Lipopolysaccharide Down-Regulates the Leukotriene C4 Synthase Gene in the Monocyte-Like Cell Line, THP-1

Abstract

We studied the effects of LPS on cysteinyl leukotriene (LT) synthesis and LTC4 synthase expression in mononuclear phagocytes. Conditioning of the monocyte-like cell line, THP-1, with LPS for 7 days resulted in significantly decreased ionophore-stimulated LTC4 release. The putative LPS receptor, Toll-like receptor 4, was expressed in THP-1 cells. LPS down-regulated LTC4 synthase mRNA in THP-1 cells in a dose- and time-dependent manner, with down-regulation observed as early as 4 h. Conditioning of actinomycin D-treated cells with LPS resulted in no change in the rate of LTC4 synthase mRNA decay. LPS treatment of THP-1 cells, transiently transfected with a LTC4 synthase promoter (1.35 kb)-reporter construct, decreased promoter activity. Neutralization of TNF-α and inhibition of mitogen-activated protein kinase kinase/extracellular signal-regulated kinase did not inhibit the effect of LPS. Treatment of cells with a Toll-like receptor 4-blocking Ab and an inhibitor of NF-κB activation resulted in inhibition of the LPS effect, while activation of NF-κB and p50/p65 overexpression down-regulated the LTC4 synthase gene. LPS down-regulates cysteinyl LT release and LTC4 synthase gene expression in mononuclear phagocytes by an NF-κB-mediated mechanism.