ErbB3 binding protein-1 (Ebp1) controls proliferation and myogenic differentiation of muscle stem cells

The structure and function of multifunctional protein ErbB3 binding protein 1 (Ebp1) and its role in diseases

ErbB3-binding protein 1(Ebp1) has two isoforms, p42 Ebp1 and p48 Ebp1, both of which can regulate cell growth and differentiation. But these isoforms often have opposite effects, including contradictory roles in regulation of cell growth in different tissues and cells. P48 Ebp1 belongs to the full-length sequence, while conformational changes in the crystal structure of p42 Ebp1 reveals a lack of an α helix at the amino terminus. Due to the differences in the structures of these two isoforms, they have different binding partners and protein modifications. Ebp1 can function as both an oncogene and a tumor suppressor factor. However, the underlying mechanisms by which these two isoforms exert opposite functions are still not fully understood. In this review, we summarize the genes and the structures of protein of these two isoforms, protein modifications, binding partners and the association of different isoforms with diseases.

Using Xenopus to discover new candidate genes involved in BOR and other congenital hearing loss syndromes

Hearing in infants is essential for brain development, acquisition of verbal language skills, and development of social interactions. Therefore, it is important to diagnose hearing loss soon after birth so that interventions can be provided as early as possible. Most newborns in the United States are screened for hearing deficits and commercially available next-generation sequencing hearing loss panels often can identify the causative gene, which may also identify congenital defects in other organs. One of the most prevalent autosomal dominant congenital hearing loss syndromes is branchio-oto-renal syndrome (BOR), which also presents with defects in craniofacial structures and the kidney. Currently, mutations in three genes, SIX1, SIX5, and EYA1, are known to be causative in about half of the BOR patients that have been tested. To uncover new candidate genes that could be added to congenital hearing loss genetic screens, we have combined the power of Drosophila mutants and protein biochemical assays with the embryological advantages of Xenopus, a key aquatic animal model with a high level of genomic similarity to human, to identify potential Six1 transcriptional targets and interacting proteins that play a role during otic development. We review our transcriptomic, yeast 2-hybrid, and proteomic approaches that have revealed a large number of new candidates. We also discuss how we have begun to identify how Six1 and co-factors interact to direct developmental events necessary for normal otic development.

Proliferation-associated 2G4 P48 is stabilized by malignant T-cell amplified sequence 1 and promotes the proliferation of head and neck squamous cell carcinoma

Background/purpose

Proliferation-associated protein 2G4 (PA2G4) has alternative transcriptional and translational initiation. One dominant transcript ENST00000303305 could be translated into two protein isoforms (PA2G4-P42 and PA2G4-P48). In this study, we aimed to explore the effects of PA2G4-P42 and PA2G4-P48 on the proliferation of head and neck squamous cell carcinoma (HNSCC) and the mechanisms regulating PA2G4-P48 stability.

Materials and methods

HNSCC cell lines HSC2 and SCC25 with relatively low PA2G4 expression were used for in-vitro cell studies. PA2G4-P42 and PA2G4-P48 overexpression lentiviruses were generated. In vitro cell proliferation was assessed by CCK-8 and colony formation. In vivo tumor cell proliferation was assessed by HSC2 cell-derived xenograft tumors. Liquid chromatography-mass spectrometry (LC-MS)/MS and co-immunoprecipitation (co-IP) assays were applied to check PA2G4-P48 interacting partners. Cycloheximide (CHX) chase and ubiquitin-based co-IP assays were also performed.

Results

PA2G4-P48 was the dominant isoform, with substantially higher expression than PA2G4-P42 in HNSCC. PA2G4-P48 overexpression enhanced HNSCC cell proliferation, but PA2G4-P42 overexpression slowed the proliferation. MCTS1 interacted with PA2G4-P48, but not PA2G4-P42. PA2G4 protein but not its mRNA expression was decreased in cells with MCTS1 knockdown. MG132 treatment abrogated this alteration. MCTS1 overexpression significantly elevated the half-life of PA2G4-P48, while its knockdown drastically reduced the half-life compared with the control cells. In addition, MCTS1 overexpression significantly decreased the polyubiquitination of exogenous flag-tagged PA2G4-P48. MCTS1 overexpression-induced cell proliferation was hampered by knocking down of PA2G4-P48.

Conclusion

PA2G4-P42 and PA2G4-P48 exert growth-suppressive and growth-promoting effects in HNSCC, respectively. MCTS1 can interact with PA2G4-P48 and prolong its half-life by reducing its poly-ubiquitination.

Urotensin II can Induce Skeletal Muscle Atrophy Associated with Upregulating Ubiquitin-Proteasome System and Inhibiting the Differentiation of Satellite Cells in CRF Mice

Skeletal muscle wasting and atrophy is highly prevalent in chronic renal failure (CRF) and increases the risk of mortality. According to our previous study, we speculate that urotensin II (UII) can induce skeletal muscle atrophy by upregulating ubiquitin-proteasome system(UPS) in CRF. C2C12 mouse myoblast cells were differentiated into myotubes, and myotubes were exposed to different concentrations of UII. Myotube diameters, myosin heavy chain(MHC), p-Fxo03A, skeletal muscle-specific E3 ubiquitin ligases such as muscle RING finger 1 (MuRF1) and muscle atrophy F-box (MAFbx/atrogin1) were detected. Three animal models (the sham operation mice as normal control (NC) group, wild-type C57BL/6 mice with 5/6 nephrectomy (WT CRF) group, UII receptor gene knock out (UT KO) mice with 5/6 nephrectomy (UT KO CRF) group) were designed. Cross-sectional area (CSA) of skeletal muscle tissues in three animal models were measured, and western blot detected protein of UII, p-Fxo03A, MAFbx and MuRF1, and immunofluorescence assays explored the satellite cell marker of Myod1 and Pax7, and PCR arrays detected the muscle protein degradation genes, protein synthesis genes and the genes which were involved in muscle components. UII could decrease mouse myotube diameters, and upregulate dephosphorylated Fxo03A protein. MAFbx and MuRF1 were higher in WT CRF group than that in NC group, but after UII receptor gene was knocked out (UT KO CRF), their expressions were downregulated. UII could inhibit the expression of Myod1 but not Pax7 in animal study. We first demonstrate that skeletal muscle atrophy induced by UII associated with upregulating ubiquitin-proteasome system and inhibiting the differentiation of satellite cells in CRF mice.

A Simplified and Effective Approach for the Isolation of Small Pluripotent Stem Cells Derived from Human Peripheral Blood

Pluripotent stem cells are key players in regenerative medicine. Embryonic pluripotent stem cells, despite their significant advantages, are associated with limitations such as their inadequate availability and the ethical dilemmas in their isolation and clinical use. The discovery of very small embryonic-like (VSEL) stem cells addressed the aforementioned limitations, but their isolation technique remains a challenge due to their small cell size and their efficiency in isolation. Here, we report a simplified and effective approach for the isolation of small pluripotent stem cells derived from human peripheral blood. Our approach results in a high yield of small blood stem cell (SBSC) population, which expresses pluripotent embryonic markers (e.g., Nanog, SSEA-3) and the Yamanaka factors. Further, a fraction of SBSCs also co-express hematopoietic markers (e.g., CD45 and CD90) and/or mesenchymal markers (e.g., CD29, CD105 and PTH1R), suggesting a mixed stem cell population. Finally, quantitative proteomic profiling reveals that SBSCs contain various stem cell markers (CD9, ITGA6, MAPK1, MTHFD1, STAT3, HSPB1, HSPA4), and Transcription reg complex factors (e.g., STAT5B, PDLIM1, ANXA2, ATF6, CAMK1). In conclusion, we present a novel, simplified and effective isolating process that yields an abundant population of small-sized cells with characteristics of pluripotency from human peripheral blood.

The emergence of the stem cell niche

Stem cell niches are composed of dynamic microenvironments that support stem cells over a lifetime. The emerging niche is distinct from the adult because its main role is to support the progenitors that build organ systems in development. Emerging niches mature through distinct stages to form the adult niche and enable proper stem cell support. As a model of emerging niches, this review highlights how differences in the skeletal muscle microenvironment influence emerging versus satellite cell (SC) niche formation in skeletal muscle, which is among the most regenerative tissue systems. We contrast how stem cell niches regulate intrinsic properties between progenitor and stem cells throughout development to adulthood. We describe new applications for generating emerging niches from human pluripotent stem cells (hPSCs) using developmental principles and highlight potential applications for regeneration and therapeutics.

