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Expression of Tcf-1 mRNA and surface TCR-CD3 complexes are reduced during apoptosis of T cells
1Institute for Molecular Biology and Genetics and Department of Molecular Biology, Seoul National University, Korea.
Abstract:
When a T cell hybridoma, 70.7, was treated with a Ca2+ ionophore (A23187), apoptotic cell death was induced. Interestingly, we observed that the expression of Tcf-1, a T cell-specific transcription factor, mRNA was reduced by approximately 5-fold in the A23187-treated apoptotic cells compared to an ethanol-treated control. The hybridoma cells, however, did not display such a reduced expression of Tcf-1 mRNA upon treatment with buthionine sulfoxide, which is known to induce a necrosis-like cell death. When another T cell hybridoma, KMIs-8.3.5, was treated with A23187 and phorbol myristate acetate, which leads to activation-induced apoptosis, Tcf-1 expression was again greatly reduced. However, a mutant line (KCIT1-8.5) derived from KMIs-8.3.5, which produces IL-2 upon activation and is resistant to apoptosis, did not show such reduction in Tcf-1 expression. We also showed that the reduced expression level of CD3epsilon mRNA and surface TCR-CD3 complex in apoptotic T cells is caused by the reduced expression of Tcf-1. When 70.7 cells were transfected with a plasmid DNA pSVtcf-1, in which Tcf-1 gene expression is driven by the SV40 promoter, such reduction of the Tcf-1 mRNA and the surface expression of the TCR-CD3 complex were not observed upon apoptosis induction. Our results suggest that the reduced expression of Tcf-1 is specific for the apoptotic, but not for the activating, process of T cells and is also responsible for the reduced surface expression of the TCR-CD3 in apoptotic T cells.
Insights
Reduced Tcf-1 mRNA expression is specific to T cell apoptosis, not T cell activation. This downregulation of Tcf-1 causes decreased TCR-CD3 complex surface expression in apoptotic T cells.
Area of Science:
- Immunology
- Molecular Biology
- Cell Death Research
Background:
- T cell activation and apoptosis are critical immune processes.
- T cell-specific transcription factors play key roles in T cell function.
- The regulation of T cell gene expression during apoptosis is not fully understood.
Purpose of the Study:
- To investigate the role of Tcf-1 transcription factor during T cell apoptosis.
- To determine if reduced Tcf-1 expression is specific to apoptosis or general T cell activation.
- To elucidate the impact of Tcf-1 downregulation on T cell surface receptor expression.
Main Methods:
- Induction of apoptosis in T cell hybridomas using calcium ionophore (A23187) and phorbol myristate acetate.
- Assessment of Tcf-1 mRNA expression levels via quantitative analysis.
- Analysis of T cell receptor (TCR)-CD3 complex surface expression.
- Transfection of T cells with a Tcf-1 expression plasmid.
Main Results:
- Apoptosis induction in T cell hybridomas led to a significant reduction in Tcf-1 mRNA expression.
- This reduction in Tcf-1 mRNA was specific to apoptosis, not observed in necrosis or T cell activation.
- Downregulation of Tcf-1 in apoptotic T cells correlated with reduced CD3epsilon mRNA and surface TCR-CD3 complex expression.
- Overexpression of Tcf-1 prevented the reduction of TCR-CD3 complex surface expression during apoptosis.
Conclusions:
- Reduced Tcf-1 expression is a specific hallmark of T cell apoptosis.
- Tcf-1 downregulation is responsible for the diminished surface expression of the TCR-CD3 complex in apoptotic T cells.
- These findings highlight a novel regulatory mechanism in T cell apoptosis impacting immune synapse formation.