INTRACELLULAR ACIDIFICATION INDUCES APOPTOSIS BY STIMULATING ICE-LIKEPROTEASE ACTIVITY

ICE-like protease activation and DNA fragmentation are preceded by a d ecrease in intracellular pH (pH(i)) during apoptosis in the IL-3 depen dent cell line BAF3. Acidification occurs after 7 hours in cells depri ved of IL-3 and after 4 hours when cells are treated with etoposide, c lose to the time of detection of ICE-like protease activity. Increasin g extracellular pH reduces ICE-like protease activation and DNA fragme ntation. Bcl-2 over-expression both delays acidification and inhibits ICE-like protease activation. Generation of a rapid intracellular pH d ecrease, using the ionophore nigericin, induces ICE-like protease acti vation and apoptosis. ZVAD, a cell permeable inhibitor of ICE-like pro teases, does not affect acidification but inhibits apoptosis induced b y IL-3 removal or nigericin treatment. These data suggest that intrace llular acidification triggers apoptosis by directly or indirectly acti vating ICE-like proteases.