Long Noncoding RNAs Involved in Cardiomyocyte Apoptosis Triggered by Different Stressors

Cardiomyocytes are essential to maintain the normal cardiac function. Ischemia, hypoxia, and drug stimulation can induce pathological apoptosis of cardiomyocytes which eventually leads to heart failure, arrhythmia, and other cardiovascular diseases. Understanding the molecular mechanisms that regulate cardiomyocyte apoptosis is of great significance for the prevention and treatment of cardiovascular diseases. In recent years, more and more evidences reveal that long noncoding RNAs (lncRNAs) play important regulatory roles in myocardial cell apoptosis. They can modulate the expression of apoptosis-related genes at post-transcriptional level by altering the translation efficacy of target mRNAs or functioning as a precursor for miRNAs or competing for miRNA-mediated inhibition. Moreover, reversing the abnormal expression of lncRNAs can attenuate and even reverse the pathological apoptosis of cardiomyocytes. Therefore, apoptosis-related lncRNAs may become a potential new field for studying cardiomyocyte apoptosis and provide new ideas for the treatment of cardiovascular diseases.

RNA-Binding Proteins in the Post-transcriptional Control of Skeletal Muscle Development, Regeneration and Disease

Embryonic myogenesis is a temporally and spatially regulated process that generates skeletal muscle of the trunk and limbs. During this process, mononucleated myoblasts derived from myogenic progenitor cells within the somites undergo proliferation, migration and differentiation to elongate and fuse into multinucleated functional myofibers. Skeletal muscle is the most abundant tissue of the body and has the remarkable ability to self-repair by re-activating the myogenic program in muscle stem cells, known as satellite cells. Post-transcriptional regulation of gene expression mediated by RNA-binding proteins is critically required for muscle development during embryogenesis and for muscle homeostasis in the adult. Differential subcellular localization and activity of RNA-binding proteins orchestrates target gene expression at multiple levels to regulate different steps of myogenesis. Dysfunctions of these post-transcriptional regulators impair muscle development and homeostasis, but also cause defects in motor neurons or the neuromuscular junction, resulting in muscle degeneration and neuromuscular disease. Many RNA-binding proteins, such as members of the muscle blind-like (MBNL) and CUG-BP and ETR-3-like factors (CELF) families, display both overlapping and distinct targets in muscle cells. Thus they function either cooperatively or antagonistically to coordinate myoblast proliferation and differentiation. Evidence is accumulating that the dynamic interplay of their regulatory activity may control the progression of myogenic program as well as stem cell quiescence and activation. Moreover, the role of RNA-binding proteins that regulate post-transcriptional modification in the myogenic program is far less understood as compared with transcription factors involved in myogenic specification and differentiation. Here we review past achievements and recent advances in understanding the functions of RNA-binding proteins during skeletal muscle development, regeneration and disease, with the aim to identify the fundamental questions that are still open for further investigations.

Temporal Proteomic Profiling During Differentiation of Normal and Dystrophin-Deficient Human Muscle Cells

BACKGROUND

Myogenesis is a dynamic process involving temporal changes in the expression of many genes. Lack of dystrophin protein such as in Duchenne muscular dystrophy might alter the natural course of gene expression dynamics during myogenesis.

OBJECTIVE

To gain insight into the dynamic temporal changes in protein expression during differentiation of normal and dystrophin deficient myoblasts to myotubes.

METHOD

A super SILAC spike-in strategy in combination and LC-MS/MS was used for temporal proteome profiling of normal and dystrophin deficient myoblasts during differentiation. The acquired data was analyzed using Proteome Discoverer 2.2. and data clustering using R to define significant temporal changes in protein expression.

RESULTS

sFour major temporal protein clusters that showed sequential dynamic expression profiles during myogenesis of normal myoblasts were identified. Clusters 1 and 2, consisting mainly of proteins involved mRNA splicing and processing expression, were elevated at days 0 and 0.5 of differentiation then gradually decreased by day 7 of differentiation, then remained lower thereafter. Cluster 3 consisted of proteins involved contractile muscle and actomyosin organization. They increased in their expression reaching maximum at day 7 of differentiation then stabilized thereafter. Cluster 4 consisting of proteins involved in skeletal muscle development glucogenesis and extracellular remodeling had a lower expression during myoblast stage then gradually increased in their expression to reach a maximum at days 11-15 of differentiation. Lack of dystrophin expression in DMD muscle myoblast caused major alteration in temporal expression of proteins involved in cell adhesion, cytoskeleton, and organelle organization as well as the ubiquitination machinery.

CONCLUSION

Time series proteome profiling using super SILAC strategy is a powerful method to assess temporal changes in protein expression during myogenesis and to define the downstream consequences of lack of dystrophin on these temporal protein expressions. Key alterations were identified in dystrophin deficient myoblast differentiation compared to normal myoblasts. These alterations could be an attractive therapeutic target.

Large-scale transcriptome sequencing in broiler chickens to identify candidate genes for breast muscle weight and intramuscular fat content

BACKGROUND

In broiler production, breast muscle weight and intramuscular fat (IMF) content are important economic traits. Understanding the genetic mechanisms that underlie these traits is essential to implement effective genetic improvement programs. To date, genome-wide association studies (GWAS) and gene expression analyses have been performed to identify candidate genes for these traits. However, GWAS mainly detect associations at the DNA level, while differential expression analyses usually have low power because they are typically based on small sample sizes. To detect candidate genes for breast muscle weight and IMF contents (intramuscular fat percentage and relative content of triglycerides, cholesterol, and phospholipids), we performed association analyses based on breast muscle transcriptomic data on approximately 400 Tiannong partridge chickens at slaughter age.

RESULTS

First, by performing an extensive simulation study, we evaluated the statistical properties of association analyses of gene expression levels and traits based on the linear mixed model (LMM) and three regularized linear regression models, i.e., least absolute shrinkage and selection operator (LASSO), ridge regression (RR), and elastic net (EN). The results show that LMM, LASSO and EN with tuning parameters that are determined based on the one standard error rule exhibited the lowest type I error rates. Using results from all three models, we detected 43 candidate genes with expression levels that were associated with breast muscle weight. In addition, candidate genes were detected for intramuscular fat percentage (1), triglyceride content (2), cholesterol content (1), and phospholipid content (1). Many of the identified genes have been demonstrated to play roles in the development and metabolism of skeletal muscle or adipocyte. Moreover, weighted gene co-expression network analyses revealed that many candidate genes were harbored by gene co-expression modules, which were also significantly correlated with the traits of interest. The results of Gene Ontology and Kyoto Encyclopedia of Genes and Genomes enrichment analyses indicated that these modules are involved in muscle development and contraction, and in lipid metabolism.

CONCLUSIONS

Our study provides valuable insight into the transcriptomic bases of breast muscle weight and IMF contents in Chinese indigenous yellow broilers. Our findings could be useful for the genetic improvement of these traits in broiler chickens.

LINC00987 knockdown inhibits the progression of acute myeloid leukemia by suppressing IGF2BP2-mediated PA2G4 expression

This study aimed to investigate the role and potential mechanisms of LINC00987 in acute myeloid leukemia (AML) progression. The expression of LINC00987 in bone marrow specimens of AML patients and cell lines was measured by quantitative reverse transcription PCR (RT-qPCR). Small interfering RNA targeting LINC00987 (si-LINC00987) was transfected into AML cell lines HL-60 and KG-1, and the proliferation, invasion and apoptosis were detected with Cell Counting Kit-8 (CCK-8), Transwell and flow cytometry, respectively. Moreover, the binding between LINC00987 and insulin like growth factor 2 mRNA binding protein 2 (IGF2BP2) was validated with an RNA pull-down assay. Co-immunoprecipitation assay was used to verify the binding between IGF2BP2 and proliferation-associated 2G4 (PA2G4). Then rescue experiments were performed to explore the effects of LINC00987/IGF2BP2/PA2G4 axis on HL-60 and KG-1 cell functions. Additionally, HL-60 cells transfected with si-LINC00987 were injected into mice, followed by the evaluation of xenograft tumor growth. LINC00987 was upregulated in AML patient specimens and cell lines. LINC00987 knockdown inhibited proliferation and invasion and promoted apoptosis in AML cells. LINC00987 could bind with IGF2BP2 and promote its expression, and IGF2BP2 overexpression reversed the effects of LINC00987 knockdown on the proliferation, invasion and apoptosis in AML cells. Besides, IGF2BP2 could bind with PA2G4. IGF2BP2 knockdown inhibited proliferation and invasion, and promoted apoptosis in AML cells, whereas PA2G4 overexpression reversed these effects. Additionally, the LINC00987 knockdown inhibited the xenograft tumor growth of AML in vivo. Knockdown of LINC00987 inhibits AML cell proliferation and invasion, and promotes apoptosis in vitro and reduces tumor growth in vivo by suppressing IGF2BP2-mediated PA2G4 expression.

The GpIA7 effector from the potato cyst nematode Globodera pallida targets potato EBP1 and interferes with the plant cell cycle programme

The potato cyst nematode Globodera pallida acquires all of its nutrients from an elaborate feeding site that it establishes in a host plant root. Normal development of the root cells is re-programmed in a process coordinated by secreted nematode effector proteins. The biological function of the G. pallida GpIA7 effector was investigated in this study. GpIA7 is specifically expressed in the subventral pharyngeal glands of pre-parasitic stage nematodes. Ectopic expression of GpIA7 in potato plants affected plant growth and development, suggesting a potential role for this effector in feeding site establishment. Potato plants overexpressing GpIA7 were shorter, with reduced tuber weight and delayed flowering. We provide evidence that GpIA7 associates with the plant growth regulator StEBP1 (ErbB-3 epidermal growth factor receptor-binding protein 1). GpIA7 modulates the regulatory function of StEBP1, altering the expression level of downstream target genes, including ribonucleotide reductase 2, cyclin D3;1 and retinoblastoma related 1, which are downregulated in plants overexpressing GpIA7. We provide an insight into the molecular mechanism used by the nematode to manipulate the host cell cycle and provide evidence that this may rely, at least in part, on hindering the function of host EBP1.

