1 Section of Nephrology, Department of Medicine, Tulane Medical Center, 3 Tulane Cancer Center, and 2 Veterans Administration Medical Center, New Orleans, Louisiana 70112
![]() |
ABSTRACT |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
We previously demonstrated that light
chain (LC) endocytosis by human proximal tubule cells (PTCs) leads to
production of cytokines through activation of NF-B. Here, we
examined the role of MAPK pathways in these responses using four
species of myeloma LCs (
1,
2,
3, and
1) previously shown to induce
cytokine production by PTCs. Among these,
1-LC, which
yielded the strongest cytokine responses, was selected for detailed
studies. Activation of MAPKs was probed by Western blot analysis for
the active kinases, ERK 1/2, JNK 1/2, and p38 in
1-LC-exposed human PTCs. To evaluate the functional role
of MAPKs in LC-induced cytokine responses, we tested the effects of
U-0126, an ERK inhibitor; SP-600125, an inhibitor of JNK; SB-203580, a
p38 inhibitor; and curcumin, a JNK-AP-1 inhibitor, all added to media
before 4-h exposure to 1.5 mg/ml
1-LC. IL-6 and monocyte
chemotactic protein-1 (MCP-1) were determined by ELISA. Both LC
and human serum albumin (HSA) activated ERK, although the HSA effect
was weaker.
1-LC stimulated all three MAPKs, although
phosphorylation of ERK was more pronounced and sustained than others.
Inhibitors of ERK, JNK, and p38 reduced LC-induced IL-6 and MCP-1
production. These findings suggest that activation of MAPKs plays a
role in LC-induced cytokine responses in PTCs. Activation of MAPKs may
be involved in cytokine responses induced by other proteins as well as
LCs and may be pivotal in the pathophysiology of tubulointerstitial
injury in proteinuric diseases.
intracellular signaling mechanisms; interleukin-6; MCP-1; progression of renal diseases; myeloma; proteinuria
![]() |
INTRODUCTION |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
INCREASED ENDOCYTOSIS
of filtered proteins in the proximal tubule has been shown to induce
cytokine production by proximal tubule cells (PTCs), possibly mediating
tubulointerstitial injury (1, 33, 47, 48). This has been
proposed as a major mechanism in the progression of kidney disease in
proteinuric states. In multiple myeloma, excessive production and
luminal delivery of light chains (LCs) to PTCs cause increased
endocytosis of LCs via the endocytic receptors cubilin and megalin and
result in eventual degradation within the lysosomes (3,
4). We previously demonstrated that increased endocytosis of
myeloma LCs by human PTCs induces inflammatory cytokine production
through activation of NF-B (38). However, possible
signaling mechanisms mediating these inflammatory responses and,
specifically, the potential role of intracellular signaling pathways
such as MAPKs have not been elucidated in response to LC endocytosis.
The present study was designed to investigate the cellular signaling
mechanisms mediating these responses in cultured human PTCs. For this
purpose, we first determined the phosphorylation of the three major
MAPKs, ERK 1/2, JNK 1/2, and p38, in 1-LC-exposed human
PTC by immunoblotting using phospho-specific antibodies. To evaluate
the functional role of phosphorylation of these MAPKs, we tested the
effects of pharmacological inhibitors of MAPKs, U-0126, an inhibitor of
ERK (11); SP-600125, an inhibitor of JNK (5,
16); SB-203580, an inhibitor of p38 (7, 46); and
curcumin, an inhibitor of the JNK-AP1 pathway (23, 27), on
1-LC-induced IL-6 and MCP-1 production. Our results
suggest that MAPK pathways are involved in LC-induced cytokine responses.
![]() |
MATERIALS AND METHODS |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Isolation and purification of myeloma LC.
Myeloma LCs isolated from the urine of myeloma patients and previously
shown to induce cytokine production through activation of NF-B in
human PTCs were used in these experiments. LCs were isolated and
purified by a slight modification of the method previously reported
from our laboratory (30, 38). Briefly, LCs were
precipitated from urine with ammonium sulfate (55 to 90% saturation
determined empirically), extensively dialyzed against distilled water
and lyophilized. The precipitated LCs were purified by dissolving the
lyophilized desalted crude protein in buffer at pH 6.0, followed by
chromatography on carboxymethyl-Sephadex (C-50; Pharmacia, Piscataway,
NJ). Under these conditions, the LCs were bound to the column,
whereas the contaminants were not. Bound LC was eluted with 0.6 mol/l
of NaCl, redialyzed against distilled water, and lyophilized. The
purity of LCs was confirmed by SDS-PAGE (21) and the
immunological identity reported from the clinical laboratory was
confirmed by Western blotting using goat anti-human
and
-LC antibodies.
