Apoptosis is a distinct mode of cell death that is responsible for deletion of cells in normal tissues; it also occurs in specific pathologic contexts. Morphologically, it involves rapid condensation and budding of the cell, with the formation of membrane-enclosed apoptotic bodies containing well-preserved organelles, which are phagocytosed and digested by nearby resident cells. There is no associated inflammation. A characteristic biochemical feature of the process is double-strand cleavage of nuclear DNA at the linker regions between nucleosomes leading to the production of oligonucleosomal fragments. In many, although not all of the circumstances in which apoptosis occurs, it is suppressed by inhibitors of messenger RNA and protein synthesis. Apoptosis occurs spontaneously in malignant tumors, often markedly retarding their growth, and it is increased in tumors responding to irradiation, cytotoxic chemotherapy, heating and hormone ablation. However, much of the current interest in the process stems from the discovery that it can be regulated by certain proto-oncogenes and the p53 tumor suppressor gene. Thus, c-myc expression has been shown to be involved in the initiation of apoptosis in some situations, and bcl-2 has emerged as a new type of proto-oncogene that inhibits apoptosis, rather than stimulating mitosis. In p53-negative tumor-derived cell lines transfected with wild-type p53, induction of the gene has, in rare cases, been found to cause extensive apoptosis, instead of growth arrest. Finally, the demonstration that antibodies against a cell-surface protein designated APO-1 or Fas can enhance apoptosis in some human lymphoid cell lines may have therapeutic implications.

Apoptosis. Its significance in cancer and cancer Therapy

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

Glutamate-induced neuronal death: A succession of necrosis or apoptosis depending on mitochondrial function

The antioxidants of human extracellular fluids.

Neurodegeneration in Excitotoxicity, Global Cerebral Ischemia, and Target Deprivation: A Perspective on the Contributions of Apoptosis and Necrosis

The incubation of human mammary adenocarcinoma cells (BT-20) with tumor necrosis factor α in the absence or presence of cycloheximide resulted in progressive DNA fragmentation. This was preceded by a sustained increase in intracellular free Ca2+ concentration and was not detected in cells pretreated with intracellular Ca2+ chelators, calmodulin antagonists, or activators of protein kinase C. Image analysis of fura-2-loaded BT-20 cells treated with tumor necrosis factor α revealed that, in many cells, the initial increase in Ca2+ level occurred in a cellular region that corresponded to the localization of the nucleus. Our findings suggest that tumor necrosis factor α can promote an increase in intranuclear free Ca2+ which, in turn, may stimulate Ca2+-dependent endonuclease activity, resulting in DNA fragmentation and apoptosis.

Tumor Necrosis Factor α Induces Apoptosis in Mammary Adenocarcinoma Cells by an Increase in Intranuclear Free Ca2+ Concentration and DNA Fragmentation

https://febs.onlinelibrary.wiley.com/doi/pdf/10.1016/0014-5793%2890%2980040-P

Calcium-dependent DNA fragmentation in human synovial cells exposed to cold shock

Alterations of surface morphology caused by the metabolism of menadione in mammalian cells are associated with the oxidation of critical sulfhydryl groups in cytoskeletal proteins.

Isolated rat thymocytes treated with methylprednisolone (MPS), cultured human synovial (McCoy's) cells exposed to cold shock and human mammary adenocarcinoma (BT-20) cells treated with Tumour Necrosis Factor (TNF), all showed DNA fragmentation and the morphological and biochemical features of cell death characteristic of a process known as apoptosis. DNA fragmentation in MPS-treated thymocytes and in cold shock-exposed McCoy's cells was preceded by a marked increase in cytosolic free Ca2+ concentration resulting either from a sustained influx of Ca2+ from the extracellular medium or from the release of Ca2+ from intracellular pools. On the other hand, in TNF-treated BT-20 cells, DNA fragmentation was not associated with any early, marked increase in the cytosolic free Ca2+ level. In all three models, however, DNA fragmentation was efficiently prevented by intracellular Ca2+ chelators, calmodulin inhibitors and activators of protein kinase C (PKC). These results suggest that the activation of common mechanisms involving Ca2+ and PKC may be essential for the development of apoptosis.

M. Perotti

Papers

Tumor Necrosis Factor α Induces Apoptosis in Mammary Adenocarcinoma Cells by an Increase in Intranuclear Free Ca2+ Concentration and DNA Fragmentation

Calcium-dependent DNA fragmentation in human synovial cells exposed to cold shock

Alterations of surface morphology caused by the metabolism of menadione in mammalian cells are associated with the oxidation of critical sulfhydryl groups in cytoskeletal proteins.

In Vitro Models for Biochemical Investigations on Programmed Cell Death