Proteomic analysis of apoptosis initiation induced by all-trans retinoic acid in human acute promyelocytic leukemia cells

The irreversible destiny of apoptosis in its early stage might play a criti cal role in the apoptosis of human acute promyelocytic leukemia (APL) cell line induced by all-trans retinoic acid (ATRA). To characterize protein alt erations during the apoptosis-Initiation phase and to understand the metabo lic status at that time, we investigated the protein profiles in the apopto sis-initiation phase of APL cell line HL-60 by proteomic analysis. ATRA-wit hdrawal was conducted to demonstrate that there was committed initiation ph ase of apoptosis triggered by 10(-6) M ATRA at day 3. Only after that time point, ATRA-treated cells irreversibly went to apoptosis. Also at that time point, the positive regulators of apoptosis such as STAT3 increased at pro tein level, whereas negative regulators (Bcl-2 and p-STAT3) decreased. In a ddition, caspase-3 also increased after that time. Furthermore, comparative proteomic analysis was utilized to examine the protein expression profiles during the initiation stage of apoptosis. Our results showed 12 upregulate d and 7 downregulated proteins experiencing twofold alteration, including k ey regulators of signal transduction such as G-proteins and nucleic recepto rs, proteins related with metabolism, oxidation and reduction, proteins ass ociated with the nucleus and cytoskeleton-related proteins. Some of them co uld be positive modulators to trigger apoptosis, whereas others could contr ibute to intracellular defense against apoptosis induced by exogenous trigg ers. The results above suggest that there is a subtle balance between apopt osis and the intracellular defense against apoptosis. Once the balance is d isturbed, cells would irreversibly initiate to undergo the execution of apo ptosis.