Cell cultures. In all experiments, SV40 immortalized human PTCs were used. Grown as a monolayer, these cells show marker brush-border enzymes and have biochemical and morphological characteristics similar to other widely used PTC lines, including LLC-PK1, OK, HK-2, and human PTCs in stable culture (31). Brush-border enzymes and phloridzin-inhibitable glucose transport were similar to other established PTC models. This transformed cell line's response to inflammatory stimuli was extensively compared with parental PTCs and was found similar (14). Cells were routinely grown in DRM-23E medium supplemented with 0.5% (vol:vol) fetal bovine serum in T-75 flasks (Falcon, Becton Dickinson Labware) at 37°C in a humidified atmosphere of 95% air-5% CO2 and refed at intervals of 2 or 3 days. At confluence, the culture medium was aspirated, the cultures were rinsed with HBSS, and the cells were removed by trypsin/ethylene-diamine tetraacetic acid digestion, reseeded into T-75 flasks containing the complete medium, and cultured to confluence.
Preparation of whole cell lysates. Cells planted onto 35-mm sterile tissue culture dishes (Corning Glass Works, Corning, NY) or six-well tissue culture plates were grown at 37°C in serum-free medium in an incubator for 24 h. After each experiment, medium was removed and cells were washed with PBS. The following steps were done on ice: 200 µl of RIPA buffer consisting of 50 mM Tris · HCl (pH 7.4), 1% NP-40 (IGEPAL-CA630), 0.25% Na-deoxycholate, 150 mM NaCl, 1 mM EDTA (EGTA) (pH 8.0), protease inhibitors (aprotinin, leupeptin, and pepstatin, 1 µg/ml each, and freshly added), 1 mM Na3VO4, and 1 mM PMSF (added immediately before use) were added to the dishes. After 10 min of incubation, dishes were scraped with a cell scraper and then lysates were transferred to 1.5-ml microcentrifuge tubes using syringes fitted with 21-gauge needles. Lysates were passed through a 21-gauge needle to shear DNA and centrifuged at 13,000 g for 10 min at 4°C. Finally, supernatants were harvested as whole cell lysates and used in immunoblotting studies.
Protein concentrations were determined in whole cell lysates prepared from PTCs by using Pierce BCA Protein Assay (Rockford, IL).Western blot analysis for MAPKs. Equal amounts of proteins were separated by NuPAGE Bis-Tris gel by using precast gels (10% acrylamide) and a minigel apparatus (Novex). Electrophoresis was performed according to manufacturer's recommendations. Separated proteins were electrophoretically transferred to nitrocellulose membranes for 1 h at 30 V by using a semi-dry blotting apparatus (Novex). Proteins were probed with polyclonal phospho-specific antibodies against ERK 1/2, JNK 1/2, and p38 (1:5,000, 1:2,000, and 1:5,000 dilutions, respectively) by using a Western Breeze Chemiluminescent Kit according to the manufacturer's protocol (Novex). Integrity of phospho-specific antibodies against MAPKs was tested using sorbitol and nerve growth factor-treated PC12 cell extracts provided by the antibody supplier (Promega, Madison, WI). We determined total MAPKs using primary antibodies (1:1,000 dilution, Cell Signaling, Beverly, MA) to confirm equal protein loading in the gels for each experiment. Representative blots from one of at least three separate experiments were selected for illustration.
We examined the effects of four different myeloma LCs (
|
|
|
Effects of pharmacological inhibitors on activation of MAPKs.
To test the effects of MAPK inhibitors, after 24-h serum deprivation,
confluent monolayers of cells were pretreated with the MAPK inhibitors
(U-0126, SP-600125, and SB-203580) for 1 h at 1, 5, and 15 µM
concentrations and then treated with 1.5 mg/ml (50 µM) of
1-LC in the continued presence of inhibitors. These inhibitors are considered selective for their respective pathways by
many investigators (5, 7, 11, 16, 23, 27, 46). After 10 min of exposure, cell lysates were prepared using the method described
above. Blotting studies were performed using primary antibodies
against phosphorylated and total forms of MAPK pathways (Fig. 4,
A-C).
|
Effect of MAPK inhibitors on IL-6 and MCP-1 production.
