Human embryonic stem cells are capable of executing G1/S checkpoint activation.
Embryonic stem cells progress very rapidly through the cell cycle, allowing limited time for cell cycle regulatory circuits that typically function in somatic cells. Mechanisms that inhibit cell cycle progression upon DNA damage are of particular importance, as their malfunction may contribute to the genetic instability observed in human embryonic stem cells (hESCs). In this study, we exposed undifferentiated hESCs to DNA-damaging ultraviolet radiation-C range (UVC) light and examined their progression through the G1/S transition. We show that hESCs irradiated in G1 phase undergo cell cycle arrest before DNA synthesis and exhibit decreased cyclin-dependent kinase two (CDK2) activity. We also show that the phosphatase Cdc25A, which directly activates CDK2, is downregulated in irradiated hESCs through the action of the checkpoint kinases Chk1 and/or Chk2. Importantly, the classical effector of the p53-mediated pathway, protein p21, is not a regulator of G1/S progression in hESCs. Taken together, our data demonstrate that cultured undifferentiated hESCs are capable of preventing entry into S-phase by activating the G1/S checkpoint upon damage to their genetic complement.
Bárta
Tomás
T
Department of Biology, Faculty of Medicine, Masaryk University, Brno, Czech Republic.
Vinarský
Vladimír
V
Holubcová
Zuzana
Z
Dolezalová
Dása
D
Verner
Jan
J
Pospísilová
Sárka
S
Dvorák
Petr
P
Hampl
Ales
A
D002454:Cell Differentiation; D002460:Cell Line; D000071877:Checkpoint Kinase 1; D064447:Checkpoint Kinase 2; D051357:Cyclin-Dependent Kinase 2 / Q000378:metabolism; D004249:DNA Damage; D016193:G1 Phase / Q000528:radiation effects; D006801:Humans; D011494:Protein Kinases / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D016196:S Phase / Q000528:radiation effects; D015398:Signal Transduction; D013234:Stem Cells / Q000166:cytology* / Q000378:metabolism / Q000528:radiation effects; D020687:cdc25 Phosphatases / Q000378:metabolism
D011494:Protein Kinases; D064447:Checkpoint Kinase 2; C000605867:CHEK1 protein, human; C578634:CHEK2 protein, human; D000071877:Checkpoint Kinase 1; D017346:Protein Serine-Threonine Kinases; C495894:CDK2 protein, human; D051357:Cyclin-Dependent Kinase 2; C517004:CDC25A protein, human; D020687:cdc25 Phosphatases