The effects of Thymidine phsphorylase on tumor angiogenesis and on the sensitivity to anti-tumor drugs

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Human thymidine phsphorylase (dThdPase) is thought to be indentical to an angiogenic factor, Platelet-derived endothelial cell growth factor (PD-ECGF) .However, the whole amino acid sequence of dThdPase is still unknown. N-termina amino acid sequencing of dThdPase isolated human placenta gave the sequence Ac-AALMTPGTGAPPAPG.Comparison with the sequence predicted from the PD-ECGFcDNA reveals that residues 2-16 of dThdPase are indentical to that of PD-ECGF.The primary translational product of dThdPase would be processed one amino acid from the translation-initiating methionine residue and Ala-2 acetylated.dThdPase has angiogenic activity. To investigate whether the dThdpase activity of PD-ECGF/dThdpase is indispensable to its angiogenic activity, three PD-ECGF/dThdpase mutant which have no dThdpase activity were made by site-derected mutagenesis. The lysates of COS cells transfected with the wild-type PD-ECGF/dThdpase cDNA had angiogenic activity, but those transfected with the mutant PD-ECGF/dThdpase 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 angiogenic activity of PD-ECGF/dThdpase.Human KB epidermal carcinoma cells transfected with PD-ECGF cDNA expressed a 55-kDa protein that was detected with anti-dThdPase antibody and the cell lysate had dThdPase activity. The sensitivity of the transfected cells to 5'-deoxy-5-fluorouridine was higher than that of untransfected KB cells. These results demonstrate that dThdPase is involved in the activation of these anticancer agents.