TY - JOUR
T1 - Ligand-stimulated β2-adrenergic receptor internalization via the constitutive endocytic pathway into rab5-containing endosomes
AU - Moore, Robert H.
AU - Sadovnikoff, Nicholas
AU - Hoffenberg, Simon
AU - Liu, Shaobin
AU - Woodford, Pamela
AU - Angelides, Kimon
AU - Trial, Jo Ann
AU - Carsrud, N. D.Victor
AU - Dickey, Burton F.
AU - Knoll, Brian J.
PY - 1995/9
Y1 - 1995/9
N2 - The small GTPase rab5 appears to be rate-limiting for the constitutive internalization of transferrin receptor and for fluid-phase endocytosis. However, it is unknown whether rab5 regulates receptors whose internalization is stimulated by the binding of ligand, and whether such receptors change the underlying rate of the endocytic pathways they utilize. As a model for ligand-stimulated endocytosis, we used transfected HEK293 cells expressing high levels of an epitope-tagged human β2-adrenergic receptor. Nearly all receptors were on the cell surface in the absence of agonist, but within ten minutes of agonist addition > 50% of receptors internalized and colocalized extensively with rab5. Hypertonic sucrose blocked β2-adrenergic receptor internalization, as well as that of transferrin receptor, suggesting a clathrin-mediated process. In contrast, an inhibitor of potocytosis had little effect upon β2-adrenergic receptor internalization, suggesting that this process did not require active caveolae. Consistent with this finding, caveolin was not detectable in the 12β6 line, as assessed by western blotting with a polyclonal anti-caveolin antibody. Stimulated receptor internalization did not affect the rate or capacity of the constitutive endocytic pathway since there was no detectable increase in fluid-phase endocytosis after addition of β-agonist, nor was there a significant change in the amount of surface transferrin receptor. Altogether, these data suggest that β2-adrenergic receptors internalize by a clathrin-mediated and rab5-regulated constitutive endocytic pathway. Further, agonist-stimulated receptor internalization has no detectable effect upon the function of this pathway.
AB - The small GTPase rab5 appears to be rate-limiting for the constitutive internalization of transferrin receptor and for fluid-phase endocytosis. However, it is unknown whether rab5 regulates receptors whose internalization is stimulated by the binding of ligand, and whether such receptors change the underlying rate of the endocytic pathways they utilize. As a model for ligand-stimulated endocytosis, we used transfected HEK293 cells expressing high levels of an epitope-tagged human β2-adrenergic receptor. Nearly all receptors were on the cell surface in the absence of agonist, but within ten minutes of agonist addition > 50% of receptors internalized and colocalized extensively with rab5. Hypertonic sucrose blocked β2-adrenergic receptor internalization, as well as that of transferrin receptor, suggesting a clathrin-mediated process. In contrast, an inhibitor of potocytosis had little effect upon β2-adrenergic receptor internalization, suggesting that this process did not require active caveolae. Consistent with this finding, caveolin was not detectable in the 12β6 line, as assessed by western blotting with a polyclonal anti-caveolin antibody. Stimulated receptor internalization did not affect the rate or capacity of the constitutive endocytic pathway since there was no detectable increase in fluid-phase endocytosis after addition of β-agonist, nor was there a significant change in the amount of surface transferrin receptor. Altogether, these data suggest that β2-adrenergic receptors internalize by a clathrin-mediated and rab5-regulated constitutive endocytic pathway. Further, agonist-stimulated receptor internalization has no detectable effect upon the function of this pathway.
KW - Endocytosis
KW - rab5
KW - β-adrenergic receptor
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M3 - Article
C2 - 8537438
AN - SCOPUS:0028981467
SN - 0021-9533
VL - 108
SP - 2983
EP - 2991
JO - Journal of cell science
JF - Journal of cell science
IS - 9
ER -