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.
Michieli
P
P
Laboratory of Cellular and Molecular Biology, National Cancer Institute, NIH, Bethesda, Maryland 20892.
Chedid
M
M
Lin
D
D
Pierce
J H
JH
Mercer
W E
WE
Givol
D
D
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