REGULATION OF T-CELL DEATH GENES - SELECTIVE-INHIBITION OF FASL-MEDIATED BUT NOT FAS-MEDIATED FUNCTION

Activation-induced cell death (AICD) requires coexpression of Fas and FasL. Hybridoma T-cells express detectable Past mRNA 3 to 5 hr after c ulture in anti-CD3-coated wells. High and steady expression of Fast mR NA was observed after 8-10 hr of activation. Expression of Fast cytoto xicity and AICD is consistent with the time-course of Fast mRNA induct ion. Fas-Ig was effective in inhibiting AICD when added no later than 5 hr after activation, but was ineffective when added after 8-10 hr of activation. These observations suggest that Fast gene activation is a critical step for AICD. By contrast, Pas was constitutively expressed and the time-course study did not support the idea that up-regulation of Pas is critical for AICD. The critical role of Fast gene activatio n for AICD was confirmed by studies using inhibitors of AICD. Dexameth asone (Dex) inhibited Fast induction and Pas up-regulation, but not ba sal Pas expression of hybridoma T-cells. All-trans retinoic acid (RA) inhibited Fast induction, but had little effect on Pas up-regulation. Both agents inhibited Fast cytotoxicity. The Fas-mediated death pathwa y distal to Fas/FasL interactions remained intact in the protected hyb ridoma T-cells. These results demonstrate that Fast gene activation, b ut not Pas up-regulation, is critical for AICD and that Dex and all-tr ans RA selectively inhibits Fast but not Pas function. The system may prove useful for the identification of critical factors regulating T-c ell death genes. It may also serve as a useful system to study gene re gulation in AICD-dependent phenomena. (C) 1996 Academic Press, Inc.