TRAIL (TNF-related apoptosis inducing Ligand), like other members of the TNF family of proteins, is able to induce apoptosis in sensitive target cells. Recently, cell-surface TRAIL has been shown to be expressed by activated human and mouse T lymphocytes, raising the possibility that TRAIL might be involved in T cell-mediated cytotoxicity and/or immune regulation. In the present study we show by semiquantitative reverse transcriptase polymerase chain reaction (RT-PCR) analysis that activated, but not resting, mouse T cells express abundant TRAIL mRNA. TRAIL transcripts were detectable within 4 h of T cell activation. A panel of pharmacologic inhibitors was used to investigate the signal transduction pathways involved in TRAIL gene induction following T lymphocyte activation. TRAIL gene expression was sensitive to the src-like protein tyrosine kinase (PTK inhibitor herbimycin A, as well as the more general PTK inhibitor genistein, suggesting the involvement of a src family PTK, The PRC inhibitors staurosporine and calphostin C, and the phosphatidylinositol 3-kinase (PI3-K) inhibitors wortmannin. and LY294002,also prevented TRAIL mRNA transcription by activated T cells, indicating a role for PKC and PI3-K, In addition, TRAIL induction was inhibited by cyclosporin A, implicating the Ca2+/calmodulin-dependent protein phosphatase calcineurin. TRAIL expression was also blocked by rapamycin, which inhibits p70 S6 kinase involved in CD28 and interleukin (IL)-2 receptor signaling. However, TRAIL mRNA expression was not induced by IL-2, suggesting that TRAIL gene induction is not coupled to the IL-2 receptor. Data obtained by RT-PCR were confirmed at the protein level by immunoblotting with TRAIL-specific antibody. We conclude that TRAIL gene induction is initiated through a T cell receptor-associated signaling pathway similar to that responsible for the expression of cytokine genes such as IL-2. (C) 1999 Academic Press.
