The
antimetabolite 1-beta-D-arabinofuranosylcytosine (
ara-C) has been used as a highly effective agent for the treatment of
leukemia. The active metabolite 1-beta-D-arabinofuranosylcytosine
triphosphate (
ara-CTP) is a potent inhibitor of
DNA polymerases alpha, delta, and epsilon, and is responsible for inhibiting intact cell
DNA synthesis. We have shown that a multiprotein complex, exhibiting many of the properties expected of the human cell DNA replication apparatus, can be readily isolated from human cells and tissues and is capable of supporting origin-dependent
DNA synthesis in vitro.
DNA polymerases alpha, delta, and epsilon are components of this multiprotein complex, termed the
DNA synthesome, and we report here that the activities of these
DNA synthesome-associated
DNA polymerases are inhibited differentially by
ara-CTP. Inhibition of the
DNA synthesome-associated
DNA polymerase alpha increased in a concentration-dependent manner, and was correlated closely with the inhibition of simian virus 40 (SV40) origin-dependent in vitro DNA replication, whereas
DNA synthesome-associated
DNA polymerase delta activity was not inhibited significantly by
ara-CTP at 100 microM. Recent work has shown that the synthesome-associated
DNA polymerase epsilon does not function in in vitro SV40 DNA replication, suggesting that only polymerases alpha and delta drive the DNA replication fork. Therefore, our results suggest that inhibition of the activity of the mammalian cell
DNA synthesome by
ara-CTP is due primarily to the inhibition of the
DNA synthesome-associated
DNA polymerase alpha. This observation implies that the
drug may target specific phases of the
DNA synthetic process in human cells.