In hepatocytes the DNA repair enzyme poly(ADP-ribose)polymerase (PARP) is n
ot proteolytically cleaved during apoptosis. The reason for this was invest
igated using a cell-free system that consisted of isolated nuclei from hepa
tocytes or thymocytes and cytosolic extracts from hepatocytes or thymocytes
undergoing apoptosis. It was found that liver PARP is resistant to proteol
ytic cleavage by the caspases present in the cytosolic extracts, Furthermor
e, liver PARP was not cleaved by recombinant human caspase-3. It is conclud
ed that PARP proteolysis cannot be used as a marker for hepatocyte apoptosi
s. (C) 1999 Academic Press.