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      What Are the bona fide GSK3 Substrates?

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      International Journal of Alzheimer's Disease
      SAGE-Hindawi Access to Research

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          Abstract

          Nearly 100 proteins are proposed to be substrates for GSK3, suggesting that this enzyme is a fundamental regulator of almost every process in the cell, in every tissue in the body. However, it is not certain how many of these proposed substrates are regulated by GSK3 in vivo. Clearly, the identification of the physiological functions of GSK3 will be greatly aided by the identification of its bona fide substrates, and the development of GSK3 as a therapeutic target will be highly influenced by this range of actions, hence the need to accurately establish true GSK3 substrates in cells. In this paper the evidence that proposed GSK3 substrates are likely to be physiological targets is assessed, highlighting the key cellular processes that could be modulated by GSK3 activity and inhibition.

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          Most cited references240

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          Inhibition of glycogen synthase kinase-3 by insulin mediated by protein kinase B.

          Glycogen synthase kinase-3 (GSK3) is implicated in the regulation of several physiological processes, including the control of glycogen and protein synthesis by insulin, modulation of the transcription factors AP-1 and CREB, the specification of cell fate in Drosophila and dorsoventral patterning in Xenopus embryos. GSK3 is inhibited by serine phosphorylation in response to insulin or growth factors and in vitro by either MAP kinase-activated protein (MAPKAP) kinase-1 (also known as p90rsk) or p70 ribosomal S6 kinase (p70S6k). Here we show, however, that agents which prevent the activation of both MAPKAP kinase-1 and p70S6k by insulin in vivo do not block the phosphorylation and inhibition of GSK3. Another insulin-stimulated protein kinase inactivates GSK3 under these conditions, and we demonstrate that it is the product of the proto-oncogene protein kinase B (PKB, also known as Akt/RAC). Like the inhibition of GSK3 (refs 10, 14), the activation of PKB is prevented by inhibitors of phosphatidylinositol (PI) 3-kinase.
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            TSC2 integrates Wnt and energy signals via a coordinated phosphorylation by AMPK and GSK3 to regulate cell growth.

            Mutation in the TSC2 tumor suppressor causes tuberous sclerosis complex, a disease characterized by hamartoma formation in multiple tissues. TSC2 inhibits cell growth by acting as a GTPase-activating protein toward Rheb, thereby inhibiting mTOR, a central controller of cell growth. Here, we show that Wnt activates mTOR via inhibiting GSK3 without involving beta-catenin-dependent transcription. GSK3 inhibits the mTOR pathway by phosphorylating TSC2 in a manner dependent on AMPK-priming phosphorylation. Inhibition of mTOR by rapamycin blocks Wnt-induced cell growth and tumor development, suggesting a potential therapeutic value of rapamycin for cancers with activated Wnt signaling. Our results show that, in addition to transcriptional activation, Wnt stimulates translation and cell growth by activating the TSC-mTOR pathway. Furthermore, the sequential phosphorylation of TSC2 by AMPK and GSK3 reveals a molecular mechanism of signal integration in cell growth regulation.
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              The glamour and gloom of glycogen synthase kinase-3.

              Glycogen synthase kinase-3 (GSK3) is now recognized as a key component of a surprisingly large number of cellular processes and diseases. Several mechanisms play a part in controlling the actions of GSK3, including phosphorylation, protein complex formation, and subcellular distribution. These are used to control and direct the far-reaching influences of GSK3 on cellular structure, growth, motility and apoptosis. Dysregulation of GSK3 is linked to several prevalent pathological conditions, such as diabetes and/or insulin resistance, and Alzheimer's disease. Therefore, much effort is currently directed towards understanding the functions and control of GSK3, and identifying methods capable of diminishing the deleterious impact of GSK3 in pathological conditions.
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                Author and article information

                Journal
                Int J Alzheimers Dis
                IJAD
                International Journal of Alzheimer's Disease
                SAGE-Hindawi Access to Research
                2090-0252
                2011
                18 May 2011
                : 2011
                : 505607
                Affiliations
                Biomedical Research Institute, University of Dundee, Dundee DD1 9SY, UK
                Author notes

                Academic Editor: Adam Cole

                Article
                10.4061/2011/505607
                3100594
                21629754
                b7504ee9-5c6a-4757-8803-656b2f6f87c2
                Copyright © 2011 Calum Sutherland.

                This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

                History
                : 9 February 2011
                : 9 March 2011
                Categories
                Review Article

                Neurology
                Neurology

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