ROLE OF THYMIDINE PHOSPHORYLASE-ACTIVITY IN THE ANGIOGENIC EFFECT OF PLATELET-DERIVED ENDOTHELIAL-CELL GROWTH-FACTOR THYMIDINE PHOSPHORYLASE

Human thymidine phosphorylase (dThdPase) has been reported to be identical with the platelet-derived endothelial cell growth factor (PD-FCGF). To investigate whether the dThdPase activity of PD-ECGF/dThdPase is indispensable to its angiogenic activity, three PD-ECGF/dThdPase mutants, K115E (Lys-115 --> Glu), L148R (Leu-148 --> Arg) and R202S (Arg-202 --> Ser) were made by site-directed mutagenesis. Although the expression level of the three mutant PD-ECGF/dThdPases in the COS-7 cells was similar to that of wild-type PD-ECGF/dThdPase, dThdPase activity was not detected in the COS-7 cells transfected with the mutant PD-ECGF/dThdPase cDNA. The lysates of COS-7 cells transfected with the wild-type PD-ECGF/dThdPase cDNA had angiogenic activity, but those transfected with the mutant PD-ECGF/dThdPase cDNAs did not. An inhibitor of dThdPase, 6-amino-5-chlorouracil, inhibited the angiogenic activity of purified dThdPase. These findings indicate that dThdPase activity is indispensable to the angiogenic activity of PD-ECGF/dThdPase.