title: The regulator of G protein signaling domain of axin selectively interacts with Galpha12 but not Galpha13.
abstract: Axin, a negative regulator of the Wnt signaling pathway, contains a canonical regulator of G protein signaling (RGS) core domain. Herein, we demonstrate both in vitro and in cells that this domain interacts with the alpha subunit of the heterotrimeric G protein G12 but not with the closely related Galpha13 or with several other heterotrimeric G proteins. Axin preferentially binds the activated form of Galpha12, a behavior consistent with other RGS proteins. However, unlike other RGS proteins, that of axin (axinRGS) does not affect intrinsic GTP hydrolysis by Galpha12. Despite its inability to act as a GTPase-activating protein, we demonstrate that in cells, axinRGS can compete for Galpha12 binding with the RGS domain of p115RhoGEF, a known G12-interacting protein that links G12 signaling to activation of the small G protein Rho. Moreover, ectopic expression of axinRGS specifically inhibits Galpha12-directed activation of the Rho pathway in MDA-MB 231 breast cancer cells. These findings establish that the RGS domain of axin is able to directly interact with the alpha subunit of heterotrimeric G protein G12 and provide a unique tool to interdict Galpha12-mediated signaling processes.
authors.affiliation: Department of Pathology, Duke University Medical Center, Box 3712, Durham, NC 27710, USA.
authors.forename: Laura N
authors.initials: LN
authors.lastname: Stemmle
authors.forename: Timothy A
authors.initials: TA
authors.lastname: Fields
authors.forename: Patrick J
authors.initials: PJ
authors.lastname: Casey
mesh_terms: D060466:Axin Protein; D002460:Cell Line; D044365:GTP-Binding Protein alpha Subunits, G12-G13 / Q000378:metabolism*; D019204:GTP-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D017434:Protein Structure, Tertiary; D012097:Repressor Proteins / Q000378:metabolism*; D015398:Signal Transduction; D014162:Transfection
chemical_list: D060466:Axin Protein; D012097:Repressor Proteins; D019204:GTP-Binding Proteins; D044365:GTP-Binding Protein alpha Subunits, G12-G13