Apoptosis is a morphologically and biochemically distinct form of cell death that occurs under a variety of physiological and pathological conditions. In the present study, the proteolytic cleavage of poly(ADP-ribose) polymerase (pADPRp) during the course of chemotherapy-induced apoptosis was examined. Treatment of HL-60 human leukemia cells with the topoisomerase II-directed anticancer agent etoposide resulted in morphological changes characteristic of apoptosis. Endonucleolytic degradation of DNA to generate nucleosomal fragments occurred simultaneously. Western blotting with epitope-specific monoclonal and polyclonal antibodies revealed that these characteristic apoptotic changes were accompanied by early, quantitative cleavage of the M(r) 116,000 pADPRp polypeptide to an M(r) approximately 25,000 fragment containing the amino-terminal DNA-binding domain of pADPRp and an M(r) approximately 85,000 fragment containing the automodification and catalytic domains. Activity blotting revealed that the M(r) approximately 85,000 fragment retained basal pADPRp activity but was not activated by exogenous nicked DNA. Similar cleavage of pADPRp was observed after exposure of HL-60 cells to a variety of chemotherapeutic agents including cis-diaminedichloroplatinum(II), colcemid, 1-beta-D-arabinofuranosylcytosine, and methotrexate; to gamma-irradiation; or to the protein synthesis inhibitors puromycin or cycloheximide. Similar changes were observed in MDA-MB-468 human breast cancer cells treated with trifluorothymidine or 5-fluoro-2'-deoxyuridine and in gamma-irradiated or glucocorticoid-treated rat thymocytes undergoing apoptosis. Treatment with several compounds (tosyl-L-lysine chloromethyl ketone, tosyl-L-phenylalanine chloromethyl ketone, N-ethylmaleimide, iodoacetamide) prevented both the proteolytic cleavage of pADPRp and the internucleosomal fragmentation of DNA. The results suggest that proteolytic cleavage of pADPRp, in addition to being an early marker of chemotherapy-induced apoptosis, might reflect more widespread proteolysis that is a critical biochemical event early during the process of physiological cell death.

https://cancerres.aacrjournals.org/content/canres/53/17/3976.full.pdf

Specific Proteolytic Cleavage of Poly(ADP-ribose) Polymerase: An Early Marker of Chemotherapy-induced Apoptosis

Zinc and immune function: the biological basis of altered resistance to infection.

I. Introduction DEATH, along with growth and differentiation, is a critical part of the life cycle of a cell. Homeostatic control of cell number is thought to be the result of the dynamic balance between cell proliferation and cell death. It is only in the past few years, however, that attention has been focused on the physiological occurrence of cell death and its role in homeostasis. Researchers have become increasingly more aware during this time that this type of “natural” death, which is now called apoptosis or programmed cell death, is a widespread phenomenon that plays a crucial role in a myriad of physiological and pathological processes. This review first briefly covers some historical perspective on the discovery of apoptotic cell death, the characteristic morphology that accompanies this process, and the numerous cell types and mediators with which programmed cell death is associated. The bulk of the review discusses our current understanding of the biochemical and molecular mechanisms by which...

Apoptosis: the biochemistry and molecular biology of programmed cell death.

In addition to its diverse role in many physiological systems, zinc (Zn) has now been shown to be an important regulator of apoptosis. The purpose of this review is to integrate previously published knowledge on Zn and apoptosis with current attempts to elucidate the mechanisms of action of this biometal. This paper begins with an introduction to apoptosis and then briefly reviews the evidence relating Zn to apoptosis. The major focus of this review is the mechanistic actions of Zn and its candidate intracellular targets. In particular, we examine the cytoprotective functions of Zn which suppress major pathways leading to apoptosis, as well as the more direct influence of Zn on the apoptotic regulators, especially the caspase family of enzymes. These two mechanisms are closely related since a decline in intracellular Zn below a critical threshold level may not only trigger pathways leading to caspase activation but may also facilitate the process by which the caspases are activated. Studies by our laboratory in airway epithelial cells show that Zn is co-localized with the precursor form of caspase-3, mitochondria and microtubules, suggesting this Zn is critically placed to control apoptosis. Further understanding the different pools of Zn and how they interact with apoptotic pathways should have importance in human disease.

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The role of zinc in caspase activation and apoptotic cell death

Work reported here investigated aspects of macrophage-mediated tumor cell death, in particular the role of apoptosis as a mechanism for nitric oxide (NO)-mediated macrophage tumor cytotoxicity. Nitric oxide induced apoptosis in P815 cells in macrophage P815 cocultures where fragmentation of tumor cell [3H]thymidine-labeled DNA preceded cell lysis (as measured by 51Cr release), paralleled nitrite accumulation, and was prevented by a specific inhibitor of NO synthase, N-MMA. DNA from P815 cells separated from macrophages in culture by a cell-impermeable membrane or exposed to authentic NO gas showed the pattern of internucleosomal cleavage that is characteristic of apoptosis. Additionally, culture of P815 cells with the NO donor sodium nitroprusside was followed by DNA fragmentation. Macrophages also induced apoptosis in L929 cells but, in this case, apoptosis was NO independent and partially inhibited in cocultures by an antitumor necrosis factor α monoclonal antibody. The anti-tumor necrosis factor α monoclonal antibody fully prevented apoptosis when macrophages and L929 were separated by a cell-impermeable membrane. Exposure of L929 cells to NO gas or sodium nitroprusside did not result in their apoptotic death. Like other immune cytotoxic cells, macrophages can determine tumor cell death through the induction of apoptosis and do so through more than one effector mechanism.

https://cancerres.aacrjournals.org/content/canres/54/9/2462.full.pdf

M. Egan

Papers

Apoptosis induced in macrophages and T blasts by the mycotoxin sporidesmin and protection by Zn2+ salts.