Uracil accumulation induced by folate depletion is dependent on uracil DNA glycosylase (UDG) activity

We have previously reported that folate depletion inhibits DNA repair capacity. Here we investigate the impact of folate depletion on DNA damage and repair to determine whether the response to folate depletion is cell‐type specific. We find that DNA base excision repair (BER) capacity and uracil accumulation is a function of the ability of the cell to initiate BER when folate is limiting. Folate depletion induces Uracil DNA glycosylase (UDG) and BER in mouse liver, but does not induce uracil accumulation. Accordingly, mouse BNL‐C2 liver cells grown in folate‐free media exhibit significant induction in UDG (88% increase, p<0.01) and BER (12% increase, p<0.01), with no change in uracil accumulation. However, MEFs grown in folate‐free media exhibit significant downregulation in UDG (40% decrease, p<0.01) and BER capacity (21%, p<0.01), and significant increase in uracil accumulation (30% increase, p<0.01). Likewise, homozygous deletion of UDG significantly increases the impact of folate depletion on uracil accumulation, demonstrating a direct role for UDG and BER initiation on uracil accumulation when folate is limiting. We are presently measuring expression of folate‐metabolizing enzymes to determine whether the BER and uracil accumulation phenotypes are related to cell type specific changes in folate metabolism when folate is absent. Research support: The Ellison Medical Foundation