title: The G2 block induced by DNA damage: a caffeine-resistant component independent of Cdc25C, MPM-2 phosphorylation, and H1 kinase activity.
abstract: Treatment of cells with agents that cause DNA damage often results in a delay in G2. There is convincing evidence showing that inhibition of p34cdc2 kinase activation is involved in the DNA damage-induced G2 delay. In this study, we have demonstrated the existence of an additional pathway, independent of the p34cdc2 kinase activation pathway, that leads to a G2 arrest in etoposide-treated cells. Both the X-ray-induced and the etoposide-induced G2 arrest were associated with inhibition of the p34cdc2 H1 kinase activation pathway as judged by p34cdc2 H1 kinase activity and phosphorylation of cdc25C. Caffeine treatment restored these activities after either of the treatments. However, the etoposide-treated cells did not resume cycling, revealing the presence of an alternative pathway leading to a G2 arrest. To explore the possibility that this additional pathway involved phosphorylation of the MPM-2 epitope that is shared by a large family of mitotic phosphoproteins, we monitored the phosphorylation status of the MPM-2 epitope after DNA damage and after treatment with caffeine. Phosphorylation of the MPM-2 epitope was depressed in both X-ray and etoposide-treated cells, and the depression was reversed by caffeine in both cases. The results indicate that the pathway affecting MPM-2 epitope phosphorylation is involved in the G2 delay caused by DNA damage. However, it is not part of the caffeine-insensitive pathway leading to a G2 block seen in etoposide-treated cells.
authors.affiliation: Department of Pathology and Laboratory Medicine, University of Pennsylvania, Philadelphia 19104, USA.
authors.forename: R A
authors.initials: RA
authors.lastname: Barratt
authors.forename: G
authors.initials: G
authors.lastname: Kao
authors.forename: W G
authors.initials: WG
authors.lastname: McKenna
authors.forename: J
authors.initials: J
authors.lastname: Kuang
authors.forename: R J
authors.initials: RJ
authors.lastname: Muschel
mesh_terms: D000972:Antineoplastic Agents, Phytogenic / Q000494:pharmacology*; D016203:CDC2 Protein Kinase / Q000235:genetics / Q000378:metabolism; D002110:Caffeine / Q000494:pharmacology*; D018797:Cell Cycle Proteins / Q000187:drug effects* / Q000378:metabolism; D000697:Central Nervous System Stimulants / Q000494:pharmacology*; D004249:DNA Damage / Q000187:drug effects*; D000939:Epitopes / Q000378:metabolism; D005047:Etoposide / Q000494:pharmacology*; D016195:G2 Phase / Q000187:drug effects* / Q000235:genetics / Q000528:radiation effects; D006367:HeLa Cells / Q000166:cytology / Q000187:drug effects / Q000528:radiation effects; D006801:Humans; D009363:Neoplasm Proteins / Q000235:genetics; D010766:Phosphorylation / Q000187:drug effects; D011494:Protein Kinases / Q000378:metabolism; D014407:Tumor Cells, Cultured / Q000187:drug effects; D020687:cdc25 Phosphatases
chemical_list: D000972:Antineoplastic Agents, Phytogenic; D018797:Cell Cycle Proteins; D000697:Central Nervous System Stimulants; D000939:Epitopes; D009363:Neoplasm Proteins; D002110:Caffeine; D005047:Etoposide; D011494:Protein Kinases; C102333:histone H1 kinase; D016203:CDC2 Protein Kinase; C517009:CDC25C protein, human; D020687:cdc25 Phosphatases