Opposing control of rhabdomyosarcoma growth and differentiation by myogenin and interleukin 4

A dysfunctional miR-1-TRPS1-MYOG axis drives ERMS by suppressing terminal myogenic differentiation

Rhabdomyosarcoma is the most common pediatric soft tissue tumor, comprising two major subtypes: the PAX3/7-FOXO1 fusion-negative embryonal and the PAX3/7-FOXO1 fusion-positive alveolar subtype. Here, we demonstrate that the expression levels of the transcriptional repressor TRPS1 are specifically enhanced in the embryonal subtype, resulting in impaired terminal myogenic differentiation and tumor growth. During normal myogenesis, expression levels of TRPS1 have to decrease to allow myogenic progression, as demonstrated by overexpression of TRPS1 in myoblasts impairing myotube formation. Consequentially, myogenic differentiation in embryonal rhabdomyosarcoma in vitro as well as in vivo can be achieved by reducing TRPS1 levels. Furthermore, we show that TRPS1 levels in RD cells, the bona fide model cell line for embryonal rhabdomyosarcoma, are regulated by miR-1 and that TRPS1 and MYOD1 share common genomic binding sites. The myogenin (MYOG) promoter is one of the critical targets of TRPS1 and MYOD1; we demonstrate that TRPS1 restricts MYOG expression and thereby inhibits terminal myogenic differentiation. Therefore, reduction of TRPS1 levels in embryonal rhabdomyosarcoma might be a therapeutic approach to drive embryonal rhabdomyosarcoma cells into myogenic differentiation, thereby generating postmitotic myotubes.

Non-coding RNA in rhabdomyosarcoma progression and metastasis

Rhabdomyosarcoma (RMS) is a soft tissue sarcoma of skeletal muscle differentiation, with a predominant occurrence in children and adolescents. One of the major challenges facing treatment success is the presence of metastatic disease at the time of diagnosis, commonly associated with the more aggressive fusion-positive subtype. Non-coding RNA (ncRNA) can regulate gene transcription and translation, and their dysregulation has been associated with cancer development and progression. MicroRNA (miRNA) are short non-coding nucleic acid sequences involved in the regulation of gene expression that act by targeting messenger RNA (mRNA), and their aberrant expression has been associated with both RMS initiation and progression. Other ncRNA including long non-coding RNA (lncRNA), circular RNA (circRNA) and ribosomal RNA (rRNA) have also been associated with RMS revealing important mechanistic roles in RMS biology, but these studies are still limited and require further investigation. In this review, we discuss the established roles of ncRNA in RMS differentiation, growth and progression, highlighting their potential use in RMS prognosis, as therapeutic agents or as targets of treatment.

Interleukin-4 Receptor Inhibition Targeting Metastasis Independent of Macrophages

Rhabdomyosarcoma (RMS) is the most common soft tissue sarcoma occurring in children and carries a dismal prognosis when metastatic disease is detected. Our previous work has suggested the cytokine receptor IL4Rα may play a role in contributing to metastasis in the alveolar subtype of rhabdomyosarcoma (aRMS), and thus could present a therapeutic target. The IL4 signaling axis has been characterized in various adult cancers as well; however, pediatric trials often follow similar adult trials and the role of the IL4Rα receptor has not been explored in the context of a mediator of metastasis in adult disease. Here, we demonstrate that the impact of IL4Rα blockade in an orthotopic allograft model of aRMS is not mediated by a macrophage response. We further examine the effect of IL4 blockade in adult colon, breast, and prostate cancers and find that inhibition of IL4Rα signaling modulates in vitro cell viability of HCT-116 colon carcinoma cells; however, this finding did not translate to an autocrine-related in vivo difference in tumor burden or lung metastasis. Our results suggest that if humanized IL4 mouse host strains are not available (or not ideal due to the need for immunosuppressing the host innate immune response for xenograft systems), then genetically-engineered mice and mouse allograft studies may be the best indicator of therapeutic targeting efficacy.

