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

Abstract

BackgroundPPP1R6 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.ResultsPPP1R6 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.ConclusionsPPP1R6 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.

The dynamic life of the glycogen granule

“…Consistent with the above observations, training-induced increases in glycogen storage in rodents showed no significant correlation with GN protein levels or activity (46,47). Supporting the existence of coordinated mechanisms regulating the number and size of glycogen granules, Montori-Grau et al (48) showed that the overexpression of different protein phosphatase 1 (PP1) glycogen targeting subunits in cultured myotubes resulted in distinct alterations in both granule numbers and size. Overexpression of any of the targeting subunits resulted in Table 2 Primary THEMATIC MINIREVIEW: Dynamic life of the glycogen granule more granules: overexpression of PPP1R6 led to smaller average granule size (ϳ14 nm), but overexpression of PPP1R3C/ PTG increased the average granule size (to ϳ37 nm), resulting in 1.4-and 12-fold increases in glycogen content, respectively.…”

The endogenous molecular clock orchestrates the temporal separation of substrate metabolism in skeletal muscle

“…Glycogenesis is regulated by both glucose-6P concentrations and the enzymatic activity of glycogen synthase [ 111 , 112 ]. The gene Ppp1r3c (CT 20.0) reaches peak expression around the mid-inactive phase and encodes a regulatory subunit of the protein phosphatase-1 (PP-1) responsible for activating glycogen synthase while also inhibiting glycogen breakdown (Figure 3 ) [ 113 ]. Enzymatic activity of PP-1, and subsequent activation of glycogen synthase, is regulated downstream of the insulin signaling pathway [ 114 ].…”

Negatively charged AuNP modified with monoclonal antibody against novel tumor antigen FAT1 for tumor targeting

“…5c ). Glycogen granule (Gl), scattered in the cytoplasm, has similar morphological characteristics with Au nanoparticles except for larger size about 40 nm [ 36 ] in diameter. It should be strictly distinguished from Au nanoparticles.…”