title: Cell cycle-dependent regulation of telomerase activity by auxin, abscisic acid and protein phosphorylation in tobacco BY-2 suspension culture cells.
abstract: Telomerase is a specialized RNA-directed DNA polymerase that adds telomeric repeats onto the ends of linear eukaryotic chromosomes. It was recently reported that the low, basal level of telomerase activity markedly increased at early S-phase of the cell cycle, and auxin further increased the S-phase-specific telomerase activity in tobacco BY-2 cells. In this study we show that abscisic acid (ABA), a phytohormone known to induce the cyclin-dependent protein kinase inhibitor, effectively abolished both the auxin- and S-phase-specific activation of telomerase in a concentration- and time-dependent fashion in synchronized tobacco BY-2 cells. These results suggest that there exists a hormonal cross-talk between auxin and ABA for the regulation of telomerase activity during the cell cycle of tobacco cells. Treatment of synchronized BY-2 cells with the protein kinase inhibitor staurosporine or H-7 effectively prevented the S-phase-specific activation of telomerase activity. By contrast, when okadaic acid or cantharidin, potent inhibitors of protein phosphatase 2A (PP2A), was applied to the cells, the S-phase-specific high level of telomerase activity was continuously maintained in the cell cycle for at least 14 h after release from M-phase arrest. Incubation of tobacco cell extracts with exogenous PP2A rapidly abrogated in vitro telomerase activity, while okadaic acid and cantharidin blocked the action of PP2A, effectively restoring in vitro telomerase activity. Taken together, these findings are discussed in the light of the suggestion that antagonistic functions of auxin and ABA, and reciprocal phosphorylation and dephosphorylation of telomerase complex, are necessarily involved in the cell cycle-dependent modulation of telomerase activity in tobacco cells.
authors.affiliation: Department of Biology, College of Science, Yonsei University, Seoul 120-749, Korea.
authors.forename: Seong Wook
authors.initials: SW
authors.lastname: Yang
authors.forename: EonSeon
authors.initials: E
authors.lastname: Jin
authors.forename: In Kwon
authors.initials: IK
authors.lastname: Chung
authors.forename: Woo Taek
authors.initials: WT
authors.lastname: Kim
mesh_terms: D019307:1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine / Q000494:pharmacology; D015084:2,4-Dichlorophenoxyacetic Acid / Q000494:pharmacology; D000040:Abscisic Acid / Q000494:pharmacology; D002193:Cantharidin / Q000494:pharmacology; D002453:Cell Cycle / Q000502:physiology*; D018797:Cell Cycle Proteins / Q000378:metabolism*; D002478:Cells, Cultured; D018844:Cyclin-Dependent Kinases / Q000037:antagonists & inhibitors; D004305:Dose-Response Relationship, Drug; D007210:Indoleacetic Acids / Q000494:pharmacology; D019319:Okadaic Acid / Q000494:pharmacology; D010749:Phosphoprotein Phosphatases / Q000037:antagonists & inhibitors; D010766:Phosphorylation / Q000187:drug effects; D010937:Plant Growth Regulators / Q000494:pharmacology*; D054648:Protein Phosphatase 2; D019311:Staurosporine / Q000494:pharmacology; D019098:Telomerase / Q000378:metabolism*; D016615:Telomere / Q000201:enzymology; D013997:Time Factors; D014026:Nicotiana / Q000166:cytology / Q000187:drug effects* / Q000201:enzymology
chemical_list: D018797:Cell Cycle Proteins; D007210:Indoleacetic Acids; D010937:Plant Growth Regulators; D019319:Okadaic Acid; D015084:2,4-Dichlorophenoxyacetic Acid; D000040:Abscisic Acid; D019307:1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine; D018844:Cyclin-Dependent Kinases; D019098:Telomerase; D010749:Phosphoprotein Phosphatases; D054648:Protein Phosphatase 2; D019311:Staurosporine; D002193:Cantharidin