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Cutting Edge |

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Turku Centre for Biotechnology, University of Turku/Åbo Akademi University, and
Turku Graduate School of Biomedical Sciences, Turku, Finland
| Abstract |
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| Introduction |
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When TCRs become activated, several signaling pathways are initiated
that later converge in NFAT activation (15, 16). Pathways
dependent on protein kinase C and Ras induce AP-1 expression, while
calcium-dependent pathways lead to
dephosphorylation of the NFATc transcription factor
and its translocation to the nucleus. AP-1 and NFATc then cooperatively
activate genes such as IL-2, IL-4, GM-CSF, and TNF-
. Nuclear import
of NFATc family members has been reported to be opposed by
phosphorylation of critical serine residues by several
kinases, including glycogen synthase kinase-3, protein kinase A,
casein kinases, and several mitogen-activated protein kinases
(17, 18, 19, 20). In this study we demonstrate that Pim-1 can also
phosphorylate NFATc1, but, unlike all the other known NFATc
kinases, it does not prevent the nuclear entry of NFATc1. By contrast,
Pim-1 acts downstream of Ras to enhance NFAT-mediated transactivation
as well as IL-2 production in activated Jurkat T cells.
| Materials and Methods |
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Murine pim-1 cDNA (kindly provided by A. Berns,
Netherlands Cancer Institute, Amsterdam, The Netherlands) was amplified
by PCR and cloned into pLTRpoly vector (21). PCR
was also used to mutate the AP-1 binding sites in the NFAT-luciferase
(LUC)3 reporter from
TGTTTCA to CTGGAAT, to introduce the K67M mutation in Pim-1 that
abolished its kinase activity, and to transfer the protein coding
regions of wild-type and mutant Pim-1 into the pGEX-2T (Amersham
Pharmacia Biotech, Uppsala, Sweden) or pECFP-C1 (Clontech
Laboratories, Palo Alto, CA) fusion vectors. pEF-ras plasmid
and LUC reporters containing either NFAT binding sites derived from the
IL-2 promoter or AP-1 binding sites from the metallothionein promoter
were provided by G. R. Crabtree (Stanford University, Stanford,
CA), pGEX-3X-NFATc1 (1418 aa) and pBJ5-NFATc1-FLAG by S.
N. Ho (Stanford University) and pLXSNpimNT81 by M. Lilly
(Loma Linda University, Loma Linda, CA). The pM plasmid encoding the
Gal4 DNA binding domain and the VP16 activation domain fused to it were
obtained from Clontech Laboratories and the pSV-
-galactosidase
reporter from Promega (Madison, WI).
Transactivation assays and IL-2 measurements
Jurkat T cells or their derivatives, JTAg cells, expressing the
SV40 T Ag (22) were transfected by electroporation with 2
µg of reporter plasmids and indicated amounts of Pim-1 and other
expression vectors. Two days after transfection, cells were left
unstimulated or stimulated for 69 h with 15 ng/ml PMA (Sigma-Aldrich,
St. Louis, MO) and/or 1 µM ionomycin (Calbiochem, La Jolla, CA),
collected and analyzed for LUC activity using Luminoskan luminometer
(Labsystems, Helsinki, Finland). The transfection efficiencies were
normalized against
-galactosidase activities. Shown are means and
mean deviations of representative experiments with duplicate or
triplicate samples. For measuring IL-2 production, cells had been
cotransfected with 2 µg of pEGFP (Clontech Laboratories). Twenty-four
hours after transfection enhanced green fluorescent protein
(EGFP)-positive cells were sorted out with
FACStarPlus (BD Biosciences, San Jose, CA) and
allowed to recover for another 24 h before stimulation.
Concentrations of IL-2 in the growth medium were determined with OptEIA
Human IL-2 Set (BD PharMingen, San Diego, CA). Data from both assays
were analyzed for significant differences by Students t
test (p
0.05).
Coprecipitation assays
COS-7 cells were transfected by electroporation with 1 or 2 µg of indicated plasmids. Two days later cells were collected, lysed by freeze-thawing in 20 mM PIPES (pH 7), 30 mM NaCl, and 5 mM MgCl2 plus protease inhibitors and immunoprecipitated with M2 anti-FLAG mAb (Kodak, Rochester, NY) in 50 mM Tris (pH 7.4), 150 mM NaCl, and 1% Tween 20. Precipitated proteins were then separated by SDS-PAGE, immobilized onto polyvinylidene difluoride plus membrane (Micron Separations, Westboro, MA), stained with anti-green fluorescent protein (GFP) antiserum (Clontech Laboratories) and anti-rabbit-HRP, and visualized by ECL plus reagents (Amersham Pharmacia Biotech). To determine protein expression levels, part of the lysates were directly analyzed by Western blotting with anti-FLAG or anti-GFP Abs.
