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Calcium-dependent immediate-early gene induction in lymphocytes is negatively regulated by p21Ha-ras
C Y Chen1, L W Forman, D V Faller
1Department of Medicine, Boston University School of Medicine, Massachusetts 02118, USA.
Abstract:
The induction of immediate-early (IE) response genes, such as egr-1, c-fos, and c-jun, occurs rapidly after the activation of T lymphocytes. The process of activation involves calcium mobilization, activation of protein kinase C (PKC), and phosphorylation of tyrosine kinases. p21(ras), a guanine nucleotide binding factor, mediates T-cell signal transduction through PKC-dependent and PKC-independent pathways. The involvement of p21(ras) in the regulation of calcium-dependent signals has been suggested through analysis of its role in the activation of NF-AT. We have investigated the inductions of the IE genes in response to calcium signals in Jurkat cells (in the presence of activated p21(ras)) and their correlated consequences. The expression of activated p21(ras) negatively regulated the induction of IE genes by calcium ionophore. This inhibition of calcium-activated IE gene induction was reversed by treatment with cyclosporin A, suggesting the involvement of calcineurin in this regulation. A later result of inhibition of this activation pathway by p21(ras) was down-regulation of the activity of the transcription factor AP-1 and subsequent coordinate reductions in IL-2 gene expression and protein production. These results suggest that p2l(ras) is an essential mediator in generating not only positive but also negative modulatory mechanisms controlling the competence of T cells in response to inductive stimulations.
Insights
Activated p21(ras) inhibits T-cell immediate-early gene induction via calcium signals, but this effect is reversible. This regulation impacts Interleukin-2 production, highlighting p21(ras) as a key T-cell modulator.
Area of Science:
- Immunology
- Molecular Biology
- Cell Signaling
Background:
- T-lymphocyte activation involves rapid induction of immediate-early (IE) response genes.
- Key signaling events include calcium mobilization, protein kinase C (PKC) activation, and tyrosine kinase phosphorylation.
- p21(ras), a guanine nucleotide-binding factor, is implicated in T-cell signal transduction via PKC-dependent and -independent pathways.
Purpose of the Study:
- To investigate the impact of activated p21(ras) on IE gene induction in response to calcium signals in Jurkat T cells.
- To elucidate the downstream consequences of p21(ras)-mediated regulation of T-cell activation pathways.
Main Methods:
- Utilized Jurkat T cells engineered to express activated p21(ras).
- Stimulated cells with calcium ionophore to induce IE genes.
- Assessed IE gene induction, NF-AT activation, and AP-1 transcription factor activity.
- Investigated the effect of cyclosporin A on calcium-activated IE gene induction.
Main Results:
- Activated p21(ras) expression negatively regulated the induction of IE genes triggered by calcium ionophore.
- This inhibitory effect was reversed by cyclosporin A, indicating calcineurin involvement.
- p21(ras) led to the down-regulation of transcription factor AP-1 activity.
- Reduced AP-1 activity resulted in decreased Interleukin-2 (IL-2) gene expression and protein production.
Conclusions:
- p21(ras) acts as a critical mediator in T-cell activation, exerting both positive and negative regulatory control.
- p21(ras) negatively modulates calcium-dependent IE gene induction and IL-2 production.
- The findings suggest p21(ras) plays a significant role in controlling T-cell responsiveness to stimulation.