GSKIP is homologous to the Axin GSK3beta interaction domain and functions as a negative regulator of GSK3beta.
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.
Chou
He-Yen
HY
Graduate Institute of Biochemistry, Kaohsiung Medical University, Kaohsiung, Taiwan, ROC.
Howng
Shen-Long
SL
Cheng
Tai-Shan
TS
Hsiao
Yun-Ling
YL
Lieu
Ann-Shung
AS
Loh
Joon-Khim
JK
Hwang
Shiuh-Lin
SL
Lin
Ching-Chih
CC
Hsu
Ching-Mei
CM
Wang
Chihuei
C
Lee
Chu-I
CI
Lu
Pei-Jung
PJ
Chou
Chen-Kung
CK
Huang
Chi-Ying
CY
Hong
Yi-Ren
YR
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
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