ziegler, D. B. Parekh, D. R. Alessi, P. Cohen, and
P. J. Parker. 1998. Protein kinase C isotypes controlled by phosphoinositide 3-ki-
nase through the protein kinase PDK1. Science 281:2042.
25. Chou, M. M., W. Hou, J. Johnson, L. K. Graham, M. H. Lee, C.-S. Chen,
A. C. Newton, B. S. Schaffhausen, and A. Toker. 1998. Regulation of protein
kinase C
'
by PI 3-kinase and PDK-1. Curr. Biol. 8:1069.
26. Stephens, L., K. Anderson, D. Stokoe, H. Erdjument-Bromage, G. F. Painter,
A. B. Holmes, P. R. J. Gaffney, C. B. Reese, F. McCormick, P. Tempst, et al.
1998. Protein kinase B kinases that mediate phosphatidylinositol 3,4,5-trisphos-
phate-dependent activation of protein kinase B. Science 279:710.
27. Dutil, E. M., A. Toker, and A. C. Newton. 1998. Regulation of conventional
protein kinase C isozymes by phosphoinositide-dependent kinase 1 (PDK-1).
Curr. Biol. 8:1366.
28. Liu, W. S., and C. A. Heckman. 1998. The sevenfold way of PKC regulation.
Cell. Signaling 10:529.
29. Downward, J. 1998. Mechanisms and consequences of activation of protein ki-
nase B/Akt. Curr. Opin. Cell Biol. 10:262.
30. Ludowyke, R. I., L. L. Scurr, and C. M. McNally. 1996. Calcium ionophore-
induced secretion from mast cells correlates with myosin light chain phosphor-
ylation by protein kinase C. J. Immunol. 157:5130.
31. Marquardt, D. L., J. L. Alongi, and L. L. Walker. 1996. The phosphatidylinositol
3-kinase inhibitor wortmannin blocks mast cell exocytosis but not IL-6 produc-
tion. J. Immunol. 156:1942.
32. Damen, J. E., L. Liu, P. Rosten, R. K. Humphries, A. B. Jefferson, P. W. Majerus,
and G. Krystal. 1996. The 145-kDa protein induced to associate with Shc by
multiple cytokines is an inositol tetraphosphate and phosphatidylinositol 3,4,5-
trisphosphate 5-phosphatase. Proc. Natl. Acad. Sci. USA 93:1689.
33. Toker, A., and L. C. Cantley. 1997. Signalling through the lipid products of
phosphoinositide-3-OH kinase. Nature 387:673.
34. Downward, J. 1998. Lipid-regulated kinases: some common themes at last. Sci-
ence 279:673.
35. Cissel, D. S., P. F. Fraundorfer, and M. A. Beaven. 1998. Thapsigargin-induced
secretion is dependent on activation of a cholera toxin-sensitive and phosphati-
dylinositol-3-kinase-regulated phospholipase D in a mast cell line. J. Pharmacol.
Exp. Ther. 285:110.
36. Ahmed, N. N., H. L. Grimes, A. Bellacosa, T. O. Chan, and P. N. Tsichlis. 1997.
Transduction of interleukin-2 antiapoptotic and proliferative signals via Akt pro-
tein kinase. Proc. Natl. Acad. Sci. USA 94:3627.
37. Songyang, Z., D. Baltimore, L. C. Cantley, D. R. Kaplan, and T. F. Franke. 1997.
Interleukin 3-dependent survival by the Akt protein kinase. Proc. Natl. Acad. Sci.
USA 94:11345.
38. Datta, S. R., H. Dudek, X. Tao, S. Masters, H. Fu, Y. Gotoh, and
M. E. Greenberg. 1997. Akt phosphorylation of BAD couples survival signals to
the cell-intrinsic death machinery. Cell 91:231.
39. Pap, M., and G. M. Cooper. 1998. Role of glycogen synthase kinase-3 in the
phosphatidylinositol 3-kinase/Akt cell survival pathway. J. Biol. Chem.
273:19929.
132 THAPSIGARGIN ACTIVATES PI-3 KINASE-DEPENDENT PATHWAYS
at RWTH Aachen Bibliotheksverwaltung Medizin on March 11, 2013http://jimmunol.org/Downloaded from
40. Cardone, M. H., N. Roy, H. R. Stennicke, G. S. Salvesen, T. F. Franke,
E. Stanbridge, S. Frisch, and J. C. Reed. 1998. Regulation of cell death protease
caspase-9 by phosphorylation. Science 282:1318.
41. Brunet, A., A. Bonni, M. J. Zigmond, M. Z. Lin, P. Juo, L. S. Hu, M. J. Anderson,
K. C. Arden, J. Blenis, and M. E. Greenberg. 1999. Akt promotes cell survival by
phosphorylating and inhibiting a Forkhead transcription factor. Cell 96:857.
42. Khwaja, A. 1999. Akt is more than just a bad kinase. Nature 401:33.
43. Fulton, D., J.-P. Gratton, T. J. McCabe, J. Fontana, Y. Fujio, K. Walsh,
T. F. Franke, A. Papapetropoulos, and W. C. Sessa. 1999. Regulation of endo-
thelium-derived nitric oxide production by the protein kinase Akt. Nature 399:
597.
44. Dimmeler, S., I. Fleming, B. Fisslthaler, C. Hermann, R. Busse, and
A. M. Zeiher. 1999. Activation of nitric oxide synthase in endothelial cells by
Akt-dependent phosphorylation. Nature 399:601.
45. Zimmermann, S., and K. Moelling. 1999. Phosphorylation and regulation of Raf
by Akt (protein kinase B). Science 286:1741.
46. Chin, B. Y., I. Petrache, A. M. Choi, and M. E. Choi. 1999. Transforming growth
factor
$
1 rescues serum deprivation-induced apoptosis via the mitogen-activated
protein kinase (MAPK) pathway in macrophages. J. Biol. Chem. 274:11362.
47. Gonzales, M., K. Haan, S. E. Baker, M. Fitchmun, I. Todorov, S. Weitzman, and
J. C. R. Jones. 1999. A cell signal pathway involving laminin-5,
%
3
$
1
integrin,
and mitogen-activated protein kinase can regulate epithelial cell proliferation.
Mol. Biol. Cell 10:259.
48. Cao, X., Y. Zhou, and A. S. Lee. 1995. Requirement of tyrosine- and serine/
threonine kinases in the transcriptional activation of the mammalian grp78/BiP
promoter by thapsigargin. J. Biol. Chem. 270:494.
49. Chao, T.-S. O., K. L. Byron, K.-M. Lee, M. Villereal, and M. R. Rosner. 1992.
Activation of MAP kinase by calcium-dependent and calcium-independent path-
ways: stimulation by thapsigargin and epidermal growth factor. J. Biol. Chem.
267:19876.
50. Chao, T. S., D. A. Foster, U. R. Rapp, and M. R. Rosner. 1994. Differential Raf-1
requirement for activation of MAP kinase by growth factors and tumor promot-
ers. J. Biol. Chem. 269:7337.
51. Conus, N. M., B. A. Hemmings, and R. B. Pearson. 1998. Differential regulation
by calcium reveals distinct signaling requirements for the activation of Akt and
p70
S6K
.J. Biol. Chem. 273:4776.
133The Journal of Immunology
at RWTH Aachen Bibliotheksverwaltung Medizin on March 11, 2013http://jimmunol.org/Downloaded from
