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J. Biol. Chem., Vol. 278, Issue 49, 48861-48871, December 5, 2003

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A Defect in the p53 Response Pathway Induced by de Novo Purine Synthesis Inhibition^*

Julie L. Bronder and Richard G. Moran

From the Department of Pharmacology and Toxicology and The Massey Cancer Center, Medical College of Virginia Campus of Virginia Commonwealth University, Richmond, Virginia 23298

p53 is believed to sense cellular ribonucleotide depletion in the absence of DNA strand breaks and to respond by imposition of a p21-dependent G₁ cell cycle arrest. We now report that the p53-dependent G₁ checkpoint is blocked in human carcinoma cell lines after inhibition of de novo purine synthesis by folate analogs inhibitory to glycinamide ribonucleotide formyltransferase (GART). p53 accumulated in HCT116, MCF7, or A549 carcinoma cells upon GART inhibition, but, surprisingly, transcription of several p53 targets, including p21^cip1/waf1, was impaired. The mechanism of this defect was examined. The p53 accumulating in these cells was nuclear but was not phosphorylated at serines 6, 15, and 20, nor was it acetylated at lysines 373 or 382. The DDATHF-stabilized p53 bound to the p21 promoter in vitro and in vivo but did not activate histone acetylation over the p53 binding sites in the p21 promoter that is an integral part of the transcriptional response mediated by the DNA damage pathway. We concluded that the robust initial response of the p53 pathway to GART inhibitors is not transcriptionally propagated to target genes due to a defect in p53 post-translational modifications and a failure to open chromatin structure despite promoter binding of this unmodified p53.

Received for publication, May 8, 2003 , and in revised form, August 26, 2003.

^* This work was supported in part by Grant CA-27605 from the DHHS, National Institutes of Health. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

To whom correspondence should be addressed: Medical College of Virginia Campus of Virginia Commonwealth University, Richmond, VA 23298-0230. Tel.: 804-828-5783; Fax: 804-828-5782; E-mail: rmoran{at}hsc.vcu.edu.

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