Glycogen synthase kinase-3β activity is required for androgen-stimulated gene expression in prostate cancer

Abstract

Despite the specificity inferred by its name, glycogen synthase kinase (GSK)-3β is an important kinase with a plethora of significant cellular targets, including cytoskeletal proteins and transcription factors, and its activity is regulated by phosphorylation on tyrosine/serine residues. As part of our efforts to dissect the molecular basis responsible for androgen-independent progression of prostate cancer, we investigated the role of GSK-3β in androgen-stimulated gene expression in human prostate cancer cells. Pretreatment of prostate cancer cells harboring wild-type or mutant androgen receptor with the GSK-3β inhibitors, lithium chloride (LiCl), RO318220, or GF109203X, inhibited R1881-stimulated androgen-responsive reporter activity in a dose- and time-dependent manner. In addition, the expression of two endogenous androgen-stimulated gene products, prostate-specific antigen and matrix metalloproteinase-2, was suppressed by the GSK-3β inhibitors in those cells. Most importantly, knocking down GSK-3β expression via a small interference RNA-mediated gene silencing approach also reduced R1881-stimulated gene expression, demonstrating the specificity of GSK-3β involvement. Moreover, R1881 treatment of the cells increased phosphorylation status of GSK-3β on tyrosine residue Y216 but not on serine residue S 9. Pretreatment of the cells with phosphatidylinositol 3-kinase inhibitor LY294002 or wortmannin, which blocks androgen action in cells, abolished R1881-induced GSK-3β Y216 phosphorylation. However, the phosphatidylinositol 3-kinase or GSK-3β inhibitors did not block R1881-induced nuclear translocation of androgen receptor. Finally, knocking down the expression of Akt or β-catenin, the two GSK-3β-related signaling molecules, via siRNA-mediated gene silencing did not significant affect R1881-stimulated gene expression. These findings suggest that GSK-3β activity is required for androgen-stimulated gene expression in prostate cancer cells.