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Logo of bmcbiocBioMed Centralsearchsubmit a manuscriptregisterthis articleBMC Biochemistry
 
BMC Biochem. 2011; 12: 57.
Published online Nov 4, 2011. doi:  10.1186/1471-2091-12-57
PMCID: PMC3240831
Differential pattern of glycogen accumulation after protein phosphatase 1 glycogen-targeting subunit PPP1R6 overexpression, compared to PPP1R3C and PPP1R3A, in skeletal muscle cells
Marta Montori-Grau,corresponding author1,2 Maria Guitart,1,2 Cèlia García-Martínez,1,3 Anna Orozco,1,2 and Anna Maria Gómez-Foix1,2
1CIBER de Diabetes y Enfermedades Metabólicas Asociadas (CIBERDEM) Pg de la Bonanova 69, 6a planta, 08017-Barcelona, Spain
2Departament de Bioquímica i Biologia Molecular, IBUB, Facultat de Biologia, Universitat de Barcelona, Diagonal 643, 08028-Barcelona, Spain
3Departament de Patologia i Terapèutica Experimental, Unitat organitzativa Bellvitge, Universitat de Barcelona, Pavelló de Govern, Pl. 5a, Feixa Llarga, S/N, 08907-Hospitalet de Llobregat, Spain
corresponding authorCorresponding author.
Marta Montori-Grau: mmontori/at/ub.edu; Maria Guitart: maguita022002/at/yahoo.es; Cèlia García-Martínez: celiagarcia/at/ub.edu; Anna Orozco: aorozco/at/ub.edu; Anna Maria Gómez-Foix: agomezfoix/at/ub.edu
Received March 25, 2011; Accepted November 4, 2011.
Abstract
Background
PPP1R6 is a protein phosphatase 1 glycogen-targeting subunit (PP1-GTS) abundant in skeletal muscle with an undefined metabolic control role. Here PPP1R6 effects on myotube glycogen metabolism, particle size and subcellular distribution are examined and compared with PPP1R3C/PTG and PPP1R3A/GM.
Results
PPP1R6 overexpression activates glycogen synthase (GS), reduces its phosphorylation at Ser-641/0 and increases the extracted and cytochemically-stained glycogen content, less than PTG but more than GM. PPP1R6 does not change glycogen phosphorylase activity. All tested PP1-GTS-cells have more glycogen particles than controls as found by electron microscopy of myotube sections. Glycogen particle size is distributed for all cell-types in a continuous range, but PPP1R6 forms smaller particles (mean diameter 14.4 nm) than PTG (36.9 nm) and GM (28.3 nm) or those in control cells (29.2 nm). Both PPP1R6- and GM-derived glycogen particles are in cytosol associated with cellular structures; PTG-derived glycogen is found in membrane- and organelle-devoid cytosolic glycogen-rich areas; and glycogen particles are dispersed in the cytosol in control cells. A tagged PPP1R6 protein at the C-terminus with EGFP shows a diffuse cytosol pattern in glucose-replete and -depleted cells and a punctuate pattern surrounding the nucleus in glucose-depleted cells, which colocates with RFP tagged with the Golgi targeting domain of β-1,4-galactosyltransferase, according to a computational prediction for PPP1R6 Golgi location.
Conclusions
PPP1R6 exerts a powerful glycogenic effect in cultured muscle cells, more than GM and less than PTG. PPP1R6 protein translocates from a Golgi to cytosolic location in response to glucose. The molecular size and subcellular location of myotube glycogen particles is determined by the PPP1R6, PTG and GM scaffolding.
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