In this study, we have found that: 1 GM-CSF-mediated MLN51 upregulation is attributable to both transcriptional and post-translational control in rheumatoid arthritis fibroblast-like syno
Trang 1hyperproliferation of fibroblast-like synoviocytes in the pathogenesis of rheumatoid arthritis
Ju-Eun Ha1, Young-Eun Choi1, Jinah Jang2, Cheol-Hee Yoon1, Ho-Youn Kim3and Yong-Soo Bae1,2
1 Department of Biological Science, Sungkyunkwan University, Suwon, Gyeonggi-do, South Korea
2 Division of DC Immunotherapy, CreaGene Research Institute, Seongnam-shi, Gyeonggi-do, South Korea
3 Department of Medicine, Division of Rheumatology, Center for Rheumatoid Diseases and Rheumatism Research Center (RhRC), Catholic Research Institutes of Medical Sciences, Catholic University of Korea, Seoul, South Korea
Rheumatoid arthritis (RA) is a chronic inflammatory
arthritis characterized by synovial hyperplasia with
local invasion of bone and cartilage Accumulating
evi-dence suggests that RA fibroblast-like synoviocytes
(FLSs) possess unique characteristics in RA
patho-genesis [1] FLSs play a key role in the development of
sustained inflammation and angiogenesis in arthritic
joints [2–4] Several cytokines and RA factors existing
in the RA environment stimulate the overgrowth of
FLSs, leading to the aggravation of disease Amongst
these factors, granulocyte–macrophage
colony-stimu-lating factor (GM-CSF) also plays an important role
in the pathogenesis of RA [5–7] GM-CSF blockade results in less severe disease and reduces cytokine levels
in tissue in vivo [8]
In RA synovium, FLSs express both tumor necrosis factor-a (TNF-a) and Fas receptors, and their ligands are detected in nearby macrophages or T cells [9,10] However, previous studies have demonstrated that Fas activation induces apoptosis in only a small proportion
of FLSs, because of their constitutive expression of the FLICE-inhibitory protein (FLIP) [11] FLIP expression mediates the recruitment and activation of nuclear fac-tor-jB kinase and several mitogen-activated protein
Keywords
FLICE-inhibitory protein; granulocyte–
macrophage colony-stimulating factor;
metastatic lymph node 51;
mitogen-activated protein kinase; rheumatoid arthritis
fibroblast-like synoviocyte
Correspondence
Y.-S Bae, Department of Biological Science,
Sungkyunkwan University, 300
Chunchun-dong, Jangan-gu, Suwon, Gyeonggi-do
440-746, South Korea
Fax: +82 31 290 7087
Tel: +82 31 290 5911
E-mail: ysbae04@skku.edu
(Received 23 January 2008, revised 5 April
2008, accepted 9 May 2008)
doi:10.1111/j.1742-4658.2008.06500.x
One of the characteristic features of the pathogenesis of rheumatoid arth-ritis is synovial hyperplasia We have reported previously that metastatic lymph node 51 (MLN51) and granulocyte–macrophage colony-stimulating factor (GM-CSF) are involved in the proliferation of fibroblast-like synovi-ocytes in the pathogenesis of rheumatoid arthritis In this study, we have found that: (1) GM-CSF-mediated MLN51 upregulation is attributable to both transcriptional and post-translational control in rheumatoid arthritis fibroblast-like synoviocytes; (2) p38 mitogen-activated protein kinase plays
a key role in the upregulation of MLN51; and (3) FLICE-inhibitory pro-tein is upregulated downstream of MLN51 in response to GM-CSF, result-ing in the proliferation of fibroblast-like synoviocytes These results imply that GM-CSF signaling activates mitogen-activated protein kinase, followed by the upregulation of MLN51 and FLICE-inhibitory protein, resulting in fibroblast-like synoviocyte hyperplasia in rheumatoid arthritis
Abbreviations
DC, dendritic cell; ERK, extracellular signal-regulated kinase; FLIP, FLICE-inhibitory protein; FLS, fibroblast-like synoviocyte; JNK, c-Jun N-terminal kinase; MAPK, mitogen-activated protein kinase; MLN51, metastatic lymph node 51; MTT, 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-tetrazolium bromide; OA, osteoarthritis; RA, rheumatoid arthritis; TNF-a, tumor necrosis factor-a.
