Axin, a negative regulator of the Wnt signaling pathway, forms a complex with GSK-3beta and beta -catenin and promotes GSK-3beta -dependent phosphorylation of beta -catenin

Abstract

Glycogen synthase kinase-3 (GSK-3) mediates epidermal growth factor, insulin and Wnt signals to various downstream events such as glycogen metabolism, gene expression, proliferation and differentiation. We have isolated here a GSK-3β-interacting protein from a rat brain cDNA library using a yeast twohybrid method. This protein consists of 832 amino acids and possesses Regulators of G protein Signaling (RGS) and dishevelled (Dsh) homologous domains in its N-and C-terminal regions, respectively. The predicted amino acid sequence of this GSK-3β-interacting protein shows 94% identity with mouse Axin, which recently has been identified as a negative regulator of the Wnt signaling pathway; therefore, we termed this protein rAxin (rat Axin). rAxin interacted directly with, and was phosphorylated by, GSK-3β. rAxin also interacted directly with the armadillo repeats of β-catenin. The binding site of rAxin for GSK-3β was distinct from the β-catenin-binding site, and these three proteins formed a ternary complex. Furthermore, rAxin promoted GSK-3β-dependent phosphorylation of β-catenin. These results suggest that rAxin negatively regulates the Wnt signaling pathway by interacting with GSK-3β and β-catenin and mediating the signal from GSK-3β to β-catenin.

PAWS 1 controls Wnt signalling through association with casein kinase 1α

“…In this model, rather than directly regulating catalytic activity, scaffold proteins facilitate kinase activity by regulating substrate proximity to the kinase 52. For example, Axin, which interacts with GSK3β, enhances β‐catenin phosphorylation by CK1α and GSK3β, without altering CK1α kinase activity 53, 54, 55, 56. Similarly, PAWS1 may act as a scaffold by regulating the access of CK1α to its substrates.…”

Controlled levels of canonical Wnt signaling are required for neural crest migration

“…Under unstimulated conditions cytoplasmic level of ß-catenin is kept low through the dual phosphorylation (Liu et al, 2002) by glycogen synthase kinase 3β (GSK-3β) (Hart et al, 1999;Yost et al, 1996) and casein kinase 1α (CK1α) (Price, 2006;Amit et al, 2002), which together with the adenomatous polyposis coli tumor suppressor protein (APC) (Hart et al, 1999;Ha et al, 2004), protein phosphatase 2A (PP2A) (Hsu et al, 1999;Seeling et al, 1999;Ratcliffe et al, 2000;Yamamoto et al, 2001) and Axin (Hart et al, 1999;Ikeda et al, 1998;Dajani et al, 2003) form a destruction complex (Stamos and Weis, 2013).…”

GSK-3β-dependent phosphorylation of adenomatous polyposis coli gene product can be modulated by β-catenin and protein phosphatase 2A complexed with Axin

“…Since b-catenin directly binds to Axin and APC (Polakis, 1997;Ikeda et al, 1998), the e ect of bcatenin on the GSK-3b-dependent phosphorylation of APC was examined. Hexahistidine-tagged b-catenin (His6-b-catenin) did not a ect the phosphorylation of GST-APC-(1211-2075) by GST-GSK-3b in the absence of MBP-rAxin (full length), while in its presence His6-b-catenin enhanced the phosphorylation (Figure 3a).…”

“…Axin also facilitates GSK-3b-dependent phosphorylation of APC, and Axin itself is phosphorylated by GSK-3b (Hart et al, 1998;Ikeda et al, 1998). It is likely that three substrates, APC, b-catenin, and Axin, form a complex with GSK-3b and that their phosphorylation occurs e ciently.…”