Regulation of Cyp1a1 Induction by Dioxin as a Function of Cell Cycle Phase

• Published in: The Journal of pharmacology and experimental therapeutics 2001-11, Vol.299 (2), p.718-728
• Main Authors: Santini, R P, Myrand, S, Elferink, C, Reiners, Jr, J J
• Format: Article
• Language: English
• Subjects: Blotting, Western; CDC2 Protein Kinase - metabolism; Cell Cycle - drug effects; Centrifugation; Chromosomes - drug effects; Chromosomes - ultrastructure; Cytochrome P-450 CYP1A1 - biosynthesis; Dioxins - pharmacology; Enzyme Activation - drug effects; Enzyme Activators - pharmacology; Flow Cytometry; Fluorescent Antibody Technique; Humans; Orotic Acid - metabolism; Polychlorinated Dibenzodioxins - pharmacology; Receptors, Aryl Hydrocarbon - metabolism; Reverse Transcriptase Polymerase Chain Reaction; RNA, Messenger - biosynthesis; RNA, Messenger - genetics; RNA, Nuclear - biosynthesis
• ISSN: 0022-3565; 1521-0103

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 G 2 /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 G 2 /M cultures. Quantitative reverse transcriptase-polymerase chain reaction analyses of CYP1A1 heterogeneous nuclear RNA (hnRNA) revealed that Cyp1a1 transcription was suppressed in G 2 /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 G 2 /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 G 1 /early S phase cells had CYP1A1 mRNA contents ∼1.4- and 3-fold higher than the contents of asynchronous/early G 1 and G 2 /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 G 2 /M cells.