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Regulation by p38 MAPK: Involvement of NF-
B with Implications for Therapy in Rheumatoid Arthritis1
Kennedy Institute of Rheumatology Division, Imperial College School of Medicine Hammersmith, London, United Kingdom
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Abstract |
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is a key factor in a variety of inflammatory diseases. This study examines the role of p38 MAPK in the regulation of TNF- in primary human cells relevant to inflammation, e.g., macrophages and rheumatoid synovial cells. Using a dominant negative variant (D168A) of p38 MAPK and a kinase inhibitor, SB203580, we confirm in primary human macrophages that p38 MAPK regulates TNF- production using a posttranscriptional mechanism requiring the 3' untranslated region of the gene. However, in LPS-activated primary human macrophages we also detect a second previously unidentified mechanism, the p38 MAPK modulation of TNF- transcription. This is mediated through p38 MAPK regulation of NF-
B. Interestingly this mechanism was not observed in rheumatoid synovial cells. Importantly however, the dominant negative mutant of p38 MAPK, but not SB203580 was effective at inhibiting spontaneous TNF- production in these ex vivo rheumatoid synovial cell cultures. These data indicate there are potential major differences in the role of p38 MAPK in inflammatory signaling that have a bearing on the use of this kinase as a target for therapy. These results indicate despite disappointing results with p38 MAPK inhibitors in the clinic, this kinase is a valid target in rheumatoid disease. |
Introduction |
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function has demonstrated an essential role for this cytokine in the pathophysiology of rheumatoid arthritis and other autoinflammatory diseases (1, 2). However, the cost and inconvenience of using biologicals has lead to considerable effort being directed to finding orally available, small m.w. inhibitors of TNF- expression. As the major TNF--producing cells in inflammation are macrophages, there has been considerable interest in the signal transduction mechanisms that regulate TNF- production, with the hope of identifying suitable "drug-prone" targets such as kinases (3, 4). However, despite considerable effort few signaling molecules have been validated as being involved in this process with NF-B probably being the best described (5, 6, 7, 8). Other signaling molecules implicated in regulating TNF- expression are the family of MAPKs particularly p38 MAPK (9).
Originally described as an LPS-activated kinase (10) the relevance of p38 MAPK to TNF- production was demonstrated by the discovery of pyridinyl imidazole-based inhibitors (e.g., SB203580 (9)). Initial studies with these inhibitors indicated that p38 MAPK was exclusively involved in the translational control of TNF- expression (9, 11), a view supported by more recent studies (12). Also, mice defective in the expression of MAPK-activated protein kinase-2, an immediate substrate of p38 MAPK, have a profound defect in translation of the TNF- mRNA (13). In contrast other studies have shown that p38 MAPK controls TNF- mRNA stability (14, 15) possibly by inhibiting the deadenylation process (16). It is unclear why such discrepancies exist between studies, but a contributing factor could be the transformed nature of the myeloid cell lines often used in these experiments (e.g., THP-1 (9), RAW264.7 (15)). Another possibility is that SB203580 may inhibit the related p54 JNK (17) as well as the phosphoinositide-dependent kinase 1 and 2, a part of the PI3K cascade (18), at higher concentrations (low micromolecular range). However, regardless of whether p38 MAPK regulates mRNA stability or translation, the mechanism involved appears to require the AU rich elements (ARE)7 found in 3' untranslated regions (3'UTR) (19, 20, 21, 22). p38 MAPK also regulates several transcription factors including activating transcription factor-2 (23), myocyte enhancer factor 2C (24), C/EBP homologous protein 1 (25), and also NF-B (26). A recent study has suggested that p38 MAPK regulates NF-B via MAPK and stress-activated protein kinase (SAPK)-1 that also requires p42/p44 Erk for activation (27). MAPK and SAPK-1 in turn phosphorylate serine 276 of the p65 NF-B subunit. Alternately, p38 MAPK has been proposed to regulate NF-B indirectly by regulating the access to DNA through histone H3 phosphorylation (28). In contrast, p38 MAPK has also been shown to inhibit NF-B activation (29, 30) although it is unclear how such conflicting mechanisms might coexist. Although NF-B can be required for TNF- expression (7, 8), there are no data showing that p38 MAPK regulates TNF- transcription.
