PT - JOURNAL ARTICLE AU - Matjaz Humar AU - Soeren E. Pischke AU - Torsten Loop AU - Alexander Hoetzel AU - Rene Schmidt AU - Christoph Klaas AU - Heike L. Pahl AU - Klaus K. Geiger AU - Benedikt H. J. Pannen TI - Barbiturates Directly Inhibit the Calmodulin/Calcineurin Complex: a Novel Mechanism of Inhibition of Nuclear Factor of Activated T Cells AID - 10.1124/mol.65.2.350 DP - 2004 Feb 01 TA - Molecular Pharmacology PG - 350--361 VI - 65 IP - 2 4099 - http://molpharm.aspetjournals.org/content/65/2/350.short 4100 - http://molpharm.aspetjournals.org/content/65/2/350.full SO - Mol Pharmacol2004 Feb 01; 65 AB - Barbiturates are frequently used for the treatment of intracranial hypertension after brain injury but their application is associated with a profound increase in the infection rate. The mechanism of barbiturate-induced failure of protective immunity is still unknown. We provide evidence that nuclear factor of activated T cells (NFAT), an essential transcription factor in T cell activation, is a target of barbiturate-mediated immunosuppression in human T lymphocytes. Treatment of primary CD3+ lymphocytes with barbiturates inhibited the PMA and ionomycin induced increase in DNA binding of NFAT, whereas the activity of other transcription factors, such as Oct-1, SP-1, or the cAMP response element-binding protein, remained unaffected. Moreover, barbiturates suppressed the expression of a luciferase reporter gene under control of NFAT (stably transfected Jurkat T cells), and of the cytokine genes interleukin-2 and interferon-γ that contain functional binding motifs for NFAT within their regulatory promotor domains (human peripheral blood CD3+ lymphocytes). Neither GABA receptor-initiated signaling nor direct interactions of barbiturates with nuclear proteins affected the activity of NFAT. In contrast, barbiturates suppressed the calcineurin-dependent dephosphorylation of NFAT in intact T cells and also inhibited the enzymatic activity of calcineurin in a cell-free system, excluding upstream regulation. Thus, our results demonstrate a novel mechanism of direct inhibition of the calcineurin/calmodulin complex that may explain some of the known immunosuppressive effects associated with barbiturate treatment.