Exp Mol Med.  2007 Aug;39(4):524-534.

Signaling pathway for 2,3,7,8-tetrachlorodibenzo- p-dioxin-induced TNF-alpha production in differentiated THP-1 human macrophages

• Cheon HJ
• Woo YS
• Lee JY
• Kim HS
• Kim HJ
• Cho S
• Won NH
• Sohn J

Abstract

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.

Keyword

extracellular signal-regulated MAP kinases; macrophages; receptors, aryl hydrocarbon; receptor, epidermal growth factor; tetrachlorodibenzodioxin; tumor necrosis factor-alpha

MeSH Terms

Animals
Benzoflavones/pharmacology
Cell Differentiation
Cell Line, Tumor
Enzyme Activation
Genistein/pharmacology
Hazardous Substances/*toxicity
Humans
MAP Kinase Signaling System/drug effects/physiology
Macrophages/*metabolism
Mice
Phosphorylation
Pyrimidines/pharmacology
Quinazolines/pharmacology
RNA, Messenger/metabolism
Receptor, Epidermal Growth Factor/antagonists & inhibitors/metabolism
Receptors, Aryl Hydrocarbon/antagonists & inhibitors
Signal Transduction
Tetrachlorodibenzodioxin/*toxicity
Tumor Necrosis Factor-alpha/*biosynthesis
src-Family Kinases/antagonists & inhibitors/metabolism