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J. Cell Biol.,
Volume 140, Number 3, February 9, 1998 603-616


* Department of Cell Biology, Washington University School of Medicine, St. Louis, Missouri 63110; We have shown previously that the ADP-
ribosylation factor (ARF)-6 GTPase localizes to the
plasma membrane and intracellular endosomal compartments. Expression of ARF6 mutants perturbs endosomal trafficking and the morphology of the peripheral membrane system. However, another study on the
distribution of ARF6 in subcellular fractions of Chinese
hamster ovary (CHO) cells suggested that ARF6 did
not localize to endosomes labeled after 10 min of horseradish peroxidase (HRP) uptake, but instead was
uniquely localized to the plasma membrane, and that its
reported endosomal localization may have been a result of overexpression. Here we demonstrate that at the
lowest detectable levels of protein expression by cryoimmunogold electron microscopy, ARF6 localized
predominantly to an intracellular compartment at the
pericentriolar region of the cell. The ARF6-labeled vesicles were partially accessible to HRP only on prolonged exposure to the endocytic tracer but did not localize to early endocytic structures that labeled with HRP shortly after uptake. Furthermore, we have
shown that the ARF6-containing intracellular compartment partially colocalized with transferrin receptors
and cellubrevin and morphologically resembled the recycling endocytic compartment previously described in
CHO cells. HRP labeling in cells expressing ARF6(Q67L),
a GTP-bound mutant of ARF6, was restricted to small
peripheral vesicles, whereas the mutant protein was enriched on plasma membrane invaginations. On the
other hand, expression of ARF6(T27N), a mutant of
ARF6 defective in GDP binding, resulted in an accumulation of perinuclear ARF6-positive vesicles that
partially colocalized with HRP on prolonged exposure
to the tracer. Taken together, our findings suggest that
ARF activation is required for the targeted delivery of
ARF6-positive, recycling endosomal vesicles to the
plasma membrane.
Department of Cell
Biology and the Graduate School of Biomembranes, University of Utrecht Medical School, Heidelberglaan 100, 3584 CX
Utrecht, The Netherlands; and § Department of Rheumatology and Immunology, Brigham and Women's Hospital, Harvard
Medical School, Boston, Massachusetts 02115
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