EFFECTS OF THE INHIBITION OF P38 RK MAP KINASE ON INDUCTION OF 5 FOS AND JUN GENES BY DIVERSE STIMULI/

The ERK, JNK/SAPK and p38/RK MAP kinase subtypes are differentially ac tivated by physiological, pharmacological and stress stimuli; all thre e subtypes are implicated in immediate-early (IF) gene induction by th ese agents, Here, we have asked whether inhibition of a single MAP kin ase subtype under these conditions would generally alter induction of several IF genes in a similar way or whether this would differentially up-and down-regulate particular IF genes, an issue which bears on the question of whether individual MAP kinases ape strictly targeted to s pecific IE genes, or whether they might catalyse phosphorylation event s that affect several IF genes in the same way, SB 203580, an inhibito r of p38/RK, has been used to analyse the role of this kinase in the i nduction of five IF genes (c-fos, fosB, c-jun, junB and junD) under di verse conditions of stimulation, Bn C3H 10T1/2 cells, p38/RK and its d ownstream kinase MAPKAP K-2 are activated by all stimuli used with the exception of TPA, The specificity of SB 203580 as a p38/RK inhibitor in these cells is demonstrated; it does not affect ERKs or JNK/SAPKs b ut does result in a small increase in the activity of the upstream kin ase MKK6, the principal p38/RK activator in these cells. We find that inhibition of p38/RK under these conditions produces general effects o n all five IE genes as a group in three ways, First, induction of all five genes in response to okadaic acid or tumour necrosis factor-alpha (TNF-alpha) is not significantly altered by SB 203580, Second, in cel ls stimulated with anisomycin or U.V. radiation, SB 203580 potently in hibits all of the induced IE genes. Finally, SB 203580 enhances induct ion of all five IE genes in EGF-treated cells; these enhanced mRNA lev els are not due to stabilisation of labile mRNA transcripts, The signi ficance of these results to current thinking on the relationship betwe en distinct MAP kinase subtypes and specific IF genes is discussed.