Trang 2kinases (MAPKs), leading to cell survival, proliferation
or proinflammatory gene expression [12–14] FLIP
expression is also upregulated during the
differentia-tion of monocytes into dendritic cells (DCs) [15] In
addition, GM-CSF is a key component in the
differen-tiation of monocytes into DCs [16], and is generally
detected in RA synovial fluid [7,17] Taken together,
these reports suggest that GM-CSF is probably
associ-ated with FLIP expression
Our previous studies have demonstrated that active
RA FLSs express substantial amounts of metastatic
lymph node 51 (MLN51) in the presence of
GM-CSF, and the upregulation of MLN51 is associated
with the hyperproliferation of FLSs [7] MLN51 was
first identified in breast cancer cells Later, it was
reported that MLN51 is associated with the exon
junction complex in the nucleus and remains stably
associated with mRNA in the cytoplasm [18,19] A
recent study has found that MLN51 is essential for
the formation of stress granules occurring in
malig-nant tumors [20]
In the present study, we have investigated the
mech-anism underlying the GM-CSF-mediated and
MLN51-associated hyperproliferation of FLSs using an RA FLS cell line, MH7A [21] We found that GM-CSF upregulates MLN51 expression through the activation
of MAPK, followed by the induction of FLIP expres-sion The present data strongly suggest that MLN51 and MLN51-induced FLIP play critical roles in FLS hyperplasia under GM-CSF conditions by facilitating cell proliferation and blocking apoptosis in the patho-genesis of RA
Results
GM-CSF induces the proliferation of MH7A cells and the expression of MLN51
Our recent study has shown that GM-CSF is involved in the proliferation of primary RA FLSs [7] In the present study, we investigated cell proli-feration and MLN51 expression using an RA FLS cell line, MH7A, in the presence of GM-CSF As shown in Fig 1A, MH7A cell proliferation was enhanced by GM-CSF treatment in a dose-dependent manner at concentrations up to 100 ngÆmL)1, but
0 10 50 100 300 500 (ng·mL –1 )
MLN51
0 10 50 100 300 500 (ng·mL –1 )
MLN51
0 0.25 0.5 1 1.5 2 6 12 24 (h)
0 0.25 0.5 1 1.5 2 6 12 24 (h)
MLN51 MLN51
0.0 0.5 1.0 1.5 2.0
2.5
A
B
C
4 )
*
hMLN51 β-actin
β-actin
β-actin
β-actin β-actin
0 0.5 1 3 6 12 0 0.5 1 3 6 12 (h)
GM-CSF
Fig 1 GM-CSF induces FLS proliferation
and MLN51 expression (A) MH7A cells
were incubated with GM-CSF at various
concentrations for 24 h Cell proliferation
was assessed by MTT assay The results
are expressed as the mean ± standard
devi-ation in triplicate *P < 0.01 (B) Dose
kinet-ics (left) and time kinetkinet-ics (right) of GM-CSF
effects on MLN51 expression in MH7A
cells MH7A cells were treated with various
concentrations of GM-CSF for 1 h for dose
kinetics, and with 100 ngÆmL)1of GM-CSF
for different periods of time for time
kinet-ics MLN51 expression was then assessed
by western blot (WB) analysis and RT-PCR
at the protein (top) and mRNA (bottom)
levels (C) Time kinetics of GM-CSF effects
on MLN51 expression in primary RA FLSs.
Primary RA FLS cells were treated with
100 ngÆmL)1of GM-CSF for the periods of
time shown in the figure MLN51
expres-sion was then assessed by RT-PCR.
