Uric acid accumulation in DNA-damaged tumor cells induces NKG2D ligand expression and antitumor immunity by activating TGF-β-activated kinase 1.

DNA damage by genotoxic drugs such as gemcitabine and 5-fluorouracil (5-FU) activates the ataxia telangiectasia, mutated (ATM)-Chk pathway and induces the expression of NKG2D ligands such as the MHC class I-related chain A and B (MICA/B). The mechanisms underlying this remain incompletely understood. Here we report that xanthine oxidoreductase (XOR), a rate-limiting enzyme that produces uric acid in the purine catabolism pathway, promotes DNA damage-induced MICA/B expression. Inhibition of the ATM-Chk pathway blocks genotoxic drug-induced uric acid production, TGF-β-activated kinase 1 (TAK1) activation, ERK phosphorylation, and MICA/B expression. Inhibition of uric acid production by the XOR inhibitor allopurinol blocks DNA damage-induced TAK1 activation and MICA/B expression in genotoxic drug-treated cells. Exogenous uric acid activates TAK1, NF-κB, and the MAP kinase pathway. TAK1 inhibition blocks gemcitabine- and uric acid-induced MAP kinase activation and MICA/B expression. Exogenous uric acid in its salt form, monosodium urate (MSU), induces MICA/B expression and sensitizes tumor cells to NK cell killing. MSU immunization with irradiated murine breast cancer cell line RCAS-Neu retards breast cancer growth in syngeneic breast cancer models and delays breast cancer development in a somatic breast cancer model. Our study suggests that uric acid accumulation plays an important role in activating TAK1, inducing DNA damage-induced MICA/B expression, and enhancing antitumor immunity.