NRG/ErbB signaling regulates neonatal muscle growth but not neuromuscular contractures in neonatal brachial plexus injury

Neonatal brachial plexus injury (NBPI) causes disabling and incurable muscle contractures that are driven by impaired growth of denervated muscles. A rare form of NBPI, which maintains afferent muscle innervation despite motor denervation, does not cause contractures. As afferent innervation regulates various aspects of skeletal muscle homeostasis through NRG/ErbB signaling, our current study investigated the role of this pathway in modulating contracture development. Through pharmacologic modification with an ErbB antagonist and NRG1 isoforms, we discovered that NRG/ErbB signaling does not modulate the development of contractures in neonatal mice. Instead, ErbB inhibition impeded growth in nondenervated skeletal muscles, whereas increased ErbB activation exacerbated denervation-induced skeletal muscle atrophy. This potential regulatory effect of NRG/ErbB signaling on neonatal muscle growth warrants deeper investigation.

Macrophages provide a transient muscle stem cell niche via NAMPT secretion

Skeletal muscle regenerates through the activation of resident stem cells. Termed satellite cells, these normally quiescent cells are induced to proliferate by wound-derived signals¹. Identifying the source and nature of these cues has been hampered by an inability to visualize the complex cell interactions that occur within the wound. Here we use muscle injury models in zebrafish to systematically capture the interactions between satellite cells and the innate immune system after injury, in real time, throughout the repair process. This analysis revealed that a specific subset of macrophages 'dwell' within the injury, establishing a transient but obligate niche for stem cell proliferation. Single-cell profiling identified proliferative signals that are secreted by dwelling macrophages, which include the cytokine nicotinamide phosphoribosyltransferase (Nampt, which is also known as visfatin or PBEF in humans). Nampt secretion from the macrophage niche is required for muscle regeneration, acting through the C-C motif chemokine receptor type 5 (Ccr5), which is expressed on muscle stem cells. This analysis shows that in addition to their ability to modulate the immune response, specific macrophage populations also provide a transient stem-cell-activating niche, directly supplying proliferation-inducing cues that govern the repair process that is mediated by muscle stem cells. This study demonstrates that macrophage-derived niche signals for muscle stem cells, such as NAMPT, can be applied as new therapeutic modalities for skeletal muscle injury and disease.

A structural view of PA2G4 isoforms with opposing functions in cancer

The role of proliferation-associated protein 2G4 (PA2G4), alternatively known as ErbB3-binding protein 1 (EBP1), in cancer has become apparent over the past 20 years. PA2G4 expression levels are correlated with prognosis in a range of human cancers, including neuroblastoma, cervical, brain, breast, prostate, pancreatic, hepatocellular, and other tumors. There are two PA2G4 isoforms, PA2G4-p42 and PA2G4-p48, and although both isoforms of PA2G4 regulate cellular growth and differentiation, these isoforms often have opposing roles depending on the context. Therefore, PA2G4 can function either as a contextual tumor suppressor or as an oncogene, depending on the tissue being studied. However, it is unclear how distinct structural features of the two PA2G4 isoforms translate into different functional outcomes. In this review, we examine published structures to identify important structural and functional components of PA2G4 and consider how they may explain its crucial role in the malignant phenotype. We will highlight the lysine-rich regions, protein-protein interaction sites, and post-translational modifications of the two PA2G4 isoforms and relate these to the functional cellular role of PA2G4. These data will enable a better understanding of the function and structure relationship of the two PA2G4 isoforms and highlight the care that will need to be undertaken for those who wish to conduct isoform-specific structure-based drug design campaigns.

The roles of multifunctional protein ErbB3 binding protein 1 (EBP1) isoforms from development to disease

The roles of the two isoforms of ErbB3-binding protein 1 (Ebp1) in cellular function and its regulation in disease and development is a stimulating area in current fields of biology, such as neuroscience, cancer biology, and structural biology. Over the last two decades, a growing body of studies suggests have suggested different functions for the EBP1 isoforms in various cancers, along with their specific binding partners in the ubiquitin-proteasome system. Owing to the specific cellular context or spatial/temporal expression of the EBP1 isoforms, either transcriptional repression or the activation function of EBP1 has been proposed, and epigenetic regulation by p48 EBP1 has also been observed during in the embryo development, including in brain development and neurologic disorders, such as schizophrenia, in using an Ebp1 knockout mouse model. Here, we review recent findings that have shaped our current understanding of the emerging function of EBP1 isoforms in cellular events and gene expression, from development to disease.

A pair of proteins that originate from a common gene exert strikingly different effects on embryonic development as well as tumor growth and progression. RNA transcripts generated from the PA2G4 gene can undergo enzymatic processing to yield two different protein products, p42 EB1 and p48 EB1. These proteins differ by the presence or absence of 54 amino acids at one end, and Jee-Yin Ahn at the Sungkyunkwan University School of Medicine, Suwon, South Korea, and colleagues have reviewed current insights into the functional consequences of this difference. The two proteins bind to distinct sets of molecular partners. The p48 form appears to regulate a host of genes involved in brain development, but also appears to drive cancerous growth in various tumors. In contrast, p42 is scarcer during development, and appears to inhibit tumor formation.

In-depth proteome analysis of more than 12,500 proteins in buffalo mammary epithelial cell line identifies protein signatures for active proliferation and lactation

The mature mammary gland is made up of a network of ducts that terminates in alveoli. The innermost layer of alveoli is surrounded by the differentiated mammary epithelial cells (MECs), which are responsible for milk synthesis and secretion during lactation. However, the MECs are in a state of active proliferation during pregnancy, when they give rise to network like structures in the mammary gland. Buffalo (Bubalus bubalis) constitute a major source of milk for human consumption, and the MECs are the major precursor cells which are mainly responsible for their lactation potential. The proteome of MECs defines their functional state and suggests their role in various cellular activities such as proliferation and lactation. To date, the proteome profile of MECs from buffalo origin is not available. In the present study, we have profiled in-depth proteome of in vitro cultured buffalo MECs (BuMECs) during active proliferation using high throughput tandem mass spectrometry (MS). MS analysis identified a total of 8330, 5970, 5289, 4818 proteins in four sub-cellular fractions (SCFs) that included cytosolic (SCF-I), membranous and membranous organelle’s (SCF-II), nuclear (SCF-III), and cytoskeletal (SCF-IV). However, 792 proteins were identified in the conditioned media, which represented the secretome. Altogether, combined analysis of all the five fractions (SCFs- I to IV, and secretome) revealed a total of 12,609 non-redundant proteins. The KEGG analysis suggested that these proteins were associated with 325 molecular pathways. Some of the highly enriched molecular pathways observed were metabolic, MAPK, PI3-AKT, insulin, estrogen, and cGMP-PKG signalling pathway. The newly identified proteins in this study are reported to be involved in NOTCH signalling, transport and secretion processes.

DEPDC1B is a key regulator of myoblast proliferation in mouse and man

OBJECTIVES

DISHEVELLED, EGL-10, PLECKSTRIN (DEP) domain-containing 1B (DEPDC1B) promotes dismantling of focal adhesions and coordinates detachment events during cell cycle progression. DEPDC1B is overexpressed in several cancers with expression inversely correlated with patient survival. Here, we analysed the role of DEPDC1B in the regulation of murine and human skeletal myogenesis.

MATERIALS AND METHODS

Expression dynamics of DEPDC1B were examined in murine and human myoblasts and rhabdomyosarcoma cells in vitro by RT-qPCR and/or immunolabelling. DEPDC1B function was mainly tested via siRNA-mediated gene knockdown.

RESULTS

DEPDC1B was expressed in proliferating murine and human myoblasts, with expression then decreasing markedly during myogenic differentiation. SiRNA-mediated knockdown of DEPDC1B reduced myoblast proliferation and induced entry into myogenic differentiation, with deregulation of key cell cycle regulators (cyclins, CDK, CDKi). DEPDC1B and β-catenin co-knockdown was unable to rescue proliferation in myoblasts, suggesting that DEPDC1B functions independently of canonical WNT signalling during myogenesis. DEPDC1B can also suppress RHOA activity in some cell types, but DEPDC1B and RHOA co-knockdown actually had an additive effect by both further reducing proliferation and enhancing myogenic differentiation. DEPDC1B was expressed in human Rh30 rhabdomyosarcoma cells, where DEPDC1B or RHOA knockdown promoted myogenic differentiation, but without influencing proliferation.

