JS-K–induced apoptosis is mediated via the JNK pathway. (A) JS-K induces phosphorylation of JNK in MM.1S cells. MM.1S cells were exposed to 0.6 μM JS-K for 0 to 4 hours, and then whole-cell lysates were subjected to Western blotting with antiphospho(Thr183/Tyr185)-JNK antibody. Reblotting with anti-JNK antibody confirmed equal loading. Representative Western blots (left panel), and percentage of mean quantitative densitometric values (± SD) from 3 independent experiments (right panel) are shown. *P < .01 compared with 0-hour control. (B) MM.1S cells were cultured with (or without) JS-K (0.6 μM) for 48 hours after 2 hours of preincubation with JNK inhibitor II (0, 10, or 20 μM). Cells were then assayed for apoptosis by Annexin V/PI staining. Data represent mean (± SD) of triplicate experiments. *P < .01 compared with no JNK inhibitor II, JS-K (0.6 μM) control