PEITC specifically interferes with downstream signaling to SAPK/JNK. HeLa cells were incubated with PEITC at the indicated concentrations for 7 minutes at 37°C. Hyperosmotic shock was induced by addition of sorbitol to a final concentration of 400 mM, and the cells incubated for an additional 20 minutes. Cell lysates were analyzed by immunoblotting with antibodies for phosphorylated forms of the MAPKs as indicated to the right. Duplicate gels were probed with antibodies to each MAPK, to confirm equivalent protein expression. PEITC interferes with the activation of SAPK, but not ERK or p38, in a dose dependent manner.