Protein Targeting to Glycogen Overexpression Results in the Specific Enhancement of Glycogen Storage in 3T3-L1 Adipocytes

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ID: 266033
2003
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Abstract
Protein phosphatase-1 (PP1) plays an important role in the regulation of glycogen synthesis by insulin. Protein targeting to glycogen (PTG) enhances glycogen accumulation by increasing PP1 activity against glycogen-metabolizing enzymes. However, the specificity of PTG's effects on cellular dephosphorylation and glucose metabolism is unclear. Overexpression of PTG in 3T3-L1 adipocytes using a doxycycline-controllable adenoviral construct resulted in a 10–20-fold increase in PTG levels and an 8-fold increase in glycogen levels. Inclusion of 1 μg/ml doxycycline in the media suppressed PTG expression, and fully reversed all PTG-dependent effects. Infection of 3T3-L1 adipocytes with the PTG adenovirus caused a marked dephosphorylation and activation of glycogen synthase. The effects of PTG seemed specific, because basal and insulin-stimulated phosphorylation of a variety of signaling proteins was unaffected. Indeed, glycogen synthase was the predominant protein whose phosphorylation state was decreased in 32P-labeled cells. PTG overexpression did not alter PP1 protein levels but increased PP1 activity 6-fold against phosphorylase in vitro. In contrast, there was no change in PP1 activity measured using myelin basic protein, suggesting that PTG overexpression specifically directed PP1 activity against glycogen-metabolizing enzymes. To investigate the metabolic consequences of altering PTG levels, glucose uptake and storage in 3T3-L1 adipocytes was measured. PTG overexpression did not affect 2-deoxy-glucose transport rates in basal and insulin-stimulated cells but dramatically enhanced glycogen synthesis rates under both conditions. Despite the large increases in cellular glucose flux upon PTG overexpression, basal and insulin-stimulated glucose incorporation into lipid were unchanged. Cumulatively, these data indicate that PTG overexpression in 3T3-L1 adipocytes discretely stimulates PP1 activity against glycogen synthase and phosphorylase, resulting in a marked and specific increase in glucose uptake and storage as glycogen.
Reference Key
brady2003journalprotein Use this key to autocite in the manuscript while using SciMatic Manuscript Manager or Thesis Manager
Authors Cynthia C. Greenberg,Kimberly N. Meredith,Limei Yan,Matthew J. Brady;Cynthia C. Greenberg;Kimberly N. Meredith;Limei Yan;Matthew J. Brady;
Journal journal of biological chemistry
Year 2003
DOI
10.1074/jbc.m303846200
URL
https://sciprofiles.com/publication/view/5908da3f77c7161f18b1b61e050aebca
Keywords
protein insulin phosphorylation glycogen synthesis storage in 3t3 l1 enhances glycogen ptg overexpression

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