Trang 3not at extreme concentrations such as 500 ngÆmL)1
(Fig 1A)
We have reported previously that MLN51 is
upregu-lated in the FLSs of RA patients, and is enhanced
6 days after GM-CSF treatment [7] In the present
experiments, we assessed the dose and time kinetics of
the effects of GM-CSF on MLN51 expression in MH7A
cells MLN51 was fully induced at the protein level
fol-lowing treatment with GM-CSF at a concentration of
50–100 ngÆmL)1 (left panel in Fig 1B) for 1–2 h (right
panel in Fig 1B) However, GM-CSF treatment did not
affect the mRNA level of MLN51 over the entire range
of kinetics in MH7A cells (Fig 1B) These data suggest
that GM-CSF-mediated MLN51 upregulation in
MH7A cells is likely to depend on translational or
post-translational control However, in the case of primary
RA FLSs, MLN51 expression was induced at both
mRNA and protein levels within 12 h following
GM-CSF treatment (Fig 1C), suggesting that GM-
GM-CSF-mediated MLN51 upregulation in primary RA FLSs is,
at least in part, dependent on transcriptional control
GM-CSF-mediated MLN51 upregulation is
attributable to both transcriptional and
post-translational control in RA FLSs
As a next step, we investigated the control
mecha-nism underlying the expression of MLN51 following
GM-CSF treatment When MH7A cells were
pretreat-ed with a-amanitin or cycloheximide, the mRNA and protein levels, respectively, of MLN51 were signifi-cantly decreased compared with those of untreated cells (Fig 2A,B) However, pretreatment with a-amani-tin (Fig 2A) or cycloheximide (Fig 2B) did not affect the GM-CSF-mediated upregulation of MLN51 in MH7A cells, suggesting that the GM-CSF-mediated upregulation of MLN51 in MH7A cells is not depen-dent on transcriptional or translational control In contrast, GM-CSF-mediated MLN51 upregulation was completely obliterated and significant amounts of MLN51 were detected even in the absence of GM-CSF
in MH7A cells following pretreatment with MG-132, a proteasome inhibitor (Fig 2C) In order to confirm this result, we treated the MH7A cells with MG-132 in the presence of GM-CSF, and measured MLN51 pro-tein expression at different time points In accordance with the results shown in Fig 2C, once cells had been pretreated with MG-132, significant amounts of MLN51 were detected from the beginning, and were maintained for longer than 4 h without any additional effects of GM-CSF (Fig 2D) However, in the case of
RA FLSs, MG-132 pretreatment showed additive effects on the GM-CSF-mediated upregulation of MLN51 expression at the protein level (Fig 2E) These findings suggest that GM-CSF-mediated MLN51 upregulation in primary RA FLSs is, to some extent,
MG-132
0 0.5 1 4 0 0.5 1 4 (h)
MLN51
GM-CSF
MLN51
GM-CSF
A B
C
E
D
MLN51
β-actin
β-actin
β-actin β-actin
β-actin
β-actin
– + – +
α-amanitin
CHX
MLN51
MLN51
MG-132
MLN51
MLN51
GM-CSF – + – +
MG132
MLN51
MG132
RA-FLS
0
5
10
15
20
25
30
Fig 2 GM-CSF-induced MLN51 expression acts as a post-transcriptional regulator rather than a transcriptional or translational control MLN51 expressed in MH7A cells was assessed in the presence or absence of
10 lgÆmL)1of a-amanitin for 20 h (A),
25 lgÆmL)1of cycloheximide (CHX) for 20 h (B) and 20 l M MG-132 for 6 h (C) The expression of MLN51 was assessed by RT-PCR and western blot (WB) analysis (D) The expression of MLN51 was assessed via
WB analysis after treatment with GM-CSF for the indicated periods of time in the pres-ence or abspres-ence of MG-132 (E) MLN51 expressed in primary RA FLSs was assessed in the presence or absence of
20 l M MG-132 for 6 h The expression of MLN51 was assessed by WB analysis (left) The histogram (right) represents the relative band intensity of the WB data, assessed by
Trang 4dependent on both post-translational and
transcrip-tional control, probably by blocking of the proteasome
degradation pathway
GM-CSF-induced MLN51 is involved in the
hyperproliferation and anti-apoptosis of MH7A
cells via the upregulation of FLIP
Next, we investigated the contribution of MLN51 to
MH7A cell proliferation When MLN51 was knocked
down by transfection of siRNA (si-MLN51), cell
pro-liferation was completely abrogated, whereas the