For MAPK inhibitor experiments, serum-deprived (24 h) cells were
pretreated for 1 h with MAPK inhibitors (Figs.
5-8). Concentrations of the inhibitors (1-15 µM for
U-0126, SP-600125, curcumin, and SB-203580) used in these experiments were
determined from published literature (5, 7, 11, 16, 23, 27,
46) and pilot studies in our laboratory. These concentrations of
inhibitors had negligible effects on basal cytokine production (see
RESULTS). Cell viability was determined by trypan blue
exclusion assays; in all experiments, at least 85% of cells remained
viable (7). After pretreatment with inhibitors, cells were
incubated with 1-LC (1.5 mg/ml, ~50 µM) for 4 h
in the presence and absence of the MAPK inhibitors (Figs. 5-8).
After exposure, culture supernatants were harvested and stored at
70°C for ELISA assays.
|
|
|
|
Measurement of IL-6 and MCP-1 levels by ELISA. IL-6 and MCP-1 were measured in the supernatants using commercial human ELISA kits (Quantikine; R&D Systems) according to the manufacturer's protocol. The sensitivity of the ELISA is 0.7 pg/ml for IL-6 and 5 pg/ml for MCP-1 assays. Cytokine concentrations in the unknown samples were determined by comparison with a standard curve developed with known amounts of recombinant human cytokines provided with the kits. Experiments were conducted in triplicate using 96-well microplates, and results were read in a microplate reader. Cells were trypsinized and counted and expressed as picograms of cytokine per 106 cells. Results were presented as fold-increase over either basal or LC-stimulated responses normalized to 1.
Reagents and antibodies. Cell culture products and all other reagents were obtained from Sigma (St. Louis, MO) unless otherwise specified. Antibodies against active (phosphorylated) ERK 1/2, JNK 1/2, and p38 were purchased from Promega. MAPK inhibitors (U-0126 and SB-203580) were purchased from Calbiochem (San Diego, CA). SP-600125 was purchased from Biomol (Plymouth Meeting, PA). Antibodies against total MAPKs were purchased from Cell Signaling.
Statistical analysis. Results were expressed as means ± SE. Multiple comparisons were made by ANOVA and Bonferroni's multiple-comparison tests. Statistical analyses, curve fitting, and calculations were done using GraphPad Prism, version 3 for Windows NT (1999, GraphPad Software, San Diego, CA). Statistical significance was defined as P < 0.05.
![]() |
RESULTS |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
LCs induce activation of ERK in PTCs.
Four different LCs (1,
2,
3, and
1) at 1.5-mg/ml concentration
induced activation of ERK 1/2 compared with control (Fig. 1). There was
a weaker response to HSA (1.5 mg/ml) also, although this protein did
not elicit cytokine responses in human PTCs (38).
1-LC induces activation of ERK, JNK, and p38 in
PTCs.
Human PTCs exposed to
1-LC (1.5 mg/ml, ~50 µM) for
10-240 min resulted in marked activation of ERK 1/2, JNK 1/2, and
p38. ERK activation was detected as early as 10 min, decreasing but persisting over 4 h (Fig. 2A). The
1-LC-induced phosphorylation of both JNK 1/2 and p38 was
again discernible at 10 min and sustained for up to 4 h, although
phospho-JNK 1/2 bands seemed to fade after 40 min (Fig. 2, B
and C). Blots for total MAPKs remained constant throughout
the duration of the experiments.
Effects of pharmacological inhibitors on activation of MAPKs. We tested the effects of MAPK inhibitors at the concentrations (1, 5, and 15 µM) used in these experiments on respective MAPK pathways. These agents inhibited phospho-MAPKs at the same concentrations demonstrated to inhibit IL-6 and MCP-1 production, although the degree of apparent MAPK inhibition did not always seem proportionate to the degree of inhibition in the cytokine response. These inhibitors had no effect on total MAPKs (Fig. 4, A-C).
MAPK inhibitors suppress 1-LC-induced IL-6 and MCP-1
production.
We tested the effect of the pharmacological inhibitors of ERK, JNK,
JNK-AP-1, and p38 pathways on production of IL-6 and MCP-1 in control
cells and in cells exposed to
1-LC, 1.5 mg/ml for 4 h.
