[Molecular basis for the inhibition of anticancer agents-induced apoptosis by thymidine phosphorylase].
An angiogenic factor, platelet-derived endothelial cell growth factor/thymidine phosphorylase (PD-ECGF/TP), stimulates the chemotaxis of endothelial cells and confers resistance to apoptosis induced by hypoxia. 2-Deoxy-D-ribose, a degradation product of thymidine generated by TP enzymatic activity, partially prevented hypoxia-induced apoptosis. TP was expressed at higher levels in tumor tissues compared to the adjacent non-neoplastic tissues in a variety of human carcinomas. High expression of TP is associated with an unfavorable prognosis. To investigate the effect of TP on cisplatin-induced apoptosis, human leukemia Jurkat cells were transfected with wild-type or mutant (L148R) TP cDNA. Jurkat cells transfected with TP cDNA (Jurkat/TP) and mutant TP cDNA (Jurkat/TPMu) expressed high levels of TP, while Jurkat/CV cells which were transfected with a control vector did not express TP. A high TP enzyme activity was detected in Jurkat/TP cells, but not in Jurkat/CV and Jurkat/TPMu cells. Sensitivities to cisplatin of these cells were determined by MTT assay. IC50 values for cisplatin of Jurkat/CV, Jurkat/TP, and Jurkat/TPMu cells were 4.50, 14.08, 13.40 microM, respectively. Jurkat/TP and Jurkat/TPMu cells were about three times more resistant to cisplatin than Jurkat/CV cells. TP inhibited activation of caspase 3, 9 and mitochondrial cytochrome c release induced by cisplatin. These findings suggest a mechanism by which TP confers the resistance to cisplatin-induced apoptosis. Moreover, mutant TP that has no enzymatic activity also suppressed the cisplatin-induced apoptosis. These suggest that TP molecules have cytoprotective functions against cytotoxic agents.
Ikeda
Ryuji
R
Department of Clinical Pharmacy, Kagoshima University Hospital, Kagoshima City, Japan. ikeda@m.kufm.kagoshima-u.ac.jp
D000970:Antineoplastic Agents / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects*; D002945:Cisplatin / Q000494:pharmacology; D019008:Drug Resistance, Neoplasm; D006801:Humans; D009369:Neoplasms / Q000473:pathology; D013939:Thymidine Phosphorylase / Q000737:chemistry / Q000502:physiology*; D014407:Tumor Cells, Cultured
D000970:Antineoplastic Agents; D013939:Thymidine Phosphorylase; D002945:Cisplatin