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Atypical signaling defects prevent IL-2 gene expression in lpr/lpr CD4-CD8- cells
1Institute of Molecular Biology, Academia Sinica, National Yang-Ming University, Taipei, Taiwan ROC.
Abstract:
T cells with CD4-CD8- (double negative, DN) phenotype in MRL-lpr/lpr mouse serve as a model to establish the correlation between the extremely low IL-2 gene expression and the specific signaling inactivation. The extent of nonresponsiveness in lpr DN cells was distinctive in several unusual defects. First, the poor IL-2 production in lpr DN cells could not be restored by supplement of signals known to augment IL-2 response in normal T cells. Second, the activations of both mitogen-activated protein (MAP) kinase and c-Jun N-terminal kinase (JNK) were attenuated in lpr DN cells upon direct activation by TPA/A23187. Third, IL-2 mRNA was degraded much faster in lpr DN cells than that in normal T cells. Fourth, of the four major transcriptional elements on IL-2 promoter, only AP-1 and nuclear factor of activated T cells (NFAT)-binding activities were suppressed in lpr DN T cells. Altogether, these results suggest that an extremely low level of IL-2 production in lpr DN T cells was due to both the increased instability of mRNA and the reduced activation of IL-2 gene promoter, the latter defect could be attributed to the inactivation of AP-1 and NF-AT as well as the poor activation of the upstream MAP kinase and JNK.
Insights
Double negative (DN) T cells in MRL-lpr/lpr mice show impaired IL-2 gene expression due to faster mRNA degradation and reduced promoter activation. This defect involves MAP kinase and JNK signaling inactivation, impacting AP-1 and NF-AT activity.
Area of Science:
- Immunology
- Molecular Biology
- Cell Signaling
Background:
- MRL-lpr/lpr mice possess CD4-CD8- (double negative, DN) T cells exhibiting a nonresponsive phenotype.
- Understanding the molecular basis of impaired Interleukin-2 (IL-2) gene expression in these cells is crucial.
Purpose of the Study:
- To investigate the correlation between extremely low IL-2 gene expression and specific signaling pathway inactivation in DN T cells from MRL-lpr/lpr mice.
- To elucidate the molecular defects underlying the nonresponsiveness of lpr DN T cells.
Main Methods:
- Analysis of IL-2 production and restoration capacity in lpr DN cells compared to normal T cells.
- Assessment of mitogen-activated protein (MAP) kinase and c-Jun N-terminal kinase (JNK) activation upon T-cell stimulation.
- Quantification of IL-2 mRNA stability.
- Evaluation of transcriptional element binding activities (AP-1, NFAT) on the IL-2 promoter.
Main Results:
- lpr DN T cells demonstrated significantly reduced IL-2 production that could not be rescued by standard augmentation signals.
- Activation of MAP kinase and JNK pathways was attenuated in lpr DN cells.
- IL-2 mRNA exhibited increased degradation rates in lpr DN cells.
- Suppression of AP-1 and NFAT binding activities was observed on the IL-2 promoter in lpr DN T cells.
Conclusions:
- The extremely low IL-2 production in lpr DN T cells results from a combination of accelerated mRNA instability and impaired IL-2 gene promoter activation.
- Defects in MAP kinase and JNK signaling contribute to the reduced activation of AP-1 and NFAT, leading to suppressed IL-2 gene transcription.
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