Radicicol, a Protein Tyrosine Kinase Inhibitor, Suppresses the Expression of Mitogen-inducible Cyclooxygenase in Macrophages Stimulated with Lipopolysaccharide and in Experimental Glomerulonephritis (∗)

• Published in: The Journal of biological chemistry 1995-03, Vol.270 (10), p.5418-5426
• Main Authors: Chanmugam, Prithiva, Feng, Lili, Liou, Shuenn, Jang, Byeong C., Boudreau, Mary, Yu, Gang, Lee, Jong H., Kwon, Ho J., Beppu, Teruhiko, Yoshida, Minoru, Xia, Yiyang, Wilson, Curtis B., Hwang, Daniel
• Format: Article
• Language: English
• Subjects: Animals; Anti-Inflammatory Agents, Non-Steroidal - pharmacology; Antibodies - toxicity; Antifungal Agents - pharmacology; Basement Membrane - immunology; Blotting, Western; Gene Expression - drug effects; Glomerulonephritis - enzymology; Glyceraldehyde-3-Phosphate Dehydrogenases - biosynthesis; Inflammation; Isoenzymes - biosynthesis; Kidney Glomerulus - drug effects; Kidney Glomerulus - enzymology; Kidney Glomerulus - immunology; Kinetics; Lactones - chemistry; Lactones - isolation & purification; Lactones - pharmacology; Lipopolysaccharides - pharmacology; Macrolides; Macrophages, Alveolar - drug effects; Macrophages, Alveolar - enzymology; Mitogens - pharmacology; Molecular Structure; Prostaglandin-Endoperoxide Synthases - analysis; Prostaglandin-Endoperoxide Synthases - biosynthesis; Protein-Tyrosine Kinases - antagonists & inhibitors; Rats; Rats, Sprague-Dawley; RNA, Messenger - analysis; RNA, Messenger - biosynthesis; Tetradecanoylphorbol Acetate - pharmacology; Time Factors
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.270.10.5418

Two isoforms of cyclooxygenase (COX) have been identified in eukaryotic cells: a constitutively expressed COX-1 and mitogen-inducible COX-2, which is selectively expressed in response to various inflammatory stimuli. Thus, COX-2 instead of COX-1 is implicated to produce prostanoids mediating inflammatory responses. Major efforts have been focused on identifying nonsteroidal anti-inflammatory drugs (NSAIDS) which can selectively inhibit the enzyme activity of COX-2. Such NSAIDS would be more desirable anti-inflammatory agents in comparison to NSAIDS which inhibit both COX-1 and COX-2. Other than glucocorticoids, pharmacological agents which can selectively suppress the expression of COX-2 without affecting that of COX-1 have not been identified. We report here that radicicol, a fungal antibiotic, is a potent protein tyrosine kinase inhibitor, and that it inhibits the expression of COX-2 without affecting COX-1 expression in lipopolysaccharide (LPS)-stimulated macrophages with the IC50 value of 27 nM. Radicicol inhibited tyrosine phosphorylation of p53/56lyn, a Src family tyrosine kinase and one of the major tyrosine-phosphorylated proteins in LPS-stimulated macrophages. Radicicol also inhibited COX-2 expression in vivo in glomeruli of rats with experimental glomerulonephritis induced by the anti-glomerular basement membrane antibodies, in which COX-2 expression is known to be enhanced. The enzyme activity of COX-1 or COX-2 was not affected by radicicol in macrophages. Radicicol also suppressed the COX-2 expression induced by IL-1β in rat smooth muscle cells. Other protein tyrosine kinase inhibitors suppressed the LPS-induced COX-2 expression in macrophages but at much higher concentrations than needed for radicicol. Radicicol did not inhibit the COX-2 expression induced by phorbol 12-myristate 13-acetate in macrophages. These results suggest that the activation of tyrosine-specific protein kinases is the proximal obligatory step in the LPS-induced signal transduction pathway leading to the induction of COX-2 expression in macrophages. The magnitude of the inhibition of COX-2 protein synthesis by radicicol was much greater than that of the steady state levels of COX-2 mRNA. These results suggest that radicicol inhibits COX-2 expression mainly at post-transcriptional steps.