Identification of apoptotic tyrosine-phosphorylated proteins after etoposide or retinoic acid treatment.

A main shortcoming of using HL-60 cells as a model of granulocyte-macrophage differentiation is that some cells in the differentiating population undergo apoptosis. To address this issue, we have identified which tyrosine-phosphorylated proteins are involved in apoptosis and differentiation, respectively. HL-60 cells were induced specifically to undergo apoptosis with 68 microM etoposide, and to undergo granulocytic differentiation with 1 microM retinoic acid (RA). The corresponding two-dimensional electrophoretic maps of tyrosine-phosphorylated proteins from treated cells were compared. In the 8 h etoposide-treated HL-60 cell population, 83% of the cells were apoptotic. In the 120 h RA-treated cells, 50% of the cells were apoptotic. Eighteen cytosolic and nuclear tyrosine-phosphorylated proteins were found in both the 8 h etoposide- and the 120 h RA-treated cells, but not in the proliferating HL-60 cell population. Matrix-assisted laser desorption/ionization-time of flight mass spectrometry analyses suggested that some of the proteins may be involved in signal transduction pathways (NFkappaB, GTP-binding protein, protein disulfide isomerase, Cyclophilin A), others in cell transcriptional and translational control (hnRNP H, hnRNP L, Hsp60, Hp1, Hcc-1, 26S proteasome beta-subunit, ATP synthase beta-chain), and a third group in cell cytoskeleton organization and receptor cycling (profilin, caveolin-1). An understanding of signal transduction in apoptosis initiation by screening for tyrosine-phosphorylated proteins associated with apoptosis may provide new targets for the treatment of leukemia.