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

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.

Structural basis of DNA binding to human YB-1 cold shock domain regulated by phosphorylation

“…On the other hand, it was also reported that acute stimulation of YB-1 phosphorylation does not promote YB-1 nuclear translocation ( 25 ) and both phosphorylated and non-phosphorylated YB-1 can be detected in the nucleus ( 53 ). Contrary to the reports that phosphorylation of YB-1 promotes its binding to DNA, the study on mouse MSY3 (YB-3) showed that phosphorylation decreases its binding to DNA ( 54 ). MYS3 is a close family member of YB-1.…”

mTORC1 and PKB/Akt control the muscle response to denervation by regulating autophagy and HDAC4

“…Upon denervation, AChRs are destabilized and their synthesis increases, resulting in a strong increase in their turnover rates 16–22 . In non-synaptic muscle regions, release of the repression of synaptic genes promotes ectopic AChR cluster formation 23–26 . HDAC4 induction and HDAC9 repression control the underlying epigenetic and transcriptional changes following denervation 26–28 .…”

Initiating aerobic exercise with low glycogen content reduces markers of myogenesis but not mTORC1 signaling

“…Given the differences in AKT between treatments, we hypothesize that lower phosphorylation of AKT in LOW facilitated lower myogenic regulatory factor expression compared to AD. AKT is an important upstream regulator of myogenesis [28,29]. Overexpression of AKT in C2C12 myoblasts induces myogenic differentiation by increasing myogenic regulator factor expression to simulate myotube formation, while inhibition of AKT decreases myogenesis [28][29][30].…”

“…AKT is an important upstream regulator of myogenesis [ 28 , 29 ]. Overexpression of AKT in C2C12 myoblasts induces myogenic differentiation by increasing myogenic regulator factor expression to simulate myotube formation, while inhibition of AKT decreases myogenesis [ 28 – 30 ]. In the current study, alterations in myogenesis via AKT were likely through downstream activation of GSK-3β [ 31 ].…”