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 anti-cancer 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 miR-27a and miR-27b. These microRNAs were shown to repress DPD expression through two conserved recognition sites in DPYD. The IC50 of 5-FU for HCT116 cells over-expressing miR-27a or miR-27b was 4.4 µM (both), significantly lower than that for cells expressing a non-targeting (scramble) control microRNA (14.3 µM; P=3.3×10-5 and P=1.5×10-7, respectively). Mouse liver DPD enzyme activity was inversely correlated with expression levels of miR-27a (R2=0.49, P=0.0012) and miR-27b (R2=0.29, P=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=0.029) and in a transgenic overexpression model (P=0.0011). Furthermore, rs895819 was associated with reduced DPD enzyme activity (P=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.
- Received October 15, 2013.
- Revision received November 25, 2013.
- Accepted January 2, 2014.
- Copyright © 2014, American Association for Cancer Research.