Inhibition by cAMP and glucocorticoids of activation-induced cell death: Role of NFKB and FasL promoter chromatinization

DAMIAN REFOJO; ANA LIBERMAN; SANDRA WALSER; FLORIAN HOLSBOER; EDUARDO ARZT

FASEB JOURNAL

Año: 2007

0892-6638

The induction of FasL is a critical event in the triggering of activation-induced cell death in T cells. Glucocorticoids (GC) exert strong effects upon T cell death and survival and a critical role has been assigned to GC in thymic negative selection and T cell homeostasis. On the other hand cAMP, a signalling molecule critically involved in T cell function, also modulates activation-induced cell death and FasL expression. Here we evaluated in T cell hybridomas the influence of cAMP and GC on different signalling pathways - NFKB, ERK1/2, p38, c-Myc, Nur77 and NFAT - known to mediate TCR-induced FasL activation. The cAMP inhibited TCR-induced NFKB and ERK pathways through a PKA-dependent mechanism and dexamethasone (Dex) blocks the activation-induced NFKB signalling evidencing that these pathways are the targets of cAMP and GC to block activation-mediated FasL induction. Besides, we show that while GC and cAMP block the induction of endogenous FasL mRNA, the same ligands potentiate TCR-induced activation of FasL promoter reporters in transient transfections assays. Alternative splicing isoforms, differential kinetics in the maturation process of the RNA and artificial tritation of transcriptional co-factors were evaluated and discarded as possible explanation of these discrepancies. When the activity of the FasL promoter was evaluated in stably transfected T cell hybridomas, the facilitatory effect of GC and cAMP turned inhibitory, resembling the effects on endogenous FasL mRNA. Therefore, the increased chromatinization status known to occur in genomic DNA-inserted plasmids vs episomic plasmids is critical for proper regulation of FasL by cAMP and GR, two critical controllers in activation-induced cell death.