title: Caffeine-mediated override of checkpoint controls. A requirement for rhp6 (Schizosaccharomyces pombe).
abstract: Cells exposed to inhibitors of DNA synthesis or suffering DNA damage are arrested or delayed in interphase through the action of checkpoint controls. If the arrested cell is exposed to caffeine, relatively normal cell cycle progression is resumed and, as observed in checkpoint control mutants, loss of checkpoint control activity is associated with a reduction in cell viability. To address the mechanism of caffeine's action on cell progression, fission yeast mutants that take up caffeine but are not sensitized to hydroxyurea (HU) by caffeine were selected. Mutants 788 and 1176 are point mutants of rhp6, the fission yeast homolog of the budding yeast RAD6 gene. Mutant rhp6-788 is slightly HU sensitive, radiosensitive, and exhibits normal checkpoint responses to HU, radiation, or inactivation of DNA ligase. However, the addition of caffeine does not override the associated cell cycle blocks. Both point and deletion mutations show synthetic lethality at room temperature with temperature-sensitive mutations in cyclin B (cdc13-117) or the phosphatase cdc25 (cdc25-22). These observations suggest that the rhp6 gene product, a ubiquitin-conjugating enzyme required for DNA damage repair, promotes entry to mitosis in response to caffeine treatment.
authors.affiliation: Department of Radiation Oncology, University of Utah Medical Center, Salt Lake City, Utah 84132, USA. roy.rowley@hsc.utah.edu
authors.forename: R
authors.initials: R
authors.lastname: Rowley
authors.forename: J
authors.initials: J
authors.lastname: Zhang
mesh_terms: D002110:Caffeine / Q000494:pharmacology*; D002453:Cell Cycle; D018797:Cell Cycle Proteins / Q000378:metabolism; D002470:Cell Survival; D003001:Cloning, Molecular; D019926:Cyclin B / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004307:Dose-Response Relationship, Radiation; D016195:G2 Phase / Q000502:physiology; D006918:Hydroxyurea / Q000494:pharmacology; D008025:Ligases / Q000502:physiology*; D016296:Mutagenesis; D019384:Nucleic Acid Synthesis Inhibitors / Q000494:pharmacology; D010726:Phosphodiesterase Inhibitors / Q000494:pharmacology*; D010749:Phosphoprotein Phosphatases / Q000378:metabolism; D012568:Schizosaccharomyces / Q000502:physiology*; D029702:Schizosaccharomyces pombe Proteins; D013696:Temperature; D013997:Time Factors; D044763:Ubiquitin-Conjugating Enzymes; D020687:cdc25 Phosphatases
chemical_list: D018797:Cell Cycle Proteins; D019926:Cyclin B; D019384:Nucleic Acid Synthesis Inhibitors; D010726:Phosphodiesterase Inhibitors; D029702:Schizosaccharomyces pombe Proteins; D002110:Caffeine; D044763:Ubiquitin-Conjugating Enzymes; C063863:rhp6 protein, S pombe; D010749:Phosphoprotein Phosphatases; D020687:cdc25 Phosphatases; D008025:Ligases; D006918:Hydroxyurea