Mice lacking dystrophin or alpha sarcoglycan spontaneously develop embryonal rhabdomyosarcoma with cancer-associated p53 mutations and alternatively spliced or mutant Mdm2 transcripts

Pediatric Soft Tissue Sarcoma in Limb-Girdle Muscular Dystrophy: Molecular Findings and Clinical Implications

BACKGROUND Limb-girdle muscular dystrophy recessive 1 (LGMDR1) is an autosomal recessive degenerative muscle disorder characterized by progressive muscular weakness caused by pathogenic variants in the CAPN3 gene. Desmoplastic small round cell tumors (DSRCT) are ultra-rare and aggressive soft tissue sarcomas usually in the abdominal cavity, molecularly characterized by the presence of a EWSR1::WT1 fusion transcript. Mouse models of muscular dystrophy, including LGMDR1, present an increased risk of soft tissue sarcomas. However, the DSRCT risk and general cancer risk in patients with LGMD is unknown. Here, we delineate the clinical, molecular, and genetic findings of a patient with LGMDR1 who developed a DSRCT. CASE REPORT The patient was a boy who was diagnosed at the age of 9 years with LGMDR1, caused by the biallelic pathogenic variants NP_000061.1:p.(Arg448Cys) and NP_000061.1:p.(Thr184ArgfsTer36) in CAPN3. At 17 years of age, a pathologic soft tissue mass was found in the right pelvis. Immunostaining was positive for Desmin and negative for Myogenin and MyoD1, and RNA sequencing showed a EWSR1::WT1 fusion transcript, confirming the diagnosis of DSRCT. The patient relapsed after 1 year and, following a second relapse, he was started on palliative treatment. No germline variants in childhood cancer predisposition genes were detected by whole genome sequencing. CONCLUSIONS We describe a patient with LGMDR1 who developed a DSRCT. Since associations between LGMD and pediatric cancer are hitherto unknown, further studies are warranted, as little information is currently published about the pediatric cancer risk in this patient group.

Cancer Risk in Patients With Muscular Dystrophy and Myotonic Dystrophy: A Register-Based Cohort Study

BACKGROUND AND OBJECTIVES

Muscular dystrophies and myotonic disorders are genetic disorders characterized by progressive skeletal muscle degeneration and weakness. Epidemiologic studies have found an increased cancer risk in myotonic dystrophy, although the cancer risk spectrum is poorly characterized. In patients with muscular dystrophy, the cancer risk is uncertain. We aimed to determine the overall cancer risk and cancer risk spectrum in patients with muscular dystrophy and myotonic dystrophy using data from the Swedish National registers.

METHODS

We performed a matched cohort study in all patients with muscular dystrophy or myotonic dystrophy born in Sweden 1950-2017 and 50 matched comparisons by sex, year of birth, and birth county per individual. The association with cancer overall and specific malignancies was estimated using stratified Cox proportional hazard models.

RESULTS

We identified 2,355 and 1,968 individuals with muscular dystrophy and myotonic dystrophy, respectively. No increased overall cancer risk was found in muscular dystrophy. However, we observed an increased risk of astrocytomas and other gliomas during childhood (hazard ratio [HR] 8.70, 95% CI 3.57-21.20) and nonthyroid endocrine cancer (HR 2.35, 95% CI 1.03-5.34) and pancreatic cancer (HR 4.33, 95% CI 1.55-12.11) in adulthood. In myotonic dystrophy, we found an increased risk of pediatric brain tumors (HR 3.23, 95% CI 1.16-9.01) and an increased overall cancer risk in adults (HR 2.26, CI 1.92.2.66), specifically brain tumors (HR 10.44, 95% CI 7.30-14.95), thyroid (HR 3.92, 95% CI 1.70-9.03), and nonthyroid endocrine cancer (HR 7.49, 95% CI 4.47-12.56), endometrial (HR 8.32, 95% CI 4.22-16.40), ovarian (HR 4.00, 95% CI 1.60-10.01), and nonmelanoma skin cancer (HR 3.27, 95% CI 1.32-8.13).

DISCUSSION

Here, we analyze the cancer risk spectrum of patients with muscular dystrophy and myotonic dystrophy. To the best of our knowledge, this is the first report of an increased risk for CNS tumors in childhood and adult nonthyroid endocrine and pancreatic cancer in muscular dystrophy. Furthermore, for myotonic dystrophy, we confirmed previously reported associations with cancer and expanded the cancer spectrum, finding an unreported increased risk for nonthyroid endocrine cancer. Additional studies confirming the cancer risk and delineating the cancer spectrum in different genetic subtypes of muscular dystrophies are warranted before considering altered cancer screening recommendations than for the general population.

Efficient exon skipping by base-editor-mediated abrogation of exonic splicing enhancers

Duchenne muscular dystrophy (DMD) is a severe genetic disease caused by the loss of the dystrophin protein. Exon skipping is a promising strategy to treat DMD by restoring truncated dystrophin. Here, we demonstrate that base editors (e.g., targeted AID-mediated mutagenesis [TAM]) are able to efficiently induce exon skipping by disrupting functional redundant exonic splicing enhancers (ESEs). By developing an unbiased and high-throughput screening to interrogate exonic sequences, we successfully identify novel ESEs in DMD exons 51 and 53. TAM-CBE (cytidine base editor) induces near-complete skipping of the respective exons by targeting these ESEs in patients' induced pluripotent stem cell (iPSC)-derived cardiomyocytes. Combined with strategies to disrupt splice sites, we identify suitable single guide RNAs (sgRNAs) with TAM-CBE to efficiently skip most DMD hotspot exons without substantial double-stranded breaks. Our study thus expands the repertoire of potential targets for CBE-mediated exon skipping in treating DMD and other RNA mis-splicing diseases.

Ectopic PLAG1 induces muscular dystrophy in the mouse

Even though various genetic mutations have been identified in muscular dystrophies (MD), there is still a need to understand the biology of MD in the absence of known mutations. Here we reported a new mouse model of MD driven by ectopic expression of PLAG1. This gene encodes a developmentally regulated transcription factor known to be expressed in developing skeletal muscle, and implicated as an oncogene in certain cancers including rhabdomyosarcoma (RMS), an aggressive soft tissue sarcoma composed of myoblast-like cells. By breeding loxP-STOP-loxP-PLAG1 (LSL-PLAG1) mice into the MCK-Cre line, we achieved ectopic PLAG1 expression in cardiac and skeletal muscle. The Cre/PLAG1 mice died before 6 weeks of age with evidence of cardiomyopathy significantly limiting left ventricle fractional shortening. Histology of skeletal muscle revealed dystrophic features, including myofiber necrosis, fiber size variation, frequent centralized nuclei, fatty infiltration, and fibrosis, all of which mimic human MD pathology. QRT-PCR and Western blot revealed modestly decreased Dmd mRNA and dystrophin protein in the dystrophic muscle, and immunofluorescence staining showed decreased dystrophin along the cell membrane. Repression of Dmd by ectopic PLAG1 was confirmed in dystrophic skeletal muscle and various cell culture models. In vitro studies showed that excess IGF2 expression, a transcriptional target of PLAG1, phenocopied PLAG1-mediated down-regulation of dystrophin. In summary, we developed a new mouse model of a lethal MD due to ectopic expression of PLAG1 in heart and skeletal muscle. Our data support the potential contribution of excess IGF2 in this model. Further studying these mice may provide new insights into the pathogenesis of MD and perhaps lead to new treatment strategies.