over-expression of MLN51 enhanced MH7A cell
proliferation (Fig 3A) These results strongly suggest
that MLN51 plays a critical role in the proliferation of
MH7A cells
In order to determine whether MLN51 is involved
in the anti-apoptosis as well as cell proliferation of
MH7A in response to GM-CSF, we examined the
apoptosis of normal and MLN51-knockdown MH7A
cells in the presence or absence of GM-CSF As shown
in Fig 3B, cell apoptosis was substantially increased
by MLN51-knockdown, and the increased apoptosis
was not attenuated by additional GM-CSF treatment
These data suggest that MLN51 is also involved in
anti-apoptosis
Amongst the several anti-apoptotic molecules, FLIP
mRNA was markedly enhanced by MLN51
over-expression in MH7A cells (Fig 3C) Once treated with
GM-CSF, FLIP mRNA was also increased, together
with MLN51 mRNA, in primary RA FLSs, but was
undetectable in osteoarthritis (OA) FLSs even in the
presence of GM-CSF (Fig 3D) Transient expression
of MLN51 induced the expression of FLIP (Fig 3E),
whereas MLN51-knockdown attenuated FLIP
expres-sion in MH7A cells regardless of GM-CSF treatment
(Fig 3F) These results indicate that MLN51 causes
the upregulation of FLIP expression, followed by the
blocking of FLS apoptosis
FLIP upregulated by MLN51 plays a crucial role in
the anti-apoptosis of MH7A cells
We examined whether FLIP was involved in the
anti-apoptosis of MH7A cells As shown in other cells [22],
FLIP-knockdown (si-FLIP) completely abrogated
MH7A cell proliferation, even in the presence of
GM-CSF, when compared with control cells (si-con)
(Fig 4A) In addition, FLIP-knockdown markedly
increased the cell apoptosis of MH7A, and the
apopto-tic ratio was not attenuated by GM-CSF treatment
(Fig 4B) These data suggest that FLIP plays an
important role in GM-CSF-mediated cell proliferation
and anti-apoptosis In contrast, FLIP-knockdown did not show any discernible effects on the expression of MLN51 (Fig 4C), implying that FLIP works down-stream of MLN51 in the GM-CSF-mediated signaling pathway to FLS proliferation
MAPK functions in the upregulation of MLN51 under GM-CSF conditions
Activation of the GM-CSF receptor leads to the acti-vation of multiple cytoplasmic signaling molecules, including MAPK The MAPKs are key regulators of cytokine and metalloproteinase production, and thus may be targeted in RA It has been reported previ-ously that all three MAPK families, extracellular signal-regulated kinase (ERK), c-Jun N-terminal kinase (JNK) and p38, are expressed in rheumatoid synovial tissue, and also play a key role in RA FLS activation [23] We investigated whether or not GM-CSF activates MAPK in MH7A cells Following the addition of GM-CSF to cultures of MH7A cells, JNK and p38 were dramatically phosphorylated within approximately 1 h, whereas ERK phosphoryla-tion was slightly enhanced during the same period of time (Fig 5A) In good accordance with the data shown in Fig 5A, pretreatment of MH7A cells with SB203580 (p38 inhibitor) completely abrogated the effects of GM-CSF on the upregulation of MLN51, whereas pretreatment with SP600125 (JNK inhibitor)
or PD98059 (ERK inhibitor) partially or barely atten-uated the effects of GM-CSF on the expression of MLN51 and FLIP, respectively (Fig 5B) These data indicate that MAPKs, particularly p38 and partly JNK, but not ERK, play an important role in the upregulation of MLN51 and FLS overgrowth upstream of MLN51 under the GM-CSF signaling pathway, as summarized in Fig 6
Discussion
Inflammatory cell infiltration and the expansion of an aggressive FLS population in the synovial membrane are the pathological hallmarks of RA [1,24] A number
of growth factors and cytokines have been described in association with the proliferative response of FLSs, including transforming growth factor-b, platelet-derived growth factor, fibroblast growth factor, inter-leukin-1b, TNF-a and interleukin-6 However, these factors are not sufficient to cover the active prolifera-tion capacity of RA FLSs, thus indicating that other factors must be involved in this proliferation In our previous studies, we have determined that GM-CSF in the synovial fluid plays an important role in the