Given the importance of p38 MAPK to regulating TNF- expression, it is disappointing that inhibitors of this kinase have not reached the clinic for the treatment of inflammatory disease such as rheumatoid arthritis. To investigate possible factors that may ultimately influence p38 MAPK as a target for treatment we have studied the role of this kinase in regulating TNF- expression in systems highly relevant to disease, i.e., primary human macrophages, rheumatoid arthritis fibroblasts, and synovium. Because SB203580 has other cellular targets, we have also used a dominant negative kinase defective variant p38 D168A. We show for the first time that p38 MAPK does regulate TNF- production in rheumatoid arthritis synovium, although SB203580 itself is a poor inhibitor in these circumstances. Moreover, inhibition of p38 MAPK results in a reduction of TNF- mRNA in human macrophages. Furthermore, the kinase regulates TNF- expression by a dual mechanism, in part by the 3'UTR as previously suggested but also via the 5' promoter region, putatively through NF-B. However the regulation of NF-B by p38 MAPK is not universal, occurring in macrophages but not synovial fibroblasts or rheumatoid arthritis synovial cultures. These observations could have a major bearing on our approach to p38 MAPK as a target for inhibitors of TNF- expression and anti-inflammatory drugs in general.
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Materials and Methods |
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The human embryonic kidney 293 cell lines were from BD Clontech (Palo Alto, CA). These cells were cultured in DMEM supplemented with 10% FCS (Sigma-Aldrich, Poole, U.K.). Primary human monocytes were isolated from single-donor buffy coats obtained from the North London Blood Transfusion Centre (Colindale, London, U.K.) by Ficoll-Hypaque centrifugation followed by centrifugal elutriation using a J6 elutriator (Beckman Coulter, High Wycombe, U.K.). Monocyte purity was assessed by flow cytometry and was routinely higher than 90%. Cells were cultured in RPMI 1640 (BioWhittaker, Wokingham, U.K.) supplemented with 5% FCS. For macrophage differentiation, monocytes were cultured with macrophage CSF (M-CSF) at 100 ng/ml (kindly provided by Dr. G. Larsen, Genetics Institute, Boston, MA) for 48 h before infection. Synovium from patients with rheumatoid arthritis undergoing joint surgery were dissociated by cutting into small pieces and were digested with collagenase and DNase (31). The total cell mixture was cultured at 37°C in RPMI 1640 medium with 25 mM HEPES and 2 mM L-glutamine, supplemented with 5% heat-inactivated FBS. Cells were stimulated with 10 ng/ml LPS (Sigma-Aldrich) purified through phenol/chloroform extraction. SB203580 (catalog no. 559389), PD98059 (catalog no. 513001), and proteasome inhibitor I (PSI; catalog no. 539160) were from Calbiochem (Nottingham, U.K.).
Production of recombinant adenoviruses
Recombinant, replication-deficient adenoviral constructs were prepared using the AdEasy system, previously described (32). cDNAs encoding wild-type p38 MAPK and kinase-deficient p38 MAPK with a glutamate to alanine mutation at residue 168 (D168A), kindly provided by Dr. P. Young (SmithKline Beecham, King of Prussia, PA) were subcloned into AdTrackCMV transfer vector using KpnI and EcoRV. p38 MAPK-containing transfer vectors were inserted into the AdEasy viral backbone vector by bacterial recombination in the Escherichia coli strain BJ5183, as previously described (32). Recombined vectors were propagated in human embryonic kidney 293 cells and viral stocks prepared by ultracentrifugation through two caesium chloride gradients. Titers of viral stocks were determined by plaque assay and viral aliquots were stored at –70°C. AdvGFP adenovirus was prepared according to this protocol using AdTrackGFP with no insert. pAdTrack-TNF-Luc-3'UTR and pAdTrack-TNF-Luc were generated, as previously described (33). The NF-B luciferase reporter adenovirus (Adv NF-B-Luc) contains four tandem copies of the enhancer element located upstream of the firefly luciferase gene (34). This adenovirus was provided by Dr. P. B. McCray, Jr. (University of Iowa, Iowa City, IA) and is a modification of the pNF-B reporter vector (BD Biosciences/Clontech, Palo Alto, CA).