Proteins implicated in muscular dystrophy and cancer are functional constituents of the centrosome

Aberrant expression of dystrophin, utrophin, dysferlin, or calpain-3 was originally identified in muscular dystrophies (MDs). Increasing evidence now indicates that these proteins might act as tumor suppressors in myogenic and non-myogenic cancers. As DNA damage and somatic aneuploidy, hallmarks of cancer, are early pathological signs in MDs, we hypothesized that a common pathway might involve the centrosome. Here, we show that dystrophin, utrophin, dysferlin, and calpain-3 are functional constituents of the centrosome. In myoblasts, lack of any of these proteins caused excess centrosomes, centrosome misorientation, nuclear abnormalities, and impaired microtubule nucleation. In dystrophin double-mutants, these defects were significantly aggravated. Moreover, we demonstrate that also in non-myogenic cells, all four MD-related proteins localize to the centrosome, including the muscle-specific full-length dystrophin isoform. Therefore, MD-related proteins might share a convergent function at the centrosome in addition to their diverse, well-established muscle-specific functions. Thus, our findings support the notion that cancer-like centrosome-related defects underlie MDs and establish a novel concept linking MDs to cancer.

Identification of Feature Genes of a Novel Neural Network Model for Bladder Cancer

Background: The combination of deep learning methods and oncogenomics can provide an effective diagnostic method for malignant tumors; thus, we attempted to construct a reliable artificial neural network model as a novel diagnostic tool for Bladder cancer (BLCA). Methods: Three expression profiling datasets (GSE61615, GSE65635, and GSE100926) were downloaded from the Gene Expression Omnibus (GEO) database. GSE61615 and GSE65635 were taken as the train group, while GSE100926 was set as the test group. Differentially expressed genes (DEGs) were filtered out based on the logFC and FDR values. We also performed Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses to explore the biological functions of the DEGs. Consequently, we utilized a random forest algorithm to identify feature genes and further constructed a neural network model. The test group was given the same procedures to validate the reliability of the model. We also explored immune cells' infiltration degree and correlation coefficients through the CiberSort algorithm and corrplot R package. The qRT-PCR assay was implemented to examine the expression level of the feature genes in vitro. Results: A total of 265 DEGs were filtered out and significantly enriched in muscle system processes, collagen-containing and focal adhesion signaling pathways. Based on the random forest algorithm, we selected 14 feature genes to construct the neural network model. The area under the curve (AUC) of the training group was 0.950 (95% CI: 0.850-1.000), and the AUC of the test group was 0.667 (95% CI: 0.333-1.000). Besides, we observed significant differences in the content of immune infiltrating cells and the expression levels of the feature genes. Conclusion: After repeated verification, our neural network model had clinical feasibility to identify bladder cancer patients and provided a potential target to improve the management of BLCA.

Rhabdomyosarcoma in a Patient With Duchenne Muscular Dystrophy: A Possible Association

Duchenne muscular dystrophy (DMD), caused by a mutation in the DMD gene, is known to be associated with co-morbidities including cardiomyopathy, respiratory failure, neuromuscular scoliosis and intellectual disability. Animal studies have explored the susceptibility of dystrophin-deficient mice with the development of myogenic tumors. While there is adequate literature describing both DMD and rhabdomyosarcoma (RMS) separately, there has yet to be a comprehensive literature review investigating the possibility that patients with DMD may be at a higher risk of developing RMS and other myogenic tumors. We present the case of a pediatric patient with DMD who developed alveolar RMS and review the literature for susceptibility to development of myogenic tumors in cases of DMD gene mutation.

Loss of p16/Ink4a drives high frequency of rhabdomyosarcoma in a rat model of Duchenne muscular dystrophy

Rhabdomyosarcoma (RMS) is an aggressive type of soft tissue sarcoma, and pleomorphic RMS is a rare subtype of RMS found in adult. p16 is a tumor suppressor which inhibits cell cycle. In human RMS, p16 gene is frequently deleted, but p16-null mice do not develop RMS. We reported that genetic ablation of p16 by the crossbreeding of p16 knock-out rats (p16-KO rats) improved the dystrophic phenotype of a rat model of Duchenne muscular dystrophy (Dmd-KO rats). However, p16/Dmd double knock-out rats (dKO rats) unexpectedly developed sarcoma. In the present study, we raised p16-KO, Dmd-KO, and dKO rats until 11 months of age. Twelve out of 22 dKO rats developed pleomorphic RMS after 9 months of age, while none of p16-KO rats and Dmd-KO rats developed tumor. The neoplasms were connected to skeletal muscle tissue with indistinct borders and characterized by diffuse proliferation of pleomorphic cells which had eosinophilic cytoplasm and atypical nuclei with anisokaryosis. For almost all cases, the tumor cells immunohistochemically expressed myogenic markers including desmin, MyoD, and myogenin. The single cell cloning from tumor primary cells gained 20 individual Pax7-negative MyoD-positive RMS cell clones. Our results demonstrated that double knock-out of p16 and dystrophin in rats leads to the development of pleomorphic RMS, providing an animal model that may be useful to study the developmental mechanism of pleomorphic RMS.

Have Duchenne Muscular Dystrophy Patients an Increased Cancer Risk?

BACKGROUND

Increasing evidence suggests that Duchenne muscular dystrophy (DMD) gene is involved in the occurrence of different types of cancer. Moreover, development of sarcomas was reported in mdx mice, the murine model of DMD, in older age. So far, nine isolated DMD patients were reported with concomitant cancer, four of whom with rhabdomyosarcoma (RMS), but no systematic investigation was performed about the true incidence of cancer in DMD.

METHODS

All members of the Italian Association of Myology were asked about the occurrence of cancer in their DMD patients in the last 30 years.

RESULTS

Four DMD patients with cancer were reported after checking 2455 medical records. One developed brain tumour at the age of 35 years. Two patients had alveolar RMS at 14 and 17 years of age. The fourth patient had a benign enchondroma when 11-year-old.

CONCLUSION

Prevalence of cancer in general in the Italian DMD patients does not seem to be different from that in the general population with the same age range. Although the small numbers herein presented do not allow definitive conclusion, the frequent occurrence of RMS in DMD patients raises an alert for basic researchers and clinicians. The role of DMD gene in cancer merits further investigations.

