Inhibition of lipopolysaccharide-induced nitric oxide synthesis by nicotine through S6K1-p42/44 MAPK pathway and STAT3 (Ser 727) phosphorylation in Raw 264.7 cells.
Lipopolysaccharide (LPS) has been known to produce inflammatory modulators such as tumor necrosis factor alpha (TNF-alpha) or nitric oxide (NO). In this study, we examined the effects of nicotine on LPS enhanced NO synthesis and inducible nitric oxide synthase (iNOS) expression in macrophages. LPS-induced NO synthesis and iNOS expression were significantly decreased by nicotine. To investigate the signaling mechanism of nicotine induced suppression of NO synthesis and iNOS expression induced by LPS, we focused on the possible roles of p42/44 MAPK, S6K1, and signal transducers and activators of transcription 3 (STAT3) signaling. LPS is known to activate p42/44 MAPK and S6K1, which in turn activates STAT3 to induce inflammatory regulators. Pretreatment of cells with nicotine blocked LPS-induced p42/44 MAPK and S6K1 as well as iNOS promoter activity. Furthermore, we found that LPS-induced phosphorylation of STAT3 at serine 727 is mediated by S6K1-p42/44 MAPK pathway, and this STAT3 phosphorylation was also blocked by nicotine. We also found that downregulation of STAT3 using STAT3 siRNA resulted in suppression of the NO synthesis and iNOS expression. Taken together, our results suggest that nicotine inhibits LPS-induced NO synthesis through suppression of S6K1-p42/44 MAPK pathway and phosphorylation of STAT3 in Raw 264.7 cells.
Park
Shin-Young
SY
Department of Biochemistry and Molecular Biology, College of Medicine, Hanyang University, 17 Haengdang-Dong Sungdong-Gu, Seoul 133-791, Republic of Korea.
Baik
Yong Hae
YH
Cho
Ju Hwan
JH
Kim
Sung
S
Lee
Ki-Sung
KS
Han
Joong-Soo
JS
D000818:Animals; D002460:Cell Line; D004789:Enzyme Activation / Q000187:drug effects; D008070:Lipopolysaccharides / Q000037:antagonists & inhibitors*; D008264:Macrophages; D051379:Mice; D019950:Mitogen-Activated Protein Kinase 1 / Q000502:physiology*; D048052:Mitogen-Activated Protein Kinase 3 / Q000502:physiology*; D009538:Nicotine / Q000494:pharmacology*; D009569:Nitric Oxide / Q000096:biosynthesis*; D052247:Nitric Oxide Synthase Type II / Q000096:biosynthesis; D010766:Phosphorylation; D038744:Ribosomal Protein S6 Kinases, 90-kDa / Q000502:physiology*; D050796:STAT3 Transcription Factor / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects; D015533:Transcriptional Activation
D008070:Lipopolysaccharides; D050796:STAT3 Transcription Factor; C494087:Stat3 protein, mouse; D009569:Nitric Oxide; D009538:Nicotine; D052247:Nitric Oxide Synthase Type II; C496317:Nos2 protein, mouse; D038744:Ribosomal Protein S6 Kinases, 90-kDa; C512964:Rps6ka1 protein, mouse; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3