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Originally published online as doi:10.1189/jlb.1107790 on December 26, 2008

Published online before print December 26, 2008
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(Journal of Leukocyte Biology. 2009;85:469-480.)
© 2009 by Society for Leukocyte Biology

Retinoic acid regulates Fas-induced apoptosis in Jurkat T cells: reversal of mitogen-mediated repression of Fas DISC assembly

Nikolai Engedal*,{dagger},1, Patrick Auberger{ddagger} and Heidi Kiil Blomhoff*

* Department of Biochemistry, Institute of Basic Medical Sciences, University of Oslo, Oslo, Norway;
{dagger} Department of Biochemistry, Institute for Cancer Research, The Norwegian Radium Hospital, Oslo, Norway; and
{ddagger} INSERM U526, IFR50, Faculté de Médecine Pasteur, Nice, France

1 Correspondence at current address: Department of Biochemistry, Institute for Cancer Research, The Norwegian Radium Hospital, Montebello, N-0310, Oslo, Norway. E-mail: nikolai.engedal{at}rr-research.no

The effect of the immune regulator vitamin A on T cell death has been poorly characterized. In the present study, we demonstrate that an active metabolite of vitamin A, retinoic acid (RA), promotes cell death in Jurkat leukemic T cells by counteracting mitogen-mediated repression of Fas-induced apoptosis. The effect of RA was dose-dependent, and at the optimal concentration of 1 µM, repression of Fas-induced cell death by the mitogens 12-O-tetradecanoylphorbol 13-acetate (TPA) or Con A was reversed by ~50% and 30%, respectively. RA promoted apoptosis rather than necrosis, as judged by analysis of cell morphology, mitochondrial membrane depolarization, and DNA fragmentation. TPA-mediated protection from Fas-induced apoptosis is dependent on ERK and NF-{kappa}B. However, analyses of ERK and NF-{kappa}B activities and expression of target genes indicated that RA-mediated counteraction of the protective effect of TPA did not involve negative crosstalk with ERK or NF-{kappa}B survival pathways. RA-induced cell death was accompanied by enhanced cleavage of procaspase-3, -6, and -8, as well as enhanced cleavage of DNA fragmentation factor 45. Interestingly, RA-mediated cleavage of procaspase-8 occurred very early and before any effect of RA could be detected on procaspase-3 cleavage, suggesting that RA might act at the level of the Fas death-inducing signaling complex (DISC). Indeed, DISC immunoprecipitation studies revealed that RA treatment reversed the inhibitory effect of TPA on CH11-induced recruitment and processing of procaspase-8 at the DISC. In conclusion, we have identified a role of RA in abrogating mitogen-mediated repression of Fas DISC assembly, thus enhancing Fas-induced apoptosis in leukemic T cells.

Key Words: phorbol ester • concanavalin A • caspase-8