Activation of the p53 DNA damage response pathway after inhibition of DNA methyltransferase by 5-aza-2'-deoxycytidine.
Transcriptional silencing of tumor suppressor genes by DNA methylation occurs in cancer cell lines and in human tumors. This has led to the pursuit of DNA methyltransferase inhibition as a drug target. 5-Aza-2'-deoxycytidine [5-aza-CdR (decitabine)], a potent inhibitor of DNA methyltransferase, is a drug currently in clinical trials for the treatment of solid tumors and leukemia. The efficacy of 5-aza-CdR may be related to the induction of methylation-silenced tumor suppressor genes, genomic hypomethylation, and/or enzyme-DNA adduct formation. Here, we test the hypothesis that 5-aza-CdR treatment is perceived as DNA damage, as assessed by the activation of the tumor suppressor p53. We show that 1) colon tumor cell lines expressing wild-type p53 are more sensitive to 5-aza-CdR mediated growth arrest and cytotoxicity; 2) the response to 5-aza-CdR treatment includes the induction and activation of wild-type but not mutant p53 protein; and 3) the induction of the downstream p53 target gene p21 is partially p53-dependent. The induction of p53 protein after 5-aza-CdR treatment did not correlate with an increase in p53 transcripts, indicating that hypomethylation at the p53 promoter does not account for the p53 response. It is relevant that 5-aza-CdR has shown the greatest promise in clinical trials for the treatment of chronic myelogenous leukemia, a malignancy in which functional p53 is often retained. Our data raise the hypothesis that p53 activation may contribute to the clinical efficacy and/or toxicity of 5-aza-CdR.
Division of Molecular Pharmacology, Huntsman Cancer Institute, University of Utah, Salt Lake City, Utah 84112, USA.
A R
AR
Karpf
B C
BC
Moore
T O
TO
Ririe
D A
DA
Jones
D000964:Antimetabolites, Antineoplastic / Q000494:pharmacology; D001374:Azacitidine / Q000031:analogs & derivatives* / Q000494:pharmacology*; D002470:Cell Survival / Q000187:drug effects; D003110:Colonic Neoplasms / Q000378:metabolism*; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins / Q000172:deficiency / Q000235:genetics / Q000378:metabolism; D004249:DNA Damage; D019175:DNA Methylation / Q000187:drug effects; D015254:DNA Modification Methylases / Q000037:antagonists & inhibitors*; D000077209:Decitabine; D004791:Enzyme Inhibitors / Q000494:pharmacology; D016193:G1 Phase / Q000187:drug effects; D005786:Gene Expression Regulation / Q000187:drug effects; D019073:HT29 Cells; D006801:Humans; D009154:Mutation; D012333:RNA, Messenger / Q000378:metabolism; D014407:Tumor Cells, Cultured; D016159:Tumor Suppressor Protein p53 / Q000235:genetics / Q000378:metabolism*
D000964:Antimetabolites, Antineoplastic; C493956:CDKN1A protein, human; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins; D004791:Enzyme Inhibitors; D012333:RNA, Messenger; D016159:Tumor Suppressor Protein p53; D000077209:Decitabine; D015254:DNA Modification Methylases; D001374:Azacitidine