PROTEASOME REGULATION OF ACTIVATION-INDUCED T-CELL DEATH

Lactacystin, a microbial metabolite that inhibits protease activity on ly in the proteasome, was used to study the role of the proteasome in the activation-induced cell death (AICD) of T cells. Lactacystin induc es DNA fragmentation and apoptosis in a T cell hybridoma (DO.11.10) in a dose-dependent manner. Between 1 and 10 mu M, the mildly cytotoxic lactacystin inhibited the AICD of DO.11.10 tells cultured in anti-CD3- coated wells. Degradation of I kappa B beta and the translocation of t he NF-kappa B (p50/RelA) into the nucleus, which occurred at 1.5 hr af ter anti-CD3 activation, were inhibited by lactacystin. Lactacystin di d not inhibit the expression of nuclear transcription factor Oct-1. Th e activation-induced expression of the immediate-early gene, Nur77, an d the T cell death genes, CD95 (Fas) and CD95 ligand (Fast), were inhi bited. Functional expression of FasL cytotoxicity and the increase of cell surface Fas were also inhibited. Lactacystin must be added within 2 hr of activation to efficiently block AICD. In addition, lactacysti n failed to inhibit the killing of DO.11.10 by Fast-expressing allo-sp ecific cytotoxic effector cells. These observations strongly suggest a direct link between the proteasome-dependent degradation of I kappa B beta and the AICD that occurs through activation of the Fast gene and up-regulation of the Fas gene.