Profiling the molecular difference between Patched- and p53-dependent rhabdomyosarcoma

Genetic Characterization, Current Model Systems and Prognostic Stratification in PAX Fusion-Negative vs. PAX Fusion-Positive Rhabdomyosarcoma

Rhabdomyosarcoma (RMS) is the most common soft tissue sarcoma in children and adolescents and accounts for approximately 2% of soft tissue sarcomas in adults. It is subcategorized into distinct subtypes based on histological features and fusion status (PAX-FOXO1/VGLL2/NCOA2). Despite advances in our understanding of the pathobiological and molecular landscape of RMS, the prognosis of these tumors has not significantly improved in recent years. Developing a better understanding of genetic abnormalities and risk stratification beyond the fusion status are crucial to developing better therapeutic strategies. Herein, we aim to highlight the genetic pathways/abnormalities involved, specifically in fusion-negative RMS, assess the currently available model systems to study RMS pathogenesis, and discuss available prognostic factors as well as their importance for risk stratification to achieve optimal therapeutic management.

CDK1 and CCNB1 as potential diagnostic markers of rhabdomyosarcoma: validation following bioinformatics analysis

Background

Rhabdomyosarcoma (RMS), a common soft-tissue malignancy in pediatrics, presents high invasiveness and mortality. However, besides known changes in the PAX3/7-FOXO1 fusion gene in alveolar RMS, the molecular mechanisms of the disease remain incompletely understood. The purpose of the study is to recognize potential biomarkers related with RMS and analyse their molecular mechanism, diagnosis and prognostic significance.

Methods

The Gene Expression Omnibus was used to search the RMS and normal striated muscle data sets. Differentially expressed genes (DEGs) were filtered using R software. The DAVID has become accustomed to performing functional annotations and pathway analysis on DEGs.

The protein interaction was constructed and further processed by the STRING tool and Cytoscape software. Kaplan–Meier was used to estimate the effect of hub genes on the ending of sarcoma sufferers, and the expression of these genes in RMS was proved by real-time polymerase chain reaction (RT-PCR). Finally, the expression of CDK1 and CCNB1 in RMS was validated by immunohistochemistry (IHC).

Results

A total of 1932 DEGs were obtained, amongst which 1505 were up-regulated and 427were down-regulated. Up-regulated genes were largely enriched in the cell cycle, ECM-receptor interaction, PI3K/Akt and p53 pathways, whilst down-regulated genes were primarily enriched in the muscle contraction process. CDK1, CCNB1, CDC20, CCNB2, AURKB, MAD2L1, HIST2H2BE, CENPE, KIF2C and PCNA were identified as hub genes by Cytoscape analyses. Survival analysis showed that, except for HIST2H2BE, the other hub genes were highly expressed and related to poor prognosis in sarcoma. RT-PCR validation showed that CDK1, CCNB1, CDC20, CENPE and HIST2H2BE were significantly differential expression in RMS compared to the normal control. IHC revealed that the expression of CDK1 (28/32, 87.5%) and CCNB1 (26/32, 81.25%) were notably higher in RMS than normal controls (1/9, 11.1%; 0/9, 0%). Moreover, the CCNB1 was associated with the age and location of the patient’s onset.

Conclusions

These results show that these hub genes, especially CDK1 and CCNB1, may be potential diagnostic biomarkers for RMS and provide a new perspective for the pathogenesis of RMS.

A familial syndrome of hypothalamic hamartomas, polydactyly, and SMO mutations: a clinical report of 2 cases

Hypothalamic hamartomas are benign tumors known to cause gelastic or dacrystic seizures, precocious puberty, developmental delay, and medically refractory epilepsy. These tumors are most often sporadic but rarely can be associated with Pallister-Hall syndrome, an autosomal dominant familial syndrome caused by truncation of glioblastoma transcription factor 3, a downstream effector in the sonic hedgehog pathway. In this clinical report, the authors describe two brothers with a different familial syndrome. To the best of the authors' knowledge, this is the first report in the literature describing a familial syndrome caused by germline mutations in the Smoothened (SMO) gene and the first familial syndrome associated with hypothalamic hamartomas other than Pallister-Hall syndrome. The authors discuss the endoscopic endonasal biopsy and subtotal resection of a large hypothalamic hamartoma in one of the patients as well as the histopathological findings encountered. Integral to this discussion is the understanding of the hedgehog pathway; therefore, the underpinnings of this pathway and its clinical associations to date are also reviewed.