Signaling pathways in Rhabdomyosarcoma invasion and metastasis

Rhabdomyosarcoma (RMS) is an aggressive childhood mesenchymal tumor with two major molecular and histopathologic subtypes: fusion-positive (FP)RMS, characterized by the PAX3-FOXO1 fusion protein and largely of alveolar histology, and fusion-negative (FN)RMS, the majority of which exhibit embryonal tumor histology. Metastatic disease continues to be associated with poor overall survival despite intensive treatment strategies. Studies on RMS biology have provided some insight into autocrine as well as paracrine signaling pathways that contribute to invasion and metastatic propensity. Such pathways include those driven by the PAX3-FOXO1 fusion oncoprotein in FPRMS and signaling pathways such as IGF/RAS/MEK/ERK, PI3K/AKT/mTOR, cMET, FGFR4, and PDGFR in both FP and FNRMS. In addition, specific cytoskeletal proteins, G protein coupled receptors, Hedgehog, Notch, Wnt, Hippo, and p53 pathways play a role, as do specific microRNA. Paracrine factors, including secreted proteins and RMS-derived exosomes that carry cargo of protein and miRNA, have also recently emerged as potentially important players in RMS biology. This review summarizes the known factors contributing to RMS invasion and metastasis and their implications on identifying targets for treatment and a better understanding of metastatic RMS.

CASZ1 induces skeletal muscle and rhabdomyosarcoma differentiation through a feed-forward loop with MYOD and MYOG

Embryonal rhabdomyosarcoma (ERMS) is a childhood cancer that expresses myogenic master regulatory factor MYOD but fails to differentiate. Here, we show that the zinc finger transcription factor CASZ1 up-regulates MYOD signature genes and induces skeletal muscle differentiation in normal myoblasts and ERMS. The oncogenic activation of the RAS-MEK pathway suppresses CASZ1 expression in ERMS. ChIP-seq, ATAC-seq and RNA-seq experiments reveal that CASZ1 directly up-regulates skeletal muscle genes and represses non-muscle genes through affecting regional epigenetic modifications, chromatin accessibility and super-enhancer establishment. Next generation sequencing of primary RMS tumors identified a single nucleotide variant in the CASZ1 coding region that potentially contributes to ERMS tumorigenesis. Taken together, loss of CASZ1 activity, due to RAS-MEK signaling or genetic alteration, impairs ERMS differentiation, contributing to RMS tumorigenesis.

c-Myb regulates tumorigenic potential of embryonal rhabdomyosarcoma cells

Rhabdomyosarcomas (RMS) are a heterogeneous group of mesodermal tumors, the most common sub-types are embryonal (eRMS) and alveolar (aRMS) rhabdomyosarcoma. Immunohistochemical analysis revealed c-Myb expression in both eRMS and aRMS. c-Myb has been reported to be often associated with malignant human cancers. We therefore investigated the c-Myb role in RMS using cellular models of RMS. Specific suppression of c-Myb by a lentiviral vector expressing doxycycline (Dox)-inducible c-Myb shRNA inhibited proliferation, colony formation, and migration of the eRMS cell line (RD), but not of the aRMS cell line (RH30). Upon c-Myb knockdown in eRMS cells, cells accumulated in G0/G1 phase, the invasive behaviour of cells was repressed, and elevated levels of myosin heavy chain, marker of muscle differentiation, was detected. Next, we used an RD-based xenograft model to investigate the role of c-Myb in eRMS tumorigenesis in vivo. We found that Dox administration did not result in efficient suppression of c-Myb in growing tumors. However, when c-Myb-deficient RD cells were implanted into SCID mice, we observed inefficient tumor grafting and attenuation of tumor growth during the initial stages of tumor expansion. The presented study suggests that c-Myb could be a therapeutic target in embryonal rhabdomyosarcoma assuming that its expression is ablated.

