Abstract
To test the hypothesis that the toxicity of rubratoxin B is a consequence of apoptosis, we investigated fragmentation of nuclei and internucleosomal fragmentation (DNA ladder). Exposure to rubratoxin B caused HL-60 cells to condense their chromatin and fragment their nuclei, showing that rubratoxin B induces apoptosis. We observed DNA ladder in HL-60 cells treated with rubratoxin B for 24 hr. Cycloheximide did not affect rubratoxin B-induced DNA ladder. Therefore, rubratoxin B-induced apoptosis is considered not to require protein synthe-sis. Twenty four-hr treatment of rubratoxin B or ethylene glycol-bis (β-aminoethyl ether)-tetraacetic acid (EGTA) alone resulted in DNA ladder, but no DNA ladder treated with both chemicals for 24 hr. Eight-hr treatment of rubratoxin B and EGTA resulted in DNA ladder, suggesting that long exposure to both chemicals led to post-apoptotic DNA degradation. Since the addition of Ca2+ inhibited the effect of EGTA, the reduction of extracellular Ca2+ concentra-tion by EGTA appears to cause an enhancement of rubratoxin B-induced DNA degradation.