Preclinical In Vivo Modeling of Pediatric Sarcoma-Promises and Limitations

Pediatric sarcomas are an extremely heterogeneous group of genetically distinct diseases. Despite the increasing knowledge on their molecular makeup in recent years, true therapeutic advancements are largely lacking and prognosis often remains dim, particularly for relapsed and metastasized patients. Since this is largely due to the lack of suitable model systems as a prerequisite to develop and assess novel therapeutics, we here review the available approaches to model sarcoma in vivo. We focused on genetically engineered and patient-derived mouse models, compared strengths and weaknesses, and finally explored possibilities and limitations to utilize these models to advance both biological understanding as well as clinical diagnosis and therapy.

The Duchenne muscular dystrophy gene and cancer

BACKGROUND

Mutation of the Duchenne muscular dystrophy (DMD) gene causes Duchenne and Becker muscular dystrophy, degenerative neuromuscular disorders that primarily affect voluntary muscles. However, increasing evidence implicates DMD in the development of all major cancer types. DMD is a large gene with 79 exons that codes for the essential muscle protein dystrophin. Alternative promotor usage drives the production of several additional dystrophin protein products with roles that extend beyond skeletal muscle. The importance and function(s) of these gene products outside of muscle are not well understood.

CONCLUSIONS

We highlight a clear role for DMD in the pathogenesis of several cancers, including sarcomas, leukaemia's, lymphomas, nervous system tumours, melanomas and various carcinomas. We note that the normal balance of DMD gene products is often disrupted in cancer. The short dystrophin protein Dp71 is, for example, typically maintained in cancer whilst the full-length Dp427 gene product, a likely tumour suppressor, is frequently inactivated in cancer due to a recurrent loss of 5' exons. Therefore, the ratio of short and long gene products may be important in tumorigenesis. In this review, we summarise the tumours in which DMD is implicated and provide a hypothesis for possible mechanisms of tumorigenesis, although the question of cause or effect may remain. We hope to stimulate further study into the potential role of DMD gene products in cancer and the development of novel therapeutics that target DMD.

From Development to Aging: The Path to Cellular Senescence

Significance: Senescence is a cellular state induced by internal or external stimuli, which result in cell cycle arrest, morphological changes, and dysfunctions in mitochondrial and lysosomal functionality as well as the senescence-associated secretory phenotype. Senescent cells accumulate in tissues in physiological and pathological conditions such as development, tissue repair, aging, and cancer. Recent Advances: Growing evidences indicate that senescent cells in vivo are a heterogeneous cell population due to different cell-autonomous activated pathways and distinct microenvironmental contexts. Critical Issues: In this review, we discuss the different contexts where senescence assumes a key role with beneficial or harmful outcomes. The heterogeneous nature of senescence pushes toward resolution of the specific molecular profile and secretome to typify senescent cells in physiological and pathological contexts. Future Directions: Future research will enable exploring the heterogeneity of the senescent population to precisely map the progression of cells through senescent trajectories and study the impact of the therapeutic advantage of senolytic drugs for translational strategies toward supporting the health span. Antioxid. Redox Signal. 34, 294-307.

Low expression of ANT1 confers oncogenic properties to rhabdomyosarcoma tumor cells by modulating metabolism and death pathways

Rhabdomyosarcoma (RMS) is the most frequent form of pediatric soft-tissue sarcoma. It is divided into two main subtypes: ERMS (embryonal) and ARMS (alveolar). Current treatments are based on chemotherapy, surgery, and radiotherapy. The 5-year survival rate has plateaued at 70% since 2000, despite several clinical trials. RMS cells are thought to derive from the muscle lineage. During development, myogenesis includes the expansion of muscle precursors, the elimination of those in excess by cell death and the differentiation of the remaining ones into myofibers. The notion that these processes may be hijacked by tumor cells to sustain their oncogenic transformation has emerged, with RMS being considered as the dark side of myogenesis. Thus, dissecting myogenic developmental programs could improve our understanding of RMS molecular etiology. We focused herein on ANT1, which is involved in myogenesis and is responsible for genetic disorders associated with muscle degeneration. ANT1 is a mitochondrial protein, which has a dual functionality, as it is involved both in metabolism via the regulation of ATP/ADP release from mitochondria and in regulated cell death as part of the mitochondrial permeability transition pore. Bioinformatics analyses of transcriptomic datasets revealed that ANT1 is expressed at low levels in RMS. Using the CRISPR-Cas9 technology, we showed that reduced ANT1 expression confers selective advantages to RMS cells in terms of proliferation and resistance to stress-induced death. These effects arise notably from an abnormal metabolic switch induced by ANT1 downregulation. Restoration of ANT1 expression using a Tet-On system is sufficient to prime tumor cells to death and to increase their sensitivity to chemotherapy. Based on our results, modulation of ANT1 expression and/or activity appears as an appealing therapeutic approach in RMS management.

Muscle Stem Cells Give Rise to Rhabdomyosarcomas in a Severe Mouse Model of Duchenne Muscular Dystrophy

Most human cancers originate from high-turnover tissues, while low-proliferating tissues, like skeletal muscle, exhibit a lower incidence of tumor development. In Duchenne muscular dystrophy (DMD), which induces increased skeletal muscle regeneration, tumor incidence is increased. Rhabdomyosarcomas (RMSs), a rare and aggressive type of soft tissue sarcoma, can develop in this context, but the impact of DMD severity on RMS development and its cell of origin are poorly understood. Here, we show that RMS latency is affected by DMD severity and that muscle stem cells (MuSCs) can give rise to RMS in dystrophic mice. We report that even before tumor formation, MuSCs exhibit increased self-renewal and an expression signature associated with RMSs. These cells can form tumorspheres in vitro and give rise to RMSs in vivo. Finally, we show that the inflammatory genes Ccl11 and Rgs5 are involved in RMS growth. Together, our results show that DMD severity drives MuSC-mediated RMS development.

Exogenous expression of the glycosyltransferase LARGE1 restores α-dystroglycan matriglycan and laminin binding in rhabdomyosarcoma

Background

α-Dystroglycan is the highly glycosylated component of the dystrophin-glycoprotein complex (DGC) that binds with high-affinity to extracellular matrix (ECM) proteins containing laminin-G-like (LG) domains via a unique heteropolysaccharide [-GlcA-beta1,3-Xyl-alpha1,3-]_n called matriglycan. Changes in expression of components of the DGC or in the O-glycosylation of α-dystroglycan result in muscular dystrophy but are also observed in certain cancers. In mice, the loss of either of two DGC proteins, dystrophin or α-sarcoglycan, is associated with a high incidence of rhabdomyosarcoma (RMS). In addition, glycosylation of α-dystroglycan is aberrant in a small cohort of human patients with RMS. Since both the glycosylation of α-dystroglycan and its function as an ECM receptor require over 18 post-translational processing enzymes, we hypothesized that understanding its role in the pathogenesis of RMS requires a complete analysis of the expression of dystroglycan-modifying enzymes and the characterization of α-dystroglycan glycosylation in the context of RMS.

