Rearrangement of the PAX3 paired box gene in the paediatric solid tumour alveolar rhabdomyosarcoma

Soft tissue tumours of the retroperitoneum

Purpose. This review summarizes the more prevalent soft tissue tumours arising in the retroperitoneum and highlights some recent fundamental and diagnostic developments relevant to mesenchymal tumours.

Discussion. The retroperitoneum is an underestimated site for benign and malignant neoplastic disease, and represents the second most common site of origin of primary malignant soft tissue tumours (sarcomas) after the deep tissues of the lower extremity. In contrast to the predominance of benign soft tissue lesions over malignant sarcomas elsewhere, retroperitoneal mesenchymal lesions are far more likely to be malignant. The differential diagnosis is primarily with the more common lymphoproliferative and parenchymatous epithelial lesions arising in this area, and with metastatic disease from known or unknown primary sites elsewhere.The most prevalent mesenchymal tumours at this site are of a lipomatous, myogenic or neural nature.Their generally late clinical presentation and poorly accessible location provides numerous clinical challenges; optimal radiological imaging and a properly performed biopsy are essential cogs in the management route. Histopathological diagnosis may be complicated, but has been aided by developments in the fields of immunohistochemistry and tumour (cyto)genetics. Despite significant advances in oncological management protocols, the prognosis remains generally less favourable than for similar tumours at more accessible sites.

Nephroblastoma overexpressed (NOV/CCN3) gene: a paired-domain-specific PAX3-FKHR transcription target that promotes survival and motility in alveolar rhabdomyosarcoma cells

The CCN (Cy61, CTGF and NOV) family of proteins is a group of matricellular biomolecules involved in both physiological and pathological processes. Elevated expression of the CCN3 (also known as NOV, Nephroblastoma overexpressed) gene has been detected in clinical samples of the skeletal muscle cancer rhabdomyosarcoma, with the highest expression found in the alveolar subtype (aRMS). Over 80% of aRMSs are characterized by a chromosomal translocation-derived fusion transcription factor PAX3-FKHR. In this study, we linked elevated CCN3 levels in aRMS cells to PAX3-FKHR expression. We found reduced CCN3 levels in aRMS cells following small interfering RNA knockdown of PAX3-FKHR, and increased CCN3 levels in C2 myoblasts following ectopic expression of PAX3-FKHR. Promoter, electrophoretic mobility shift assay and chromatin immunoprecipitation analyses confirmed that the CCN3 gene was a direct target for PAX3-FKHR transcriptional activation through a paired-domain DNA sequence in the first intron of the CCN3 gene. To determine the function of CCN3, we showed that knockdown and ectopic expression of CCN3 decreased survival and increased differentiation in aRMS cells, respectively. In addition, we found that exogenously supplied CCN3 protein promoted aRMS cell adhesion, migration and Matrigel invasion. Taken together, data from this study have (1) provided a mechanistic basis for the CCN3 overexpression in aRMS cells, and (2) identified CCN3 as an autocrine/paracrine factor that contributes to the aggressive behavior of aRMS cells, perhaps through a positive feedback loop. Thus, CCN3 may be an attractive target for therapeutic intervention in aRMS.

miRNA Profiling: How to Bypass the Current Difficulties in the Diagnosis and Treatment of Sarcomas

Sarcomas are divided into a group with specific alterations and a second presenting a complex karyotype, sometimes difficult to diagnose or with few therapeutic options available. We assessed if miRNA profiling by TaqMan low density arrays could predict the response of undifferentiated rhabdomyosarcoma (RMS) and osteosarcoma to treatment. We showed that miRNA signatures in response to a therapeutic agent (chemotherapy or the mTOR inhibitor RAD-001) were cell and drug specific on cell lines and a rat osteosarcoma model. This miRNA signature was related to cell or tumour sensitivity to this treatment and might be not due to chromosomal aberrations, as revealed by a CGH array analysis of rat tumours. Strikingly, miRNA profiling gave promising results for patient rhabdomyosarcoma, discriminating all types of RMS: (Pax+) or undifferentiated alveolar RMS as well as embryonal RMS. As highlighted by these results, miRNA profiling emerges as a potent molecular diagnostic tool for complex karyotype sarcomas.

Molecular testing of solid tumors

CONTEXT

Molecular testing of solid tumors is steadily becoming a vital component of the contemporary anatomic pathologist's armamentarium. These sensitive and specific ancillary tools are useful for confirming ambiguous diagnoses suspected by light microscopy and for guiding therapeutic decisions, assessing prognosis, and monitoring patients for residual neoplastic disease after therapy.

