Identification of an N-terminal glycogen synthase kinase 3 phosphorylation site which regulates the functional localization of polycystin-2 in vivo and in vitro

Glycogen synthase kinase-3 beta is a ubiquitously and constitutively expressed molecule with pleiotropic function. It acts as a protooncogene in the development of several solid tumors including pancreatic cancer through its involvement in various cellular processes including cell proliferation, survival, invasion and metastasis, as well as autophagy. Furthermore, the level of aberrant glycogen synthase kinase-3 beta expression in the nucleus is inversely correlated with tumor differentiation and survival in both in vitro and in vivo models of pancreatic cancer. Small molecule inhibitors of glycogen synthase kinase-3 beta have demonstrated therapeutic potential in pre-clinical models and are currently being evaluated in early phase clinical trials involving pancreatic cancer patients with interim results showing favorable results. Moreover, recent studies support a rationale for the combination of glycogen synthase kinase-3 beta inhibitors with chemotherapy and immunotherapy, warranting the evaluation of novel combination regimens in the future.

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Priming-Dependent Phosphorylation and Regulation of the Tumor Suppressor pVHL by Glycogen Synthase Kinase 3

Molecular and Cellular Biology ◽

10.1128/mcb.00232-06 ◽

2006 ◽

Vol 26 (15) ◽

pp. 5784-5796 ◽

Cited By ~ 60

Author(s):

Alexander Hergovich ◽

Joanna Lisztwan ◽

Claudio R. Thoma ◽

Christiane Wirbelauer ◽

Robert E. Barry ◽

...

Keyword(s):

Tumor Suppressor ◽

Glycogen Synthase ◽

Human Cancer ◽

Suppressor Gene ◽

Binding Activity ◽

Glycogen Synthase Kinase ◽

Normal Operation ◽

Glycogen Synthase Kinase 3

ABSTRACT Inactivation of the von Hippel-Lindau (VHL) tumor suppressor gene is linked to the development of tumors of the eyes, kidneys, and central nervous system. VHL encodes two gene products, pVHL30 and pVHL19, of which one, pVHL30, associates functionally with microtubules (MTs) to regulate their stability. Here we report that pVHL30 is a novel substrate of glycogen synthase kinase 3 (GSK3) in vitro and in vivo. Phosphorylation of pVHL on serine 68 (S68) by GSK3 requires a priming phosphorylation event at serine 72 (S72) mediated in vitro by casein kinase I. Functional analysis of pVHL species carrying nonphosphorylatable or phosphomimicking mutations at S68 and/or S72 reveals a central role for these phosphorylation events in the regulation of pVHL's MT stabilization (but not binding) activity. Taken together, our results identify pVHL as a novel priming-dependent substrate of GSK3 and suggest a dual-kinase mechanism in the control of pVHL's MT stabilization function. Since GSK3 is a component of multiple signaling pathways that are altered in human cancer, our results further imply that normal operation of the GSK3-pVHL axis may be a critical aspect of pVHL's tumor suppressor mechanism through the regulation of MT dynamics.

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Glycogen Synthase Kinase 3 Inhibition Promotes Adult Hippocampal Neurogenesis in Vitro and in Vivo

ACS Chemical Neuroscience ◽

10.1021/cn300110c ◽

2012 ◽

Vol 3 (11) ◽

pp. 963-971 ◽

Cited By ~ 80

Author(s):

Jose A. Morales-Garcia ◽

Rosario Luna-Medina ◽

Sandra Alonso-Gil ◽

Marina Sanz-SanCristobal ◽

Valle Palomo ◽

...

Keyword(s):

Glycogen Synthase ◽

Hippocampal Neurogenesis ◽

Adult Hippocampal Neurogenesis ◽

Glycogen Synthase Kinase ◽

Glycogen Synthase Kinase 3

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Hierarchical phosphorylation at N-terminal transformation-sensitive sites in c-Myc protein is regulated by mitogens and in mitosis.

