THE ACID DEOXYRIBONUCLEASE OF NEUTROPHILS - A POSSIBLE PARTICIPANT INAPOPTOSIS-ASSOCIATED GENOME DESTRUCTION

Human neutrophils are terminally differentiated cells that spontaneous ly undergo apoptosis in tissue culture. Apoptosis in these cells can b e delayed by culture in the presence of granulocyte colony-stimulating factor or other inflammatory mediators. Neutrophils were found to con tain an acid endonuclease that appeared to be responsible for the inte rnucleosomal DNA cleavage that accompanies apoptosis. As measured by a plasmid nicking assay, this endonuclease had a molecular weight (M(r) ) of 35,000, a pH optimum of 5.5, and a threshold for activity of pH 6 .6 to 6.8, It was weakly inhibited by divalent cations (Ca2+, Mg2+, an d Zn2+) and more strongly inhibited by aurintricarboxylic acid and N-b romosuccinimide. DNA from neutrophils treated with nigericin in buffer s of defined pH displayed nucleosomal ladders whose prominence varied with pH in a manner that paralleled the pH dependence of the plasmid c leavage assays, consistent with internucleosomal DNA cleavage by the a cid endonuclease. We have previously shown that neutrophils undergo ac idification to a pH value as low as 6.0 during apoptosis; we suggest t hat this endonuclease may be responsible for the DNA cleavage seen in apoptotic neutrophils. (C) 1995 by The American Society of Hematology.