Trang 5hyper-proliferation of RA FLSs through the upregulation of
MLN51 [7]
In the present study, we have investigated the
mechanism underlying the GM-CSF-mediated and
MLN51-associated hyperproliferation of FLSs using
an RA FLS cell line, MH7A As shown previously with primary RA FLSs, GM-CSF treatment increased the number of MH7A cells in culture, as well as the expression of MLN51 in these cells (Fig 1)
MLN51
Bcl2 c-IAP x-IAP
NF K B (p65)
NF K B (p50)
FLIP
Control pcDNA3.1pcDNA-MLN51
MLN51 FLIP
MLN51 FLIP
si -con pcDNA3.1 si -MLN51 pcDNA-MLN51
2.5
2.0 1.5 1.0 0.5 0.0
4 )
pcDNA3.1
-hMLN51
UntreatedGM-CSF
MLN51
β-actin MLN51 -siRNA con -siRNA
β-actin
β-actin
11.05
si-con
25.81
si-MLN51
+
+ GM-CSF
Annexin V
26.52
si-MLN51
hMLN51 FLIP
Fig 3 MLN51 induces FLIP expression in the GM-CSF-mediated proliferation of FLSs (A) MH7A cells were transfected with 200 pmol
siR-NA against MLN51 (si-MLN51) or with 3 lg of pcDsiR-NA3.1-MLN51 plasmids using Lipofectamine 2000 One day later, the cells were stimu-lated with GM-CSF for 24 h or were left unstimustimu-lated Cell numbers were assessed by MTT assay, and expressed as the mean ± standard deviation in triplicate *P < 0.01 (B) MH7A cells transfected with 200 pmol of MLN51 siRNA (si-MLN51) or non-targeting siRNA (si-con) were stimulated with 100 ngÆmL)1of GM-CSF for 24 h, or were left unstimulated Apoptosis of each sample was assessed by flow cytome-try after Annexin V–FITC staining (C) MH7A cells were transfected with 1 lg of mock vector or pcDNA3.1-MLN51 plasmids The levels of several anti-apoptotic gene mRNAs were assessed by semi-quantitative RT-PCR with specific PCR primer sets (D) Primary RA and OA FLS samples were cultured for 6 h in the presence or absence of GM-CSF The mRNAs of MLN51 and FLIP were assessed by semi-quantitative RT-PCR with specific PCR primer sets (E) MH7A cells transfected with 1 lg of pcDNA3.1-MLN51 or 200 pmol MLN51 siRNA were har-vested at 24 h post-transfection, and subjected to western blot analysis for the expression of MLN51and FLIP (F) MH7A cells transfected with control (si-con) or MLN51 (si-MLN51) siRNAs were treated with 100 ngÆmL)1of GM-CSF, or were left untreated The cells were har-vested and assessed by western blot analysis for the expression of MLN51and FLIP.
Trang 6In our previous paper [7], we examined the mRNA and protein levels of MLN51 6 days after GM-CSF treatment of a culture of RA FLSs In the present study, however, MLN51 expression was examined within 24 h after GM-CSF treatment in MH7A cells
at both mRNA and protein levels In the case of MH7A cells, MLN51 was constitutively expressed at the mRNA level under normal conditions, and was not changed by GM-CSF treatment over 24 h In con-trast, the protein level of MLN51 was low in the untreated control, but rapidly increased over 1–2 h following GM-CSF treatment, and the enhanced level lasted longer than 24 h When the cells were pretreated with MG-132, the protein level of MLN51 was as high
as that of GM-CSF-treated cells, even in the absence
of GM-CSF, suggesting that GM-CSF-mediated MLN51 upregulation in MH7A cells is probably post-translational
However, when examined in primary RA FLSs over
12 h, both mRNA and protein levels of MLN51 were enhanced at 3–12 h following GM-CSF treatment (Fig 1C) The pretreatment of RA FLSs with MG-132 showed an additional increment in the protein level of GM-CSF-induced MLN51 (Fig 2E) These data indi-cate that GM-CSF not only induces the expression of MLN51, but also blocks the proteasome-mediated degradation of MLN51 in RA FLSs by an un-known mechanism In other words, GM-CSF-mediated MLN51 upregulation is attributable to both transcrip-tional and post-translatranscrip-tional control in RA FLSs The overgrowth of RA FLSs may result from unbal-anced proliferation and apoptosis, and both processes have been detected on tissue sections of rheumatoid synovium [25,26] In the present study, the MLN51-knockdown and ectopic expression of MLN51 (Fig 3A,B) experiments have shown that MLN51 plays
