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Bcl-2 intersects the NFkappaB signalling pathway and suppresses apoptosis in ventricular myocytes
1Institute of Cardiovascular Sciences, St. Boniface General Hospital Research Centre, and the Department of Physiology, Faculty of Medicine, University of Manitoba, Winnipeg. Lorrie@sbrc.umanitoba.ca
Abstract:
As a first step toward identifying putative regulators of apoptosis in the heart, the impact of the anti-apoptosis protein Bcl-2 (B-cell lymphoma gene) on the NFkappaB (nuclear factor kappa beta) signalling pathway in suppressing apoptosis in ventricular myocytes was studied. The data indicate that adenovirus-mediated delivery of Bcl-2 resulted in a significant increase in NFkappaB-dependent DNA binding and NFkappaB-directed gene transcription. No change in NFkappaB protein content was observed in myocytes expressing Bcl-2. Moreover, the Bcl-2-mediated NFkappaB activation was found to be related to changes in the activity of the NFkappaB regulatory protein IkappaBalpha (inhibitor of kappa beta). In this regard, a marked reduction in IkappaBalpha protein content was observed in ventricular myocytes expressing Bcl-2. The mode by which Bcl-2 regulates IkappaBalpha was related to the N-terminal phosphorylation and degradation of IkappaBalpha by the proteasome since an N-terminal deletion mutant of IkappaBalpha or the proteasome inhibitor lactacystin abrogated Bcl-2's inhibitory effects on IkappaBalpha and prevented NFkappaB activation. Furthermore, adenovirus-mediated delivery of a phosphorylation defective form of IkappaBalpha rendered ventricular myocytes incapable of NFkappaB activation and susceptible to tumour necrosis factor alpha-mediated apoptosis. Moreover, Bcl-2's anti-apoptotic function was lost in cells defective for NFkappaB activation. The data provide evidence for a link between Bcl-2 and the NFkappaB signalling pathway for the suppression of apoptosis in ventricular myocytes.
Insights
The anti-apoptosis protein Bcl-2 enhances nuclear factor kappa beta (NFkappaB) signaling in heart cells by reducing IkappaBalpha. This pathway is crucial for Bcl-2
Area of Science:
- Cardiovascular Biology
- Molecular Cell Biology
- Apoptosis Research
Background:
- Apoptosis, or programmed cell death, is critical in cardiac function and disease.
- The nuclear factor kappa beta (NFkappaB) pathway is a key regulator of inflammation and cell survival.
- Bcl-2 is an anti-apoptotic protein with known roles in various cell types.
Purpose of the Study:
- To investigate the role of the anti-apoptosis protein Bcl-2 in regulating the NFkappaB signaling pathway within ventricular myocytes.
- To determine if Bcl-2 influences NFkappaB-dependent DNA binding and gene transcription in the context of apoptosis suppression.
Main Methods:
- Adenovirus-mediated gene delivery to introduce Bcl-2 into ventricular myocytes.
- Assessment of NFkappaB-dependent DNA binding and gene transcription.
- Analysis of IkappaBalpha protein content and its regulation via phosphorylation and proteasomal degradation.
Main Results:
- Bcl-2 expression significantly increased NFkappaB-dependent DNA binding and gene transcription.
- Bcl-2 reduced IkappaBalpha protein levels, linked to its N-terminal phosphorylation and proteasomal degradation.
- Blocking NFkappaB activation or IkappaBalpha degradation abolished Bcl-2's anti-apoptotic effects.
Conclusions:
- Bcl-2 suppresses apoptosis in ventricular myocytes by activating the NFkappaB signaling pathway.
- The mechanism involves the regulation of IkappaBalpha phosphorylation and subsequent proteasomal degradation.
- This study establishes a functional link between Bcl-2 and NFkappaB in cardiac cell survival.