cDNA microarrays detect activation of a myogenic transcription program by the PAX3-FKHR fusion oncogene

Upregulation of the AMPK-FOXO1-PDK4 pathway is a primary mechanism of pyruvate dehydrogenase activity reduction in tafazzin-deficient cells

Barth syndrome (BTHS) is a rare disorder caused by mutations in the TAFAZZIN gene. Previous studies from both patients and model systems have established metabolic dysregulation as a core component of BTHS pathology. In particular, features such as lactic acidosis, pyruvate dehydrogenase (PDH) deficiency, and aberrant fatty acid and glucose oxidation have been identified. However, the lack of a mechanistic understanding of what causes these conditions in the context of BTHS remains a significant knowledge gap, and this has hindered the development of effective therapeutic strategies for treating the associated metabolic problems. In the current study, we utilized tafazzin-knockout C2C12 mouse myoblasts (TAZ-KO) and cardiac and skeletal muscle tissue from tafazzin-knockout mice to identify an upstream mechanism underlying impaired PDH activity in BTHS. This mechanism centers around robust upregulation of pyruvate dehydrogenase kinase 4 (PDK4), resulting from hyperactivation of AMP-activated protein kinase (AMPK) and subsequent transcriptional upregulation by forkhead box protein O1 (FOXO1). Upregulation of PDK4 in tafazzin-deficient cells causes direct phospho-inhibition of PDH activity accompanied by increased glucose uptake and elevated intracellular glucose concentration. Collectively, our findings provide a novel mechanistic framework whereby impaired tafazzin function ultimately results in robust PDK4 upregulation, leading to impaired PDH activity and likely linked to dysregulated metabolic substrate utilization. This mechanism may underlie previously reported findings of BTHS-associated metabolic dysregulation.

Upregulation of the AMPK-FOXO1-PDK4 pathway is a primary mechanism of pyruvate dehydrogenase activity reduction and leads to increased glucose uptake in tafazzin-deficient cells

Barth syndrome (BTHS) is a rare disorder caused by mutations in the TAFAZZIN gene. Previous studies from both patients and model systems have established metabolic dysregulation as a core component of BTHS pathology. In particular, features such as lactic acidosis, pyruvate dehydrogenase (PDH) deficiency, and aberrant fatty acid and glucose oxidation have been identified. However, the lack of a mechanistic understanding of what causes these conditions in the context of BTHS remains a significant knowledge gap, and this has hindered the development of effective therapeutic strategies for treating the associated metabolic problems. In the current study, we utilized tafazzin-knockout C2C12 mouse myoblasts (TAZ-KO) and cardiac and skeletal muscle tissue from tafazzin-knockout mice to identify an upstream mechanism underlying impaired PDH activity in BTHS. This mechanism centers around robust upregulation of pyruvate dehydrogenase kinase 4 (PDK4), resulting from hyperactivation of AMP-activated protein kinase (AMPK) and subsequent transcriptional upregulation by forkhead box protein O1 (FOXO1). Upregulation of PDK4 in tafazzin-deficient cells causes direct phospho-inhibition of PDH activity accompanied by increased glucose uptake and elevated intracellular glucose concentration. Collectively, our findings provide a novel mechanistic framework whereby impaired tafazzin function ultimately results in robust PDK4 upregulation, leading to impaired PDH activity and likely linked to dysregulated metabolic substrate utilization. This mechanism may underlie previously reported findings of BTHS-associated metabolic dysregulation.

Preclinical development of a chimeric antigen receptor T cell therapy targeting FGFR4 in rhabdomyosarcoma

Pediatric patients with relapsed or refractory rhabdomyosarcoma (RMS) have dismal cure rates, and effective therapy is urgently needed. The oncogenic receptor tyrosine kinase fibroblast growth factor receptor 4 (FGFR4) is highly expressed in RMS and lowly expressed in healthy tissues. Here, we describe a second-generation FGFR4-targeting chimeric antigen receptor (CAR), based on an anti-human FGFR4-specific murine monoclonal antibody 3A11, as an adoptive T cell treatment for RMS. The 3A11 CAR T cells induced robust cytokine production and cytotoxicity against RMS cell lines in vitro. In contrast, a panel of healthy human primary cells failed to activate 3A11 CAR T cells, confirming the selectivity of 3A11 CAR T cells against tumors with high FGFR4 expression. Finally, we demonstrate that 3A11 CAR T cells are persistent in vivo and can effectively eliminate RMS tumors in two metastatic and two orthotopic models. Therefore, our study credentials CAR T cell therapy targeting FGFR4 to treat patients with RMS.

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.

SIX1 reprograms myogenic transcription factors to maintain the rhabdomyosarcoma undifferentiated state

Rhabdomyosarcoma (RMS) is a pediatric muscle sarcoma characterized by expression of the myogenic lineage transcription factors (TFs) MYOD1 and MYOG. Despite high expression of these TFs, RMS cells fail to terminally differentiate, suggesting the presence of factors that alter their functions. Here, we demonstrate that the developmental TF SIX1 is highly expressed in RMS and critical for maintaining a muscle progenitor-like state. SIX1 loss induces differentiation of RMS cells into myotube-like cells and impedes tumor growth in vivo. We show that SIX1 maintains the RMS undifferentiated state by controlling enhancer activity and MYOD1 occupancy at loci more permissive to tumor growth over muscle differentiation. Finally, we demonstrate that a gene signature derived from SIX1 loss correlates with differentiation status and predicts RMS progression in human disease. Our findings demonstrate a master regulatory role of SIX1 in repression of RMS differentiation via genome-wide alterations in MYOD1 and MYOG-mediated transcription.

SNAI2-Mediated Repression of BIM Protects Rhabdomyosarcoma from Ionizing Radiation

Ionizing radiation (IR) and chemotherapy are mainstays of treatment for patients with rhabdomyosarcoma, yet the molecular mechanisms that underlie the success or failure of radiotherapy remain unclear. The transcriptional repressor SNAI2 was previously identified as a key regulator of IR sensitivity in normal and malignant stem cells through its repression of the proapoptotic BH3-only gene PUMA/BBC3. Here, we demonstrate a clear correlation between SNAI2 expression levels and radiosensitivity across multiple rhabdomyosarcoma cell lines. Modulating SNAI2 levels in rhabdomyosarcoma cells through its overexpression or knockdown altered radiosensitivity in vitro and in vivo. SNAI2 expression reliably promoted overall cell growth and inhibited mitochondrial apoptosis following exposure to IR, with either variable or minimal effects on differentiation and senescence, respectively. Importantly, SNAI2 knockdown increased expression of the proapoptotic BH3-only gene BIM, and chromatin immunoprecipitation sequencing experiments established that SNAI2 is a direct repressor of BIM/BCL2L11. Because the p53 pathway is nonfunctional in the rhabdomyosarcoma cells used in this study, we have identified a new, p53-independent SNAI2/BIM signaling axis that could potentially predict clinical responses to IR treatment and be exploited to improve rhabdomyosarcoma therapy. SIGNIFICANCE: SNAI2 is identified as a major regulator of radiation-induced apoptosis in rhabdomyosarcoma through previously unknown mechanisms independent of p53.

