Inhibition of p38 MAP kinase increases okadaic acid mediated AP-1 expression and DNA binding but has no effect on TRE dependent transcription

By performing in vitro kinase assays we found in papilloma producing 308 mo use keratinocytes that okadaic acid elevated activities of extracellular si gnal-regulated kinase (ERK) 1/2, c-Jun N-terminal kinases (JNKs) and p38 mi togen-activated protein kinases (MAPKs). This okadaic acid mediated activat ion of MAP kinases correlated with increased AP-1 binding to a consensus TP A responsive element (TRE) and elevated TRE dependent transcription. To det ermine the role of p38 MAP kinases in these processes we employed the speci fic p38 MAP kinase inhibitor SB 203580. Using orthophosphate labeling we sh owed a decrease in phosphorylation of MAPK activated protein kinase-2 (MAPK AP-K2) indicating reduced activity of p38 MAPKs utilizing this kinase as su bstrate. In contrast, we found the SB 203580 raised activities of ERK-1/2 a nd JNKs. Electrophoretic mobility shift assays revealed an increase in TRE binding activity in response to SB 203580 most likely resulting from increa sed expression of the major TRE binding components JunD and FosB as indicat ed by Western blot analyses. Increased TRE DNA binding failed to lead to in creased transactivation correlating with the inability of SB 203580 to incr ease phosphorylation of these AP-1 proteins. These data indicate that SB 20 3580 sensitive p38 MAP kinases are not involved in okadaic acid mediated in creases in TRE DNA binding and transactivation.