Project description:HuR promotes myogenesis by stabilizing MyoD, Myogenin and p21 mRNAs during the fusion step of muscle cells to form myotubes. Here we show that HuR, via a novel mRNA destabilizing activity, promotes the early steps of myogenesis by reducing the expression of the cell cycle promoter nucleophosmin (NPM). Depletion of HuR stabilizes the NPM mRNA, increases NPM protein levels and inhibits myogenesis, while its overexpression elicits the opposite effects. NPM mRNA destabilization involves the association of HuR with the decay factor KSRP as well as the ribonuclease PARN and the exosome complex. The C-terminus of HuR mediates the formation of the HuR-KSRP complex and is sufficient for maintaining a low level of the NPM mRNA as well as promoting the commitment of muscle cells to myogenesis. We therefore propose a model whereby the downregulation of the NPM mRNA, mediated by the HuR/KSRP complex and its associated ribonucleases, is required for proper myogenesis. RNA was extracted from C2C12 treated with siRNA against HuR and compared to control siRNA
Project description:HuR promotes myogenesis by stabilizing MyoD, Myogenin and p21 mRNAs during the fusion step of muscle cells to form myotubes. Here we show that HuR, via a novel mRNA destabilizing activity, promotes the early steps of myogenesis by reducing the expression of the cell cycle promoter nucleophosmin (NPM). Depletion of HuR stabilizes the NPM mRNA, increases NPM protein levels and inhibits myogenesis, while its overexpression elicits the opposite effects. NPM mRNA destabilization involves the association of HuR with the decay factor KSRP as well as the ribonuclease PARN and the exosome complex. The C-terminus of HuR mediates the formation of the HuR-KSRP complex and is sufficient for maintaining a low level of the NPM mRNA as well as promoting the commitment of muscle cells to myogenesis. We therefore propose a model whereby the downregulation of the NPM mRNA, mediated by the HuR/KSRP complex and its associated ribonucleases, is required for proper myogenesis.
Project description:Here we show that, when compared to control mice, muscle specific HuR knockout (muHuR-KO) animals have higher exercise endurance that is associated with a significant increase in oxygen consumption and carbon dioxide production. Histological analysis demonstrates that the absence of HuR significantly enhances the proportion of oxidative type I fibers in several skeletal muscles, showing that under normal conditions, HuR promotes the formation of glycolytic type II fibers. HuR mediates this outcome by collaborating with the mRNA decay factor KSRP, to destabilize the PGC-1α mRNA, a well-known promoter of type I fiber formation. Furthermore, the type I fiber-enriched phenotype of muHuR-KO mice is associated with a protection against cancer cachexia-induced muscle wasting
Project description:Poly(ADP-ribosylation)(PARylation)is apost-translational modification mediated by asubset of ADP-ribosyl transferases (ARTs). Although PARylation-inhibition based therapies areconsidered as an avenue to combat debilitating diseases such as cancerand myopathies, the roleof thismodificationinphysiological processes such ascell differentiation remainsunclear. Here we showthat Tankyrase1 (TNKS1), aPARylating ART, plays a major role in myogenesis, a vital process known to drivemuscle fiber formation and regeneration.Althoughallbona fidePARPs are expressed in muscle cells, experiments using siRNA-mediated knockdownor pharmacological inhibitionshow thatTKNS1 is the enzyme responsible ofcatalyzing PARylation during myogenesis. Via this activity,TKNS1controlsthe turnoverof mRNAs encoding myogenic regulatory factors such as nucleophosmin(NPM) and myogenin.TKNS1 mediates these effectsby targeting RNA-binding proteinssuch as Human Antigen R (HuR). HuR harbors a conserved TNKS-binding motif (TBM), the mutation of which not only prevents theassociation of HuR with TKNS1 anditsPARylation, but also precludes HuR from regulating the turnover of NPMand myogeninmRNAsas well as from promoting myogenesis. Therefore, our data uncovera new role forTNKS1as akeymodulator of RBP-mediated post transcriptionaleventsrequired for vitalprocesses suchasmyogenesis.
