Analysis of signal transduction pathways triggered by a surface receptor of T cells, termed GITR.

T cells become activated when they encounter antigens presented by antigen presenting cells (APCs). Activated T cells express members of the tumor necrosis factor receptor (TNFR) family on their cell surface, including glucocorticoid-induced TNFR (GITR). TNFRs are crucial regulators of signal transduction pathways that control cell survival and cell death. Upon binding to its ligand, termed GITR-L, GITR triggers signal transduction pathways by binding adapter proteins, such as TNFR- associated factors (TRAFs), which initiate the activation of kinases and transcription factors, including nuclear factor &kappaBB (NF-&kappaBB). Upon activation, NF-&kappaBB translocates to the nucleus, where it initiates the transcription of target genes containing NF-&kappaBB binding sites in their promoters. If these signaling pathways are interrupted or inhibited, cell survival and apoptosis are disturbed. We were interested in whether GITR utilizes a specific adapter protein, termed TRAF2. Immunoprecipitation and Western blot analysis revealed an interaction between GITR and TRAF2. Functional studies indicated that TRAF2 does not promote signaling downstream of GITR, but inhibits GITR-induced NF-&kappaBB activation. In response to GITR-induced signaling in the absence of TRAF2, we detected a strong signal in a luciferase reporter assay, meaning NF- &kappaBB had translocated to the nucleus. However, when TRAF2 was overexpressed, the luciferase signal was significantly decreased, indicating that TRAF2 inhibits the signaling pathways that normally occur downstream of GITR. Ongoing and future experiments are designed to characterize the molecular mechanisms regulating this novel inhibitory function of TRAF2 downstream of GITR.