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J. Cell Biol.,
Volume 141, Number 1, April 6, 1998 85-99
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* Department of Molecular Neuroscience, The dynamins comprise an expanding family
of ubiquitously expressed 100-kD GTPases that have
been implicated in severing clathrin-coated pits during
receptor-mediated endocytosis. Currently, it is unclear whether the different dynamin isoforms perform redundant functions or participate in distinct endocytic
processes. To define the function of dynamin II in
mammalian epithelial cells, we have generated and
characterized peptide-specific antibodies to domains that either are unique to this isoform or conserved
within the dynamin family. When microinjected into
cultured hepatocytes these affinity-purified antibodies
inhibited clathrin-mediated endocytosis and induced
the formation of long plasmalemmal invaginations with attached clathrin-coated pits. In addition, clusters of
distinct, nonclathrin-coated, flask-shaped invaginations resembling caveolae accumulated at the plasma
membrane of antibody-injected cells. In support of this,
caveola-mediated endocytosis of labeled cholera toxin
B was inhibited in antibody-injected hepatocytes. Using immunoisolation techniques an anti-dynamin antibody
isolated caveolar membranes directly from a hepatocyte postnuclear membrane fraction. Finally, double label immunofluorescence microscopy revealed a striking
colocalization between dynamin and the caveolar coat protein caveolin. Thus, functional in vivo studies as well
as ultrastructural and biochemical analyses indicate
that dynamin mediates both clathrin-dependent endocytosis and the internalization of caveolae in mammalian cells.
Department of Biochemistry and Molecular Biology, and § Center for Basic Research
in Digestive Diseases, Mayo Clinic, Rochester, Minnesota 55905
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