Signaling Pathway for 2,3,7,8-tetrachlorodibenzo-p-dioxin-induced TNF-alpha Production in Differentiated THP-1 Human Macrophages

Exp Mol Med. 2007 Aug 31;39(4):524-34. doi: 10.1038/emm.2007.58.

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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

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

Substances

  • AG 1879
  • Benzoflavones
  • Hazardous Substances
  • Polychlorinated Dibenzodioxins
  • Pyrimidines
  • Quinazolines
  • RNA, Messenger
  • Receptors, Aryl Hydrocarbon
  • Tumor Necrosis Factor-alpha
  • alpha-naphthoflavone
  • Genistein
  • ErbB Receptors
  • src-Family Kinases
  • 4-((3-bromophenyl)amino)-6,7-dimethoxyquinazoline