BIOLOGICAL EFFECTS OF A RELATIVELY LOW CONCENTRATION OF 1-BETA-D-ARABINOFURANOSYLCYTOSINE IN K562 CELLS - ALTERATIONS OF THE CELL-CYCLE, ERYTHROID-DIFFERENTIATION, AND APOPTOSIS

Therapeutic strategies for leukemia are directed to induction of diffe rentiation and apoptosis as well as growth inhibition. One of the key antileukemic agents, 1-beta-D-arabinofuranosylcytosine (ara C), is cli nically applied according to these therapeutic aims. However, the mole cular effects of 0.1 mu g/ml of ara C, a concentration that correspond s to the serum level in leukemic patients on a conventional dose of ar a C, have not been well disclosed. Here, we addressed these issues usi ng K562 cells which derived from a blastic crisis of chronic myeloid l eukemia. DNA synthesis of treated cells was suppressed from 1-6 h. But , it recovered at 12 h and no further inhibition was observed. The num ber of cells was not decreased but DNA fragmentation was observed at 7 2 h, The number of erythroid-differentiated cells also increased to 30 % at 72 h. Along with treatment, no marked alteration of mRNAs for cel l cycle-regulating genes was found and the retinoblastoma gene product remained hyperphosphorylated throughout treatment. The expression of mRNAs for apoptosis-regulating genes also remained unchanged, except f or slight down-regulation of Bar. c-myc protein was not found later th an 48 h, and Max mRNA was downregulated. c-jun was immediately induced , followed by the fluctuated expression level along with treatment. Th ese findings suggest that the 0.1 mu g/ml ara C changed the proliferat ion, differentiation and death of K562 cells in a biphasic manner. In the early phase, DNA synthesis was inhibited without altering the expr ession of cell cycle regulating-genes. In the latter phase, cell death and erythroid-differentiation occurred in accordance with the down-re gulation of c-myc.