OBJECTIVE

To review current molecular biomarkers and tumor-specific assays most useful in solid tumor testing, specifically of breast, colon, lung, thyroid, and soft tissue tumors, malignant melanoma, and tumors of unknown origin. A few upcoming molecular diagnostic assays that may become standard of care in the near future will also be discussed.

DATA SOURCES

Original research articles, review articles, and the authors' personal practice experience.

CONCLUSIONS

Molecular testing in anatomic pathology is firmly established and will continue to gain ground as the need for more specific diagnoses and new targeted therapies evolve. Knowledge of the more common and clinically relevant molecular tests available for solid tumor diagnosis and management, and their indications and limitations, is necessary if anatomic pathologists are to optimally use these tests and act as consultants for fellow clinicians directly involved in patient care.

Seeking consent to tissue banking: a survey of health professionals in childhood cancer

To identify the views of health professionals working in childhood cancer on seeking consent to tissue banking from potential donors. Self-completion questionnaires sent to 553 UK paediatric oncology health professionals. The response rate was 60%. Respondents (100%) were in favour of using tissue samples from children with cancer for research. A substantial minority (30%) had concerns about the impact of the law on their professional role in relation to tissue banking. Almost all (90%) reported that both the parent(s) and the child, if able, should be asked for consent, though the UK Human Tissue Act provides that a competent child's consent is sufficient. Most (94%) supported 'generic' rather than 'specific' consent. Barriers to obtaining consent included: (1) timing of the approach to families; (2) availability of suitable staff; (3) sensitivity of the issues; (4) difficulties of managing the process; and (5) problems of maintaining a paper trail. Many would welcome training on seeking consent. Personal knowledge and relationships with families are often seen as important in guiding the proper approach to consent rather than formalized rules. There is widespread support among health professionals for tissue banking in childhood cancer. In sensitive situations, disciplined exercise of professional discretion might better deliver on aspirations for regulation than rigid procedures.

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.

Myogenesis and rhabdomyosarcoma the Jekyll and Hyde of skeletal muscle

Rhabdomyosarcoma, a neoplasm composed of skeletal myoblast-like cells, represents the most common soft tissue sarcoma in children. The application of intensive chemotherapeutics and refined surgical and radiation therapy approaches have improved survival for children with localized disease over the past 3 decades; however, these approaches have not improved the dismal outcome for children with metastatic and recurrent rhabdomyosarcoma. Elegant studies have defined the molecular mechanisms driving skeletal muscle lineage commitment and differentiation, and the machinery that couples differentiation with irreversible cell proliferation arrest. Further, detailed molecular analyses indicate that rhabdomyosarcoma cells have lost the capacity to fully differentiate when challenged to do so in experimental models. We review the intersection of normal skeletal muscle developmental biology and the molecular genetic defects in rhabdomyosarcoma with the underlying premise that understanding how the differentiation process has gone awry will lead to new treatment strategies aimed at promoting myogenic differentiation and concomitant cell cycle arrest.

Notch pathway inhibition significantly reduces rhabdomyosarcoma invasiveness and mobility in vitro

PURPOSE

Rhabdomyosarcoma (RMS) is the most common type of soft tissue sarcoma in children and can be divided into two main subtypes: embryonal and alveolar RMS. Patients with metastatic disease continue to have very poor prognosis although aggressive therapies and recurrences are common in advanced localized disease. The oncogenic potential of the Notch pathway has been established in some cancers of the adult and in some pediatric malignancies.

EXPERIMENTAL DESIGN

A real-time PCR assay was used to ascertain the expression of several Notch pathway components in a wide panel of RMS and cell lines. Four γ-secretase inhibitors (GSIs) were tested for pathway inhibition and the degree of inhibition was assessed by analysis of Hes1 and Hey1 expression. The putative effects of Notch pathway inhibition were evaluated by wound-healing, matrigel/transwell invasion, cell-cycle, and apoptosis assays.

RESULTS

The Notch pathway was widely expressed and activated in RMS and underwent substantial inhibition when treated with GSIs or transfected with a dominant negative form of MAML1. RMS cells showed a significant decrease in its mobility and invasiveness when the Notch pathway was properly inhibited; conversely, its inhibition had no noticeable effect on cell cycle or apoptosis.

