Targeting Src-mediated Tyr216 phosphorylation and activation of GSK-3 in prostate cancer cells inhibit prostate cancer progressionin vitroandin vivo

Abstract

Recent studies suggest a positive correlation between glycogen synthase kinase-3 (GSK-3) activation and tumor growth. Currently, it is unclear how both Akt that inhibits GSK-3 and active GSK-3 are maintained concurrently in tumor cells. We investigated the role of GSK-3 and the existence of an Akt-resistant pathway for GSK-3 activation in prostate cancer cells. Our data show that Src, a non-receptor tyrosine kinase is responsible for Y216GSK-3 phosphorylation leading to its activation even when Akt is active. Experiments involving mouse embryonic fibroblasts lacking cSrc, Yes and Fyn, as well as Src activity modulation in prostate cancer cells with constitutively active (CA-Src) and dominant negative Src (DN-Src) plasmids demonstrated the integral role of Src in Y216GSK-3 phosphorylation and activity modulation. Inhibition of GSK-3 with SB415286 in PC3 cells resulted in impaired motility, proliferation and colony formation. Treatment of PC3 cells with the Src inhibitor dasatinib reduced Y216GSK-3 phosphorylation and inhibited proliferation, invasion and micrometastasis in vitro. Dasatinib treatment of athymic nude mice resulted in impaired growth of PC3 cell tumor xenograft. Together, we provide novel insight into the Src-mediated Y216GSK-3 phosphorylation and activation in prostate cancer cells and reveal the potential benefits of targeting Src-GSK-3 axis using drugs such as dasatinib.

Activation of Glycogen Synthase Kinase 3β Ameliorates Diabetes-induced Kidney Injury

“…In contrast to our data, Src activates GSK3␤ by tyrosine phosphorylation in prostate cancer (40), suggesting cell-and contextspecific regulation of GSK3␤ by its upstream kinases. Further studies are needed to understand the mechanisms involved in diabetes-induced activation of Src and Pyk2 in the kidney.…”

Discrete functions of GSK3α and GSK3β isoforms in prostate tumor growth and micrometastasis

“…We reported the first evidence on the role of GSK3 in advanced, androgen insensitive prostate cancer cells. Pharmacological inhibition or SiRNA-mediated knockdown of GSK3 inhibited androgen-independent prostate cancer cell function in vitro and tumor growth in vivo [13]. This was in agreement with the clinical report from human prostate cancer patient tumor tissues indicating increased protein and mRNA expression of GSK3α starting from the early tumor growth and increased expression of GSK3β specifically in advanced cancers [28].…”

“…However, several recent studies, including ours indicated that GSK3 inhibition directly impairs the cancer cell function in vitro, and growth and metastasis of multiple cancers in vivo such as prostate [13], pancreas [9, 10], oral [8], and ovarian [21]. Reports indicated the specific role of GSK3β isoform in pancreatic [7] and non-small cell lung cancer cells [22].…”

“…On the contrary, recent reports indicated that inhibition of GSK3 activity has tumor suppressive effect on various cancers [7-12], raising the question how Akt and GSK3 can concurrently be active in cancers. We recently provided the first evidence that both Akt and GSK3 can be maintained active simultaneously in prostate cancer cells and mouse embryonic fibroblasts via another activating phosphorylation of a tyrosine residue in GSK3 (Tyrosine 216) by Src family of kinases [13]. However, until today precise role of GSK3 in multiple cellular functions and clinical conditions is controversial, and isoform specific functions of GSK3 and their specific downstream targets in various cancers remain unclear.…”

A screen for transcription factor targets of Glycogen Synthase Kinase-3 highlights an inverse correlation of NFκB and Androgen Receptor Signaling in Prostate Cancer

“…AR transcriptional activity is regulated by co-activator and co-repressor proteins and by posttranslational modifications, such as phosphorylation by kinases [4, 8–11], including GSK-3, which is important for AR stability, nuclear localization and transcriptional activity [4, 5, 12]. The mechanism of action of GSK-3 is however complex and context-dependent, since its overexpression in some cell types inhibits AR [10, 11] and there are instances where GSK-3 inhibitors reduce proliferation of AR-negative PCa cells [13, 14]. In addition, GSK-3 regulates other signals, such as those mediated by Wnt and NFκB, which are themselves linked [15].…”