A human Myogenin promoter modified to be highly active in alveolar rhabdomyosarcoma drives an effective suicide gene therapy

Rhabdomyosarcoma is a rare childhood soft tissue cancer whose cells resemble poorly differentiated skeletal muscle, expressing myogenic proteins including MYOGENIN. Alveolar rhabdomyosarcoma (ARMS) accounts for ~40% of cases and is associated with a poorer prognosis than other rhabdomyosarcoma variants, especially if containing the chromosomal translocation generating the PAX3-FOXO1 hybrid transcription factor. Metastasis is commonly present at diagnosis, with a five-year survival rate of <30%, highlighting the need for novel therapeutic approaches. We designed a suicide gene therapy by generating an ARMS-targeted promoter to drive the herpes simplex virus thymidine kinase (HSV-TK) suicide gene. We modified the minimal human MYOGENIN promoter by deleting both the NF1 and MEF3 transcription factor binding motifs to produce a promoter that is highly active in ARMS cells. Our bespoke ARMS promoter driving HSV-TK efficiently killed ARMS cells in vitro, but not skeletal myoblasts. Using a xenograft mouse model, we also demonstrated that ARMS promoter-HSV-TK causes apoptosis of ARMS cells in vivo. Importantly, combining our suicide gene therapy with standard chemotherapy agents used in the treatment of rhabdomyosarcoma, reduced the effective drug dose, diminishing deleterious side effects/patient burden. This modified, highly ARMS-specific promoter could provide a new therapy option for this difficult-to-treat cancer.

Immunohistochemical detection of PAX-FOXO1 fusion proteins in alveolar rhabdomyosarcoma using breakpoint specific monoclonal antibodies

Alveolar Rhabdomyosarcoma (ARMS) is an aggressive pediatric cancer with about 80% of cases characterized by either a t(1;13)(p36;q14) or t(2;13)(q35;q14), which results in the formation of the fusion oncogenes PAX7-FOXO1 and PAX3-FOXO1, respectively. Since patients with fusion-positive ARMS (FP-RMS) have a poor prognosis and are treated with an aggressive therapeutic regimen, correct classification is of clinical importance. Detection of the translocation by different molecular methods is used for diagnostics, including fluorescence in situ hybridization and RT-PCR or NGS based approaches. Since these methods are complex and time consuming, we developed specific monoclonal antibodies (mAbs) directed to the junction region on the PAX3-FOXO1 fusion protein. Two mAbs, PFM.1 and PFM.2, were developed and able to immunoprecipitate in vitro-translated PAX3-FOXO1 and cellular PAX3-FOXO1 from FP-RMS cells. Furthermore, the mAbs recognized a 105 kDa band in PAX3-FOXO1-transfected cells and in FP-RMS cell lines. The mAbs did not recognize proteins in fusion-negative embryonal rhabdomyosarcoma cell lines, nor did they recognize PAX3 or FOXO1 alone when compared to anti-PAX3 and anti-FOXO1 antibodies. We next evaluated the ability of mAb PFM.2 to detect the fusion protein by immunohistochemistry. Both PAX3-FOXO1 and PAX7-FOXO1 were detected in HEK293 cells transfected with the corresponding cDNAs. Subsequently, we stained 26 primary tumor sections and a rhabdomyosarcoma tissue array and detected both fusion proteins with a positive predictive value of 100%, negative predictive value of 98%, specificity of 100% and a sensitivity of 91%. While tumors are stained homogenously in PAX3-FOXO1 cases, the staining pattern is heterogenous with scattered positive cells only in tumors expressing PAX7-FOXO1. No staining was observed in stromal cells, embryonal rhabdomyosarcoma, and fusion-negative rhabdomyosarcoma. These results demonstrate that mAbs specific for the chimeric oncoproteins PAX3-FOXO1 and PAX7-FOXO1 can be used efficiently for simple and fast subclassification of rhabdomyosarcoma in routine diagnostics via immunohistochemical detection.

ACTA1 is inhibited by PAX3-FOXO1 through RhoA-MKL1-SRF signaling pathway and impairs cell proliferation, migration and tumor growth in Alveolar Rhabdomyosarcoma

Background

Alveolar Rhabdomyosarcoma (ARMS) is a pediatric malignant soft tissue tumor with skeletal muscle phenotype. Little work about skeletal muscle proteins in ARMS was reported. PAX3-FOXO1 is a specific fusion gene generated from the chromosomal translocation t (2;13) (q35; q14) in most ARMS. ACTA1 is the skeletal muscle alpha actin gene whose transcript was detected in ARMS. However, ACTA1 expression and regulation in ARMS have not been well investigated. This work aims to explore the expression, regulation and potential role of ACTA1 in ARMS.

Results

ACTA1 protein was detected in the studied RH30, RH4 and RH41 ARMS cells. ACTA1 was found to be inhibited by PAX3-FOXO1 at transcription and protein levels by employing western blot, luciferase reporter, qRT-PCR and immunofluorescence assays. The activities of ACTA1 gene reporter induced by RhoA, MKL1, SRF, STARS or Cytochalasin D molecule were reduced in the presence of overexpressed PAX3-FOXO1 protein. CCG-1423 is an inhibitor of RhoA-MKL1-SRF signaling, we observed there was a synergistic effect between this inhibitor and PAX3-FOXO1 to suppress ACTA1 reporter activity. Furthermore, PAX3-FOXO1 overexpression decreased ACTA1 protein level and knockdown of PAX3-FOXO1 by siRNA enhanced ACTA1 expression. In addition, both MKL1 and SRF, but not RhoA were also found to be inhibited by PAX3-FOXO1 gene at protein levels and increased once knockdown of PAX3-FOXO1 expression. The association between MKL1 and SRF in cells was decreased accordingly with ectopic expression of PAX3-FOXO1. However, the distribution of MKL1 and SRF in nuclear or cytoplasm fraction was not changed by PAX3-FOXO1 expression. Finally, we showed that ACTA1 overexpression in RH30 cells could inhibit cell proliferation and migration in vitro and impair tumor growth in vivo compared with the control groups.

Conclusions

ACTA1 is inhibited by PAX3-FOXO1 at transcription and protein levels through RhoA-MKL1-SRF signaling pathway and this inhibition may partially contribute to the tumorigenesis and development of ARMS. Our findings improved the understanding of PAX3-FOXO1 in ARMS and provided a potential strategy for the treatment of ARMS in future.

The PAX-FOXO1s trigger fast trans-differentiation of chick embryonic neural cells into alveolar rhabdomyosarcoma with tissue invasive properties limited by S phase entry inhibition

The chromosome translocations generating PAX3-FOXO1 and PAX7-FOXO1 chimeric proteins are the primary hallmarks of the paediatric fusion-positive alveolar subtype of Rhabdomyosarcoma (FP-RMS). Despite the ability of these transcription factors to remodel chromatin landscapes and promote the expression of tumour driver genes, they only inefficiently promote malignant transformation in vivo. The reason for this is unclear. To address this, we developed an in ovo model to follow the response of spinal cord progenitors to PAX-FOXO1s. Our data demonstrate that PAX-FOXO1s, but not wild-type PAX3 or PAX7, trigger the trans-differentiation of neural cells into FP-RMS-like cells with myogenic characteristics. In parallel, PAX-FOXO1s remodel the neural pseudo-stratified epithelium into a cohesive mesenchyme capable of tissue invasion. Surprisingly, expression of PAX-FOXO1s, similar to wild-type PAX3/7, reduce the levels of CDK-CYCLIN activity and increase the fraction of cells in G1. Introduction of CYCLIN D1 or MYCN overcomes this PAX-FOXO1-mediated cell cycle inhibition and promotes tumour growth. Together, our findings reveal a mechanism that can explain the apparent limited oncogenicity of PAX-FOXO1 fusion transcription factors. They are also consistent with certain clinical reports indicative of a neural origin of FP-RMS.

