dictyNews Volume 43 Number 18

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

Please submit abstracts of your papers as soon as they have been 
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========= 
Abstracts 
========= 

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  [adachih@mail.ecc.u-tokyo.ac.jp 
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[End dictyNews, volume 43, number 18]