title: 2,3,7,8-Tetrachlorodibenzo-p-dioxin induces suppressor of cytokine signaling 2 in murine B cells.
abstract: The B cell, a major component of humoral immunity, is a sensitive target for the immunotoxic effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), possibly by rendering cells less responsive to antigenic or mitogenic stimulation. Potential mechanisms of TCDD action on B cells were examined in murine B cell lymphoma cells (CH12.LX) treated with 3 nM TCDD or dimethyl sulfoxide vehicle using sequence-verified cDNA microarrays. One transcript that was significantly induced by TCDD was suppressor of cytokine signaling 2 (Socs2). Changes in Socs2 mRNA levels paralleled that of Cyp1a1 with a maximal 3-fold induction observed at 4 h, as determined by quantitative real-time polymerase chain reaction. Socs2 induction seems B cell-specific, because no induction was observed in TCDD-responsive mouse hepatoma cells or human breast cancer cells. TCDD-mediated induction of Socs2 mRNA was dose-dependent and exhibited the characteristic structure-activity relationships observed for the aryl hydrocarbon receptor (AhR) ligands 3,3',4,4',5-pentachlorobiphenyl (PCB-126), indolo[3,2-b]-carbazole, and beta-naphthoflavone. Experiments with cycloheximide and AhR-deficient B cells indicated that Socs2 mRNA induction is a primary effect that is AhR-dependent. Western blot analysis confirmed that Socs2 and Cyp1a1 protein levels were also induced in CH12.LX cells. Promoter analysis revealed the presence of four dioxin-response elements within 1000 base pairs upstream of the Socs2 transcriptional start site, and a reporter gene regulated by the Socs2 promoter was inducible by TCDD. Promoter activity was also dependent on a functional AhR signaling pathway. These results indicate that Socs2 is a primary TCDD-inducible gene that may represent a novel mechanism by which TCDD elicits its immunosuppressive effects.
authors.affiliation: Department of Biochemistry and Molecular Biology, National Food Safety and Toxicology Center, Michigan State University, East Lansing, Michigan 48824-1319, USA.
authors.forename: Darrell R
authors.initials: DR
authors.lastname: Boverhof
authors.forename: Elaine
authors.initials: E
authors.lastname: Tam
authors.forename: Allison S
authors.initials: AS
authors.lastname: Harney
authors.forename: Robert B
authors.initials: RB
authors.lastname: Crawford
authors.forename: Norbert E
authors.initials: NE
authors.lastname: Kaminski
authors.forename: Timothy R
authors.initials: TR
authors.lastname: Zacharewski
mesh_terms: D000818:Animals; D001402:B-Lymphocytes / Q000187:drug effects / Q000502:physiology*; D001483:Base Sequence; D045744:Cell Line, Tumor; D019363:Cytochrome P-450 CYP1A1 / Q000235:genetics; D017931:DNA Primers; D004268:DNA-Binding Proteins / Q000235:genetics*; D005786:Gene Expression Regulation / Q000187:drug effects; D016393:Lymphoma, B-Cell; D051379:Mice; D020411:Oligonucleotide Array Sequence Analysis; D000072317:Polychlorinated Dibenzodioxins / Q000494:pharmacology*; D012097:Repressor Proteins / Q000235:genetics*; D015398:Signal Transduction; D050826:Suppressor of Cytokine Signaling Proteins; D015534:Trans-Activators / Q000235:genetics*
chemical_list: D017931:DNA Primers; D004268:DNA-Binding Proteins; D000072317:Polychlorinated Dibenzodioxins; D012097:Repressor Proteins; C491409:Socs2 protein, mouse; D050826:Suppressor of Cytokine Signaling Proteins; D015534:Trans-Activators; D019363:Cytochrome P-450 CYP1A1