Tristetraprolin Mediates Anti-inflammatory Effects of Nicotine in Lipopolysaccharide-stimulated Macrophages

Abstract

Nicotine inhibits the release of TNF-␣ from macrophage through activation of STAT3. Tristetraprolin (TTP) is known to destabilize pro-inflammatory transcripts containing AU-rich elements (ARE) in 3-untranslated region (3-UTR). Here we show that in LPS-stimulated human macrophages the anti-inflammatory action of nicotine is mediated by TTP. Nicotine induced activation of STAT3 enhanced STAT3 binding to the TTP promoter, increased TTP promoter activity, and increased TTP expression resulting in the suppression of LPS-stimulated TNF-␣ production. Overexpression of a dominant negative mutant of STAT3 (R382W) or down-regulation of STAT3 by siRNA abolished nicotine-induced TTP expression and suppression of LPS-stimulated TNF-␣ production. Nicotine enhanced the decay of TNF-␣ mRNA and decreased luciferase expression of a TNF-␣ 3-UTR reporter plasmid in U937 cells. However, siRNA to TTP abrogated these effects of nicotine. In this experiment, we are reporting for the first time the involvement of TTP in the cholinergic anti-inflammatory cascade consisting of nicotine-STAT3-TTP-dampening inflammation.The cholinergic nervous system controls inflammation response (1, 2). Acetylcholine and nicotine inhibit the production of pro-inflammatory cytokines from endotoxin-stimulated macrophages through a ␣7 nicotinic acetylcholine receptor subunit (␣7nAChR)-dependent mechanism (3-6). The antiinflammatory effects of ␣7nAChR activation are mediated by the activation of the Jak2 and STAT3 (7). STAT3 is a negative regulator of the inflammatory response (8, 9). Nicotine, the prototypical ␣7nAChR agonist, fails to inhibit TNF production in macrophages overexpressing STAT3 with decreased DNA binding capacity (7), suggesting that DNA binding ability of STAT3 is important for its regulatory activity. Consistent with that finding, missense mutants of STAT3 that exhibit reduced DNA binding ability have been found to be associated with Hyper-IgE syndrome and showed dominant-negative effects when co-expressed with wild-type STAT3 (10, 11). However, the precise mechanism by which ␣7nAChR-activated STAT3 inhibits inflammatory response remains unclear.The inflammatory response has been reported to be modulated by the post-transcriptional control (12, 13). The posttranscriptional control of inflammatory transcripts is strongly dependent on AU-rich element (ARE) 4 -mediated mechanisms (14 -16). The destabilizing function of AREs is believed to be regulated by ARE-binding proteins (17). Tristetraprolin (TTP) is an ARE-binding protein that promotes degradation of a number of inflammatory mediators including TNF-␣, GM-CSF, IL-2, IL-3, CCL2, CCL3, iNOS,. TTPknock-out mice develop severe inflammatory arthritis, autoimmune dysfunction, and myeloid hyperplasia, demonstrating the importance of TTP in limiting the inflammatory response (25).Here we provide evidence that nicotine stimulates TTP production, thereby mediating the anti-inflammatory effect of nicotine in U937 cells. Further, we show that nicotine-activated STAT3 directly binds to the promoter r...

IL-6 blockade by monoclonal antibodies inhibits apolipoprotein (a) expression and lipoprotein (a) synthesis in humans

“…E: One representative EMSA out of at least n = 3 independent experiments using oligonucleotides being complementary to IL-6-RE 6 of the LPA promoter (left panel) and using oligonucleotides in which the specifi c STAT3 binding sequence (CTGGGA) of IL-6-RE 6 is mutated (right panel). The STAT3 supershift antibody used specifi cally blocks the DNA binding domain resulting in disappearance of the STAT3 shift [also see ( 36 )]. In summary, the data obtained in the present study suggest that IL-6 blockade by monoclonal antibodies might be a promising future therapeutic approach to treat elevated serum Lp(a) concentrations and to reduced CVD risk in affected patients and might therefore be a convenient alternative to lipid apheresis.…”

Tristetraprolin: a novel mediator of the anticancer properties of resveratrol

“…Upregulation of TTP is a new method of cancer prevention (Griseri et al, 2011;Kim et al, 2012). TTP expression can be regulated through NF-kB, p38MAPK, STATs and other signaling pathways Joe et al, 2011). Resveratrol has been confirmed to have effective actions on these signaling pathways (Bhardwaj et al, 2007).…”

“…It has been shown that TTP expression can be regulated through NF-kB, p38MAPK, STATs, and other signaling pathways Joe et al, 2011). Resveratrol has been confirmed to play effective roles in the same signaling pathways (Bhardwaj et al, 2007).…”

“…We conducted the RNA interference experiments using the method described by Joe et al (2011). TTP siRNA, 5'-UCGCCACC CCAAGUA CAAATT-3' (cis) and 5'-CUCUGCCACAAGUUCUACCTT-3' (trans), as well as the control siRNA, which is not homologous with any known human genes, were synthesized by Shanghai Biological Engineering company.…”

Tristetraprolin Down-Regulates IL-23 Expression in Colon Cancer Cells

“…However, LPS stimulation does not enhance the TTP-mediated degradation of ARE-containing mRNA because it also activates p38 MAPK, which can phosphorylate and inactivate TTP (Chrestensen et al, 2004;Stoecklin et al, 2004). Stimulation with IFN-γ (Sauer et al, 2006), IL-10 (Schaljo et al, 2009) or nicotine (Joe et al, 2011) has been reported to induce TTP expression but not p38 MAPK activity and thus these agents increase the induction of mRNA decay by TTP. IFN-γ has been reported to increase both the level and the activity of TTP and enhance the TTPmediated degradation of IL-23 mRNA in macrophages (Qian et al, 2011).…”