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IL-2 protects T lymphocytes from glucocorticoid-induced DNA fragmentation and cell death
1Instituto de Investigaciones Biomédicas del CSIC, Madrid, Spain.
Abstract:
In the IL-2-dependent T cell clone CTLL-2, dexamethasone, a synthetic glucocorticoid, induces a suicide program characterized by the early degradation of chromatin in oligonucleosome-length fragments which precedes the loss of cell viability by 2 to 4 h. These effects are most likely mediated through the interaction with a specific glucocorticoid receptor as suggested by the structure-activity relationship of the various steroids tested. Incubation of nuclei of glucocorticoid-untreated cells in the presence of calcium and magnesium ions induces the cleavage of DNA in the linker region between nucleosomes, suggesting that fragmentation of chromatin in intact cells by glucocorticoids may involve the activation of a preexisting endonuclease. Interestingly, the presence of a saturating dose of IL-2 during the treatment of CTLL-2 cells with glucocorticoids completely blocks the cell death program.
Insights
Dexamethasone triggers T cell death by degrading DNA, but interleukin-2 (IL-2) blocks this glucocorticoid-induced suicide program. This suggests a potential therapeutic target for T cell-mediated diseases.
Area of Science:
- Immunology
- Molecular Biology
- Cell Biology
Background:
- Glucocorticoids, like dexamethasone, are potent regulators of immune responses.
- Interleukin-2 (IL-2) is crucial for T cell proliferation and survival.
- T cell apoptosis can be induced by various stimuli, playing a role in immune homeostasis.
Purpose of the Study:
- To investigate the mechanism by which dexamethasone induces apoptosis in IL-2-dependent T cells.
- To explore the role of chromatin degradation in glucocorticoid-induced T cell death.
- To determine if IL-2 can prevent dexamethasone-mediated T cell apoptosis.
Main Methods:
- Utilized the IL-2-dependent T cell clone CTLL-2.
- Treated cells with dexamethasone and various steroids.
- Analyzed DNA fragmentation using oligonucleosome-length fragment assays.
- Assessed cell viability over time.
- Investigated nuclear endonuclease activity in vitro.
- Examined the effect of IL-2 on dexamethasone-induced cell death.
Main Results:
- Dexamethasone induced a T cell suicide program characterized by early chromatin degradation into oligonucleosome-length fragments.
- This DNA fragmentation preceded loss of cell viability by 2–4 hours.
- Steroid structure-activity relationships suggested specific glucocorticoid receptor mediation.
- Nuclear incubation with Ca2+/Mg2+ ions induced DNA cleavage, implying activation of a pre-existing endonuclease.
- Saturating doses of IL-2 completely blocked dexamethasone-induced T cell death.
Conclusions:
- Dexamethasone-induced T cell apoptosis involves early, specific DNA fragmentation.
- A glucocorticoid receptor and a calcium/magnesium-dependent endonuclease likely mediate this process.
- IL-2 actively protects T cells from glucocorticoid-induced apoptosis, highlighting a critical survival pathway.