Role of caspases (ICE/CED 3 proteases) in DNA damage and cell death in response to a mitochondrial inhibitor, antimycin A

Crucial role of apopain in the peroxynitrite-induced apoptotic DNA fragmentation

Peroxynitrite, a cytotoxic oxidant formed in the reaction of superoxide and nitric oxide is known to cause programmed cell death. However, the mechanisms of peroxynitrite-induced apoptosis are poorly defined. The present study was designed to characterize the molecular mechanisms by which peroxynitrite induces apoptosis in HL-60 cells, with special emphasis on the role of caspases. Peroxynitrite induced the activation of apopain/caspase-3, but not ICE/caspase-1 as measured by the cleavage of fluorogenic peptides. Considering the short half-life of peroxynitrite and the kinetics of caspase-3 activation (starting 3-4 h after peroxynitrite treatment), the enzyme is not likely to become activated directly by the oxidant. Caspase-3 activation proved to be essential for DNA fragmentation, because pretreatment of the cells with the specific tetrapeptide inhibitor DEVD-fmk completely blocked peroxynitrite-induced DNA fragmentation. Peroxynitrite-induced cytotoxicity was also significantly altered by the inhibition of caspase-3, whereas phosphatidylserine exposure was unaffected by DEVD-fmk treatment. Because many of the effects of peroxynitrite are mediated by poly(ADP-ribose) synthetase (PARS) activation, we have also investigated the effect of PARS-inhibition on peroxynitrite-induced apoptosis. We have found that PARS-inhibition modulates peroxynitrite-induced apoptotic DNA fragmentation in the HL-60 cells. The effect of the PARS inhibitors, 3-aminobenzamide and 5-iodo-6-amino-1,2-benzopyrone were dependent on the concentration of peroxynitrite used. While PARS-inhibition resulted in increased DNA-fragmentation at low doses (15 microM) of peroxynitrite, a decreased DNA-fragmentation was found at high doses (60 microM) of peroxynitrite. PARS inhibition negatively affected viability as determined by flow cytometry. These data demonstrate the crucial role of caspase-3 in mediating apoptotic DNA fragmentation in HL-60 cells exposed to peroxynitrite.

Peroxynitrite-induced thymocyte apoptosis: the role of caspases and poly (ADP-ribose) synthetase (PARS) activation

The mechanisms by which immature thymocyte apoptosis is induced during negative selection are poorly defined. Reports demonstrated that cross-linking of T-cell receptor leads to stromal cell activation, expression of inducible nitric oxide synthase (iNOS) and, subsequently, to thymocyte apoptosis. Therefore we examined, whether NO directly or indirectly, through peroxynitrite formation, causes thymocyte apoptosis. Immuno-histochemical detection of nitrotyrosine revealed in vivo peroxynitrite formation in the thymi of naive mice. Nitrotyrosine, the footprint of peroxynitrite, was predominantly found in the corticomedullary junction and the medulla of naive mice. In the thymi of mice deficient in the inducible isoform of nitric oxide synthase, considerably less nitrotyrosine was found. Exposure of thymocytes in vitro to low concentrations (10 microM) of peroxynitrite led to apoptosis, whereas higher concentrations (50 microM) resulted in intense cell death with the characteristics of necrosis. We also investigated the effect of poly (ADP-ribose) synthetase (PARS) inhibition on thymocyte apoptosis. Using the PARS inhibitor 3-aminobenzamide (3-AB), or thymocytes from PARS-deficient animals, we established that PARS determines the fate of thymocyte death. Suppression of cellular ATP levels, and the cellular necrosis in response to peroxynitrite were prevented by PARS inhibition. Therefore, in the absence of PARS, cells are diverted towards the pathway of apoptotic cell death. Similar results were obtained with H2O2 treatment, while apoptosis induced by non-oxidative stimuli such as dexamethasone or anti-FAS antibody was unaffected by PARS inhibition. In conclusion, we propose that peroxynitrite-induced apoptosis may play a role in the process of thymocyte negative selection. Furthermore, we propose that the physiological role of PARS cleavage by apopain during apoptosis may serve as an energy-conserving step, enabling the cell to complete the process of apoptosis.

Identification of gene family of caspases in rat kidney and altered expression in ischemia-reperfusion injury

In the present study, we demonstrate that rat kidney contains caspase activity that was markedly inhibited by specific peptide inhibitors of caspases but not by inhibitors of Ser, Cys, Asp, or metalloproteinases. Using primers based on the nucleotide sequence of known members of Ced-3/interleukin-1 beta-converting enzyme (ICE) family from human origin, we have identified by reverse-transcription (RT) polymerase chain reaction (PCR) analyses that rat kidney transcribes the genes for caspase-1 (ICE), caspase-2 (Nedd2), caspase-3 (CPP32), and caspase-6 (Mch2). RT-PCR products, when subcloned and sequenced, provided full-length cDNAs for ICE (1,209 bp) and CPP32 (786 bp) and partial cDNA products for Mch2 (561 bp) and Nedd2 (811 bp). The sequence analysis of the caspase cDNAs showed conserved catalytic site QACRG as well as Asp cleavage site. Rat kidneys subjected to ischemia-reperfusion injury revealed differential expression of caspases with marked increase in CPP32 and ICE mRNA and proteins during reperfusion, transient increase in Nedd2 mRNA and proteins during ischemia and the early period of reperfusion, and little change in Mch2 expression during the ischemia or reperfusion period. The altered expression suggests that caspases may act in concert in a cascade and may play an important role in ischemic acute renal failure.