Rac activates MRTF partially through PAK and p38. (A) pSMA-Luc/pRL-TK reporters were cotransfected with 0.5 μg CA-Rac and 2 μg empty vector (control) or DN constructs as indicated. Luciferase assays were performed 48 h later. (B) SMA promoter activation upon 1 μM Jasplakinolide treatment (24 h, Jaspla) was determined in control or SB203580 pretreated (30 min) samples. (C) Cells were transfected with CA-Rac (0.5 μg, 48 h) along with empty vector (Non) or DN-PAK. Where indicated, cells were treated with SB203850 30 min prior to transfection. Cells were doubly stained for MRTF (red) and Myc (green). (D) MRTF localization (cytoplasmic: Cp, homogeneous: Ho, and nuclear: Nu) was quantified.