CONCLUSION

Pharmacological or genetic blockage of the pathway significantly reduced invasiveness of RMS cell lines, thereby suggesting a possible role of the Notch pathway in the regulation of the metastatic process in RMS.

Establishment and characterization of the rhabdomyosarcoma cell line designated NUTOS derived from the human tongue sarcoma: Special reference to the susceptibility of anti-cancer drugs

Primary alveolar type of rhabdomyosarcoma (RMS) tumor tissue was collected from the tongue of a 17-year-old Japanese woman and used to successfully establish a rhabdomyosarcoma cell line, which has been designated NUTOS. The chromosomal distribution revealed that the NUTOS cell line was hyper-tetraploid with chromosomal translocation. The cells were grown in Dulbecco's modified eagle medium/F12 supplemented with 15% fetal bovine serum, 0.1% non-essential amino acids solution (NEAA), 50 microg of streptomycin, 50 U/mL of penicillin and 0.25 microg /mL of Fungizone. The NUTOS shapes included small spindles, large spindles and long, thick multinucleated cells. All three cell types were immunostained with anti-desmin antibody, which is a marker protein for middle sized myofilaments. Furthermore, immunocytochemical staining revealed that the cells were positively immunostained with anti-MyoD, myogenin, alpha-sarcomeric actin, myosin and troponin T. Mitotic figures were only observed in the small spindle cells. These cells were coadunated with each other at the lateral portion of the apex of the cells. Subsequently, these cells grew into large multinucleated cells. Autonomic contractions (approximately 20 times/min) were observed in both the large spindle cells and the large multinucleated cells. NUTOS cells incorporated serotonin from the serum in the growth medium. Histopathological observations of the NUTOS cell grafts in the subcutis of nude mice exhibited characteristics similar to those seen for the primary rhabdomyosarcoma of the tongue. Susceptibility tests for the anti-cancer drugs revealed that NUTOS cells were susceptive to cisplatin, paclitaxel, and docetaxel, but not to adriacin.

Overlapping and distinct role of CXCR7-SDF-1/ITAC and CXCR4-SDF-1 axes in regulating metastatic behavior of human rhabdomyosarcomas

We have demonstrated that the α-chemokine stromal-derived factor (SDF)-1-CXCR4 axis plays an important role in rhabdomyosarcoma (RMS) metastasis. With the recent description of CXCR7, a new receptor for SDF-1 that also binds the interferon-inducible T-cell α chemoattractant (ITAC) chemokine, we became interested in the role of the CXCR7-SDF-1/ITAC axis in RMS progression. To address this issue, we evaluated 6 highly metastatic alveolar (A)RMS and 3 less metastatic embryonal (E)RMS cell lines and found that all these cell lines express CXCR7. Although CXCR4 was expressed at a much higher level by highly metastatic ARMS lines, CXCR7 was present at a high level on ERMS lines. We also noticed that CXCR7 expression on RMS cells was downregulated in hypoxic conditions. More importantly, the CXCR7 receptor on RMS cell lines was functional after stimulation with ITAC and SDF-1 as evidenced by mitogen-activated protein kinase (MAPK)p42/44 and AKT phosphorylation as well as CXCR7 internalization, chemotaxis, cell motility and adhesion assays. Similarly to CXCR4, signaling from activated CXCR7 was not associated with increased RMS proliferation or cell survival. Moreover, CXCR7(+) RMS cells responded to SDF-1 and I-TAC in the presence of CXCR4 antagonists (T140, AMD3100). Furthermore, while intravenous injection of RMS cells with overexpressed CXCR7 resulted in increased seeding efficiency of tumor cells to bone marrow, CXCR7 downregulation showed the opposite effect. In conclusion, the CXCR7-SDF-1/ITAC axis is involved in the progression of RMS; targeting of the CXCR4-SDF-1 axis alone without simultaneous blockage of CXCR7 will be an inefficient strategy for inhibiting SDF-1-mediated prometastatic responses of RMS cells.

