Phosphorylation of β-Catenin by Cyclic AMP-Dependent Protein Kinase Stabilizes β-Catenin through Inhibition of Its Ubiquitination

Abstract

The mechanism of cross talk between the Wnt signaling and cyclic AMP (cAMP)-dependent protein kinase (protein kinase A [PKA]) pathways was studied. Prostaglandin E 1 (PGE 1 ), isoproterenol, and dibutyryl cAMP (Bt 2 cAMP), all of which activate PKA, increased the cytoplasmic and nuclear ␤-catenin protein level, and these actions were suppressed by a PKA inhibitor and RNA interference for PKA. PGE 1 and Bt 2 cAMP also increased T-cell factor (Tcf)-dependent transcription through ␤-catenin. Bt 2 cAMP suppressed degradation of ␤-catenin at the protein level. Although PKA did not affect the formation of a complex between glycogen synthase kinase 3␤ (GSK-3␤), ␤-catenin, and Axin, phosphorylation of ␤-catenin by PKA inhibited ubiquitination of ␤-catenin in intact cells and in vitro. Ser675 was found to be a site for phosphorylation by PKA, and substitution of this serine residue with alanine in ␤-catenin attenuated inhibition of the ubiquitination of ␤-catenin by PKA, PKA-induced stabilization of ␤-catenin, and PKA-dependent activation of Tcf. These results indicate that PKA inhibits the ubiquitination of ␤-catenin by phosphorylating ␤-catenin, thereby causing ␤-catenin to accumulate and the Wnt signaling pathway to be activated.

A Rac1/PAK1 cascade controls β-catenin activation in colon cancer cells

“…Rac1 was included, as it functions upstream of PAK1. Forskolin, a potent activator of PKA, was used as a positive control (Hino et al, 2005;Fang et al, 2007). As expected, both S552 and S675 were heavily phosphorylated upon forskolin treatment (Figure 3b).…”

“…The key event of both Wnt signaling transduction and cancerous cell proliferation is the regulation of b-catenin stability and activity. In addition to its N-terminal residues, Ser552 (Fang et al, 2007) and Ser675 (Hino et al, 2005;Taurin et al, 2006) of b-catenin have also been identified as potential phosphorylation sites and may affect its signaling activity or protein stability.…”

Caffeine Inhibits Cell Proliferation and Regulates PKA/GSK3β Pathways in U87MG Human Glioma Cells

“…2B). As GSK3β is a downstream target of PKA (Fang et al, 2000;Hino et al, 2005), the effects of caffeine on these proteins were investigated. Caffeine (20 μM) increased PKA and GSK3β phosphorylation in a time-dependent manner (Fig.…”

SOX9 determines RUNX2 transactivity by directing intracellular degradation

“…(49) Significantly, SOX9 seems to have a more general function to regulate the ubiquitination status and/or degradation pathway for different signaling proteins. For example, we found that both RUNX2 and b-catenin, a wellknown protein degraded through the ubiquitin-proteasome pathway, (50,51) were subject to SOX9-directed lysosomal compartmentalization. b-Catenin is a key component of the canonical Wnt signaling pathway.…”