Comparative Analysis of Mutational Profile of Sonic hedgehog Gene in Gallbladder Cancer

BACKGROUND

Gallbladder cancer has high incidence in northeastern India; mortality too is high as the disease is often diagnosed late. Numerous studies have shown the role of sonic hedgehog (shh) in different cancers, an important ligand of the hedgehog signaling pathway.

AIM

This study was carried out to evaluate the shh gene mutations in gallbladder cancer patients.

METHODS

PCR-SSCP was performed for shh gene in 50 samples each of gallbladder cancer, cholelithiasis, and control. The samples showing aberration in banding pattern were sequenced.

RESULTS

Variation in banding pattern was observed in 20% gallbladder cancer cases, 10% in cholelithiasis, and none of the control (χ 2 = 11.111; p < 0.05). Sequencing results revealed seven novel point mutations in GBC cases. These novel mutations were found to be associated with histopathology (p < 0.05) and stage (p < 0.05) of gallbladder cancer.

CONCLUSION

This study reveals several novel individual and repetitive mutations of shh gene in GBC and cholelithiasis samples that may be used as diagnostic markers for gallbladder carcinogenesis.

Hedgehog-driven myogenic tumors recapitulate skeletal muscle cellular heterogeneity

Hedgehog (Hh) pathway activation in R26-SmoM2;CAGGS-CreER mice, which carry a tamoxifen-inducible activated Smoothened allele (SmoM2), results in numerous microscopic tumor foci in mouse skeletal muscle. These tumors exhibit a highly differentiated myogenic phenotype and resemble human fetal rhabdomyomas. This study sought to apply previously established strategies to isolate lineally distinct populations of normal mouse myofiber-associated cells in order to examine cellular heterogeneity in SmoM2 tumors. We demonstrate that established SmoM2 tumors are composed of cells expressing myogenic, adipocytic and hematopoietic lineage markers and differentiation capacity. SmoM2 tumors thus recapitulate the phenotypic and functional hetereogeneity observed in normal mouse skeletal muscle. SmoM2 tumors also contain an expanded population of PAX7+ and MyoD+ satellite-like cells with extremely low clonogenic activity. Selective activation of Hh signaling in freshly isolated muscle satellite cells enhanced terminal myogenic differentiation without stimulating proliferation. Our findings support the conclusion that SmoM2 tumors represent an aberrant skeletal muscle state and demonstrate that, similar to normal muscle, myogenic tumors contain functionally distinct cell subsets, including cells lacking myogenic differentiation potential.

Mutations in Hedgehog pathway genes in fetal rhabdomyomas

Ligand-independent, constitutive activation of Hedgehog signalling in mice expressing a mutant, activated SmoM2 allele results in the development of multifocal, highly differentiated tumours that express myogenic markers (including desmin, actin, MyoD and myogenin). The histopathology of these tumours, commonly classified as rhabdomyosarcomas, more closely resembles human fetal rhabdomyoma (FRM), a benign tumour that can be difficult to distinguish from highly differentiated rhabdomyosarcomas. We evaluated the spectrum of Hedgehog (HH) pathway gene mutations in a cohort of human FRM tumours by targeted Illumina sequencing and fluorescence in situ hybridization testing for PTCH1. Our studies identified functionally relevant aberrations at the PTCH1 locus in three of five FRM tumours surveyed, including a PTCH1 frameshift mutation in one tumour and homozygous deletions of PTCH1 in two tumours. These data suggest that activated Hedgehog signalling contributes to the biology of human FRM.

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.

