Smad7:β-catenin complex regulates myogenic gene transcription

FoxP1 Represses MEF2A in Striated Muscle

Myocyte enhancer factor 2 (MEF2) proteins are involved in multiple developmental, physiological, and pathological processes in vertebrates. Protein-protein interactions underlie the plethora of biological processes impacted by MEF2A, necessitating a detailed characterization of the MEF2A interactome. A nanobody based affinity-purification/mass spectrometry strategy was employed to achieve this goal. Specifically, the MEF2A protein complexes were captured from myogenic lysates using a GFP-tagged MEF2A protein immobilized with a GBP-nanobody followed by LC-MS/MS proteomic analysis to identify MEF2A interactors. After bioinformatic analysis, we further characterized the interaction of MEF2A with a transcriptional repressor, FOXP1. FOXP1 coprecipitated with MEF2A in proliferating myogenic cells which diminished upon differentiation (myotube formation). Ectopic expression of FOXP1 inhibited MEF2A driven myogenic reporter genes (derived from the creatine kinase muscle and myogenin genes) and delayed induction of endogenous myogenin during differentiation. Conversely, FOXP1 depletion enhanced MEF2A transactivation properties and myogenin expression. The FoxP1:MEF2A interaction is also preserved in cardiomyocytes and FoxP1 depletion enhanced cardiomyocyte hypertrophy. FOXP1 prevented MEF2A phosphorylation and activation by the p38MAPK pathway. Overall, these data implicate FOXP1 in restricting MEF2A function in order to avoid premature differentiation in myogenic progenitors and also to possibly prevent re-activation of embryonic gene expression in cardiomyocyte hypertrophy.

Dynamic chromatin architectures provide insights into the genetics of cattle myogenesis

BACKGROUND

Sharply increased beef consumption is propelling the genetic improvement projects of beef cattle in China. Three-dimensional genome structure is confirmed to be an important layer of transcription regulation. Although genome-wide interaction data of several livestock species have already been produced, the genome structure states and its regulatory rules in cattle muscle are still limited.

RESULTS

Here we present the first 3D genome data in Longissimus dorsi muscle of fetal and adult cattle (Bos taurus). We showed that compartments, topologically associating domains (TADs), and loop undergo re-organization and the structure dynamics were consistent with transcriptomic divergence during muscle development. Furthermore, we annotated cis-regulatory elements in cattle genome during myogenesis and demonstrated the enrichments of promoter and enhancer in selection sweeps. We further validated the regulatory function of one HMGA2 intronic enhancer near a strong sweep region on primary bovine myoblast proliferation.

CONCLUSIONS

Our data provide key insights of the regulatory function of high order chromatin structure and cattle myogenic biology, which will benefit the progress of genetic improvement of beef cattle.

TAZ exhibits phase separation properties and interacts with Smad7 and β-catenin to repress skeletal myogenesis

Hippo signaling in Drosophila and mammals is prominent in regulating cell proliferation, death and differentiation. Hippo signaling effectors (YAP/TAZ) exhibit crosstalk with transforming growth factor-β (TGF-β)-Smad and Wnt-β-catenin pathways. Previously, we implicated Smad7 and β-catenin in myogenesis. Therefore, we assessed a potential role of TAZ on theSmad7/β-catenin complex in muscle cells. Here, we document functional interactions between Smad7, TAZ and β-catenin in myogenic cells. Ectopic TAZ expression resulted in repression of the muscle-specific creatine kinase muscle (ckm) gene promoter and its corresponding protein level. Depletion of endogenous TAZ enhanced ckm promoter activation. Ectopic TAZ, while potently active on a TEAD reporter (HIP-HOP), repressed myogenin and myod enhancer regions and Myogenin protein level. Additionally, a Wnt/β-catenin readout (TOP flash) demonstrated TAZ inhibition of β-catenin activity. In myoblasts, TAZ is predominantly localized in nuclear speckles, while in differentiation conditions TAZ is hyperphosphorylated at Ser 89 leading to enhanced cytoplasmic sequestration. Finally, live cell imaging indicates that TAZ exhibits properties of liquid-liquid phase separation (LLPS). These observations indicate that TAZ, as an effector of Hippo signaling, supresses the myogenic differentiation machinery.

Temporal mechanisms of myogenic specification in human induced pluripotent stem cells

Understanding the mechanisms of myogenesis in human induced pluripotent stem cells (hiPSCs) is a prerequisite to achieving patient-specific therapy for diseases of skeletal muscle. hiPSCs of different origin show distinctive kinetics and ability to differentiate into myocytes. To address the unique cellular and temporal context of hiPSC differentiation, we perform a longitudinal comparison of the transcriptomic profiles of three hiPSC lines that display differential myogenic specification, one robust and two blunted. We detail temporal differences in mechanisms that lead to robust myogenic specification. We show gene expression signatures of putative cell subpopulations and extracellular matrix components that may support myogenesis. Furthermore, we show that targeted knockdown of ZIC3 at the outset of differentiation leads to improved myogenic specification in blunted hiPSC lines. Our study suggests that β-catenin transcriptional cofactors mediate cross-talk between multiple cellular processes and exogenous cues to facilitate specification of hiPSCs to mesoderm lineage, leading to robust myogenesis.

