ABSTRACT
ß-Catenin is crucial in the canonical Wnt signaling pathway. This pathway is up-regulated by CK2 which is associated with an enhanced expression of the antiapoptotic protein survivin, although the underlying molecular mechanism is unknown. AKT/PKB kinase phosphorylates and promotes ß-catenin transcriptional activity, whereas CK2 hyperactivates AKT by phosphorylation at Ser129; however, the role of this phosphorylation on ß-catenin transcriptional activity and cell survival is unclear. We studied in HEK-293T cells, the effect of CK2-dependent hyperactivation of AKT on cell viability, as well as analyzed ß-catenin subcellular localization and transcriptional activity and survivin expression. CK2α overexpression led to an augmented ß-catenin-dependent transcription and protein levels of survivin, and consequently an enhanced resistance to apoptosis. However, CK2α-enhancing effects were reversed when an AKT mutant deficient in Ser129 phosphorylation by CK2 was co-expressed. Therefore, our results strongly suggest that CK2α-specific enhancement of ß-catenin transcriptional activity as well as cell survival may depend on AKT hyperactivation by CK2.
Subject(s)
Casein Kinase II/metabolism , Inhibitor of Apoptosis Proteins/metabolism , Proto-Oncogene Proteins c-akt/metabolism , beta Catenin/metabolism , Apoptosis , Cell Nucleus/metabolism , Cell Survival , HEK293 Cells , Humans , Mutant Proteins/metabolism , Phosphorylation , Protein Binding , Protein Transport , Up-RegulationABSTRACT
ß-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 ß-catenin at Ser552, which in turn, promotes its nuclear localization and transcriptional activity. However, the consequences of CK2-dependent hyperactivation of AKT on ß-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 ß-catenin-dependent transcriptional activity, survivin expression and viability in HEK-293T cells. We observed that CK2α overexpression up-regulated the ß-catenin transcriptional activity, which correlated to an increased nuclear localization of ß-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 ß-catenin stability. Taken together, the data suggest that the CK2α-dependent up-regulation of ß-catenin activity requires phosphorylation of AKT in human embryonic kidney cells.