LEF1 reduces tumor progression and induces myodifferentiation in a subset of rhabdomyosarcoma

Rhabdomyosarcoma (RMS) is the most common soft tissue sarcoma in children and show characteristics of skeletal muscle differentiation. The two major RMS subtypes in children are alveolar (ARMS) and embryonal RMS (ERMS). We demonstrate that approximately 50% of ARMS and ERMS overexpress the LEF1/TCF transcription factor LEF1 when compared to normal skeletal muscle and that LEF1 can restrain aggressiveness especially of ARMS cells. LEF1 knockdown experiments in cell lines reveal that depending on the cellular context, LEF1 can induce pro-apoptotic signals. LEF1 can also suppress proliferation, migration and invasiveness of RMS cells both in vitro and in vivo. Furthermore, LEF1 can induce myodifferentiation of the tumor cells. This may involve regulation of other LEF1/TCF factors i.e. TCF1, whereas β-catenin activity plays a subordinate role. Together these data suggest that LEF1 rather has tumor suppressive functions and attenuates aggressiveness in a subset of RMS.

High expression of IL-4R enhances proliferation and invasion of hepatocellular carcinoma cells

OBJECTIVE

In this study, we aimed to investigate the expression and function of interleukin-4 receptor (IL-4R) in hepatocellular carcinoma (HCC).

METHODS

We collected 40 pairs of human HCC and adjacent normal tissue specimens and examined the expression levels of IL-4R. After IL-4R knockdown in HCC cell lines, cell proliferation and invasion ability were examined. Cell cycle and apoptosis were analyzed by flow cytometry. The activity of multiple signaling pathways was examined by Western blot.

RESULTS

IL-4R was overexpressed in HCC tumors compared with adjacent normal control tissues and was associated with tumor differentiation status. IL-4R knockdown resulted in enhanced apoptosis, impaired proliferation and reduced invasion of HCC cells. Furthermore, IL-4R knockdown abolished IL-4-induced activation of the Janus Kinase 1 (JAK1)/signal transducer and activator of transcription 6 (STAT6) and JUN N-terminal kinase (JNK)/extracellular signal-regulated kinase 1/2 (ERK1/2) signaling pathways.

CONCLUSIONS

IL-4R plays an important role in regulating HCC cell survival and metastasis, and regulates the activity of the JAK1/STAT6 and JNK/ERK1/2 signaling pathways. We therefore suggest that IL-4/IL-4R may be a new therapeutic target for HCC.

Regulation of Skeletal Muscle Myoblast Differentiation and Proliferation by Pannexins

Pannexins are newly discovered channels that are now recognized as mediators of adenosine triphosphate release from several cell types allowing communication with the extracellular environment. Pannexins have been associated with various physiological and pathological processes including apoptosis, inflammation, and cancer. However, it is only recently that our work has unveiled a role for Pannexin 1 and Pannexin 3 as novel regulators of skeletal muscle myoblast proliferation and differentiation. Myoblast differentiation is an ordered multistep process that includes withdrawal from the cell cycle and the expression of key myogenic factors leading to myoblast differentiation and fusion into multinucleated myotubes. Eventually, myotubes will give rise to the diverse muscle fiber types that build the complex skeletal muscle architecture essential for body movement, postural behavior, and breathing. Skeletal muscle cell proliferation and differentiation are crucial processes required for proper skeletal muscle development during embryogenesis, as well as for the postnatal skeletal muscle regeneration that is necessary for muscle repair after injury or exercise. However, defects in skeletal muscle cell differentiation and/or deregulation of cell proliferation are involved in various skeletal muscle pathologies. In this review, we will discuss the expression of pannexins and their post-translational modifications in skeletal muscle, their known functions in various steps of myogenesis, including myoblast proliferation and differentiation, as well as their possible roles in skeletal muscle development, regeneration, and diseases such as Duchenne muscular dystrophy.