CONCLUSION

DEPDC1B plays a central role in myoblasts by driving proliferation and preventing precocious myogenic differentiation during skeletal myogenesis in both mouse and human.

A Comprehensive Analysis of Runs of Homozygosity of Eleven Cattle Breeds Representing Different Production Types

Simple Summary

Runs of homozygosity (ROH) regions are known to be common in the genomes of cattle and have become a subject of interest of various research in recent years. ROH can be used as a valuable tool to estimate inbreeding, which needs to be controlled in livestock populations. Moreover, analysis of ROH is considered to be an effective method of identifying genome regions that are a subject of selection pressure, which may help in understanding the genetic aspects of production traits under selection. In this study, we analyzed ROH characteristics of 11 cattle breeds, both commercial and native, maintained in Poland. We presented distinct differences in the length, quantity and frequency of ROH between the analyzed breeds as well as in the levels of genomic inbreeding. Higher levels of inbreeding were characteristic for commercial breeds, especially beef breeds. In addition, within ROH islands, we observed a number of genes with a confirmed influence on the level of production traits. The presented results and identified genes can be a basis for further research focused on the identification of genes and markers essential in the determination of the most important production traits in cattle.

Abstract

In the presented research, BovineSNP50 microarrays (Illumina) were applied to determine runs of homozygosity in the genomes of 11 cattle breeds maintained in Poland. These cattle breeds represent three basic utility types: milk, meat and dual purpose. Analysis of runs of homozygosity allowed the evaluation of the level of autozygosity within each breed in order to calculate the genomic inbreeding coefficient (F_ROH), as well as to identify regions of the genome with a high frequency of ROH occurrence, which may reflect traces of directional selectin left in their genomes. Visible differences in the length and distribution of runs of homozygosity in the genomes of the analyzed cattle breeds have been observed. The highest mean number and mean sums of lengths of runs of homozygosity were characteristic for Hereford cattle and intermediate for the Holstein-Friesian Black-and-White variety, Holstein-Friesian Red-and-White variety, Simmental, Limousin, Montbeliarde and Charolais breeds. However, lower values were observed for cattle of conserved breeds. Moreover, the selected livestock differed in the level of inbreeding estimated using the F_ROH coefficient. In regions of the genome with a high frequency of ROH occurrence, which may reflect the impact of directional selection, a number of genes were observed that can be potentially related to the production traits which are under selection pressure for specific production types. The most important detected genes were GHR, MSTN, DGAT1, FABP4, and TRH, with a known influence on the milk and meat traits of the studied cattle breeds.

Roles of ErbB3-binding protein 1 (EBP1) in embryonic development and gene-silencing control

ErbB3-binding protein 1 (EBP1) is implicated in diverse cellular functions, including apoptosis, cell proliferation, and differentiation. Here, by generating genetic inactivation of Ebp1 mice, we identified the physiological roles of EBP1 in vivo. Loss of Ebp1 in mice caused aberrant organogenesis, including brain malformation, and death between E13.5 and 15.5 owing to severe hemorrhages, with massive apoptosis and cessation of cell proliferation. Specific ablation of Ebp1 in neurons caused structural abnormalities of brain with neuron loss in [Nestin-Cre; Ebp1 ^flox/flox ] mice. Notably, global methylation increased with high levels of the gene-silencing unit Suv39H1/DNMT1 in Ebp1-deficient mice. EBP1 repressed the transcription of Dnmt1 by binding to its promoter region and interrupted DNMT1-mediated methylation at its target gene, Survivin promoter region. Reinstatement of EBP1 into embryo brain relived gene repression and rescued neuron death. Our findings uncover an essential role for EBP1 in embryonic development and implicate its function in transcriptional regulation.

Drugging MYCN Oncogenic Signaling through the MYCN-PA2G4 Binding Interface

MYCN is a major driver for the childhood cancer, neuroblastoma, however, there are no inhibitors of this target. Enhanced MYCN protein stability is a key component of MYCN oncogenesis and is maintained by multiple feedforward expression loops involving MYCN transactivation target genes. Here, we reveal the oncogenic role of a novel MYCN target and binding protein, proliferation-associated 2AG4 (PA2G4). Chromatin immunoprecipitation studies demonstrated that MYCN occupies the PA2G4 gene promoter, stimulating transcription. Direct binding of PA2G4 to MYCN protein blocked proteolysis of MYCN and enhanced colony formation in a MYCN-dependent manner. Using molecular modeling, surface plasmon resonance, and mutagenesis studies, we mapped the MYCN-PA2G4 interaction site to a 14 amino acid MYCN sequence and a surface crevice of PA2G4. Competitive chemical inhibition of the MYCN-PA2G4 protein-protein interface had potent inhibitory effects on neuroblastoma tumorigenesis in vivo. Treated tumors showed reduced levels of both MYCN and PA2G4. Our findings demonstrate a critical role for PA2G4 as a cofactor in MYCN-driven neuroblastoma and highlight competitive inhibition of the PA2G4-MYCN protein binding as a novel therapeutic strategy in the disease. SIGNIFICANCE: Competitive chemical inhibition of the PA2G4-MYCN protein interface provides a basis for drug design of small molecules targeting MYC and MYCN-binding partners in malignancies driven by MYC family oncoproteins.

MiR-423 is differentially expressed in patients with stable and unstable coronary artery disease: A pilot study

Coronary artery disease (CAD) and acute myocardial infarction (AMI) are the leading causes of death worldwide. Since only a subset of CAD patients develops myocardial infarction, it is likely that unique factors predispose to AMI. Circulating microRNAs represent diagnostic powerful biomarkers for detection of heart injuries and patients’ risk stratification. Using an array-based approach, the expression of 84 circulating miRNAs was analyzed in plasma of pooled stable CAD patients (CAD; n = 5) and unstable CAD patients (AMI_T0; n = 5) enrolled within 24 hours from an AMI event. The array experiments showed 27 miRNAs differentially expressed with a two-fold up- or down-regulation (10 up- and 17 down-regulated miRNAs). Among them, miR-423-5p dis-regulation was confirmed in a larger case study (n = 99). Circulating miR-423-5p resulted to be significantly down-regulated within 24 hours from the AMI event (FC = -2, p≤0.05). Interestingly, miR-423-5p expression resulted to be increased (FC = +2; p≤0.005) in a subgroup of the same AMI patients (AMI_T1; n = 11) analyzed after 6 months from the acute event. We extended miR-423-5p expression study on PBMCs (peripheral blood mononuclear cells), confirming also in this tissue its up-regulation at 6 months post-AMI. Receiver operating characteristic analyses (ROC) were performed to detect the power of miR-423-5p to discriminate stable and unstable CAD. In plasma, miR-423-5p expression accurately distinguishes stable and unstable CAD patients (AUC = 0.7143, p≤0.005). Interestingly, the highest discriminatory value (AUC = 0.8529 p≤0.0005) was identified in blood cells, where miR-423-5p expression is able to differentiate unstable CAD patients during an acute event (AMI_T0) from those at six months post-AMI (AMI_T1). Furthermore, cellular miR-423-5p may discriminate also stable CAD patients from unstable CAD patients after six months post-AMI (AUC = 0.7355 p≤0.05). The results of this pilot-study suggest that miR-423-5p expression level both in plasma and blood cells, could represent a new promising biomarker for risk stratification of CAD patients.

Conserved functions of RNA-binding proteins in muscle

Animals require different types of muscle for survival, for example for circulation, motility, reproduction and digestion. Much emphasis in the muscle field has been placed on understanding how transcriptional regulation generates diverse types of muscle during development. Recent work indicates that alternative splicing and RNA regulation are as critical to muscle development, and altered function of RNA-binding proteins causes muscle disease. Although hundreds of genes predicted to bind RNA are expressed in muscles, many fewer have been functionally characterized. We present a cross-species view summarizing what is known about RNA-binding protein function in muscle, from worms and flies to zebrafish, mice and humans. In particular, we focus on alternative splicing regulated by the CELF, MBNL and RBFOX families of proteins. We discuss the systemic nature of diseases associated with loss of RNA-binding proteins in muscle, focusing on mis-regulation of CELF and MBNL in myotonic dystrophy. These examples illustrate the conservation of RNA-binding protein function and the marked utility of genetic model systems in understanding mechanisms of RNA regulation.

Satellite cells delivered in their niche efficiently generate functional myotubes in three-dimensional cell culture

Biophysical/biochemical cues from the environment contribute to regulation of the regenerative capacity of resident skeletal muscle stem cells called satellites cells. This can be observed in vitro, where muscle cell behaviour is influenced by the particular culture substrates and whether culture is performed in a 2D or 3D environment, with changes including morphology, nuclear shape and cytoskeletal organization. To create a 3D skeletal muscle model we compared collagen I, Fibrin or PEG-Fibrinogen with different sources of murine and human myogenic cells. To generate tension in the 3D scaffold, biomaterials were polymerised between two flexible silicone posts to mimic tendons. This 3D culture system has multiple advantages including being simple, fast to set up and inexpensive, so providing an accessible tool to investigate myogenesis in a 3D environment. Immortalised human and murine myoblast lines, and primary murine satellite cells showed varying degrees of myogenic differentiation when cultured in these biomaterials, with C2 myoblasts in particular forming large multinucleated myotubes in collagen I or Fibrin. However, murine satellite cells retained in their niche on a muscle fibre and embedded in 3D collagen I or Fibrin gels generated aligned, multinucleated and contractile myotubes.