Calcitriol inhibits hedgehog signaling and induces vitamin d receptor signaling and differentiation in the patched mouse model of embryonal rhabdomyosarcoma

Rhabdomyosarcoma (RMS) is the most common soft tissue sarcoma in children. Aberrant Hedgehog (Hh) signaling is characteristic of the embryonal subtype (ERMS) and of fusion-negative alveolar RMS. In the mouse, ERMS-like tumors can be induced by mutations in the Hh receptor Patched1 (Ptch). As in humans these tumors show increased Hh pathway activity. Here we demonstrate that the treatment with the active form of vitamin D₃, calcitriol, inhibits Hh signaling and proliferation of murine ERMS in vivo and in vitro. Concomitantly, calcitriol activates vitamin D receptor (Vdr) signaling and induces tumor differentiation. In addition, calcitriol inhibits ERMS growth in Ptch-mutant mice, which is, however, a rather late response. Taken together, our results suggest that exogenous supply of calcitriol could be beneficial in the treatment of RMS, especially in those which are associated with aberrant Hh signaling activity.

Morphological and Immunohistochemical Characterization of Sarcomatous Tumors in Wild-Type and Genetically Engineered Mice

Malignant soft tissue tumors are commonly observed in wild-type and gene-targeted mice. These tumors have different degrees of differentiation, cellularity, cellular atypia, nuclear pleomorphism, normal and abnormal mitosis, and giant tumor cells with enlarged polylobulated nuclei. They are often diagnosed as pleomorphic sarcoma, undifferentiated sarcoma, fibrosarcoma, malignant fibrous histiocytoma, sarcoma, or sarcoma, not otherwise specified. Pleomorphic sarcomas have no morphological differentiation toward a differentiated mesenchymal or other tumor type in hematoxylin and eosin–stained sections. With the use of immunohistochemistry, human and mouse, tumors associated with these broad nonspecific diagnoses can often be demonstrated to be of a specific cellular lineage. With mouse models being used to delineate the molecular mechanisms, pathogenesis, and cellular origin of human sarcomas, it will be necessary to correlate the morphological and cellular lineage and the molecular profiles of the pleomorphic tumors associated with these mouse models. The results presented here show that with the use of immunohistochemistry, the cellular lineage of many mouse tumors with pleomorphic features can be determined.

Uncommitted precursor cells might contribute to increased incidence of embryonal rhabdomyosarcoma in heterozygous Patched1-mutant mice

Embryonal rhabdomyosarcoma (ERMS) is a tumor of the skeletal muscle in children and is frequently initiated by heterozygous germline mutations in the Hedgehog (Hh) receptor Patched1 (Ptch), both in humans and mice. Using a conditional knock-out strategy in Ptch(flox/+) mice, we demonstrate that early embryonic stages are more susceptible to ERMS development than later stages and that cells normally not committed to undergo myogenesis at this stage represent the major source of ERMS. We found that deletion of a single copy of the Ptch allele at E9.5 using the ubiquitously active Rosa26CreERT2 resulted in a tumor incidence of 88% but reached only 44% and 12% when the Ptch allele was inactivated at E11.5 and E13.5, respectively. Induction of the Ptch mutation at E9.5 did also significantly shorten ERMS-free survival and increased tumor multiplicity compared with tumor induction at E11.5 and E13.5. Interestingly, we observed a more that 10-fold reduction of ERMS incidence when the Ptch mutation was specifically introduced in Myf5-expressing cells, which is the myogenic factor expressed in all muscle cells at E9.5. We conclude that Myf5-negative cells are more susceptible to ERMS development than Myf5-positive embryonic precursors. As the propensity to undergo tumorigenic transformation declined with age, concomitant with the increase of stably committed muscle cells, it seems likely that the Ptch mutation favors tumor formation in progenitor cells, which have not yet acquired a muscle cell fate.

