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Published 10 October 2005. doi:10.1083/jcb.200501086
The Rockefeller University Press, 0021-9525 $8.00
JCB, Volume 171, Number 1, 133-142
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Article

 A WASp-binding type II phosphatidylinositol 4-kinase required for actin polymerization-driven endosome motility

Fanny S. Chang1, Gil-Soo Han2, George M. Carman2, and Kendall J. Blumer1

1 Department of Cell Biology and Physiology, Washington University School of Medicine, St. Louis, MO 63110
2 Department of Food Science, Rutgers University, New Brunswick, NJ 08901

Correspondence to Kendall J. Blumer: kblumer{at}cellbio.wustl.edu

Endosomes in yeast have been hypothesized to move through the cytoplasm by the momentum gained after actin polymerization has driven endosome abscision from the plasma membrane. Alternatively, after abscission, ongoing actin polymerization on endosomes could power transport. Here, we tested these hypotheses by showing that the Arp2/3 complex activation domain (WCA) of Las17 (Wiskott-Aldrich syndrome protein [WASp] homologue) fused to an endocytic cargo protein (Ste2) rescued endosome motility in las17{Delta}WCA mutants, and that capping actin filament barbed ends inhibited endosome motility but not endocytic internalization. Motility therefore requires continual actin polymerization on endosomes. We also explored how Las17 is regulated. Endosome motility required the Las17-binding protein Lsb6, a type II phosphatidylinositol 4-kinase. Catalytically inactive Lsb6 interacted with Las17 and promoted endosome motility. Lsb6 therefore is a novel regulator of Las17 that mediates endosome motility independent of phosphatidylinositol 4-phosphate synthesis. Mammalian type II phosphatidylinositol 4-kinases may regulate WASp proteins and endosome motility.

Abbreviations used in this paper: GPCR, G protein–coupled receptor; Lsb, Las17-binding protein; MSD, mean squared displacement; PI 4-kinase, phosphatidylinositol 4-kinase; PI4P, phosphatidylinositol 4-phosphate; PI4,5P2, phosphatidylinositol 4,5-bisphosphate; SCAR, suppressor of cAMP receptor; WASp, Wiskott-Aldrich syndrome protein; WAVE, WASP family Verprolin homology protein; WCA, Arp2/3 complex activating region (WASp homology 2, central region, acidic region).


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