S-Nitrosylation of Bcl-2 Negatively Affects Autophagy in Lung Epithelial Cells.
J Cell Biochem 2016;
117:521-32. [PMID:
26241894 DOI:
10.1002/jcb.25303]
[Citation(s) in RCA: 24] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/05/2015] [Accepted: 08/03/2015] [Indexed: 01/08/2023]
Abstract
Autophagy is a catabolic cellular mechanism involving lysosomal degradation of unwanted cellular components. Interaction between Beclin-1 and Bcl-2 proteins is known to play a critical role in the initiation of autophagy. We report that malignantly transformed lung epithelial cells are resistant to autophagy and express lower basal levels of autophagic proteins, Beclin-1 and LC3-II as compared to non-tumorigenic cells. Additionally, increased levels of nitric oxide (NO) and Bcl-2 were observed in transformed cells. Nitric oxide was found to negatively regulate autophagy initiation and autophagic flux by nitrosylating Bcl-2 and stabilizing its interaction with Beclin-1, resulting in inhibition of Beclin-1 activity. An increase in the apoptotic initiator caspase-9 and the apoptosis and autophagy-associated kinase p38/MAPK in both cell types indicated possible autophagy-apoptosis crosstalk. Pre-treatments with ABT-737 (Bcl-2 inhibitor) and aminoguanidine (NO inhibitor), and transfection with a non-nitrosylable Bcl-2 cysteine double-mutant plasmid resulted in increased autophagic flux (LC3-II/p62 upregulation) corresponding with decreased S-nitrocysteine expression, thus corroborating the regulatory role of Bcl-2 S-nitrosylation in autophagy. In conclusion, our study reveals a novel mechanism of autophagy resistance via post-translational modification of Bcl-2 protein by NO, which may be critical in driving cellular tumorigenesis.
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