| Primary Identifier | IPR028326 | Type | Family |
| Short Name | FASL |
| description | Like all apoptotic cell death, T cell receptor (TCR)-mediated death can bedivided into two phases: an inductive phase and an effector phase. The effector phase includes a sequence of steps that are common to apoptosis inmany cell types, which, if not interrupted, will lead to cell death. Theinduction phase, which often requires the expression of new genes, consistsof a set of signals that activate the effector phase. Outside the thymus,most, if not all, of the TCR-mediated apoptosis of mature T cells (sometimesreferred to as activation-induced cell death (AICD)) is induced through thesurface antigen Fas pathway: activation through the TCR induces expressionof the Fas (CD95) ligand (FasL); the expression of FasL on either aneighbouring cell, or on the Fas-bearing cell, induces trimerisation of Fas,which then initiates a signal-transduction cascade, leading to apoptosis of the Fas-bearing cell. This commitment stage requires the activation of keydeath-inducing enzymes, termed caspases, which act by cleaving proteins thatare essential for cell survival and proliferation[, ]. However whathappens to FasL itself remains unknown. It is possible that it is cleavedfrom the effector cells and internalised into the target cells; it may bedownregulated in the effector cells; or it may be phagocytosed by the targetcells.Fas is also known to be essential in the death of hyperactivated peripheralCD4 cells: in the absence of Fas, mature peripheral T cells do not die, butthe activated cells continue to proliferate, producing cytokines that leadto grossly enlarged lymph nodes and spleen. Defects in the Fas-FasL systemare associated with various disease syndromes. Mice with non-functional Fasor FasL display characteristics of lymphoproliferative disorder, such as lymphadenopathy, splenomegaly, and elevated secretion of IgM and IgG. Thesemice also secrete anti-DNA autoantibodies and rheumatoid factor [].FasL (also known as tumor necrosis factor ligand superfamily member 6) is a 40kDa type II membrane protein belonging to the tumour necrosisfactor (TNF) family. Its binding to the cognate Fas receptor triggers the apoptosis that plays a pivotal role in the maintenance of immune system homeostasis. It is expressed on activated lymphocytes, NK cells,platelets, certain immune-privileged cells and some tumour cells[, ]. The cell death-inducing property of FasL has been associated with its extracellular domain, which can be cleaved off by metalloprotease activity to produce soluble FasL [].Human and mouse FasL induce apoptosis in cells expressing either mouse orhuman Fas with the same specificity. Although the amino acid sequence ofFasL is highly conserved between human and mouse, the similarity betweenhuman and murine Fas is much less pronounced. Greater conservation of theligand than the receptor is also observed in other members of the TNF family.By comparison with other TNF family members, FasL has a long N-terminal intracellular region rich in proline residues, which is known tobind to the SH3 domain. SH3 domains play important roles in mediating specificprotein-protein interactions, specifically in the cytoskeleton. |
