ABSTRACT
Tristetraprolin (TTP) is an acute phase protein, and its expression is rapidly up-regulated by inflammatory signals, such as lipopolysaccharide (LPS) and cytokines. TTP regulates gene expression by governing the mRNA stability of its target genes, which include cytokines and growth factors. MAP kinase phosphatase-1 (MKP-1) is a nuclear phosphatase that inhibits p38 mitogen-activated protein kinase (MAPK) signaling. This study investigated the role of MKP-1 in TTP expression in A549 human lung epithelial cells, THP-1 human macrophages, J774 mouse macrophages, and primary mouse macrophages. TTP and MKP-1 expression was increased by cytokines or LPS. Silencing of MKP-1 by siRNA enhanced TTP expression in response to LPS, and LPS-induced TTP expression was increased in macrophages from MKP-1 (-/-) mice as compared with that in macrophages from wild-type animals. The inhibition of p38 MAPK by SB202190 reduced TTP expression. In conclusion, MKP-1 suppressed TTP expression by inhibiting p38 MAPK pathway.
Subject(s)
Dual Specificity Phosphatase 1/metabolism , MAP Kinase Signaling System , Macrophages/metabolism , Tristetraprolin/biosynthesis , Animals , Cell Line , Cell Line, Tumor , Cytokines/pharmacology , Down-Regulation , Dual Specificity Phosphatase 1/genetics , Gene Expression Regulation , Humans , Imidazoles/pharmacology , Lipopolysaccharides/immunology , MAP Kinase Signaling System/drug effects , Mice , Mice, Inbred C57BL , Mice, Knockout , Pyridines/pharmacology , RNA Interference , RNA, Messenger/genetics , RNA, Messenger/metabolism , RNA, Small Interfering , p38 Mitogen-Activated Protein Kinases/metabolismABSTRACT
Dual specificity phosphatase 1 (DUSP1) dephosphorylates and, hence, regulates the activity of MAP kinases. The present study investigated the effect of DUSP1 on inflammatory gene expression and on the development of carrageenan-induced inflammation. It was found that DUSP1 expression was increased by LPS, and the down-regulation of DUSP1 by siRNA enhanced the phosphorylation of p38 MAPK, while JNK phosphorylation was not affected in murine macrophages. LPS-induced interleukin (IL)-6, tumor-necrosis factor (TNF) and cyclooxygenase-2 (COX2) expression were enhanced in bone marrow-derived macrophages (BMMs) from DUSP1(-/-) mice as compared to those from wild-type mice. In addition, down-regulation of DUSP1 by siRNA enhanced IL-6, TNF and COX2 expression in J774 macrophages, while p38 MAPK inhibitors SB202190 and BIRB 796 inhibited the expression of those inflammatory factors. In vivo, the intensity of the carrageenan-induced paw edema reaction was increased in DUSP1(-/-) mice as compared to the wild-type animals. In conclusion, DUSP1 is an important negative regulator of the acute inflammatory response by limiting p38 MAPK, and compounds which enhance DUSP1 expression or activity may hold a promise as anti-inflammatory drugs.
Subject(s)
Dual Specificity Phosphatase 1/immunology , Gene Expression Regulation/immunology , Inflammation/immunology , Signal Transduction/immunology , p38 Mitogen-Activated Protein Kinases/immunology , Animals , Blotting, Western , Carrageenan/toxicity , Cells, Cultured , Dual Specificity Phosphatase 1/genetics , Dual Specificity Phosphatase 1/metabolism , Enzyme-Linked Immunosorbent Assay , Gene Expression , Inflammation/genetics , Inflammation/metabolism , Irritants/toxicity , Macrophages/immunology , Macrophages/metabolism , Mice , Mice, Knockout , RNA, Small Interfering , Reverse Transcriptase Polymerase Chain Reaction , Signal Transduction/genetics , p38 Mitogen-Activated Protein Kinases/genetics , p38 Mitogen-Activated Protein Kinases/metabolismABSTRACT
The role of dual specificity phosphatase 1 (DUSP1) in inducible nitric oxide synthase (iNOS) expression in A549 human pulmonary epithelial cells, J774 mouse macrophages and primary mouse bone marrow-derived macrophages (BMMs) was investigated. iNOS expression was induced by a cytokine mixture (TNF, IFNγ and IL-1ß) in A549 cells and by LPS in J774 cells, and it was inhibited by p38 MAPK inhibitors SB202190 and BIRB 796. Stimulation with cytokine mixture or LPS enhanced also DUSP1 expression. Down-regulation of DUSP1 by siRNA increased p38 MAPK phosphorylation and iNOS expression in A549 and J774 cells. In addition, LPS-induced iNOS expression was enhanced in BMMs from DUSP1((-/-)) mice as compared to that in BMMs from wild-type mice. The results indicate that DUSP1 suppresses iNOS expression by limiting p38 MAPK activity in human and mouse cells. Compounds that enhance DUSP1 expression or modulate its function may be beneficial in diseases complicated with increased iNOS-mediated NO production.
