Apoptosis by death factor.

Fas ligand (FasL), a cell surface molecule belonging to the tumor necrosis factor family, binds to its receptor Fas, thus inducing apoptosis of Fas-bearing cells. Various cells express Fas, whereas FasL is expressed predominantly in activated T cells. In the immune system, Fas and FasL are involved in down-regulation of immune reactions as well as in T cell-mediated cytotoxicity. Malfunction of the Fas system causes lymphoproliferative disorders and accelerates autoimmune diseases, whereas its exacerbation may cause tissue destruction.

https://science.sciencemag.org/content/sci/267/5203/1449.full.pdf

The Fas Death Factor

The homeostasis of animals is regulated not only by the growth and differentiation of cells, but also by cell death through a process known as apoptosis. Apoptosis is mediated by members of the caspase family of proteases, and eventually causes the degradation of chromosomal DNA. A caspase-activated deoxyribonuclease (CAD) and its inhibitor (ICAD) have now been identified in the cytoplasmic fraction of mouse lymphoma cells. CAD is a protein of 343 amino acids which carries a nuclear-localization signal; ICAD exists in a long and a short form. Recombinant ICAD specifically inhibits CAD-induced degradation of nuclear DNA and its DNase activity. When CAD is expressed with ICAD in COS cells or in a cell-free system, CAD is produced as a complex with ICAD: treatment with caspase 3 releases the DNase activity which causes DNA fragmentation in nuclei. ICAD therefore seems to function as a chaperone for CAD during its synthesis, remaining complexed with CAD to inhibit its DNase activity; caspases activated by apoptotic stimuli then cleave ICAD, allowing CAD to enter the nucleus and degrade chromosomal DNA.

A caspase-activated DNase that degrades DNA during apoptosis, and its inhibitor ICAD

Identification and characterization of a new member of the TNF family that induces apoptosis

A critical event during programmed cell death (PCD) appears to be the acquisition of plasma membrane (PM) changes that allows phagocytes to recognize and engulf these cells before they rupture. The majority of PCD seen in higher organisms exhibits strikingly similar morphological features, and this form of PCD has been termed apoptosis. The nature of the PM changes that occur on apoptotic cells remains poorly defined. In this study, we have used a phosphatidylserine (PS)-binding protein (annexin V) as a specific probe to detect redistribution of this phospholipid, which is normally confined to the inner PM leaflet, during apoptosis. Here we show that PS externalization is an early and widespread event during apoptosis of a variety of murine and human cell types, regardless of the initiating stimulus, and precedes several other events normally associated with this mode of cell death. We also report that, under conditions in which the morphological features of apoptosis were prevented (macromolecular synthesis inhibition, overexpression of Bcl-2 or Abl), the appearance of PS on the external leaflet of the PM was similarly prevented. These data are compatible with the notion that activation of an inside-outside PS translocase is an early and widespread event during apoptosis.

https://rupress.org/jem/article-pdf/182/5/1545/1107564/1545.pdf

Early redistribution of plasma membrane phosphatidylserine is a general feature of apoptosis regardless of the initiating stimulus: inhibition by overexpression of Bcl-2 and Abl.

DURING mammalian development, many cells are programmed to die1,2 most mediated by apoptosis3. The Fas antigen4 coded by the structural gene for mouse lymphoproliferation mutation (lpr)5,6, is a cell surface protein belonging to the tumour necrosis factor/nerve growth factor receptor family7,8, and mediates apoptosis7. The Fas antigen messenger RNA is expressed in the thymus, liver, heart, lung and ovary8. We prepared a monoclonal antibody against mouse Fas antigen, which immunoprecipitated the antigen (Mr 45K) and had cytolytic activity against cell lines expressing mouse Fas antigen. We report here that staining of mouse thymocytes with the antibody indicated that thymocytes from the wild-type and lprcg mice expressed the Fas antigen, whereas little expression of the Fas antigen was found in lpr mice. Intraperitoneal administration of the anti-Fas antibody into mice rapidly killed the wild-type mice but neither lpr nor lprcg mice. Biochemical, histological and electron microscope analyses indicated severe damage of the liver by apoptosis. These findings suggest that the Fas antigen is important in programmed cell death in the liver, and may be involved in fulminant hepatitis in some cases.

