Okadaic acid, a phosphatase inhibitor, enhances the phorbol ester-induced interleukin-1 beta expression via an AP-1-mediated mechanism.
Protein kinase C (PKC)-activating phorbol esters are known to induce the expression of several genes in monocytic cells. As the effect of serine-threonine kinases, such as PKC, is often counteracted by specific protein phosphatases, we have now examined the role of phosphatases in the regulation of the phorbol ester (PMA)-induced interleukin-1 beta (IL-1 beta) gene expression in the THP-1 monocytic leukaemia cell line. Okadaic acid (OA) is a potent tumour promoter, the function of which is based on its activity to inhibit the serine/threonine specific phosphatases 1 and 2A (PP1 and PP2A, respectively). Thus, it mimicks or potentiates the action of PKC activators in several cell types. Our data demonstrate that alone OA induced a very weak expression of IL-1 beta mRNA, but it strongly enhanced the PMA-induced IL-1 beta expression. To analyse the site of action of OA, the cells were transiently transfected with a chloramphenicol acetyl transferase (CAT)-reporter plasmid containing the AP-1 binding site as the enhancer. Alone, OA was a weak inducer of CAT-activity in these cells, but again it strongly enhanced the PMA-induced response. Similar data were obtained with cells transfected with a reporter plasmid containing the PMA-responsive element (containing a putative AP-1 binding site) of the IL-1 beta gene. Thus, these data indicate that the PMA-induced AP-1 enhancer activity, which is required for the expression of the IL-1 beta gene, is controlled in these cells by PP1 and/or PP2A. As OA did not synergize with PMA in the induction of expression of genes encoding the AP-1 proteins (c-fos, c-jun, junB), it is likely that OA potentiates the AP-1 enhancer activity by its effect on protein phosphorylation.
Hurme
M
M
Department of Bacteriology and Immunology, University of Helsinki, Finland.
Matikainen
S
S
D002460:Cell Line; D004587:Electrophoresis, Agar Gel; D004988:Ethers, Cyclic / Q000494:pharmacology*; D005786:Gene Expression Regulation / Q000187:drug effects / Q000502:physiology*; D006801:Humans; D007375:Interleukin-1 / Q000096:biosynthesis* / Q000235:genetics; D009000:Monocytes / Q000378:metabolism; D019319:Okadaic Acid; D010749:Phosphoprotein Phosphatases / Q000037:antagonists & inhibitors / Q000502:physiology*; D010766:Phosphorylation; D016755:Proto-Oncogene Proteins c-jun / Q000378:metabolism*; D012333:RNA, Messenger / Q000032:analysis; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D014162:Transfection; D014407:Tumor Cells, Cultured
D004988:Ethers, Cyclic; D007375:Interleukin-1; D016755:Proto-Oncogene Proteins c-jun; D012333:RNA, Messenger; D019319:Okadaic Acid; D010749:Phosphoprotein Phosphatases; D013755:Tetradecanoylphorbol Acetate