Viral infection of M-CSF-treated monocytes, rheumatoid arthritis synovial cells and fibroblast-like synoviocytes
Macrophages susceptible to virus infection were generated by culturing freshly elutriated monocytes for 48 h with 100 ng/ml M-CSF; these cells were then infected, as previously described (7). Synovium from rheumatoid arthritis patients was infected as previously described (7). Human fibroblast-like synoviocytes were cultured and infected as previously described (35).
ELISA
Following stimulation of human macrophages or culture of human tissue cells, supernatants were harvested. Concentrations of TNF-, IL-1R antagonist, and IL-10 (BD Pharmingen, San Diego, CA) were determined by ELISA, following the manufacturer’s instruction. Absorbance read and analyzed at 450 nM on a spectrophotometric ELISA plate reader (Labsystems Multiskan Biochromic) using the Ascent version 2.4.2 software program. Results are expressed as the mean concentration of triplicate cultures ± SD.
Immunoprecipitation and MAPK-activated protein kinase-2 assays
A total of 2 x 106 cells were lysed in 200 µl of lysis buffer, as previously described (17) and protein concentration of lysates were determined by Bradford assay. Lysates of equivalent protein content were incubated with 0.1 mg/ml anti-MAPK-activated protein kinase-2 Ab (Upstate Biotechnology, Lake Placid, NY) and 15 µl of protein G-Sepharose at 4°C overnight. Immunoprecipitates were washed twice with RIPA buffer and twice with kinase assay buffer and then resuspended in 20 µl of assay buffer containing recombinant hsp27 (Bioquote, York, U.K.) at a concentration of 0.1 mg/ml. Kinase reactions were initiated by the addition of a further 20 µl of assay buffer containing ATP at 20 µM and [
-32P]ATP at 0.25 µCi/ml. Reactions were terminated by the addition of 20 µl of 4x gel sample buffer after 20 min. Samples were separated by SDS-PAGE (12.5%) and phosphorylated substrates were visualized by autoradiography and Phosphorimager analysis of dried gels.
Western blot analysis
Western blotting for p38 MAPK, phospho-JNK/SAPK, and phospho-p42/p44 ERK was performed, as previously described (36). Ab for p38 MAPK (SAK7) was from Prof. J. Saklatvala (Kennedy Institute, London, U.K.) and phosphospecific Abs were from New England Biolabs (Hitchin, Herts, U.K.). IB and p65 phosphoserine 536 were obtained from Santa Cruz Biotechnology (Santa Cruz, CA) and Cell Signaling Technology (Beverly, MA), respectively.
Luciferase assays
After LPS stimulation, cells were washed once in PBS and lysed with 100 µl of CAT lysis buffer (0.65%(v/v) of Nonidet P-40, 10 mM Tris-HCl pH 8, 0.1 mM EDTA pH 8, 150 mM NaCl). Cell lysate (50 µl) were transferred into the well of a luminometer cuvette strip containing 120 µl of luciferase assay buffer (25 mM Tris-phosphate pH 7.8, 8 mM MgCl2, 1 mM EDTA, 1%(v/v) Triton X-100, 1%(v/v) glycerol, 1 mM DTT, 0.5 mM ATP). Luciferase activity was measured with a LabSystem Luminometer by dispensing 30 µl of luciferin (Bright-Glo luciferase assay system; Promega, Madison, WI) per assay point. Cell lysates were assayed for protein concentration by bicinchoninic acid assay and luciferase activity adjusted accordingly.
Extraction of cytoplasmic and nuclear cellular fractions
Following stimulation, cells were scraped into ice-cold PBS and lysed in hypotonic lysis buffer (0.125% Nonidet P-40, 5 mM HEPES (pH 7.9), 10 mM KCl, 1.5 mM MgCl2), and cells harvested by centrifugation at 1000 x g for 5 min. Supernatant, containing cytoplasmic fraction, was aspirated and nuclei resuspended in hypertonic lysis buffer (5 mM HEPES (pH 7.9), 25% glycerol, 500 mM NaCl, 1.5 mM MgCl2, 0.2 mM EDTA) for 2 h with constant agitation. Cellular debris was removed by centrifugation at 13,000 x g for 20 min.
