Fig. 5. Ras- and Raf-induced alternative splicing depends on MEK activity. (A) LB-17 cells were co-transfected with 2 µg of pETCatEBLucv5 and 2 µg of expression vectors for constitutively active HaRas L61 and Raf-BxB, respectively, or corresponding empty vectors (pRC-CMV or pkRSPA). U0126 (10 µM) was added 3 h after transfection. Cells were harvested 24 h later and luciferase assays were performed. (B and C) ERK and JNK pathway activation was assayed after co-transfection of the Gal-Elk or Gal-Jun luciferase reporter system with 2 µg of expression plasmids for constitutively active HaRas L61, Raf-BxB or a control vector. Inhibitor treatment was performed as described in (A).