![]() |
DISCUSSION |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Cytokine production in response to filtered serum
proteins has recently attracted increasing attention as a major
mechanism of progression of kidney diseases in proteinuric states
(1, 32, 33, 43, 47, 48). We recently showed that excessive LC endocytosis causes IL-6, MCP-1, and IL-8 production through activation of NF-B in cultured human PTCs and proposed that this may
be an important mechanism of tubulointerstitial disease commonly seen
in multiple myeloma (38). However, the potential role of signaling pathways such as MAPKs in these responses is unknown.
MAPKs are important mediators of cellular stress responses
phosphorylating selected intracellular proteins, including
transcription factors when challenged with a wide variety of stimuli
(12, 37). Three major MAPK families have been identified
in mammalian cells: ERK 1 and 2, also known as p42/44 MAP kinase; JNK,
also known as SAPK 1; and p38 MAP kinase, also known as SAPK 2 (28, 34). They have been shown to be activated as early
responses to a variety of stimuli, including peptide mitogens, growth
factors, oxidants, proinflammatory-inflammatory cytokines, lipid
mediators, complement, albumin, and physical stressors in many cultured
cell systems (8-10, 13, 15, 18, 19, 22, 26, 35, 36, 41,
45). Increased production of inflammatory cytokines through activation of different MAPKs has been described in response to IL-1, TNF-
, and physical pressure in both cultured mesangial and
PTCs (22, 35, 40). Many transcription factors, such as c-Jun, ELK-1, ATF1, ATF2, NF-
B, and cAMP response element binding protein, have been shown to be regulated by MAPK pathways (20, 44). MAPKs could act via the transcription factors
and they could directly or indirectly regulate cytokine gene
transcription (17, 41).
We recently observed that inflammatory cytokine production in response
to excessive LC endocytosis in cultured human PTCs is mediated via
activation of NF-B (38). In the present study, we
demonstrated that LC-induced cytokine responses involve activation of
MAPKs. Among these MAPKs, ERK 1/2 appeared to play the dominant role in
LC-exposed cells. However, all three MAPKs appeared to participate,
suggesting that LC-induced cytokine responses involve complex and
multiple mechanisms.
Our studies provide two lines of evidence supporting these conclusions. First, we found that phosphorylated MAPKs are upregulated in LC-exposed cells. Immunoblotting experiments showed activation of all three MAPKs studied here. The most robust and sustained responses were seen with ERK at exposures as early as 10 min and decreasing over time but persisting as long as 4 h (Fig. 2A). Second, the inhibitors of the three major MAPKs as well as the JNK-AP-1 inhibitor curcumin all resulted in significant inhibition of LC-induced IL-6 and MCP-1 production (Figs. 5-8). Taken together, these two lines of evidence show that MAPKs are involved in LC-induced cytokine production in human PTCs.
Although the ERK pathway appeared to be more prominent than other kinases, all three MAPKs tested here were clearly involved. That all three signaling cascades might participate in cytokine responses is not surprising, because it is well documented that there may be considerable overlap and perhaps "cross talk" among these MAPKs (41). Furthermore, cell stress responses are well known to use multiple effector pathways.
The effects of pharmacological inhibitors of MAPKs should be
interpreted with caution, however. Although many investigators consider
these inhibitors specific for their respective pathways (5, 7,
11, 16, 23, 27, 46), it has been shown that some of these agents
may have either variable or additional effects that may be relevant to
the responses observed here. For example, SB-203580 can directly
inhibit thromboxane synthase and cyclooxygenase-1 and -2 (6,
25). Curcumin, considered a selective AP-1 inhibitor, at higher
concentrations (40-60 µM) has been shown to inhibit TNF-,
phorbol ester-, and hydrogen peroxide-mediated NF-B activation at a
step before I-
B phosphorylation in a myeloid cell line
(39). In another study, curcumin was shown to inhibit AP-1, NF-
B, as well as Egr-1 in cultured endothelial cells
(29). At lower concentrations, i.e., 10 µM, curcumin was
demonstrated to inhibit endogenous VCAM-1 expression in human
microvascular endothelial cells independent of and without an effect on
NF-
B. In this study, antibodies against c-Jun and c-Fos inhibited
NF-
B activation, suggesting an interaction between AP-1 and NF-
B
(2). Although these studies were conducted in different
cell lines and used inhibitors at higher concentrations than used in
our studies, they raise the possibility that some of the
cytokine-blocking effects of these pharmacological inhibitors of MAPKs
may be mediated through other pathways and may involve overlapping
mechanisms. In our experiments, the apparent effects of the MAPK
inhibitors on their respective MAPKs were not always proportionate to
the degree of cytokine inhibition, and this is also consistent with the
possibility that the effects of MAPK inhibitors on cytokine responses
may involve additional mechanisms.