In vitro phosphorylation assays
GST-Pim-1 and GST-NFATc1 (1418 aa) fusion proteins grown in
Escherichia coli and attached to glutathione Sepharose beads
(Amersham Pharmacia Biotech) were mixed with each other in kinase
buffer (20 mM PIPES (pH 7), 5 mM MnCl2, 7 mM
2-ME, 0.25 mM
-glycerophosphate, 0.4 mM spermine, 10 µM rATP)
supplemented with 10 µCi of [
32P]ATP and
incubated at 30°C for 30 min. Part of the samples were washed with
dephosphorylation buffer (50 mM Tris-HCl (pH 7.4),
1 mM NiCl2, 0.5 mg/ml BSA), resuspended in the
buffer with 1 U of calcineurin (Promega) and 1 U of calmodulin
(Sigma-Aldrich), and incubated at 30°C for 15 min. Activity of
calcineurin was confirmed according to the manufacturers instructions
by using p-nitrophenyl phosphate (Sigma-Aldrich) as a
substrate. All samples were further analyzed by SDS-PAGE followed by
autoradiography. For phosphoamino acid analysis,
phosphorylated proteins from the in vitro kinase assay were
transferred from gel to Immobilon-P membrane (Millipore, Bedford, MA).
Phosphoamino acids were released by acid hydrolysis and separated on
two dimensions under different pH conditions on thin layer plates
(23). The migration patterns of radioactive spots revealed
by autoradiography were then compared with those of nonradioactive
phosphoamino acid standards visualized by ninhydrin staining.
| Results |
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To determine whether the Pim-1 kinase could be involved in
signaling pathways that lead to NFAT activation, we
transfectedJurkat T cells with a pim-1 expression vector
together with a LUC reporter construct containing multiple NFAT binding
sites. To mimic TCR activation, cells were stimulated with the phorbol
ester PMA and the calcium ionophore ionomycin. Ectopic expression of
pim-1 enhanced drug-induced NFAT-LUC activity in a
dose-dependent fashion but had no effects in unstimulated cells (Fig. 1
A and data not shown). Very
similar results were also obtained when TCRs of transfected cells were
activated with anti-CD3 Abs (data not shown). The effects of Pim-1
were reproducible and statistically highly significant
(p < 0.001). Pim-1-induced enhancement of
NFAT-LUC activity was mediated by endogenous AP-1 and NFATc family
members and depended on the presence of intact NFAT binding sites,
because reporter constructs with mutated or no binding sites remained
unaffected (Fig. 1
B and data not shown). Furthermore, Pim-1
enhanced AP-1-LUC activity only slightly (p >
0.05; Fig. 1
B), suggesting that the major effects of Pim-1
are targeted toward the NFATc component of the NFAT-binding protein
complex.
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Pim-1 acts in a novel pathway downstream of Ras
Pim-1 was unable to replace the requirements for either PMA or
ionomycin (data not shown), suggesting that its effects on endogenous
NFAT activity in Jurkat T cells are dependent on convergence of the
drug-induced pathways. As expected, a constitutively active Ras mutant
was able to cooperate with the ionomycin-induced pathway to induce NFAT
activity also in the absence of PMA (Fig. 1
E).
Interestingly, coexpression of Ras and Pim-1 in ionomycin-stimulated
cells resulted in NFAT activity comparable to that in control cells
stimulated with both ionomycin and PMA. In addition, the enhancing
effects of Ras in double-stimulated cells were further potentiated by
coexpression of Pim-1. By contrast, the NT81 mutant of Pim-1 inhibited
the effects of Ras irrespective of which way the cells were treated.
These statistically significant results (p <
0.05) suggest that Pim-1 and its kinase activity are at least partially
responsible for the Ras-induced downstream signaling leading to NFAT
activation in Jurkat T cells.
To test whether the effects of Pim-1 on NFAT activity were directly
mediated through the transcriptional regulatory domain of NFATc1, we
fused the N-terminal half (aa 1418) of NFATc1 to the Gal4 DNA binding
domain and measured Gal4-dependent LUC activity in transiently
transfected Jurkat T cells. In accordance with the results obtained
from NFAT-LUC assays, coexpression of Pim-1 augmented transcriptional
activity of NFATc1 but did not significantly affect the activity of the
VP16 activation domain fused to Gal4 (Fig. 1
F). Because the
Gal4-NFATc1 fusion protein was able to enter the nucleus via the Gal4
domain and activate transcription independently of AP-1, stimulation of
cells with PMA and ionomycin was not required. Without stimulation the
overall activity of Gal4-NFATc1 remained lower than in stimulated
cells, but in both cases Pim-1 enhanced it to a very similar
extent.
