The role of thymidine phosphorylase in the induction of early growth response protein-1 and thrombospondin-1 by 5-fluorouracil in human cancer carcinoma cells

Thymidine phosphorylase (TP) is an enzyme involved in reversible conversion of thymidine to thymine TP is identical to an angiogenic factor, pletelet-derived endothelial cell growth factor (PD-ECGF) and the expression levels of TP in a variety of malignant tumors were higher than the adjacent non-neoplastic tissues To investigate the molecular basis for the effect of TP on the metabolic process and the anticancer effect of 5-fluorouracil (5-FU). human gastric carcinoma AZ521 cells and epidermoid carcinoma KB cells were transfected with TP cDNA. and AZ521/TP and KB/TP were cloned AZ521/TP and KB/TP cells overexpressed TP and were more sensitive to 5-FU than the counterpart parental cells TPI. a newly synthesized inhibitor for TP (Ki=2 36x10(-9)M). decreased the sensitivity to 5-FU of the TP expressing cells but not of the parental cells 5-Formyltetrahydrofolate (leucovorin: LV) stabilized the complex of thymidylate synt base (TS) and 5-fluoro-deoxyuridine-monophosphate (HUMP). increased the sensitivity to 5-FU of TP expressing AZ521 cells, but not of the parental cells The levels of FdUMP in TP expressing cells were significantly higher than in parental cells and TPI considerably decreased FdUMP to the level comparable to that in the parental cells 5-FU increased the expression of early growth response protein-1 (Egr-1) and an angiogenesis inhibitor. thrombospondin-1 (TSP-1), in KB/TP cells but only slightly in KB/CV cells, if any TPI attenuated the induction of Egr-1 and TSP-1 mRNA by 5-FU. while LV increased the expression of Egr-1 and TSP-1 mRNA in KB/TP cells These findings demonstrate that the TP has a principal role in the production of FdUMP and the enhanced responses to 5-FU by leucovorin in TP-overexpressing KB and AZ521 cells. and FdUMP but not Fun) is implicated in the induction of Egr-1 and TSP-1 in KB cells