Activation of Stat1, IRF-1, and NF-κB is Required for the Induction of Uridine Phosphorylase by Tumor Necrosis Factor-α and Interferon-γ

Abstract

Uridine phosphorylase (UPase) has been shown to be induced in various human and murine tumors and could potentially serve as a specific target for the modulation of tumor-selectivity of fluoropyrimidines. However, the signaling mechanisms underlying the regulation of UPase gene expression have not been determined. In this study, we investigated the effects of IFN-γ on the regulation of TNF-α-induced UPase activity and have uncovered the molecular mechanisms of this potentiation, utilizing murine EMT6 breast cancer cells. Our data has shown that IFN-γ can significantly increase UPase mRNA expression and the enzymatic activity induced by TNF-α in a dose-dependent manner, resulting in an enhanced sensitivity to 5-fluorouracil (5-FU) and 5′-Deoxy-5-fluorouridine (5′DFUR). We have previously shown that TNF-α activates NF-κB through increased translocation of NF-κB p65 from the cytoplasm into the nuclei. Exposure to IFN-γ mainly affects nuclear IRF-1 and STAT1 in EMT6, but inhibits NF-κB p65 activity, indicating that the cooperative stimulation was the result of the independent activation of NF-κB, STAT1 and IRF-1 transcriptional factors through binding to their unique sites in the UPase promoter. Notably, the activation of NF-κB and STAT1 in human breast tissues is consistent with UPase activity; signifying their role in the up-regulation of the UPase gene expression in human tumors.