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Akt-mediated phosphorylation controls the activity of the Y-box protein MSY3 in skeletal muscle.

De Angelis L, Balasubramanian S, Berghella L - Skelet Muscle (2015)

Bottom Line: This correlated well with the reduction of phosphorylated active Akt.Knocking down Akt expression increased the amount of dephosphorylated MSY3 and reduced myogenin expression and muscle differentiation.These results support the hypothesis that MSY3 phosphorylation by Akt interferes with MSY3 repression of myogenin circuit activity during muscle development.

View Article: PubMed Central - PubMed

Affiliation: DAHFMO, Unit of Histology and Medical Embryology, University La Sapienza, Via Scarpa 16, Rome, 00161 Italy.

ABSTRACT

Background: The Y-box protein MSY3/Csda represses myogenin transcription in skeletal muscle by binding a highly conserved cis-acting DNA element located just upstream of the myogenin minimal promoter (myogHCE). It is not known how this MSY3 activity is controlled in skeletal muscle. In this study, we provide multiple lines of evidence showing that the post-translational phosphorylation of MSY3 by Akt kinase modulates the MSY3 repression of myogenin.

Methods: Skeletal muscle and myogenic C2C12 cells were used to study the effects of MSY3 phosphorylation in vivo and in vitro on its sub-cellular localization and activity, by blocking the IGF1/PI3K/Akt pathway, by Akt depletion and over-expression, and by mutating potential MSY3 phosphorylation sites.

Results: We observed that, as skeletal muscle progressed from perinatal to postnatal and adult developmental stages, MSY3 protein became gradually dephosphorylated and accumulated in the nucleus. This correlated well with the reduction of phosphorylated active Akt. In C2C12 myogenic cells, blocking the IGF1/PI3K/Akt pathway using LY294002 inhibitor reduced MSY3 phosphorylation levels resulting in its accumulation in the nuclei. Knocking down Akt expression increased the amount of dephosphorylated MSY3 and reduced myogenin expression and muscle differentiation. MSY3 phosphorylation by Akt in vitro impaired its binding at the MyogHCE element, while blocking Akt increased MSY3 binding activity. While Akt over-expression rescued myogenin expression in MSY3 overexpressing myogenic cells, ablation of the Akt substrate, (Ser126 located in the MSY3 cold shock domain) promoted MSY3 accumulation in the nucleus and abolished this rescue. Furthermore, forced expression of Akt in adult skeletal muscle induced MSY3 phosphorylation and myogenin derepression.

Conclusions: These results support the hypothesis that MSY3 phosphorylation by Akt interferes with MSY3 repression of myogenin circuit activity during muscle development. This study highlights a previously undescribed Akt-mediated signaling pathway involved in the repression of myogenin expression in myogenic cells and in mature muscle. Given the significance of myogenin regulation in adult muscle, the Akt/MSY3/myogenin regulatory circuit is a potential therapeutic target to counteract muscle degenerative disease.

No MeSH data available.


Related in: MedlinePlus

Akt phosphorylates MSY3 in C2C12 cells, decreasing its binding activity and increasing myogenin expression. a Chromatin immunoprecipitation (ChIP) analysis for control IgG and MSY3 antibodies used individually to enrich fixed chromatin from undifferentiated (GM) or differentiated (DM) C2C12 cells, treated (+) or not (−) with LY2940002 (LY). qRT-PCR is used to quantify sequences from the myogenin promoter. b Measurements of endogenous myogenin expression by qRT-PCR in mock transfected C2C12 (−MSY3, −Akt) and MSY3 over-expressing C2C12 multiclones transfected (+MSY3, +Akt) or not (+MSY3, −Akt) with myristoylated Akt in proliferation medium (GM) or upon different times cultured in differentiation medium (24–72–96 h DM). GAPDH was used to normalize expression levels
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Fig5: Akt phosphorylates MSY3 in C2C12 cells, decreasing its binding activity and increasing myogenin expression. a Chromatin immunoprecipitation (ChIP) analysis for control IgG and MSY3 antibodies used individually to enrich fixed chromatin from undifferentiated (GM) or differentiated (DM) C2C12 cells, treated (+) or not (−) with LY2940002 (LY). qRT-PCR is used to quantify sequences from the myogenin promoter. b Measurements of endogenous myogenin expression by qRT-PCR in mock transfected C2C12 (−MSY3, −Akt) and MSY3 over-expressing C2C12 multiclones transfected (+MSY3, +Akt) or not (+MSY3, −Akt) with myristoylated Akt in proliferation medium (GM) or upon different times cultured in differentiation medium (24–72–96 h DM). GAPDH was used to normalize expression levels

Mentions: In order to further assess if Akt phosphorylation of MSY3 interferes with its binding of myogHCE in vivo, we performed chromatin immunoprecipitation (ChIP) on proliferating (GM) and differentiated C2C12 cells (DM) treated with the PI3K inhibitor LY, using the anti-MSY3 Ab ZONAB. ChIP on proliferating C2C12 myoblasts treated with LY showed a modest enrichment for MSY3 at the myogenin promoter compared to untreated myoblasts. In comparison, C2C12 myotubes treated with LY showed an increased enrichment when compared to their untreated counterparts (Fig. 5a). This evidence suggests that Akt inactivation results in increased levels of dephosphorylated MSY3, which in turn leads to increased MSY3 binding at the myogenin promoter region.Fig. 5


Akt-mediated phosphorylation controls the activity of the Y-box protein MSY3 in skeletal muscle.

