dictyNews
Electronic Edition
Volume 43, number 18
August 11, 2017

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=========
Abstracts
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The F-actin-binding RapGEF GflB is required for efficient macropinocytosis 
in Dictyostelium

Hironori Inaba1,2,3, Koji Yoda1, Hiroyuki Adachi1

1Department of Biotechnology, Graduate School of Agricultural and Life 
Sciences, The University of Tokyo, Bunkyo-ku, Tokyo 113-8657, Japan
2Department of Cell Biology and 3The Center for Brain Integration Research, 
Graduate School of Medical and Dental Science, Tokyo Medical and Dental 
University, Bunkyo-ku, Tokyo 113-8510, Japan


J. Cell Sci., in press

Macropinocytosis involves the uptake of large volumes of fluid, which is 
regulated by various small GTPases. The Dictyostelium discoideum protein 
GflB is a guanine nucleotide exchange factor (GEF) of Rap1, involved in 
chemotaxis. Here we studied the role of GflB in macropinocytosis, 
phagocytosis, and cytokinesis. In plate culture of vegetative cells, compared 
with the parental strain AX2, gflB KO cells were flatter and more polarized, 
whereas GflB-overproducing cells were rounder. The gflB KO cells exhibited 
impaired crown formation and retraction, particularly retraction, resulting in 
more crowns (macropinocytic cups) per cell and longer crown lifetimes. 
Accordingly, gflB KO cells showed defects in macropinocytosis and also in 
phagocytosis and cytokinesis. F-actin was elevated in gflB KO cells. GflB 
localized to the actin cortex especially at crowns and phagocytic cups. The 
villin headpiece domain (VHP)-like N-terminal domain of GflB directly 
interacted with F-actin in vitro. Furthermore, a domain enriched in basic 
amino acids interacted with specific membrane cortex structures such as the 
cleavage furrow. In conclusion, GflB acts as a key local regulator of actin-
driven membrane protrusion possibly by modulating Rap1 signaling pathways.


submitted by: Hiroyuki Adachi  [[log in to unmask]
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[End dictyNews, volume 43, number 18]