Zebrafish models of rhabdomyosarcoma

Rhabdomyosarcoma (RMS), an aggressive malignant neoplasm that shows features of skeletal muscle, is the most common soft tissue tumor of childhood. In children, the major subtypes are embryonal and alveolar. Although localized disease responds to a multimodal treatment, the prognosis for patients with high-risk features and metastasis remains dismal. Several in vivo models of RMS have been developed in mouse, human xenografts, zebrafish, and Drosophila to better understand the underlying mechanisms governing malignancy. The findings so far have indicated the potential role of skeletal muscle precursor cells in malignant transformation. To better understand histogenesis and different aspects of tumorigenesis in RMS, we have previously developed a robust zebrafish model of kRAS-induced RMS, which shares morphologic and immunophenotypic features with the human counterpart. Cross-species mircroarray comparisons confirm that conserved genetic pathways drive RMS growth. The ease for ex vivo manipulation allows the development of different transgenic and co-injection strategies to induce tumor formation in zebrafish. In contrast to other vertebrate model systems, the tumor onset in zebrafish is short, allowing for efficient study of different tumor processes including tumor growth, self-renewal, and maintenance.

Activation of the hedgehog pathway confers a poor prognosis in embryonal and fusion gene-negative alveolar rhabdomyosarcoma

Rhabdomyosarcoma (RMS) is the most common soft tissue sarcoma in children and comprises two major histological subtypes: alveolar rhabdomyosarcoma (ARMS) and embryonal rhabdomyosarcoma (ERMS). Seventy-five percent of ARMS harbor reciprocal chromosomal translocations leading to fusion genes of the forkhead transcription factor FOXO1 and PAX3 or PAX7. The hedgehog (Hh) pathway has been implied in tumor formation and progression of various cancers including RMS. However, whether Hh pathway activation presents a general feature of RMS or whether it is restricted to specific subgroups has not yet been addressed. Here, we report that marker genes of active Hh signaling, that is, Patched1 (Ptch1), Gli1, Gli3 and Myf5, are expressed at significantly higher levels in ERMS and fusion gene-negative ARMS compared with fusion gene-positive ARMS in two distinct cohorts of RMS patients. Consistently, Gli1 expression correlates with Ptch1 expression in ERMS and fusion gene-negative ARMS, but not in fusion gene-positive ARMS. In addition, expression levels of MyoD1 are significantly lower in ERMS and fusion gene-negative ARMS, pointing to an inverse association of Hh activation and early muscle differentiation. Moreover, Myf5 is identified as a novel excellent class predictor for RMS by receiver operating characteristic analysis. Importantly, high expression of Ptch1 or low MyoD1 expression significantly correlate with reduced cumulative survival in fusion gene-negative RMS underscoring the clinical relevance of these findings. By showing that Hh signaling is preferentially activated in specific subgroups of RMS, our study has important implications for molecular targeted therapies, such as small molecule Hh inhibitors, in RMS.

SHP (small heterodimer partner) suppresses the transcriptional activity and nuclear localization of Hedgehog signalling protein Gli1

Gli (glioma-associated oncogene homologue) proteins act as terminal effectors of the Hedgehog signalling pathway, which is implicated in the development of many human malignancies. Gli activation is important for cell proliferation and anti-apoptosis in various cancers. Several studies have suggested that nuclear receptors have anti-cancer effects by inhibiting the activation of various oncoproteins. However, the involvement of nuclear receptors on the Hedgehog/Gli signalling pathway is poorly defined. In the present study we identified SHP (small heterodimer partner) as a nuclear receptor that decreased the expression of Gli target genes by repressing the transcriptional activity of Gli1. The inhibitory effect of SHP was associated with the inhibition of Gli1 nuclear localization via protein-protein interaction. Finally, SHP overexpression decreased the expression of Gli target genes and SHP knockdown increased the expression of these genes. Taken together, these results suggest that SHP can play a negative role in Hedgehog/Gli1 signalling.

TRAIL and Taurolidine induce apoptosis and decrease proliferation in human fibrosarcoma

BACKGROUND

Disseminated soft tissue sarcoma still represents a therapeutic dilemma because effective cytostatics are missing. Therefore we tested TRAIL and Tarolidine (TRD), two substances with apoptogenic properties on human fibrosarcoma (HT1080).

