Accumulation of Hsp70/Hsc70 molecular chaperone regulator BAG-1 on COPI-coated structures in gastric epithelial cells
Affiliations: First Department of Internal Medicine, Cancer Research Institute, Sapporo Medical University School of Medicine, Sapporo 060-8543, Japan
- Published online on: November 1, 2003 https://doi.org/10.3892/ijo.23.5.1301
- Pages: 1301-1308
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The multifunctional protein BAG-1 binds to molecular chaperones Hsc70/Hsp70 and regulates their activity. While a role for BAG-1 in regulating Hsc70 chaperone activity is firmly established in vitro, physiological roles of this regulation remain obscure. Here we show that BAG-1 is highly expressed in gastrointestinal epithelial cells and accumulates at the Golgi apparatus, probably through interaction with COPI coated structure. Subcellular fractionation of gastric mucosa revealed that BAG-1 was mainly recovered in the Golgi-enriched fractions. Confocal immunofluorescence studies revealed that BAG-1 was overlapped with a cis-Golgi matrix protein GM130 and a COPI component β-COP in the vicinity of the Golgi. In response to brefeldin A, which blocks recruitment of COPI coats to the Golgi membrane, BAG-1 was dispersed throughout the cytoplasm as β-COP was. Extensive overlap of BAG-1 immunofluorescence with β-COP was still observed when cells were treated with nocodazole, which depolymerizes microtubules and induces fragmentation of the Golgi stacks. Immunoelectron microscopy revealed that BAG-1 signals were predominantly found on vesicular membrane structures adjacent to Golgi stacks, but not on mitochondrial membrane. Taken together, we suggest that BAG-1 is targeted to the COPI coated structures, implying its contribution toward the COPI vesicular transport in gastrointestinal epithelial cells.