Methods

A series of cell lines and biopsy samples from human and mouse RMS were analyzed for the glycosylation status of α-dystroglycan and for expression of the genes encoding the responsible enzymes, in particular those required for the addition of matriglycan. Furthermore, the glycosyltransferase LARGE1 was ectopically expressed in RMS cells to determine its effects on matriglycan modifications and the ability of α-dystroglycan to function as a laminin receptor.

Results

Immunohistochemistry and immunoblotting of a collection of primary RMS tumors show that although α-dystroglycan is consistently expressed and glycosylated in these tumors, α-dystroglycan lacks matriglycan and the ability to bind laminin. Similarly, in a series of cell lines derived from human and mouse RMS, α-dystroglycan lacks matriglycan modification and the ability to bind laminin. RNAseq data from RMS cell lines was analyzed for expression of the genes known to be involved in α-dystroglycan glycosylation, which revealed that, for most cell lines, the lack of matriglycan can be attributed to the downregulation of the dystroglycan-modifying enzyme LARGE1. Ectopic expression of LARGE1 in these cell cultures restored matriglycan to levels comparable to those in muscle and restored high-affinity laminin binding to α-dystroglycan.

Conclusions

Collectively, our findings demonstrate that a lack of matriglycan on α-dystroglycan is a common feature in RMS due to the downregulation of LARGE1, and that ectopic expression of LARGE1 can restore matriglycan modifications and the ability of α-dystroglycan to function as an ECM receptor.

Genomic analysis identifies frequent deletions of Dystrophin in olfactory neuroblastoma

Olfactory neuroblastoma (ONB) is a rare malignant neoplasm arising in the upper portion of the sinonasal cavity. To better understand the genetic bases for ONB, here we perform whole exome and whole genome sequencing as well as single nucleotide polymorphism array analyses in a series of ONB patient samples. Deletions involving the dystrophin (DMD) locus are found in 12 of 14 (86%) tumors. Interestingly, one of the remaining tumors has a deletion in LAMA2, bringing the number of ONBs with deletions of genes involved in the development of muscular dystrophies to 13 or 93%. This high prevalence implicates an unexpected functional role for genes causing hereditary muscular dystrophies in ONB.

RAS-MAPK Pathway-Driven Tumor Progression Is Associated with Loss of CIC and Other Genomic Aberrations in Neuroblastoma

Mutations affecting the RAS-MAPK pathway frequently occur in relapsed neuroblastoma tumors, which suggests that activation of this pathway is associated with a more aggressive phenotype. To explore this hypothesis, we generated several model systems to define a neuroblastoma RAS-MAPK pathway signature. Activation of this pathway in primary tumors indeed correlated with poor survival and was associated with known activating mutations in ALK and other RAS-MAPK pathway genes. Integrative analysis showed that mutations in PHOX2B, CIC, and DMD were also associated with an activated RAS-MAPK pathway. Mutation of PHOX2B and deletion of CIC in neuroblastoma cell lines induced activation of the RAS-MAPK pathway. This activation was independent of phosphorylated ERK in CIC knockout systems. Furthermore, deletion of CIC caused a significant increase in tumor growth in vivo These results show that the RAS-MAPK pathway is involved in tumor progression and establish CIC as a powerful tumor suppressor that functions downstream of this pathway in neuroblastoma.Significance: This work identifies CIC as a powerful tumor suppressor affecting the RAS-MAPK pathway in neuroblastoma and reinforces the importance of mutation-driven activation of this pathway in cancer. Cancer Res; 78(21); 6297-307. ©2018 AACR.

The human, F-actin-based cytoskeleton as a mutagen sensor

Background

Forty years ago the actin cytoskeleton was determined to be disrupted in fibroblasts from persons with DNA repair-defective, hereditary colon cancer, with no clear connection between the cytoskeleton and DNA repair defects at that time. Recently, the large number of sequenced genomes has indicated that mammalian mutagenesis has a large stochastic component. As a result, large coding regions are large mutagen targets. Cytoskeletal protein-related coding regions (CPCRs), including extra-cellular matrix proteins, are among the largest coding regions in the genome and are indeed very commonly mutated in cancer.

Methods

To determine whether mutagen sensitivity of the actin cytoskeleton could be assessed experimentally, we treated tissue culture cells with 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone and quantified overall cytoskeleton integrity with rhodamine-phalloidin stains for F-actin.

Results

The above approach indicated cytoskeletal degradation with increasing mutagen exposure, consistent with increased mutagenesis of CPCRs in TCGA, smoker samples, where overall mutation rates correlate with CPCR mutation rates (R² = 0.8694; p < 0.00001). In addition, mutagen exposure correlated with a decreasing cell perimeter to area ratio, raising questions about potential decreasing, intracellular diffusion and concentrations of chemotherapy drugs, with increasing mutagenesis and decreasing cytoskeleton integrity.

Conclusion

Determination of cytoskeletal integrity may provide the opportunity to assess mutation burdens in nonclonal cell populations, such as in intact tissues, where DNA sequencing for heterogeneous mutation burdens can be challenging.

Increased FSHD region gene1 expression reduces in vitro cell migration, invasion, and angiogenesis, ex vivo supported by reduced expression in tumors

Facioscapulohumeral muscular dystrophy (FSHD) region gene 1 (FRG1) is a candidate gene for FSHD. FRG1 regulates various muscle-related functions, but studies have proposed its role in development and angiogenesis also, where it is involved with tumor-associated molecules. Therefore, we decided to look into its role in tumor progression, tumor angiogenesis, and its impact on cellular properties. Cell proliferation, migration, invasion and in vitro angiogenesis assays were performed to decipher the effect of FRG1 on endothelial and epithelial cell functions. Q-RT PCR was done for human embyonic kidney (HEK293T) cells with altered FRG1 levels to identify associated molecules. Further, immunohistochemistry was done to identify FRG1 expression levels in various cancers and its association with tumor angiogenesis. Subsequently, inference was drawn from Oncomine and Kaplan-Meier plotter analysis, for FRG1 expression in different cancers. Ectopic expression of FRG1 affected cell migration and invasion in both HEK293T and human umbilical vein endothelial cells (HUVECs). In HUVECs, FRG1 overexpression led to reduced angiogenesis in vitro No effect was observed in cell proliferation in both the cell types. Q-RT PCR data revealed reduction in granulocyte-colony stimulating factor (G-CSF) expression with FRG1 overexpression and increased expression of matrix metalloproteinase 10 (MMP10) with FRG1 knockdown. Immunohistochemistry analysis showed reduced FRG1 levels in tumors which were supported by in silico analysis data. These findings suggest that reduction in FRG1 expression in gastric, colon and oral cavity tumor might have a role in tumor progression, by regulating cell migration and invasiveness. To elucidate a better understanding of molecular signaling involving FRG1 in angiogenesis regulation, further study is required.

