MK3 is a negative regulator of ERK. (A,D) mRNA expression of PRC1 target gene ATF3 as a function of kinase inhibition (A) or MK3OE (D) in TIG3 cells. (B,C, E, F) (p)ERK (B), (p)P38 (C), H3S28ph (E) and (p)MEK (F) levels in starved and stimulated U2-OS cells in relation to MK function; t (min): time post-stimulation in minutes; *: loading controls for corresponding panels; t+: longer exposure. Samples corresponding to control and experiment (MK3OE or MKi) were always loaded on the same gel to enable direct quantitative analysis (corresponding sections are shown separately; representative experiment shown; quantification pERK profiles: compare Additional file 3: Figure S3B). (G) Mitogen-induced DUSP2 and DUSP5-mRNA in control, MK3OE and MKi TIG3 cells.