Protein Kinase A Activation Enhances β-Catenin Transcriptional Activity through Nuclear Localization to PML Bodies

Abstract

The Protein Kinase A (PKA) and Wnt signaling cascades are fundamental pathways involved in cellular development and maintenance. In the osteoblast lineage, these pathways have been demonstrated functionally to be essential for the production of mineralized bone. Evidence for PKA-Wnt crosstalk has been reported both during tumorigenesis and during organogenesis, and the nature of the interaction is thought to rely on tissue and cell context. In this manuscript, we analyzed bone tumors arising from mice with activated PKA caused by mutation of the PKA regulatory subunit Prkar1a. In primary cells from these tumors, we observed relocalization of β-catenin to intranuclear punctuate structures, which were identified as PML bodies. Cellular redistribution of β-catenin could be recapitulated by pharmacologic activation of PKA. Using 3T3-E1 pre-osteoblasts as a model system, we found that PKA phosphorylation sites on β-catenin were required for nuclear re-localization. Further, β-catenin's transport to the nucleus was accompanied by an increase in canonical Wnt-dependent transcription, which also required the PKA sites. PKA-Wnt crosstalk in the cells was bi-directional, including enhanced interactions between β-catenin and the cAMP-responsive element binding protein (CREB) and transcriptional crosstalk between the Wnt and PKA signaling pathways. Increases in canonical Wnt/β-catenin signaling were associated with a decrease in the activity of the non-canonical Wnt/Ror2 pathway, which has been shown to antagonize canonical Wnt signaling. Taken together, this study provides a new understanding of the complex regulation of the subcellular distribution of β-catenin and its differential protein-protein interaction that can be modulated by PKA signaling.

Positive cross talk between protein kinase D and β-catenin in intestinal epithelial cells: impact on β-catenin nuclear localization and phosphorylation at Ser552

“…Although ␤-catenin phosphorylation at Ser 552 is implicated in the regulation of its function (17,60,61,84), we found that treatment of IEC-18 cells with FSK ϩ IBMX (i.e., bypassing the PKDs) was not sufficient to induce ␤-catenin nuclear localization in IEC-18 cells. Consequently, we anticipated that PKDs stimulate ␤-catenin nuclear localization, not only via PKD/PKA-mediated phosphorylation at Ser 552 , but also through an additional PKD-dependent mechanism(s).…”

“…␤-Catenin phosphorylation at Ser 552 has been implicated in inflammation-induced dysplastic transformation in the colon (27) and in intestinal polyposis (16). ␤-Catenin phosphorylation at Ser 552 is regulated via phosphatidylinositol 3-kinase (PI3K)/Akt (11,27) and/or cAMP/PKA (17,60,61,84) through poorly understood cross-talk mechanisms with other signaling pathways (72).…”

Delamination of neural crest cells requires transient and reversible Wnt inhibition mediated by DACT1/2

“…This additional data reinforces our model whereby the Dact1/2 scaffold proteins expressed in the dorsal NT control the subcellular distribution of β-catenin, transiently preventing transcriptional responses. The localisation of β-catenin to NBs has been observed in tumour cells (Satow et al, 2012;Zhang et al, 2014), where a direct interaction between the armadillo repeat of β-catenin and the product of promyelocytic leukaemia (PML) protein was reported (Satow et al, 2012). Among the different NBs, not only the PML NBs but also the polycomb group (PcG) NBs act as SUMOylation centres and hubs for gene repression.…”

Transcriptomic characterization of fibrolamellar hepatocellular carcinoma

“…In normal tissue, PKA is involved in many cellular functions (23). It phosphorylates many targets, including transcription factors such as cAMP response element-binding protein (CREB) (24), GATA3, GATA6 (25), NF-κB (26), β-catenin [activating downstream elements of the wnt pathway (27)], the transcription coactivator yes-associated protein 1 (YAP) (28), and ETV1 (29) and indirectly activates XBP1 (30). Any or all of these molecular events could have significant effects on gene expression.…”