title: Asef2 functions as a Cdc42 exchange factor and is stimulated by the release of an autoinhibitory module from a concealed C-terminal activation element.
abstract: Asef (herein called Asef1) was identified as a Rac1-specific exchange factor stimulated by adenomatous polyposis coli (APC), contributing to colorectal cancer cell metastasis. We investigated Asef2, an Asef1 homologue having a similar N-terminal APC binding region (ABR) and Src-homology 3 (SH3) domain. Contrary to previous reports, we found that Asef1 and Asef2 exchange activity is Cdc42 specific. Moreover, the ABR of Asef2 did not function independently but acted in tandem with the SH3 domain to bind APC. The ABRSH3 also bound the C-terminal tail of Asef2, allowing it to function as an autoinhibitory module within the protein. Deletion of the C-terminal tail did not constitutively activate Asef2 as predicted; rather, a conserved C-terminal segment was required for augmented Cdc42 GDP/GTP exchange. Thus, Asef2 activation involves APC releasing the ABRSH3 from the C-terminal tail, resulting in Cdc42 exchange. These results highlight a novel exchange factor regulatory mechanism and establish Asef1 and Asef2 as Cdc42 exchange factors, providing a more appropriate context for understanding the contribution of APC in establishing cell polarity and migration.
authors.affiliation: Division of Oncology Research, Mayo Clinic, 200 First Street SW, Rochester, MN 55905, USA.
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Hamann
authors.forename: Casey M
authors.initials: CM
authors.lastname: Lubking
authors.forename: Doris N
authors.initials: DN
authors.lastname: Luchini
authors.forename: Daniel D
authors.initials: DD
authors.lastname: Billadeau
mesh_terms: D025601:Adenomatous Polyposis Coli Protein / Q000378:metabolism; D000595:Amino Acid Sequence; D045744:Cell Line, Tumor; D002465:Cell Movement; D025461:Feedback, Physiological; D020690:GTPase-Activating Proteins / Q000378:metabolism; D020869:Gene Expression Profiling; D020662:Guanine Nucleotide Exchange Factors / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D006367:HeLa Cells; D006801:Humans; D008954:Models, Biological; D008969:Molecular Sequence Data; D011485:Protein Binding; D011554:Pseudopodia / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D013379:Substrate Specificity; D020764:cdc42 GTP-Binding Protein / Q000378:metabolism*; D018909:src Homology Domains
chemical_list: D025601:Adenomatous Polyposis Coli Protein; D020690:GTPase-Activating Proteins; D020662:Guanine Nucleotide Exchange Factors; D020764:cdc42 GTP-Binding Protein