Lethal effect of the anti-Fas antibody in mice

Fas, a type I membrane protein that transduces an apoptotic signal, is expressed in lymphocytes as well as in various tissues such as the liver, lung and heart. The mouse lymphoproliferation (lpr) mutation is a leaky mutation in Fas. By means of gene targeting, we generated a mouse strain which is completely deficient in Fas. In addition to the massive production of lymphocytes, the Fas-null mice showed substantial liver hyperplasia, which was accompanied by the enlargement of nuclei in hepatocytes. The Fas system seems to play a role in the apoptotic process to maintain homeostasis of the liver as well as the peripheral lymphoid organs.

Targeted mutation in the Fas gene causes hyperplasia in peripheral lymphoid organs and liver.

Fas is a 45-kDa membrane protein that transduces an apoptotic signal. The mouse lymphoproliferation (lpr) mutation is a leaky mutation of Fas. In this study, we examined lymphocyte development in Fas-null mice generated by gene targeting. The Fas-/- mice progressively accumulated abnormal T cells (Thy1+, B220+, CD4-, and CD8-) and developed lymphadenopathy and splenomegaly, which were much more accelerated and pronounced than those in lpr mice. In addition, the Fas-null mice showed lymphocytosis, accompanied by lymphocytic infiltration in the lungs and liver. The number of apparently normal B cells also increased, and large amounts of immunoglobulins, including anti-DNA antibodies, were produced. Thymic clonal deletion, assessed by deletion of T cells reactive to mouse endogenous superantigens, was apparently normal in the Fas-/- mice, whereas the peripheral clonal deletion of mature T cells against a bacterial superantigen was impaired. These results suggested that Fas plays a decisive role in peripheral clonal deletion but not in negative selection in the thymus.

Enhanced and accelerated lymphoproliferation in Fas-null mice

Fas-mediated apoptosis in primary cultured mouse hepatocytes.

Fas is a cell surface protein that mediates apoptosis. A mouse mutant, lpr (lymphoproliferation), has a mutation in the Fas gene. In this report, we studied the expression and function of Fas in various subpopulations of mouse thymocytes. Abundant expression of Fas was detected on CD4+CD8+ double positive as well as CD4+ or CD8+ single positive thymocytes in wild-type mice. Little or low levels of Fas were expressed in CD4-CD8- double negative thymocytes except for the CD4-CD8-CD3+ phenotype, which expresses Fas as abundantly as double positive or single positive subsets. On the other hand, no Fas expression was detected in any population of thymocytes from lpr mice. When the wild-type thymocytes were treated with the agonistic anti-Fas antibody, double positive cells from the wild-type mice were selectively killed by apoptosis, whereas, the single positive cells were resistant to its cytolytic activity despite their abundant expression of Fas. Unlike the apoptosis of thymocytes induced by glucocorticoid or T cell activator, the Fas-induced apoptosis of thymocytes was enhanced by metabolic inhibitors such as cycloheximide. Furthermore, intraperitoneal administration of the anti-Fas antibody into mice caused rapid apoptosis of thymocytes in vivo.

/pdf/selective-apoptosis-of-cd4-cd8-thymocytes-by-the-anti-fas-3nsy4f6mk0.pdf

Jun Ogasawara

Papers

Lethal effect of the anti-Fas antibody in mice

Targeted mutation in the Fas gene causes hyperplasia in peripheral lymphoid organs and liver.

Enhanced and accelerated lymphoproliferation in Fas-null mice

Fas-mediated apoptosis in primary cultured mouse hepatocytes.

Selective apoptosis of CD4+CD8+ thymocytes by the anti-Fas antibody.