METHODS

Viability, apoptosis and necrosis were visualized by TUNEL-Assay and quantitated by FACS analysis (Propidiumiodide/AnnexinV staining). Gene expression was analysed by RNA-Microarray and the results validated for selected genes by rtPCR. Protein level changes were documented by Western Blot analysis. NFKB activity was analysed by ELISA and proliferation assays (BrdU) were performed.

RESULTS AND DISCUSSION

The single substances TRAIL and TRD induced apoptotic cell death and decreased proliferation in HT1080 cells significantly. Gene expression of several genes related to apoptotic pathways (TRAIL: ARHGDIA, NFKBIA, TNFAIP3; TRD: HSPA1A/B, NFKBIA, GADD45A, SGK, JUN, MAP3K14) was changed. The combination of TRD and TRAIL significantly increased apoptotic cell death compared to the single substances and lead to expression changes in a variety of genes (HSPA1A/B, NFKBIA, PPP1R15A, GADD45A, AXL, SGK, DUSP1, JUN, IRF1, MYC, BAG5, BIRC3). NFKB activity assay revealed an antipodal regulation of the several subunits of NFKB by TRD and TRD+TRAIL compared to TRAIL alone.

CONCLUSION

TRD and TRAIL are effective to induce apoptosis and decrease proliferation in human fibrosarcoma. A variety of genes seems to be involved, pointing to the NFKB pathway as key regulator in TRD/TRAIL-mediated apoptosis.

Heterogeneous in vitro effects of doxorubicin on gene expression in primary human liposarcoma cultures

BACKGROUND

Doxorubicin is considered one of the most potent established chemotherapeutics in the treatment of liposarcoma; however, the response rates usually below 30%, are still disappointing. This study was performed to identify gene expression changes in liposarcoma after doxorubicin treatment.

METHODS

Cells of 19 primary human liposarcoma were harvested intraoperatively and brought into cell culture. Cells were incubated with doxorubicin for 24 h, RNA was isolated and differential gene expression was analysed by the microarray technique.

RESULTS

A variety of genes involved in apoptosis were up and down regulated in different samples revealing a heterogeneous expression pattern of the 19 primary tumor cell cultures in response to doxorubicin treatment. However, more than 50% of the samples showed up-regulation of pro-apoptotic genes such as TRAIL Receptor2, CDKN1A, GADD45A, FAS, CD40, PAWR, NFKBIA, IER3, PSEN1, RIPK2, and CD44. The anti-apoptotic genes TNFAIP3, PEA15, Bcl2A1, NGFB, and BIRC3 were also up-regulated. The pro-apoptotic CD14, TIA1, and ITGB2 were down-regulated in more than 50% of the tumor cultures after treatment with doxorubicin, as was the antiapoptotic YWHAH.

CONCLUSION

Despite a correlation of the number of differentially regulated genes to the tumor grading and to a lesser extent histological subtype, the expression patterns varied strongly; however, especially among high grade tumors the responses of selected apoptosis genes were similar. The predescribed low clinical response rates of low grade liposarcoma to doxorubicin correspond to our results with only little changes on gene expression level and also divergent findings concerning the up- and down-regulation of single genes in the different sarcoma samples.

Hedgehog: functions and mechanisms

The Hedgehog (Hh) family of proteins control cell growth, survival, and fate, and pattern almost every aspect of the vertebrate body plan. The use of a single morphogen for such a wide variety of functions is possible because cellular responses to Hh depend on the type of responding cell, the dose of Hh received, and the time cells are exposed to Hh. The Hh gradient is shaped by several proteins that are specifically required for Hh processing, secretion, and transport through tissues. The mechanism of cellular response, in turn, incorporates multiple feedback loops that fine-tune the level of signal sensed by the responding cells. Germline mutations that subtly affect Hh pathway activity are associated with developmental disorders, whereas somatic mutations activating the pathway have been linked to multiple forms of human cancer. This review focuses broadly on our current understanding of Hh signaling, from mechanisms of action to cellular and developmental functions. In addition, we review the role of Hh in the pathogenesis of human disease and the possibilities for therapeutic intervention.