an important role in GM-CSF-mediated MH7A cell proliferation In order to determine whether MLN51 is also involved in anti-apoptosis, we investigated the anti-apoptotic molecules, and found that FLIP expres-sion was upregulated by MLN51 (Fig 3C,D) MLN51
is a subunit of the exon junction complex, which is involved in post-splicing events, such as mRNA export, nonsense-mediated mRNA decay and translation [27–29] Taken together, these findings allow us to assume that MLN51 may facilitate the export of FLIP mRNA from the nucleus, or stabilize FLIP mRNA in the cytoplasm, followed by the blocking of cell apopto-sis, and therefore involvement in FLS overgrowth Apoptosis stimulators, such as TNF-a and FasL, nor-mally induce cell apoptosis In RA FLSs, however, activation of the TNF-a receptor or Fas receptor
0.0
0.5
1.0
1.5
2.0
si-con
A
B
C
si-FLIP
si-con
si-FLIP
+ GM-CSF
si-FLIP
Annexin V
46.92
14.06
44.57
si-con si-FLIP
GM-CSF – + – +
MLN51 β-actin FLIP
Fig 4 MAPK and FLIP are involved in the GM-CSF-mediated FLS
proliferation mechanism upstream and downstream of MLN51,
respectively (A) MH7A cells transfected with 100 pmol of FLIP
(si-FLIP) or control (si-con) siRNAs were stimulated with
100 ngÆmL)1 of GM-CSF 24 h post-transfection, or were left
unstimulated At 24 h after treatment, cell numbers were assessed
by MTT assay The results are expressed as the mean ± standard
deviation in triplicate *P < 0.01 (B) Control (si-con) or FLIP
si-RNA-transfected (si-FLIP) cells were treated with 100 ngÆmL)1 of
GM-CSF for 24 h, or were left untreated They were assessed for
cell apoptosis by flow cytometry after Annexin V–FITC staining (C)
Control (si-con) or FLIP si-RNA-transfected (si-FLIP) cells were
trea-ted with 100 ngÆmL)1of GM-CSF for 24 h, or were left untreated.
FLIP and MLN51 expression was assessed in the cells by western
blot analysis.
Trang 7induces NF-jB translocation, which leads to increased
FLIP expression [30] This NF-jB loop may protect
RA FLSs from TNF-a⁄ FasL-mediated cell death,
resulting in FLS overgrowth However, we found that
MLN51 induced FLIP expression in the absence of
TNF-a or FasL stimulation These data suggest that
RA FLSs are resistant to cell apoptosis via, at least
in part, MLN51-mediated FLIP upregulation under
GM-CSF conditions
The activation of MAPK is almost exclusively found
in synovial tissue from RA patients This activation is
induced by inflammatory cytokines [23] Amongst
these proinflammatory cytokines, GM-CSF induces
phosphorylation of Ser345 in the MAPK consensus
sequence [31]
We have found that GM-CSF induces the
phos-phorylation of p38 and JNK predominantly
(Fig 5A), and that a p38 inhibitor (SB203580) com-pletely abrogates the GM-CSF-mediated upregulation
of MLN51 and FLIP in MH7A cells (Fig 5B) Although ERK (p42⁄ 44) is constitutively activated in MH7A cells (Fig 5A), as reported previously [21], ERK inhibitor (PD98059) does not affect MLN51 and FLIP induction in MH7A cells (Fig 5B), indi-cating that ERK is unlikely to be involved in the GM-CSF-mediated induction of MLN51 and FLIP
in RA FLSs These data suggest that MAPK, partic-ularly p38, is activated by GM-CSF, and plays an important role in the post-translational modification
of MLN51, resulting in the protection of MLN51 from ubiquitin-mediated degradation
In summary, in RA FLSs: (1) GM-CSF signaling activates p38 MAPK; (2) this is followed by MLN51 upregulation via both transcriptional and post-transla-tional control; (3) FLIP expression is induced; and (4) this results in the anti-apoptotic proliferation of FLS, contributing to the pathogenesis of RA (Fig 6) MLN51 and MLN51-induced FLIP are believed to play important roles in FLS hyperplasia by participat-ing in FLS proliferation and anti-apoptosis in RA pathogenesis Thus, MLN51 and FLIP are attractive targets for the development of new RA therapeutics
Experimental procedures
Isolation and establishment of RA FLSs from RA patients
Fibroblast-like synoviocyte samples were obtained from synovectomized tissue of RA and OA patients undergoing
Fig 6 Summary diagram showing the role of MLN51 in the GM-CSF-mediated proliferation of RA FLSs via MAPK activation and induction of FLIP expression.