MERTK in cancer therapy: Targeting the receptor tyrosine kinase in tumor cells and the immune system

The receptor tyrosine kinase MERTK is aberrantly expressed in numerous human malignancies, and is a novel target in cancer therapeutics. Physiologic roles of MERTK include regulation of tissue homeostasis and repair, innate immune control, and platelet aggregation. However, aberrant expression in a wide range of liquid and solid malignancies promotes neoplasia via growth factor independence, cell cycle progression, proliferation and tumor growth, resistance to apoptosis, and promotion of tumor metastases. Additionally, MERTK signaling contributes to an immunosuppressive tumor microenvironment via induction of an anti-inflammatory cytokine profile and regulation of the PD-1 axis, as well as regulation of macrophage, myeloid-derived suppressor cell, natural killer cell and T cell functions. Various MERTK-directed therapies are in preclinical development, and clinical trials are underway. In this review we discuss MERTK inhibition as an emerging strategy for cancer therapy, focusing on MERTK expression and function in neoplasia and its role in mediating resistance to cytotoxic and targeted therapies as well as in suppressing anti-tumor immunity. Additionally, we review preclinical and clinical pharmacological strategies to target MERTK.

MERTK in cancer therapy: Targeting the receptor tyrosine kinase in tumor cells and the immune system

The receptor tyrosine kinase MERTK is aberrantly expressed in numerous human malignancies, and is a novel target in cancer therapeutics. Physiologic roles of MERTK include regulation of tissue homeostasis and repair, innate immune control, and platelet aggregation. However, aberrant expression in a wide range of liquid and solid malignancies promotes neoplasia via growth factor independence, cell cycle progression, proliferation and tumor growth, resistance to apoptosis, and promotion of tumor metastases. Additionally, MERTK signaling contributes to an immunosuppressive tumor microenvironment via induction of an anti-inflammatory cytokine profile and regulation of the PD-1 axis, as well as regulation of macrophage, myeloid-derived suppressor cell, natural killer cell and T cell functions. Various MERTK-directed therapies are in preclinical development, and clinical trials are underway. In this review we discuss MERTK inhibition as an emerging strategy for cancer therapy, focusing on MERTK expression and function in neoplasia and its role in mediating resistance to cytotoxic and targeted therapies as well as in suppressing anti-tumor immunity. Additionally, we review preclinical and clinical pharmacological strategies to target MERTK.

NuRD subunit CHD4 regulates super-enhancer accessibility in rhabdomyosarcoma and represents a general tumor dependency

The NuRD complex subunit CHD4 is essential for fusion-positive rhabdomyosarcoma (FP-RMS) survival, but the mechanisms underlying this dependency are not understood. Here, a NuRD-specific CRISPR screen demonstrates that FP-RMS is particularly sensitive to CHD4 amongst the NuRD members. Mechanistically, NuRD complex containing CHD4 localizes to super-enhancers where CHD4 generates a chromatin architecture permissive for the binding of the tumor driver and fusion protein PAX3-FOXO1, allowing downstream transcription of its oncogenic program. Moreover, CHD4 depletion removes HDAC2 from the chromatin, leading to an increase and spread of histone acetylation, and prevents the positioning of RNA Polymerase 2 at promoters impeding transcription initiation. Strikingly, analysis of genome-wide cancer dependency databases identifies CHD4 as a general cancer vulnerability. Our findings describe CHD4, a classically defined repressor, as positive regulator of transcription and super-enhancer accessibility as well as establish this remodeler as an unexpected broad tumor susceptibility and promising drug target for cancer therapy.

Identification of upstream miRNAs of SNAI2 and their influence on the metastasis of gastrointestinal stromal tumors

Background

SNAI2, a member of the snail zinc finger protein family, plays an important role in the metastasis of several types of carcinoma.

Objective

This study aims to investigate the upstream miRNAs of SNAI2 and their influence on the metastasis of gastrointestinal stromal tumors (GISTs).

Methods

The expression levels of SNAI2, CDH1, and CDH2 in GISTs were determined by immunohistochemistry, and the correlations with their clinicopathologic characteristics were analyzed. Subsequently, the miRNAs involved in regulating SNAI2 expression were predicted by bioinformatics technique, screened by miRNA microarray tests, and verified by real-time PCR, dual luciferase reporter assay, and invasion assay. The influence of SNAI2 and miRNAs on the invasive ability of the GIST cells and the related mechanism were detected.

Outcomes

SNAI2 expression significantly increased and CDH1 expression markedly decreased in the cases of GISTs with distant metastasis. Silencing of the SNAI2 gene impaired the invasiveness of GIST cells in vitro. MiR-200b-3p, miR-30c-1-3P, and miR-363-3P were verified as the upstream metastasis-associated miRNAs of SNAI2 in GISTs by miRNA microarray, real-time PCR, dual luciferase reporter assay, and invasion assay. They bound to the 3′-UTR of SNAI2, downregulated SNAI2 expression, and inhibited the invasiveness of GIST cells. SNAI2 targetedly bound to the promoter of the CDH1 gene, downregulated the expression of CDH1, and contributed to the metastasis of GISTs.

Conclusion

SNAI2 and CDH1 correlated with the metastasis of GISTs, and silencing of the SNAI2 gene impaired the invasiveness of GIST cells. MiR-200b-3p, miR-30c-1-3P, and miR-363-3P contribute to the metastasis of GISTs in vitro by mediating the SNAI2/CDH1 axis. SNAI2 may be a potential target for the treatment of GISTs in the future.

Genetics, epigenetics and redox homeostasis in rhabdomyosarcoma: Emerging targets and therapeutics

Rhabdomyosarcoma (RMS) is the most common soft tissue sarcoma accounting for 5-8% of malignant tumours in children and adolescents. Children with high risk disease have poor prognosis. Anti-RMS therapies include surgery, radiation and combination chemotherapy. While these strategies improved survival rates, they have plateaued since 1990s as drugs that target differentiation and self-renewal of tumours cells have not been identified. Moreover, prevailing treatments are aggressive with drug resistance and metastasis causing failure of several treatment regimes. Significant advances have been made recently in understanding the genetic and epigenetic landscape in RMS. These studies have identified novel diagnostic and prognostic markers and opened new avenues for treatment. An important target identified in high throughput drug screening studies is reactive oxygen species (ROS). Indeed, many drugs in clinical trials for RMS impact tumour progression through ROS. In light of such emerging evidence, we discuss recent findings highlighting key pathways, epigenetic alterations and their impacts on ROS that form the basis of developing novel molecularly targeted therapies in RMS. Such targeted therapies in combination with conventional therapy could reduce adverse side effects in young survivors and lead to a decline in long-term morbidity.

PAX3-FOXO1 escapes miR-495 regulation during muscle differentiation

Pax3 plays an essential role in myogenesis. Previously, we found a tumor-signature chimeric fusion RNA, PAX3-FOXO1 also present during muscle differentiation, raising the possibility of its physiological role. Here we demonstrated that the fusion is needed transiently for muscle lineage commitment. Interestingly, the fusion ortholog was not found in seven mouse muscle differentiation/regeneration systems, nor in other stem cell differentiation systems of another three mammal species. We noticed that Pax3 is expressed at a much lower level in human stem cells, and during muscle differentiation than in other mammals. Given the fact that the fusion and the parental Pax3 share common downstream targets, we reasoned that forming the fusion may be a mechanism for human cells to escape certain microRNA regulation on Pax3. By sequence comparison, we identified 16 candidate microRNAs that may specifically target the human PAX3 3'UTR. We used a luciferase reporter assay, examined the microRNAs expression, and conducted mutagenesis on the reporters, as well as a CRISPR/Cas9 mediated editing on the endogenous allele. Finally, we identified miR-495 as a microRNA that specifically targets human PAX3. Examining several other fusion RNAs revealed that the human-specificity is not limited to PAX3-FOXO1. Based on these observations, we conclude that PAX3-FOXO1 fusion RNA is absent in mouse, or other mammals we tested, the fusion RNA is a mechanism to escape microRNA, miR-495 regulation in humans, and that it is not the only human-specific fusion RNA.