Sonic Hedgehog regulates Hes1 through a novel mechanism that is independent of canonical Notch pathway signalling

Aberrant regulation of signalling mechanisms that normally orchestrate embryonic development, such as the Hedgehog, Wnt and Notch pathways, is a common feature of tumorigenesis. In order to better understand the neoplastic events mediated by Hedgehog signalling, we identified over 200 genes regulated by Sonic Hedgehog in multipotent mesodermal cells. Widespread crosstalk with other developmental signalling pathways is evident, suggesting a complex network of interactions that challenges the often over-simplistic representation of these pathways as simple linear entities. Hes1, a principal effector of the Notch pathway, was found to be a target of Sonic Hedgehog in both C3H/10T1/2 mesodermal and MNS70 neural cells. Desert Hedgehog also elicited a strong Hes1 response. While Smoothened function was found necessary for upregulation of Hes1 in response to Sonic Hedgehog, the mechanism does not require gamma-secretase-mediated cleavage of Notch receptors, and appears to involve transcription factors other than RBP-Jkappa. Thus, we have defined a novel mechanism for Hes1 regulation in stem-like cells that is independent of canonical Notch signalling.

Global gene expression profiling of PAX-FKHR fusion-positive alveolar and PAX-FKHR fusion-negative embryonal rhabdomyosarcomas

Paediatric rhabdomyosarcomas (RMS) are classified into two major subtypes based on histological appearance, embryonal (ERMS) and alveolar (ARMS), but this clinically critical distinction is often difficult on morphological grounds alone. ARMS, the more aggressive subtype, is associated in most cases with unique recurrent translocations fusing the PAX3 or PAX7 transcription factor genes to FKHR. In contrast, ERMS lacks unique genetic alterations. To identify novel diagnostic markers and potential therapeutic targets, we analysed the global gene expression profiles of these two RMS subtypes in 23 ARMS (16 PAX3-FKHR, 7 PAX7-FKHR) and 15 ERMS (all PAX-FKHR-negative) using Affymetrix HG-U133A oligonucleotide arrays. A statistically stringent supervised comparison of the ARMS and ERMS expression profiles revealed 121 genes that were significantly differentially expressed, of which 112 were higher in ARMS, including genes of interest as potential diagnostic markers or therapeutic targets, such as CNR1, PIPOX (sarcosine oxidase), and TFAPbeta. Interestingly, many known or putative downstream targets of PAX3-FKHR were highly overexpressed in ARMS relative to ERMS, including CNR1, DCX, ABAT, ASS, JAKMIP2, DKFZp762M127, and NRCAM. We validated the highly differential expression of five genes, including CNR1, DKFZp762M127, DCX, PIPOX, and FOXF1 in ARMS relative to ERMS by quantitative RT-PCR on an independent set of samples. Finally, we developed a ten-gene microarray-based predictor that distinguished ARMS from ERMS with approximately 95% accuracy both in our data by cross-validation and in an independent validation using a published dataset of 26 samples. The gene expression signature of ARMS provides a source of potential diagnostic markers, therapeutic targets, and PAX-FKHR downstream genes, and can be used to reliably distinguish these sarcomas from ERMS.

Patched haploinsufficient mouse rhabdomyosarcoma overexpress secreted phosphoprotein 1 and matrix metalloproteinases

Rhabdomyosarcoma is the most common soft tissue sarcoma of childhood. Improving the management of rhabdomyosarcoma requires a better understanding of growth regulation. Patched haploinsufficient (Ptch+/-) mice spontaneously develop soft tissue sarcomas that resemble human rhabdomyosarcomas. Using microarray profiling and quantitative real-time reverse transcriptase polymerase chain reaction, we identified candidate genes differentially expressed in Ptch+/- mouse rhabdomyosarcoma relative to mature muscle. Overexpressed genes include Secreted Phosphoprotein 1 (Spp1, Osteopontin), and Matrix Metalloproteinases-2 and -14 (Mmp2 and Mmp14). Spp1 is an integrin-binding phosphoglycoprotein upregulated in carcinomas, and Mmps regulate tumour invasion. Immunochemical analyses of murine and human rhabdomyosarcoma specimens confirmed increased expression of Spp1, Mmp2, Mmp14, nuclear factor-kappa B (NF-kappaB) p65 and its phosphorylated active isoform. Neutralising Spp1 antibody decreased Mmp14 RNA in murine rhabdomyosarcoma cultures, indicating a positive regulatory role for extracellular Spp1. Plasma from rhabdomyosarcoma patients display elevated levels of SPP1. These results implicate Spp1, NF-kappaB, and Mmp activation as a putative signalling pathway involved in rhabdomyosarcoma growth.

