Regulation of glycogen synthase kinase-3 by thymosin beta-4 is associated with gastric cancer cell migration

Thymosin beta-4 (T beta 4), actin-sequestering protein, plays important roles in many cellular functions including cancer cell migrations. Glycogen synthase kinase (GSK) in Wnt signaling pathway is a key molecule to control intercellular interaction. Here, we investigated whether GSK-3 activity is regulated by T beta 4 and it is associated with T beta 4-mediated migration in gastric cancer cells. Various expression level of T beta 4 was observed in human gastric tumor tissues. Migration in gastric cancer cells, SNU638 and SNU668, was dependent on a relative expression level of T beta 4. Cell migration was higher in SNU668 with a higher expression level of T beta 4 than that in SNU638 with a lower T beta 4. Although the level of phosphorylated(p)-GSK-3a (inactive), beta-catenin, E-cadherin and E-cadherin:beta-catenin complex was relatively higher, p-GSK-3 beta (inactive) was lower in SNU638 compared to those in SNU668 cells. LiCl, GSK-3a/beta inhibitor, reduced lung metastasis of B16F10 mouse melanoma cells and SNU668 cell migration. Small interference (si)RNA of GSK-3a increased SNU638 cell migration in accordance with the reduction of E-cadherin:beta-catenin complex formation through a decrease in beta-catenin and E-cadherin. Expression level of GSK-3a/beta, beta-catenin and E-cadherin in SNU668 and SNU638 was reversed by T beta 4-siRNA and by the treatment with acetylated-serine-aspartic acid-lysine-proline (SDKP) tetrapeptide of T beta 4, respectively. E-cadherin expression in SNU638 cells was decreased by beta-catenin-siRNA. PD98059, MEK inhibitor, or U0126, ERK inhibitor, reduced SNU668 cell migration accompanying an increase in p-GSK-3a, beta-catenin and E-cadherin. Taken together, data indicated that the expression of GSK-3a, beta-catenin and E-cadherin could be negatively regulated by T beta 4-induced ERK phosphorylation. It suggests that T beta 4 could be a novel regulator to control Wnt signaling pathways.