Pim-1 phosphorylates NFATc1 in vitro on serine residues
To examine whether NFATc1 could be a direct substrate for Pim-1,
we conducted in vitro kinase assays with GST-fusion proteins of either
wild-type or mutant Pim-1 and the N-terminal regulatory domain of
NFATc1 (aa 1418). Hardly any phosphorylation was
detected with the kinase-deficient K67M mutant of Pim-1, whereas the
wild-type kinase was able to phosphorylate both NFATc1 and
itself but not GST-derived sequences (Fig. 2
A). To find out whether Pim-1
phosphorylates NFATc1 on the same sites that the
calcium-dependent phosphatase calcineurin dephosphorylates,
part of the samples prephosphorylated by Pim-1 were further
incubated in the presence of calcineurin. However, calcineurin had no
effects (Fig. 2
B), even though under the same experimental
conditions it properly dephosphorylated its known
substrates such as p-nitrophenyl phosphate as well as
endogenously phosphorylated, FLAG-tagged NFATc1 protein
immunoprecipitated from transfected COS-7 cells (data not shown). These
results indicated that the target sites of Pim-1 in NFATc1 are distinct
from those recognized by calcineurin. Phosphoamino acid analyses of
proteins phosphorylated by Pim-1 showed that significant
amounts of phosphate were incorporated only on serine residues in both
Pim-1 and NFATc1 (Fig. 2
C). These results were of interest
because all in vivo phosphate in NFATc1 has been reported to be
attached to serines (24).
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| Discussion |
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It has previously been shown that nuclear NFATc is not completely dephosphorylated by calcineurin (25). Furthermore, a detailed analysis of NFATc2 has revealed that in addition to 13 serine residues that are dephosphorylated upon T cell activation there is also one site that is inducibly phosphorylated (26). These results fit well with our observations that calcineurin cannot dephosphorylate the in vitro target sites of Pim-1 in NFATc1 and that both calcineurin and Pim-1 enhance NFAT activity despite their opposing enzymatic activities. Moreover, our results with the constitutively nuclear Gal4-NFATc1 fusion protein indicate that activation of calcineurin is dispensable for enhancement of NFAT activity by Pim-1.
The kinetics of pim-1 expression during T cell activation (14) suggests that Pim-1 is not needed for the initial induction of NFAT activity but may be necessary at later points to allow continuous IL-2 production. Because Pim-1 can enhance IL-2 production and because IL-2 in turn can up-regulate Pim-1 production (8, 9), this may even lead to a positive feedback loop. This conclusion is further supported by the observation that cytokines that induce Pim-1 expression also enhance cell responsiveness to IL-2 (27). Thus, even a slight but constitutive overexpression of Pim-1, as is often observed in human patients with lymphoid or myeloid malignancies (28), could thereby result in increased proliferation and/or cell survival.
Phosphorylation of Pim-1 target sites in NFATc1 may result in conformational changes and/or recruitment of additional coactivators such as CREB-binding protein or p300 which have been reported to bind to NFATc1 and enhance its activity (29). This would fit well with our previous observation that, in cooperation with the p100 transcriptional coactivator, Pim-1 can stimulate the activity of another hematopoietic cell transcription factor, c-Myb (30). Even more intriguingly, our current and previous data indicate that kinase-deficient mutants of Pim-1 can inhibit the positive effects of Ras on both NFATc and c-Myb activities, suggesting that Pim-1 acts as one of the downstream effectors of activated Ras. This conclusion is further supported by the ability of wild-type Pim-1 to partially rescue inhibition of both NFATc andc-Myb activities by dominant negative versions of Ras (Ref. 30 and our unpublished observations). Taken together, our results may explain the ability of overexpressed Pim-1 to enhance lymphoproliferation and even lymphomagenesis, especially in collaboration with Myc or Bcl-2 oncoproteins.
| Acknowledgments |
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| Footnotes |
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2 Address correspondence and reprint requests to Dr. Päivi J. Koskinen, Turku Centre for Biotechnology, University of Turku/Åbo Akademi University, Tykistökatu 6B; 20520 Turku, Finland. E-mail address: paivi.koskinen{at}btk.utu.fi ![]()
3 Abbreviations used in this paper: LUC, luciferase; GFP, green fluorescent protein; EGFP, enhanced GFP; ECFP, enhanced cyan fluorescent protein. ![]()
Received for publication November 1, 2001. Accepted for publication December 17, 2001.
| References |
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activates multiple STAT proteins and upregulates proliferation associated IL-2R
, c-myc and pim-1 genes in human T cells. Blood 93:1980.This article has been cited by other articles:
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||||
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||||
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||||
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||||
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J. Roman, A. F. de Arriba, S. Barron, P. Michelena, M. Giral, M. Merlos, E. Bailon, M. Comalada, J. Galvez, A. Zarzuelo, et al. UR-1505, a New Salicylate, Blocks T Cell Activation through Nuclear Factor of Activated T Cells Mol. Pharmacol., August 1, 2007; 72(2): 269 - 279. [Abstract] [Full Text] [PDF] |
||||
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||||
![]() |
T L Cibull, T D Jones, L Li, J N Eble, L Ann Baldridge, S R Malott, Y Luo, and L Cheng Overexpression of Pim-1 during progression of prostatic adenocarcinoma. J. Clin. Pathol., March 1, 2006; 59(3): 285 - 288. [Abstract] [Full Text] [PDF] |
||||
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||||
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||||
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||||
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||||
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||||
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||||
![]() |
P. G. Hogan, L. Chen, J. Nardone, and A. Rao Transcriptional regulation by calcium, calcineurin, and NFAT Genes & Dev., September 15, 2003; 17(18): 2205 - 2232. [Full Text] [PDF] |
||||
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||||
![]() |
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||||
![]() |
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