NF-B EMSA
NF-B DNA binding activities were determined by incubating 5 µg of nuclear protein of each extract with [-32P]ATP-labeled double-stranded NF-B consensus oligonucleotide (Promega), followed by resolution on a 5% (w/v) nondenaturing polyacrylamide gel. Gels were dried on to filter paper and retarded DNA; protein complexes were visualized by autoradiography.
Northern blot analysis and hybridization
Total RNA was isolated using the RNeasy kit (Qiagen, Hilden, Germany). A total of 2 µg of total RNA was resolved by electrophoresis on a 1.5% (w/v) agarose denaturing formaldehyde gel. The gel was transferred to Hybond N membrane by capillary blotting in 20x SSC and RNA UV fixed to membrane. RNA was detected using a 495-bp TNF--specific coding region cDNA probe (courtesy J. Dean, Kennedy Institute, London, U.K.) labeled with [-32P]CTP. Hybridization was conducted overnight in UltraHyb (Ambion, Austin, TX) at 42°C. The membrane was washed in a series of SSC/SDS buffers and visualized using Fuji FLA-2000 phosphor imager.
Taqman RT-PCR
M-CSF-treated monocytes were plated at 5 x 105 cells/well in 24-well plates and infected as previously described. Total RNA was extracted using RNeasy kit (Qiagen) according to the manufacturer’s instructions. All semiquantitative RT-PCR was performed using an ABI PRISM 7700 Sequence Detection System, Taqman One Step RT-PCR reagent, and TNF-, IL-6, and GAPDH predeveloped assay reagents (Applied Biosystems, Foster City, CA and PerkinElmer, Wellesley, MA). ABI PRISM 7700 Sequence detector was programmed for the reverse transcription step of 30 min at 48°C followed by a 5 min deactivation step at 95°C. Subsequent PCR amplification consisted of 40 cycles of denaturation at 94°C for 15 s and annealing/extension at 60°C for 60 s. The cycle number at which the amplification plot crosses a fixed threshold above baseline is defined as threshold cycle (Ct). To control variation in mRNA concentration, all results were normalized to the housekeeping gene, GAPDH. Relative quantitation was performed using the comparative 
Ct method according to the manufacturer’s instructions.
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Results |
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production either induced by LPS or released spontaneously in rheumatoid arthritis synovium
Adenoviral vectors encoding p38 MAPK and the kinase-deficient variant D168A (Advp38WT and Advp38D168A, respectively) were generated. Infection of human macrophages or rheumatoid arthritis synovial cultures with these adenoviruses at a multiplicity of infection (MOI) of 100 resulted in >90% infection (data not shown) as has been observed with other adenoviral vectors (7, 8). Infection of cells with either virus resulted in the over-expression of p38 MAPK as determined by immunoblotting (Fig. 1A), whereas a control virus (AdvGFP) had no effect. p38D168A acted as a dominant negative inhibiting the LPS-induced activation of the p38 MAPK substrate kinase, MAPK-activated protein kinase-2, in macrophages by 
90% as measured in immunokinase assays using hsp27 as a substrate (Fig. 1, B and C). The inhibitory effect of p38D168A appeared to be specific, as phospho-Western blot analysis of the related MAPKs, p42/p44/ERK and p54/JNK demonstrated no inhibition of LPS-induced activation of these kinases (data not shown).
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production at 18 h poststimulation. This reached a plateau of 80% at MOI of 100 (Fig. 2A). Similar results were achieved at 4 h post-LPS stimulation (data not shown). In contrast to the effect on TNF- expression; p38D168A did not inhibit the production of the anti-inflammatory factors, IL-10 or IL-1R antagonist (Fig. 2B). Advp38D168A was also effective at blocking the spontaneous production of TNF- (67% p < 0.002) by rheumatoid arthritis synovium (Fig. 2C). Again, p38D168A had no effect on IL-10 or IL-1R antagonist production (Fig. 2D), indicating that the effects seen are not due to any toxicity of inhibiting p38 MAPK or viral infection. In comparison, studies with SB203580 showed that the drug was much less effective on rheumatoid arthritis synovium compared with LPS-stimulated macrophages. In rheumatoid arthritis synovial cultures the IC50 of >1000 nM was 100-fold higher than that found for LPS-activated macrophages (IC50 > 10 nM; Fig. 2, E and F). The possible reasons for this will be considered in Discussion.
