Induction of WAF1/CIP1 by a p53-independent pathway.
The p53-inducible gene WAF1/CIP1 encodes a M(r) 21,000 protein (p21) that has been shown to arrest cell growth by inhibition of cyclin-dependent kinases. Induction of WAF1/CIP1 in cells undergoing p53-dependent G1 arrest or apoptosis supports the idea that WAF1/CIP1 is a critical downstream effector of p53. In the present study, we used embryonic fibroblasts from p53 "knock-out" mice to demonstrate p53-independent induction of WAF1/CIP1. We show that serum or individual growth factors such as platelet-derived growth factor, fibroblast growth factor, and epidermal growth factor but not insulin are able to induce WAF1/CIP1 in quiescent p53-deficient cells as well as in normal cells. The kinetics of this transient induction, which is enhanced by cycloheximide, demonstrates that WAF1/CIP1 is an immediate-early gene the transcript of which reaches a peak at approximately 2 h following serum or growth factor stimulation. On the other hand, DNA damage elicited by gamma-irradiation induces WAF1/CIP1 in normal human and mouse fibroblasts but does not affect WAF1/CIP1 expression in p53-deficient cells. These results suggest the existence of two separate pathways for the induction of WAF1/CIP1, a p53-dependent one activated by DNA damage and a p53-independent one activated by mitogens at the entry into the cell cycle. The possible function of p21 at this early stage is discussed.
Laboratory of Cellular and Molecular Biology, National Cancer Institute, NIH, Bethesda, Maryland 20892.
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P
Michieli
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M
Chedid
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D
Lin
J H
JH
Pierce
W E
WE
Mercer
D
D
Givol
D016475:3T3 Cells; D000818:Animals; D001483:Base Sequence; D003513:Cycloheximide / Q000494:pharmacology; D016193:G1 Phase / Q000235:genetics*; D005786:Gene Expression Regulation / Q000502:physiology*; D017781:Genes, Immediate-Early / Q000187:drug effects / Q000502:physiology* / Q000528:radiation effects; D016147:Genes, Tumor Suppressor / Q000187:drug effects / Q000502:physiology* / Q000528:radiation effects; D016158:Genes, p53 / Q000187:drug effects / Q000502:physiology / Q000528:radiation effects; D006133:Growth Substances / Q000494:pharmacology; D007328:Insulin / Q000494:pharmacology; D051379:Mice; D008969:Molecular Sequence Data; D010982:Platelet-Derived Growth Factor / Q000494:pharmacology; D014407:Tumor Cells, Cultured; D016159:Tumor Suppressor Protein p53 / Q000172:deficiency
D006133:Growth Substances; D007328:Insulin; D010982:Platelet-Derived Growth Factor; D016159:Tumor Suppressor Protein p53; D003513:Cycloheximide