A novel mouse model of rhabdomyosarcoma underscores the dichotomy of MDM2-ALT1 function in vivo

Alternative splicing of the oncogene murine double minute 2 (MDM2) is induced in response to genotoxic stress. MDM2-ALT1, the major splice variant generated, is known to activate the p53 pathway and impede full-length MDM2's negative regulation of p53. Despite this perceptible tumor-suppressive role, MDM2-ALT1 is also associated with several cancers. Furthermore, expression of MDM2-ALT1 has been observed in aggressive metastatic disease in pediatric rhabdomyosarcoma (RMS), irrespective of histological subtype. Therefore, we generated a transgenic MDM2-ALT1 mouse model that would allow us to investigate the effects of this splice variant on the progression of tumorigenesis. Here we show that when MDM2-ALT1 is ubiquitously expressed in p53 null mice it leads to increased incidence of spindle cell sarcomas, including RMS. Our data provide evidence that constitutive MDM2-ALT1 expression is itself an oncogenic lesion that aggravates the tumorigenesis induced by p53 loss. On the contrary, when MDM2-ALT1 is expressed solely in B-cells in the presence of homozygous wild-type p53 it leads to significantly increased lymphomagenesis (56%) when compared with control mice (27%). However, this phenotype is observable only at later stages in life (⩾18 months). Moreover, flow cytometric analyses for B-cell markers revealed an MDM2-ALT1-associated decrease in the B-cell population of the spleens of these animals. Our data suggest that the B-cell loss is p53 dependent and is a response mounted to persistent MDM2-ALT1 expression in a wild-type p53 background. Overall, our findings highlight the importance of an MDM2 splice variant as a critical modifier of both p53-dependent and -independent tumorigenesis, underscoring the complexity of MDM2 posttranscriptional regulation in cancer. Furthermore, MDM2-ALT1-expressing p53 null mice represent a novel mouse model of fusion-negative RMS.

Protected cytoskeletal-related proteins: Towards a resolution of contradictions regarding the role of the cytoskeleton in cancer

Initial reports of the role of the cytoskeleton in cancer indicated that tumor cells with a more disorganized cytoskeleton were more tumorigenic. These reports were based on stains for the F-actin cytoskeleton, for example, using phalloidin or anti-F-actin antibody reagents, and gave a basic impression of F-actin-based cytoskeletal integrity. Later developments emphasized the significance of the cytoskeletal elements in cell migration, presumably associated with either basement membrane invasion or metastasis, or both, with several specific proteins implicated in the formation of cell invadopodia. With the advent of genomics approaches, it has become clear that cytoskeletal related proteins are indeed common targets of mutagenesis in cancer and commonly rank among the most mutated proteins in cancers, presumably due to large coding region sizes and the significant stochastic component to human mutagenesis. This cytoskeletal genomics result is consistent with the loss of cytoskeleton integrity as a hallmark of tumor development, but raises the question of whether such mutational sensitivity relates to the migration and invadopodia aspects of tumor progression. In the present study, the authors report that it is possible to identify a set of cytoskeletal related proteins protected from mutation, in comparison to the commonly mutated cytoskeleton related proteins in certain, but not all cancer, datasets.

Identification of Sets of Cytoskeletal Related and Adhesion-related Coding Region Mutations in the TCGA Melanoma Dataset that Correlate with a Negative Outcome

BACKGROUND

Relatively little cancer genome atlas data has been associated with clinically relevant stratifications of individual cancers.

RESULTS

Mutations in two subsets of a cytoskeletal related and adhesion-related protein coding region set (CAPCRs) were determined to have strong associations with a negative outcome for melanoma, in-cluding a subset constituted by: DSCAM, FAT3, MUC17 and PCDHGC5 (p < 0.0001).

CONCLUSION

Roles for CAPCR mutations in cancer progression raise a question about the potential dominant negative impact of these mutations for multi-meric subcellular and extra-cellular protein struc-tures.

Deletion of Galgt2 (B4Galnt2) reduces muscle growth in response to acute injury and increases muscle inflammation and pathology in dystrophin-deficient mice

Transgenic overexpression of Galgt2 (official name B4Galnt2) in skeletal muscle stimulates the glycosylation of α dystroglycan (αDG) and the up-regulation of laminin α2 and dystrophin surrogates known to inhibit muscle pathology in mouse models of congenital muscular dystrophy 1A and Duchenne muscular dystrophy. Skeletal muscle Galgt2 gene expression is also normally increased in the mdx mouse model of Duchenne muscular dystrophy compared with the wild-type mice. To assess whether this increased endogenous Galgt2 expression could affect disease, we quantified muscular dystrophy measures in mdx mice deleted for Galgt2 (Galgt2(-/-)mdx). Galgt2(-/-) mdx mice had increased heart and skeletal muscle pathology and inflammation, and also worsened cardiac function, relative to age-matched mdx mice. Deletion of Galgt2 in wild-type mice also slowed skeletal muscle growth in response to acute muscle injury. In each instance where Galgt2 expression was elevated (developing muscle, regenerating muscle, and dystrophic muscle), Galgt2-dependent glycosylation of αDG was also increased. Overexpression of Galgt2 failed to inhibit skeletal muscle pathology in dystroglycan-deficient muscles, in contrast to previous studies in dystrophin-deficient mdx muscles. This study demonstrates that Galgt2 gene expression and glycosylation of αDG are dynamically regulated in muscle and that endogenous Galgt2 gene expression can ameliorate the extent of muscle pathology, inflammation, and dysfunction in mdx mice.

Facioscapulohumeral dystrophy myoblasts efficiently repair moderate levels of oxidative DNA damage

Facioscapulohumeral dystrophy (FSHD) is a progressive muscular dystrophy linked to a deletion of a subset of D4Z4 macrosatellite repeats accompanied by a chromatin relaxation of the D4Z4 array on chromosome 4q. In vitro, FSHD primary myoblasts show altered expression of oxidative-related genes and are more susceptible to oxidative stress. Double homeobox 4 (DUX4) gene, encoded within each D4Z4 unit, is normally transcriptionally silenced but is found aberrantly expressed in skeletal muscles of FSHD patients. Its expression leads to a deregulation of DUX4 target genes including those implicated in redox balance. Here, we assessed DNA repair efficiency of oxidative DNA damage in FSHD myoblasts and DUX4-transfected myoblasts. We have shown that the DNA repair activity is altered neither in FSHD myoblasts nor in immortalized human myoblasts transiently expressing DUX4. DNA damage caused by moderate doses of an oxidant is efficiently repaired while FSHD myoblasts exposed for 24 h to high levels of oxidative stress accumulated more DNA damage than normal myoblasts, suggesting that FSHD myoblasts remain more vulnerable to oxidative stress at high doses of oxidants.

Flat cells come full sphere: Are mutant cytoskeletal-related proteins oncoprotein-monsters or useful immunogens?

