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Vol. 16, Issue 4, 1617-1628, April 2005
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Department of Molecular Immunology, Institute of Development, Aging, and Cancer, Tohoku University, Sendai 980-8575, Japan
Submitted August 10, 2004;
Revised December 10, 2004;
Accepted January 10, 2005
Monitoring Editor: Juan S. Bonifacino
ADP-ribosylation factor 6 (Arf6) is a small-GTPase that regulates the membrane trafficking between the plasma membrane and endosome. It is also involved in the reorganization of the actin cytoskeleton. GTPase-activating protein (GAP) is a critical regulator of Arf function as it inactivates Arf. Here, we identified a novel species of GAP denoted as SMAP1 that preferentially acts on Arf6. Although overexpression of SMAP1 did not alter the subcellular distribution of the actin cytoskeleton, it did block the endocytosis of transferrin receptors. Knock down of endogenous SMAP1 also abolished transferrin internalization, which confirms that SMAP1 is needed for this endocytic process. SMAP1 overexpression had no effect on clathrin-independent endocytosis, however. Intriguingly, SMAP1 binds directly to the clathrin heavy chain via its clathrin-box and mutation studies revealed that its GAP domain and clathrin-box both contribute to the role SMAP1 plays in clathrin-dependent endocytosis. These observations suggest that SMAP1 may be an Arf6GAP that specifically regulates one of the multiple functions of Arf6, namely, clathrin-dependent endocytosis, and that it does so by binding directly to clathrin.
Abbreviations used: Arf, ADP-ribosylation factor; CHC, clathrin heavy chain; GAP, GTPase-activating protein; GEF, guanine-nucleotide exchange factor; GST, glutathione S-transferase; HA, influenza hemagglutinin; IL-2R, interleukin-2 receptor; M6PR, mannose 6-phosphate receptor; PIP2, phosphatidylinositol (4, 5)-bisphosphate; siRNA, small interfering RNA; TGN, trans-Golgi network.
Address correspondence to: Masanobu Satake (satake{at}idac.tohoku.ac.jp).
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