Molecular and Cellular Biology ◽

10.1128/mcb.14.8.5510 ◽

1994 ◽

Vol 14 (8) ◽

pp. 5510-5522 ◽

Cited By ~ 152

Author(s):

B Lutterbach ◽

S R Hann

Keyword(s):

Glycogen Synthase ◽

Mitogen Activated Protein Kinase ◽

Glycogen Synthase Kinase ◽

Glycogen Synthase Kinase 3 ◽

Terminal Domain ◽

In Vivo Experiments ◽

Phosphopeptide Mapping ◽

Hierarchical Phosphorylation

The N-terminal domain of the c-Myc protein has been reported to be critical for both the transactivation and biological functions of the c-Myc proteins. Through detailed phosphopeptide mapping analyses, we demonstrate that there is a cluster of four regulated and complex phosphorylation events on the N-terminal domain of Myc proteins, including Thr-58, Ser-62, and Ser-71. An apparent enhancement of Ser-62 phosphorylation occurs on v-Myc proteins having a mutation at Thr-58 which has previously been correlated with increased transforming ability. In contrast, phosphorylation of Thr-58 in cells is dependent on a prior phosphorylation of Ser-62. Hierarchical phosphorylation of c-Myc is also observed in vitro with a specific glycogen synthase kinase 3 alpha, unlike the promiscuous phosphorylation observed with other glycogen synthase kinase 3 alpha and 3 beta preparations. Although both p42 mitogen-activated protein kinase and cdc2 kinase specifically phosphorylate Ser-62 in vitro and cellular phosphorylation of Thr-58/Ser-62 is stimulated by mitogens, other in vivo experiments do not support a role for these kinases in the phosphorylation of Myc proteins. Unexpectedly, both the Thr-58 and Ser-62 phosphorylation events, but not other N-terminal phosphorylation events, can occur in the cytoplasm, suggesting that translocation of the c-Myc proteins to the nucleus is not required for phosphorylation at these sites. In addition, there appears to be an unusual block to the phosphorylation of Ser-62 during mitosis. Finally, although the enhanced transforming properties of Myc proteins correlates with the loss of phosphorylation at Thr-58 and an enhancement of Ser-62 phosphorylation, these phosphorylation events do not alter the ability of c-Myc to transactivate through the CACGTG Myc/Max binding site.

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Selective Glycogen Synthase Kinase 3 Inhibitors Potentiate Insulin Activation of Glucose Transport and Utilization In Vitro and In Vivo

Diabetes ◽

10.2337/diabetes.52.3.588 ◽

2003 ◽

Vol 52 (3) ◽

pp. 588-595 ◽

Cited By ~ 297

Author(s):

D. B. Ring ◽

K. W. Johnson ◽

E. J. Henriksen ◽

J. M. Nuss ◽

D. Goff ◽

...

Keyword(s):

Glucose Transport ◽

Glycogen Synthase ◽

Glycogen Synthase Kinase ◽

Glycogen Synthase Kinase 3

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Shared Roles of Yeast Glycogen Synthase Kinase 3 Family Members in Nitrogen-Responsive Phosphorylation of Meiotic Regulator Ume6p

Molecular and Cellular Biology ◽

10.1128/mcb.20.15.5447-5453.2000 ◽

2000 ◽

Vol 20 (15) ◽

pp. 5447-5453 ◽

Cited By ~ 38

Author(s):

Yang Xiao ◽

Aaron P. Mitchell

Keyword(s):

Gene Expression ◽

Nitrogen Limitation ◽

Glycogen Synthase ◽

Gene Activation ◽

Glycogen Synthase Kinase ◽

Glycogen Synthase Kinase 3 ◽

Meiotic Gene ◽

Transduction Mechanisms

ABSTRACT Nitrogen limitation activates meiosis and meiotic gene expression in yeast, but nitrogen-responsive signal transduction mechanisms that govern meiotic gene expression are poorly understood. We show here that Ume6p, a subunit of the Ume6p-Ime1p meiotic transcriptional activator, undergoes increased phosphorylation in vivo in response to nitrogen limitation. Phosphorylation depends on an N-terminal glycogen synthase kinase 3 (GSK3) target site in which substitutions cause reduced Ume6p-Ime1p interaction and meiotic gene expression, thus arguing that phosphorylation promotes functional Ume6p-Ime1p interaction. Phosphorylation of this site depends on two GSK3 homologs, Rim11p and Mck1p. Prior studies indicate that Rim11p phosphorylates both Ume6p and Ime1p in vitro and is required for Ume6p-Ime1p interaction, but no evidence has linked Mck1p function to Ume6p activity. Here we find that Mck1p-Ume6p interaction is detectable by two-hybrid assays and that meiosis in a partially defective rim11-K68R mutant is completely dependent on Mck1p. These findings argue that nitrogen limitation governs Rim11p/Mck1p-dependent phosphorylation of Ume6p, which in turn is required for Ume6p-Ime1p interaction and meiotic gene activation.