The role of ErbB3 binding protein 1 in cancer: Friend or foe?

ErbB3, a member of the epidermal growth factor receptor family, reportedly plays an essential role in the regulation of cancer progression and therapeutic resistance. Numerous studies have indicated that ErbB3 binding protein 1 (Ebp1), a binding partner for ErbB3, plays an important regulatory role in the expression and function of ErbB3, but there is no agreement as to whether Ebp1 also has an ErbB3-independent function in cancer and how it might contribute to tumorigenesis. In this review, we will discuss the different functions of the two Ebp1 isoforms, p48 and p42, that may be responsible for the potentially dual role of Ebp1 in cancer growth.

Low-level laser irradiation induces a transcriptional myotube-like profile in C2C12 myoblasts

Low-level laser irradiation (LLLI) has been used as a non-invasive method to improve muscular regeneration capability. However, the molecular mechanisms by which LLLI exerts these effects remain largely unknown. Here, we described global gene expression profiling analysis in C2C12 myoblasts after LLLI that identified 514 differentially expressed genes (DEG). Gene ontology and pathway analysis of the DEG revealed transcripts among categories related to cell cycle, ribosome biogenesis, response to stress, cell migration, and cell proliferation. We further intersected the DEG in C2C12 myoblasts after LLLI with publicly available transcriptomes data from myogenic differentiation studies (myoblasts vs myotube) to identify transcripts with potential effects on myogenesis. This analysis revealed 42 DEG between myoblasts and myotube that intersect with altered genes in myoblasts after LLLI. Next, we performed a hierarchical cluster analysis with this set of shared transcripts that showed that LLLI myoblasts have a myotube-like profile, clustering away from the myoblast profile. The myotube-like transcriptional profile of LLLI myoblasts was further confirmed globally considering all the transcripts detected in C2C12 myoblasts after LLLI, by bi-dimensional clustering with myotubes transcriptional profiles, and by the comparison with 154 gene sets derived from previous published in vitro omics data. In conclusion, we demonstrate for the first time that LLLI regulates a set of mRNAs that control myoblast proliferation and differentiation into myotubes. Importantly, this set of mRNAs revealed a myotube-like transcriptional profile in LLLI myoblasts and provide new insights to the understanding of the molecular mechanisms underlying the effects of LLLI on skeletal muscle cells.

The long non-coding RNA H19 promotes cardiomyocyte apoptosis in dilated cardiomyopathy

In the previous study, we generated a rat model of dilated cardiomyopathy (DCM) induced by adriamycin and found that the expression of lncRNA H19 was significantly upregulated in myocardial tissue. The present study was aimed to investigate the potential role of H19 in the pathogenesis of adriamycin-induced DCM. H19 knockdown in the myocardium of DCM rats attenuated cardiomyocyte apoptosis and improved left ventricular structure and function. Adriamycin treatment was associated with elevated H19 and miR-675 expression and increased apoptosis in neonatal cardiomyocytes. Enforced expression of miR-675 was found to induce apoptosis in cardiomyocytes with adriamycin treatment and H19-siRNA transfection. The 3'-untranslated region of PA2G4 was cloned downstream of a luciferase reporter construct and cotransfected into HEK293 cells with miR-675 mimic. The results of luciferase assay showed that PA2G4 was a direct target of miR-675. The expression of PA2G4 was reduced in cardiomyocytes transfected with miR-675 mimic. Moreover, H19 knockdown was found to increase PA2G4 expression and suppress apoptosis in cardiomyocytes exposed to adriamycin. In conclusion, our study suggests that H19/miR-675 axis is involved in the promotion of cardiomyocyte apoptosis by targeting PA2G4, which may provide a new therapeutic strategy for the treatment of adriamycin-induced DCM.

ERBB3-Binding Protein 1 (EBP1) Is a Novel Developmental Pluripotency-Associated-4 (DPPA4) Cofactor in Human Pluripotent Cells

Developmental Pluripotency-Associated-4 (DPPA4) is one of the few core pluripotency genes lacking clearly defined molecular and cellular functions. Here, we used a proteomics screening approach of human embryonic stem cell (hESC) nuclear extract to determine DPPA4 molecular functions through identification of novel cofactors. Unexpectedly, the signaling molecule ERBB3-binding protein 1 (EBP1) was the strongest candidate binding partner for DPPA4 in hESC. EBP1 is a growth factor signaling mediator present in two isoforms, p48 and p42. The two isoforms generally have opposing functions, however their roles in pluripotent cells have not been established. We found that DPPA4 preferentially binds p48 in pluripotent and NTERA-2 cells, but this interaction is largely absent in non-pluripotent cells and is reduced with differentiation. The DPPA4-EBP1 interaction is mediated at least in part in DPPA4 by the highly conserved SAF-A/B, Acinus and PIAS (SAP) domain. Functionally, we found that DPPA4 transcriptional repressive function in reporter assays is significantly increased by specific p48 knockdown, an effect that was abolished with an interaction-deficient DPPA4 ΔSAP mutant. Thus, DPPA4 and EBP1 may cooperate in transcriptional functions through their physical association in a pluripotent cell specific context. Our study identifies EBP1 as a novel pluripotency cofactor and provides insight into potential mechanisms used by DPPA4 in regulating pluripotency through its association with EBP1. Stem Cells 2018;36:671-682.

ERBB3 and NGFR mark a distinct skeletal muscle progenitor cell in human development and hPSCs

Human pluripotent stem cells (hPSCs) can be directed to differentiate into skeletal muscle progenitor cells (SMPCs). However, the myogenicity of hPSC-SMPCs relative to human fetal or adult satellite cells remains unclear. We observed that hPSC-SMPCs derived by directed differentiation are less functional in vitro and in vivo compared to human satellite cells. Using RNA sequencing, we found that the cell surface receptors ERBB3 and NGFR demarcate myogenic populations, including PAX7 progenitors in human fetal development and hPSC-SMPCs. We demonstrated that hPSC skeletal muscle is immature, but inhibition of transforming growth factor-β signalling during differentiation improved fusion efficiency, ultrastructural organization and the expression of adult myosins. This enrichment and maturation strategy restored dystrophin in hundreds of dystrophin-deficient myofibres after engraftment of CRISPR-Cas9-corrected Duchenne muscular dystrophy human induced pluripotent stem cell-SMPCs. The work provides an in-depth characterization of human myogenesis, and identifies candidates that improve the in vivo myogenic potential of hPSC-SMPCs to levels that are equal to directly isolated human fetal muscle cells.

Tumor-derived cytokines impair myogenesis and alter the skeletal muscle immune microenvironment

Muscle wasting is a decline in skeletal muscle mass and function that is associated with aging, obesity, and a spectrum of pathologies including cancer. Cancer-associated wasting not only reduces quality of life, but also directly impacts cancer mortality, chemotherapeutic efficacy, and surgical outcomes. There is an incomplete understanding of the role of tumor-derived factors in muscle wasting and sparse knowledge of how these factors impact in vivo muscle regeneration. Here, we identify several cytokines/chemokines that negatively impact in vitro myogenic differentiation. We show that one of these cytokines, CXCL1, potently antagonizes in vivo muscle regeneration and interferes with in vivo muscle satellite cell homeostasis. Strikingly, CXCL1 triggers a robust and specific neutrophil/M2 macrophage response that likely underlies or exacerbates muscle repair/regeneration defects. Taken together, these data highlight the pleiotropic nature of a novel tumor-derived cytokine and underscore the importance of cytokines in muscle progenitor cell regulation.

Ebp1 regulates myogenic differentiation of myoblast cells via SMAD2/3 signaling pathway

Regulation of skeletal muscle development requires many of the regulatory networks that are fundamental to developmental myogenesis. ErbB3 binding protein-1 (Ebp1) is involved in the control of myoblasts development in chicken. However, the expression and biological functions of Ebp1 in the progress of myogenesis are unclear. This study focused on determining the effect of Ebp1 on myogenic proliferation and differentiation using a primary myoblasts culture model. Ebp1 was found to upregulate in proliferating myoblasts and decrease at the early stage of myogenic differentiation. The level of endogenous Ebp1 increased from E9 to E20 chicken leg muscles. Knockdown of Ebp1 had no effect on myoblasts proliferation. However, myogenic differentiation into multinucleated myotubes was significantly reduced. The mRNA and protein expression of MRFs was decreased when Ebp1 was knocked down. Downregulation of Ebp1, accompanied by elevated levels of pSMAD2/3, suggests that Ebp1 is involved in regulating myogenic differentiation via SMAD2/3 inhibition. The phosphorylation of SMAD2/3 was activated and the expression of MYOD and MYOG was reduced in Ebp1 knockdown myoblasts, but addition of LY2109761 (an inhibitor specified to SMAD2/3) blocked these effects. Collectively, these results indicate that Ebp1 promotes myoblast differentiation by inhibition of SMAD2/3 signaling pathway during chicken myogenesis. These data provide new insights into the biological role of Ebp1 in embryonic chicken skeletal muscle development.