Rhabdomyosarcoma

Rhabdomyosarcoma (RMS) is the most common soft tissue sarcoma in children and represents a high-grade neoplasm of skeletal myoblast-like cells. Decades of clinical and basic research have gradually improved our understanding of the pathophysiology of RMS and helped to optimize clinical care. The two major subtypes of RMS, originally characterized on the basis of light microscopic features, are driven by fundamentally different molecular mechanisms and pose distinct clinical challenges. Curative therapy depends on control of the primary tumour, which can arise at many distinct anatomical sites, as well as controlling disseminated disease that is known or assumed to be present in every case. Sophisticated risk stratification for children with RMS incorporates various clinical, pathological and molecular features, and that information is used to guide the application of multifaceted therapy. Such therapy has historically included cytotoxic chemotherapy as well as surgery, ionizing radiation or both. This Primer describes our current understanding of RMS epidemiology, disease susceptibility factors, disease mechanisms and elements of clinical care, including diagnostics, risk-based care of newly diagnosed and relapsed disease and the prevention and management of late effects in survivors. We also outline potential opportunities to further translate new biological insights into improved clinical outcomes.

Reactive Oxygen Species (ROS)-Inducing Triterpenoid Inhibits Rhabdomyosarcoma Cell and Tumor Growth through Targeting Sp Transcription Factors

Methyl 2-trifluoromethyl-3,11-dioxo-18β-olean-1,12-dien-3-oate (CF₃DODA-Me) is derived synthetically from glycyrrhetinic acid, a major component of licorice, and this compound induced reactive oxygen species (ROS) in RD and Rh30 rhabdomyosarcoma (RMS) cells. CF₃DODA-Me also inhibited growth and invasion and induced apoptosis in RMS cells, and these responses were attenuated after cotreatment with the antioxidant glutathione, demonstrating the effective anticancer activity of ROS in RMS. CF₃DODA-Me also downregulated expression of specificity protein (Sp) transcription factors Sp1, Sp3, and Sp4 and prooncogenic Sp-regulated genes including PAX3-FOXO1 (in Rh30 cells). The mechanism of CF₃DODA-Me-induced Sp-downregulation involved ROS-dependent repression of c-Myc and cMyc-regulated miR-27a and miR-17/20a, and this resulted in induction of the miRNA-regulated Sp repressors ZBTB4, ZBTB10, and ZBTB34. The cell and tumor growth effects of CF₃DODA-Me further emphasize the sensitivity of RMS cells to ROS inducers and their potential clinical applications for treating this deadly disease. IMPLICATIONS: CF₃DODA-Me and HDAC inhibitors that induce ROS-dependent Sp downregulation could be developed for clinical applications in treating rhabdomyosarcoma.

PAX3-FOXO1 transgenic zebrafish models identify HES3 as a mediator of rhabdomyosarcoma tumorigenesis

Alveolar rhabdomyosarcoma is a pediatric soft-tissue sarcoma caused by PAX3/7-FOXO1 fusion oncogenes and is characterized by impaired skeletal muscle development. We developed human PAX3-FOXO1 -driven zebrafish models of tumorigenesis and found that PAX3-FOXO1 exhibits discrete cell lineage susceptibility and transformation. Tumors developed by 1.6–19 months and were primitive neuroectodermal tumors or rhabdomyosarcoma. We applied this PAX3-FOXO1 transgenic zebrafish model to study how PAX3-FOXO1 leverages early developmental pathways for oncogenesis and found that her3 is a unique target. Ectopic expression of the her3 human ortholog, HES3, inhibits myogenesis in zebrafish and mammalian cells, recapitulating the arrested muscle development characteristic of rhabdomyosarcoma. In patients, HES3 is overexpressed in fusion-positive versus fusion-negative tumors. Finally, HES3 overexpression is associated with reduced survival in patients in the context of the fusion. Our novel zebrafish rhabdomyosarcoma model identifies a new PAX3-FOXO1 target, her3/HES3, that contributes to impaired myogenic differentiation and has prognostic significance in human disease.

One of the most common cancers in children and adolescents is rhabdomyosarcoma, a cancer of soft tissue such as muscle, tendon or cartilage. The fusion of DNA on two different chromosomes causes the most aggressive form of rhabdomyosarcoma. The fused DNA produces an abnormal protein called PAX3-FOXO1. During normal muscle development, a subset of rapidly growing cells eventually slow down and form mature, working muscle cells. It is still unclear how exactly rhabdomyosarcoma develops, but it is thought that PAX3-FOXO1 stops muscle cells from maturing and the cells that grow out of control result in a tumor. Learning how PAX3-FOXO1 hijacks normal muscle development could lead to new treatments for rhabdomyosarcoma.

One treatment approach is to slow the growth of a tumor and force the cells to mature. Then, young patients might avoid chemotherapy or radiation treatments and their side effects. Efforts to improve treatment for this type of cancer face several obstacles. Currently, only one vertebrate animal model of the disease is available to test drugs, and it is still not known how PAX3-FOXO1 causes healthy cells to become cancerous. It is also hard to turn off PAX3-FOXO1 itself, so scientists must find additional proteins that collaborate with it to target with drugs.

Now, Kendall et al. show that genetically engineered zebrafish with human PAX3-FOXO1 develop rhabdomyosarcoma-like tumors. Experiments on these zebrafish showed that the protein turns on a gene called her3. Humans have a similar gene called HES3. In zebrafish or mouse cells, human HES3 interferes with muscle-cell maturation and allows cells that acquire PAX3-FOXO1 to persist during development instead of dying. It also increases the cell growth and cancerous behavior in human tumor cells. Kendall et al. further looked at HES3 levels in tumors collected from patients with rhabdomyosarcoma and found that having higher levels of HES3 increased the risk of death from the cancer.

Human rhabdomyosarcoma tumors with high HES3 levels were also more likely to have certain cell-growth and cell-differentiation related proteins. Drugs that turn off or modify the activity of these proteins already exist. Testing these drugs that target processes such as cell growth in the zebrafish with rhabdomyosarcoma-like tumors may help scientists determine if they reduce tumor growth. If they do, additional trials could determine if they would help patients with rhabdomyosarcoma.

DNA Chips: The Future of Biomarkers

DNA chips are small, solid supports such as microscope slides onto which thousands of cDNAs or oligonucleotides are arrayed, representing known genes or simply EST clones, or covering the entire sequence of a gene with all its possible mutations. Fluorescently labeled DNA or RNA extracted from tissues is hybridized to the array. Laser scanning of the chip permits quantitative evaluation of each individual complementary sequence present in the sample.

DNA chip technology is currently being proposed for qualitative and quantitative applications, firstly for the detection of point mutations, small deletions and insertions in genes involved in human diseases or affected during cancer progression; secondly, to determine on a genome-wide basis the pattern of gene expression in tumors, as well as in a number of experimental situations.

The extraordinary power of DNA chips will have a strong impact on medicine in the near future, both in the molecular characterization of tumors and genetic diseases and in drug discovery and evaluation. Quantitative applications will soon spread through all fields of biology.

Identification of rare paired box 3 variant in strabismus by whole exome sequencing

AIM

To identify the potentially pathogenic gene variants that contributes to the etiology of strabismus.