Macrophage migration inhibitory factor is secreted by rhabdomyosarcoma cells, modulates tumor metastasis by binding to CXCR4 and CXCR7 receptors and inhibits recruitment of cancer-associated fibroblasts

The overexpression of macrophage migration inhibitory factor (MIF) has been observed in many tumors and is implicated in oncogenic transformation and tumor progression. MIF activates CXCR2 and CD74 receptors and, as recently reported, may also bind to the stromal-derived factor-1 (SDF-1)-binding receptor CXCR4. Here, we report that human rhabdomyosarcoma (RMS) cell lines secrete MIF and that this chemokine (a) induces phosphorylation of mitogen-activated protein kinase (MAPK) p42/44 and AKT, (b) stimulates RMS cell adhesion, (c) enhances tumor vascularization, but surprisingly (d) decreases recruitment of cancer-associated fibroblasts (CAF). Because RMS cells used in our studies do not express CXCR2 and CD74 receptors, the biological effects of MIF on RMS cells depend on its interaction with CXCR4, and as we report here for the first time, MIF may also engage another SDF-1-binding receptor (CXCR7) as well. Interestingly, downregulation of MIF in RMS cells inoculated into immunodeficient mice led to formation of larger tumors that displayed higher stromal cell support. Based on these observations, we postulate that MIF is an important autocrine/paracrine factor that stimulates both CXCR4 and CXCR7 receptors to enhance the adhesiveness of RMS cells. We also envision that when locally secreted by a growing tumor, MIF prevents responsiveness of RMS to chemoattractants secreted outside the growing tumor (e.g., SDF-1) and thereby prevents release of cells into the circulation. On the other hand, despite its obvious proangiopoietic effects, MIF inhibits in CXCR2/CD74-dependent manner recruitment of CAFs to the growing tumor. Our data indicate that therapeutic inhibition of MIF in RMS may accelerate metastasis and tumor growth.

Macrophage migration inhibitory factor is secreted by rhabdomyosarcoma cells, modulates tumor metastasis by binding to CXCR4 and CXCR7 receptors and inhibits recruitment of cancer-associated fibroblasts

The overexpression of macrophage migration inhibitory factor (MIF) has been observed in many tumors and is implicated in oncogenic transformation and tumor progression. MIF activates CXCR2 and CD74 receptors and, as recently reported, may also bind to the stromal-derived factor-1 (SDF-1)-binding receptor CXCR4. Here, we report that human rhabdomyosarcoma (RMS) cell lines secrete MIF and that this chemokine (a) induces phosphorylation of mitogen-activated protein kinase (MAPK) p42/44 and AKT, (b) stimulates RMS cell adhesion, (c) enhances tumor vascularization, but surprisingly (d) decreases recruitment of cancer-associated fibroblasts (CAF). Because RMS cells used in our studies do not express CXCR2 and CD74 receptors, the biological effects of MIF on RMS cells depend on its interaction with CXCR4, and as we report here for the first time, MIF may also engage another SDF-1-binding receptor (CXCR7) as well. Interestingly, downregulation of MIF in RMS cells inoculated into immunodeficient mice led to formation of larger tumors that displayed higher stromal cell support. Based on these observations, we postulate that MIF is an important autocrine/paracrine factor that stimulates both CXCR4 and CXCR7 receptors to enhance the adhesiveness of RMS cells. We also envision that when locally secreted by a growing tumor, MIF prevents responsiveness of RMS to chemoattractants secreted outside the growing tumor (e.g., SDF-1) and thereby prevents release of cells into the circulation. On the other hand, despite its obvious proangiopoietic effects, MIF inhibits in CXCR2/CD74-dependent manner recruitment of CAFs to the growing tumor. Our data indicate that therapeutic inhibition of MIF in RMS may accelerate metastasis and tumor growth.

Role of I-TAC-binding receptors CXCR3 and CXCR7 in proliferation, activation of intracellular signaling pathways and migration of various tumor cell lines

Chemokines and its receptors stimulate tumor growth, migration and invasion. In this study we evaluated the expression and function of CXCR3 and CXCR7 receptors in cervical carcinoma, rhabdomyosarcoma and glioblastoma cell lines. We found that both receptors were expressed at different degree by tumor cells. CXCR7 was expressed at both mRNA and protein level by all tumor cell lines. The expression of CXCR7 differed between rhabdomyosarcoma subtypes. The receptor was highly expressed in alveolar rhabdomyosarcoma and the expression was low in embryonal rhabdomyosarcoma. The expression of CXCR3 was low in majority of the tumor cell lines. Upon I-TAC stimulation AKT and MAPK kinases were activated. However, the activation of growth promoting pathways did not increased the proliferation rate of tumor cells. Since chemokines stimulate the migration of various cell types the ability of I-TAC to stimulate migration of tumor cells were studied. We did not observe the migration of tumor cells toward I-TAC gradient alone. However, at the low dose, I-TAC sensitized tumor cells toward SDF-1beta gradient and synergized with SDF-1beta in activation of intracellular pathways. Our data suggest an important role of I-TAC and its receptors in biology of solid tumors and we postulate that I-TAC-binding receptors might be used as the potential targets for antitumor therapy.

