RRC ID 39778
Author Komatsu N, Nakagawa M, Oda T, Muramatsu T.
Title Depletion of intracellular NAD(+) and ATP levels during ricin-induced apoptosis through the specific ribosomal inactivation results in the cytolysis of U937 cells.
Journal J Biochem
Abstract Our previous studies demonstrated that ricin induces the apoptotic death of U937 cells as evidenced by DNA fragmentation, nuclear morphological changes, and increases in caspase-like activities. In this study, we have found that intracellular NAD(+) and ATP levels decrease in ricin-treated U937 cells and that this decrease is followed by the ricin-mediated protein synthesis inhibition. The PARP inhibitor, 3-aminobenzamide (3-ABA), prevents the depletion in NAD(+) and ATP levels and concomitantly protects U937 cells from the lysis that follows ricin treatment. Hence, the protective action of 3-ABA is due to the inhibition of PARP and does not result from its other pharmacological side effects. Moreover, the enzymatic activity of PARP gradually increases and reaches a maximum level after ricin exposure for 3 h, whereas no significant change in activity was observed in untreated cells. However, 3-ABA has no effect on ricin-mediated DNA fragmentation. In addition, immunoblot analysis revealed that significant PARP cleavage occurred more than 12 h after ricin addition, while DNA fragmentation reached a maximum level within 6 h of incubation. Thus, in the case of ricin-induced apoptosis, it appears that PARP cleavage is not an early apoptotic event associated with the onset of apoptosis. Our results suggest that multiple apoptotic signaling pathways may be triggered by ricin-treatment. Probably, the pathway leading to cell lysis via PARP activation and NAD(+) depletion is independent of the pathway leading to DNA fragmentation in which caspases may be profoundly involved. Other protein synthesis inhibitors, including diphtheria toxin and cycloheximide, were less effective in terms of inducing DNA fragmentation and cytolysis, even at concentrations that cause significant inhibition of protein synthesis. Thus, a specific ricin action mechanism through which ribosomes are inactivated may be responsible for the apoptotic events induced by ricin.
Volume 128(3)
Pages 463-70
Published 2000-9
DOI 10.1093/oxfordjournals.jbchem.a022775
PMID 10965046
MeSH Adenosine Triphosphate / metabolism* Apoptosis / drug effects* Benzamides / metabolism Benzamides / pharmacology Blotting, Western Cells, Cultured / drug effects Diphtheria Toxin / pharmacology Humans Microscopy, Fluorescence NAD / metabolism* Plant Proteins / isolation & purification Poly(ADP-ribose) Polymerases / metabolism* Protein Synthesis Inhibitors Ribosomes / physiology* Ricin / pharmacology* Time Factors U937 Cells / drug effects* U937 Cells / metabolism
IF 2.23
Times Cited 48
Human and Animal Cells