Project description:Upon muscle injury the high mobility group box 1 (HMGB1) protein is up-regulated and secreted to initiate reparative responses. Here we show that HMGB1 controls myogenesis both in vitro and in vivo, during development and after adult muscle injury. HMGB1 expression in muscle cells is regulated at the translational level: the miRNA miR-1192 inhibits HMGB1 translation and the RNA-binding protein HuR promotes it. HuR binds to a cis-element, HuRBS, located in the 3'UTR of the HMGB1 transcript, and at the same time miR-1192 is recruited to an adjacent seed element. The binding of HuR to the HuRBS prevents the recruitment of Argonaute 2 (Ago2), overriding miR-1192-mediated translation inhibition. Depleting HuR reduces myoblast fusion and silencing miR-1192 re-establishes the fusion potential of HuR-depleted cells. We propose that HuR promotes the commitment of myoblasts to myogenesis by enhancing the translation of HMGB1 and suppressing the translation inhibition mediated by miR-1192. RNA content was extracted following immunoprecipitation of HuR using a monoclonal antibody (3A2) and the levels of mRNA were compared to an IgG control in order to determine which transcripts were enriched in the HuR ribonucleoprotein complex.
Project description:Upon muscle injury the high mobility group box 1 (HMGB1) protein is up-regulated and secreted to initiate reparative responses. Here we show that HMGB1 controls myogenesis both in vitro and in vivo, during development and after adult muscle injury. HMGB1 expression in muscle cells is regulated at the translational level: the miRNA miR-1192 inhibits HMGB1 translation and the RNA-binding protein HuR promotes it. HuR binds to a cis-element, HuRBS, located in the 3'UTR of the HMGB1 transcript, and at the same time miR-1192 is recruited to an adjacent seed element. The binding of HuR to the HuRBS prevents the recruitment of Argonaute 2 (Ago2), overriding miR-1192-mediated translation inhibition. Depleting HuR reduces myoblast fusion and silencing miR-1192 re-establishes the fusion potential of HuR-depleted cells. We propose that HuR promotes the commitment of myoblasts to myogenesis by enhancing the translation of HMGB1 and suppressing the translation inhibition mediated by miR-1192. RNA content was extracted following immunoprecipitation of HuR using a monoclonal antibody (3A2) and the levels of mRNA were compared to an IgG control in order to determine which transcripts were enriched in the HuR ribonucleoprotein complex.
Project description:Precise control of mRNA decay is fundamental for robust yet not exaggerated inflammatory responses to pathogens. Parameters determining the specificity and extent of mRNA degradation within the entire inflammation-associated transcriptome remain incompletely understood. Using transcriptome-wide high resolution occupancy assessment of the mRNA-destabilizing protein TTP, a major inflammation-limiting factor, we qualitatively and quantitatively characterize TTP binding positions and functionally relate them to TTP-dependent mRNA decay in immunostimulated macrophages. We identify pervasive TTP binding with incompletely penetrant linkage to mRNA destabilization. A necessary but not sufficient feature of TTP-mediated mRNA destabilization is binding to 3â untranslated regions (UTRs). Mapping of binding positions of the mRNA-stabilizing protein HuR in activated macrophages revealed that TTP and HuR binding sites in 3â UTRs occur mostly in different transcripts implicating only a limited co-regulation of inflammatory mRNAs by these proteins. Remarkably, we identify robust and widespread TTP binding to introns of stable transcripts. Nuclear TTP is associated with spliced-out introns and maintained in the nucleus throughout the inflammatory response. Our study establishes a functional annotation of binding positions dictating TTP-dependent mRNA decay in immunostimulated macrophages. The findings allow navigating the transcriptome-wide landscape of RNA elements controlling inflammation. PAR-iCLIP for TTP (3 replicates) and for HuR (2 replicates)
Project description:Skeletal muscle atrophy is a serious and highly prevalent condition that remains poorly understood at the molecular level. Previous work found that skeletal muscle atrophy involves an increase in skeletal muscle Gadd45a expression, which is necessary and sufficient for skeletal muscle fiber atrophy. However, the direct mechanism by which Gadd45a promotes skeletal muscle atrophy was unknown. To address this question, we biochemically isolated skeletal muscle fiber proteins that associate with Gadd45a as it induces skeletal muscle atrophy in living mice. We found that Gadd45a interacts with multiple proteins in skeletal muscle fibers, including, most prominently, the MAP kinase kinase kinase MEKK4. Furthermore, by forming a complex with MEKK4 in skeletal muscle fibers, Gadd45a increases MEKK4 protein kinase activity, which is sufficient to induce skeletal muscle fiber atrophy and required for Gadd45a-mediated skeletal muscle fiber atrophy. Together, these results identify a direct biochemical mechanism by which Gadd45a induces skeletal muscle atrophy and provide new insight into way that skeletal muscle atrophy occurs at the molecular level.
