Masashi Adachi

Bio: Masashi Adachi is an academic researcher from Osaka University. The author has contributed to research in topics: Apoptosis & Fas receptor. The author has an hindex of 12, co-authored 16 publications receiving 4437 citations. Previous affiliations of Masashi Adachi include Osaka Bioscience Institute.

Lethal effect of the anti-Fas antibody in mice

Abstract: 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.

Downregulation of Fas ligand by shedding

Abstract: Apoptosis-inducing Fas ligand (FasL) is a type II membrane protein, predominantly expressed in the activated T cells. FasL is cleaved by a putative metalloproteinase to produce a soluble form. Here, we blocked the shedding of human FasL by deleting its cleavage site. Although human Jurkat cells and mouse primary hepatocytes that express a low level of Fas were resistant to the soluble form of FasL, they were efficiently killed by membrane-bound FasL. Furthermore, soluble FasL inhibited cytotoxicity of the membrane-bound FasL. These results indicate that the membrane-bound form of FasL is the functional form and suggest that shedding of FasL is to prevent the killing of the healthy bystander cells by cytotoxic T cells.

Aberrant transcription caused by the insertion of an early transposable element in an intron of the Fas antigen gene of lpr mice

Abstract: The mouse lpr (lymphoproliferation) mutation carries a rearrangement in the chromosomal gene for the Fas antigen, which mediates apoptosis. Isolation and characterization of mouse Fas antigen chromosomal gene from wild-type and lpr mice indicated an insertion of an early transposable element (ETn) in intron 2 of the Fas antigen gene of lpr mice. Hybrid transcripts carrying the Fas antigen and ETn sequences were expressed in the thymus and liver of the mutant. This indicated that premature termination and aberrant splicing of the Fas antigen transcript caused by the insertion of the ETn in the intron are responsible for the lymphoproliferation and autoimmune phenotype of the mutant mouse. On the other hand, an insertion of the ETn into an intron of a mammalian expression vector dramatically but not completely reduced the expression efficiency. These findings suggest that lpr mice are able to express a very low level of the Fas antigen.

Essential roles of the Fas ligand in the development of hepatitis

Abstract: The Fas ligand (FasL) is expressed in activated T cells and induces apoptosis in Fas-bearing cells. A cytotoxic T lymphocyte (CTL) clone specific for hepatitis B surface antigen (HBsAg) causes an acute liver disease in HBsAg transgenic mice. Here we observed that the CTL clone killed hepatocytes expressing HBsAg in a Fas-dependent manner. Administration of the soluble form of Fas into HBsAg transgenic mice prevented the CTL-induced liver disease. In the second model, mice were primed with Propionibacterium acnes. A subsequent challenge with lipopolysaccharide (LPS) killed the mice by inducing liver injury. Neutralization of FasL rescued the mice from LPS-induced mortality, and Fas-null mice were resistant to LPS-induced mortality. These results suggest that FasL has an essential role in the development of hepatitis.

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

Abstract: 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.

The Fas Death Factor

Abstract: 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.

Biological properties of extracellular vesicles and their physiological functions

Abstract: In the past decade, extracellular vesicles (EVs) have been recognized as potent vehicles of intercellular communication, both in prokaryotes and eukaryotes. This is due to their capacity to transfer proteins, lipids and nucleic acids, thereby influencing various physiological and pathological functions of both recipient and parent cells. While intensive investigation has targeted the role of EVs in different pathological processes, for example, in cancer and autoimmune diseases, the EV-mediated maintenance of homeostasis and the regulation of physiological functions have remained less explored. Here, we provide a comprehensive overview of the current understanding of the physiological roles of EVs, which has been written by crowd-sourcing, drawing on the unique EV expertise of academia-based scientists, clinicians and industry based in 27 European countries, the United States and Australia. This review is intended to be of relevance to both researchers already working on EV biology and to newcomers who will encounter this universal cell biological system. Therefore, here we address the molecular contents and functions of EVs in various tissues and body fluids from cell systems to organs. We also review the physiological mechanisms of EVs in bacteria, lower eukaryotes and plants to highlight the functional uniformity of this emerging communication system.

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

Abstract: 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.