Accumulation of Hsp70/Hsc70 molecular chaperone regulator BAG-1 on COPI-coated structures in gastric epithelial cells.
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 beta-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 beta-COP was. Extensive overlap of BAG-1 immunofluorescence with beta-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.
Takamura
Atsushi
A
First Department of Internal Medicine, Cancer Research Institute, Sapporo Medical University School of Medicine, Sapporo 060-8543, Japan.
Adachi
Masaaki
M
Wada
Ikuo
I
Mitaka
Toshihiro
T
Takayama
Shinichi
S
Imai
Kohzoh
K
D020126:Brefeldin A / Q000494:pharmacology; D022181:COP-Coated Vesicles / Q000737:chemistry*; D002352:Carrier Proteins / Q000378:metabolism*; D045744:Cell Line, Tumor; D002499:Centrifugation, Density Gradient; D004268:DNA-Binding Proteins; D004847:Epithelial Cells / Q000473:pathology*; D006056:Golgi Apparatus / Q000378:metabolism / Q000473:pathology; D050883:HSC70 Heat-Shock Proteins; D018840:HSP70 Heat-Shock Proteins / Q000096:biosynthesis*; D006801:Humans; D015151:Immunoblotting; D007150:Immunohistochemistry; D007472:Iohexol / Q000494:pharmacology; D018613:Microscopy, Confocal; D008856:Microscopy, Fluorescence; D016253:Microscopy, Immunoelectron; D018832:Molecular Chaperones / Q000378:metabolism*; D015739:Nocodazole / Q000494:pharmacology; D011485:Protein Binding; D013347:Subcellular Fractions / Q000378:metabolism; D013997:Time Factors; D014157:Transcription Factors
C091732:BCL2-associated athanogene 1 protein; D002352:Carrier Proteins; D004268:DNA-Binding Proteins; D050883:HSC70 Heat-Shock Proteins; D018840:HSP70 Heat-Shock Proteins; C494371:HSPA8 protein, human; D018832:Molecular Chaperones; D014157:Transcription Factors; D020126:Brefeldin A; D007472:Iohexol; D015739:Nocodazole