Sadot, E., Department of Molecular Cell Biology, Weizmann Institute of Science, Rehovot 76100, Israel
Conacci-Sorrell, M., Department of Molecular Cell Biology, Weizmann Institute of Science, Rehovot 76100, Israel
Zhurinsky, J., Department of Molecular Cell Biology, Weizmann Institute of Science, Rehovot 76100, Israel
Zhnizer, D., Department of Molecular Cell Biology, Weizmann Institute of Science, Rehovot 76100, Israel
Lando, Z., Department of Molecular Cell Biology, Weizmann Institute of Science, Rehovot 76100, Israel
Zharhary, D., Department of Molecular Cell Biology, Weizmann Institute of Science, Rehovot 76100, Israel
Kam, Z., Department of Molecular Cell Biology, Weizmann Institute of Science, Rehovot 76100, Israel
Ben-Ze'ev, A., Department of Molecular Cell Biology, Weizmann Institute of Science, Rehovot 76100, Israel
Geiger, B., Department of Molecular Cell Biology, Weizmann Institute of Science, Rehovot 76100, Israel

A novel phosphorylation-specific antibody (αpβ-catenin) was generated against a peptide corresponding to amino acids 33-45 of human β-catenin, which contained phosphorylated serines at positions 33 and 37. This antibody is specific to phosphorylated β-catenin and reacts neither with the non-phosphorylated protein nor with phosphorylated or non-phosphorylated plakoglobin. It weakly interacts with S33Y β-catenin but not with the S37A mutant. pβ-catenin is hardly detectable in normal cultured cells and accumulates (up to 55% of total β-catenin) upon overexpression of the protein or after blocking its degradation by the proteasome. Inhibition of both GSK-3β and the proteasome resulted in a rapid (t1/2=10 minutes) and reversible reduction in pβ-catenin levels, suggesting that the protein can undergo dephosphorylation in live cells, at a rate comparable to its phosphorylation by GSK-3β. pβ-catenin interacts with LEF-1, but fails to form a ternary complex with DNA, suggesting that it is transcriptionally inactive. Immunofluorescence microscopy indicated that pβ-catenin accumulates in the nuclei of MDCK and BCAP cells when overexpressed and is transiently associated with adherens junctions shortly after their formation. pβ-catenin only weakly interacts with co-transfected N-cadherin, although it forms a complex with the ubiquitin ligase component β-TrCP. SW480 colon cancer cells that express a truncated APC, at position 1338, contain high levels of pβ-catenin, whereas HT29 cells, expressing APC truncated at position 1555, accumulate non-phosphorylated β-catenin, suggesting that the 1338-1555 amino acid region of APC is involved in the differential regulation of the dephosphorylation and degradation of pβ-catenin.