MAPK does not influence CEBPα phosphorylation by GSK3. (A) Recombinant Flag-C/EBPα (6 pmol) was incubated for 60 min with or without p42 MAPK (10 U/ml) and/or GSK3β (2 U/ml) and Mg ATP, as indicated in figure. The reaction was stopped and separated by SDS-PAGE and subjected to Western Blot. (B) AD293 cells were transfected with 10 μg of Flag-C/EBPα, Flag-C/EBPα-AA, or Flag-C/EBPα-S230A prior to 24 h incubation with 10 μM PD98059, SB203580 or DMSO, lysis and Western Blot analysis. A representative immunoblot of two such experiments is given.