1-beta-D-arabinofuranosylcytosine activates tyrosine phosphorylation of p34cdc2 and its association with the Src-like p56/p53lyn 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 immunoprecipitation studies demonstrate that HL-60 cells respond to ara-C with tyrosine phosphorylation of the cell cycle regulatory protein p34cdc2 and a decrease in the activity of this kinase. This effect was detectable at 15 min of ara-C exposure. Coimmunoprecipitations with anti-p34cdc2 support binding of this protein to the Src-like p56/p53lyn 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/p53lyn and that ara-C-induced p56/p53lyn activity is blocked by the protein tyrosine inhibitors herbimycin A and genistein. Studies with a glutathione S-transferase-Lyn fusion protein confirm interaction of p34cdc2 and p56/p53lyn in lysates of ara-C-treated cells. Moreover, we demonstrate that (1) p56/p53lyn phosphorylates Tyr-15 of p34cdc2 in vitro and (2) phosphorylation of p34cdc2 by p56/p53lyn inhibits p34cdc2 activity. These findings indicate that the cellular response to ara-C includes activation of p56/p53lyn and that association of p56/p53lyn with p34cdc2 may contribute to regulation of the cell cycle progression in ara-C-treated cells.