Jak2/Stat3 pathway regulated the expression of IL-6 in cooperation with other IL-6 downstream pathways. (A-F) Pharmacological inhibition of Jak2/Stat3, PI3-K/Akt, MEK/Erk and NF-κB pathways decreased the secretion of IL-6 in drug resistant cancer cells. Of the six drug resistant cancer cells used in this experiment, four were KB-derived, (A) to (D), respectively: KB-CPT100 is resistant to camptothecin; KB-TAX50 to paclitaxel, KB-VIN10 to vincristine and KB-7D to etoposide. The other two were MCF-7-derived multidrug resistant MCF-7/ADR cells (E) and A549-derived paclitaxel resistant A549-T12 cells (F). All cells were seeded for 24 hours and then treated with AG490 (40 μM), LY294002 (20 μM), U0126 (5 μM), BAY11-7082 (20 μM), or medium alone for 1, 3, 8, or 24 hours. The culture supernatants were collected at the indicated time points and IL-6 secretion was measured by ELISA. The graphs (A-F) represent the results as mean ± SEM. Student's t test: *p < 0.05, **p < 0.01, and ***p < 0.001. For a clearer demonstration, statistical significances are shown for the 24-hour time points only.