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Pyridinylimidazole Compound SB 203580 Inhibits the Activity but Not the Activation of p38 Mitogen-Activated Protein Kinase

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Abstract

p38 MAPK is a Ser/Thr protein kinase activated by various inflammatory cytokines and a variety of stress stimuli. It is involved in many physiological processes, including the production of inflammatory cytokines. We have previously reported the design and synthesis of a series of pyridinylimidazole compounds that are selective inhibitors of p38 MAPK. These compounds, exemplified by SB 203580, are exceptionally effective in cell-based assays, including the inhibition of inflammatory cytokine production. SB 203580 is widely used as a tool to dissect the role of p38 MAPK in various physiological processes. It has previously been established that SB 203580 acts primarily to block the catalytic activity of p38 MAPK. However, it has been suggested that in cells, the compounds could also inhibit p38 MAPK activation by virtue of their ability to bind to the inactive enzyme. We undertook careful studies to definitively demonstrate that treatment with SB 203580 had no effect on Thr180 and Tyr182 phosphorylation, and hence activation of p38 in vivo. SB 203580, however, potently inhibited the activity of p38 MAPK as demonstrated by the inhibition of the activation of MAPKAP K2, a specific physiological substrate of p38 MAPK. This was observed regardless of stimuli or cell type. Identical results were obtained when the p38 MAPK cascade was partially reconstituted in vitro. Thus, our data clearly indicate that SB 203580 specifically inhibits the activity of p38 MAPK but not its activation by upstream MAPKK.

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    Abbreviations used: ERK; extracellular signal regulated kinase, MAPK; mitogen-activated protein kinase, MAPKAP K2; MAPK-activated protein kinase 2, MKK; MAP kinase kinase, ATF2; activating transcription factor 2, GST; glutathione S-transferase, TNF; tumor necrosis factor, IL-1; interleukin-1, LPS; lipopolysaccharide, MBP; myelin basic protein, SDS; sodium dodecyl sulfate, PAGE; polyacrylamide gel electrophoresis

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    To whom correspondence should be addressed at Department of Bone and Cartilage Biology, UW 2109, SmithKline Beecham Pharmaceuticals, P.O. Box 1539, King of Prussia, PA 19406-0939. Fax: 610-270-5598. E-mail: [email protected].

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