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Mol. Cell. Biol., 08 1996, 4088-4094, Vol 16, No. 8
S Munemitsu, I Albert, B Rubinfeld and P Polakis
Regulation of cell adhesion and cell signaling by beta-catenin occurs
through a mechanism likely involving the targeted degradation of the
protein. Deletional analysis was used to generate a beta-catenin refractory
to rapid turnover and to examine its effects on complexes containing either
cadherin or the adenomatous polyposis coli (APC) protein. The results show
that amino-terminal deletion of beta-catenin results in a protein with
increased stability that acts in a dominant fashion with respect to
wild-type beta-catenin. Constitutive expression in AtT20 cells of a
beta-catenin lacking 89 N-terminal amino acids (deltaN89beta-catenin)
resulted in severely reduced levels of the more labile wild-type
beta-catenin. The mutant beta-catenin was expressed at endogenous levels
but displaced the vast majority of wild-type beta- catenin associated with
N-cadherin. The deltaN89beta-catenin accumulated on the APC protein to a
level 10-fold over that of wild- type beta-catenin and recruited a kinase
into the APC complex. The kinase was highly active toward APC in vitro and
promoted a sodium dodecyl sulfate gel band shift that was also evident for
endogenous APC from cells expressing the mutant beta-catenin. Unlike
wild-type beta- catenin, which partitions solely as part of a
high-molecular-weight complex, the deltaN89 mutant protein also
fractionated as a stable monomer, indicating that it had escaped the
requirement to associate with other proteins. That similar N-terminal
mutants of beta-catenin have been implicated in cellular transformation
suggests that their abnormal association with APC may, in part, be
responsible for this phenotype.
Copyright © 1996, American Society for Microbiology
Deletion of an amino-terminal sequence beta-catenin in vivo and promotes hyperphosporylation of the adenomatous polyposis coli tumor suppressor protein
Onyx Pharmaceuticals, Richmond, California 94806, USA.
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