TY - JOUR
T1 - Phosphorylation and ubiquitination of oncogenic mutants of β-catenin containing substitutions at Asp32
AU - Al-Fageeh, Mohamed
AU - Li, Qingjie
AU - Dashwood, W. Mohaiza
AU - Myzak, Melinda C.
AU - Dashwood, Roderick H.
N1 - Funding Information:
Expression constructs for WT b-catenin, TCF-4, TOPflash and FOPflash as well as a-ABC antibody were kindly provided by Dr Marc van de Wetering and Dr Hans Clevers, University Hospital Utrecht, The Netherlands. Dr Akira Kikuchi of Hiroshima University School of Medicine generously supplied a construct for rAxin. We thank Dr Robert Tanguay for use of the gel scanner and associated software. We are grateful for services provided by the Center for Gene Research and Biotechnology, Oregon State University. This work was supported in part by NIH Grants CA65525, CA80176 and CA90890.
PY - 2004/6/17
Y1 - 2004/6/17
N2 - β-Catenin, a member of the Wnt signaling pathway, is downregulated by glycogen synthase kinase-3β (GSK-3β)-dependent phosphorylation of Ser/Thr residues in the N-terminus of the protein, followed by ubiquitination and proteosomal degradation. In human and rodent cancers, mutations that substitute one of the critical Ser/Thr residues in the GSK-3β region of β-catenin stabilize the protein and activate β-catenin/TCF/LEF target genes. This study examined three oncogenic β-catenin mutants from rat colon tumors containing substitutions adjacent to amino-acid residue Ser33, a key target for phosphorylation by GSK-3β. Compared with wild-type β-catenin (WT), the β-catenin mutants D32G, D32N, and D32Y strongly activated TCF-4-dependent transcription in HEK293 cells, and there was accumulation of β-catenin in the cell lysates. Immunoblotting with phosphospecific antibodies indicated that there was little if any effect on the phosphorylation of Ser37, Thr41 or Ser45; however, the phosphorylation of Ser33 appeared to be affected in the β-catenin mutants. Specifically, antiphospho-β-catenin 33/37/41 antibody identified high, intermediate and low expression levels of phosphorylated β-catenin in cells transfected with D32G, D32N and D32Y, respectively. Experiments with the proteosome inhibitor N-acetyl-Leu-Leu-norleucinal (ALLN) revealed ubiquitinated bands on all three mutant β-catenins, as well as on WT β-catenin. The relative order of ubiquitination was WT > D32G > D32N > D32Y, in parallel with findings from the phosphorylation studies. These results are discussed in the context of previous studies, which indicated that amino-acid residue D32 lies within the ubiquitination recognition motif of β-catenin.
AB - β-Catenin, a member of the Wnt signaling pathway, is downregulated by glycogen synthase kinase-3β (GSK-3β)-dependent phosphorylation of Ser/Thr residues in the N-terminus of the protein, followed by ubiquitination and proteosomal degradation. In human and rodent cancers, mutations that substitute one of the critical Ser/Thr residues in the GSK-3β region of β-catenin stabilize the protein and activate β-catenin/TCF/LEF target genes. This study examined three oncogenic β-catenin mutants from rat colon tumors containing substitutions adjacent to amino-acid residue Ser33, a key target for phosphorylation by GSK-3β. Compared with wild-type β-catenin (WT), the β-catenin mutants D32G, D32N, and D32Y strongly activated TCF-4-dependent transcription in HEK293 cells, and there was accumulation of β-catenin in the cell lysates. Immunoblotting with phosphospecific antibodies indicated that there was little if any effect on the phosphorylation of Ser37, Thr41 or Ser45; however, the phosphorylation of Ser33 appeared to be affected in the β-catenin mutants. Specifically, antiphospho-β-catenin 33/37/41 antibody identified high, intermediate and low expression levels of phosphorylated β-catenin in cells transfected with D32G, D32N and D32Y, respectively. Experiments with the proteosome inhibitor N-acetyl-Leu-Leu-norleucinal (ALLN) revealed ubiquitinated bands on all three mutant β-catenins, as well as on WT β-catenin. The relative order of ubiquitination was WT > D32G > D32N > D32Y, in parallel with findings from the phosphorylation studies. These results are discussed in the context of previous studies, which indicated that amino-acid residue D32 lies within the ubiquitination recognition motif of β-catenin.
KW - APC
KW - CTNNB1
KW - Colorectal cancer
KW - Ctnnb1
KW - Human β-catenin gene
KW - Rat β-catenin gene
KW - TCF/LEF
KW - Wnt signaling
KW - β-catenin
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U2 - 10.1038/sj.onc.1207634
DO - 10.1038/sj.onc.1207634
M3 - Article
C2 - 15064718
AN - SCOPUS:3042805301
SN - 0950-9232
VL - 23
SP - 4839
EP - 4846
JO - Oncogene
JF - Oncogene
IS - 28
ER -