The transcriptional factor Tcf-4 contains different binding sites for beta-catenin and plakoglobin.
beta-Catenin and plakoglobin are two related armadillo proteins necessary for the establishment of adhesion junctions and desmosomes. Moreover, beta-catenin can also act as a transcriptional co-activator through its interaction with the members of Tcf/LEF-1 transcriptional factor family. We show here that Tcf-4 can be phosphorylated in vitro by protein kinase CK2 stoichiometrically in amino acids Ser-58-Ser-59-Ser-60. Phosphorylation of these residues does not modify the interaction of Tcf-4 with beta-catenin but reduces its association to plakoglobin. The binding sites of Tcf-4 for these two proteins were compared; whereas beta-catenin requires the N-terminal first 50 amino acids, plakoglobin interacts mainly with residues 51-80. Tcf-4-(51-80) binds plakoglobin in the region of armadillo repeats 1-6. Ternary complexes composed by beta-catenin/Tcf-4/plakoglobin could be detected in vitro, demonstrating that simultaneous binding of the two armadillo proteins to Tcf-4 is possible. Experiments performed using a Tcf-4 mutant with decreased interaction to plakoglobin demonstrated that binding to this protein negatively affected the transcriptional activity of Tcf-4. These results indicate that Tcf-4 contains two different sites for binding of beta-catenin and plakoglobin, and the interaction of the latter hinders the transcriptional activity of the complex.
Miravet
Susana
S
Unitat de Biofisica, Departament de Bioquimica i Biologia Molecular, Facultat de Medicina, Universitat Autònoma de Barcelona, 08193 Bellaterra, Spain.
Piedra
Jose
J
Miró
Francesc
F
Itarte
Emilio
E
García de Herreros
Antonio
A
Duñach
Mireia
M
D001483:Base Sequence; D001665:Binding Sites; D047390:Casein Kinase II; D003598:Cytoskeletal Proteins / Q000378:metabolism*; D017931:DNA Primers; D051180:Desmoplakins; D006801:Humans; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D015534:Trans-Activators; D014157:Transcription Factors / Q000378:metabolism*; D051176:beta Catenin; D051185:gamma Catenin
C495270:CTNNB1 protein, human; D003598:Cytoskeletal Proteins; D017931:DNA Primers; D051180:Desmoplakins; D015534:Trans-Activators; D014157:Transcription Factors; D051176:beta Catenin; D051185:gamma Catenin; D047390:Casein Kinase II; D017346:Protein Serine-Threonine Kinases