A
B
Fig 5 MLN51 expression via MAPK activation by GM-CSF (A)
MH7A cells were treated with 100 ngÆmL)1of GM-CSF for the
indi-cated periods of time Cells were assessed by western blotting for
the expression of three different MAPKs and their phospho-forms.
(B) MH7A cells were pre-incubated with 20 l M SP600125, 50 l M
PD98059 and 20 l M SB203580 for 1 h, and were then cultured in
the presence or absence of GM-CSF (100 ngÆmL)1) for an additional
1 h MLN51 and FLIP expression in each sample was assayed by
western blot analysis DMSO, dimethylsulfoxide.
Trang 8joint replacement surgery at Kangnam St Mary Hospital,
Catholic University of Korea, Seoul, South Korea
Institu-tional Review Board (IRB) approval and patient informed
consent from each enrolled participant were obtained RA
and OA FLS cells were prepared as described previously
[7]
Cell line, chemicals and antibodies
A human synovial cell line (MH7A), which was prepared
from FLSs isolated from the knee joint of an RA patient,
was obtained from Riken Cell Bank, Tsukuba, Ibaraki,
Japan MH7A cells were maintained in RPMI1640
(HyClone, Logan, UT, USA) supplemented with 10% fetal
bovine serum (Gibco, Grand Island, NY, USA)
and 100 lgÆmL)1 each of penicillin and streptomycin
GM-CSF (LG Life Science, Seoul, Korea), cycloheximide
(Calbiochem, San Diego, CA, USA), a-amanitin (Sigma,
St Louis, MO, USA), MAPK inhibitors SP600125,
PD98059, SB203580 (Calbiochem) and MG-132 (AG
Scien-tific Inc., San Diego, CA, USA) were used in the present
experiments FLIP antibodies were purchased from Santa
Cruz Co (Santa Cruz, CA, USA) SAPT⁄ JNK,
phospho-SAPT⁄ JNK, ERK, phospho-ERK, p38 and phospho-p38
antibodies were purchased from Cell Signaling Inc
(Dan-vers, MA, USA) Anti-b-actin (Sigma), anti-rabbit and
anti-mouse IgG-HRP (Sigma) and Annexin V–fluorescein
isothiocyanate (Becton Dickinson, Mountain View, CA,
USA) IgG were also used in this study
Recombinant plasmids
MLN51-expressing plasmids (pcDNA3.1-MLN51 and
pET28-MLN51) were prepared by cloning full-length
hMLN51 cDNA into pcDNA3.1 (Invitrogen, San Diego,
CA, USA) at the EcoRI⁄ XhoI site and partial hMLN51
cDNA into the pET28a(+) vector (Novagen, Madison,
WI, USA) at the HindIII⁄ XhoI site, respectively Full-length
and partial cDNAs of hMLN51 [18] were prepared by
RT-PCR amplification of MH7A mRNA using appropriate
primer pairs for cDNAs of hMLN51: full-length, 5¢-TATG
AATTCGTTCTCCGTAAGATGGCGGAC-3¢ and 5¢-TA
TCTCGAGTTAACTGGAACCCCTGCTTACAA-3¢;
par-tial length, 5¢-ATCAAGCTTTGGTGCGTAAGGAGCT
GAC-3¢ and 5¢-ATACTCGAGCTTAGCAGCTGGAGTC
GTTT-3¢
Preparation of recombinant MLN51 protein and
antiserum
Recombinant BL21(DE3) cells that had been transformed
by pET28a(+)-MLN51 were cultured in 2· yeast extract
and tryptophan medium Recombinant proteins were
purified using a nickel nitrilotriacetic acid-conjugated
bead column MLN51 antiserum was prepared by immu-nizing New Zealand white rabbits three times at 3-week intervals with recombinant hMLN51 proteins emulsified with Freund’s adjuvant (Sigma) New Zealand white rab-bits were obtained from Orient Bio (Gyeonggi-do, South Korea) and were maintained in the Animal Care Facility
of Sungkyunkwan University according to the Korean Experimental Animal Care Guidelines
Cell proliferation assay
