title: GSKIP is homologous to the Axin GSK3beta interaction domain and functions as a negative regulator of GSK3beta.
abstract: Although prominent FRAT/GBP exhibits a limited degree of homology to Axin, the binding sites on GSK3 for FRAT/GBP and Axin may overlap to prevent the effect of FRAT/GBP in stabilizing beta-catenin in the Wnt pathway. Using a yeast two-hybrid screen, we identified a novel protein, GSK3beta interaction protein (GSKIP), which binds to GSK3beta. We have defined a 25-amino acid region in the C-terminus of GSKIP that is highly similar to the GSK3beta interaction domain (GID) of Axin. Using an in vitro kinase assay, our results indicate that GSKIP is a good GSK3beta substrate, and both the full-length protein and a C-terminal fragment of GSKIP can block phosphorylation of primed and nonprimed substrates in different fashions. Similar to Axin GID(381-405) and FRATtide, synthesized GSKIPtide is also shown to compete with and/or block the phosphorylation of Axin and beta-catenin by GSK3beta. Furthermore, our data indicate that overexpression of GSKIP induces beta-catenin accumulation in the cytoplasm and nucleus as visualized by immunofluorescence. A functional assay also demonstrates that GSKIP-transfected cells have a significant effect on the transactivity of Tcf-4. Collectively, we define GSKIP as a naturally occurring protein that is homologous with the GSK3beta interaction domain of Axin and is able to negatively regulate GSK3beta of the Wnt signaling pathway.
authors.affiliation: Graduate Institute of Biochemistry, Kaohsiung Medical University, Kaohsiung, Taiwan, ROC.
authors.forename: He-Yen
authors.initials: HY
authors.lastname: Chou
authors.forename: Shen-Long
authors.initials: SL
authors.lastname: Howng
authors.forename: Tai-Shan
authors.initials: TS
authors.lastname: Cheng
authors.forename: Yun-Ling
authors.initials: YL
authors.lastname: Hsiao
authors.forename: Ann-Shung
authors.initials: AS
authors.lastname: Lieu
authors.forename: Joon-Khim
authors.initials: JK
authors.lastname: Loh
authors.forename: Shiuh-Lin
authors.initials: SL
authors.lastname: Hwang
authors.forename: Ching-Chih
authors.initials: CC
authors.lastname: Lin
authors.forename: Ching-Mei
authors.initials: CM
authors.lastname: Hsu
authors.forename: Chihuei
authors.initials: C
authors.lastname: Wang
authors.forename: Chu-I
authors.initials: CI
authors.lastname: Lee
authors.forename: Pei-Jung
authors.initials: PJ
authors.lastname: Lu
authors.forename: Chen-Kung
authors.initials: CK
authors.lastname: Chou
authors.forename: Chi-Ying
authors.initials: CY
authors.lastname: Huang
authors.forename: Yi-Ren
authors.initials: YR
authors.lastname: Hong
mesh_terms: D000595:Amino Acid Sequence; D060466:Axin Protein; D002478:Cells, Cultured; D003001:Cloning, Molecular; D038362:Glycogen Synthase Kinase 3 / Q000037:antagonists & inhibitors* / Q000378:metabolism*; D000071679:Glycogen Synthase Kinase 3 beta; D006367:HeLa Cells; D006801:Humans; D008969:Molecular Sequence Data; D010766:Phosphorylation; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D021381:Protein Transport; D012097:Repressor Proteins / Q000737:chemistry* / Q000378:metabolism*; D016415:Sequence Alignment; D017385:Sequence Homology; D015398:Signal Transduction; D051153:Wnt Proteins / Q000378:metabolism
chemical_list: D060466:Axin Protein; C514503:GSKIP protein, human; D012097:Repressor Proteins; D051153:Wnt Proteins; C000605506:GSK3B protein, human; D000071679:Glycogen Synthase Kinase 3 beta; D038362:Glycogen Synthase Kinase 3