Interleukin-4 receptor signaling and its binding mechanism: A therapeutic insight from inhibitors tool box

Studies on Interlukin-4 (IL-4) disclosed great deal of information about its various physiological and pathological roles. All these roles depend upon its interaction and signaling through either type-I (IL-4Rα/common γ-chain) or type-II (IL-4Rα/IL-13Rα) receptors. Another cytokine, IL-13, shares some of the functions of IL-4, because both cytokines use a common receptor subunit, IL-4Rα. Here in this review, we discuss the structural details of IL-4 and IL-4Rα subunit and the structural similarities between IL-4 and IL-13. We also describe detailed chemistry of type-I and type-II receptor complexes and their signaling pathways. Furthermore, we elaborate the strength of type-II hetero dimer signals in response to IL-4 and IL-13. These cytokines are prime players in pathogenesis of allergic asthma, allergic hypersensitivity, different cancers, and HIV infection. Recent advances in the structural and binding chemistry of these cytokines various types of inhibitors were designed to block the interaction of IL-4 and IL-13 with their receptor, including several IL-4 mutant analogs and IL-4 antagonistic antibodies. Moreover, different targeted immunotoxins, which is a fusion of cytokine protein with a toxin or suicidal gene, are the new class of inhibitors to prevent cancer progression. In addition few small molecular inhibitors such as flavonoids have also been developed which are capable of binding with high affinity to IL-4Rα and, therefore, can be very effective in blocking IL-4-mediated responses.

Overexpression of the skNAC gene in human rhabdomyosarcoma cells enhances their differentiation potential and inhibits tumor cell growth and spreading

Skeletal and heart muscle-specific variant of the alpha subunit of nascent polypeptide complex (skNAC) is exclusively present in striated muscle cells. During skeletal muscle cell differentiation, skNAC expression is strongly induced, suggesting that the protein might be a regulator of the differentiation process. Rhabdomyosarcoma is a tumor of skeletal muscle origin. Since there is a strong inverse correlation between rhabdomyosarcoma cell differentiation status and metastatic potential, we analyzed skNAC expression patterns in a set of rhabdomyosarcoma cell lines: Whereas RD/12 and RD/18 cells showed a marked induction of skNAC gene expression upon the induction of differentiation-similarly as the one seen in nontransformed myoblasts-skNAC was not induced in CCA or Rh30 cells. Overexpressing skNAC in CCA and Rh30 cells led to a reduction in cell cycle progression and cell proliferation accompanied by an upregulation of specific myogenic differentiation markers, such as Myogenin or Myosin Heavy Chain. Furthermore, in contrast to vector-transfected controls, a high percentage of the cells formed long, Myosin Heavy Chain-positive, multinucleate myotubes. Consistently, soft agar assays revealed a drop in the metastatic potential of skNAC-overexpressing cells. Taken together, these data indicate that reconstitution of skNAC expression can enhance the differentiation potential of rhabdomyosarcoma cells and reduces their metastatic potential, a finding which might have important therapeutic implications.

Defective RAGE activity in embryonal rhabdomyosarcoma cells results in high PAX7 levels that sustain migration and invasiveness

Rhabdomyosarcoma is a muscle-derived malignant tumor mainly affecting children. The most frequent variant, embryonal rhabdomyosarcoma (ERMS) is characterized by overexpression of the transcription factor, PAX7 which prevents ERMS cells from exiting the cell cycle and terminally differentiating. However, a role for PAX7 in the invasive properties of ERMS cells has not been investigated in detail thus far. Here we show that ectopic expression of receptor for advanced glycation end-products (RAGE) in human ERMS cells results in the activation of a RAGE/myogenin axis which downregulates PAX7 by transcriptional and post-translational mechanisms, as in normal myoblasts, and reduces metastasis formation. High PAX7 sustains migration and invasiveness in ERMS cells by upregulating EPHA3 and EFNA1 and downregulating NCAM1 thus decreasing the neural cell adhesion molecule (NCAM)/polysialylated-NCAM ratio. Microarray gene expression analysis shows that compared with the RAGE(-ve) TE671/WT cells and similarly to primary human myoblasts, TE671/RAGE cells show upregulation of genes involved in muscle differentiation and cell adhesion, and downregulation of cell migration related and major histocompatibility complex class I genes. Our data reveal a link between PAX7 and metastasis occurrence in ERMSs, and support a role for the RAGE/myogenin axis in metastasis suppression. Thus, low RAGE expression in ERMS primary tumors may be predictive of metastatic behavior.

