References
PMID:10581160
PMID:17318175
PMID:10421629
Recruitment of CTNNB1 via the degradation complex of APC/AXIN1 is regulated by a series of ordered phosphorylation events.
Phosphorylation of AXIN1 by CSNK1 (casein kinase 1) and GSK3B can increase axin binding to CTNNB1.
PMID:8638126
PMID:11487578
PMID:15327768
AXIN1 also promotes phosphorylation of APC by CSNK1 and GSK3B.
Phosphorylated APC has higher affinity to CTNNB1.
PMID:12554650
Finally, these phosphorylation events allo CTNNB1 to be a more efficient substrate of both CSNK1 (at S45) and the GSK3B (at T41, S33, S37).
The affinity of phosphorylated APC to CTNNB1 is higher than that of phosphorylated AXIN1.
Therefore upon phosphorylation, APC can displace AXIN1 from CTNNB1, allowing AXIN1 to bind another molecule of CTNNB1.