Purification of a 24-kD protease from apoptotic tumor cells that activates DNA fragmentation

Apoptosis--molecular mechanisms and biomedical implications

Apoptosis is a distinct form of cell death of importance in tissue development and homeostasis and in several diseases. This review summarizes current knowledge about the regulation and molecular mechanisms of apoptosis and discusses the potential role of disregulated apoptosis in several major diseases. Finally, we speculate that modulation of apoptosis may be a target in future drug therapy.

Protease inhibitors block apoptosis at intermediate stages: a compared analysis of DNA fragmentation and apoptotic nuclear morphology

The possible correlation between DNA digestion and changes in nuclear morphology in apoptosis was studied by blocking the apoptotic process at intermediate stages. The apoptogenic action of three drugs: etoposide, puromycin, tributyltin, was contrasted with protease inhibitors with different specificity on U937 cells. The inhibitors interfered with the development of the apoptotic features without shifting cell death to necrosis: treated cells showed abnormal morphologies, which could be recognized as intermediate stages of apoptosis; accordingly, DNA analysis showed an inhibitor-dependent block of the apoptotic DNA digestion. The comparison between size of DNA fragments and nuclear morphology suggested the following correlations: loss of normal nuclear shape with the appearance of a > or = 2 Mb DNA band; ongoing chromatin condensation with the progressive DNA digestion up to 50 kb; nuclear fragmentation with DNA laddering. Protease inhibitors in etoposide-treated cells did not allow the formation of 700-300 kb fragments, suggesting that they possibly derive from a cell-mediated effect.

A rabbitpox virus serpin gene controls host range by inhibiting apoptosis in restrictive cells

Poxviruses are unique among viruses in encoding members of the serine proteinase inhibitor (serpin) superfamily. Orthopoxviruses contain three serpins, designated SPI-1, SPI-2, and SPI-3. SPI-1 encodes a 40-kDa protein that is required for the replication of rabbitpox virus (RPV) in PK-15 or A549 cells in culture (A. N. Ali, P. C. Turner, M. A. Brooks, and R. W. Moyer, Virology 202:305-314, 1994). Examination of nonpermissive human A549 cells infected with an RPV mutant disrupted in the SPI-1 gene (RPV delta SPI-1) suggests there are no gross defects in protein or DNA synthesis. The proteolytic processing of late viral structural proteins, a feature of orthopoxvirus infections associated with the maturation of virus particles, also appears relatively normal. However, very few mature virus particles of any kind are produced compared with the level found in infections with wild-type RPV. Morphological examination of RPV delta SPI-1-infected A549 cells, together with an observed fragmentation of cellular DNA, suggests that the host range defect is associated with the onset of apoptosis. Apoptosis is seen only in RPV delta SPI-1 infection of nonpermissive (A549 or PK-15) cells and is absent in all wild-type RPV infections and RPV delta SPI-2 mutant infections examined to date. Although the SPI-1 gene is expressed early, before DNA replication, the triggering apoptotic event occurs late in the infection, as RPV delta SPI-1-infected A549 cells do not undergo apoptosis when infections are carried out in the presence of cytosine arabinoside. While the SPI-2 (crmA) gene, when transfected into cells, has been shown to inhibit apoptosis, our experiments provide the first indication that a poxvirus serpin protein can inhibit apoptosis during a poxvirus infection.

Isolation and partial characterization of a protease involved in Fas-induced apoptosis

Protease involvement has been implicated in the signalling process of activation-induced apoptosis. Here we report the isolation of a protease from Jurkat T cells undergoing Fas-induced apoptosis. Although the protease probably is a serine protease, it seems to be distantly related to members of the ICE/ced-3/Ich-1(nedd-2) family. In a cell-free system using isolated thymocyte nuclei, the protease rapidly induces DNA fragmentation and morphological changes typically seen in apoptosis. Our results clearly show protease activation downstream to Fas-ligation and implicate an important role for the isolated protease in signalling of Fas-induced apoptosis.

Involvement of multiple proteases during Fas-mediated apoptosis in T lymphocytes

The mechanism of Fas antigen-mediated apoptosis is at present unclear. We show here that the 100,000 x g supernatant from cell lysates prepared from anti-Fas-stimulated JUR-KAT T cells, induces chromatin fragmentation in isolated nuclei with concomitant morphological changes typically seen in apoptosis. The formation of this apoptotic nuclei promoting activity (ANPA) in JURKAT T cells after Fas antigen ligation was blocked by the serine protease inhibitors, TPCK and DCI, and by the interleukin 1-beta-converting enzyme inhibitor, VAD-FMK. In addition, chromatin degradation and morphological changes mediated by the ANPA in isolated nuclei were inhibited by TPCK, but not by DCI or VAD-FMK. These results suggest that Fas-mediated apoptosis in T cells involves the activation of a cascade of proteases.