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Much of what we know about apoptosis in human cells stems from pioneering genetic studies in the nematode C. elegans . However, one important way in which the regulation of mammalian cell death appears to differ from that of its nematode counterpart is in the employment of TNF and TNF receptor superfamilies . No members of these families are present in C. elegans, yet TNF factors play prominent roles in mammalian development and disease . Here, we describe the cloning and characterization of Eiger, a unique TNF homolog in Drosophila. Like a subset of mammalian TNF proteins, Eiger is a potent inducer of apoptosis. Unlike its mammalian counterparts, however, the apoptotic effect of Eiger does not require the activity of the caspase-8 homolog DREDD, but it completely depends on its ability to activate the JNK pathway. Eiger-induced cell death requires the caspase-9 homolog DRONC and the Apaf-1 homolog DARK. Our results suggest that primordial members of the TNF superfamily can induce cell death indirectly by triggering JNK signaling, which, in turn, causes activation of the apoptosome. A direct mode of action via the apical FADD/caspase-8 pathway may have been coopted by some TNF signaling systems only at subsequent stages of evolution. [Copyright &y& Elsevier]

Hypohydrotic Ectodermal Dysplasia (HED) is a genetic disease seen in humans and mice. It is characterized by loss of hair, sweat glands, and teeth. The predominant X-linked form results from mutations in ectodysplasin-A (EDA), a TNF-like ligand . A phenotypically indistinguishable autosomal form of the disease results from mutations in the receptor for EDA (EDAR) . EDAR is a NF-κB-activating, death domain-containing member of the TNF receptor family . crinkled, a distinct autosomal form of HED, was discovered in a mouse strain in which both the ligand (EDA) and receptor (EDAR) were wild-type, suggestive of a disruption further downstream in the signaling pathway . Employing a forward genetic approach, we have cloned crinkled (CR) and find it to encode a novel death domain-containing adaptor. crinkled binds EDAR through a homotypic death domain interaction and mediates engagement of the NF-κB pathway, possibly by recruiting TRAF2 to the receptor-signaling complex. This is an unprecedented example of naturally occurring mutations in ligand, receptor, or adaptor giving rise to the same phenotypic disease characterized by a defect in the proper development of epidermal appendages. [Copyright &y& Elsevier]

The tumor necrosis factor (TNF)-related ligand B lymphocyte stimulator (BLyS) binds two TNF receptor family members, transmembrane activator and calcium-modulating and cyclophilin ligand interactor (TACI) and B cell maturation molecule (BCMA). Mice that are transgenic for BLyS show B cell accumulation, activation and autoimmune lupus-like nephritis. The existence of at least two distinct BLyS receptors raises the question of the relative contribution of each to B cell functions. We therefore generated mice that were deficient in TACI. TACI-/- mice showed increased B cell accumulation and marked splenomegaly. Isolated TACI-/- B cells hyperproliferated and produced increased amounts of immunoglobulins in vitro. In vivo antigen challenge resulted in enhanced antigen-specific antibody production. Thus, TACI may play an unexpected inhibitory role in B cell activation that helps maintain immunological homeostasis. [ABSTRACT FROM AUTHOR]

Interactions of the tumor necrosis factor superfamily members B lymphocyte stimulator (BLyS) and a proliferation-inducing ligand (APRIL) with their receptors?transmembrane activator and CAML interactor (TACI) and B cell maturation molecule (BCMA)?on B cells play an important role in the humoral immune response. Whereas BCMA is restricted to B cells, TACI is also expressed on activated T cells; we show here that TACI-Fc blocks the activation of T cells in vitro and inhibits antigen-specific T cell activation and priming in vivo. In a mouse model for rheumatoid arthritis (RA), an autoimmune disease that involves both B and T cell components, TACI-Fc treatment substantially inhibited inflammation, bone and cartilage destruction and disease development. Thus, BLyS and/or APRIL are important not only for B cell function but for T cell?mediated immune responses. Inhibition of these ligands might have therapeutic benefits for autoimmune diseases, such as RA, that involve both B and T cells. [ABSTRACT FROM AUTHOR]

B ymphocyte stimulator (BLyS) is a member of the tumor necrosis factor (TNF) superfamily. BLyS stimulates proliferation of, and immunoglobulin production by, B cells. However, the relative importance of BLyS in physiological B cell activation is unclear. We identified a B cell receptor for BLyS through expression cloning as TACI, an orphan TNF receptor homologue of unknown function. Binding of BLyS to TACI activated signaling by nuclear factor-κB (NF-κB). In vitro soluble TACI-Fc fusion protein blocked BLyS-induced NF-κB activation in B lymphoma cells and IgM production in peripheral blood B cells. In vivo treatment of immunized mice with TACI-Fc inhibited production of antigen-specific IgM and IgG1 antibodies and abolished splenic germinal center (GC) formation. Thus, BLyS activity must play a critical role in the humoral immune response. [ABSTRACT FROM AUTHOR]

EDA is a tumor necrosis factor family member involved in ectodermal development. Splice variants EDA-A1 and EDA-A2 differ only by the presence of Glu 308 and Val 309 in the expected receptor binding region of EDA-A1 but not EDA-A2. This two amino acid difference functions as a switch controlling receptor specificity. EDA-A1 binds only to EDAR, while EDA-A2 is specific for XEDAR. In order to understand the structural basis of this switch, we determined the X-ray crystal structures of the TNF domain of both EDA-A1 and EDA-A2 at 2.3 A˚ and 2.2 A˚, respectively. While the backbone conformation around the splice difference is similar in both isoforms, the conformation of the following loop, the surface charge, and the shape of the expected receptor binding site differ significantly. [Copyright &y& Elsevier]