title: Abi is required for modulation and stability but not localization or activation of the SCAR/WAVE complex.
abstract: The SCAR/WAVE complex drives actin-based protrusion, cell migration, and cell separation during cytokinesis. However, the contribution of the individual complex members to the activity of the whole remains a mystery. This is primarily because complex members depend on one another for stability, which limits the scope for experimental manipulation. Several studies suggest that Abi, a relatively small complex member, connects signaling to SCAR/WAVE complex localization and activation through its polyproline C-terminal tail. We generated a deletion series of the Dictyostelium discoideum Abi to investigate its exact role in regulation of the SCAR complex and identified a minimal fragment that would stabilize the complex. Surprisingly, loss of either the N terminus of Abi or the C-terminal polyproline tail conferred no detectable defect in complex recruitment to the leading edge or the formation of pseudopods. A fragment containing approximately 20% Abi--and none of the sites that couple to known signaling pathways--allowed the SCAR complex to function with normal localization and kinetics. However, expression of N-terminal Abi deletions exacerbated the cytokinesis defect of the Dictyostelium abi mutant, which was earlier shown to be caused by the inappropriate activation of SCAR. This demonstrates, unexpectedly, that Abi does not mediate the SCAR complex's ability to make pseudopods, beyond its role in complex stability. Instead, we propose that Abi has a modulatory role when the SCAR complex is activated through other mechanisms.
authors.affiliation: Beatson Institute for Cancer Research, Bearsden, Glasgow, United Kingdom.
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Davidson
authors.forename: Seiji
authors.initials: S
authors.lastname: Ura
authors.forename: Peter A
authors.initials: PA
authors.lastname: Thomason
authors.forename: Gabriela
authors.initials: G
authors.lastname: Kalna
authors.forename: Robert H
authors.initials: RH
authors.lastname: Insall
mesh_terms: D048868:Adaptor Proteins, Signal Transducing / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D000595:Amino Acid Sequence; D002465:Cell Movement; D048749:Cytokinesis; D004023:Dictyostelium / Q000166:cytology / Q000235:genetics / Q000378:metabolism* / Q000502:physiology; D017353:Gene Deletion; D008969:Molecular Sequence Data; D010455:Peptides / Q000737:chemistry; D011485:Protein Binding; D055550:Protein Stability; D017434:Protein Structure, Tertiary; D021381:Protein Transport; D015800:Protozoan Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D011554:Pseudopodia / Q000378:metabolism
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D010455:Peptides; D015800:Protozoan Proteins; C491975:SCAR protein, Dictyostelium; C011083:polyproline
references.citation: Nat Cell Biol. 2004 Apr;6(4):319-27
references.pmid: 15048123
references.citation: J Cell Sci. 2001 Jul;114(Pt 14):2673-83
references.pmid: 11683394
references.citation: Nature. 2002 Aug 15;418(6899):790-3
references.pmid: 12181570
references.citation: J Cell Biol. 2012 Aug 20;198(4):501-8
references.pmid: 22891261
references.citation: Nat Cell Biol. 2007 Feb;9(2):193-200
references.pmid: 17220879
references.citation: J Cell Sci. 2010 Jul 1;123(Pt 13):2246-55
references.pmid: 20530573
references.citation: J Cell Sci. 2009 Aug 1;122(Pt 15):2575-8
references.pmid: 19625501
references.citation: Curr Biol. 2003 Oct 28;13(21):1867-75
references.pmid: 14588242
references.citation: J Cell Biol. 2003 Jan 6;160(1):17-23
references.pmid: 12515821
references.citation: Mol Biol Cell. 2007 May;18(5):1609-20
references.pmid: 17314411
references.citation: Curr Biol. 2001 Jun 5;11(11):891-5
references.pmid: 11516653
references.citation: Curr Biol. 2006 Apr 4;16(7):717-22
references.pmid: 16581519
references.citation: PLoS Genet. 2007 Dec;3(12):e237
references.pmid: 18159949
references.citation: Mol Cell. 2009 Nov 13;36(3):512-24
references.pmid: 19917258
references.citation: Curr Biol. 2011 Jan 25;21(2):R66-8
references.pmid: 21256435
references.citation: J Cell Sci. 2002 May 15;115(Pt 10):2241-51
references.pmid: 11973364
references.citation: Proc Natl Acad Sci U S A. 2005 Jan 25;102(4):1098-103
references.pmid: 15657136
references.citation: Nature. 2010 Nov 25;468(7323):533-8
references.pmid: 21107423
references.citation: Proc Natl Acad Sci U S A. 1998 May 26;95(11):6181-6
references.pmid: 9600938
references.citation: Curr Biol. 2008 Feb 12;18(3):203-10
references.pmid: 18261908
references.citation: Proc Natl Acad Sci U S A. 2004 Mar 30;101(13):4379-83
references.pmid: 15070726
references.citation: J Cell Biol. 1999 May 31;145(5):1009-26
references.pmid: 10352018
references.citation: Curr Biol. 1998 Dec 17-31;8(25):1347-56
references.pmid: 9889097
references.citation: Curr Biol. 2012 Apr 10;22(7):553-61
references.pmid: 22386315