Common and Distinctive Functions of the Hippo Effectors Taz and Yap in Skeletal Muscle Stem Cell Function

Hippo pathway downstream effectors Yap and Taz play key roles in cell proliferation and regeneration, regulating gene expression especially via Tead transcription factors. To investigate their role in skeletal muscle stem cells, we analyzed Taz in vivo and ex vivo in comparison with Yap. Small interfering RNA knockdown or retroviral‐mediated expression of wild‐type human or constitutively active TAZ mutants in satellite cells showed that TAZ promoted proliferation, a function shared with YAP. However, at later stages of myogenesis, TAZ also enhanced myogenic differentiation of myoblasts, whereas YAP inhibits such differentiation. Functionally, while muscle growth was mildly affected in Taz (gene Wwtr1^–/–) knockout mice, there were no overt effects on regeneration. Conversely, conditional knockout of Yap in satellite cells of Pax7^Cre‐ERT2/+: Yap^fl°^x/fl°^x:Rosa26^Lacz mice produced a regeneration deficit. To identify potential mechanisms, microarray analysis showed many common TAZ/YAP target genes, but TAZ also regulates some genes independently of YAP, including myogenic genes such as Pax7, Myf5, and Myod1 (ArrayExpress–E‐MTAB‐5395). Proteomic analysis revealed many novel binding partners of TAZ/YAP in myogenic cells, but TAZ also interacts with proteins distinct from YAP that are often involved in myogenesis and aspects of cytoskeleton organization (ProteomeXchange–PXD005751). Neither TAZ nor YAP bind members of the Wnt destruction complex but both regulated expression of Wnt and Wnt‐cross talking genes with known roles in myogenesis. Finally, TAZ operates through Tead4 to enhance myogenic differentiation. In summary, Taz and Yap have overlapping functions in promoting myoblast proliferation but Taz then switches to enhance myogenic differentiation. Stem Cells2017;35:1958–1972

Distinct Interactions of EBP1 Isoforms with FBXW7 Elicits Different Functions in Cancer

The ErbB3 receptor-binding protein EBP1 encodes two alternatively spliced isoforms P48 and P42. While there is evidence of differential roles for these isoforms in tumorigenesis, little is known about their underlying mechanisms. Here, we demonstrate that EBP1 isoforms interact with the SCF-type ubiquitin ligase FBXW7 in distinct ways to exert opposing roles in tumorigenesis. EBP1 P48 bound to the WD domain of FBXW7 as an oncogenic substrate of FBXW7. EBP1 P48 binding sequestered FBXW7α to the cytosol, modulating its role in protein degradation and attenuating its tumor suppressor function. In contrast, EBP1 P42 bound to both the F-box domain of FBXW7 as well as FBXW7 substrates. This adapter function of EBP1 P42 stabilized the interaction of FBXW7 with its substrates and promoted FBXW7-mediated degradation of oncogenic targets, enhancing its overall tumor-suppressing function. Overall, our results establish distinct physical and functional interactions between FBXW7 and EBP1 isoforms, which yield their mechanistically unique isoform-specific functions of EBP1 in cancer. Cancer Res; 77(8); 1983-96. ©2017 AACR.

Neuron-specific expression of p48 Ebp1 during murine brain development and its contribution to CNS axon regeneration

P48 Ebp1 is expressed in rapidly proliferating cells such as cancer cells and accelerates cell growth and survival. However, its expression pattern and role in central nervous system development have not been studied. Here, we demonstrated the spatiotemporal expression pattern of p48 Ebp1 during embryonic development and the postnatal period. During embryonic development, p48 Ebp1 was highly expressed in the brain. Expression gradually decreased after birth but was still more abundant than p42 expression after birth. Strikingly, we found that p48 Ebp1 was expressed in a cell type specific manner in neurons but not astrocytes. Moreover, p48 Ebp1 physically interacted with beta tubulin but not alpha tubulin. This fits with its accumulation in distal microtubule growth cone regions. Furthermore, in injured hippocampal slices, p48 Ebp1 introduction promoted axon regeneration. Thus, we speculate that p48 Ebp1 might contribute to microtubule dynamics acting as an MAP and promotes CNS axon regeneration. [BMB Reports 2017; 50(3): 126-131].

In vitro drug testing based on contractile activity of C2C12 cells in an epigenetic drug model

Skeletal muscle tissue engineering holds great promise for pharmacological studies. Herein, we demonstrated an in vitro drug testing system using tissue-engineered skeletal muscle constructs. In response to epigenetic drugs, myotube differentiation of C2C12 myoblast cells was promoted in two-dimensional cell cultures, but the levels of contractile force generation of tissue-engineered skeletal muscle constructs prepared by three-dimensional cell cultures were not correlated with the levels of myotube differentiation in two-dimensional cell cultures. In contrast, sarcomere formation and contractile activity in two-dimensional cell cultures were highly correlated with contractile force generation of tissue-engineered skeletal muscle constructs. Among the epigenetic drugs tested, trichostatin A significantly improved contractile force generation of tissue-engineered skeletal muscle constructs. Follistatin expression was also enhanced by trichostatin A treatment, suggesting the importance of follistatin in sarcomere formation of muscular tissues. These observations indicate that contractility data are indispensable for in vitro drug screening.

Selective Expansion of Skeletal Muscle Stem Cells from Bulk Muscle Cells in Soft Three-Dimensional Fibrin Gel

Muscle stem cells (MuSCs) exhibit robust myogenic potential in vivo, thus providing a promising curative treatment for muscle disorders. Ex vivo expansion of adult MuSCs is highly desired to achieve a therapeutic cell dose because of their scarcity in limited muscle biopsies. Sorting of pure MuSCs is generally required for all the current culture systems. Here we developed a soft three‐dimensional (3D) salmon fibrin gel culture system that can selectively expand mouse MuSCs from bulk skeletal muscle preparations without cell sorting and faithfully maintain their regenerative capacity in culture. Our study established a novel platform for convenient ex vivo expansion of MuSCs, thus greatly advancing stem cell‐based therapies for various muscle disorders. Stem Cells Translational Medicine2017;6:1412–1423

Pa2G4 is a novel Six1 co-factor that is required for neural crest and otic development

Mutations in SIX1 and in its co-factor, EYA1, underlie Branchiootorenal Spectrum disorder (BOS), which is characterized by variable branchial arch, otic and kidney malformations. However, mutations in these two genes are identified in only half of patients. We screened for other potential co-factors, and herein characterize one of them, Pa2G4 (aka Ebp1/Plfap). In human embryonic kidney cells, Pa2G4 binds to Six1 and interferes with the Six1-Eya1 complex. In Xenopus embryos, knock-down of Pa2G4 leads to down-regulation of neural border zone, neural crest and cranial placode genes, and concomitant expansion of neural plate genes. Gain-of-function leads to a broader neural border zone, expanded neural crest and altered cranial placode domains. In loss-of-function assays, the later developing otocyst is reduced in size, which impacts gene expression. In contrast, the size of the otocyst in gain-of-function assays is not changed but the expression domains of several otocyst genes are reduced. Together these findings establish an interaction between Pa2G4 and Six1, and demonstrate that it has an important role in the development of tissues affected in BOS. Thereby, we suggest that pa2g4 is a potential candidate gene for BOS.

Differential protein expression in the estuarine copepod Eurytemora affinis after diuron and alkylphenol exposures

Proteomics was used in the calanoid copepod Eurytemora affinis for screening of protein expression modifications induced by organic contaminants. The copepods were exposed in a continuous flow-through system for 86 h to environmentally relevant concentrations of contaminants representative of the pollution in the Seine Estuary (Haute-Normandie, France; diuron, 500 ng L(-1) ; alkylphenol mixture, 1000 ng L(-1) ). Proteome analysis of whole-body copepod extracts by 2-dimensional gel electrophoresis revealed that the contaminants induced modifications in protein expression, with the highest quantitative variations occurring after diuron exposure. Specifically, 88 and 41 proteins were differentially expressed after diuron and alkylphenol treatments, respectively. After mass spectrometry analysis, 51 (diuron exposure) and 15 (alkylphenol exposure) proteins were identified. The identified proteins were potentially related to energy metabolism, cell growth, nervous signal conductivity, excitotoxicity, oxidative stress response, and antioxidant defense. The data suggest a massive general disturbance of physiological functions of E. affinis after diuron exposure, whereas alkylphenols induced an alteration of a few targeted physiological functions. The protein expression signatures identified after contaminant exposure deserve further investigation in terms of the development of novel potential biomarkers for water quality assessment. Environ Toxicol Chem 2016;35:1860-1871. © 2015 SETAC.

