P53 Represses Pyrimidine Catabolic Gene Dihydropyrimidine Dehydrogenase (Dpyd) Expression Following Thymidylate Synthase (Ts) Inhibition

Nucleotide catabolism by cancer cells can influence malignant behavior and intrinsic resistance to therapy. The rate-limiting enzyme in the pyrimidine catabolic pathway, dihydropyrimidine dehydrogenase (DPYD) contributes to the pharmacokinetics of fluorouracil (5-FU). Using in silico/chromatin-immunoprecipitation (ChIP) analysis we identify a conserved p53 DNA-binding site (p53BS) downstream of the DPYD gene with increased p53 occupancy following 5-FU. Histone H3K9 acetylation marks at the DPYD promoter is diminished concomitantly with reduced expression of DPYD mRNA and protein in a p53-dependent manner. Notably we find that the P72 allele of p53 suppresses DPYD expression more than the R72 p53 allele following 5-FU treatment in mouse embryo fibroblasts. Mechanistic studies reveal inhibition of DPYD expression by p53 is augmented following thymidylate synthase (TS) inhibition by 5-FU, methotrexate (MTX), raltitrexed and siRNA in cancer cells in vitro as well as in mice in vivo. DPYD repression by p53 is dependent on DNA-PK and ATM-signaling since pharmacologic targeting of these kinases reverses the transcriptional repression of DPYD by p53. Mice lacking p53 in their livers have increased conversion of 5-FU to 5-FUH2 in plasma and elicit a diminished 5-FU therapeutic response in syngeneic colorectal tumor xenografts as compared to littermates with an intact p53 allele consistent with increased DPYD-activity. Our data suggest that p53 plays an important role in controlling pyrimidine catabolism through its ability to regulate DPYD, particularly following metabolic stress imposed by nucleotide imbalance. The findings have implications for the toxicity and efficacy of the cancer therapeutic 5-fluorouracil. Citation Format: Prashanth Ravishankar Gokare, Niklas Finnberg, Jenny Dai, Maureen Murphy, Wafik El-Deiry. p53 represses pyrimidine catabolic gene dihydropyrimidine dehydrogenase (DPYD) expression following thymidylate synthase (TS) inhibition. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 3706.