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 ident ical 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 muta nts, K115E (Lys-115 --> Glu), L148R (Leu-148 --> Arg) and R202S (Arg-2 02 --> Ser) were made by site-directed mutagenesis. Although the expre ssion level of the three mutant PD-ECGF/dThdPases in the COS-7 cells w as similar to that of wild-type PD-ECGF/dThdPase, dThdPase activity wa s 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-ty pe PD-ECGF/dThdPase cDNA had angiogenic activity, but those transfecte d with the mutant PD-ECGF/dThdPase cDNAs did not. An inhibitor of dThd Pase, 6-amino-5-chlorouracil, inhibited the angiogenic activity of pur ified dThdPase. These findings indicate that dThdPase activity is indi spensable to the angiogenic activity of PD-ECGF/dThdPase.