ARAP3 is essential for formation of lamellipodia after growth factor stimulation.
Rho and Arf family small GTPases control dynamic actin rearrangements and vesicular trafficking events. ARAP3 is a dual GAP for RhoA and Arf6 that is regulated by phosphatidylinositol (3,4,5)-trisphosphate [PtdIns(3,4,5)P(3)], a product of the phosphoinositide 3-kinase (PI3K) signalling pathway. To investigate the physiological function of ARAP3, we used an RNAi-based approach in an endothelial cell model. ARAP3-deficient cells showed increased activities of RhoA and Arf6. Phenotypically, they were more rounded than control counterparts and displayed very fine stress fibres. ARAP3-deficient cells were not capable of producing lamellipodia upon growth factor stimulation, a process known to depend on PI3K and Rac activities. Rac was transiently activated in stimulated ARAP3 RNAi cells although its cellular localisation was altered, a likely consequence of increased Arf6 activity. We conclude that ARAP3 recruitment to sites of elevated PtdIns(3,4,5)P(3) is crucial to allow localised inactivation of RhoA and cycling of Arf6, both of which are necessary to allow growth factor-stimulated formation of lamellipodia.
Krugmann
Sonja
S
The Inositide Laboratory, The Babraham Institute, Cambridge, CB2 4AT, UK. sonja.krugmann@bbsrc.ac.uk
Andrews
Simon
S
Stephens
Len
L
Hawkins
Phillip T
PT
D000089982:ADP-Ribosylation Factor 6; D020727:ADP-Ribosylation Factors / Q000378:metabolism; D048868:Adaptor Proteins, Signal Transducing / Q000172:deficiency / Q000378:metabolism*; D000818:Animals; D001693:Biological Transport, Active / Q000502:physiology; D002460:Cell Line; D022162:Cytoplasmic Vesicles / Q000378:metabolism; D042783:Endothelial Cells / Q000166:cytology / Q000378:metabolism*; D020690:GTPase-Activating Proteins / Q000172:deficiency / Q000378:metabolism*; D006801:Humans; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D011554:Pseudopodia / Q000378:metabolism*; D015398:Signal Transduction / Q000502:physiology*; D020742:rhoA GTP-Binding Protein / Q000378:metabolism
D000089982:ADP-Ribosylation Factor 6; D020727:ADP-Ribosylation Factors; D048868:Adaptor Proteins, Signal Transducing; D020690:GTPase-Activating Proteins; D019869:Phosphatidylinositol 3-Kinases; D020742:rhoA GTP-Binding Protein; C446512:ARAP3 protein, human; C000715348:ARF6 protein, human