A conserved C-terminal domain of EFA6-family ARF6-guanine nucleotide exchange factors induces lengthening of microvilli-like membrane protrusions.
We recently reported the identification of EFA6 (exchange factor for ARF6), a brain-specific Sec7-domain-containing guanine nucleotide exchange factor that works specifically on ARF6. Here, we have characterized the product of a broadly expressed gene encoding a novel 1056 amino-acid protein that we have named EFA6B. We show that EFA6B, which contains a Sec7 domain that is highly homologous to EFA6, works as an ARF6-specific guanine exchange factor in vitro. Like EFA6, which will be referred to as EFA6A from now on, EFA6B is involved in membrane recycling and colocalizes with ARF6 in actin-rich membrane ruffles and microvilli-like protrusions on the dorsal cell surface in transfected baby hamster kidney cells. Strikingly, homology between EFA6A and EFA6B is not limited to the Sec7 domain but extends to an adjacent pleckstrin homology (PH) domain and a approximately 150 amino-acid C-terminal region containing a predicted coiled coil motif. Association of EFA6A with membrane ruffles and microvilli-like structures depends on the PH domain, which probably interacts with phosphatidylinositol 4,5-biphosphate. Moreover, we show that overexpression of the PH domain/C-terminal region of EFA6A or EFA6B in the absence of the Sec7 domain promotes lengthening of dorsal microvillar protrusions. This morphological change requires the integrity of the coiled-coil motif. Lastly, database analysis reveals that the EFA6-family comprises at least four members in humans and is conserved in multicellular organisms throughout evolution. Our results suggest that EFA6 family guanine exchange factors are modular proteins that work through the coordinated action of the catalytic Sec7 domain to promote ARF6 activation, through the PH domain to regulate association with specific subdomains of the plasma membrane and through the C-terminal region to control actin cytoskeletal reorganization.
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Laboratoire de la Dynamique de la Membrane et du Cytosquelette, UMR 144, Centre National de la Recherche Scientifique, Institut Curie, Section Recherche. 26 rue d'Ulm, 75241 Paris Cedex 5, France.
Couillault
Carole
C
Franco
Michel
M
Martineau
Stéphanie
S
Montcourrier
Philippe
P
Houlgatte
Rémi
R
Chavrier
Philippe
P
D000089982:ADP-Ribosylation Factor 6; D020727:ADP-Ribosylation Factors / Q000235:genetics / Q000378:metabolism*; D008841:Actin Cytoskeleton / Q000235:genetics / Q000378:metabolism; D000818:Animals; D020134:Catalytic Domain / Q000235:genetics; D002451:Cell Compartmentation / Q000235:genetics; D002462:Cell Membrane / Q000378:metabolism* / Q000648:ultrastructure; D002465:Cell Movement / Q000502:physiology; D048429:Cell Size / Q000502:physiology; D002478:Cells, Cultured; D003001:Cloning, Molecular; D006224:Cricetinae; D005057:Eukaryotic Cells / Q000378:metabolism* / Q000648:ultrastructure; D019143:Evolution, Molecular; D049452:Green Fluorescent Proteins; D020662:Guanine Nucleotide Exchange Factors / Q000235:genetics / Q000302:isolation & purification*; D008164:Luminescent Proteins; D008855:Microscopy, Electron, Scanning; D008871:Microvilli / Q000378:metabolism* / Q000648:ultrastructure; D008969:Molecular Sequence Data; D010445:Peptide Elongation Factors / Q000235:genetics / Q000302:isolation & purification*; D010802:Phylogeny; D017434:Protein Structure, Tertiary / Q000235:genetics; D017386:Sequence Homology, Amino Acid; D012689:Sequence Homology, Nucleic Acid
D000089982:ADP-Ribosylation Factor 6; D020662:Guanine Nucleotide Exchange Factors; D008164:Luminescent Proteins; D010445:Peptide Elongation Factors; D049452:Green Fluorescent Proteins; D020727:ADP-Ribosylation Factors; C000715348:ARF6 protein, human