Osteogenesis imperfecta is inherited as a dominant disease because if one allele is mutated, it contributes a mutant, destructive subunit polypeptide to collagen, which requires many subunits to form normal, polymeric, collagenous structures. Recent cancer genome atlas (TCGA) data indicate that cytoskeletal-related proteins are among the most commonly mutated proteins in human cancers, in distinct mutation frequency groups, i.e., including low mutation frequency groups. Part of the explanation for this observation is likely to be the fact that many of the coding regions for these proteins are very large, and indeed, it is likely these coding regions are mutated in many cells that never become cancerous. However, it would not be surprising if mutations in cytoskeletal proteins, when combined with oncoprotein or tumor suppressor protein mutations, had significant impacts on cancer development, for a number of reasons, including results obtained almost 5 decades ago indicating that well-spread cells in tissue culture, with well-formed cytoskeletons, were less tumorigenic than spherical cells with disrupted cytoskeletons. This raises the question, are mutant cytoskeletal proteins, which would likely interfere with polymer formation, a new class of oncoproteins, in particular, dominant negative oncoproteins? If these proteins are so commonly mutant, could they be the bases for common cancer vaccines?

Probing for a deeper understanding of rhabdomyosarcoma: insights from complementary model systems

Rhabdomyosarcoma (RMS) is a mesenchymal malignancy composed of neoplastic primitive precursor cells that exhibit histological features of myogenic differentiation. Despite intensive conventional multimodal therapy, patients with high-risk RMS typically suffer from aggressive disease. The lack of directed therapies against RMS emphasizes the need to further uncover the molecular underpinnings of the disease. In this Review, we discuss the notable advances in the model systems now available to probe for new RMS-targetable pathogenetic mechanisms, and the possibilities for enhanced RMS therapeutics and improved clinical outcomes.

MURC/cavin-4 Is Co-Expressed with Caveolin-3 in Rhabdomyosarcoma Tumors and Its Silencing Prevents Myogenic Differentiation in the Human Embryonal RD Cell Line

The purpose of this study was to investigate whether MURC/cavin-4, a plasma membrane and Z-line associated protein exhibiting an overlapping distribution with Caveolin-3 (Cav-3) in heart and muscle tissues, may be expressed and play a role in rhabdomyosarcoma (RMS), an aggressive myogenic tumor affecting childhood. We found MURC/cavin-4 to be expressed, often concurrently with Cav-3, in mouse and human RMS, as demonstrated through in silico analysis of gene datasets and immunohistochemical analysis of tumor samples. In vitro expression studies carried out using human cell lines and primary mouse tumor cultures showed that expression levels of both MURC/cavin-4 and Cav-3, while being low or undetectable during cell proliferation, became robustly increased during myogenic differentiation, as detected via semi-quantitative RT-PCR and immunoblotting analysis. Furthermore, confocal microscopy analysis performed on human RD and RH30 cell lines confirmed that MURC/cavin-4 mostly marks differentiated cell elements, colocalizing at the cell surface with Cav-3 and labeling myosin heavy chain (MHC) expressing cells. Finally, MURC/cavin-4 silencing prevented the differentiation in the RD cell line, leading to morphological cell impairment characterized by depletion of myogenin, Cav-3 and MHC protein levels. Overall, our data suggest that MURC/cavin-4, especially in combination with Cav-3, may play a consistent role in the differentiation process of RMS.

Cavin-1 and Caveolin-1 are both required to support cell proliferation, migration and anchorage-independent cell growth in rhabdomyosarcoma

Rhabdomyosarcoma (RMS) is a childhood soft tissue tumor with broad expression of markers that are typically found in skeletal muscle. Cavin-1 is a recently discovered protein actively cooperating with Caveolin-1 (Cav-1) in the morphogenesis of caveolae and whose role in cancer is drawing increasing attention. Using a combined in silico and in vitro analysis here we show that Cavin-1 is expressed in myogenic RMS tumors as well as in human and primary mouse RMS cultures, exhibiting a broad subcellular localization, ranging from nuclei and cytosol to plasma membrane. In particular, the coexpression and plasma membrane interaction between Cavin-1 and Cav-1 characterized the proliferation of human and mouse RMS cell cultures, while a downregulation of their expression levels was observed during the myogenic differentiation. Knockdown of Cavin-1 or Cav-1 in the human RD and RH30 cells led to impairment of cell proliferation and migration. Moreover, loss of Cavin-1 in RD cells impaired the anchorage-independent cell growth in soft agar. While the loss of Cavin-1 did not affect the Cav-1 protein levels in RMS cells, Cav-1 overexpression and knockdown triggered a rise or depletion of Cavin-1 protein levels in RD cells, respectively, in turn reflecting on increased or decreased cell proliferation, migration and anchorage-independent cell growth. Collectively, these data indicate that the interaction between Cavin-1 and Cav-1 underlies the cell growth and migration in myogenic tumors.

Dystrophin is a tumor suppressor in human cancers with myogenic programs

Many common human mesenchymal tumors, including gastrointestinal stromal tumor (GIST), rhabdomyosarcoma (RMS) and leiomyosarcoma (LMS), feature myogenic differentiation. Here we report that intragenic deletion of the dystrophin-encoding and muscular dystrophy-associated DMD gene is a frequent mechanism by which myogenic tumors progress to high-grade, lethal sarcomas. Dystrophin is expressed in the non-neoplastic and benign counterparts of GIST, RMS and LMS tumors, and DMD deletions inactivate larger dystrophin isoforms, including 427-kDa dystrophin, while preserving the expression of an essential 71-kDa isoform. Dystrophin inhibits myogenic sarcoma cell migration, invasion, anchorage independence and invadopodia formation, and dystrophin inactivation was found in 96%, 100% and 62% of metastatic GIST, embryonal RMS and LMS samples, respectively. These findings validate dystrophin as a tumor suppressor and likely anti-metastatic factor, suggesting that therapies in development for muscular dystrophies may also have relevance in the treatment of cancer.

Cancer-related genes in the transcription signature of facioscapulohumeral dystrophy myoblasts and myotubes

Muscular dystrophy is a condition potentially predisposing for cancer; however, currently, only Myotonic dystrophy patients are known to have a higher risk of cancer. Here, we have searched for a link between facioscapulohumeral dystrophy (FSHD) and cancer by comparing published transcriptome signatures of FSHD and various malignant tumours and have found a significant enrichment of cancer-related genes among the genes differentially expressed in FSHD. The analysis has shown that gene expression profiles of FSHD myoblasts and myotubes resemble that of Ewing's sarcoma more than that of other cancer types tested. This is the first study demonstrating a similarity between FSHD and cancer cell expression profiles, a finding that might indicate the existence of a common step in the pathogenesis of these two diseases.

