APOPTOSIS INDUCED IN JURKAT CELLS BY SEVERAL AGENTS IS PRECEDED BY INTRACELLULAR ACIDIFICATION

We have previously shown that in neutrophils deprived of granulocyte c olony-stimulating factor, apoptosis is preceded by acidification and t hat the protection against apoptosis conferred on neutrophils by granu locyte colony-stimulating factor is dependent upon delay of this acidi fication, To test the hypothesis that acidification could be a general feature of apoptosis, we examined intracellular pH changes in another cell line, Jurkat cells, a T-lymphoblastoid line, were induced to und ergo apoptosis with anti-Fas IgM, cycloheximide, or exposure to short- wavelength UV light, We found that acidification occurred in response to treatment with these agents and that acidification preceded DNA fra gmentation, Jurkat cells were also found to possess an acid endonuclea se that is active below pH 6.8, compatible with a possible role for th is enzyme in chromatin digestion during apoptosis, Incubation of the c ells with the bases imidazole or chloroquine during treatment with ant i Fas antibody or cycloheximide or after UV exposure decreased apoptos is as assessed by nuclear morphology and DNA content, The alkalinizing effect of imidazole and chloroquine was shown by the demonstration th at the percentage of cells with an intracellular pH below 6.8 after tr eatment with anti-Fas antibody, cycloheximide, or UV was diminished in the presence of base as compared with similarly treated cells incubat ed in the absence of base, We conclude that acidification is an early event in programmed cell death and may be essential for genome destruc tion.