Signaling pathway for 2,3,7,8-tetrachlorodibenzo-p-dioxin-induced TNF-alpha production in differentiated THP-1 human macrophages.
2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), a prototypic halogenated aromatic hydrocarbon (HAH), is known as one of the most potent toxicants. At least a part of its toxic effects appears to be derived from its ability to induce TNF-alpha production. However, the signaling pathway of TCDD that leads to TNF-alpha expression has not been elucidated. In this study, we investigated the signaling mechanism of TCDD-induced TNF-alpha expression in PMA-differentiated THP-1 macrophages. TCDD induced both mRNA and protein expression of TNF-alpha in a dose- and time-dependent manner. Alpha-naphthoflavone (NF), an aryl hydrocarbon receptor (AhR) inhibitor, prevented the TCDD-induced expression of TNF-alpha at both mRNA and protein levels. Genistein, a protein tyrosine kinase (PTK) inhibitor, and PD153035, an EGFR inhibitor, also blocked the increase of TNF-alpha expression by TCDD, indicating the role of EGFR in TCDD-induced TNF-alpha expression. On the other hand, PP2, a c-Src specific inhibitor, did not affect TCDD-induced TNF-alpha expression. EGFR phosphorylation was detected as early as 5 min after TCDD treatment. TCDD-induced EGFR activation was AhR-dependent since co-treatment with alpha-NF prevented it. ERK was found to be a downstream effector of EGFR activation in the signaling pathway leading to TNF-alpha production after TCDD stimulation. Activation of ERK was observed from 30 min after TCDD treatment. PD98059, an inhibitor of the MEK-ERK pathway, completely prevented the TNF-alpha mRNA and protein expression induced by TCDD, whereas inhibitors of JNK and p38 MAPK had no effect. PD153035, an EGFR inhibitor, as well as alpha-NF significantly reduced ERK phosphorylation, suggesting that ERK activation by TCDD was mediated by both EGFR and AhR. These results indicate that TNF-alpha production by TCDD in differentiated THP-1 macrophages is AhR-dependent and involves activation of EGFR and ERK, but not c-Src, JNK, nor p38 MAPK. A signaling pathway is proposed where TCDD induces sequential activation of AhR, EGFR and ERK, leading to the increased expression of TNF-alpha.
Cheon
HyeonJoo
H
Department of Biochemistry, Korean Institute of Molecular Medicine and Nutrition, Korea University College of Medicine, Seoul 136-705, Korea.
Woo
Young-Seok
YS
Lee
Ji Young
JY
Kim
Hee Sook
HS
Kim
Hyun Jin
HJ
Cho
Sungwon
S
Won
Nam Hee
NH
Sohn
Jeongwon
J
D000818:Animals; D001571:Benzoflavones / Q000494:pharmacology; D002454:Cell Differentiation; D045744:Cell Line, Tumor; D004789:Enzyme Activation; D066246:ErbB Receptors / Q000037:antagonists & inhibitors / Q000378:metabolism; D019833:Genistein / Q000494:pharmacology; D015386:Hazardous Substances / Q000633:toxicity*; D006801:Humans; D020935:MAP Kinase Signaling System / Q000187:drug effects / Q000502:physiology; D008264:Macrophages / Q000378:metabolism*; D051379:Mice; D010766:Phosphorylation; D000072317:Polychlorinated Dibenzodioxins / Q000633:toxicity*; D011743:Pyrimidines / Q000494:pharmacology; D011799:Quinazolines / Q000494:pharmacology; D012333:RNA, Messenger / Q000378:metabolism; D018336:Receptors, Aryl Hydrocarbon / Q000037:antagonists & inhibitors; D015398:Signal Transduction; D014409:Tumor Necrosis Factor-alpha / Q000096:biosynthesis*; D019061:src-Family Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism
C412373:AG 1879; D001571:Benzoflavones; D015386:Hazardous Substances; D000072317:Polychlorinated Dibenzodioxins; D011743:Pyrimidines; D011799:Quinazolines; D012333:RNA, Messenger; D018336:Receptors, Aryl Hydrocarbon; D014409:Tumor Necrosis Factor-alpha; C011512:alpha-naphthoflavone; D019833:Genistein; D066246:ErbB Receptors; D019061:src-Family Kinases; C088860:4-((3-bromophenyl)amino)-6,7-dimethoxyquinazoline