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Hierarchical phosphorylation at N-terminal transformation-sensitive sites in c-Myc protein is regulated by mitogens and in mitosis

Molecular and Cellular Biology ◽

10.1128/mcb.14.8.5510-5522.1994 ◽

1994 ◽

Vol 14 (8) ◽

pp. 5510-5522

Author(s):

B Lutterbach ◽

S R Hann

Keyword(s):

Glycogen Synthase ◽

Mitogen Activated Protein Kinase ◽

Glycogen Synthase Kinase ◽

Glycogen Synthase Kinase 3 ◽

Terminal Domain ◽

In Vivo Experiments ◽

Phosphopeptide Mapping ◽

Hierarchical Phosphorylation

The N-terminal domain of the c-Myc protein has been reported to be critical for both the transactivation and biological functions of the c-Myc proteins. Through detailed phosphopeptide mapping analyses, we demonstrate that there is a cluster of four regulated and complex phosphorylation events on the N-terminal domain of Myc proteins, including Thr-58, Ser-62, and Ser-71. An apparent enhancement of Ser-62 phosphorylation occurs on v-Myc proteins having a mutation at Thr-58 which has previously been correlated with increased transforming ability. In contrast, phosphorylation of Thr-58 in cells is dependent on a prior phosphorylation of Ser-62. Hierarchical phosphorylation of c-Myc is also observed in vitro with a specific glycogen synthase kinase 3 alpha, unlike the promiscuous phosphorylation observed with other glycogen synthase kinase 3 alpha and 3 beta preparations. Although both p42 mitogen-activated protein kinase and cdc2 kinase specifically phosphorylate Ser-62 in vitro and cellular phosphorylation of Thr-58/Ser-62 is stimulated by mitogens, other in vivo experiments do not support a role for these kinases in the phosphorylation of Myc proteins. Unexpectedly, both the Thr-58 and Ser-62 phosphorylation events, but not other N-terminal phosphorylation events, can occur in the cytoplasm, suggesting that translocation of the c-Myc proteins to the nucleus is not required for phosphorylation at these sites. In addition, there appears to be an unusual block to the phosphorylation of Ser-62 during mitosis. Finally, although the enhanced transforming properties of Myc proteins correlates with the loss of phosphorylation at Thr-58 and an enhancement of Ser-62 phosphorylation, these phosphorylation events do not alter the ability of c-Myc to transactivate through the CACGTG Myc/Max binding site.

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Glycogen Synthase Kinase 3 Is an Insulin-Regulated C/EBPα Kinase

Molecular and Cellular Biology ◽

10.1128/mcb.19.12.8433 ◽

1999 ◽

Vol 19 (12) ◽

pp. 8433-8441 ◽

Cited By ~ 138

Author(s):

Sarah E. Ross ◽

Robin L. Erickson ◽

Nahid Hemati ◽

Ormond A. MacDougald

Keyword(s):

Conformational Changes ◽

Kinase Inhibitor ◽

Glycogen Synthase ◽

Glycogen Synthase Kinase ◽

Glycogen Synthase Kinase 3 ◽

Phosphatidylinositol 3 Kinase ◽

Pharmacological Agents ◽

Enhancer Binding Protein

ABSTRACT CCAAT/enhancer binding protein α (C/EBPα) is a transcription factor involved in creating and maintaining the adipocyte phenotype. We have shown previously that insulin stimulates dephosphorylation of C/EBPα in 3T3-L1 adipocytes. Studies to identify the insulin-sensitive sites of phosphorylation reveal that a C/EBPα peptide (amino acids H215 to K250) is phosphorylated on T222, T226, and S230 in vivo. The context of these phosphoamino acids implicates glycogen synthase kinase 3 (GSK3), whose activity is known to be repressed in response to insulin, as a potential kinase for phosphorylation of T222 and T226. Accordingly, GSK3 phosphorylates the predicted region of C/EBPα on threonine in vitro, and GSK3 uses C/EBPα as a substrate in vivo. In addition, the effect of pharmacological agents on GSK3 activity correlates with regulation of C/EBPα phosphorylation. Treatment of 3T3-L1 adipocytes with the phosphatidylinositol 3-kinase inhibitor wortmannin results in phosphorylation of C/EBPα, whereas treatment with the GSK3 inhibitor lithium results in dephosphorylation of C/EBPα. Collectively, these data indicate that insulin stimulates dephosphorylation of C/EBPα on T222 and T226 through inactivation of GSK3. Since dephosphorylation of C/EBPα in response to lithium is blocked by okadaic acid, strong candidates for the T222 and T226 phosphatase are protein phosphatases 1 and 2a. Treatment of adipocytes with insulin alters the protease accessibility of widespread sites within the N terminus of C/EBPα, consistent with phosphorylation causing profound conformational changes. Finally, phosphorylation of C/EBPα and other substrates by GSK3 may be required for adipogenesis, since treatment of differentiating preadipocytes with lithium inhibits their conversion to adipocytes.

