The aurora kinase A regulates GSK-3β in gastric cancer cells

Aurora kinase A (AURKA) is located at 20q13, a region that is frequently amplified in gastric cancer. In this study, we have investigated the role of AURKA in regulating glycogen synthase kinase (GSK)-3β and β-catenin/TCF complex in gastric cancer cells. Our results demonstrate a significant increase in the phosphorylation of GSK-3β at Ser 9 following the overexpression of AURKA in AGS cells. The immunoprecipitation with antibodies specific for AURKA and GSK-3β indicated that the two proteins coexist in the same protein complex. The recombinant human AURKA protein phosphorylated the GSK-3β protein at Ser 9 in a concentration-dependent manner, in vitro. The phosphorylation of β-catenin (Ser33/37/Thr41) by GSK-3β is known to target β-catenin towards degradation. In line with our findings, the increase in phospho-GSK-3β level was accompanied by a significant decrease in β-catenin phosphorylation (Ser33/37/Thr41) and accumulation of β-catenin protein. The knockdown of AURKA reversed the phosphorylation of GSK-3β and the β-catenin protein levels. The immunofluorescence analysis demonstrated colocalization of AURKA and GSK-3β proteins and a significant increase in the nuclear β-catenin levels in cells overexpressing AURKA. The β-catenin/TCF transcription activity was measured using the pTopFlash and its mutant pFopFlash luciferase reporter vectors. Indeed, AURKA overexpression led to a significant increase in the pTopFlash reporter activity, whereas kinase dead AURKA mutant (D274A) had no effect. Consistent with these findings, we detected a significant mRNA up-regulation of several direct targets of the β-catenin/TCF transcription complex (cyclin D1, c-MYC, c-MYC-binding protein, CLDN1, FGF18 and vascular endothelial growth factor), and a two-fold increase in the proliferation rate in AURKA overexpressing cells. We conclude that the AURKA/GSK-3β interaction is important in regulating β-catenin, underscoring a novel oncogenic potential for AURKA in gastric tumorigenesis.