De Angelis L, Balasubramanian S, Berghella L - Skelet Muscle (2015)

Akt phosphorylates MSY3 in C2C12 cells, decreasing its binding activity and increasing myogenin expression. a Chromatin immunoprecipitation (ChIP) analysis for control IgG and MSY3 antibodies used individually to enrich fixed chromatin from undifferentiated (GM) or differentiated (DM) C2C12 cells, treated (+) or not (−) with LY2940002 (LY). qRT-PCR is used to quantify sequences from the myogenin promoter. b Measurements of endogenous myogenin expression by qRT-PCR in mock transfected C2C12 (−MSY3, −Akt) and MSY3 over-expressing C2C12 multiclones transfected (+MSY3, +Akt) or not (+MSY3, −Akt) with myristoylated Akt in proliferation medium (GM) or upon different times cultured in differentiation medium (24–72–96 h DM). GAPDH was used to normalize expression levels
© Copyright Policy - open-access
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC4491233&req=5

Fig5: Akt phosphorylates MSY3 in C2C12 cells, decreasing its binding activity and increasing myogenin expression. a Chromatin immunoprecipitation (ChIP) analysis for control IgG and MSY3 antibodies used individually to enrich fixed chromatin from undifferentiated (GM) or differentiated (DM) C2C12 cells, treated (+) or not (−) with LY2940002 (LY). qRT-PCR is used to quantify sequences from the myogenin promoter. b Measurements of endogenous myogenin expression by qRT-PCR in mock transfected C2C12 (−MSY3, −Akt) and MSY3 over-expressing C2C12 multiclones transfected (+MSY3, +Akt) or not (+MSY3, −Akt) with myristoylated Akt in proliferation medium (GM) or upon different times cultured in differentiation medium (24–72–96 h DM). GAPDH was used to normalize expression levels
Mentions: In order to further assess if Akt phosphorylation of MSY3 interferes with its binding of myogHCE in vivo, we performed chromatin immunoprecipitation (ChIP) on proliferating (GM) and differentiated C2C12 cells (DM) treated with the PI3K inhibitor LY, using the anti-MSY3 Ab ZONAB. ChIP on proliferating C2C12 myoblasts treated with LY showed a modest enrichment for MSY3 at the myogenin promoter compared to untreated myoblasts. In comparison, C2C12 myotubes treated with LY showed an increased enrichment when compared to their untreated counterparts (Fig. 5a). This evidence suggests that Akt inactivation results in increased levels of dephosphorylated MSY3, which in turn leads to increased MSY3 binding at the myogenin promoter region.Fig. 5

Bottom Line: This correlated well with the reduction of phosphorylated active Akt.Knocking down Akt expression increased the amount of dephosphorylated MSY3 and reduced myogenin expression and muscle differentiation.These results support the hypothesis that MSY3 phosphorylation by Akt interferes with MSY3 repression of myogenin circuit activity during muscle development.

View Article: PubMed Central - PubMed

Affiliation: DAHFMO, Unit of Histology and Medical Embryology, University La Sapienza, Via Scarpa 16, Rome, 00161 Italy.

ABSTRACT

Background: The Y-box protein MSY3/Csda represses myogenin transcription in skeletal muscle by binding a highly conserved cis-acting DNA element located just upstream of the myogenin minimal promoter (myogHCE). It is not known how this MSY3 activity is controlled in skeletal muscle. In this study, we provide multiple lines of evidence showing that the post-translational phosphorylation of MSY3 by Akt kinase modulates the MSY3 repression of myogenin.

Methods: Skeletal muscle and myogenic C2C12 cells were used to study the effects of MSY3 phosphorylation in vivo and in vitro on its sub-cellular localization and activity, by blocking the IGF1/PI3K/Akt pathway, by Akt depletion and over-expression, and by mutating potential MSY3 phosphorylation sites.

Results: We observed that, as skeletal muscle progressed from perinatal to postnatal and adult developmental stages, MSY3 protein became gradually dephosphorylated and accumulated in the nucleus. This correlated well with the reduction of phosphorylated active Akt. In C2C12 myogenic cells, blocking the IGF1/PI3K/Akt pathway using LY294002 inhibitor reduced MSY3 phosphorylation levels resulting in its accumulation in the nuclei. Knocking down Akt expression increased the amount of dephosphorylated MSY3 and reduced myogenin expression and muscle differentiation. MSY3 phosphorylation by Akt in vitro impaired its binding at the MyogHCE element, while blocking Akt increased MSY3 binding activity. While Akt over-expression rescued myogenin expression in MSY3 overexpressing myogenic cells, ablation of the Akt substrate, (Ser126 located in the MSY3 cold shock domain) promoted MSY3 accumulation in the nucleus and abolished this rescue. Furthermore, forced expression of Akt in adult skeletal muscle induced MSY3 phosphorylation and myogenin derepression.

Conclusions: These results support the hypothesis that MSY3 phosphorylation by Akt interferes with MSY3 repression of myogenin circuit activity during muscle development. This study highlights a previously undescribed Akt-mediated signaling pathway involved in the repression of myogenin expression in myogenic cells and in mature muscle. Given the significance of myogenin regulation in adult muscle, the Akt/MSY3/myogenin regulatory circuit is a potential therapeutic target to counteract muscle degenerative disease.

No MeSH data available.


Related in: MedlinePlus