TNF- stimulates p38 MAPK-dependent CREB phosphorylation. (A) U937 cells were treated with SB203580 or vehicle for 20 minutes and then stimulated with TNF- (10 μg/mL) for the indicated times. Whole-cell lysates were separated by SDS-PAGE and immunoblot analysis to detect phospho-CREB (top) was performed and reprobed to detect CREB (bottom). (B) Cells were treated with SB203580 (1 μmol/L) or vehicle alone for 20 minutes and stimulated with either TNF- (10 μg/mL; T) for 5 minutes or forskolin (40 μmol/L) for 10 minutes.