Activation of Stat1, IRF-1, and NF-kappaB is required for the induction of uridine phosphorylase by tumor necrosis factor-alpha and interferon-gamma.
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-gamma on the regulation of TNF-alpha-induced UPase activity and have uncovered the molecular mechanisms of this potentiation, utilizing murine EMT6 breast cancer cells. Our data has shown that IFN-gamma can significantly increase UPase mRNA expression and the enzymatic activity induced by TNF-alpha 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-alpha activates NF-kappaB through increased translocation of NF-kappaB p65 from the cytoplasm into the nuclei. Exposure to IFN-gamma mainly affects nuclear IRF-1 and STAT1 in EMT6, but inhibits NF-kappaB p65 activity, indicating that the cooperative stimulation was the result of the independent activation of NF-kappaB, STAT1 and IRF-1 transcriptional factors through binding to their unique sites in the UPase promoter. Notably, the activation of NF-kappaB 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.
Wan
Laxiang
L
Department of Internal Medicine (Medical Oncology), Yale University School of Medicine, New Haven, Connecticut, USA.
Cao
Deliang
D
Zeng
Jianmin
J
Ziemba
Amy
A
Pizzorno
Giuseppe
G
D000818:Animals; D015153:Blotting, Western; D024202:Electrophoretic Mobility Shift Assay; D004789:Enzyme Activation / Q000187:drug effects; D005260:Female; D015870:Gene Expression / Q000187:drug effects; D006801:Humans; D066298:In Vitro Techniques; D050856:Interferon Regulatory Factor-1 / Q000378:metabolism*; D007371:Interferon-gamma / Q000494:pharmacology*; D051379:Mice; D016328:NF-kappa B / Q000378:metabolism*; D050794:STAT1 Transcription Factor / Q000378:metabolism*; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology*; D014543:Uridine Phosphorylase / Q000378:metabolism*
D050856:Interferon Regulatory Factor-1; D016328:NF-kappa B; D050794:STAT1 Transcription Factor; D014409:Tumor Necrosis Factor-alpha; D007371:Interferon-gamma; D014543:Uridine Phosphorylase