Inhibition of mono-ADP-ribosyltransferase activity during the execution phase of apoptosis prevents apoptotic body formation

The objective of this study was to understand factors responsible for apopt otic body formation and release during apoptosis, We have found that inhibi tion of mono-ADP ribosylation after ultraviolet (UV) light induction of apo ptosis in HL-60 cells does not block caspase-3 activation, gelsolin cleavag e, or endonucleolytic DNA fragmentation. However, the cytoskeletal features of apoptosis leading to apoptotic body formation and release were inhibite d by meta-iodobenzylguanidine (MIBG) and novobiocin, potent inhibitors of a rginine-specific mono-ADP-ribosyltransferases (mono-AD-PRTs), Suppression o f mono-ADP ribosylation as late as 120 min following UV irradiation blocked the depolymerization of actin and release of apoptotic bodies. This sugges ted that the cytoskeletal changes of apoptosis may be decoupled from the ca spase cascade and that there may be a biochemical event either distal to or independent of caspase-3 that regulates apoptotic body formation. To test the hypothesis that ADP ribosylation of actin may occur with the induction of apoptosis, an in vivo assay of mono-ADPRT activity using an antibody aga inst ADP-ribosylarginine was used, An approximately 64% increase in the ADP ribosylation of actin was observed at 2 h following exposure to UV light. When MIBG or novobiocin was present, the ADP ribosylation of actin was only 14-18% above the levels observed in control nonirradiated cells, The curre nt study is the first to demonstrate a relationship between ADP-ribosylatio n of actin and the formation of apoptotic bodies. (C) 2001 Academic Press.