METHODS

A Chinese pedigree with strabismus was collected and the exomes of two affected individuals were sequenced using the next-generation sequencing technology. The resulting variants from exome sequencing were filtered by subsequent bioinformatics methods and the candidate mutation was verified as heterozygous in the affected proposita and her mother by sanger sequencing.

RESULTS

Whole exome sequencing and filtering identified a nonsynonymous mutation c.434G-T transition in paired box 3 (PAX3) in the two affected individuals, which were predicted to be deleterious by more than 4 bioinformatics programs. This altered amino acid residue was located in the conserved PAX domain of PAX3. This gene encodes a member of the PAX family of transcription factors, which play critical roles during fetal development. Mutations in PAX3 were associated with Waardenburg syndrome with strabismus.

CONCLUSION

Our results report that the c.434G-T mutation (p.R145L) in PAX3 may contribute to strabismus, expanding our understanding of the causally relevant genes for this disorder.

PAX3-FOXO1 Establishes Myogenic Super Enhancers and Confers BET Bromodomain Vulnerability

Alveolar rhabdomyosarcoma is a life-threatening myogenic cancer of children and adolescent young adults, driven primarily by the chimeric transcription factor PAX3-FOXO1. The mechanisms by which PAX3-FOXO1 dysregulates chromatin are unknown. We find PAX3-FOXO1 reprograms the cis-regulatory landscape by inducing de novo super enhancers. PAX3-FOXO1 uses super enhancers to set up autoregulatory loops in collaboration with the master transcription factors MYOG, MYOD, and MYCN. This myogenic super enhancer circuitry is consistent across cell lines and primary tumors. Cells harboring the fusion gene are selectively sensitive to small-molecule inhibition of protein targets induced by, or bound to, PAX3-FOXO1-occupied super enhancers. Furthermore, PAX3-FOXO1 recruits and requires the BET bromodomain protein BRD4 to function at super enhancers, resulting in a complete dependence on BRD4 and a significant susceptibility to BRD inhibition. These results yield insights into the epigenetic functions of PAX3-FOXO1 and reveal a specific vulnerability that can be exploited for precision therapy.Significance: PAX3-FOXO1 drives pediatric fusion-positive rhabdomyosarcoma, and its chromatin-level functions are critical to understanding its oncogenic activity. We find that PAX3-FOXO1 establishes a myoblastic super enhancer landscape and creates a profound subtype-unique dependence on BET bromodomains, the inhibition of which ablates PAX3-FOXO1 function, providing a mechanistic rationale for exploring BET inhibitors for patients bearing PAX-fusion rhabdomyosarcoma. Cancer Discov; 7(8); 884-99. ©2017 AACR.This article is highlighted in the In This Issue feature, p. 783.

The CINSARC signature as a prognostic marker for clinical outcome in multiple neoplasms

We previously reported the CINSARC signature as a prognostic marker for metastatic events in soft tissue sarcomas, breast carcinomas and lymphomas through genomic instability, acting as a major factor for tumor aggressiveness. In this study, we used a published resource to investigate CINSARC enrichment in poor outcome-associated genes at pan-cancer level and in 39 cancer types. CINSARC outperformed more than 15,000 defined signatures (including cancer-related), being enriched in top-ranked poor outcome-associated genes of 21 cancer types, widest coverage reached among all tested signatures. Independently, this signature demonstrated significant survival differences between risk-groups in 33 published studies, representing 17 tumor types. As a consequence, we propose the CINSARC prognostication as a general marker for tumor aggressiveness to optimize the clinical managements of patients.

An Examination of the Role of Transcriptional and Posttranscriptional Regulation in Rhabdomyosarcoma

Rhabdomyosarcoma (RMS) is an aggressive family of soft tissue tumors that most commonly manifests in children. RMS variants express several skeletal muscle markers, suggesting myogenic stem or progenitor cell origin of RMS. In this review, the roles of both recently identified and well-established microRNAs in RMS are discussed and summarized in a succinct, tabulated format. Additionally, the subtypes of RMS are reviewed along with the involvement of basic helix-loop-helix (bHLH) proteins, Pax proteins, and microRNAs in normal and pathologic myogenesis. Finally, the current and potential future treatment options for RMS are outlined.

Increased Six1 expression is associated with poor prognosis in patients with osteosarcoma

Sine oculis homeobox homolog 1 (Six1) is an evolutionarily conserved transcription factor that acts as master regulator of development and is frequently dysregulated in various types of cancer. Six1 has been demonstrated to be upregulated in human osteosarcoma cell lines compared with osteoblastic cell lines. However, the association of Six1 expression with the progression and prognosis of osteosarcoma patients remains unclear. The purpose of the present study was to investigate the association between Six1 expression and the clinicopathological characteristics and prognosis of osteosarcoma. Six1 protein was detected by immunohistochemistry in a series of 100 osteosarcoma patients, and Kaplan-Meier survival analysis was performed to assess prognosis. The results revealed that increased Six1 protein expression was prevalent in osteosarcoma and was significantly associated with Enneking stage (P=0.002) and tumor size (P=0.010). Additionally, according to the log-rank test and Cox regression model, expression of Six1 is indicated to be an independent prognostic factor in osteosarcoma patients. In summary, positive expression of Six1 protein is closely associated with the tumor progression and poor survival of osteosarcoma patients. The results suggest that Six1 is a overexpressed in individuals with poor prognosis, and may thus be used as a prognostic biomarker in patients with osteosarcoma.

Six1 expression is associated with a poor prognosis in patients with glioma

Glioma is the most common human brain cancer and has poor prognosis. Messenger RNA profiling identified that sineoculis homeobox homolog 1 (Six1) is dysregulated in glioma tumor progenitor cells from glial progenitor cells isolated from normal white matter. However, the expression and role of Six1 in glioma remains unclear. The purpose of the present study was to investigate the expression level of Six1 in glioma tissues and the association between Six1 expression and clinicopathological characteristics and prognosis of gliomas. The Six1 protein was detected by immunohistochemistry in 163 glioma tissues of distinct malignancy grades, and Kaplan-Meier survival analysis was performed to assess the prognosis of the patients. The Six1 protein was stained in 49.1% (80 out of 163) of the glioma tissues, including 34.2% of low-grade [World Health Organization (WHO) I/II] gliomas and 80.8% of high-grade (WHO III/IV) gliomas. Normal brain tissues rarely expressed the Six1 protein. In addition, Six1 expression was significantly associated with WHO grade (P<0.001). According to the log-rank test and Cox regression model, Six1 may be suggested as an independent prognostic factor, in addition to the WHO grade. Overall, Six1 protein expression varies between different grades of glioma and is associated with the WHO grade. Upregulation of Six1 is more frequent in high-grade glioma and is an independent prognostic factor of poor clinical outcome.

PAX3-FOXO1A Expression in Rhabdomyosarcoma Is Driven by the Targetable Nuclear Receptor NR4A1

Alveolar rhabdomyosarcoma (ARMS) is a devastating pediatric disease driven by expression of the oncogenic fusion gene PAX3-FOXO1A. In this study, we report overexpression of the nuclear receptor NR4A1 in rhabdomyosarcomas that is sufficient to drive high expression of PAX3-FOXO1A there. RNAi-mediated silencing of NR4A1 decreased expression of PAX3-FOXO1A and its downstream effector genes. Similarly, cell treatment with the NR4A1 small-molecule antagonists 1,1-bis(3-indolyl)-1-(p-hydroxy or p-carbomethoxyphenyl)methane (C-DIM) decreased PAX3-FOXO1A. Mechanistic investigations revealed a requirement for the NR4A1/Sp4 complex to bind GC-rich promoter regions to elevate transcription of the PAX3-FOXO1A gene. In parallel, NR4A1 also regulated expression of β1-integrin, which with PAX3-FOXO1A, contributed to tumor cell migration that was blocked by C-DIM/NR4A1 antagonists. Taken together, our results provide a preclinical rationale for the use of NR4A1 small-molecule antagonists to treat ARMS and other rhabdomyosarcomas driven by PAX3-FOXO1A. Cancer Res; 77(3); 732-41. ©2016 AACR.

