Wnt signals are transmitted through N‐terminally dephosphorylated β‐catenin

Abstract

β-catenin mediates Wnt signaling by acting as the essential co-activator for TCF transcription factors. Wnt signaling increases the half-life and therefore the absolute level of β-catenin in responding cells. The current model states that these changes in β-catenin stability set the threshold for Wnt signaling. However, we find that pharmacological inhibition of proteasome activity by ALLN leads to accumulation of cytosolic β-catenin but not to increased TCF-mediated transcription. In addition, in temperature-sensitive ubiquitylation mutant CHO cells inhibition of ubiquitylation increases β-catenin levels, but does not induce transcriptional activation of TCF reporter genes. Using an antibody specific for β-catenin dephosphorylated at residues Ser37 and Thr41, we show that Wnt signals specifically increase the levels of dephosphorylated β-catenin, whereas ALLN does not. We conclude that changes in the phosphorylation status of the N-terminus of β-catenin that occur upon Wnt signaling independently affect the signaling properties and half-life of β-catenin. Hence, Wnt signals are transduced via N-terminally dephosphorylated β-catenin.

Notch and Wnt signaling in T-lymphocyte development and acute lymphoblastic leukemia

“…When a Wnt protein binds to the receptor complex consisting of a member of the Frizzled (Fz) family of seven transmembrane proteins 71 and an LDL-receptorrelated protein (LRP5 or LRP6), 72 b-catenin is no longer phosphorylated, resulting in its accumulation and activation. 73 Deposphorylated b-catenin translocates to the nucleus, where it activates Tcf/Lef transcription factors, 74,75 in thymocytes predominantly Tcf-1. 76,77 Next to the canonical Wnt-signaling pathway, b-catenin-independent mechanisms exist (reviewed by Veeman et al 78 ), but their implications for T-cell development have not been studied in detail.…”

Gastrin-mediated activation of cyclin D1 transcription involves β-catenin and CREB pathways in gastric cancer cells

“…These studies indicated that Since cyclin D1 is a direct target of the b-catenin/ lymphoid enhancer factor (LEF)-mediated pathway (Tetsu and McCormick, 1999), we determined whether G-17 could induce cyclin D1 transcription, via the activation of the Wnt-signaling pathway. To address this, we first determined the effect of G-17 on b-catenin expression, by Western blot analysis of AGSE wholecell protein extracts, treated without (À) or with ( þ ) 100 nM G-17, using antibodies specific to total b-catenin, as well as N-terminally dephosphorylated/activated bcatenin (ABC b-catenin), as reported previously (Staal et al, 2002). The results indicated significant induction of dephosphorylated/activated b-catenin (Figure 3c, À and þ lanes) and minor induction of total b-catenin (Figures 3a and b) following G-17 stimulation, which was associated with an increase in b-catenin nuclear translocation (Figure 3d, compare V panel with G-17 panel).…”

The levels of epithelial anchor proteins β-catenin and zona occludens-1 are altered by E7 of human papillomaviruses 5 and 8

“…The sections were rinsed in PBS and non-specific binding of antibodies was blocked with serum for 30 min at room temperature, before application of the primary antibody. Primary antibodies used in this study were: anti-b-catenin (reacting with total human and mouse b-catenin, BD Biosciences), aABC-b-catenin (reacting with nonphosphorylated Ser-37 and Thr-41, the active forms of b-catenin; Staal et al, 2002;van Noort et al, 2002;clone 8E7, Millipore), anti-ZO-1 (clone 61-7300, Life Technologies) and anti-actin (clone C4, Millipore). For controls, the primary antibody was omitted to verify expression patterns (data not shown).…”

“…This monoclonal antibody reacts against nonphosphorylated forms of b-catenin, which are active within the canonical Wnt signalling pathway (Staal et al, 2002;van Noort et al, 2002). Non-phospho-b-catenin detection showed a membranous, suprabasal expression pattern in control as well as HPV8-E7 positive OSC.…”