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Differential Regulation of the p21/WAF-1 and mdm2 Genes after High-Dose UV Irradiation: p53-Dependent and p53-Independent Regulation of the mdm2 Gene

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Abstract

Background

DNA damage in mammalian cells stabilizes the p53 protein which then functions as a cell cycle checkpoint by leading to growth arrest or apoptosis. p53 is a transcription factor and positively regulates the expression of the p21/WAF-l gene and the mdm2 gene. After high-dose UV irradiation, p53 increases the expression of the p21/WAF-1 gene immediately (2 to 5 hours after irradiation) while the induction of the mdm2 gene is delayed (8 to 12 hours after irradiation). Experiments presented here explore this differential expression of two different p53-regulated genes.

Materials and Methods

IP-Western (protein) and Northern (mRNA) blot experiments are used to follow mdm2 and p21/WAF-l expression in primary rat or mouse cells after a low-dose (4 J/m2) or a high-dose (20 J/M2) of UV irradiation. Northern blot and nuclear run-on experiments are employed to study mRNA stability as well as transcription rates of selected genes.

Results

After high-dose UV irradiation, p53 is rapidly stabilized and the expression of p21/WAF1 is immediately increased. By contrast, both protein and mRNA levels of mdm2 first decrease in a p53-independent manner, and later increase in a p53-dependent manner. The initial decline of mdm2 expression following high-dose UV irradiation is UV-dosage dependent and regulated at the level of transcription.

Conclusion

p53 regulates two genes, p21/WAF1 (blocks cell cycle progression) and mdm2 (reverses p53 activity), that mediate opposite actions. This process is regulated in a temporal fashion after high-dose UV irradiation, so that cell cycle progression can be halted while DNA repair continues prior to reversal of p53-mediated arrest by mdm2.

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Acknowledgments

The authors thank Drs. J. Hank Bayle, Stuart Lutzker, and Maureen Murphy for helpful discussions. We also thank Drs. Deborah Freedman, Maureen Murphy, and Dawn Resnick for critical reading of the manuscript. Special thanks to Yu-qiao Shen for his help and support. This work was supported by a grant from the NCI, P01-41086.

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  1. Department of Molecular Biology, Princeton University, Lewis Thomas Laboratory, Princeton, New Jersey, 08544-1014, USA

    Lin Wu &  Arnold J. Levine

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  1. Lin Wu
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Correspondence to Arnold J. Levine.

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Wu, L., Levine, A.J. Differential Regulation of the p21/WAF-1 and mdm2 Genes after High-Dose UV Irradiation: p53-Dependent and p53-Independent Regulation of the mdm2 Gene. Mol Med 3, 441–451 (1997). https://doi.org/10.1007/BF03401691

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