Project description:KSRP knock-down and BMP2 treatment produce a largely overlapping reshape of the transcriptome in C2C12 cells. microRNAs (miRNAs) are essential regulators of development, physiology, and evolution with miRNA biogenesis being strictly controlled at multiple levels. Regulatory proteins, such as KH-type splicing regulatory protein (KSRP), modulate rates and timing of the enzymatic reactions responsible for maturation of select miRNAs from their primary transcripts in response to specific stimuli. Induction of myogenic miRNAs (myomiRs) is essential for muscle differentiation with KSRP phosphorylation being required to convey myogenic signals to enhanced myomiR maturation. Here we show that either KSRP silencing or Bone Morphogenetic Protein (BMP)2-signaling activation in mesenchimal C2C12 cells prevented myogenic differentiation while induced osteoblastic differentiation as revealed by the reshaping of the whole transcriptome analyzed by RNA deep-sequencing. The most striking feature common to both BMP2 signaling activation and KSRP silencing was a blockade of myomiR maturation. Our results demonstrate that phosphorylated SMAD proteins, the transducers of BMP signaling, associate with KSRP and block its interaction with primary-myomiRs. This, in turn, abrogates KSRP-dependent myomiR maturation with the knock-down of SMAD4, 5, and 9 being able to rescue KSRP function. SMAD-induced blockade of KSRP-dependent myomiR maturation, in parallel to the well known SMAD function on gene transcription, inhibits C2C12 cell differentiation into myofibers and contributes to orient cells towards osteoblast lineage. We propose that remodeling of co-regulatory complexes affecting primary-miRNA processing is a mechanism well suited to guide cell fate determination in eukaryotes. Total RNA was prepared from 1. untreated mock-transfected C2C12 cells; 2. BMP2-treated mock-transfected C2C12 cells; 3. untreated shKSRP-transfected C2C12 cells and analyzed by RNA-seq
Project description:KSRP is involved in RNA processing at multiple levels including alternative splicing, mRNA stability, mRNA localization and translation efficiency. Dysregulation KSRP can cause to hematological malignancies. However, the direct contribution of KSRP to myeloid lineage differentiation is poorly understood. KSRP, as a KH-type splicing regulatory protein, which interacts with single-stand AU-rich element containing mRNA and mediated mRNA decay, also serves as a component of Drosha and Dicer complexes and regulates the biogenesis of miRNAs. Whether KSRP mediated miRNAs maturation participated in myeloid lineage differentiation is unknown. Here, we analysis the miRNAs processing during over-expression KSRP in THP-1 cells by poly-A(riched) RNA-seq and miRNA-Seq. Our results suggest that KSRP regulate a class of miRNAs maturation and have a critical function in myeloid lineage differentiation.