Muscular dystrophies share pathogenetic mechanisms with muscle sarcomas

Several lines of recent evidence have opened a new debate on the mechanisms underlying the genesis of rhabdomyosarcoma, a pediatric soft tissue tumor with a widespread expression of muscle-specific markers. In particular, it is increasingly evident that the loss of skeletal muscle integrity observed in some mouse models of muscular dystrophy can favor rhabdomyosarcoma formation. This is especially true in old age. Here, we review these experimental findings and focus on the main molecular and cellular events that can dictate the tumorigenic process in dystrophic muscle, such as the loss of structural or regulatory proteins with tumor suppressor activity, the impaired DNA damage response due to oxidative stress, the chronic inflammation and the conflicting signals arising within the degenerated muscle niche.

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.

Dystroglycan function is a novel determinant of tumor growth and behavior in prostate cancer

BACKGROUND

Dystroglycan is a ubiquitously expressed cell adhesion molecule frequently found to be altered or reduced in adenocarcinomas, however the mechanisms or consequences of dystroglycan loss have not been studied extensively.

METHODS

We examined the consequence of overexpression or RNAi depletion of dystroglycan on properties of in vitro growth migration and invasion of LNCaP, PC3, and DU145 prostate cancer cell lines.

RESULTS

Using LNCaP cells we observed cell density-dependent changes in β-dystroglycan with the appearance of several lower molecular weight species ranging in size from 43 to 26 kDa. The bands of 31 and 26 kDa were attributed to proteolysis, whereas bands between 43 and 38 kDa were a consequence of mis-glycosylation. The localization of β-dystroglycan in LNCaP colonies in culture also varied, cells with a mesenchymal appearance at the periphery of the colony had more pronounced membrane localization of dystroglycan. Whereas some cells demonstrated nuclear dystroglycan. Increased dystroglycan levels were inhibitory to growth in soft agar but promoted Matrigel invasion, whereas reduced dystroglycan levels promoted growth in soft agar but inhibited invasion. Similar results were also obtained for PC3 and DU145 cells.

CONCLUSIONS

This study suggests that changes in β-dystroglycan distribution within the cell and/or the loss of dystroglycan during tumorigenesis, through a combination of proteolysis and altered glycosylation, leads to an increased ability to grow in an anchorage independent manner, however dystroglycan may need to be re-expressed for cell invasion and metastasis to occur.

A role for β-dystroglycan in the organization and structure of the nucleus in myoblasts

We recently characterized a nuclear import pathway for β-dystroglycan; however, its nuclear role remains unknown. In this study, we demonstrate for the first time, the interaction of β-dystroglycan with distinct proteins from different nuclear compartments, including the nuclear envelope (NE) (emerin and lamins A/C and B1), splicing speckles (SC35), Cajal bodies (p80-coilin), and nucleoli (Nopp140). Electron microscopy analysis revealed that β-dystroglycan localized in the inner nuclear membrane, nucleoplasm, and nucleoli. Interestingly, downregulation of β-dystroglycan resulted in both mislocalization and decreased expression of emerin and lamin B1, but not lamin A/C, as well in disorganization of nucleoli, Cajal bodies, and splicing speckles with the concomitant decrease in the levels of Nopp140, and p80-coilin, but not SC35. Quantitative reverse transcription PCR and cycloheximide-mediated protein arrest assays revealed that β-dystroglycan deficiency did not change mRNA expression of NE proteins emerin and lamin B1 bud did alter their stability, accelerating protein turnover. Furthermore, knockdown of β-dystroglycan disrupted NE-mediated processes including nuclear morphology and centrosome-nucleus linkage, which provides evidence that β-dystroglycan association with NE proteins is biologically relevant. Unexpectedly, β-dystroglycan-depleted cells exhibited multiple centrosomes, a characteristic of cancerous cells. Overall, these findings imply that β-dystroglycan is a nuclear scaffolding protein involved in nuclear organization and NE structure and function, and that might be a contributor to the biogenesis of nuclear envelopathies.

Rhabdomyosarcomas: an overview on the experimental animal models

Rhabdomyosarcomas (RMS) are aggressive childhood soft-tissue malignancies deriving from mesenchymal progenitors that are committed to muscle-specific lineages. Despite the histopathological signatures associated with three main histological variants, termed embryonal, alveolar and pleomorphic, a plethora of genetic and molecular changes are recognized in RMS. Over the years, exposure to carcinogens or ionizing radiations and gene-targeting approaches in vivo have greatly contributed to disclose some of the mechanisms underlying RMS onset. In this review, we describe the principal distinct features associated with RMS variants and focus on the current available experimental animal models to point out the molecular determinants cooperating with RMS development and progression.

Dystrophin and dysferlin double mutant mice: a novel model for rhabdomyosarcoma

Although researchers have yet to establish a link between muscular dystrophy (MD) and sarcomas in human patients, literature suggests that the MD genes dystrophin and dysferlin act as tumor suppressor genes in mouse models of MD. For instance, dystrophin-deficient mdx and dysferlin-deficient A/J mice, models of human Duchenne MD and limb-girdle MD type 2B, respectively, develop mixed sarcomas with variable penetrance and latency. To further establish the correlation between MD and sarcoma development, and to test whether a combined deletion of dystrophin and dysferlin exacerbates MD and augments the incidence of sarcomas, we generated dystrophin and dysferlin double mutant mice (STOCK-Dysf(prmd)Dmd(mdx-5Cv)). Not surprisingly, the double mutant mice develop severe MD symptoms and, moreover, develop rhabdomyosarcoma (RMS) at an average age of 12 months, with an incidence of >90%. Histological and immunohistochemical analyses, using a panel of antibodies against skeletal muscle cell proteins, electron microscopy, cytogenetics, and molecular analysis reveal that the double mutant mice develop RMS. The present finding bolsters the correlation between MD and sarcomas, and provides a model not only to examine the cellular origins but also to identify mechanisms and signal transduction pathways triggering development of RMS.

Advances in pediatric rhabdomyosarcoma characterization and disease model development

Rhabdomyosarcoma (RMS), a form of soft tissue sarcoma, is one of the most common pediatric malignancies. A complex disease with at least three different subtypes, it is characterized by perturbations in a number of signaling pathways and genetic abnormalities. Extensive clinical studies have helped classify these tumors into high and low risk groups to facilitate different treatment regimens. Research into the etiology of the disease has helped uncover numerous potential therapeutic intervention points which can be tested on various animal models of RMS; both genetically modified models and tumor xenograft models. Taken together, there has been a marked increase in the survival rate of RMS patients but the highly invasive, metastatic forms of the disease continue to baffle researchers. This review aims to highlight and summarize some of the most important developments in characterization and in vivo model generation for RMS research, in the last few decades.

