Role of p21(Waf-1) in regulating the G1 and G2/M checkpoints in ultraviolet-irradiated keratinocytes.
This study examines the role of p21(Waf-1) , a p53-dependent protein, in regulating mechanisms that protect keratinocytes against ultraviolet-B-induced cellular damage. Keratinocytes from p21(Waf-1) or p53-deficient mice were irradiated with ultraviolet B, and examined for DNA repair, cell cycle progression, and cell death. Both p21(Waf-1) -deficient and p53-deficient cells failed to maintain G2 arrest, and p21(Waf-1) -deficient cells, and to a lesser extent p53-deficient cells, also failed to undergo G1 arrest. After exposure to ultraviolet B, p53-deficient cells were more susceptible to cell death than wild-type cells. p21(Waf-1) -deficient cells did not undergo apoptotic cell death more often, however, but did have an increased frequency of nuclear abnormalities, suggesting mitotic catastrophe. TUNEL assay showed DNA fragmentation in the p53 +/+, p21(Waf-1) +/+, and p53 -/- cells, but not in p21(Waf-1) -/- cells. This result is consistent with the suggestion that p21(Waf-1) -deficient keratinocytes undergo mitotic cell death (catastrophe) after exposure to ultraviolet B irradiation in the system. Western analysis demonstrated that p21(Waf-1) expression was upregulated in p53-proficient and -deficient keratinocytes, supporting the notion that a p53-independent mechanism contributes to the response to ultraviolet B in keratinocytes. Finally, p21(Waf-1) -deficient cells had slightly less efficient nucleotide excision repair. In summary, this study suggests that p21(Waf-1) regulates the ultraviolet-B-induced G2/M checkpoint through p53, and the G1 checkpoint partially through p53. p21(Waf-1) does not significantly regulate DNA repair in ultraviolet-irradiated keratinocytes, however.
Department of Laboratory Medicine and Pathology, University of Alberta, Faculty of Medicine, 4B1 WC. Mackenzie Health Science Center, Edmonton, Canada.
Tomoko
T
Maeda
Michelle T
MT
Chong
Robin A
RA
Espino
Prescillia P
PP
Chua
Jefferey Q
JQ
Cao
Eugene G
EG
Chomey
Le
L
Luong
Victor A
VA
Tron
D017209:Apoptosis; D002453:Cell Cycle / Q000528:radiation effects*; D002478:Cells, Cultured; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins / Q000235:genetics / Q000502:physiology*; D053938:DNA Fragmentation; D004260:DNA Repair; D016193:G1 Phase / Q000528:radiation effects; D016195:G2 Phase / Q000528:radiation effects; D006801:Humans; D015603:Keratinocytes / Q000528:radiation effects*; D008938:Mitosis / Q000528:radiation effects; D012333:RNA, Messenger / Q000032:analysis; D016159:Tumor Suppressor Protein p53 / Q000502:physiology; D014466:Ultraviolet Rays / Q000009:adverse effects*
C493956:CDKN1A protein, human; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins; D012333:RNA, Messenger; D016159:Tumor Suppressor Protein p53