Genome-wide identification of PAX3-FKHR binding sites in rhabdomyosarcoma reveals candidate target genes important for development and cancer

The PAX3-FKHR fusion protein is present in a majority of alveolar rhabdomyosarcomas associated with increased aggressiveness and poor prognosis. To better understand the molecular pathogenesis of PAX3-FKHR, we carried out the first, unbiased genome-wide identification of PAX3-FKHR binding sites and associated target genes in alveolar rhabdomyosarcoma. The data shows that PAX3-FKHR binds to the same sites as PAX3 at both MYF5 and MYOD enhancers. The genome-wide analysis reveals that the PAX3-FKHR sites are (a) mostly distal to transcription start sites, (b) conserved, (c) enriched for PAX3 motifs, and (d) strongly associated with genes overexpressed in PAX3-FKHR-positive rhabdomyosarcoma cells and tumors. There is little evidence in our data set for PAX3-FKHR binding at the promoter sequences. The genome-wide analysis further illustrates a strong association between PAX3 and E-box motifs in these binding sites, suggestive of a common coregulation for many target genes. We also provide the first direct evidence that FGFR4 and IGF1R are the targets for PAX3-FKHR. The map of PAX3-FKHR binding sites provides a framework for understanding the pathogenic roles of PAX3-FKHR, as well as its molecular targets to allow a systematic evaluation of agents against this aggressive rhabdomyosarcoma.

PAX3 across the spectrum: from melanoblast to melanoma

The PAX3 transcription factor is critical for the proper development of neural crest lineages including melanocytes. These cells show continued PAX3 expression from formation to differentiation. While many expression, misexpression and mutation studies clarify the importance of PAX3 in melanocyte development, less well understood, and more perplexing, is the continued PAX3 expression in the adult skin. In this article we explore the multiple roles of PAX3 in melanocyte genesis, and draw on evidence from expression in developing melanoblasts, adult melanocytes and melanocyte stem cells. From this, we present a more encompassing theory that PAX3 is a key regulator of the myriad steps in melanocytic cell determination. These roles may be accomplished by differential association with cofactors, via alternate transcripts or posttranslational protein modification(s). In light of the plethora of information gleaned from development we then consider its roles in melanoma and provide here a comprehensive consideration of the significance of PAX3 expression in melanoma. PAX3 and Pax3 indicate human and mouse transcription factors respectively.

Inhibition of rhabdomyosarcoma's metastatic behavior through downregulation of MET receptor signaling

Rhabdomyosarcoma (RMS) is a soft tissue sarcoma usually diagnosed in children. In advanced and metastatic stages the prognosis is often poor. RMS cell lines were used for evaluation of the role of MET receptor inhibition on chemotaxis and invasion. In vivo studies were performed using NOD-SCID xenograft model. This study shows that blocking of MET expression has strong influence on metastatic behavior of RMS. MET negative cells possess a reduced potential to migrate and to invade. Downregulation of MET suppressed the ability of RMS cells to populate bone marrow. Inhibition of MET negative tumor cells engraftment into bone marrow was observed. MET negative tumors were also two to four times smaller than their wild type counterparts. Since MET receptor plays a very important role in facilitating metastasis of RMS cells, blocking of HGF-MET axis might be considered as a therapeutic option for RMS patients, at more advanced and metastatic stages.

The clinical relevance of molecular genetics in soft tissue sarcomas

Bone and soft tissue sarcomas are an infrequent and heterogeneous group of mesenchymal tumors including more than a hundred different entities attending to histologic patterns. Research into the molecular aspects of sarcomas has increased greatly in the last few years. This enormous amount of knowledge has allowed, for instance, to refine the classification of sarcomas, improve the diagnosis, and increase the number of therapeutical targets available, most of them under preclinical evaluation. However, other important key issues, such as sarcomagenesis and the cell of origin of sarcomas, remain unresolved. From a molecular point of view, these neoplasias are grouped into 2 main types: (a) sarcomas showing relatively simple karyotypes and translocations, which originate gene fusions (eg, EWS-FLI1 in Ewing sarcoma) or point mutations (eg, c-kit in the gastrointestinal tumors) and (b) sarcomas showing unspecific gene alterations, very complex karyotypes, and no translocations. The discovery of the early mechanisms involved in the genesis of sarcomas, the more relevant signaling pathways, and the development of genetically engineered mouse models could also provide a new individualized therapeutic strategy against these tumors. This review describes the clinical application of some of the molecular alterations found in sarcomas, some advances in the field of sarcomagenesis, and the development of animal models.