Effects of single genetic damage in carbohydrate-recognizing proteins in mouse serum N-glycan profile revealed by simple glycotyping analysis

Gene knock-out of C-type lectin receptors expressed in dendritic cells induced significant alteration of serum N-glycans compared with that of gender-matched controls. Glycotyping analysis suggested that putative-core fucosylation is strongly influenced by differences in the dominant mechanisms after carbohydrate recognition by pattern-recognition receptors, endocytosis of ligands, or induction of cytokines/chemokines. However, the loss of galectin-9, a ligand for T-helper type 1-specific cell-surface molecule, did not affect most N-glycan profiles. Interestingly, lack of the Chst3 gene (chondroitin 6-sulfotransferase) appeared to influence markedly the expression of most N-glycans, especially highly modified glycoforms bearing multiple Neu5Gc, Fuc, and LacNAc units. In contrast, genetic mutations in B4galnt1 and B4galnt2 (GalNAc transferase, responsible for the synthesis of many gangliosides) induced no discernable alteration. These results indicate that the biosynthesis of N-glycans of serum glycoproteins can be affected not only by direct genetic mutations in the glycosyltransferases but also by changes in metabolite availability in sugar nucleotide synthesis and Golgi N-glycosylation pathways caused concertedly in whole cells, tissues, and organs by milder deficiencies in immune cell-surface lectins. Many common chronic conditions, such as autoimmunity, metabolic syndrome, and aging/dementia result.

Induction of a regenerative microenvironment in skeletal muscle is sufficient to induce embryonal rhabdomyosarcoma in p53-deficient mice

We have previously reported that mice with muscular dystrophy, including mdx mice, develop embryonal rhabdomyosarcoma (eRMS) with a low incidence after 1 year of age and that almost all such tumours contain cancer-associated p53 mutations. To further demonstrate the relevance of p53 inactivation, we created p53-deficient mdx mice. Here we demonstrate that loss of one or both p53 (Trp53) alleles accelerates eRMS incidence in the mdx background, such that almost all Trp53(-/-) mdx animals develop eRMS by 5 months of age. To ascertain whether increased tumour incidence was due to the regenerative microenvironment found in dystrophic skeletal muscles, we induced muscle regeneration in Trp53(+/+) and Trp53(-/-) animals using cardiotoxin (Ctx). Wild-type (Trp53(+/+) ) animals treated with Ctx, either once every 7 days or once every 14 days from 1 month of age onwards, developed no eRMS; however, all similarly Ctx-treated Trp53(-/-) animals developed eRMS by 5 months of age at the site of injection. Most of these tumours displayed markers of human eRMS, including over-expression of Igf2 and phosphorylated Akt. These data demonstrate that the presence of a regenerative microenvironment in skeletal muscle, coupled with Trp53 deficiency, is sufficient to robustly induce eRMS in young mice. These studies further suggest that consideration should be given to the potential of the muscle microenvironment to support tumourigenesis in regenerative therapies for myopathies.

Myostatin is elevated in congenital heart disease and after mechanical unloading

BACKGROUND

Myostatin is a negative regulator of skeletal muscle mass whose activity is upregulated in adult heart failure (HF); however, its role in congenital heart disease (CHD) is unknown.

METHODS

We studied myostatin and IGF-1 expression via Western blot in cardiac tissue at varying degrees of myocardial dysfunction and after biventricular support in CHD by collecting myocardial biopsies from four patient cohorts: A) adult subjects with no known cardiopulmonary disease (left ventricle, LV), (Adult Normal), (n = 5); B) pediatric subjects undergoing congenital cardiac surgery with normal RV size and function (right ventricular outflow tract, RVOT), (n = 3); C) pediatric subjects with worsening but hemodynamically stable LV failure [LV and right ventricle (LV, RV,)] with biopsy collected at the time of orthotopic heart transplant (OHT), (n = 7); and D) pediatric subjects with decompensated bi-ventricular failure on BiVAD support with biopsy collected at OHT (LV, RV, BiVAD), (n = 3).

RESULTS

The duration of HF was longest in OHT patients compared to BIVAD. The duration of BiVAD support was 4.3±1.9 days. Myostatin expression was significantly increased in LV-OHT compared to RV-OHT and RVOT, and was increased more than double in decompensated biventricular HF (BiVAD) compared to both OHT and RVOT. An increased myostatin/IGF-1 ratio was associated with ventricular dysfunction.

CONCLUSIONS

Myostatin expression in increased in CHD, and the myostatin/IGF-1 ratio increases as ventricular function deteriorates. Future investigation is necessary to determine if restoration of the physiologic myostatin/IGF-1 ratio has therapeutic potential in HF.

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.

DNA damage, somatic aneuploidy, and malignant sarcoma susceptibility in muscular dystrophies

Albeit genetically highly heterogeneous, muscular dystrophies (MDs) share a convergent pathology leading to muscle wasting accompanied by proliferation of fibrous and fatty tissue, suggesting a common MD–pathomechanism. Here we show that mutations in muscular dystrophy genes (Dmd, Dysf, Capn3, Large) lead to the spontaneous formation of skeletal muscle-derived malignant tumors in mice, presenting as mixed rhabdomyo-, fibro-, and liposarcomas. Primary MD–gene defects and strain background strongly influence sarcoma incidence, latency, localization, and gender prevalence. Combined loss of dystrophin and dysferlin, as well as dystrophin and calpain-3, leads to accelerated tumor formation. Irrespective of the primary gene defects, all MD sarcomas share non-random genomic alterations including frequent losses of tumor suppressors (Cdkn2a, Nf1), amplification of oncogenes (Met, Jun), recurrent duplications of whole chromosomes 8 and 15, and DNA damage. Remarkably, these sarcoma-specific genetic lesions are already regularly present in skeletal muscles in aged MD mice even prior to sarcoma development. Accordingly, we show also that skeletal muscle from human muscular dystrophy patients is affected by gross genomic instability, represented by DNA double-strand breaks and age-related accumulation of aneusomies. These novel aspects of molecular pathologies common to muscular dystrophies and tumor biology will potentially influence the strategies to combat these diseases.

All kinds of muscular dystrophies (MDs) are characterized by progressive muscle wasting due to life-long proliferation of precursor cells of myo- (muscle), fibro- (connective tissue), and lipogenic (fat) origin. Despite discovery of many MD genes over the past 25 years, MDs still represent debilitating, incurable diseases, which frequently lead to premature death. Thus, it is imperative to gain novel insights into the underlying MD pathomechanisms. Here, we show that different mouse models for the most common human MDs frequently develop skeletal musculature-associated tumors, presenting as complex sarcomas, consisting of myo-, lipo-, and fibrogenic compartments. Collectively, these tumors are characterized by profound genomic instability such as DNA damage, recurring mutations in cancer genes, and aberrant chromosome copy numbers. We also demonstrate the presence of these cancer-related aberrations in dystrophic muscles from MD mice prior to formation of visible sarcomas. Moreover, we discovered corresponding genomic lesions also in skeletal muscles from human MD patients, as well as stem cells cultured thereof, and show that genomic instability precedes muscle degeneration in MDs. We thus propose that cancer-like genomic instability represents a novel, unifying pathomechanism underlying the entire group of genetically distinct MDs, which will hopefully open new therapeutic avenues.