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The Adipocyte Plasma Membrane Caveolin Functional/Structural Organization Is Necessary for the Efficient Endocytosis of GLUT4
Ist Teil von
The Journal of biological chemistry, 2003-03, Vol.278 (12), p.10683-10690
Ort / Verlag
United States: American Society for Biochemistry and Molecular Biology
Erscheinungsjahr
2003
Quelle
MEDLINE
Beschreibungen/Notizen
It is well established that insulin stimulation of glucose uptake requires the translocation of intracellular localized GLUT4
protein to the cell surface membrane. This plasma membrane-redistributed GLUT4 protein was partially co-localized with caveolin
as determined by confocal fluorescent microscopy but was fully excluded from lipid rafts based upon Triton X-100 extractability.
Cholesterol depletion with methyl-β-cyclodextrin, filipin, or cholesterol oxidase resulted in an insulin-independent increase
in the amount of plasma membrane-localized GLUT4 that was fully reversible by cholesterol replenishment. This basal accumulation
of cell surface GLUT4 occurred due to an inhibition of GLUT4 endocytosis. However, this effect was not specific since cholesterol
extraction also resulted in a dramatic inhibition of clathrin-mediated endocytosis as assessed by transferrin receptor internalization.
To functionally distinguish between caveolin- and clathrin-dependent endocytic processes, we took advantage of a dominant-interfering
caveolin 1 mutant (Cav1/S80E) that specifically disrupts caveolae organization. Expression of Cav1/S80E, but not the wild
type (Cav1/WT) or Cav1/S80A mutant, inhibited cholera toxin B internalization without any significant effect on transferrin
receptor endocytosis. In parallel, Cav1/S80E expression increased the amount of plasma membrane-localized GLUT4 protein in
an insulin-independent manner. Although Cav1/S80E also decreased GLUT4 endocytosis, the extent of GLUT4 internalization was
only partially reduced (â¼40%). In addition, expression of Cav1/WT and Cav1/S80A enhanced GLUT4 endocytosis by â¼20%. Together,
these data indicate that the endocytosis of GLUT4 requires clathrin-mediated endocytosis but that the higher order structural
organization of plasma membrane caveolin has a significant influence on this process.