Differential pattern of glycogen accumulation after protein phosphatase 1 glycogen-targeting subunit PPP1R6 overexpression, compared to PPP1R3C and PPP1R3A, in skeletal muscle cells

• Published in: BMC biochemistry Vol. 12; no. 1; p. 57
• Main Authors: Montori-Grau, Marta, Guitart, Maria, García-Martínez, Cèlia, Orozco, Anna, Gómez-Foix, Anna Maria
• Format: Journal Article
• Language: English
• Published: England BioMed Central Ltd 04-11-2011; BioMed Central
• Subjects: Adenoviruses; Animals; Aparell locomotor; Carrier Proteins - genetics; Carrier Proteins - metabolism; Cytosol - metabolism; Diabetes; Enzymes; ErbB Receptors - genetics; ErbB Receptors - metabolism; Expressió gènica; Fatty acids; Fetge; Gene expression; Gene Expression Regulation; Genetic aspects; Genetic regulation; Glicogen; Glycogen; Glycogen - biosynthesis; Glycogen - metabolism; Glycogen - ultrastructure; Glycogen Phosphorylase - metabolism; HEK293 Cells; Humans; Liver; Metabolic regulation; Metabolism; Metabolisme; Mice; Microfilament Proteins - genetics; Microfilament Proteins - metabolism; Muscle cells; Muscle Fibers, Skeletal - metabolism; Muscle Fibers, Skeletal - ultrastructure; Muscle, Skeletal - cytology; Muscle, Skeletal - ultrastructure; Muscular system; Musculoskeletal system; Nerve Tissue Proteins - genetics; Nerve Tissue Proteins - metabolism; Phosphatases; Phosphoprotein Phosphatases - genetics; Phosphoprotein Phosphatases - metabolism; Phosphorylation; Physiological aspects; Proteins; Regulació del metabolisme; Regulació genètica; Rodents; Signal Transduction; Àcids grassos; Spain
• ISSN: 1471-2091; 1471-2237; 1471-2091
• DOI: 10.1186/1471-2091-12-57

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/G(M).
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 G(M). 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 G(M) (28.3 nm) or those in control cells (29.2 nm). Both PPP1R6- and G(M)-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.
PPP1R6 exerts a powerful glycogenic effect in cultured muscle cells, more than G(M) 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 G(M) scaffolding.