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Correlation between structure of Bcl-2 and its inhibitory function of JNK and caspase activity in dopaminergic
W S Choi1, S Y Yoon, I I Chang
1Department of Biology, Yonsei University College of Science and Institute of Life Science, Seoul, Korea.
Abstract:
To examine the correlation between the structure of Bcl-2 and its inhibitory function of c-Jun N-terminal kinase (JNK) and caspase activity, we established a dopaminergic neuronal cell line, MN9D overexpressing Bcl-2 (MN9D/Bcl-2) or its structural mutants. The mutants comprised a point mutation in the BH1 (G145A; MN9D/BH1) or BH2 (W188A; MN9D/BH2) domain and a deletion mutation in the C-terminal (MN9D/C22), BH3 (MN9D/BH3), or BH4 (MN9D/BH4) domain. As determined by the TUNEL (terminal deoxynucleotidyltransferase nick end-labeling) and MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide] reduction assay, apoptotic death of MN9D/Neo cells reached 80-90% within 24 h in response to 1 microM staurosporine. Upon staurosporine treatment, JNK activity increased six- to sevenfold over the basal level within 2-4 h. Treatment of MN9D/Neo with both staurosporine and a caspase inhibitor, Z-VAD, attenuated cell death without suppressing JNK activation. Both staurosporine-induced cell death and JNK activation were attenuated in MN9D/Bcl-2. As determined by cleavage of poly(ADP-ribose) polymerase into 85 kDa, Bcl-2 blocked caspase activity as well. When cells overexpressing one of the Bcl-2 mutants were treated with staurosporine, death was attenuated in MN9D/BH1, MN9D/BH2, and MN9D/C22 but not in MN9D/BH3 and MN9D/BH4. Similarly, both JNK and caspase activation were blocked in MN9D/BH1, MN9D/BH2, and MN9D/C22, whereas they were not suppressed in MN9D/BH3 and MN9D/BH4. Taken together, our data indicate that there exists a close structural and functional correlation of Bcl-2 to JNK and caspase activity in staurosporine-induced dopaminergic neuronal cell death.
Insights
Bcl-2
Area of Science:
- Neuroscience
- Molecular Biology
- Cell Biology
Background:
- Bcl-2 protein regulates apoptosis.
- c-Jun N-terminal kinase (JNK) and caspase pathways are involved in neuronal cell death.
- Dopaminergic neurons are vulnerable to apoptotic stimuli.
Purpose of the Study:
- To investigate the structural and functional relationship between Bcl-2 and its inhibition of JNK and caspase activity.
- To determine which domains of Bcl-2 are critical for its anti-apoptotic function in dopaminergic neurons.
Main Methods:
- Established MN9D dopaminergic neuronal cell lines overexpressing Bcl-2 or its mutants (BH1, BH2, C-terminal, BH3, BH4 domains).
- Induced apoptosis using staurosporine and measured cell death via TUNEL and MTT assays.
- Assessed JNK and caspase activity through enzymatic assays and poly(ADP-ribose) polymerase cleavage analysis.
Main Results:
- Overexpression of Bcl-2 attenuated staurosporine-induced dopaminergic neuronal cell death, JNK activation, and caspase activity.
- Mutations in BH1, BH2, or C-terminal domains of Bcl-2 retained partial inhibitory function.
- Mutations in BH3 or BH4 domains abrogated the protective effects of Bcl-2 against staurosporine-induced cell death and pathway activation.
Conclusions:
- Bcl-2's anti-apoptotic function in dopaminergic neurons is closely correlated with its structure.
- Specific domains (BH1, BH2, C-terminal) are crucial for Bcl-2's ability to inhibit JNK and caspase activity.
- BH3 and BH4 domains are essential for Bcl-2's full inhibitory capacity in this context.