A polybasic motif in ErbB3-binding protein 1 (EBP1) has key functions in nucleolar localization and polyphosphoinositide interaction

We reveal the identification of a polybasic motif necessary for polyphosphoinositide interaction and nucleolar targeting of ErbB3 binding protein 1 (EBP1). EBP1 interacts directly with phosphatidylinositol(3,4,5)-triphosphate and their association is detected in the nucleolus, implying regulatory roles of nucleolar processes.

Polyphosphoinositides (PPIns) are present in the nucleus where they participate in crucial nuclear processes, such as chromatin remodelling, transcription and mRNA processing. In a previous interactomics study, aimed to gain further insight into nuclear PPIns functions, we identified ErbB3 binding protein 1 (EBP1) as a potential nuclear PPIn-binding protein in a lipid pull-down screen. EBP1 is a ubiquitous and conserved protein, located in both the cytoplasm and nucleolus, and associated with cell proliferation and survival. In the present study, we show that EBP1 binds directly to several PPIns via two distinct PPIn-binding sites consisting of clusters of lysine residues and positioned at the N- and C-termini of the protein. Using interaction mutants, we show that the C-terminal PPIn-binding motif contributes the most to the localization of EBP1 in the nucleolus. Importantly, a K372N point mutation, located within the C-terminal motif and found in endometrial tumours, is sufficient to alter the nucleolar targeting of EBP1. Our study reveals also the presence of the class I phosphoinositide 3-kinase (PI3K) catalytic subunit p110β and its product PtdIns(3,4,5)P₃ together with EBP1 in the nucleolus. Using NMR, we further demonstrate an association between EBP1 and PtdIns(3,4,5)P₃ via both electrostatic and hydrophobic interactions. Taken together, these results show that EBP1 interacts directly with PPIns and associate with PtdIns(3,4,5)P₃ in the nucleolus. The presence of p110β and PtdIns(3,4,5)P₃ in the nucleolus indicates their potential role in regulating nucleolar processes, at least via EBP1.

Overexpression of a Hevea brasiliensis ErbB-3 Binding protein 1 Gene Increases Drought Tolerance and Organ Size in Arabidopsis

Rubber trees are economically important tropical tree species and the major source of natural rubber, which is an essential industrial material. This tropical perennial tree is susceptible to cold stress and other abiotic stresses, especially in the marginal northern tropics. Recent years, the genome sequencing and RNA-seq projects produced huge amount of sequence data, which greatly facilitated the functional genomics study. However, the characterization of individual functional gene is in urgent demands, especially for those involved in stress resistance. Here we identified and characterized the rubber tree gene ErbB-3 binding protein 1, which undergoes changes in expression in response to cold, drought stress and ABA treatment. HbEBP1 overexpression (OE) in Arabidopsis increased organ size, facilitated root growth and increased adult leaf number by delaying the vegetative-to-reproductive transition. In addition, HbEBP1 OE enhanced the resistance of the Arabidopsis plants to freezing and drought stress, demonstrating that this gene participates in the regulation of abiotic stress resistance. RD29a, RD22 and CYCD3;1 expression was also greatly enhanced by HbEBP1 OE, which explains its regulatory roles in organ size and stress resistance. The regulation of drought stress resistance is a novel function identified in plant EBP1 genes, which expands our understanding of the roles of EBP1 gene in response to the environment. Our results provide information that may lead to the use of HbEBP1 in genetically engineered crops to increase both biomass and abiotic stress resistance.

Detection of satellite cells during skeletal muscle wound healing in rats: time-dependent expressions of Pax7 and MyoD in relation to wound age

The study was focused on time-dependent expressions of paired-box transcription factor 7 (Pax7) and myoblast determination protein (MyoD) during skeletal muscle wound healing. An animal model of skeletal muscle contusion was established in 40 Sprague-Dawley male rats. Samples were taken at 1, 3, 5, 7, 9, 13, 17, and 21 days after injury, respectively (five rats in each posttraumatic interval). Five rats were employed as control. By morphometric analysis, the data based on the number of Pax7(+)/MyoD(-), Pax7(+)/MyoD(+), and Pax7(-)/MyoD(+) cells were highly correlated with the wound age. Pax7 and MyoD expressions were upregulated after injury by Western blot and quantitative real-time PCR assays. The relative quantity of Pax7 protein peaked at 5 days after injury, which was >1.13, and decreased thereafter. Similarly, the relative quantity of MyoD mRNA expression peaked at 3 days after injury, which was >2.59. The relative quantity of Pax7 protein >0.73 or mRNA expression >2.38 or the relative quantity of MyoD protein >1.33 suggested a wound age of 3 to 7 days. The relative quantity of MyoD mRNA expression >2.02 suggested a wound age of 1 to 7 days post-injury. In conclusion, the expressions of Pax7 and MyoD are upregulated in a time-dependent manner during skeletal muscle wound healing, suggesting that Pax7 and MyoD may be potential markers for wound age estimation in skeletal muscle.

α7nAChR is expressed in satellite cells at different myogenic status during skeletal muscle wound healing in rats

Recent study has reported that α7 nicotine acetylcholine receptor (α7nAChR) is expressed in regenerated multinucleated myotubes. But the distribution of α7nAChR in satellite cells in different myogenic status is unknown. A preliminary study on the dynamic distribution of α7nAChR in satellite cells was performed by double indirect immunofluorescent procedures during skeletal muscle wound healing in rats. An animal model of skeletal muscle contusion was established in 40 Sprague-Dawley male rats. Samples were taken at 1, 3, 5, 7, 9, 13, 17 and 21 days after injury, respectively (five rats in each posttraumatic interval). Five rats were employed as control. In normal muscle specimens, weak immunoreactivity for α7nAChR was detected in a few satellite cells (considered as quiescent). α7nAChR-positive signals were observed in proliferated and differentiated satellite cells and regenerated multinucleated myotubes in the wounded areas. By morphometric analysis, the average number of α7nAChR+/Pax7+ and α7nAChR+/MyoD+ cells climaxed at 5 days post-injury. The average number of α7nAChR+/myogenin+ cells was significantly increased from 3 to 9 days post-injury as compared with other posttraumatic intervals. The protein level of α7nAChR maximized at 9 days post-injury, which implies that α7nAChR was associated with the satellite cells status. Our observations on expression of α7nAChR in satellite cells from quiescence to myotube formation suggest that α7nAChR may be involved in muscle regeneration by regulating satellite cell status.

Using Xenopus to discover new genes involved in branchiootorenal spectrum disorders

Congenital hearing loss is an important clinical problem because, without early intervention, affected children do not properly acquire language and consequently have difficulties developing social skills. Although most newborns in the US are screened for hearing deficits, even earlier diagnosis can be made with prenatal genetic screening. Genetic screening that identifies the relevant mutated gene can also warn about potential congenital defects in organs not related to hearing. We will discuss efforts to identify new candidate genes that underlie the Branchiootorenal spectrum disorders in which affected children have hearing deficits and are also at risk for kidney defects. Mutations in two genes, SIX1 and EYA1, have been identified in about half of the patients tested. To uncover new candidate genes, we have used the aquatic animal model, Xenopus laevis, to identify genes that are part of the developmental genetic pathway of Six1 during otic and kidney development. We have already identified a large number of potential Six1 transcriptional targets and candidate co-factor proteins that are expressed at the right time and in the correct tissues to interact with Six1 during development. We discuss the advantages of using this system for gene discovery in a human congenital hearing loss syndrome.

Stable and bicistronic expression of two genes in somite- and lateral plate-derived tissues to study chick limb development

Background

Components of the limb musculoskeletal system have distinct mesoderm origins. Limb skeletal muscles originate from somites, while the skeleton and attachments (tendons and connective tissues) derive from limb lateral plate. Despite distinct mesoderm origins, the development of muscle, skeleton and attachments is highly coordinated both spatially and temporally to ensure complete function of the musculoskeletal system. A system to study molecular interactions between somitic-derived tissues (muscles) and lateral-plate-derived tissues (skeletal components and attachments) during limb development is missing.

Results

We designed a gene delivery system in chick embryos with the ultimate aim to study the interactions between the components of the musculoskeletal system during limb development. We combined the Tol2 genomic integration system with the viral T2A system and developed new vectors that lead to stable and bicistronic expression of two proteins at comparable levels in chick cells. Combined with limb somite and lateral plate electroporation techniques, two fluorescent reporter proteins were co-expressed in stoichiometric proportion in the muscle lineage (somitic-derived) or in skeleton and their attachments (lateral-plate-derived). In addition, we designed three vectors with different promoters to target muscle cells at different steps of the differentiation process.

Conclusion

Limb somite electroporation technique using vectors containing these different promoters allowed us to target all myogenic cells, myoblasts or differentiated muscle cells. These stable and promoter-specific vectors lead to bicistronic expression either in somitic-derived myogenic cells or lateral plate-derived cells, depending on the electroporation sites and open new avenues to study the interactions between myogenic cells and tendon or connective tissue cells during limb development.

