Suppression of IL-8 gene expression by radicicol is mediated through the inhibition of ERK1/2 and p38 signaling and negative regulation of NF-kappa Band AP-1

We show that radicicol, an anti-fungal agent, inhibits interleukin-8 (IL-8) production by the human monocyte line THP-1 in response to phorbol-12-myri state-13- acetate/lipopolysaccharide (PMA/LPS). IL-8 is a potent chemokine and needs for an optimal immune response-such as inflammation by activation of neutrophils. The decrease in PMA/LPS-induced IL-8 mRNA expression was d emonstrated by quantitative reverse transcription-polymerase chain reaction (RT-PCR). Since the promoter in IL-8 gene contains binding motifs for NF-k appaB, AP-1, and NF-IL-6, which appear to be important in IL-8 induction, t he effects of radicicol on the activation of these transcription factors we re examined. Treatment of radicicol to THP-I cells produced a strong inhibi tion of NF-kappaB and AP-1, while NF-IL6 was not significantly affected by radicicol. Western blot analysis showed that radicicol inhibited the phosph orylation and phosphotransferase activities of extracellular signal-regulat ed kinases I and 2 (ERK1/2) and p38. PD98059 and SB203580, known as a speci fic inhibitor of MEK1 and p38 kinase, respectively, inhibited IL-8 gene exp ression showing that both of the kinase pathways are involved in IL-8 regul ation in human monocytes, Collectively, this series of experiments indicate s that radicicol inhibits IL-8 gene expression by blocking ERK1/2 and p38 s ignaling. (C) 2001 Elsevier Science BN. All rights reserved.