Mechanisms of impaired differentiation in rhabdomyosarcoma

Rhabdomyosarcoma (RMS) is the most common soft tissue sarcoma of childhood, with presumed skeletal muscle origins, because of its myogenic phenotype. RMS is composed of two main subtypes, embryonal RMS (eRMS) and alveolar RMS (aRMS). Whereas eRMS histologically resembles embryonic skeletal muscle, the aRMS subtype is more aggressive and has a poorer prognosis. In addition, whereas the genetic profile of eRMS is not well established, aRMS is commonly associated with distinct chromosome translocations that fuse domains of the transcription factors Pax3 and Pax7 to the forkhead family member FOXO1A. Both eRMS and aRMS tumor cells express myogenic markers such as MyoD, but their ability to complete differentiation is impaired. How this impairment occurs is the subject of this review, which will focus on several themes, including signaling pathways that converge on Pax-forkhead gene targets, alterations in MyoD function, epigenetic modifications of myogenic promoters, and microRNAs whose expression patterns in RMS alter key regulatory circuits to help maintain tumor cells in an opportunistically less differentiated state.

Proof-of-concept rare cancers in drug development: the case for rhabdomyosarcoma

Rare diseases typically affect fewer than 200,000 patients annually, yet because thousands of rare diseases exist, the cumulative impact is millions of patients worldwide. Every form of childhood cancer qualifies as a rare disease-including the childhood muscle cancer, rhabdomyosarcoma (RMS). The next few years promise to be an exceptionally good era of opportunity for public-private collaboration for rare and childhood cancers. Not only do certain governmental regulation advantages exist, but these advantages are being made permanent with special incentives for pediatric orphan drug-product development. Coupled with a growing understanding of sarcoma tumor biology, synergy with pharmaceutical muscle disease drug-development programs, and emerging publically available preclinical and clinical tools, the outlook for academic-community-industry partnerships in RMS drug development looks promising.

Caveolins in rhabdomyosarcoma

Caveolins are scaffolding proteins that play a pivotal role in numerous processes, including caveolae biogenesis, vesicular transport, cholesterol homeostasis and regulation of signal transduction. There are three different isoforms (Cav-1, -2 and -3) that form homo- and hetero-aggregates at the plasma membrane and modulate the activity of a number of intracellular binding proteins. Cav-1 and Cav-3, in particular, are respectively expressed in the reserve elements (e.g. satellite cells) and in mature myofibres of skeletal muscle and their expression interplay characterizes the switch from muscle precursors to differentiated elements. Recent findings have shown that caveolins are also expressed in rhabdomyosarcoma, a group of heterogeneous childhood soft-tissue sarcomas in which the cancer cells seem to derive from progenitors that resemble myogenic cells. In this review, we will focus on the role of caveolins in rhabdomyosarcomas and on their potential use as markers of the degree of differentiation in these paediatric tumours. Given that the function of Cav-1 as tumour conditional gene in cancer has been well-established, we will also discuss the relationship between Cav-1 and the progression of rhabdomyosarcoma.

IL-4R drives dedifferentiation, mitogenesis, and metastasis in rhabdomyosarcoma

PURPOSE

Rhabdomyosarcoma (RMS) is the most common soft tissue sarcoma in childhood. The alveolar subtype of rhabdomyosarcoma (ARMS) is a paradigm for refractory and incurable solid tumors because more than half of the children at diagnosis have either regional lymph node or distant metastases. These studies follow our previous observation that Interleukin-4 receptor α (IL-4Rα) is upregulated in both human and murine ARMS, and that the IL-4R signaling pathway may be a target for abrogating tumor progression.

EXPERIMENTAL DESIGN

By in vitro biochemical and cell biology studies as well as preclinical studies using a genetically engineered mouse model, we evaluated the role of IL-4 and IL-13 in IL-4R-mediated mitogenesis, myodifferentiation, and tumor progression.