Potential roles of mediator Complex Subunit 13 in Cardiac Diseases

Mediator complex subunit 13 (MED13, previously known as THRAP1 and TRAP240) is a subunit of the cyclin-dependent kinase 8 (CDK8) kinase module in the eukaryotic mediator complex. MED13 has been known to play critical roles in cell cycle, development, and growth. The purpose of this review is to comprehensively discuss its newly identified potential roles in myocardial energy metabolism and non-metabolic cardiovascular diseases. Evidence indicates that cardiac MED13 mainly participates in the regulation of nuclear receptor signaling, which drives the transcription of genes involved in modulating cardiac and systemic energy homeostasis. MED13 is also associated with several pathological conditions, such as metabolic syndrome and thyroid disease-associated heart failure. Therefore, MED13 constitutes a potential therapeutic target for the regulation of metabolic disorders and other cardiovascular diseases.

Mediator's Kinase Module: A Modular Regulator of Cell Fate

Selective gene expression is crucial in maintaining the self-renewing and multipotent properties of stem cells. Mediator is a large, evolutionarily conserved, multi-subunit protein complex that modulates gene expression by relaying signals from cell type-specific transcription factors to RNA polymerase II. In humans, this complex consists of 30 subunits arranged in four modules. One critical module of the Mediator complex is the kinase module consisting of four subunits: MED12, MED13, CDK8, and CCNC. The kinase module exists in variable association with the 26-subunit Mediator core and affects transcription through phosphorylation of transcription factors and by controlling Mediator structure and function. Many studies have shown the kinase module to be a key player in the maintenance of stem cells that is distinct from a general role in transcription. Genetic studies have revealed that dysregulation of this kinase subunit contributes to the development of many human diseases. In this review, we discuss the importance of the Mediator kinase module by examining how this module functions with the more recently identified transcriptional super-enhancers, how changes in the kinase module and its activity can lead to the development of human disease, and the role of this unique module in directing and maintaining cell state. As we look to use stem cells to understand human development and treat human disease through both cell-based therapies and tissue engineering, we need to remain aware of the on-going research and address critical gaps in knowledge related to the molecular mechanisms that control cell fate.

Maintenance of the Undifferentiated State in Myogenic Progenitor Cells by TGFβ Signaling is Smad Independent and Requires MEK Activation

Transforming growth factor β (TGFβ) is a pluripotent cytokine and regulates a myriad of biological processes. It has been established that TGFβ potently inhibits skeletal muscle differentiation; however, the molecular mechanism is not clearly defined. Previously, we reported that inhibition of the TGFβ canonical pathway by an inhibitory Smad, Smad7, does not reverse this effect on differentiation, suggesting that activation of receptor Smads (R-Smads) by TGFβ is not responsible for repression of myogenesis. In addition, pharmacological blockade of Smad3 activation by TGFβ did not reverse TGFβ's inhibitory effect on myogenesis. In considering other pathways, we observed that TGFβ potently activates MEK/ERK, and a pharmacological inhibitor of MEK reversed TGFβ's inhibitory effect on myogenesis, as indicated by a myogenin promoter-reporter gene, sarcomeric myosin heavy chain accumulation, and phenotypic myotube formation. Furthermore, we found that c-Jun, a known potent repressor of myogenesis, which is coincidently also a down-stream target of MEK/ERK signaling, was phosphorylated and accumulates in the nucleus in response to TGFβ activation. Taken together, these observations support a model in which TGFβ activates a MEK/ERK/c-Jun pathway to repress skeletal myogenesis, maintaining the pluripotent undifferentiated state in myogenic progenitors.

UBE2M promotes cell proliferation via the β-catenin/cyclin D1 signaling in hepatocellular carcinoma

Upregulated ubiquitin-conjugating enzyme E2M (UBE2M) is associated with poor prognosis in malignancies; However, the phenotype and mechanism of action of UBE2M in hepatocellular carcinoma (HCC) remain elusive. Here, we report that UBE2M is overexpressed and correlated with poor prognosis in HCC patients. The UBE2M level is an independent prognostic factor for HCC patients. UBE2M knockdown inhibits HCC cell proliferation, migration, and invasion, whereas its overexpression has an opposite effect. Mechanistically, upregulated UBE2M exerts oncogenic effects by translocation of accumulated β-catenin from the cytoplasm to the nucleus, thus activating downstream β-catenin/cyclin D1 signaling. In summary, our study demonstrates a notable role of UBE2M in promoting the growth of HCC, providing a novel strategy for HCC prevention and treatment.

Patchouli Alcohol, a Compound from Pogostemon cablin, Inhibits Obesity

Obesity predisposes people to a variety of chronic metabolic diseases. Identification of natural factors that prevent the development of obesity is likely to be the most successful means of ameliorating the current obesity epidemic. Patchouli alcohol is a sesquiterpene alcohol found in Pogostemon cablin and possesses health benefit activities. This study was designed to examine if patchouli alcohol affects adipogenesis, and investigates the underlying mechanisms whereby patchouli alcohol exerts antiobesity effect. 3T3-L1 adipocytes were differentiated with treatment of different concentrations of patchouli alcohol. An in vivo study was performed to test the effect of patchouli alcohol gavage on a high-fat diet (HFD)-induced obesity. Treatment of patchouli alcohol reduced lipid accumulation in 3T3-L1 adipocytes in a dose-dependent manner without toxicity. Regarding mechanism, treatment of patchouli alcohol reduced expression of peroxisome proliferator-activated receptor-gamma (PPARγ) and CCAAT-enhancer-binding protein-alpha (C/EBPα) and increased expression of total and active β-catenin in 3T3-L1 adipocytes. Oral gavage of patchouli alcohol led to a significant reduction of body weight and fat accumulation in the mice fed with HFD. Transcriptome analysis indicates that smad7 is most highly activated gene in patchouli alcohol-treated 3T3-L1 cells. Patchouli alcohol possesses health benefit effect through inhibiting adipogenesis and fat tissue development.