Cancer Biology and Signal Transduction microRNAs miR-27a and miR-27b Directly Regulate Liver Dihydropyrimidine Dehydrogenase Expression through Two Conserved Binding Sites

Dihydropyrimidine dehydrogenase (DPD, encoded by DPYD) is the rate-limiting enzyme in the uracil catabolic pathway and has a pivotal role in the pharmacokinetics of the commonly prescribed anticancer drug 5-fluorouracil (5-FU). Deficiency of DPD, whether due to inadequate expression or deleterious variants in DPYD, has been linked to severe toxic responses to 5-FU. Little is known about the mechanisms governing DPD expression in the liver. In this report, we show increased accumulation of RNA-induced silencing complex (RISC) proteins on DPYD mRNA in cells overexpressing the highly homologous microRNAs (miRNA) miR-27a and miR-27b. These miRNAs were shown to repress DPD expression through two conserved recognition sites in DPYD. The IC50 of 5-FU for HCT116 cells overexpressing miR27a or miR-27b was 4.4 mmol/L (both), significantly lower than that for cells expressing a nontargeting (scramble) control miRNA (14.3 mmol/L; P 1⁄4 3.3 10 5 and P1⁄4 1.5 10 , respectively). Mouse liver DPD enzyme activity was inversely correlated with expression levels of miR-27a (R1⁄4 0.49; P1⁄4 0.0012) andmiR27b (R 1⁄4 0.29; P 1⁄4 0.022). A common variant in the hairpin loop region of hsa-mir-27a (rs895819) was also shown to be associated with elevated expression of the miR-27a in a panel of cell lines (P 1⁄4 0.029) and in a transgenic overexpression model (P 1⁄4 0.0011). Furthermore, rs895819 was associated with reduced DPD enzyme activity (P 1⁄4 0.028) in a cohort of 40 healthy volunteers. Taken together, these results suggest that miR-27a and miR-27b expression may be pharmacologically relevant modulators of DPD enzyme function in the liver. Furthermore, our data suggest that rs895819 may be a potential risk allele for 5-FU sensitivity. Mol Cancer Ther; 13(3); 1–10. 2014 AACR.