We recently demonstrated that LC-induced cytokine production was
through the activation of NF-B, similar to the observations reported
by investigators attributing such responses to increased protein
endocytosis (1, 32, 33, 48). It is of interest that LC
effects were seen at concentrations as low as 25 µg/ml, concentrations that can easily occur in typical patients with myeloma
and even in proteinuric patients without myeloma (38).
LCs are well documented to undergo vigorous endocytosis in PTCs via the
endocytic receptors cubilin-megalin (3, 4). Other
investigators who demonstrated albumin endocytosis as a proinflammatory
event also proposed that albumin endocytosis is accomplished through
the tandem cubilin-megalin system (42). The interaction
between LC ligand with the endocytic receptors cubilin-megalin suggests
an attractive speculation into how endocytosis can result in activation
of MAPKs and the subsequent or simultaneous activation of nuclear
transcription factors causing increased production of inflammatory
cytokines in PTCs. Whether LC preferentially binds to cubilin and is
endocytosed by its "chaperone" megalin or binds to megalin
directly, the cytoplasmic domain of megalin, which contains NPXY motifs
(42), could easily initiate the required phosphorylation
cascade through tyrosine phosphorylation, progressing via ERK 1/2 and
eventually resulting in phosphorylation of I-B, the penultimate step
in the activation of NF-
B. Our experiments suggested a significant
role for MAPKs in LC-mediated cytokine responses. It is relevant that
MAPKs have been demonstrated to have a key role in endocytosis
(24), lending credence to our thesis that LC endocytosis
activates MAPKs.
Previous studies on the endocytosis-induced cytokines in PTC have
focused almost exclusively on albumin (1, 33, 47, 48).
These studies demonstrated that albumin exposure in various PTC lines
resulted in production of cytokines through activation of NF-B.
Albumin has also been demonstrated by Dixon and Brunskill (10) to stimulate p44/42 in opossum kidney PTCs; however,
whether this results in cytokine production has not been examined. Our observations with myeloma LCs have similarities to these findings but
also differ in fundamental ways. With the use of human PTCs and HSA
even at concentrations exceeding those reported in the literature, we
failed to elicit cytokine responses (38). In the present
study, we did observe activation of ERK by HSA, although this effect
was much weaker compared with LCs. Taken together, our observations on
LCs and HSA and the previously published studies on albumin suggest
that endocytosis of all filtered proteins may have inflammatory
consequences. Our results suggest that LCs may be more potent than
albumin in inducing cytokines in PTCs. Furthermore, LC effects were
observed at very low concentrations (~1 µM) that can occur even in
patients without myeloma, suggesting a potential role of LCs in the
progression of kidney disease in other proteinuric diseases.
This study reveals clues that may improve our understanding of how proteinuria and excessive endocytosis of serum proteins can cause inflammatory responses in PTCs. A comprehensive description of the key steps that start with endocytosis resulting in production of cytokines will require additional experiments. Elucidation of the precise mechanisms of cytokine responses involved in protein endocytosis may open up novel areas probing therapeutic interventions that may be helpful in intervening with the progression of kidney disease in proteinuria.
![]() |
ACKNOWLEDGEMENTS |
---|
These studies were supported by a Merit Review Grant from the Department of Veterans Affairs. Partial support was also provided from developmental funds of the Tulane Cancer Center (research fellowship award to S. Sengul). Parts of this study are presented as an abstract at the 2002 annual meeting of the American Society of Nephrology in Philadelphia, PA.
![]() |
FOOTNOTES |
---|
Present address of S. Sengul: Ankara University Medical School, Division of Nephrology, Ibni Sina Hospital, Ankara, Turkey.
Address for reprint requests and other correspondence: V. Batuman, Nephrology Section, SL-45, Tulane Medical School, 1430 Tulane Ave., New Orleans, LA 70112-2699 (E-mail: vbatuma{at}tulane.edu).
The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
First published February 11, 2003;10.1152/ajprenal.00350.2002
Received 27 September 2002; accepted in final form 4 February 2003.
![]() |
REFERENCES |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
1.
