Phosphorylation of AKT/PKB by CK2 is necessary for the AKT-dependent up-regulation of β-catenin transcriptional activity

Abstract

β-Catenin is a key protein in the canonical Wnt signaling pathway and in many cancers alterations in transcriptional activity of its components are observed. This pathway is up-regulated by the protein kinase CK2, but the underlying mechanism of this change is unknown. It has been demonstrated that CK2 hyperactivates AKT/PKB by phosphorylation at Ser129, and AKT phosphorylates β-catenin at Ser552, which in turn, promotes its nuclear localization and transcriptional activity. However, the consequences of CK2-dependent hyperactivation of AKT on β-catenin activity and cell viability have not been evaluated. We assessed this regulatory process by manipulating the activity of CK2 and AKT through overexpression of wild-type, constitutively active and dominant negative forms of these proteins as well as analyzing β-catenin-dependent transcriptional activity, survivin expression and viability in HEK-293T cells. We observed that CK2α overexpression up-regulated the β-catenin transcriptional activity, which correlated to an increased nuclear localization of β-catenin as well as survivin expression. Importantly, these effects were strongly reversed when an AKT-S129A mutant was co-expressed in the same cells, followed by a significant decrease in cell viability but no changes in β-catenin stability. Taken together, the data suggest that the CK2α-dependent up-regulation of β-catenin activity requires phosphorylation of AKT in human embryonic kidney cells.

Modeling human osteosarcoma in mice through 3AB‐OS cancer stem cell xenografts

“…However, during the first weeks of engraftment they contain high levels of the phosphorylated form of AKT, pAKT, which has been reported to be necessary for the AKT-dependent up-regulation of b-catenin transcriptional activity [Tian et al, 2004;Fang et al, 2007;Ponce et al, 2011]. Consistently, engrafted tumor cells show high levels of nuclear b-catenin, c-Myc, and cyclin D2, along with the hyperphosphorylated-inactive pRb form, which confirms the lack of brakes to restrain cell proliferation.…”

“…However, b-catenin level is also regulated by the b-catenin destruction complex (APC, Axin, GSK3b, and casein kinase), which modulates Wnt pathway through the GSK-3b-APC complex [MacDonald et al, 2009]. Alteration of this system leads to b-catenin stabilization and nuclear accumulation and the consequent transcription of genes (i.e., c-Myc and D cyclins) implicated in self-renewal [Ponce et al, 2011].…”

Protein kinase CK2 in hematologic malignancies: reliance on a pivotal cell survival regulator by oncogenic signaling pathways

“…14 --16 CK2 has been also demonstrated to upregulate b-catenin transcriptional activity by means of Ser129 Akt phosphorylation. 17 CK2-activated AKT in turns phosphorylates b-catenin and, as a consequence, the transcription of the b-catenindependent anti-apoptotic survivin gene is enhanced, conferring resistance to apoptosis. 18 Overall, although CK2 activity fully supports Wnt/b-catenin signaling, a formal---in vivo---demonstration of Wnt signaling modulation by CK2 is still lacking.…”

Potent and Selective CK2 Kinase Inhibitors with Effects on Wnt Pathway Signaling in Vivo

“…16 These data are consistent with the finding that CK2α-dependent up-regulation of β-catenin driven transcriptional activity requires phosphorylation of AKT. 17 In addition, Wnt pathway inhibition correlates with antiproliferative effects in DLD-1 (APC mutant) cells ( Figure 5). Similar levels of activity are observed in other CRC cell lines with constitutively activated Wnt signaling that is driven either by β-catenin (HCT-116) or APC mutations (SW620) ( Table 3).…”