STAT3 phosphorylation in IL-6–dependent and –independent cell lines.

IL-6–dependent cells were cultured continuously in IL-6–containing medium or starved from IL-6 for 10 hours (T1165), 30 hours (T2027), or 48 hours (7TD1 and B9) and restimulated with IL-6 (500 U/mL for T1165 and T2027,100 U/mL for 7TD1 and B9) for the indicated times (A). IL-6–independent cells (SP2/0, MOPC315, 7TD1Ind, and B9Ind) were cultured continuously in medium without IL-6 or were stimulated with IL-6 (100 U/mL) for the indicated times (B). Crude cell lysates were resolved by 10% SDS-PAGE, and phosphorylation of STAT3 was detected by immunoblotting with an anti-phosphorylated STAT3 antibody (STAT3 pY). Blots were stripped and reprobed with anti-STAT3 antibody.