Abbate, M,
Zoja C,
Corna D,
Capitanio M,
Bertani T,
and
Remuzzi G.
In progressive nephropathies, overload of tubular cells with filtered proteins translates glomerular permeability dysfunction into cellular signals of interstitial inflammation.
J Am Soc Nephrol
9:
1213-1224,
1998[Abstract].
2.
Ahmad, M,
Theofanidis P,
and
Medford RM.
Role of activating protein-1 in the regulation of the vascular cell adhesion molecule-1 gene expression by tumor necrosis factor-.
J Biol Chem
273:
4616-4621,
1998
3.
Batuman, V,
and
Guan S.
Receptor-mediated endocytosis of immunoglobulin light chains by renal proximal tubule cells.
Am J Physiol Renal Physiol
272:
F521-F530,
1997
4.
Batuman, V,
Verroust PJ,
Navar GL,
Kaysen JH,
Goda FO,
Campbell WC,
Simon E,
Pontillon F,
Lyles M,
Bruno J,
and
Hammond TG.
Myeloma light chains are ligands for cubilin (gp280).
Am J Physiol Renal Physiol
275:
F246-F254,
1998
5.
Bennett, BL,
Sasaki DT,
Murray BW,
O'Leary EC,
Sakata ST,
Xu W,
Leisten JC,
Motiwala A,
Pierce S,
Satoh Y,
Bhagwat SS,
Manning AM,
and
Anderson DW.
SP600125, an anthrapyrazolone inhibitor of Jun N-terminal kinase.
Proc Natl Acad Sci USA
98:
13681-13686,
2001
6.
Borsch-Haubold, AG,
Pasquet S,
and
Watson SP.
Direct inhibition of cyclooxygenase-1 and -2 by the kinase inhibitors SB 203580 and PD 98059. SB 203580 also inhibits thromboxane synthase.
J Biol Chem
273:
28766-28772,
1998
7.
Carter, AB,
Monick MM,
and
Hunninghake GW.
Both Erk and p38 kinases are necessary for cytokine gene transcription.
Am J Respir Cell Mol Biol
20:
751-758,
1999
8.
Choudhury, GG,
Karamitsos C,
Hernandez J,
Gentilini A,
Bardgette J,
and
Abboud HE.
PI-3-kinase and MAPK regulate mesangial cell proliferation and migration in response to PDGF.
Am J Physiol Renal Physiol
273:
F931-F938,
1997
9.
Cybulsky, AV,
Papillon J,
and
McTavish AJ.
Complement activates phospholipases and protein kinases in glomerular epithelial cells.
Kidney Int
54:
360-372,
1998[ISI][Medline].
10.
Dixon, R,
and
Brunskill NJ.
Albumin stimulates p44/p42 extracellular-signal-regulated mitogen- activated protein kinase in opossum kidney proximal tubular cells.
Clin Sci (Lond)
98:
295-301,
2000[ISI][Medline].
11.
English, JM,
and
Cobb MH.
Pharmacological inhibitors of MAPK pathways.
Trends Pharmacol Sci
23:
40-45,
2002[ISI][Medline].
12.
Fanger, GR,
Gerwins P,
Widmann C,
Jarpe MB,
and
Johnson GL.
MEKKs, GCKs, MLKs, PAKs, TAKs, and tpls: upstream regulators of the c-Jun amino-terminal kinases?
Curr Opin Genet Dev
7:
67-74,
1997[ISI][Medline].
13.
Gaits, F,
Salles JP,
and
Chap H.
Dual effect of lysophosphatidic acid on proliferation of glomerular mesangial cells.
Kidney Int
51:
1022-1027,
1997[ISI][Medline].
14.
Gerritsma, JS,
van Kooten C,
Gerritsen AF,
Mommaas AM,
van Es LA,
and
Daha MR.
Production of inflammatory mediators and cytokine responsiveness of an SV40-transformed human proximal tubular epithelial cell line.
Exp Nephrol
6:
208-216,
1998[ISI][Medline].
15.
Guo, YL,
Baysal K,
Kang B,
Yang LJ,
and
Williamson JR.
Correlation between sustained c-Jun N-terminal protein kinase activation and apoptosis induced by tumor necrosis factor- in rat mesangial cells.
J Biol Chem
273:
4027-4034,
1998
16.
