title: Effects of targeted Bcl-2 expression in mitochondria or endoplasmic reticulum on renal tubular cell apoptosis.
abstract: Bcl-2 family proteins are central regulators of apoptosis. As the prototypic member, Bcl-2 protects various types of cells against apoptotic insults. In mammalian cells, Bcl-2 has a dual subcellular localization, in mitochondria and endoplasmic reticulum (ER). The respective roles played by mitochondrial and ER-localized Bcl-2 in apoptotic inhibition are unclear. Using Bcl-2 constructs for targeted subcellular expression, we have now determined the contributions of mitochondrial and ER-localized Bcl-2 to the antiapoptotic effects of Bcl-2 in renal tubular cells. Wild-type Bcl-2, when expressed in renal proximal tubular cells, showed partial colocalizations with both cytochrome c and disulfide isomerase, indicating dual localizations of Bcl-2 in mitochondria and ER. In contrast, Bcl-2 constructs with mitochondria-targeting or ER-targeting sequences led to relatively restricted Bcl-2 expression in mitochondria and ER, respectively. Expression of wild-type and mitochondrial Bcl-2 showed significant inhibitory effects on tubular cell apoptosis that was induced by cisplatin or ATP depletion; however, ER-Bcl-2 was much less effective. During ATP depletion, cytochrome c was released from mitochondria into the cytosol. This release was suppressed by wild-type and mitochondrial Bcl-2, but not by ER-Bcl-2. Consistently, wild-type and mitochondrial Bcl-2, but not ER-Bcl-2, blocked Bax activation during ATP depletion, a critical event for mitochondrial outer membrane permeabilization and cytochrome c release. In contrast, ER-Bcl-2 protected against apoptosis during tunicamycin-induced ER stress. Collectively, the results suggest that the cytoprotective effects of Bcl-2 in different renal injury models are largely determined by its subcellular localizations.
authors.affiliation: Department of Cellular Biology and Anatomy, Medical College of Georgia and Veterans Affairs Medical Center, 1459 Laney Walker Blvd., Augusta, GA 30912, USA.
authors.forename: Kirti
authors.initials: K
authors.lastname: Bhatt
authors.forename: Leping
authors.initials: L
authors.lastname: Feng
authors.forename: Navjotsingh
authors.initials: N
authors.lastname: Pabla
authors.forename: Kebin
authors.initials: K
authors.lastname: Liu
authors.forename: Sylvia
authors.initials: S
authors.lastname: Smith
authors.forename: Zheng
authors.initials: Z
authors.lastname: Dong
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D000900:Anti-Bacterial Agents / Q000009:adverse effects; D000970:Antineoplastic Agents / Q000009:adverse effects; D017209:Apoptosis / Q000502:physiology*; D002460:Cell Line; D002945:Cisplatin / Q000009:adverse effects; D045304:Cytochromes c / Q000378:metabolism; D004721:Endoplasmic Reticulum / Q000378:metabolism*; D015870:Gene Expression; D007687:Kidney Tubules, Proximal / Q000378:metabolism*; D008928:Mitochondria / Q000378:metabolism*; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism*; D051381:Rats; D014415:Tunicamycin / Q000009:adverse effects; D051028:bcl-2-Associated X Protein / Q000378:metabolism
chemical_list: D000900:Anti-Bacterial Agents; D000970:Antineoplastic Agents; D019253:Proto-Oncogene Proteins c-bcl-2; D051028:bcl-2-Associated X Protein; D014415:Tunicamycin; D000255:Adenosine Triphosphate; D045304:Cytochromes c; D002945:Cisplatin