Helicase CHD4 is an epigenetic coregulator of PAX3-FOXO1 in alveolar rhabdomyosarcoma

A vast number of cancer genes are transcription factors that drive tumorigenesis as oncogenic fusion proteins. Although the direct targeting of transcription factors remains challenging, therapies aimed at oncogenic fusion proteins are attractive as potential treatments for cancer. There is particular interest in targeting the oncogenic PAX3-FOXO1 fusion transcription factor, which induces alveolar rhabdomyosarcoma (aRMS), an aggressive cancer of skeletal muscle cells for which patient outcomes remain dismal. In this work, we have defined the interactome of PAX3-FOXO1 and screened 60 candidate interactors using siRNA-mediated depletion to identify candidates that affect fusion protein activity in aRMS cells. We report that chromodomain helicase DNA binding protein 4 (CHD4), an ATP-dependent chromatin remodeler, acts as crucial coregulator of PAX3-FOXO1 activity. CHD4 interacts with PAX3-FOXO1 via short DNA fragments. Together, they bind to regulatory regions of PAX3-FOXO1 target genes. Gene expression analysis suggested that CHD4 coregulatory activity is essential for a subset of PAX3-FOXO1 target genes. Depletion of CHD4 reduced cell viability of fusion-positive but not of fusion-negative RMS in vitro, which resembled loss of PAX3-FOXO1. It also caused specific regression of fusion-positive xenograft tumors in vivo. Therefore, this work identifies CHD4 as an epigenetic coregulator of PAX3-FOXO1 activity, providing rational evidence for CHD4 as a potential therapeutic target in aRMS.

P/CAF mediates PAX3-FOXO1-dependent oncogenesis in alveolar rhabdomyosarcoma

Alveolar rhabdomyosarcoma (ARMS) is an aggressive paediatric cancer of skeletal muscle with poor prognosis. A PAX3-FOXO1 fusion protein acts as a driver of malignancy in ARMS by disrupting tightly coupled but mutually exclusive pathways of proliferation and differentiation. While PAX3-FOXO1 is an attractive therapeutic target, no current treatments are designed to block its oncogenic activity. The present work shows that the histone acetyltransferase P/CAF (KAT2B) is overexpressed in primary tumours from ARMS patients. Interestingly, in fusion-positive ARMS cell lines, P/CAF acetylates and stabilizes PAX3-FOXO1 rather than MyoD, a master regulator of muscle differentiation. Silencing P/CAF, or pharmacological inhibition of its acetyltransferase activity, down-regulates PAX3-FOXO1 levels concomitant with reduced proliferation and tumour burden in xenograft mouse models. Our studies identify a P/CAF-PAX3-FOXO1 signalling node that promotes oncogenesis and may contribute to MyoD dysfunction in ARMS. This work exemplifies the therapeutic potential of targeting chromatin-modifying enzymes to inhibit fusion oncoproteins that are a frequent event in sarcomas. Copyright © 2016 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Comparative transcriptomic analysis reveals the oncogenic fusion protein PAX3-FOXO1 globally alters mRNA and miRNA to enhance myoblast invasion

Rhabdomyosarcoma, one of the most common childhood sarcomas, is comprised of two main subtypes, embryonal and alveolar (ARMS). ARMS, the more aggressive subtype, is primarily characterized by the t(2;13)(p35;p14) chromosomal translocation, which fuses two transcription factors, PAX3 and FOXO1 to generate the oncogenic fusion protein PAX3-FOXO1. Patients with PAX3-FOXO1-postitive tumors have a poor prognosis, in part due to the enhanced local invasive capacity of these cells, which leads to the increased metastatic potential for this tumor. Despite this knowledge, little is known about the role that the oncogenic fusion protein has in this increased invasive potential. In this report we use large-scale comparative transcriptomic analyses in physiologically relevant primary myoblasts to demonstrate that the presence of PAX3-FOXO1 is sufficient to alter the expression of 70 mRNA and 27 miRNA in a manner predicted to promote cellular invasion. In contrast the expression of PAX3 alters 60 mRNA and 23 miRNA in a manner predicted to inhibit invasion. We demonstrate that these alterations in mRNA and miRNA translate into changes in the invasive potential of primary myoblasts with PAX3-FOXO1 increasing invasion nearly 2-fold while PAX3 decreases invasion nearly 4-fold. Taken together, these results allow us to build off of previous reports and develop a more expansive molecular model by which the presence of PAX3-FOXO1 alters global gene regulatory networks to enhance the local invasiveness of cells. Further, the global nature of our observed changes highlights the fact that instead of focusing on a single-gene target, we must develop multi-faceted treatment regimens targeting multiple genes of a single oncogenic phenotype or multiple genes that target different oncogenic phenotypes for tumor progression.

Pitavastatin Regulates Ang II Induced Proliferation and Migration via IGFBP-5 in VSMC

Angiotensin II (Ang II), a key mediator of hypertensive, causes structural changes in the arteries (vascular remodeling), which involve alterations in cell growth, vascular smooth muscle cell (VSMC) hypertrophy. Ang II promotes fibrotic factor like IGFBP5, which mediates the profibrotic effects of Ang II in the heart and kidneys, lung and so on. The purpose of this study was to identify the signaling pathway of IGFBP5 on cell proliferation and migration of Ang II-stimulated VSMC. We have been interested in Ang II-induced IGFBP5 and were curious to determine whether a Pitavastatin would ameliorate the effects. Herein, we investigated the question of whether Ang II induced the levels of IGFBP5 protein followed by proliferation and migration in VSMC. Pretreatment with the specific Angiotensin receptor type 1 (AT1) inhibitor (Losartan), Angiotensin receptor type 2 (AT2) inhibitor (PD123319), MAPK inhibitor (U0126), ERK1/2 inhibitor (PD98059), P38 inhibitor (SB600125) and PI3K inhibitor (LY294002) resulted in significantly inhibited IGFBP5 production, proliferation, and migration in Ang II-stimulated VSMC. In addition, IGFBP5 knockdown resulted in modulation of Ang II induced proliferation and migration via IGFBP5 induction. In addition, Pitavastatin modulated Ang II induced proliferation and migration in VSMC. Taken together, our results indicated that Ang II induces IGFBP5 through AT1, ERK1/2, P38, and PI3K signaling pathways, which were inhibited by Pitavastatin. These findings may suggest that Pitavastatin has an effect on vascular disease including hypertension.

