Regulation of the phosphorylation and nuclear import and export of β-catenin by APC and its cancer-related truncated form.
We report the first direct analysis of the endogenous β-catenin phosphorylation activity in colon cancer SW480 cells. By comparing parental SW480 cells that harbor a typical truncated adenomatous polyposis coli (APC) form, cells expressing full-length APC and APC-depleted cells, we provide the formal demonstration that APC is necessary for β-catenin phosphorylation, both for priming of the protein at residue serine 45 and for the subsequent phosphorylation of residues 33, 37 and 41. Truncated APC still sustains a surprisingly high phosphorylation activity, which requires the protein to bind to β-catenin through the APC 20-amino-acid (20AA) repeats, thus providing a biochemical explanation for the precise truncations found in cancer cells. We also show that most of the β-catenin phosphorylation activity is associated with a dense insoluble fraction. We finally examine the impact of full-length and truncated APC on β-catenin nuclear transport. We observe that β-catenin is transported much faster than previously thought. Although this fast translocation is largely insensitive to the presence of wild-type or truncated APC, the two forms appear to limit the pool of β-catenin that is available for transport, which could have an impact on β-catenin nuclear activities in normal and cancer cells.
Department of Clinical Laboratory, Qilu Hospital, Shandong University, Jinan, Shandong 250012, China.
Lili
L
Wang
Xiaoyong
X
Liu
Ekaterina
E
Gusev
Chuanxin
C
Wang
François
F
Fagotto
D021581:Active Transport, Cell Nucleus; D011125:Adenomatous Polyposis Coli / Q000235:genetics*; D025601:Adenomatous Polyposis Coli Protein / Q000502:physiology*; D060466:Axin Protein / Q000378:metabolism; D045744:Cell Line, Tumor; D002467:Cell Nucleus / Q000378:metabolism*; D018389:Codon, Nonsense; D006801:Humans; D010766:Phosphorylation; D011499:Protein Processing, Post-Translational; D060449:Wnt Signaling Pathway; D051176:beta Catenin / Q000378:metabolism*
C555337:APC protein, human; D025601:Adenomatous Polyposis Coli Protein; D060466:Axin Protein; C495270:CTNNB1 protein, human; D018389:Codon, Nonsense; D051176:beta Catenin
Cancer; Cell signaling; Nuclear transport; Wnt pathway