|
|
|
|
|
|
|
||
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
J. Cell Biol.,
Volume 140, Number 3, February 9, 1998 565-575
*
* Department of Biochemistry and Biophysics, The trafficking of GLUT4, a facilitative glucose transporter, is examined in transfected CHO cells.
In previous work, we expressed GLUT4 in neuroendocrine cells and fibroblasts and found that it was targeted
to a population of small vesicles slightly larger than synaptic vesicles (Herman, G.A, F. Bonzelius, A.M. Cieutat, and R.B. Kelly. 1994. Proc. Natl. Acad. Sci. USA. 91:
12750-12754.). In this study, we demonstrate that at 37°C,
GLUT4-containing small vesicles (GSVs) are detected
after cell surface radiolabeling of GLUT4 whereas uptake of radioiodinated human transferrin does not show
appreciable accumulation within these small vesicles. Immunofluorescence microscopy experiments show
that at 37°C, cell surface-labeled GLUT4 as well as
transferrin is internalized into peripheral and perinuclear structures. At 15°C, endocytosis of GLUT4 continues to occur at a slowed rate, but whereas fluorescently labeled GLUT4 is seen to accumulate within large
peripheral endosomes, no perinuclear structures are labeled, and no radiolabeled GSVs are detectable. Shifting cells to 37°C after accumulating labeled GLUT4 at
15°C results in the reappearance of GLUT4 in perinuclear structures and GSV reformation. Cytosol acidification or treatment with hypertonic media containing
sucrose prevents the exit of GLUT4 from peripheral
endosomes as well as GSV formation, suggesting that
coat proteins may be involved in the endocytic trafficking of GLUT4. In contrast, at 15°C, transferrin continues to traffic to perinuclear structures and overall labels
structures similar in distribution to those observed at
37°C. Furthermore, treatment with hypertonic media
has no apparent effect on transferrin trafficking from
peripheral endosomes. Double-labeling experiments
after the internalization of both transferrin and surface-labeled GLUT4 show that GLUT4 accumulates within
peripheral compartments that exclude the transferrin
receptor (TfR) at both 15° and 37°C. Thus, GLUT4 is
sorted differently from the transferrin receptor as evidenced by the targeting of each protein to distinct early
endosomal compartments and by the formation of
GSVs. These results suggest that the sorting of GLUT4
from TfR may occur primarily at the level of the plasma membrane into distinct endosomes and that the organization of the endocytic system in CHO cells more
closely resembles that of neuroendocrine cells than previously appreciated.
Department of Dermatology, The Hormone Research Institute; § Department of Pediatrics, Division of Gastroenterology and Nutrition, University of California, San Francisco, California 94143
CiteULike 
Complore 
Connotea 
Del.icio.us 
Digg 
Reddit 
Technorati What's this?
This article has been cited by other articles:
|
|
