Identification of a Novel Activation-inducible Protein of the Tumor Necrosis Factor Receptor Superfamily and Its Ligand

Abstract

Among members of the tumor necrosis factor receptor (TNFR) superfamily, 4-1BB, CD27, and glucocorticoidinduced tumor necrosis factor receptor family-related gene (GITR) share a striking homology in the cytoplasmic domain. Here we report the identification of a new member, activation-inducible TNFR family member (AITR), which belongs to this subfamily, and its ligand. The receptor is expressed in lymph node and peripheral blood leukocytes, and its expression is up-regulated in human peripheral mononuclear cells mainly after stimulation with anti-CD3/CD28 monoclonal antibodies or phorbol 12-myristate 13-acetate/ionomycin. AITR associates with TRAF1 (TNF receptor-associated factor 1), TRAF2, and TRAF3, and induces nuclear factor (NF)-B activation via TRAF2. The ligand for AITR (AITRL) was found to be an undescribed member of the TNF family, which is expressed in endothelial cells. Thus, AITR and AITRL seem to be important for interactions between activated T lymphocytes and endothelial cells.

Cloning and characterization of GITR ligand

“…Cloning and sequence analysis of murine GITRL We searched the murine genomic sequence database with TL6, the previously cloned ligand 8 for AITR, a human homologue of murine GITR. A genomic segment with B69% homology was found in murine chromosome 1 near the OX-40 ligand.…”

“…A ligand for human GITR (TL6) has been identified in two independent studies, 8,11 one of which 8 showed that TL6 was not expressed by unstimulated or stimulated T or B cells, but was constitutively expressed in umbilical vein endothelial cells. This finding underscores the fact that GITR/GITRL interactions are important in the interaction of lymphocytes with the vascular endothelium.…”

“…7 The cytoplasmic region of GITR demonstrates a marked identity with the corresponding region of other TNFRSF members, including CD40, OX-40, 4-1BB, and CD27, pointing to a new subfamily within this superfamily. 8 Recently, GITR has attracted increased attention due to its constitutive expression on the surface of CD4 þ CD25 þ regulatory T cells. 9,10 Importantly, culture of CD25 þ but not CD25 À T cells with anti-GITR and IL-2 results in a vigorous proliferative response.…”

“…However, a human homologue of GITR, called activation-inducible TNFR (AITR), has been cloned independently and its ligand (AITRL or TL6) characterized. 8,11 Although ligation of GITR by anti-GITR mAb (DTA-1), among others, downmodulates regulatory T-cell suppressive activity, 9 it is not clear if soluble GITRL-mediated signaling also contributes to the antisuppressive activity. To better understand GITR-mediated signaling in a more stringent manner, we identified and cloned murine GITRL.…”

TNF Receptor-Associated Factor (TRAF) Signaling Network in CD4⁺ T-Lymphocytes

“…TRAF1 is recruited to 4-1BB (Arch and Thompson 1998;Jang et al 1998;Saoulli et al 1998), CD30 (Gedrich et al 1996;Lee et al 1996), GITR (Kwon et al 1999), HVEM (Marsters et al 1997), OX40 (Kawamata et al 1998), and TNFR2 (Rothe et al 1994). …”