Induction of Apoptosis by Retinoids and Retinoic Acid Receptor γ-Selective Compounds in Mouse Thymocytes through a Novel Apoptosis Pathway
- Zsuzsa Szondy1,
- Uwe Reichert3,
- Jean-Michel Bernardon3,
- Serge Michel3,
- Réka Tóth1,
- Philippe Ancian3,
- Eva Ajzner2 and
- Laszlo Fesus1
- Departments of 1Biochemistry (Z.S., R.T., L.F.) and 2Clinical Chemistry (E.A.), University Medical School of Debrecen, Hungary, H-4012, and 3Centre International de Recherches Dermatologiques Galderma, 06902 Sophia Antipolis Cedex, France (U.R., J.-M.B., S.M., P.A.)
Abstract
Retinoic acids are morphogenic signaling molecules that are derived from vitamin A and involved in a variety of tissue functions. Two groups of their nuclear receptors have been identified: retinoic acid receptors (RARs) and retinoic acid X receptors (RXRs). All-trans retinoic acid is the high affinity ligand for RARs, and 9-cis retinoic acid also binds to RXRs with high affinity. In cells at high concentrations, all-trans retinoic acid can be converted to 9-cis retinoic acid via unknown mechanisms. It was previously shown that retinoic acids prevents activation-induced death of thymocytes. Here, we report that both all-trans and 9-cis retinoic acid induce apoptosis of mouse thymocytes and purified CD4+CD8+ cells in ex vivo cultures, with 9-cis retinoic acid being 50 times more effective. The induction of apoptosis by retinoic acids is mediated by RARγ because (a) the phenomenon can be reproduced only by RARγ-selective retinoic acid analogs, (b) the cell death induced by either retinoic acids or RARγ analogs can be inhibited by RARγ-specific antagonists, and (c) CD4+CD8+thymocytes express RARγ. In vivo administration of an RARγ analog resulted in thymus involution with the concomitant activation of the apoptosis-related endonuclease and induction of tissue transglutaminase. The RARγ pathway of apoptosis is RNA and protein synthesis dependent, affects the CD4+CD8+ double positive thymocytes, and can be inhibited by the addition of either Ca2+ chelators or protease inhibitors. Using various RAR- and RXR-specific analogs and antagonists, it was demonstrated that stimulation of RARα inhibits the RARγ-specific death pathway (which explains the lack of apoptosis stimulatory effects of all-trans retinoic acid at physiological concentrations) and that costimulation of the RXR receptors (in the case of 9-cis retinoic acid) can neutralize this inhibitory effect. It is suggested that formation of 9-cis retinoic acid may be a critical element in regulating both the positive selection and the “default cell death pathway” of thymocytes.
Footnotes
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Send reprint requests to: Dr. Laszlo Fesus, Department of Biochemistry, University Medical School of Debrecen, H-4012 Debrecen, Nagyerdei Krt. 98, Hungary. E-mail:fesus{at}indi.dote.hu
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↵1 B. Charpentier and J. M. Bernardon. European patent 658553 (1993).
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↵2 Z. Szondy, U. Reichert, J.-M. Bernardon, S. Michel, R. Tóth, P. Ancian, E. Ajzner, and L. Fesus, unpublished observations.
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↵3 Z. Szondy, U. Reichert, J.-M. Bernardon, S. Michel, R. Tóth, P. Ancian, E. Ajzner, and L. Fesus, unpublished observations.
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This study was supported in part by Hungarian grants from National Scientific Research Fund (OTKA F5468) and the Ministry of Welfare (T-01 408/1993).
- Abbreviations:
- TCR
- T cell receptor
- RAR
- retinoic acid receptor
- RXR
- retinoic acid X receptor
- APC
- antigen presenting cells
- FCS
- fetal calf serum
- FITC
- fluorescein isothyocyanate
- PBS
- phosphate-buffered saline
- PE
- phycoerythrine
- RA
- retinoic acid
- RT
- reverse transcription
- PCR
- polymerase chain reaction
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- Received December 4, 1996.
- Accepted February 20, 1997.
- The American Society for Pharmacology and Experimental Therapeutics