RESULTS

IL-4 and IL-13 ligands accelerated tumor cell growth and activated STAT6, Akt, or MAPK signaling pathways in the human RMS cell lines, RD and Rh30, as well as in mouse primary ARMS cell cultures. IL-4 and IL-13 treatment also decreased protein expression of myogenic differentiation factors MyoD and Myogenin, indicating a loss of muscle differentiation. Using a genetically engineered mouse model of ARMS, we have shown that inhibition of IL-4R signaling pathway with a neutralizing antibody has a profound effect on the frequency of lymph node and pulmonary metastases, resulting in significant survival extension in vivo.

CONCLUSIONS

Our results indicate that an IL-4R-dependent signaling pathway regulates tumor cell progression in RMS, and inhibition of this pathway could be a promising adjuvant therapeutic approach.

Rhabdomyosarcomas in aging A/J mice

Rhabdomyosarcomas (RSCs) are skeletal muscle neoplasms found in humans and domestic mammals. The A/J inbred strain developed a high frequency (between 70–80%) of adult pleomorphic type (APT) RSC at >20 months of age while BALB/cByJ also develop RSC but less frequently. These neoplasms invaded skeletal muscle surrounding either the axial or proximal appendicular skeleton and were characterized by pleomorphic cells with abundant eosinophilic cytoplasm, multiple nuclei, and cross striations. The diagnosis was confirmed by detection of alpha-sarcomeric actin and myogenin in the neoplastic cells using immunocytochemistry. The A/J strain, but not the related BALB/c substrains, is also characterised by a progressive muscular dystrophy homologous to limb-girdle muscular dystrophy type 2B. The association between the development of RSC in similar muscle groups to those most severely affected by the progressive muscular dystrophy suggested that these neoplasms developed from abnormal regeneration of the skeletal muscle exacerbated by the dysferlin mutation. Transcriptome analyses of RSCs revealed marked downregulation of genes in muscular development and function signaling networks. Non-synonymous coding SNPs were found in Myl1, Abra, Sgca, Ttn, and Kcnj12 suggesting these may be important in the pathogenesis of RSC. These studies suggest that A strains of mice can be useful models for dissecting the molecular genetic basis for development, progression, and ultimately for testing novel anticancer therapeutic agents dealing with rhabdomyosarcoma.

MicroRNA-206 expression levels correlate with clinical behaviour of rhabdomyosarcomas

Background:

Rhabdomyosarcomas (RMSs) are primarily paediatric sarcomas that resemble developing skeletal muscle. Our aim was to determine the effects of microRNAs (miRNA) that have been implicated in muscle development on the clinical behaviour of RMSs.

Methods:

Expression levels of miR-1, miR-206, miR-133a and miR-133b were quantified by RT–PCR in 163 primary paediatric RMSs, plus control tissues, and correlated with clinico-pathological features. Correlations with parallel gene expression profiling data for 84 samples were used to identify pathways associated with miR-206. Synthetic miR-206 was transfected into RMS cell lines and phenotypic responses assessed.

Results:

Muscle-specific miRNAs levels were lower in RMSs compared with skeletal muscle but generally higher than in other normal tissues. Low miR-206 expression correlated with poor overall survival and was an independent predictor of shorter survival in metastatic embryonal and alveolar cases without PAX3/7-FOXO1 fusion genes. Low miR-206 expression also significantly correlated with high SIOP stage and the presence of metastases at diagnosis. High miR-206 expression strongly correlated with genes linked to muscle differentiation and low expression was associated with genes linked to MAPkinase and NFKappaB pathway activation. Increasing miR-206 expression in cell lines inhibited cell growth and migration and induced apoptosis that was associated with myogenic differentiation in some, but not all, cell lines.

Conclusion:

miR-206 contributes to the clinical behaviour of RMSs and the pleiotropic effects of miR-206 supports therapeutic potential.

Molecular and cellular biology of rhabdomyosarcoma

Rhabdomyosarcoma is a group of soft-tissue sarcomas that share features of skeletal myogenesis, but show extensive heterogeneity in histology, age and site of onset, and prognosis. This review matches recent molecular data with biological features of rhabdomyosarcoma. Alterations in molecular pathways, animal models, cell of origin and potential new therapeutic targets are discussed.