Afferent Innervation, Muscle Spindles, and Contractures Following Neonatal Brachial Plexus Injury in a Mouse Model

PURPOSE

We used an established mouse model of elbow flexion contracture after neonatal brachial plexus injury (NBPI) to test the hypothesis that preservation of afferent innervation protects against contractures and is associated with preservation of muscle spindles and ErbB signaling.

METHODS

A model of preganglionic C5 through C7 NBPI was first tested in mice with fluorescent axons using confocal imaging to confirm preserved afferent innervation of spindles despite motor end plate denervation. Preganglionic and postganglionic injuries were then created in wild-type mice. Four weeks later, we assessed total and afferent denervation of the elbow flexors by musculocutaneous nerve immunohistochemistry. Biceps muscle volume and cross-sectional area were measured by micro computed tomography. An observer who was blinded to the study protocol measured elbow flexion contractures. Biceps spindle and muscle fiber morphology and ErbB signaling pathway activity were assessed histologically and immunohistochemically.

RESULTS

Preganglionic and postganglionic injuries caused similar total denervation and biceps muscle atrophy. However, after preganglionic injuries, afferent innervation was partially preserved and elbow flexion contractures were significantly less severe. Spindles degenerated after postganglionic injury but were preserved after preganglionic injury. ErbB signaling was inactivated in denervated spindles after postganglionic injury but ErbB signaling activity was preserved in spindles after preganglionic injury with retained afferent innervation. Preganglionic and postganglionic injuries were associated with upregulation of ErbB signaling in extrafusal muscle fibers.

CONCLUSIONS

Contractures after NBPI are associated with muscle spindle degeneration and loss of spindle ErbB signaling activity. Preservation of afferent innervation maintained spindle development and ErbB signaling activity, and protected against contractures.

CLINICAL RELEVANCE

Pharmacologic modulation of ErbB signaling, which is being investigated as a therapy for congestive heart failure, may be able to recapitulate the protective effects of afferent innervation in spindle development and contracture prevention. Muscle spindle preservation may also have implications in proprioception and motor learning, both of which are impaired in NBPI.

A novel bioreactor for the generation of highly aligned 3D skeletal muscle-like constructs through orientation of fibrin via application of static strain

The generation of functional biomimetic skeletal muscle constructs is still one of the fundamental challenges in skeletal muscle tissue engineering. With the notion that structure strongly dictates functional capabilities, a myriad of cell types, scaffold materials and stimulation strategies have been combined. To further optimize muscle engineered constructs, we have developed a novel bioreactor system (MagneTissue) for rapid engineering of skeletal muscle-like constructs with the aim to resemble native muscle in terms of structure, gene expression profile and maturity. Myoblasts embedded in fibrin, a natural hydrogel that serves as extracellular matrix, are subjected to mechanical stimulation via magnetic force transmission. We identify static mechanical strain as a trigger for cellular alignment concomitant with the orientation of the scaffold into highly organized fibrin fibrils. This ultimately yields myotubes with a more mature phenotype in terms of sarcomeric patterning, diameter and length. On the molecular level, a faster progression of the myogenic gene expression program is evident as myogenic determination markers MyoD and Myogenin as well as the Ca(2+) dependent contractile structural marker TnnT1 are significantly upregulated when strain is applied. The major advantage of the MagneTissue bioreactor system is that the generated tension is not exclusively relying on the strain generated by the cells themselves in response to scaffold anchoring but its ability to subject the constructs to individually adjustable strain protocols. In future work, this will allow applying mechanical stimulation with different strain regimes in the maturation process of tissue engineered constructs and elucidating the role of mechanotransduction in myogenesis.

STATEMENT OF SIGNIFICANCE

Mechanical stimulation of tissue engineered skeletal muscle constructs is a promising approach to increase tissue functionality. We have developed a novel bioreactor-based 3D culture system, giving the user the possibility to apply different strain regimes like static, cyclic or ramp strain to myogenic precursor cells embedded in a fibrin scaffold. Application of static mechanical strain leads to alignment of fibrin fibrils along the axis of strain and concomitantly to highly aligned myotube formation. Additionally, the pattern of myogenic gene expression follows the temporal progression observed in vivo with a more thorough induction of the myogenic program when static strain is applied. Ultimately, the strain protocol used in this study results in a higher degree of muscle maturity demonstrated by enhanced sarcomeric patterning and increased myotube diameter and length. The introduced bioreactor system enables new possibilities in muscle tissue engineering as longer cultivation periods and different strain applications will yield tissue engineered muscle-like constructs with improved characteristics in regard to functionality and biomimicry.

TRIM35 Interacts with pyruvate kinase isoform M2 to suppress the Warburg effect and tumorigenicity in hepatocellular carcinoma

Tripartite motif-containing protein 35 (TRIM35) is a member of RBCC family, which has a highly conserved order consisting of a RING domain followed by one or two B-Box domains and then a coiled-coil domain. We previously identified TRIM35 as a novel tumor suppressor in human hepatocellular carcinoma (HCC). However, the molecular mechanism that TRIM35 uses to suppress tumorigenicity is largely unknown. Pyruvate kinase isoform M2 (PKM2) has been demonstrated to have a central role in metabolic reprogramming during cancer progression. Phosphorylation of PKM2 tyrosine residue 105 (Y105) regulates PKM2 to provide a metabolic advantage to tumor cells, thereby promoting tumor growth. In the present work, mass spectrometry analysis demonstrated an interaction between TRIM35 and PKM2. Co-IP experiments confirmed that TRIM35 interacts with PKM2 and that the coiled-coil domain is required for such an interaction. Furthermore, the coiled-coil domain mediates decreases in the Warburg effect and in the cell proliferation of HCC cells. In addition, TRIM35 suppresses the tumorigenicity of HCC cells through the blockade of PKM2 Y105 phosphorylation. Collectively, our data reveal a new function for TRIM35, which is to regulate the Warburg effect and tumorigenicity through interaction with PKM2 in HCC.

Coordinated action of Axin1 and Axin2 suppresses β-catenin to regulate muscle stem cell function

The resident stem cells of skeletal muscle are satellite cells, which are regulated by both canonical and non-canonical Wnt pathways. Canonical Wnt signalling promotes differentiation, and is controlled at many levels, including via Axin1 and Axin2-mediated β-catenin degradation. Axin1 and Axin2 are thought equivalent suppressors of canonical Wnt signalling, although Axin2 is also a Wnt target gene. We show that Axin1 expression was higher in proliferating satellite cells, while Axin2 was up-regulated during differentiation. siRNA-mediated Axin1 knockdown changed cell morphology, suppressed proliferation and promoted myogenic differentiation. Simultaneous knockdown of both Axin1 and β-catenin rescued proliferation and partially, premature differentiation. Surprisingly, retroviral-mediated overexpression of Axin2 was unable to compensate for knockdown of Axin1 in satellite cells, indicating that Axin1 and Axin2 are not fully redundant. Isolated satellite cells from Axin2-null mice also had no major phenotype. However, siRNA-mediated knockdown of Axin1 in Axin2-null cells strongly inhibited proliferation, while inducing differentiation, clear nuclear localisation of β-catenin, up-regulation of canonical Wnt target genes (Axin2, Lef1, Tcf4, Pitx2c and Lgr5) and activation of a TCF reporter construct. Again, concomitant knockdown of Axin1 and β-catenin in Axin2-null satellite cells rescued morphology and proliferation, but only partially prevented precocious differentiation. Thus, Axin1 and Axin2 do not have equivalent functions in satellite cells, but are both involved in repression of Wnt/β-catenin signalling to maintain proliferation and contribute to controlling timely myogenic differentiation.

The downregulation of ErbB3 binding protein 1 (EBP1) is associated with poor prognosis and enhanced cell proliferation in hepatocellular carcinoma

ErbB3 binding protein 1 (EBP1) has been recently reported to function as a tumor suppressor in the progression of multiple cancers, including breast cancer, prostate cancer, salivary adenoid cystic carcinoma (ACC), and oral squamous cell carcinoma (OSCC). However, the expression and physiological significance of EBP1 in hepatocellular carcinoma (HCC) remain unclear. In the study, we showed that EBP1 was significantly downregulated in clinical HCC specimens, and that decreased expression of EBP1 was associated with enhanced proliferation in HCC cells. Western blot and immunohistochemical analyses revealed that EBP1 was remarkably downregulated in HCC tissues compared with the adjacent normal ones. The levels of EBP1 were significantly associated with histological grade (P = 0.034), tumor size (P = 0.001), and Ki67 expression (P < 0.001) in HCC specimens. Univariate and multivariate analyses showed that EBP1 could serve as an independent prognostic indicator of patients' survival. Serum starvation and refeeding assay indicated that EBP1 was accumulated in growth-arrested HCC cells, and was progressively decreased when cells entered into S phase. Moreover, the depletion of EBP1 induced growth acceleration and cell cycle progression in L02 hepatocytes. On the basis of these findings, we conclude that EBP1 may be a valuable prognostic marker and promising therapeutic target of HCC.