1-BETA-D-ARABINOFURANOSYLCYTOSINE ACTIVATES TYROSINE PHOSPHORYLATION OF P34(CDC2) ITS ASSOCIATION WITH THE SRC-LIKE P56/P53(LYN) KINASE IN HUMAN MYELOID-LEUKEMIA CELLS

Recent studies have demonstrated that treatment of human myeloid leukemia cells with 1-beta-D-arabinofuranosylcytosine (ara-C) is associated with activation of serine/threonine protein kinases and early response gene expression. The present work has examined the involvement of protein tyrosine phosphorylation in ara-C induced responses of HL-60 myeloid leukemia cells. The results of immuno-precipitation studies demonstrate that HL-60 cells respond to ara-C with tyrosine phosphorylation of the cell cycle regulatory protein p34(cdc2) a decrease in the activity of this kinase. This effect was detectable at 15 min of ara-C exposure. Coimmunoprecipitations with anti-p34(cdc2) support binding of this protein to the Src-like p56/p53(lyn) tyrosine kinase in ara-C-treated, but not untreated, cells. The results further demonstrate that ara-C treatment is associated with a dose-dependent activation of p56/p53(lyn) and that ara-C-induced p56/p53(lyn) activity is blocked by the protein tyrosine inhibitors herbimycin A and genistein. Studies with a glutathione S-transferase-Lyn fusion protein confirm interaction of p34(cdc2) and p56/p53(lyn) in lysates of ara-C-treated cells. Moreover, we demonstrate that (1) p56/p53(lyn) phosphorylates Tyr-15 of p34(cdc2) in vitro and (2) phosphorylation of p34(cdc2) by p56/p53(lyn) inhibits p34(cdc2) activity. These findings indicate that the cellular response to ara-C includes activation of p56/p53(lyn) and that association of p56/p53(lyn) with p34(cdc2) may contribute to regulation of the cell cycle progression in ara-C-treated cells.