MH7A cells were seeded in 96-well plates overnight at a density of (1–5)· 103cells per well in 100 lL of RPMI1640 containing 10% fetal bovine serum Cells that had been pretreated with appropriate reagents or transfected with siRNA were cultured in the presence or absence of various concentrations of GM-CSF After 24 h, 3-(4,5-dim-ethylthiazol-2-yl)-2,5-diphenyl-tetrazolium bromide (MTT) dye solution (20 lL per well, Promega, Madison, WI, USA) was added to each well, and incubated for another
4 h at 37C The reaction was stopped by the addition of stop solution (150 lL per well), and the absorbance of each sample was subsequently measured by a spectrophotometer (Molecular Device, Union City, CA, USA) at 570 nm
Western blot analysis
Each experiment was conducted as described previously [7]
In brief, cell lysates were normalized with Bradford reagent (Bio-Rad, Hercules, CA, USA), and 40–70 lg of lysate was subjected to 8–12% SDS-PAGE and transferred to poly(vinylidene difluoride) membranes (Millipore, Eschborn, Germany) The membranes were blocked and probed with appropriate antibody as described previously [7], and were then analyzed by an enhanced chemiluminescence western blotting system (Millipore⁄ Amersham Biosciences, Freiburg, Germany)
Quantitative RT-PCR
Quantitative RT-PCR was conducted as described previously [7,32] In brief, total RNAs were extracted using Tri-zol reagent (Invitrogen) and were then normalized RT-PCR was conducted using the pre-Mix kit (Intron Biotech, Seoul, Korea) and the following primer pairs: MLN51: sense, 5¢-AAGACACCGAGGACGAGGAATC-3¢; anti-sense, 5¢-CCTTCCATAGCTTTCGCTGACG-3¢; FLIP: sense, 5¢-GAATGTGGAATTCAAGGCTCA-3¢; anti-sense, 5¢-AT ACAGGTACCCACACCCACA-3¢; Bcl-2: sense, 5¢-TTC CTCTGGGAAGGATGGCG-3¢; anti-sense, 5¢-CGTCCC TGAAGAAGCTCCTCC-3¢; IAP: sense, 5¢-TGTTGTGGC CTGATGCTGGA-3¢; anti-sense, 5¢-CAGGCAAAGCAAG CCACTCTG-3¢; XIAP: sense, 5¢-TGGTGACCAAGTGC AGTGCT-3¢; anti-sense, 5¢-AGGGTCTTCACTGGGCTT
Trang 9CC-3¢; NF-kB(p50): sense, 5¢-AGTTTCGGCGGTGGT
AGTGG-3¢; anti-sense, 5¢-GCCAGCAGCATCTTCACG
TC-3¢; NF-kB(p65): sense, 5¢-GACAATCGTGCCCCCAA
CAC-3¢; anti-sense, 5¢-TGGGTCCGCTGAAAGGACT-3¢;
human b-actin: sense, 5¢-TGACGGGGTCACCCACACT
GTGCCCATCTA-3¢; anti-sense, 5¢-AGTCATAGTCCGC
CTAGAAGCATTTFCGGT-3¢
siRNA transfection
Human MLN51 and c-FLIP siRNAs were designed and
synthesized by Invitrogen (Stealth) with sequences of
5¢-GGGCCCUAAGCAUUUGGAUGAUGAU-3¢ and 5¢-CC
CUGGGCUAUGAAGUCCAGAAAUU-3¢, respectively
Cell transfection with siRNA was conducted using
Lipo-fectamine 2000 (Invitrogen) according to the protocol of
the manufacturer After 5 h of incubation, the media were
completely replaced and incubated further
Apoptotic analysis by flow cytometry
MH7A cells were cultured in six-well plates at 5· 105cells
per well After 24 h, cells were transfected with MLN51 or
FLIP siRNA, and cultured in the presence or absence of
100 ngÆmL)1 of GM-CSF at 37C for an additional 24 h
The cells were harvested and incubated for 15 min with
fluorescein isothiocyanate-conjugated Annexin V antibody
(Becton Dickinson) at room temperature in the dark The
cells were then analyzed using a FACS Calibur system
(Becton Dickinson) with cell quest software
Acknowledgement
This work was supported by Bio New Drug grants
(A060115 and A040010) from the Korean Ministry of
Health and Welfare
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