Abstract
The A-kinase anchoring protein (AKAP) GSK3β interaction protein (GSKIP) is a cytosolic scaffolding protein binding protein kinase A (PKA) and glycogen synthase kinase 3β (GSK3β). Here we show that both the AKAP function of GSKIP, i.e. its direct interaction with PKA, and its direct interaction with GSK3β are required for the regulation of β-catenin and thus Wnt signaling. A cytoplasmic destruction complex targets β-catenin for degradation and thus prevents Wnt signaling. Wnt signals cause β-catenin accumulation and translocation into the nucleus, where it induces Wnt target gene expression. GSKIP facilitates control of the β-catenin stabilizing phosphorylation at Ser-675 by PKA. Its interaction with GSK3β facilitates control of the destabilizing phosphorylation of β-catenin at Ser-33/Ser-37/Thr-41. The influence of GSKIP on β-catenin is explained by its scavenger function; it recruits the kinases away from the destruction complex without forming a complex with β-catenin. The regulation of β-catenin by GSKIP is specific for this AKAP as AKAP220, which also binds PKA and GSK3β, did not affect Wnt signaling. We find that the binding domain of AKAP220 for GSK3β is a conserved GSK3β interaction domain (GID), which is also present in GSKIP. Our findings highlight an essential compartmentalization of both PKA and GSK3β by GSKIP, and ascribe a function to a cytosolic AKAP-PKA interaction as a regulatory factor in the control of canonical Wnt signaling. Wnt signaling controls different biological processes, including embryonic development, cell cycle progression, glycogen metabolism, and immune regulation; deregulation is associated with diseases such as cancer, type 2 diabetes, inflammatory, and Alzheimer's and Parkinson's diseases.
Highlights
A-kinase anchoring proteins (AKAPs)3 are a family of about 50 scaffolding proteins
We find that the binding domain of AKAP220 for GSK3 is a conserved GSK3 interaction domain (GID), which is present in GSK3 interaction protein (GSKIP)
Endogenous GSKIP Regulates Wnt Signaling through Phosphorylation of -Catenin by protein kinase A (PKA)—The scaffolding protein assembling the destruction complex is Axin
Summary
Endogenous GSKIP Regulates Wnt Signaling through Phosphorylation of -Catenin by PKA—The scaffolding protein assembling the destruction complex is Axin. The wild type GSKIP triggered a significant increase in basal -catenin-induced transcription, whereas no changes were observed in the presence of the PKA-binding-deficient or GSK3-binding-deficient variants of GSKIP (Fig. 3D). Only in the presence of wild type GSKIP, Ser(P)-33/Ser37/Thr-41 -catenin was reduced significantly and cytosolic -catenin increased (Fig. 5, A and B) Collectively, it appears that GSKIP must interact with both kinases to regulate Wnt-dependent transcription through -catenin. The cytosolic fractions of untreated HEK293 cells and cells treated with Wnt3a were enriched, and -catenin levels were monitored by Western blotting (Fig. 8) These levels were strongly increased in the Wnt-stimulated samples. Precipitated FLAGGSKIP and endogenous -catenin were detected by Western blotting (WB)
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
