A food-born heterocyclic amine, 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP), suppresses tumor necrosis factor-alpha expression in lipoteichoic acid-stimulated RAW 264.7 cells.
2-Amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP), a heterocyclic amine with strong carcinogenic and mutagenic potential, is created abundantly in the overcooking of meat and fish. Carcinogenic toxicants are often implicated in immunosuppression, where cancer cells are not easily eliminated by the host immune system. Here, we investigated the effect of PhIP on tumor necrosis factor-alpha (TNF-alpha) expression by murine macrophage-like cells (RAW 264.7) stimulated with lipoteichoic acid (LTA), a major virulence factor of Gram-positive bacteria. Upon exposure to LTA purified from Staphylococcus aureus, TNF-alpha expression was substantially induced, whereas pretreatment with PhIP significantly inhibited LTA-induced TNF-alpha expression. LTA is known to activate Toll-like receptor 2 (TLR2) and NF-kappaB, resulting in TNF-alpha expression. Interestingly, PhIP did not interfere with LTA-binding to TLR2, its stimulation of TLR2, or the DNA-binding activity of NF-kappaB. However, treatment with actinomycin D facilitated the PhIP-induced attenuation of TNF-alpha mRNA expression, implying that PhIP might decrease TNF-alpha mRNA stability rather than its biosynthesis. Furthermore, Western blot analysis demonstrated that PhIP reduced the phosphorylation of ERK1/2 and JNK but not p38 kinase in LTA-stimulated cells. The addition of a protein kinase C (PKC) activator, phorbol 12-myristate 13-acetate, rescued PhIP-inhibited TNF-alpha expression in LTA-stimulated cells. These results suggest that PhIP downregulates TNF-alpha expression in LTA-stimulated macrophages by decreasing TNF-alpha mRNA stability and signaling pathways related to PKC, ERK1/2, and JNK activation.
Department of Oral Microbiology & Immunology, Dental Research Institute and BK21 Program, School of Dentistry, Seoul National University, 28 Yongon-Dong, Chongno-Gu, Seoul 110-749, Republic of Korea.
Jintaek
J
Im
Hyung Shim
HS
Choi
Sun Kyung
SK
Kim
Sang Su
SS
Woo
Young Hee
YH
Ryu
Seok-Seong
SS
Kang
Cheol-Heui
CH
Yun
Seung Hyun
SH
Han
D000818:Animals; D015153:Blotting, Western; D002273:Carcinogens / Q000494:pharmacology*; D049109:Cell Proliferation / Q000187:drug effects; D002478:Cells, Cultured; D024202:Electrophoretic Mobility Shift Assay; D006094:Gram-Positive Bacteria; D007093:Imidazoles / Q000494:pharmacology*; D008070:Lipopolysaccharides / Q000494:pharmacology*; D048670:MAP Kinase Kinase 4 / Q000378:metabolism; D008264:Macrophages / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism; D048052:Mitogen-Activated Protein Kinase 3 / Q000378:metabolism; D016328:NF-kappa B / Q000235:genetics / Q000378:metabolism; D010766:Phosphorylation / Q000187:drug effects; D011493:Protein Kinase C / Q000378:metabolism; D020871:RNA Stability / Q000187:drug effects; D051381:Rats; D015398:Signal Transduction / Q000187:drug effects*; D013211:Staphylococcus aureus; D013682:Teichoic Acids / Q000494:pharmacology*; D051195:Toll-Like Receptor 2 / Q000378:metabolism; D014409:Tumor Necrosis Factor-alpha / Q000037:antagonists & inhibitors* / Q000235:genetics / Q000378:metabolism; D048051:p38 Mitogen-Activated Protein Kinases / Q000378:metabolism
D002273:Carcinogens; D007093:Imidazoles; D008070:Lipopolysaccharides; D016328:NF-kappa B; D013682:Teichoic Acids; D051195:Toll-Like Receptor 2; D014409:Tumor Necrosis Factor-alpha; C009900:lipoteichoic acid; C049584:2-amino-1-methyl-6-phenylimidazo(4,5-b)pyridine; D011493:Protein Kinase C; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D048051:p38 Mitogen-Activated Protein Kinases; D048670:MAP Kinase Kinase 4