DNase gamma, which cleaves chromosomal
DNA into nucleosomal units (
DNA ladder formation), has been suggested to be the critical component of apoptotic machinery. Using rat
pheochromocytoma PC12 cells, which are differentiated to sympathetic neurons by
nerve growth factor (
NGF), we investigated whether
DNase gamma-like
enzyme is present in neuronal cells and is involved in neuronal cell death. The nuclear auto-digestion assay for
DNase catalyzing internucleosomal DNA cleavage revealed that nuclei from neuronal differentiated PC12 cells contain acidic and neutral
endonucleases, while nuclei from undifferentiated PC12 cells have only acidic
endonuclease. The
DNA ladder formation observed in isolated nuclei from neuronal differentiated PC12 cells at neutral pH requires both Ca(2+) and Mg(2+), and is sensitive to Zn(2+). The molecular mass of the neutral
endonuclease present in neuronal differentiated PC12 cell nuclei is 32000 as determined by activity gel analysis (zymography). The properties of the neuronal
endonuclease present in neuronal differentiated PC12 cell nuclei were similar to those of purified
DNase gamma from rat thymocytes and splenocytes. Interestingly, in neuronal differentiated PC12 cells, internucleosomal DNA fragmentation is observed following
NGF deprivation, whereas undifferentiated PC12 cells fail to exhibit
DNA ladder formation during cell death by serum
starvation. These results suggest that the
DNase gamma-like
endonuclease present in neuronal differentiated PC12 cell nuclei is involved in internucleosomal DNA fragmentation during apoptosis, induced by
NGF deprivation.