Radicicol, a protein tyrosine kinase inhibitor, suppresses the expression of mitogen-inducible cyclooxygenase in macrophages stimulated with lipopolysaccharide and in experimental glomerulonephritis.
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. Radiciciol also suppressed the COX-2 expression induced by IL-1 beta 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.
Chanmugam
P
P
Pennington Biomedical Research Center, Louisiana State University, Baton Rouge 70808.
Feng
L
L
Liou
S
S
Jang
B C
BC
Boudreau
M
M
Yu
G
G
Lee
J H
JH
Kwon
H J
HJ
Beppu
T
T
Yoshida
M
M
D000818:Animals; D000894:Anti-Inflammatory Agents, Non-Steroidal / Q000494:pharmacology; D000906:Antibodies / Q000633:toxicity; D000935:Antifungal Agents / Q000494:pharmacology*; D001485:Basement Membrane / Q000276:immunology; D015153:Blotting, Western; D015870:Gene Expression / Q000187:drug effects*; D005921:Glomerulonephritis / Q000201:enzymology*; D005987:Glyceraldehyde-3-Phosphate Dehydrogenases / Q000096:biosynthesis; D007249:Inflammation; D007527:Isoenzymes / Q000096:biosynthesis; D007678:Kidney Glomerulus / Q000187:drug effects / Q000201:enzymology* / Q000276:immunology; D007700:Kinetics; D007783:Lactones / Q000737:chemistry / Q000302:isolation & purification / Q000494:pharmacology*; D008070:Lipopolysaccharides / Q000494:pharmacology*; D018942:Macrolides; D016676:Macrophages, Alveolar / Q000187:drug effects / Q000201:enzymology*; D008934:Mitogens / Q000494:pharmacology; D015394:Molecular Structure; D011451:Prostaglandin-Endoperoxide Synthases / Q000032:analysis / Q000096:biosynthesis; D011505:Protein-Tyrosine Kinases / Q000037:antagonists & inhibitors*; D012333:RNA, Messenger / Q000032:analysis / Q000096:biosynthesis; D051381:Rats; D017207:Rats, Sprague-Dawley; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D013997:Time Factors
D000894:Anti-Inflammatory Agents, Non-Steroidal; D000906:Antibodies; D000935:Antifungal Agents; D007527:Isoenzymes; D007783:Lactones; D008070:Lipopolysaccharides; D018942:Macrolides; D008934:Mitogens; D012333:RNA, Messenger; D011451:Prostaglandin-Endoperoxide Synthases; D005987:Glyceraldehyde-3-Phosphate Dehydrogenases; D011505:Protein-Tyrosine Kinases; C035359:monorden; D013755:Tetradecanoylphorbol Acetate