beta-catenin can be transported into the nucleus in a Ran-unassisted manner.
The nuclear accumulation of beta-catenin plays an important role in the Wingless/Wnt signaling pathway. This study describes an examination of the nuclear import of beta-catenin in living mammalian cells and in vitro semi-intact cells. When injected into the cell cytoplasm, beta-catenin rapidly migrated into the nucleus in a temperature-dependent and wheat germ agglutinin-sensitive manner. In the cell-free import assay, beta-catenin rapidly migrates into the nucleus without the exogenous addition of cytosol, Ran, or ATP/GTP. Cytoplasmic injection of mutant Ran defective in its GTP hydrolysis did not prevent beta-catenin import. Studies using tsBN2, a temperature-sensitive mutant cell line that possesses a point mutation in the RCC1 gene, showed that the import of beta-catenin is insensitive to nuclear Ran-GTP depletion. These results show that beta-catenin possesses the ability to constitutively translocate through the nuclear pores in a manner similar to importin beta in a Ran-unassisted manner. We further showed that beta-catenin also rapidly exits the nucleus in homokaryons, suggesting that the regulation of nuclear levels of beta-catenin involves both nuclear import and export of this molecule.
Yokoya
F
F
Department of Anatomy and Cell Biology, Osaka University Medical School, Osaka 565-0871, Japan. yyoneda@anat3.med.osaka-u.ac.jp
Imamoto
N
N
Tachibana
T
T
Yoneda
Y
Y
D000818:Animals; D015820:Cadherins / Q000378:metabolism; D002460:Cell Line; D002467:Cell Nucleus / Q000378:metabolism*; D003001:Cloning, Molecular; D006224:Cricetinae; D003598:Cytoskeletal Proteins / Q000302:isolation & purification / Q000378:metabolism*; D003600:Cytosol / Q000378:metabolism; D004285:Dogs; D004926:Escherichia coli; D019204:GTP-Binding Proteins / Q000378:metabolism*; D006367:HeLa Cells; D006801:Humans; D028884:Karyopherins; D007668:Kidney; D007700:Kinetics; D051379:Mice; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism*; D018160:Receptors, Cytoplasmic and Nuclear / Q000235:genetics / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000302:isolation & purification / Q000378:metabolism; D013696:Temperature; D015534:Trans-Activators; D051176:beta Catenin; D020931:ran GTP-Binding Protein
C495270:CTNNB1 protein, human; C495267:CTNNB1 protein, mouse; D015820:Cadherins; D003598:Cytoskeletal Proteins; D028884:Karyopherins; D009687:Nuclear Proteins; D018160:Receptors, Cytoplasmic and Nuclear; D011993:Recombinant Fusion Proteins; D015534:Trans-Activators; D051176:beta Catenin; D019204:GTP-Binding Proteins; D020931:ran GTP-Binding Protein