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mRNA production
Previous studies with SB203580 have disagreed on whether inhibition of p38 MAPK resulted in suppression of TNF- mRNA expression (9, 17); this issue was now revisited with the Advp38D168A. TNF- mRNA expression was induced in human primary macrophages by LPS and this was inhibited to a similar degree (30%) by 1 µM SB203580 and Advp38D168A (Fig. 3, A and B). The effect of SB203580 was similar to that seen by Dean et al. (17) in human monocytes. These data would indicate that p38 MAPK does have some role in regulating TNF- expression before translation. However, the effect of blocking p38 MAPK was less than that seen with PSI (80%), which is a proteasome inhibitor that is an effective blocker of NF-B activation. As the regulation of TNF- mRNA has been a controversial area we confirmed our results by a second technique, semiquantitative Taqman RT-PCR (Fig. 3C). The results were nearly identical with those obtained by Northern blotting confirming that p38 MAPK does regulate TNF- mRNA levels in macrophages.
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reporter gene activity is mediated by both the TNF- 5' promoter and the 3'UTR region
Studies in murine cells with SB203580 have indicated that p38 MAPK regulation of TNF- was mediated only via the 3'UTR of the mRNA, which contains the ARE (15, 37). To determine whether TNF- was regulated in human primary macrophages in a similar manner we used TNF- promoter-driven luciferase reporter genes with (p5'3'UTR) or without (p5' only) the 3'UTR encoded into adenovirus (reporter virus) (33, 38, 39). As expected, expression of p38D168A or SB203580 inhibited the LPS-stimulated activation of the p5'3'UTR reporter gene expression by 60–70% (Fig. 4). Surprisingly, both drug and dominant negative also caused a significant inhibition of LPS-induced reporter gene activity in the absence of the 3'UTR (Fig. 4). The level of inhibition (30–50%) was similar to the effect seen on TNF- mRNA (Fig. 3B). These data would suggest that p38 MAPK has some regulatory role on the TNF- promoter but the significant increase in the inhibition seen in the presence of 3'UTR indicates that both elements are regulated by the kinase.
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B activation
The mechanism by which p38 MAPK regulates TNF- by the 3'UTR has been previously recognized and studied. In contrast, a regulatory mechanism involving the TNF- promoter region has not been previously observed. Although p38 MAPK has been shown to putatively regulate several transcription factors, this effect has not been related to regulation of any actual genes. Of these transcription factors only NF-B (26, 27) is known to regulate TNF- expression (4). Neither SB203580 nor expression of p38D168A was found to exert any effect in human primary macrophages on the LPS-induced degradation of IB (Fig. 5A), or NF-B DNA binding activity as measured by EMSA (Fig. 5B). However, inhibition of p38 MAPK by either approach resulted in a 65% inhibition of NF-B-induced transcription as shown by an NF-B-luciferase reporter gene (Fig. 5C). Inhibition of NF-B via p38 MAPK was not quite as effective as over-expression of IB (88% inhibition) or using an inhibitor of IB degradation (PSI; 95% inhibition) (Fig. 5C). These data indicate that the kinase was involved in modulating the transactivating function of NF-B. Next we addressed the question of whether the p38 MAPK regulation of NF-B would account for the effects seen on the 5' promoter of the TNF- gene. We therefore investigated whether inhibiting p38 MAPK would have any additional effect over PSI (NF-B inhibitor). As seen in Fig. 4D, p38D168A did not significantly inhibit 5' promoter but did have an effect on construct containing the 3'UTR in the presence of PSI. Indicating that p38 MAPK regulates the 5' promoter via NF-B.
