Immune modulation by Fas ligand reverse signaling: lymphocyte proliferation is attenuated by the intracellular Fas ligand domain

Abstract

Fas ligand (FasL) not only induces apoptosis in Fas receptor-bearing target cells, it is also able to transmit signals into the FasL-expressing cell via its intracellular domain (ICD). IntroductionFas ligand (FasL, CD95L, CD178, TNSF6) is a 40-kDa glycosylated type II transmembrane protein that belongs to the tumor necrosis factor (TNF) family. Its extracellular portion harbors a C-terminal TNF homology domain that assembles as homotrimers and mediates interactions with receptors. Interestingly, the 77-amino acid (aa)-long N-terminal mouse FasL intracellular domain (ICD) contains several conserved signaling motifs, such as a tandem casein kinase I phosphorylation site (aa 17-21), a proline-rich domain (PRD; aa 45-69) that serves as a docking site for SH3 domain-containing proteins, and a tyrosine phosphorylation site located at aa 7. 1 The FasL/Fas receptor system is renowned as a potent inducer of apoptosis in the receptor-bearing cell and is especially important for numerous immune system functions, including removal of target cells by natural killer and cytotoxic T cells, (self) elimination of effector cells after the proliferative phase of an immune response (activation-induced cell death), and maintenance of immuneprivileged sites. 2,3 Naturally occurring homozygous mutations of the Fas (lpr) and the FasL (gld) genes, which abolish Fas-mediated apoptosis, lead to development of a severe lymphoproliferative disease. 4 Because of its potent proapoptotic potential and important function, expression and activity of FasL is tightly regulated at transcriptional and posttranslational levels and is restricted to a few cell types, such as immune effector cells and cells of immuneprivileged sites (eg, eyes, testis, brain). In contrast, the Fas receptor is expressed in a wide variety of tissues, including the lymphoid tissues, liver, heart, and ovary. 1,5 In addition to its pro-death function, the Fas/FasL system also transduces nonapoptotic signals into the Fas-expressing cells. Among others, Fas is required for cell survival, proliferation and activation of T cells, liver regeneration, and neurogenesis. 6,7 A number of studies have presented evidence for alternative signal transduction via "reverse signaling" into the FasL-bearing cells, although conflicting data have been published regarding the functional implications (for review see Voss et al 1 ). First evidence The online version of this article contains a data supplement.The publication costs of this article were defrayed in part by page charge payment. Therefore, and solely to indicate this fact, this article is hereby marked ''advertisement'' in accordance with 18 USC section 1734. For personal use only. on May 8, 2018. by guest www.bloodjournal.org From for the existence of retrograde FasL signaling stems from 2 studies that demonstrated either costimulation of murine CD8 ϩ cytotoxic T lymphocyte (CTL) cell lines upon FasL cross-linking 8 or inhibition of activation-induced proliferation in murine CD4 ϩ T cells. 9 In both cases, FasL reverse signaling could...

Recombinant CD95-Fc (APG101) prevents graft-versus-host disease in mice without disabling antitumor cytotoxicity and T-cell functions

“…Even T reg numbers were identical although these cells are susceptible to homeostatic control by CD95. 42 Although CD95L activation is known to be a possible modulator of T-cell expansion, 21,22 re-isolated allogeneic T cells from APG101-treated mice showed no changes in proliferation toward alloantigen or third-party antigens compared with T cells isolated from GVHD suffering mice. T-cell expansion in APG101-treated mice was further confirmed by efficient T-cell invasion of host tissues in vivo, which was reported to be impaired if CD95L-deficient T cells were used as allogeneic effector cells.…”

“…Although CD95L is best known for its role in apoptosis induction, it may also serve a function in reverse signaling, thereby modulating the immune function of CD95L-expressing cells. 21,22 Therefore, we first tested the effect of APG101 on apoptosis inhibition and T-cell function in vitro. B6-derived spleen cells were treated with recombinant CD95L and enhancer in the presence of increasing concentrations of APG101.…”

“…19 To test whether the CD95L-mediated inhibition of tissue destruction by APG101 offers a new therapeutic approach to treat and/or prevent GVHD, we treated allogeneic BM-transplanted mice on a regular basis with APG101. Because CD95L is not only known for its function as an apoptosis inducer, but may also transmit signals into the CD95L-expressing cells, a process known as reverse signaling and predominantly affecting T-cell proliferation, [20][21][22] we further analyzed the effect of APG101 on T-cell function, antitumor cytotoxicity, and homing.…”

JAB1 Is Essential for B Cell Development and Germinal Center Formation and Inversely Regulates Fas Ligand and Bcl6 Expression

“…Interestingly, Kirkin et al (41) observed an 11-kDa FasL intracellular domain (ICD), which was generated via sequential proteolysis and subsequently translocates to the nucleus where it modulates gene transcription. Furthermore, the analysis of knockin mice lacking the FasL ICD revealed that plasma cell numbers, generation of GC B cells, and, consequently, production of Ag-specific Abs in response to immunization with T celldependent or T cell-independent Ag are negatively regulated by FasL ICD-dependent signals (42). Because of the lack of suitable reagents allowing the complete functional blockade of FasL, including retrograde signaling by FasL ICD in vivo, we have initiated mouse breedings to generate FasL-deficient mice with a B cellspecific JAB1 deletion to address the role of overexpressed FasL during B cell development.…”

A Protease-Independent Function for SPPL3 in NFAT Activation

“…SPPL2a cleaves the N-terminal fragment (NTF) of the invariant chain (Ii; CD74) and is essential for the normal development of B cells and myeloid dendritic cells (32)(33)(34). SPPL2a has also been shown to cleave Fas ligand (FasL) to generate an intracellular domain (ICD) that negatively regulates B and T cell activation and proliferation downstream of antigen receptor triggering (35). Both SPPL2a and SPPL2b can cleave tumor necrosis factor alpha (TNF-␣) to produce an ICD that elicits production of the proinflammatory cytokine interleukin 12 (IL-12) by bone marrow-derived dendritic bated at 65°C for 15 min in the presence of SDS loading buffer and were separated by SDS-PAGE on 10% gels.…”