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Suppression of signalling through transcription factor NF-AT by interactions between calcineurin and Bcl-2
F Shibasaki1, E Kondo, T Akagi
1Department of Cell Biology, Harvard Medical School, Boston, Massachusetts 02115, USA.
Abstract:
It is not known how the protein Bcl-2 inhibits cell death induced by calcium signalling and growth-factor withdrawal. Here we report that Bcl-2 forms a tight complex with calcineurin, resulting in the targeting of calcineurin to Bcl-2 sites on cytoplasmic membranes, and show that this interaction is dependent on the BH4 domain of Bcl-2. Calcineurin bound to Bcl-2 is an active phosphatase but is unable to promote the nuclear translocation of NF-AT, a transcription-factor required for induction of interleukin-2 expression, suggesting a mechanism by which Bcl-2 suppresses NF-AT activity. We also show that Bax, a pro-apoptotic member of the Bcl-2 family, interferes with interactions between calcineurin and Bcl-2. We propose that the ability of Bcl-2 to block NF-AT signalling is due to the sequestering of active calcineurin to the same domain of Bcl-2 which associates with Rad-1 (ref. 5), and that calcineurin may act in Bcl-2-regulated functions.
Insights
The anti-apoptotic protein Bcl-2 binds calcineurin, preventing the transcription factor NF-AT from entering the nucleus. This interaction inhibits cell death signaling pathways, offering new therapeutic targets for cell death regulation.
Area of Science:
- Cell Biology
- Molecular Biology
- Immunology
Background:
- The anti-apoptotic protein Bcl-2's mechanism for inhibiting cell death, particularly from calcium signaling and growth factor withdrawal, remains unclear.
- Understanding Bcl-2's role is crucial for developing strategies to control cell death in various physiological and pathological conditions.
Purpose of the Study:
- To elucidate the molecular mechanism by which Bcl-2 inhibits cell death.
- To investigate the interaction between Bcl-2 and calcineurin in the context of cell death signaling.
Main Methods:
- Co-immunoprecipitation assays to detect protein-protein interactions.
- Analysis of calcineurin phosphatase activity.
- Assessment of NF-AT nuclear translocation using reporter assays.
Main Results:
- Bcl-2 forms a tight complex with calcineurin, localized to cytoplasmic membranes via Bcl-2's BH4 domain.
- Calcineurin bound to Bcl-2 remains an active phosphatase but cannot induce NF-AT nuclear translocation, thus suppressing NF-AT activity.
- The pro-apoptotic protein Bax disrupts the Bcl-2-calcineurin interaction.
Conclusions:
- Bcl-2 inhibits cell death by sequestering active calcineurin, preventing NF-AT signaling.
- This interaction highlights a novel mechanism of Bcl-2-mediated cell death suppression.
- Calcineurin may play a role in Bcl-2-regulated cellular functions, offering potential therapeutic avenues.