Abstract
R5/PTG is one of the glycogen targeting subunits of type 1 protein phosphatase, a master regulator of glycogen synthesis. R5/PTG recruits the phosphatase to the places where glycogen synthesis occurs, allowing the activation of glycogen synthase and the inactivation of glycogen phosphorylase, thus increasing glycogen synthesis and decreasing its degradation. In this report, we show that the activity of R5/PTG is regulated by AMP-activated protein kinase (AMPK). We demonstrate that AMPK interacts physically with R5/PTG and modifies its basal phosphorylation status. We have also mapped the major phosphorylation sites of R5/PTG by mass spectrometry analysis, observing that phosphorylation of Ser-8 and Ser-268 increased upon activation of AMPK. We have recently described that the activity of R5/PTG is down-regulated by the laforin-malin complex, composed of a dual specificity phosphatase (laforin) and an E3-ubiquitin ligase (malin). We now demonstrate that phosphorylation of R5/PTG at Ser-8 by AMPK accelerates its laforin/malin-dependent ubiquitination and subsequent proteasomal degradation, which results in a decrease of its glycogenic activity. Thus, our results define a novel role of AMPK in glycogen homeostasis.
MeSH terms
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AMP-Activated Protein Kinases / genetics
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AMP-Activated Protein Kinases / metabolism*
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Animals
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CHO Cells
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Carrier Proteins / genetics
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Carrier Proteins / metabolism*
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Cricetinae
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Cricetulus
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Down-Regulation / physiology*
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Enzyme Activation / physiology
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Glycogen / genetics
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Glycogen / metabolism*
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Glycogen Phosphorylase / genetics
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Glycogen Phosphorylase / metabolism
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Glycogen Synthase / genetics
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Glycogen Synthase / metabolism
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Holoenzymes / genetics
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Holoenzymes / metabolism
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Humans
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Intracellular Signaling Peptides and Proteins
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Multienzyme Complexes / genetics
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Multienzyme Complexes / metabolism*
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Phosphoprotein Phosphatases / genetics
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Phosphoprotein Phosphatases / metabolism*
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Phosphorylation / physiology
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Proteasome Endopeptidase Complex / genetics
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Proteasome Endopeptidase Complex / metabolism
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Protein Tyrosine Phosphatases, Non-Receptor / genetics
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Protein Tyrosine Phosphatases, Non-Receptor / metabolism*
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Rabbits
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Ubiquitin-Protein Ligases / genetics
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Ubiquitin-Protein Ligases / metabolism*
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Ubiquitination / physiology
Substances
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Carrier Proteins
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Holoenzymes
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Intracellular Signaling Peptides and Proteins
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Multienzyme Complexes
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PPP1R3C protein, human
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Glycogen
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NHLRC1 protein, human
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Ubiquitin-Protein Ligases
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Glycogen Phosphorylase
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Glycogen Synthase
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AMP-Activated Protein Kinases
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Phosphoprotein Phosphatases
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Protein Tyrosine Phosphatases, Non-Receptor
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EPM2A protein, human
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Proteasome Endopeptidase Complex