Han, Z,
Boyle DL,
Chang L,
Bennett B,
Karin M,
Yang L,
Manning AM,
and
Firestein GS.
c-Jun N-terminal kinase is required for metalloproteinase expression and joint destruction in inflammatory arthritis.
J Clin Invest
108:
73-81,
2001
17.
Hulleman, E,
Bijvelt JJ,
Verkleij AJ,
Verrips CT,
and
Boonstra J.
Nuclear translocation of mitogen-activated protein kinase p42MAPK during the ongoing cell cycle.
J Cell Physiol
180:
325-333,
1999[ISI][Medline].
18.
Huwiler, A,
Stabel S,
Fabbro D,
and
Pfeilschifter J.
Platelet-derived growth factor and angiotensin II stimulate the mitogen-activated protein kinase cascade in renal mesangial cells: comparison of hypertrophic and hyperplastic agonists.
Biochem J
305:
777-784,
1995[ISI][Medline].
19.
Ingram, AJ,
Ly H,
Thai K,
Kang M,
and
Scholey JW.
Activation of mesangial cell signaling cascades in response to mechanical strain.
Kidney Int
55:
476-485,
1999[ISI][Medline].
20.
Karin, M.
The regulation of AP-1 activity by mitogen-activated protein kinases.
J Biol Chem
270:
16483-16486,
1995
21.
Laemmli, UK.
Cleavage of structural proteins during the assembly of the head of bacteriophage T4.
Nature
227:
680-685,
1970[ISI][Medline].
22.
Leonard, M,
Ryan MP,
Watson AJ,
Schramek H,
and
Healy E.
Role of MAP kinase pathways in mediating IL-6 production in human primary mesangial and proximal tubular cells.
Kidney Int
56:
1366-1377,
1999[ISI][Medline].
23.
Li, WQ,
Dehnade F,
and
Zafarullah M.
Oncostatin M-induced matrix metalloproteinase and tissue inhibitor of metalloproteinase-3 genes expression in chondrocytes requires Janus kinase/STAT signaling pathway.
J Immunol
166:
3491-3498,
2001
24.
McPherson, PS,
Kay BK,
and
Hussain NK.
Signaling on the endocytic pathway.
Traffic
2:
375-384,
2001[ISI][Medline].
25.
Minuz, P,
Gaino S,
Zuliani V,
Tommasoli RM,
Benati D,
Ortolani R,
Zancanaro C,
Berton G,
and
Santonastaso CL.
Functional role of p38 mitogen activated protein kinase in platelet activation induced by a thromboxane A2 analogue and by 8-iso-prostaglandin F2.
Thromb Haemost
87:
888-898,
2002[ISI][Medline].
26.
Mondorf, UF,
Piiper A,
Herrero M,
Bender M,
Scheuermann EH,
and
Geiger H.
Lipoprotein (a) stimulates mitogen activated protein kinase in human mesangial cells.
FEBS Lett
441:
205-208,
1998[ISI][Medline].
27.
Nakayama, K,
Furusu A,
Xu Q,
Konta T,
and
Kitamura M.
Unexpected transcriptional induction of monocyte chemoattractant protein 1 by proteasome inhibition: involvement of the c-Jun N-terminal kinase-activator protein 1 pathway.
J Immunol
167:
1145-1150,
2001
28.
Pearson, G,
Robinson F,
Beers Gibson T,
Xu BE,
Karandikar M,
Berman K,
and
Cobb MH.
Mitogen-activated protein (MAP) kinase pathways: regulation and physiological functions.
Endocr Rev
22:
153-183,
2001
29.
Pendurthi, UR,
Williams JT,
and
Rao LV.
Inhibition of tissue factor gene activation in cultured endothelial cells by curcumin. Suppression of activation of transcription factors Egr-1, AP-1, and NF-B.
Arterioscler Thromb Vasc Biol
17:
3406-3413,
1997
30.
Pote, A,
Zwizinski C,
Simon EE,
Meleg-Smith S,
and
Batuman V.
Cytotoxicity of myeloma light chains in cultured human kidney proximal tubule cells.
Am J Kidney Dis
36:
735-744,
2000[ISI][Medline].
31.
Racusen, LC,
Monteil C,
Sgrignoli A,
Lucskay M,
Marouillat S,
Rhim JG,
and
Morin JP.
Cell lines with extended in vitro growth potential from human renal proximal tubule: characterization, response to inducers, and comparison with established cell lines.
J Lab Clin Med
129:
318-329,
1997[ISI][Medline].
