title: Regulation of Cyp1a1 induction by dioxin as a function of cell cycle phase.
abstract: Analyses of CYP1A1 mRNA were used to monitor the responsiveness of murine hepatoma 1c1c7 and human monocytic U937 cells in different phases of the cell cycle to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). Concentrations of TCDD capable of inducing CYP1A1 were not cytostatic to either cell line. Steady-state CYP1A1 mRNA contents were reduced (45-90%) in TCDD-treated cultures arrested in G2/M as a consequence of exposure to microtubule disrupters (Colcemid, estramustine, vinblastine) or the microtubule stabilizer Taxol, relative to TCDD-treated asynchronous 1c1c7 cultures. The accumulation of mRNAs corresponding to Nmo1, another TCDD-inducible gene of the Ah battery, was also reduced in TCDD-treated G2/M cultures. Quantitative reverse transcriptase-polymerase chain reaction analyses of CYP1A1 heterogeneous nuclear RNA (hnRNA) revealed that Cyp1a1 transcription was suppressed in G2/M cells. This suppression reflected neither changes in the relative content of the proteins comprising the aryl hydrocarbon receptor (AHR) complex nor a suppression of AHR activation and translocation to the nucleus. Release of 1c1c7 cultures arrested in G2/M restored TCDD responsiveness. Centrifugal elutriation of TCDD-treated asynchronously growing U937 cells was used to prepare populations of cells in specific phases of the cell cycle. Within 3 h of TCDD exposure late G1/early S phase cells had CYP1A1 mRNA contents approximately 1.4- and 3-fold higher than the contents of asynchronous/early G1 and G2/M cultures, respectively. These studies suggest that the transcriptional activation of members of the Ah battery by TCDD is cell cycle-dependent, and markedly suppressed in G2/M cells.
authors.affiliation: Institute of Environmental Health Sciences, Wayne State University, Detroit, Michigan 48201, USA.
authors.forename: R P
authors.initials: RP
authors.lastname: Santini
authors.forename: S
authors.initials: S
authors.lastname: Myrand
authors.forename: C
authors.initials: C
authors.lastname: Elferink
authors.forename: J J
authors.initials: JJ
authors.lastname: Reiners
mesh_terms: D015153:Blotting, Western; D016203:CDC2 Protein Kinase / Q000378:metabolism; D002453:Cell Cycle / Q000187:drug effects; D002498:Centrifugation; D002875:Chromosomes / Q000187:drug effects / Q000648:ultrastructure; D019363:Cytochrome P-450 CYP1A1 / Q000096:biosynthesis*; D004147:Dioxins / Q000494:pharmacology*; D004789:Enzyme Activation / Q000187:drug effects; D020536:Enzyme Activators / Q000494:pharmacology; D005434:Flow Cytometry; D005455:Fluorescent Antibody Technique; D006801:Humans; D009963:Orotic Acid / Q000378:metabolism; D000072317:Polychlorinated Dibenzodioxins / Q000494:pharmacology; D012333:RNA, Messenger / Q000096:biosynthesis / Q000235:genetics; D015138:RNA, Nuclear / Q000096:biosynthesis; D018336:Receptors, Aryl Hydrocarbon / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction
chemical_list: D004147:Dioxins; D020536:Enzyme Activators; D000072317:Polychlorinated Dibenzodioxins; D012333:RNA, Messenger; D015138:RNA, Nuclear; D018336:Receptors, Aryl Hydrocarbon; D009963:Orotic Acid; D019363:Cytochrome P-450 CYP1A1; D016203:CDC2 Protein Kinase