title: DNA damage mediated s and g(2) checkpoints in human embryonal carcinoma cells.
abstract: For mouse embryonic stem (ES) cells, the importance of the S and G(2) cell cycle checkpoints for genomic integrity is increased by the absence of the G(1) checkpoint. We have investigated ionizing radiation (IR)-mediated cell cycle checkpoints in undifferentiated and retinoic acid-differentiated human embryonal carcinoma (EC) cells. Like mouse ES cells, human EC cells did not undergo G(1) arrest after IR but displayed a prominent S-phase delay followed by a G(2)-phase delay. In contrast, although differentiated EC cells also failed to arrest at G(1)-phase after IR, they quickly exited S-phase and arrested in G(2)-phase. In differentiated EC cells, the G(2)-M-phase cyclin B1/CDC2 complex was upregulated after IR, but the G(1)-S-phase cyclin E and the cyclin E/CDK2 complex were expressed at constitutively low levels, which could be an important factor distinguishing DNA damage responses between undifferentiated and differentiated EC cells. S-phase arrest and expression of p21 could be inhibited by 7-hydroxystaurosporine, suggesting that the ataxia-telangiectasia and Rad-3-related-checkpoint kinase 1 (ATR-CHK1), and p21 pathways might play a role in the IR-mediated S-phase checkpoint in EC cells. IR-mediated phosphorylation of ataxia-telangiectasia mutated, (CHK1), and checkpoint kinase 2 were distinctly higher in undifferentiated EC cells compared with differentiated EC cells. Combined with the prominent S and G(2) checkpoints and a more efficient DNA damage repair system, these mechanisms operate together in the maintenance of genome stability for EC cells.
authors.affiliation: Department of Surgery, The University of Hong Kong, Pokfulam, Hong Kong. xqwang@hkucc.hku.hk
authors.forename: XiaoQi
authors.initials: X
authors.lastname: Wang
authors.forename: Vincent C H
authors.initials: VC
authors.lastname: Lui
authors.forename: Ronnie T P
authors.initials: RT
authors.lastname: Poon
authors.forename: Ping
authors.initials: P
authors.lastname: Lu
authors.forename: Randy Y C
authors.initials: RY
authors.lastname: Poon
mesh_terms: D015153:Blotting, Western; D002460:Cell Line; D002470:Cell Survival / Q000235:genetics / Q000502:physiology; D064447:Checkpoint Kinase 2; D019927:Cyclin E / Q000378:metabolism; D004249:DNA Damage / Q000235:genetics* / Q000502:physiology; D054278:Embryonal Carcinoma Stem Cells / Q000166:cytology* / Q000378:metabolism*; D016195:G2 Phase / Q000235:genetics*; D006801:Humans; D047468:Immunoprecipitation; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D016196:S Phase / Q000235:genetics*
chemical_list: D019927:Cyclin E; D064447:Checkpoint Kinase 2; C578634:CHEK2 protein, human; C578633:Chek2 protein, mouse; D017346:Protein Serine-Threonine Kinases