The Akt protein kinase, also known as protein kinase B, plays key roles in insulin receptor signalling and regulates cell growth, survival and metabolism. Recently, we described a mechanism to enhance Akt phosphorylation that restricts access of cellular phosphatases to the Akt activation loop (Thr308 in Akt1 or protein kinase B isoform alpha) in an ATP-dependent manner. In the present paper, we describe a distinct mechanism to control Thr308 dephosphorylation and thus Akt deactivation that depends on intramolecular interactions of Akt C-terminal sequences with its kinase domain. Modifications of amino acids surrounding the Akt1 C-terminal mTORC2 (mammalian target of rapamycin complex 2) phosphorylation site (Ser473) increased phosphatase resistance of the phosphorylated activation loop (pThr308) and amplified Akt phosphorylation. Furthermore, the phosphatase-resistant Akt was refractory to ceramide-dependent dephosphorylation and amplified insulin-dependent Thr308 phosphorylation in a regulated fashion. Collectively, these results suggest that the Akt C-terminal hydrophobic groove is a target for the development of agents that enhance Akt phosphorylation by insulin.
Akt kinase C-terminal modifications control activation loop dephosphorylation and enhance insulin response
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Tung O. Chan, Jin Zhang, Brian C. Tiegs, Brian Blumhof, Linda Yan, Nikhil Keny, Morgan Penny, Xue Li, John M. Pascal, Roger S. Armen, Ulrich Rodeck, Raymond B. Penn; Akt kinase C-terminal modifications control activation loop dephosphorylation and enhance insulin response. Biochem J 1 October 2015; 471 (1): 37–51. doi: https://doi.org/10.1042/BJ20150325
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