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Role of c-jun induction in the glucocorticoid-evoked apoptotic pathway in human leukemic lymphoblasts
1Department of Human Biological Chemistry and Genetics, The University of Texas Medical Branch, Galveston, USA.
Abstract:
Accumulated evidence suggests tI AP-1 family in CEM cell clones exposed to the glucocorticoid dexamethasone (Dex) has been investigated. Dex is known to cause apoptosis of lymphoid cells in general and of sensitive human lymphoid CEM cell clones in particular. This study finds that Dex induces c-jun mRNA and cJun protein in cells of the sensitive clone CEM-C7 and of the lysis-sensitive OEM hybrid clone H10. CEM-O7 cells were screened for several other Jun/Fos family proteins. Both cFos and JunD were expressed but were unaffected by the steroid, and JunB was not detected. In the continual presence of Dex the induction of cJun began about 6 h after addition of Dex, reached a maximum by 24 h, and plateaued for 72 h, while cell death did not begin until 24-48 h. In clone OEM-Cl cells, which contain glucocorticoid receptor (GR) but are resistant to lysis by Dex, the basal, and even the fully induced, cJun levels are below the basal levels in OEM-07 and H10 cells. To test the hypothesis that cJun plays an important role in steroid-evoked apoptosis, stable transfectants expressing Dex-regulable antisense c-jun RNA were established. Mass cultures of these cells showed reduced sensitivity to Dex, and in three of three clones tested, complete resistance to Dex was obtained. This occurred even though endogenous genes (GR, c-jun) normally responsive to Dex were still inducible, indicating that the GR and basic glucocorticoid response apparatus were intact. It is concluded that Dex induces cJun levels in sensitive OEM cells before cell death and that this induction plays a role in the apoptotic process.
Insights
Glucocorticoid dexamethasone (Dex) induces c-Jun protein in sensitive lymphoid cells before apoptosis occurs. Inhibiting c-Jun expression with antisense RNA confers resistance to Dex-induced cell death, highlighting c-Jun's role in apoptosis.
Area of Science:
- Molecular Biology
- Cell Biology
- Immunology
Background:
- Glucocorticoids like dexamethasone (Dex) induce apoptosis in lymphoid cells.
- The AP-1 family of transcription factors, including c-Jun, plays roles in cellular responses.
- The precise role of c-Jun in glucocorticoid-induced apoptosis is not fully understood.
Purpose of the Study:
- To investigate the role of the AP-1 family, specifically c-Jun, in dexamethasone (Dex)-induced apoptosis of human lymphoid CEM cell clones.
- To determine if c-Jun induction precedes or follows the onset of apoptosis.
- To test the hypothesis that c-Jun is a critical mediator of steroid-evoked apoptosis.
Main Methods:
- Exposure of CEM cell clones (CEM-C7, H10, OEM-Cl) to dexamethasone (Dex).
- Measurement of c-Jun mRNA and protein levels using quantitative assays.
- Generation of stable transfectants with Dex-regulable antisense c-jun RNA to inhibit c-Jun expression.
- Assessment of cell sensitivity to Dex-induced apoptosis in transfectant clones.
Main Results:
- Dex treatment induced c-Jun mRNA and protein in sensitive CEM-C7 and H10 cells, but not in Dex-resistant OEM-Cl cells.
- c-Jun induction by Dex occurred within hours, preceding the onset of cell death by 24-48 hours.
- Stable inhibition of c-Jun expression using antisense RNA rendered cells completely resistant to Dex-induced apoptosis, despite intact glucocorticoid receptor (GR) function.
Conclusions:
- Dexamethasone (Dex) induces c-Jun protein levels in sensitive lymphoid cells prior to the initiation of apoptosis.
- c-Jun induction is a critical step in the apoptotic pathway triggered by Dex.
- Targeting c-Jun expression offers a potential strategy to modulate glucocorticoid-induced apoptosis.