The hedgehog regulated oncogenes Gli1 and Gli2 block myoblast differentiation by inhibiting MyoD-mediated transcriptional activation

The mechanism by which activation of the Hedgehog (Hh) pathway modulates differentiation and promotes oncogenesis in specific tissues is poorly understood. We therefore, analysed rhabdomyosarcomas from mice that were haploinsufficient for the Hh-binding protein, Hip1, or for the Hh receptor, Patched 1 (Ptch1). Transfection of the Hh-regulated transcription factor Gli1, which is expressed in a subset of mouse and human rhabdomyosarcomas, suppressed differentiation of myogenic rhabdomyosarcoma lines generated from Hip1+/- and Ptch1+/- mice. The closely related factor, Gli2, had similar effects. Gli1 and Gli2 inhibited myogenesis by repressing the capacity of MyoD to activate transcription. Deletion analysis of Gli1 indicated that multiple domains of Gli1 are required for efficient inhibition of MyoD. Gli1 reduced the ability of MyoD to heterodimerize with E12 and bind DNA, providing one mechanism whereby the Gli proteins modulate the activity of MyoD. This novel activity of Gli proteins provides new insights into how Hh signaling modulates terminal differentiation through inhibition of tissue-specific factors such as MyoD. This mechanism may contribute to the broad role of Hh signaling and the Gli proteins in differentiation decisions and cancer formation.

Ptc1 heterozygous knockout mice as a model of multi-organ tumorigenesis

Mutations in the Ptc1 gene are responsible for basal cell nevus (BCN) syndrome, and are commonly found in sporadic basal cell carcinomas (BCC) and in medulloblastoma (MB). Ptc1 hemizygosity in mice underlies this model's susceptibility to multi-organ tumorigenesis. Similar to BCN syndrome patients, the Ptc1 mouse model is characterized by tumor predisposition and radiation hypersensitivity. Ptc1(+/-) mice develop spontaneous rhabdomyosarcoma (RMS) and medulloblastoma (MB), as well as BCC following radiation exposure. The close phenotypic resemblance to the human disease makes these mice a unique preclinical model to test chemopreventive and therapeutic interventions.

The Fem1a gene is downregulated in Rhabdomyosarcoma

Rhabdomyosarcoma (RMS) is the most common soft tissue neoplasm of children, and those metastatic at presentation have a poor prognosis. RMS development is related to defective skeletal muscle differentiation, involving a variety of cell signaling and transcriptional control pathways, including aberrant hedgehog signaling. Here we evaluate Fem1a, a gene highly expressed in skeletal muscle, as a candidate for involvement in RMS. Fem1a is a homolog of fem-1, which controls cell fate decisions in the sex determination pathway of Caenorhabditis elegans, a pathway with homology to mammalian hedgehog signaling. We show that Fem1a expression is activated during myocyte differentiation of C2C12 myoblasts, and this expression is largely confined to the terminally differentiating pool, not to the satellite-cell-like quiescent reserve cell pool. We find that the human homolog, FEM1A, is downregulated in all of 8 different human RMS cell lines, including those derived from embryonal and alveolar RMS. Using mouse genetic models of RMS development, we further show that Fem1a is consistently downregulated in primary RMS from Ptch1+/- mice, from p53-/- mice, from p53+/-; Ptch1+/- mice, and from HGF/SF-Ink4a/Arf-/- mice. Therefore, Fem1a downregulation may be involved in, and/or a marker of, an early cell fate defect fundamental to RMS pathogenesis.