No abstract

No abstract

Mutations in the epithelial morphogen ectodysplasin-A (EDA), a member of the tumor necrosis factor (TNF) family, are responsible for the human disorder X-linked hypohidrotic ectodermal dysplasia (XLHED) characterized by impaired development of hair, eccrine sweat glands, and teeth. EDA-A1 and EDA-A2 are two splice variants of EDA, which bind distinct EDA-A1 and X-linked EDA-A2 receptors. We identified a series of novel EDA mutations in families with XLHED, allowing the identification of the following three functionally important regions in EDA: a C-terminal TNF homology domain, a collagen domain, and a furin protease recognition sequence. Mutations in the TNF homology domain impair binding of both splice variants to their receptors. Mutations in the collagen domain can inhibit multimerization of the TNF homology region, whereas those in the consensus furin recognition sequence prevent proteolytic cleavage of EDA. Finally, a mutation affecting an intron splice donor site is predicted to eliminate specifically the EDA-A1 but not the EDA-A2 splice variant. Thus a proteolytically processed, oligomeric form of EDA-A1 is required in vivo for proper morphogenesis.The ED1 gene encodes a protein, ectodysplasin-A (EDA), 1 recently recognized to be a member of the tumor necrosis factor (TNF) superfamily of ligands. Mutations within the ED1 gene cause an X-linked recessive disorder, hypohidrotic or anhidrotic ectodermal dysplasia (ED1, XLHED) (Mendelian inheritance in man 305100), involving abnormal morphogenesis of teeth, hair, and eccrine sweat glands. Various splice forms of the ED1 transcript have been detected, but two isoforms differing only by two amino acids, EDA-A1 (391 aa) and EDA-A2 (389 aa), contain a TNF homology domain (1-3). EDA is a type II transmembrane protein with a small N-terminal intracellular domain and a larger C-terminal extracellular domain containing a (Gly-X-Y) 19 collagen-like repeat with a single interruption and a C-terminal TNF homology domain (Fig. 1A). The TNF homology domain is similar to other members of the TNF family, consisting of 10 predicted anti-parallel ␤-sheets linked by variable loops (Fig. 1A). TNF family ligands homotrimerize to form a pear-shaped quaternary structure able to bind a receptor molecule at each monomer-monomer interface (4, 5). The closest EDA homologues in the TNF family are BAFF/ BLyS, APRIL, and TWEAK, although none of them contains collagen-like repeats (6 -9). All four ligands contain consensus sequences for proteolytic cleavage by furin within their extracellular domain. In the case of EDA, two overlapping consensus sites are located between the transmembrane and the collagenlike domains (Fig. 1A). EDA-A1, but not EDA-A2, has been shown to specifically bind to EDAR, a member of the TNF receptor superfamily that, like most members of the TNF receptor family, activates the NF-B and c-Jun N-terminal kinase pathways (3, 10). Mutations in DL (EDAR), the human homologue of the murine downless locus, produce an identical phenotype to loss of function of EDA (11,12)...

A proliferation-inducing ligand (APRIL) is a ligand of the tumor necrosis factor (TNF) family that stimulates tumor cell growth in vitro and in vivo. Expression of APRIL is highly upregulated in many tumors including colon and prostate carcinomas. Here we identify B cell maturation antigen (BCMA) and transmembrane activator and calcium modulator and cyclophilin ligand (CAML) interactor (TACI), two predicted members of the TNF receptor family, as receptors for APRIL. APRIL binds BCMA with higher affinity than TACI. A soluble form of BCMA, which inhibits the proliferative activity of APRIL in vitro, decreases tumor cell proliferation in nude mice. Growth of HT29 colon carcinoma cells is blocked when mice are treated once per week with the soluble receptor. These results suggest an important role for APRIL in tumorigenesis and point towards a novel anticancer strategy.

SummaryApoptosis is critically dependent on the presence of the ced-3 gene in Caenorhabditis elegans, which encodes a protein homologous to the mammalian interleukin (IL)-lfl-converting enzyme (ICE). Overexpression of ICE or ced-3 promotes apoptosis. Cytotoxic T lymphocyte-mediated rapid apoptosis is induced by the proteases granzyme A and B. ICE and granzyme B share the rare substrate site of aspartic acid, after which amino acid cleavage of precursor IL-lfl (plL-lfl) occurs. Here we show that granzyme A, but not granzyme B, converts plL-lfl to its 17-kD mature form. Major cleavage occurs at Arg120, four amino acids downstream of the authentic processing site, Asp116. IL-lfl generated by granzyme A is biologically active. When plL-lfl processing is monitored in lipopolysaccharide-activated macrophage target cells attacked by cytotoxic T lymphocytes, intracellular conversion precedes lysis. Prior granzyme inactivation blocks this processing. We conclude that the apoptosis-inducing granzyme A and ICE share at least one downstream target substrate, i.e., plL-lfl. This suggests that lymphocytes, by means of their own converting enzyme, could initiate a local inflammatory response independent of the presence of ICE.