title: Identification and characterization of Asef2, a guanine-nucleotide exchange factor specific for Rac1 and Cdc42.
abstract: The tumor suppressor adenomatous polyposis coli (APC) is mutated in sporadic and familial colorectal tumors. APC interacts with the Rac1-specific guanine-nucleotide exchange factor (GEF) Asef, which contains an APC-binding region (ABR) in addition to Dbl homology (DH), Pleckstrin (PH) and Src homology 3 (SH3) domains. APC stimulates the GEF activity of Asef, and thereby regulates cell adhesion and migration. Here, we have identified a second Asef, termed Asef2, that shows significant structural and functional similarities to Asef. We found that both the N-terminal ABR and SH3 domains of Asef2 are responsible for its interaction with APC. When expressed in HeLa cells, a mutant Asef2 lacking the ABR and SH3 domains, Asef2-DeltaABR/SH3, induced increases in the levels of the active forms of Rac1 and Cdc42. Full-length Asef2 also showed this activity when co-transfected with truncated mutant APC expressed in colorectal tumor cells. Consistent with this, either Asef2-DeltaABR/SH3 or Asef2 plus truncated mutant APC stimulated lamellipodia formation in MDCK cells and filopodia formation in HeLa cells. Furthermore, RNA interference experiments showed that Asef2 is required for migration of colorectal tumor cells expressing truncated APC. These results suggest that similar to Asef, Asef2 plays an important role in cell migration, and that Asef2 activated by truncated mutant APC is required for aberrant migration of colorectal tumor cells.
authors.affiliation: Laboratory of Molecular and Genetic Information, Institute for Molecular and Cellular Biosciences, University of Tokyo, Tokyo, Japan.
authors.forename: Y
authors.initials: Y
authors.lastname: Kawasaki
authors.forename: M
authors.initials: M
authors.lastname: Sagara
authors.forename: Y
authors.initials: Y
authors.lastname: Shibata
authors.forename: M
authors.initials: M
authors.lastname: Shirouzu
authors.forename: S
authors.initials: S
authors.lastname: Yokoyama
authors.forename: T
authors.initials: T
authors.lastname: Akiyama
mesh_terms: D025601:Adenomatous Polyposis Coli Protein / Q000235:genetics / Q000378:metabolism; D000595:Amino Acid Sequence; D000818:Animals; D002465:Cell Movement / Q000235:genetics; D002522:Chlorocebus aethiops; D015179:Colorectal Neoplasms / Q000378:metabolism / Q000473:pathology*; D004285:Dogs; D020662:Guanine Nucleotide Exchange Factors / Q000032:analysis / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D008969:Molecular Sequence Data; D009154:Mutation; D025941:Protein Interaction Mapping; D011554:Pseudopodia / Q000502:physiology; D064067:Rho Guanine Nucleotide Exchange Factors; D020764:cdc42 GTP-Binding Protein / Q000378:metabolism*; D020830:rac1 GTP-Binding Protein / Q000378:metabolism*; D018909:src Homology Domains / Q000235:genetics
chemical_list: C576602:ARHGEF4 protein, human; D025601:Adenomatous Polyposis Coli Protein; D020662:Guanine Nucleotide Exchange Factors; C107953:RAC1 protein, human; D064067:Rho Guanine Nucleotide Exchange Factors; C525704:SPATA13 protein, human; D020764:cdc42 GTP-Binding Protein; D020830:rac1 GTP-Binding Protein