TCDD-induced apoptosis in EL-4 cells deficient of the aryl hydrocarbon receptor and down-regulation of IGFBP-6 prevented the apoptotic cell death.
Although the potent environmental contaminant 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) has been well known for its immunosuppressive activity, the mechanisms of its action have been difficult to elucidate, partly because of its inability of exerting its effects in vitro. We previously reported that insulin-like growth factor-binding protein-6 (IGFBP-6) expression in the thymus was increased by TCDD treatment of mice and that the TCDD-up-regulation of the IGFBP-6 gene was also observed with EL-4 mouse thymoma cells. In the present study, we examined the effects of IGFBP-6 on the TCDD-mediated cytotoxicity in EL-4 cells. By stably expressing IGFBP-6 sense or anti-sense mRNA in the EL-4 line of mouse thymoma cells, it was possible to isolate clones in which IGFBP-6 expression was increased or decreased. Clones expressing IGFBP-6 sense mRNA displayed increased sensitivity to cytotoxicity mediated by TCDD, whereas clones expressing IGFBP-6 anti-sense mRNA displayed reduced sensitivity. TCDD-induced DNA fragmentation was less pronounced in clones expressing IGFBP-6 anti-sense mRNA than clones expressing IGFBP-6 sense mRNA or the empty vector. Caspase 3 was activated by TCDD and anti-sense IGFBP-6 expression reduced its activity. Interestingly, the effects of TCDD were exerted without aromatic hydrocarbon (Ah) receptor (AhR). Taken together, the results have shown that IGFBP-6 mediates the immunotoxic effects of TCDD in EL-4 cells in an AhR-independent pathway.
Park
Joo-Hung
JH
Department of Biology, Changwon National University, #9, Sarim-dong, Changwon, Kyungnam 641-773, South Korea. parkjh@sarim.changwon.ac.kr
Hahn
Eun-Jin
EJ
Kong
Ji-Hye
JH
Cho
Hyun-Jin
HJ
Yoon
Chun-Sik
CS
Cheong
Seon-Woo
SW
Oh
Gap-Soo
GS
Youn
Hyun-Joo
HJ
D000818:Animals; D017209:Apoptosis / Q000187:drug effects*; D015153:Blotting, Western; D053938:DNA Fragmentation; D003850:Deoxyribonuclease I / Q000494:pharmacology; D015536:Down-Regulation / Q000187:drug effects*; D004785:Environmental Pollutants / Q000633:toxicity*; D018976:Insulin-Like Growth Factor Binding Protein 6 / Q000096:biosynthesis*; D051379:Mice; D008807:Mice, Inbred BALB C; D009368:Neoplasm Transplantation; D020320:Oligoribonucleotides, Antisense / Q000494:pharmacology; D010957:Plasmids / Q000235:genetics; D000072317:Polychlorinated Dibenzodioxins / Q000633:toxicity*; D012333:RNA, Messenger / Q000096:biosynthesis; D018336:Receptors, Aryl Hydrocarbon / Q000235:genetics*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013778:Tetrazolium Salts; D013844:Thiazoles; D014407:Tumor Cells, Cultured
D004785:Environmental Pollutants; D018976:Insulin-Like Growth Factor Binding Protein 6; D020320:Oligoribonucleotides, Antisense; D000072317:Polychlorinated Dibenzodioxins; D012333:RNA, Messenger; D018336:Receptors, Aryl Hydrocarbon; D013778:Tetrazolium Salts; D013844:Thiazoles; D003850:Deoxyribonuclease I; C022616:thiazolyl blue