Abstract
Four MAP kinase pathways are currently believed to be activated in LPS stimulated macrophages: the ERK, JNK/SAPK, p38 and BMK/ERK5 pathways. We have evaluated the effect of each MAP kinase pathway and the combinational effect of these MAP kinase pathways on TNF gene expression. By co-expressing dominant active mutants of different MAP kinase activators with a TNF reporter gene, we have demonstrated that activation of a signal MAP kinase pathway produces only a modest effect on TNF gene expression. Interestingly, a dramatic co-operative effect on TNF gene expression was observed when all of the four MAP kinase pathways were activated. We have shown that this MAP kinase-induced TNF gene expression is not mediated by known cis-elements such as Egr-1, CRE, kB, AP-1, or AP-2, but by, as yet unidentified, MAP kinase responsive elements in a 100 bp region immediately upstream of the transcription initiation site. In addition to their participation in the transcriptional control of TNF gene expression, activation of MAP kinases regulates TNF by overcoming the repressive effect of the AU-rich element (ARE) located in the 3′untranslated region. Thus, MAP kinase pathways co-ordinate with each other to regulate TNF gene expression at multiple levels.