Prostaglandin A2 activates intrinsic apoptotic pathway by direct interaction with mitochondria in HL-60 cells

HL-60 cells treated by prostaglandin (PG) A2 showed characteristics of apoptosis such as accumulation of hypodiploid and annexin V positive cells, condensed and fragmented nuclei, cytochrome c (Cyt C) release from mitochondria and activation of caspase-1, -2, -3, -7 and -9. PGA2-induced cell death was rescued by inhibitors of caspase-9 and -3, but PGA2-induced Cyt C release was not prevented by caspase inhibitors. During Cyt C release by PGA2, mitochondrial transmembrane potential was maintained and mitochondrial permeability transition pore was not formed. In addition, anti-apoptotic BCL-2 family proteins like BCL-2 and BCL-XL, and ROS scavengers including ascorbic acid and 2,2,6,6-tetramethyl-1-piperidinyloxy were not able to inhibit Cyt C release as well as apoptosis by PGA2. Finally, it was shown that PGA2-induced Cyt C release in vitro from purified mitochondria in the absence of cytosolic components. Furthermore, thiol-containing compounds such as N-acetylcysteine, l-cysteine and monothioglycerol prevented Cyt C release, and hence induction of apoptosis. Taken together, these results suggest that PGA2 activates intrinsic apoptotic pathway by directly stimulating mitochondrial outer membrane permeabilization to release Cyt C, in which thiol-reactivity of PGA2 plays a pivotal role.