Comparison of apoptosis signaling through T cell receptor, fas, and calcium ionophore
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H T Maecker1, S Hedjbeli, M Alzona
1Department of Medicine/Oncology, Stanford University Medical Center, California 94305, USA.
Abstract:
The SUP-T13 cell line, a human T leukemia, is susceptible to apoptosis by various inducers, including anti-TCR mAb, calcium ionophores, and anti-fas mAb. Induction of apoptosis by these three agents was investigated, and several differences were found. All three agents induced DNA fragmentation with a similar time course, but the kinetics of cell death were different for the three agents. Anti-TCR mAb-induced apoptosis, but not A23187- or anti-fas-induced apoptosis, was rescued by anti-CD3 mAb treatment. In contrast, only anti-fas mAb-mediated apoptosis was rescued by PKC activators such as PMA. These differences suggest that each of these three agents mediate apoptosis by unique signaling pathways. Nevertheless, two variant subclones of SUP-T13 were found to be resistant to all three apoptosis-inducing agents, suggesting a point(s) of common regulation between the different pathways. To determine whether this regulation occurred through bcl-2, p53, or c-myc, their expression in the parental and variant cells was determined. The three clones expressed approximately equal amounts of these proteins, and their levels did not change significantly upon treatment with anti-TCR or anti-TCR plus anti-CD3 mAb. Thus, although the proximal signaling by various apoptosis inducers were quite different, a common mediator(s) (as yet unknown) may still regulate apoptosis induced by these multiple agents.
Insights
Investigating apoptosis in SUP-T13 leukemia cells revealed distinct signaling pathways for different inducers. However, resistant variants suggest a common regulatory point, independent of bcl-2, p53, or c-myc expression.
Area of Science:
- Immunology
- Cell Biology
- Molecular Biology
Background:
- The SUP-T13 cell line is a human T leukemia model susceptible to apoptosis.
- Apoptosis can be induced by various agents, including anti-TCR mAb, calcium ionophores, and anti-fas mAb.
Purpose of the Study:
- To investigate the distinct signaling pathways of apoptosis induction by anti-TCR mAb, calcium ionophores, and anti-fas mAb in SUP-T13 cells.
- To identify common regulatory mechanisms of apoptosis, particularly in resistant cell variants.
Main Methods:
- Induction of apoptosis in SUP-T13 cells using anti-TCR mAb, A23187 (calcium ionophore), and anti-fas mAb.
- Assessment of DNA fragmentation and cell death kinetics.
- Rescue experiments using anti-CD3 mAb and PKC activators (PMA).
- Analysis of bcl-2, p53, and c-myc expression in parental and resistant cell lines.
Main Results:
- All three agents induced DNA fragmentation similarly, but cell death kinetics differed.
- Anti-TCR mAb-induced apoptosis was rescued by anti-CD3 mAb, while anti-fas mAb-induced apoptosis was rescued by PMA.
- Two SUP-T13 variant subclones were resistant to all three apoptosis inducers.
- Expression levels of bcl-2, p53, and c-myc were similar in parental and variant cells and did not change significantly upon treatment.
Conclusions:
- Apoptosis induction by anti-TCR mAb, calcium ionophores, and anti-fas mAb involves unique proximal signaling pathways.
- A common, yet unidentified, regulatory mechanism likely controls apoptosis in SUP-T13 cells, as evidenced by resistant variants.
- The common regulation does not appear to be mediated by bcl-2, p53, or c-myc at the protein expression level.