title: The glucose transporter GLUT4 and the aminopeptidase vp165 colocalise in tubulo-vesicular elements in adipocytes and cardiomyocytes.
abstract: The aminopeptidase vp165 is one of the major polypeptides enriched in GLUT4-containing vesicles immuno-isolated from adipocytes. In the present study we have confirmed and quantified the high degree of colocalisation between GLUT4 and vp165 using double label immuno-electron microscopy on vesicles isolated from adipocytes and heart. The percentage of vp165-containing vesicles that also contained GLUT4 was 91%, 76%, and 86% in rat adipocytes, 3T3-L1 adipocytes, and rat heart, respectively. Internalisation of a transferrin/HRP (Tf/HRP) conjugate by 3T3-L1 adipocytes, followed by diaminobenzidine treatment in intact cells, resulted in ablation of only 41% and 45% of GLUT4 and vp165, respectively, whereas endosomal markers are almost quantitatively ablated. Using immuno-electron microscopy on cryosections it was determined that in atrial cardiomyocytes GLUT4 and vp165 colocalised in a population of tubulo-vesicular (T-V) elements that were often found close to the plasma membrane. Double label immunocytochemistry indicated a high degree of overlap in these T-V elements between GLUT4 and vp165. However, in atrial cardiomyocytes a large proportion of GLUT4 was also present in secretory granules containing atrial natriuretic factor (ANF). In contrast, very little vp165 was detected in ANF granules. These data indicate that GLUT4 and vp165 are colocalised in an intracellular, post-endocytic, tubulo-vesicular compartment in adipocytes and cardiomyocytes suggesting that both proteins are sorted in a similar manner in these cells. However, GLUT4 but not vp165 is additionally localised in the regulated secretory pathway in atrial cardiomyocytes.
authors.affiliation: Centre for Molecular and Cellular Biology, University of Queensland, Brisbane, QLD 4072, Australia.
authors.forename: S
authors.initials: S
authors.lastname: Martin
authors.forename: J E
authors.initials: JE
authors.lastname: Rice
authors.forename: G W
authors.initials: GW
authors.lastname: Gould
authors.forename: S R
authors.initials: SR
authors.lastname: Keller
authors.forename: J W
authors.initials: JW
authors.lastname: Slot
authors.forename: D E
authors.initials: DE
authors.lastname: James
mesh_terms: D016475:3T3 Cells / Q000737:chemistry / Q000201:enzymology; D017667:Adipocytes / Q000737:chemistry* / Q000201:enzymology / Q000648:ultrastructure; D000626:Aminopeptidases / Q000032:analysis* / Q000096:biosynthesis; D000818:Animals; D010122:Cystinyl Aminopeptidase; D011992:Endosomes / Q000737:chemistry / Q000201:enzymology; D051275:Glucose Transporter Type 4; D006325:Heart Atria / Q000737:chemistry / Q000166:cytology / Q000201:enzymology; D007425:Intracellular Membranes / Q000737:chemistry / Q000201:enzymology / Q000648:ultrastructure; D008297:Male; D051379:Mice; D016253:Microscopy, Immunoelectron; D009004:Monosaccharide Transport Proteins / Q000032:analysis* / Q000096:biosynthesis; D018485:Muscle Fibers, Skeletal / Q000737:chemistry* / Q000201:enzymology / Q000648:ultrastructure; D009124:Muscle Proteins; D009206:Myocardium / Q000737:chemistry / Q000166:cytology* / Q000201:enzymology; D051381:Rats; D017208:Rats, Wistar
chemical_list: D051275:Glucose Transporter Type 4; D009004:Monosaccharide Transport Proteins; D009124:Muscle Proteins; C495693:Slc2a4 protein, mouse; C495694:Slc2a4 protein, rat; D000626:Aminopeptidases; D010122:Cystinyl Aminopeptidase; C105964:leucyl-cystinyl aminopeptidase