Increased expression of Six1 correlates with progression and prognosis of prostate cancer

Sineoculis homeobox homolog 1 (Six1), normally a developmentally restricted transcriptional regulator, is frequently dysregulated in mutiple cancers. Increasing evidences show that overexpression of Six1 plays a key role in tumorigenesis. However, the Six1 expression status and its relationship with the clinicopathological characteristics in prostate cancer were unclear. In this study, the mRNA and protein levels of Six1 in prostate cancer tissues and normal prostate tissues were evaluated. The clinicopathological significance of Six1 was investigated by immunohistochemistry (IHC) on a prostate cancer tissue microarray. The cut-off score for high expression of Six1 was determined by the receiver-operating characteristic (ROC) analysis. The correlation between Six1 protein expression and clinicopathological characteristics of prostate cancer was analyzed by Chi-square test. Increased expression of Six1 protein was observed in the majority of prostate cancer, compared with their paired adjacent normal prostate tissues. When Six1 high expression percentage was determined to be above 55 % (area under ROC curve = 0.881, P = 0.000), high expression of Six1 was observed in 55.6 % (80/144) of prostate cancer tissues and low expression of Six1 was observed in all normal prostate tissues by IHC. Increased expression of Six1 in patients was correlated with high histological grade (χ2 = 58.651, P = 0.00), advanced clinical stage (χ2 = 57.330, P = 0.000), high Gleason score (χ2 = 63.480, P = 0.000), high primary tumor grade (χ2 = 57.330, P = 0.000) and positive regional lymph node metastasis (χ2 = 19.294, P = 0.000). Furthermore, univariate and multivariate survival analysis suggested that Six1 was an independent prognostic indicator for overall survival (P < 0.05). This study suggests that Six1 could be served as an additional biomarker in identifying prostate cancer patients at risk of tumor progression, might potentially be used for predicting survival outcome of patients with prostate cancer.

Pediatric Rhabdomyosarcoma

Rhabdomyosarcoma is the most common soft-tissue sarcoma of childhood, and despite clinical advances, subsets of these patients continue to suffer high levels of morbidity and mortality associated with their disease. Recent genetic and molecular characterization of these tumors using sophisticated genomics techniques, including next-generation sequencing experiments, has revealed multiple areas that can be exploited for new molecularly targeted therapies for this disease.

Chimeric RNAs generated by intergenic splicing in normal and cancer cells

A hallmark of many neoplasias is chromosomal rearrangement, an event that commonly results in the fusion of two separate genes. The RNA and protein resulting from these gene fusions often play critical roles in cancer development, maintenance, and progression. Traditionally, these fusion products are thought to be produced solely due to DNA level changes and are therefore considered unique to cancer. Recent advances in microarray and deep-sequencing have revealed many more fusion transcripts. Surprisingly, some are without detectable rearrangement at the DNA level. Reports have demonstrated that at least some of these chimeric RNAs are generated via intergenic splicing. In this review, we highlight three examples of these noncanonical chimeric transcripts that are formed by trans-splicing or cis-splicing of adjacent genes and summarize the knowledge we have regarding these noncanonical fusions. We discuss the implications of the chimeric RNAs in both cancer and normal physiology, as some of these fusion transcripts are found in normal, noncancerous cells with sequences identical to those generated by canonical chromosomal translocation found in cancer cells. Finally, we present methods that are currently being used to discover additional chimeric RNAs.

Reprogramming of mesenchymal stem cells by oncogenes

Mesenchymal stem cells (MSCs) originate from embryonic mesoderm and give rise to the multiple lineages of connective tissues. Transformed MSCs develop into aggressive sarcomas, some of which are initiated by specific chromosomal translocations that generate fusion proteins with potent oncogenic properties. The sarcoma oncogenes typically prime MSCs through aberrant reprogramming. They dictate commitment to a specific lineage but prevent mature differentiation, thus locking the cells in a state of proliferative precursors. Deregulated expression of lineage-specific transcription factors and controllers of chromatin structure play a central role in MSC reprogramming and sarcoma pathogenesis. This suggests that reversing the epigenetic aberrancies created by the sarcoma oncogenes with differentiation-related reagents holds great promise as a beneficial addition to sarcoma therapies.

Therapeutic cytodifferentiation in alveolar rhabdomyosarcoma without genetic change of the PAX3-FKHR chimeric fusion gene: a case study

Alveolar rhabdomyosarcoma (ARMS) is a subtype of rhabdomyosarcoma and usually occurs in childhood and adolescence. ARMS is characterized by its aggressive behavior and poor prognosis. To improve the unfavorable prognosis, new therapeutic developments and the establishment of methods for precise prognostic prediction are required. We describe a case of ARMS, solid variant, which occurred in a 10-year-old boy. After chemotherapy and radiotherapy, the tumor morphologically and immunohistochemically showed marked cytodifferentiation, whereas the exact same PAX3-FKHR chimeric fusion gene transcript was detected in samples before and after treatment. The result of this study seems to indicate that therapeutic cytodifferentiation does not always correlate with genetic change and favorable prognosis in ARMS.

MicroRNA-30a regulates zebrafish myogenesis through targeting the transcription factor Six1

Precise spatiotemporal regulation of the SIX1 homeoprotein is required to coordinate vital tissue development, including myogenesis. Whereas SIX1 is downregulated in most tissues following embryogenesis, it is re-expressed in numerous cancers, including tumors derived from muscle progenitors. Despite crucial roles in development and disease, the upstream regulation of SIX1 expression has remained elusive. Here, we identify the first direct mechanism for Six1 regulation in embryogenesis, through microRNA30a (miR30a)-mediated repression. In zebrafish somites, we show that miR30a and six1a and six1b (hereafter six1a/b) are expressed in an inverse temporal pattern. Overexpression of miR30a leads to a reduction in six1a/b levels, and results in increased apoptosis and altered somite morphology, which phenocopies six1a/b knockdown. Conversely, miR30a inhibition leads to increased Six1 expression and abnormal somite morphology, revealing a role for endogenous miR30a as a muscle-specific miRNA (myomiR). Importantly, restoration of six1a in miR30a-overexpressing embryos restores proper myogenesis. These data demonstrate a new role for miR30a at a key node in the myogenic regulatory gene network through controlling Six1 expression.

Classification of rhabdomyosarcoma and its molecular basis

Rhabdomyosarcoma (RMS), the most common soft tissue sarcoma in children, has traditionally been classified into embryonal rhabdomyosarcoma (ERMS) and alveolar rhabdomyosarcoma (ARMS) for pediatric oncology practice. This review outlines the historical development of classification of childhood RMS and the challenges that have been associated with it, particularly problems with the diagnosis of "solid variant" ARMS and its distinction from ERMS. In addition to differences in clinical presentation and outcome, a number of genetic features underpin separation of ERMS from ARMS. Genetic differences associated with RMS subclassification include the presence of reciprocal translocations and their associated fusions in ARMS, amplification of genes in ARMS and its fusion subsets, chromosomal losses and gains that mostly occur in ERMS, and allelic losses and mutations usually associated with ERMS. Chimeric proteins encoded in most ARMS from the fusion of PAX3 or PAX7 with FOXO1 are expressed, result in a distinct pattern of downstream protein expression, and appear to be the proximate cause of the bad outcome associated with this subtype. A sizeable minority of ARMS lacks these fusions and shares the clinical and biological features of ERMS. A battery of immunohistochemical tests may prove useful in separating ERMS from ARMS and fusion-positive ARMS from fusion-negative ARMS. Because of limitation of predicting outcome solely based on histologic classification, treatment protocols will begin to utilize fusion testing for stratification of affected patients into low-risk, intermediate-risk, and high-risk groups.

A chimeric RNA characteristic of rhabdomyosarcoma in normal myogenesis process

Gene fusions and their chimeric products are common features of neoplasia. Given that many cancers arise by the dysregulated recapitulation of processes in normal development, we hypothesized that comparable chimeric gene products may exist in normal cells. Here, we show that a chimeric RNA, PAX3-FOXO1, identical to that found in alveolar rhabdomyosarcoma, is transiently present in cells undergoing differentiation from pluripotent cells into skeletal muscle. Unlike cells of rhabdomyosarcoma, these cells do not seem to harbor the t(2;13) chromosomal translocation. Importantly, both PAX3-FOXO1 RNA and protein could be detected in the samples of normal fetal muscle. Overexpression of the chimera led to continuous expression of MYOD and MYOG-two myogenic markers that are overexpressed in rhabdomyosarcoma cells. Our results are consistent with a developmental role of a specific chimeric RNA generated in normal cells without the corresponding chromosomal rearrangement at the DNA level seen in neoplastic cells presumably of the same lineage.