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Glycogen Synthase Kinase 3-Dependent Phosphorylation of Mdm2 Regulates p53 Abundance

Molecular and Cellular Biology ◽

10.1128/mcb.25.16.7170-7180.2005 ◽

2005 ◽

Vol 25 (16) ◽

pp. 7170-7180 ◽

Cited By ~ 84

Author(s):

Roman Kulikov ◽

Karen A. Boehme ◽

Christine Blattner

Keyword(s):

Glycogen Synthase ◽

Glycogen Synthase Kinase ◽

Tumor Suppressor Protein ◽

Glycogen Synthase Kinase 3 ◽

Dependent Manner ◽

Mdm2 Protein ◽

Conserved Domain ◽

P53 Tumor Suppressor Protein

ABSTRACT The Mdm2 oncoprotein regulates abundance and activity of the p53 tumor suppressor protein. For efficient degradation of p53, Mdm2 needs to be phosphorylated at several contiguous residues within the central conserved domain. We show that glycogen synthase kinase 3 (GSK-3) phosphorylated the Mdm2 protein in vitro and in vivo in the central domain. Inhibition of GSK-3 rescued p53 from degradation in an Mdm2-dependent manner while its association with Mdm2 was not affected. Likewise, inhibition of GSK-3 did not alter localization of p53 and Mdm2 or the interaction of Mdm2 and MdmX. Ionizing radiation, which leads to p53 accumulation, directed phosphorylation of GSK-3 at serine 9, which preceded and overlapped with the increase in p53 levels. Moreover, expression of a GSK-3 mutant where serine 9 was replaced with an alanine reduced the accumulation of p53 and induction of its target p21WAF-1. We therefore conclude that inhibition of GSK-3 contributes to hypophosphorylation of Mdm2 in response to ionizing rays, and in consequence to p53 stabilization.

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Schizosaccharomyces pombe skp1+ encodes a protein kinase related to mammalian glycogen synthase kinase 3 and complements a cdc14 cytokinesis mutant.

Molecular and Cellular Biology ◽

10.1128/mcb.16.1.179 ◽

1996 ◽

Vol 16 (1) ◽

pp. 179-191 ◽

Cited By ~ 33

Author(s):

S E Plyte ◽

A Feoktistova ◽

J D Burke ◽

J R Woodgett ◽

K L Gould

Keyword(s):

Schizosaccharomyces Pombe ◽

Cell Fate ◽

Hormonal Regulation ◽

Glycogen Synthase ◽

Phosphorylation Site ◽

Biochemical Properties ◽

Yeast Cells ◽

Glycogen Synthase Kinase ◽

Glycogen Synthase Kinase 3

We report the cloning of the skp1+ gene, a Schizosaccharomyces pombe homolog of the glycogen synthase kinase 3 (GSK-3) family whose members in higher eukaryotes are involved in cell fate determination, nuclear signalling, and hormonal regulation. skp1 is 67% identical to mammalian GSK-3 beta and displays similar biochemical properties in vitro. Like GSK-3 beta, skp1 is phosphorylated on a conserved tyrosine residue, and this phosphorylation is required for efficient activity. skp1 is also phosphorylated at a serine which has been identified as S-335. Phosphorylation at this site is likely to inhibit its function. Unlike the mammalian enzyme, skp1 both tyrosine autophosphorylates in yeast cells and can phosphorylate other proteins on tyrosine in bacteria. The skp1+ gene is not essential. However, cells with deletions in skp1+ are sensitive to heat shock and exhibit defects in sporulation. Overexpression of wild-type skp1+ specifically complements cdc14-118, one of several mutations causing a defect in cytokinesis. In addition, certain phosphorylation site mutants induce a delay or block in cytokinesis when overexpressed. Together, these data identify novel interactions of a fission yeast GSK-3 homolog with elements of the cytokinesis machinery.

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