Inhibition of p38 MAPK phosphorylation by sphingosine 1-phosphate (S1P). A, Western blotting was used to assess total proteins in chondrocytes isolated 5 minutes after treatment with 3 μM S1P and 10 ng/ml interleukin-1β (IL-1β). The binding of antibodies against phosphorylated (p) and unphosphorylated kinases and transcription factors is visualized. Representative results from 1 of 3 samples are shown. B, Chondrocytes were treated with 10 ng/ml IL-1β along with 50 μM U0126 (UO; inhibitor of ERK-1/2), 30 μM PD169316 (PD; inhibitor of p38 MAPK), or 20 μM SP600125 (SP; inhibitor of JNK) for 3 hours. Expression of inducible nitric oxide synthase (iNOS) mRNA was quantified by real-time reverse transcription–polymerase chain reaction. Results are the mean ± SEM arbitrary units, normalized to the values for the housekeeping genes, in 3 samples. ∗ = P < 0.05; ∗∗ = P < 0.01 versus chondrocytes treated with IL-1β alone. C, Phosphorylated and total p38 MAPK from total proteins was assessed by Western blotting in chondrocytes isolated 5 minutes after treatment with 3 μM S1P, 10 ng/ml IL-1β, and 10 μM JTE-013. Representative results from 1 of 3 samples are shown.