p38-Dependent Phosphorylation of the mRNA Decay-Promoting Factor KSRP Controls the Stability of Select Myogenic Transcripts

Abstract

Transcriptional and posttranscriptional processes regulate expression of genetic networks in response to environmental cues. The extracellular signal-activated p38 MAP kinase (p38) pathway plays a fundamental role in conversion of myoblasts to differentiated myocytes. p38 phosphorylates specific transcription factors and chromatin-associated proteins promoting assembly of the myogenic transcriptome. Here, we demonstrate that p38 alpha and beta isoforms also control muscle-gene expression posttranscriptionally, by stabilizing critical myogenic transcripts. KSRP, an important factor for AU-rich element (ARE)-directed mRNA decay, undergoes p38-dependent phosphorylation during muscle differentiation. KSRP phosphorylated by p38 displays compromised binding to ARE-containing transcripts and fails to promote their rapid decay, although it retains the ability to interact with the mRNA degradation machinery. Overexpression of KSRP selectively impairs induction of ARE-containing early myogenic transcripts, without affecting p38-mediated transcriptional responses. Our results uncover an unanticipated role for KSRP in establishing a biochemical link between differentiation-activated p38 signaling and turnover of myogenic mRNAs.

PI3K/AKT signaling determines a dynamic switch between distinct KSRP functions favoring skeletal myogenesis

“…, lanes 9-12), respectively. Internally 32 P-labeled, pri-miR-206 RNA substrate was added and its processing monitored as described by Briata et al 8 Statistical significance: **Po0.01 (Student's t-test) PI3K/AKT inhibits KSRP ability to promote decay of myogenin mRNA while promotes its recruitment to myogenic miRNA processing complexes. We and others have shown that stabilization of inherently labile muscle specific transcripts takes place during C2C12 cell differentiation.…”

“…We and others have shown that stabilization of inherently labile muscle specific transcripts takes place during C2C12 cell differentiation. [6][7][8] Myogenin and p21 mRNAs are unstable in C2C12 myoblasts cultured in GM and KSRP is required for their decay while MAPK p38-induced inactivation of KSRP (which occurs in differentiating myoblasts) contributes to myogenin and p21 induction. 8 Figure 5a and Supplementary Figure S6a show that AKT increased the half life of myogenin and p21 mRNAs when activated in C2C12 myoblasts cultured in GM.…”

“…4 In the recent few years, extensive analysis of the composition of the transcriptome assembled on the chromatin of myogenic loci has been performed (reviewed in Guasconi and Puri 5 ), although knowledge on the mechanisms that post-transcriptionally regulate muscle differentiation and regeneration is more limited. [6][7][8][9] Recently, genetic, and biological evidence of an essential role of microRNAs (miRNAs) in muscle development and function has been accumulating and a group of miRNAs, highly enriched in skeletal muscle (referred to as myomiRs), has been identified (reviewed in Williams et al, 10 and Gü ller and Russell 11 ). MyomiRs influence multiple aspects of muscle development and function through their regulation of key genes controlling myogenesis.…”

“…26 KSRP distinct functions are regulated by different protein kinases, including MAPK p38, PI3K/AKT and ATM. 8,29,30 An unresolved issue is whether a specific signaling pathway regulates only a single KSRP function (i.e. affecting either mRNA decay or miRNA maturation) or is able to induce a dynamic change between KSRP functions in order to produce relevant phenotypes in a specific cellular context.…”

p38α MAPK Regulates Adult Muscle Stem Cell Fate by Restricting Progenitor Proliferation During Postnatal Growth and Repair

“…The function of p38 during myogenesis is complex, with activation of p38 during the myogenic process recruiting the SWI-SNF chromatin remodeling complexes to specific myogenic loci [19] as well as modifying gene expression posttranscriptionally via p38-mediated regulation of myogenic mRNA stability [20]. p38 increases myogenic regulatory factor (MRF) activity via phosphorylation of MEF2 [21] and E proteins, promoting heterodimerization of MRFs such as MyoD with E47.…”