Activation of deoxycytidine kinase by inhibition of DNA synthesis in humanlymphocytes

Deoxycytidine kinase (dCK, EC.2.7.1.74) is a key enzyme in the intracellula r metabolism of 2-chlorodeoxyadenosine, 1-beta -D-arabinofuranosylcytosine, difluorodeoxycytidine, and other drugs used in chemotherapy of different l eukaemias and solid tumours. Recently, stimulation of dCK activity was show n by these analogues and by other genotoxic agents such as etoposide and Na F, all of which cause severe inhibition of DNA synthesis in cell cultures. Here we describe that direct inhibition of DNA polymerases by aphidicolin s timulated dCK activity in normal lymphocytes and acute myeloid leukaemic ce lls, as well as in HL 60 promyelocytic cell cultures. Increased dCK activit y was not due to new protein synthesis under our conditions, as measured by immunoblotting. Partial purification by diethylaminoethyl-Sephadex chromat ography revealed that the activated form of dCK survived purification proce dure. Moreover, it was possible to inactivate purified dCK preparations by recombinant protein phosphatase with Ser/Thr/Tyr dephosphorylating activity . These data suggest that the activation of dCK may be due to phosphorylati on, and that deoxynucleoside salvage is promoted during inhibition of DNA s ynthesis in human lymphocytes. (C) 2001 Elsevier Science Inc. All rights re served.