SIGNIFICANCE

A chimeric fusion RNA, PAX3-FOXO1, associated with alveolar rhabdomyosarcoma, is also present in normal non-cancer cells and tissues. Its transient expression nature and the absence of t(2;13) chromosomal translocation are consistent with a posttranscriptional mechanism. When constantly expressed, PAX3-FOXO1 interfered with the muscle differentiation process, which presumably contributes to tumorigenesis.

Molecular pathways: MERTK signaling in cancer

MERTK is a receptor tyrosine kinase of the TAM (Tyro3, Axl, MERTK) family, with a defined spectrum of normal expression. However, MERTK is overexpressed or ectopically expressed in a wide variety of cancers, including leukemia, non-small cell lung cancer, glioblastoma, melanoma, prostate cancer, breast cancer, colon cancer, gastric cancer, pituitary adenomas, and rhabdomyosarcomas, potentially resulting in the activation of several canonical oncogenic signaling pathways. These include the mitogen-activated protein kinase and phosphoinositide 3-kinase pathways, as well as regulation of signal transducer and activator of transcription family members, migration-associated proteins including the focal adhesion kinase and myosin light chain 2, and prosurvival proteins such as survivin and Bcl-2. Each has been implicated in MERTK physiologic and oncogenic functions. In neoplastic cells, these signaling events result in functional phenotypes such as decreased apoptosis, increased migration, chemoresistance, increased colony formation, and increased tumor formation in murine models. Conversely, MERTK inhibition by genetic or pharmacologic means can reverse these pro-oncogenic phenotypes. Multiple therapeutic approaches to MERTK inhibition are currently in development, including ligand "traps", a monoclonal antibody, and small-molecule tyrosine kinase inhibitors.

Protein S: A multifunctional anticoagulant vitamin K-dependent protein at the crossroads of coagulation, inflammation, angiogenesis, and cancer

Since its discovery in 1970, protein S (PS) has emerged as a key vitamin K-dependent natural anticoagulant protein at the crossroads of multiple biological processes, including coagulation, apoptosis, atherosclerosis, angiogenesis/vasculogenesis, and cancer progression. Following the binding to a unique family of protein tyrosine kinase receptors referred to as Tyro-3, Axl and Mer (TAM) receptors, PS can lead to regulation of coagulation, phagocytosis of apoptotic cells, cell survival, activation of innate immunity, vessel integrity and angiogenesis, and local invasion and metastasis. Because of these dynamics and multiple functions of PS, which are largely lost following invalidation of the mouse PROS1 gene, this molecule is currently intensively studied in biomedical research. The purpose of this review is to provide a brief chronicle of the discovery and current understanding of the mechanisms of PS signaling, and how PS and their signaling partners regulate various cellular functions, with a particular focus on TAM receptors.

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.

Structural and functional studies of FKHR-PAX3, a reciprocal fusion gene of the t(2;13) chromosomal translocation in alveolar rhabdomyosarcoma

Alveolar rhabdomyosarcoma (ARMS) is an aggressive pediatric cancer of skeletal muscle. More than 70% of ARMS tumors carry balanced t(2;13) chromosomal translocation that leads to the production of two novel fusion genes, PAX3-FKHR and FKHR-PAX3. While the PAX3-FKHR gene has been intensely studied, the reciprocal FKHR-PAX3 gene has rarely been described. We report here the cloning and functional characterization of the FKHR-PAX3 gene as the first step towards a better understanding of its potential impact on ARMS biology. From RH30 ARMS cells, we detected and isolated three versions of FKHR-PAX3 cDNAs whose C-terminal sequences corresponded to PAX3c, PAX3d, and PAX3e isoforms. Unlike the nuclear-specific localization of PAX3-FKHR, the reciprocal FKHR-PAX3 proteins stayed predominantly in the cytoplasm. FKHR-PAX3 potently inhibited myogenesis in both non-transformed myoblast cells and ARMS cells. We showed that FKHR-PAX3 was not a classic oncogene but could act as a facilitator in oncogenic pathways by stabilizing PAX3-FKHR expression, enhancing cell proliferation, clonogenicity, anchorage-independent growth, and matrix adhesion in vitro, and accelerating the onset of tumor formation in xenograft mouse model in vivo. In addition to these pro-oncogenic behaviors, FKHR-PAX3 also negatively affected cell migration and invasion in vitro and lung metastasis in vivo. Taken together, these functional characteristics suggested that FKHR-PAX3 might have a critical role in the early stage of ARMS development.

Identification of target genes of PAX3-FOXO1 in alveolar rhabdomyosarcoma

Rhabdomyosarcoma (RMS) is a soft tissue sarcoma categorized into two major subtypes: alveolar RMS (ARMS) and embryonal RMS (ERMS). Most ARMS express the PAX3-FOXO1 (P3F) fusion oncoprotein generated by the 2;13 chromosomal translocation. In the present study, the downstream target genes of P3F were identified by analyzing two independent sets of gene expression profiles: primary RMS tumors and RD ERMS cells transduced with inducible P3F constructs. We found 34 potential target genes (27 upregulated and 7 downregulated) that were significantly and differentially expressed between P3F-positive and P3F-negative categories, both in primary RMS tumors and in the inducible P3F cell culture system. Gene ontology analysis of microarray data of the inducible P3F cell culture system employed indicated apoptosis, cell death, development, and signal transduction as overrepresented significant functional categories found in both upregulated and downregulated genes. Therefore, among the 34 potential target genes, the expression of cell death-related [Gremlin1, cysteine knot superfamily 1, BMP antagonist 1 (GREM1) and death-associated protein kinase 1 (DAPK1)] and development-related [myogenic differentiation 1 (MYOD1) and hairy/enhancer-of-split related with YRPW motif 1 (HEY1)] genes were further investigated. The differential expression of GREM1, DAPK1, MYOD1 and HEY1 was confirmed in independent tumors and inducible cell culture systems. The expression of GREM1, DAPK1 and MYOD1 were significantly upregulated; HEY1 was significantly downregulated in independent P3F-positive ARMS tumors and transcriptionally active P3F cells, compared to those in ERMS tumors and transcriptionally inactive P3F cells. This study identified target genes of P3F and suggested that four downstream targets (GREM1, DAPK1, MYOD1 and HEY1) can contribute to the biological activities of P3F involved in growth suppression or cell death and myogenic differentiation.

Itm2a is a Pax3 target gene, expressed at sites of skeletal muscle formation in vivo

The paired-box homeodomain transcription factor Pax3 is a key regulator of the nervous system, neural crest and skeletal muscle development. Despite the important role of this transcription factor, very few direct target genes have been characterized. We show that Itm2a, which encodes a type 2 transmembrane protein, is a direct Pax3 target in vivo, by combining genetic approaches and in vivo chromatin immunoprecipitation assays. We have generated a conditional mutant allele for Itm2a, which is an imprinted gene, by flanking exons 2–4 with loxP sites and inserting an IRESnLacZ reporter in the 3′ UTR of the gene. The LacZ reporter reproduces the expression profile of Itm2a, and allowed us to further characterize its expression at sites of myogenesis, in the dermomyotome and myotome of somites, and in limb buds, in the mouse embryo. We further show that Itm2a is not only expressed in adult muscle fibres but also in the satellite cells responsible for regeneration. Itm2a mutant mice are viable and fertile with no overt phenotype during skeletal muscle formation or regeneration. Potential compensatory mechanisms are discussed.