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B depends on cell type
The regulation of NF-B by p38 MAPK has not been a widely reported phenomenon and in HeLa and Jurkat cells we found that SB203580 failed to inhibit TNF-induced NF-B-induced reporter gene activity (data not shown). Our studies on LPS were broadened to establish whether the role of p38 MAPK might be cell type- or stimuli-specific. LPS induction of the NF-B reporter gene in primary human rheumatoid arthritis synovial-derived fibroblasts was insensitive to SB203580 or p38D168A but still effectively inhibited by PSI, IB or a dominant negative version of IB kinase 2 as expected (Fig. 6A). This was not only found for LPS stimulation but similar results were obtained from TNF- and IL-1-stimulated cells (data not shown).
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B activation in rheumatoid arthritis synovium
Because there are differences in the role of p38 MAPK in NF-B function depending on cell type and possible stimuli, we investigated whether the kinase has a role in NF-B activation in rheumatoid arthritis synovium where the stimulus is unknown. Infection of rheumatoid arthritis culture with NF-B reporter virus resulted in constitutive activation of NF-B as expected (Fig. 6B). However, this activation was not affected by SB203580 or p38D168A. The activation of the NF-B reporter gene was inhibited by PSI although less effectively than in other cells.
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Discussion |
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expression by p38 MAPK in human macrophages and rheumatoid arthritis synovial cells. Two approaches were used; the inhibitor SB203580 and an adenovirus encoding a kinase dead mutant of p38 MAPK that acts as dominant negative. This study confirmed that p38 MAPK regulates TNF- in LPS-activated human macrophages via the TNF- 3'UTR. In addition, we observed that p38 MAPK also regulated TNF- transcription through NF-B. To our knowledge this is the first time that such mechanism has been observed. However, we also showed that the regulation of NF-B by p38 MAPK is cell type-dependent as this was not seen in rheumatoid arthritis synovium or LPS-activated primary synovial fibroblasts.
Inhibiting the activity of p38 MAPK resulted in 30–50% reduction in TNF- mRNA. This observation correlated with the reduction in TNF- 5' promoter reporter construct activity in the presence of p38 MAPK inhibitors. This study also showed in human primary macrophages that p38 MAPK regulates TNF- expression through the 3'UTR, as previously demonstrated with murine cells (40). Kontoyiannis et al. (12) found that SB203580 is ineffective in mice deficient in the ARE regions of the TNF- 3'UTR. This observation differs from our results in human macrophages, however as their study also showed no inhibitory effect of SB203580 on TNF- mRNA expression in the wild-type mice controls there are clearly differences between this model and our cell system. In addition, studies by others have shown an effect of this drug on mRNA expression (15, 17, 41). This disparity could be accounted for in part by differences between the regulation of TNF- between murine and human systems (42).
The regulation of LPS-induced NF-B by p38 MAPK provided a mechanism for the transcriptional control of TNF- as this transcription factor is required for TNF- expression (7). The data also suggest that NF-B accounted for all the inhibitory effect on transcription of blocking p38 MAPK. However there is the caveat that the NF-B inhibitor, PSI, used in our studies could share targets other than NF-B with the inhibitors of p38 MAPK. The observation that p38 MAPK regulates NF-B-induced transcription is in agreement with previous studies (26, 43). How p38 MAPK controls NF-B driven transcription is unclear but prior studies have suggested both direct mechanisms, via the phosphorylation of the p65 subunit (27) or indirect mechanisms, involving the phosphorylation of histone H3 to uncover NF-B sites (28). As blocking p38 MAPK produced a more potent inhibition of the simple NF-B consensus site reporter gene than that seen on 5' TNF- promoter or TNF- mRNA, we need to examine the more highly complex nature of the promoter region. There are five potential NF-B sites in the TNF- promoter (42) and the regulation of these sites, or their role in TNF- expression, may not all require p38 MAPK activity. Alternately, p38 MAPK may have confounding effects on other elements in the 5' promoter that ameliorate the inhibition of NF-B. Unraveling these questions will be the subject of further studies.