32.
Rangan, GK,
Wang Y,
Tay YC,
and
Harris DC.
Inhibition of nuclear factor-B activation reduces cortical tubulointerstitial injury in proteinuric rats.
Kidney Int
56:
118-134,
1999[ISI][Medline].
33.
Remuzzi, G,
and
Bertani T.
Pathophysiology of progressive nephropathies.
N Engl J Med
339:
1448-1456,
1998
34.
Robinson, MJ,
and
Cobb MH.
Mitogen-activated protein kinase pathways.
Curr Opin Cell Biol
9:
180-186,
1997[ISI][Medline].
35.
Rovin, BH,
Wilmer WA,
Danne M,
Dickerson JA,
Dixon CL,
and
Lu L.
The mitogen-activated protein kinase p38 is necesssary for interleukin 1-induced monocyte chemoattractant protein 1 expression by human mesangial cells.
Cytokine
11:
118-126,
1999[ISI][Medline].
36.
Schramek, H,
Schumacher M,
and
Pfaller W.
Sustained ERK-2 activation in rat glomerular mesangial cells: differential regulation by protein phosphatases.
Am J Physiol Renal Fluid Electrolyte Physiol
271:
F423-F432,
1996
37.
Seger, R,
and
Krebs EG.
The MAPK signaling cascade.
FASEB J
9:
726-735,
1995
38.
Sengul, S,
Zwizinski C,
Simon EE,
Kapasi A,
Singhal PC,
and
Batuman V.
Endocytosis of light chains induces cytokines through activation of NF-B in human proximal tubule cells.
Kidney Int
62:
1977-1988,
2002[ISI][Medline].
39.
Singh, S,
and
Aggarwal BB.
Activation of transcription factor NF-B is suppressed by curcumin (diferuloylmethane).
J Biol Chem
270:
24995-25000,
1995
40.
Suda, T,
Osajima A,
Tamura M,
Kato H,
Iwamoto M,
Ota T,
Kanegae K,
Tanaka H,
Anai H,
Kabashima N,
Okazaki M,
and
Nakashima Y.
Pressure-induced expression of monocyte chemoattractant protein-1 through activation of MAP kinase.
Kidney Int
60:
1705-1715,
2001[ISI][Medline].
41.
Tian, W,
Zhang Z,
and
Cohen DM.
MAPK signaling and the kidney.
Am J Physiol Renal Physiol
279:
F593-F604,
2000
42.
Verroust, PJ,
Birn H,
Nielsen R,
Kozyraki R,
and
Christensen EI.
The tandem endocytic receptors megalin and cubilin are important proteins in renal pathology.
Kidney Int
62:
745-756,
2002[ISI][Medline].
43.
Wang, Y,
Rangan GK,
Tay YC,
and
Harris DC.
Induction of monocyte chemoattractant protein-1 by albumin is mediated by nuclear factor B in proximal tubule cells.
J Am Soc Nephrol
10:
1204-1213,
1999
44.
Wesselborg, S,
Bauer MK,
Vogt M,
Schmitz ML,
and
Schulze-Osthoff K.
Activation of transcription factor NF-B and p38 mitogen-activated protein kinase is mediated by distinct and separate stress effector pathways.
J Biol Chem
272:
12422-12429,
1997
45.
Wilmer, WA,
Tan LC,
Dickerson JA,
Danne M,
and
Rovin BH.
Interleukin-1 induction of mitogen-activated protein kinases in human mesangial cells. Role of oxidation.
J Biol Chem
272:
10877-10881,
1997
46.
Zhang, SL,
Tang SS,
Chen X,
Filep JG,
Ingelfinger JR,
and
Chan JS.
High levels of glucose stimulate angiotensinogen gene expression via the P38 mitogen-activated protein kinase pathway in rat kidney proximal tubular cells.
Endocrinology
141:
4637-4646,
2000
47.
Zoja, C,
Benigni A,
and
Remuzzi G.
Protein overload activates proximal tubular cells to release vasoactive and inflammatory mediators.
Exp Nephrol
7:
420-428,
1999[ISI][Medline].
48.
Zoja, C,
Donadelli R,
Colleoni S,
Figliuzzi M,
Bonazzola S,
Morigi M,
and
Remuzzi G.
Protein overload stimulates RANTES production by proximal tubular cells depending on NF-B activation.
Kidney Int
53:
1608-1615,
1998[ISI][Medline].