The tumor necrosis factor (TNF) superfamily of cytokines includes both soluble and membrane-bound proteins that regulate immune responses. A member of the human TNF family, BLyS (B lymphocyte stimulator), was identified that induced B cell proliferation and immunoglobulin secretion. BLyS expression on human monocytes could be up-regulated by interferon-gamma. Soluble BLyS functioned as a potent B cell growth factor in costimulation assays. Administration of soluble recombinant BLyS to mice disrupted splenic B and T cell zones and resulted in elevated serum immunoglobulin concentrations. The B cell tropism of BLyS is consistent with its receptor expression on B-lineage cells. The biological profile of BLyS suggests it is involved in monocyte-driven B cell activation.

DR3 is a death domain-containing receptor that is upregulated during T cell activation and whose overexpression induces apoptosis and NF-kappaB activation in cell lines. Here we show that an endothelial cell-derived TNF-like factor, TL1A, is a ligand for DR3 and decoy receptor TR6/DcR3 and that its expression is inducible by TNF and IL-1alpha. TL1A induces NF-kappaB activation and apoptosis in DR3-expressing cell lines, while TR6-Fc protein antagonizes these signaling events. Interestingly, in T cells, TL1A acts as a costimulator that increases IL-2 responsiveness and secretion of proinflammatory cytokines both in vitro and in vivo. Our data suggest that interaction of TL1A with DR3 promotes T cell expansion during an immune response, whereas TR6 has an opposing effect.

IntroductionThe tumor necrosis factor (TNF) family of ligands encompasses an ever-growing group of proteins, characterized by homologous cysteine-rich domains, that participates in the regulation of diverse immune and inflammatory responses. [1][2][3][4] All the members, with the exception of lymphotoxin-␣, are type II membrane proteins. Their effects are mediated either by cell contact, through the interaction of the membrane-bound form of the ligand with its corresponding receptor, or by processing and shedding of the soluble form of the ligand. 2,[5][6][7] In addition, many of the proteins, including CD27L, CD30L, OX40L, CD40L, FasL, and 4-1BBL, have moderate-sized cytoplasmic regions that are capable of delivering signals when engaged by their receptors. [7][8][9][10] The expression pattern of the family members is usually promiscuous, ranging from the broad cellular expression of TNF-␣ to a more restricted localization, such as that of CD40L expressed only on T cells. Moreover, the expression of the molecules is, in general, dependent on the activation state of the cells, being usually low or undetectable on resting cells.Recently, we described a novel member of the TNF family of ligands, B-lymphocyte stimulator (BLyS), which was identified by searching an expressed sequence tag (EST) database for homology with known TNF-like molecules. 11 The protein has been reported also as TALL-1 (TNF-and ApoL-related leukocyte-expressed ligand 1), BAFF (B-cell activator factor belonging to the TNF family), or THANK (TNF homologue that activates apoptosis, NF-B, and JNK). 12-14 The human BLyS gene encodes for a 285 amino acid (aa) protein presenting a transmembrane region between aa 47 and 73 and lacking a putative signal peptide sequence. The recombinant soluble protein (aa 134-285) binds selectively to human primary B cells and tumor cell lines of the B lineage. 11BLyS was shown to induce B-cell proliferation in standard costimulation assays with Staphylococcus aureus Cowan I (SAC I) or antihuman immunoglobulin M (IgM). BLyS administration in mice resulted in a 5-and 2-fold increase in serum IgM and IgA, respectively. 11 In addition, mice transgenic for BAFF developed autoimmune disorders such as increased germinal center formation, production of autoantibodies, and Ig deposition in kidneys. 15 Collectively, these findings suggest that BLyS has a crucial role in the humoral immune response and that regulation of BLyS expression might consequently modulate B-cell function. Our aim was, therefore, to study synthesis and release of BLyS from cells of myeloid lineage and to investigate the regulation of BLyS expression in response to cytokines. Materials and methods Medium and reagentsThe complete medium used for monocyte culture consisted of RPMI 1640 medium (Gibco BRL, Rockville, MD) supplemented with 10% (vol/vol) heat-inactivated fetal bovine serum (FBS), 2 M L-glutamine, and 50 g/mL gentamycin (Biofluids, Rockville, MD). The following recombinant human (rh) reagents were used: interferon-␥ (rhIFN-␥), interleukin-10 (...

Translation initiation in eukaryotes is facilitated by the cap structure, m7GpppN (where N is any nucleotide). Eukaryotic translation initiation factor 4F (eIF4F) is a cap binding protein complex that consists of three subunits: eIF4A, eIF4E and eIF4G. eIF4G interacts directly with eIF4E and eIF4A. The binding site of eIF4E resides in the N‐terminal third of eIF4G, while eIF4A and eIF3 binding sites are present in the C‐terminal two‐thirds. Here, we describe a new eukaryotic translational regulator (hereafter called p97) which exhibits 28% identity to the C‐terminal two‐thirds of eIF4G. p97 mRNA has no initiator AUG and translation starts exclusively at a GUG codon. The GUG‐initiated open reading frame (907 amino acids) has no canonical eIF4E binding site. p97 binds to eIF4A and eIF3, but not to eIF4E. Transient transfection experiments show that p97 suppresses both cap‐dependent and independent translation, while eIF4G supports both translation pathways. Furthermore, inducible expression of p97 reduces overall protein synthesis. These results suggest that p97 functions as a general repressor of translation by forming translationally inactive complexes that include eIF4A and eIF3, but exclude eIF4E.

Translation initiation in eukaryotes is mediated by the cap structure (m 7 GpppN, where N is any nucleotide) present at the 5 end of all cellular mRNAs, except organellar. The cap is recognized by eukaryotic initiation factor 4F (eIF4F), which consists of three polypeptides, including eIF4E, the cap-binding protein subunit. The interaction of the cap with eIF4E facilitates the binding of the ribosome to the mRNA. eIF4E activity is regulated in part by two translational repressors, 4E-BP1 and 4E-BP2, which bind to it and prevent its assembly into eIF4F. We report here the isolation of 4E-BP3, a new member of the 4E-BP family. 4E-BP3 is homologous to 4E-BP1 and 4E-BP2, exhibiting 57 and 59% identity, respectively. The homology is most striking in the middle region of the protein, which contains the eIF4E binding motif and residues that are phosphorylated in 4E-BP1. 4E-BP3 is a heat stable protein that binds to eIF4E in vitro as well as in vivo. Further, 4E-BP3 overexpression specifically reduces eIF4E-dependent translation. The overlapping function and expression of the different 4E-BP family members imply that there is redundancy in this translational control mechanism, underscoring its importance.