Another important observation of this study is that a role for p38 MAPK in the activation of NF-B is not a universal event. We previously found no role for p38 MAPK in the TNF-induced activation of NF-B in the Jurkat T cell line (our unpublished observation). In primary human synovial fibroblasts, p38 MAPK was not required for NF-B activation even when induced by LPS. This observation has antecedents as we have found differences in signaling mechanisms leading to NF-B, with IB kinase 2 being required for LPS-induced NF-B in human primary fibroblasts and HUVECs but not macrophages (44). Whether the two observations are directly linked or just indications of differences in mechanism is unknown but the results again emphasize the diversity of signaling mechanisms that can exist between different cell systems and help to explain why the regulation of NF-B by p38 MAPK has not been a more widely observed event. It interesting to note that others have claimed that p38 MAPK is involved in the inhibition of NF-B activation (29, 30) indicating kinase may have multiple roles in NF-B function depending on cell type and stimulus.
This study also shows that p38 MAPK would be an effective target for blocking TNF- production in human rheumatoid arthritis synovium. However is interesting to note that SB203580 is not effective in this system, unlike p38 MAPK dominant negative. These latter observations in rheumatoid arthritis synovium and fibroblasts may have some bearing on the present problems p38 MAPK inhibitors have faced in clinical trials. It is unclear why the drug was ineffective but a possibility is that unlike the simple cell systems, SB203580 is rapidly metabolized by rheumatoid arthritis tissue. Another explanation could lie in the ability of the drug to inhibit the PI3K pathway via phosphoinositide-dependent kinase 1 and 2 (18). The PI3K pathway negatively regulates TNF- production in rheumatoid arthritis tissue (45), thus SB203580 could have simultaneous opposing effects in this model. These data may explain why although many years have passed since the observation of the effect of pyridinyl imidazoles on p38 MAPK, no clinically effective anti-inflammatory drug has yet been developed from these molecules. Interestingly, blocking p38 MAPK did not inhibit the production of anti-inflammatory molecules, i.e., IL-10 or IL-1R antagonist in rheumatoid arthritis tissue.
In summary, we have investigated the role of p38 MAPK in TNF- expression by human macrophages induced by LPS and spontaneously in rheumatoid arthritis. We have shown that p38 MAPK is likely to regulate transcription of TNF- mRNA via NF-B in addition to any effects on posttranscriptional mechanisms in primary human macrophages. The data also showed that the regulation of NF-B by p38 MAPK is cell-type dependent and this may have a consequence for the anti-inflammatory efficacy of inhibitors of p38 MAPK. However, even in the absence of regulation of NF-B by the kinase in human synovial tissue, inhibition was still effective in blocking TNF-. Overall our study, although demonstrating that p38 MAPK is an important target for TNF- blockade, also reveals that there is still much to learn about how this kinase functions in different tissues, the results of which may modulate our approach to generating useful inhibitors.
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Acknowledgments |
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B luciferase adenoviral construct. |
Footnotes |
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1 This work was supported by the Arthritis Research Campaign and Wyeth. A.D. was a recipient of a European Union Marie Curie fellowship. 
2 Current address: University of California San Francisco, Stein Clinical Research, 9500 Gilman Drive, La Jolla, CA 92093-0663.
3 Current address: University of California San Francisco, Cancer Center, 2340 Sutter Street, Box 0128, San Francisco, CA 94143-0128.
4 Current address: Institute of Cancer Research, Chester Beatty Laboratories, 237 Fulham Road, SW3 6JB London, U.K.
5 Current address: Laboratoire de Chimie Biologique, Unité Mixte de Recherche 8576 du, Centre National de Recherche Scientifique, Université des Sciences et Technologies de Lille, F-59655 Villeneuve d’Ascq, France.
6 Address correspondence and reprint requests to Prof. Brian M. J. Foxwell, Kennedy Institute of Rheumatology, 1 Aspenlea Road, Hammersmith, London W6 8LH, U.K.
7 Abbreviations used in this paper: ARE, AU rich element; SAPK, stress-activated protein kinase; M-CSF, macrophage CSF; PSI, proteasome inhibitor I; MOI, multiplicity of infection; UTR, untranslated regions.
Received for publication June 9, 2004. Accepted for publication September 17, 2004.
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References |
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