Thrombin regulates the metastatic potential of human rhabdomyosarcoma cells: distinct role of PAR1 and PAR3 signaling

We observed that human rhabdomyosarcoma (RMS) cells highly express a tissue factor that promotes thrombin formation, which indirectly and directly affects RMS progression. First, we found that thrombin activates platelets to generate microvesicles (PMV), which transfer to RMS cells' alpha2beta3 integrin and increase their adhesiveness to endothelial cells. Accordingly, RMS cells covered with PMVs showed higher metastatic potential after i.v. injection into immunodeficient mice. Furthermore, PMVs activate mitogen-activated protein kinase (MAPK)p42/44 and AKT to chemoattract RMS cells. We also found that RMS cells express functional protease-activated receptor-1 (PAR1) and PAR3 and respond to thrombin stimulation by MAPKp42/44 and MAPKp38 phosphorylation. To our surprise, thrombin did not affect RMS proliferation or survival; it inhibited the chemotactic and adhesive properties of RMS cells. However, when PAR1-specific agonist thrombin receptor-activating peptide 6 was used, which does not activate PAR3, selective PAR1 stimulation enhanced RMS proliferation. To learn more on the role of PAR1 and PAR3 antagonism in RMS proliferation and metastasis, we knocked down both receptors by using a short hairpin RNA strategy. We found that although thrombin does not affect growth of PAR1(-/-) cells, it stimulated the proliferation of PAR3(-/-) cells. More importantly, PAR3(-/-) cells, in contrast to PAR1(-/-) ones, formed larger tumors in immunodeficient mice. We conclude that thrombin is a novel underappreciated modulator of RMS metastasis and that we have identified a novel role for PAR3 in thrombin signaling.

PAX3 expression in normal skin melanocytes and melanocytic lesions (naevi and melanomas)

BACKGROUND

Cutaneous Malignant Melanoma is an aggressive form of skin cancer, arising in cutaneous melanocytes. The transcription factor PAX3 regulates melanocyte specification from neural crest cells during development but expression in differentiated melanocytes is uncertain. By contrast it is frequently found in melanomas and naevi and is a marker for melanoma staging and detection. In this study we analysed the expression of PAX3 across the spectrum of melanocytic cells, from normal melanocytes to cells of benign and malignant lesions to better assess its function in these various tissues. Pax3 and PAX3 (italicized) refer to the mouse and human gene, respectively; whereas Pax3 and PAX3 (non-italicized) refer to the corresponding mouse and human protein.

METHODOLOGY AND PRINCIPAL FINDINGS

PAX3 expression was analysed by immunohistochemistry and qRT-PCR. Immunofluorescence was used for co-expression with differentiation, migration and survival markers. As expected PAX3 expression was observed in naevi and melanoma cells. It was also found in melanocytes of normal skin where it co-expressed with melanocyte markers, MITF and MLANA. Co-expression with its downstream target, antiapoptotic factor BCL2L1 confirms PAX3 as a cell survival regulator. PAX3 was also co-expressed with melanoma cell migration marker MCAM in dermal naevi and melanoma cell nests, but this downstream target of PAX3 was not present in normal epidermal melanocytes, suggesting differential roles for PAX3 in normal epidermal melanocytes and melanoma cells. Most interestingly, a proportion of PAX3-positive epidermal melanocytes in normal skin show HES1 and Ki67 co-expression, indicating their less differentiated proliferative phenotype.

CONCLUSIONS AND SIGNIFICANCE

Our results suggest that a previously identified role for PAX3, that of regulator of an undifferentiated plastic state, may operate in melanocytes of normal skin. This role, possibly required for cellular response to environmental stimuli, may contribute to formation and development of melanocytic lesions in which PAX3 expression is prominent.

Reverse transcriptase-polymerase chain reaction as an ancillary molecular technique in the diagnosis of small blue round cell tumors by fine-needle aspiration cytology

We evaluated the feasibility and usefulness of reverse transcriptase-polymerase chain reaction (RT-PCR) on fine-needle aspirates for categorization of small blue round cell tumors (SBRCTs). A total of 51 cases, including 25 Ewing sarcoma/peripheral primitive neuroectodermal tumors (PNETs), 11 rhabdomyosarcomas, 13 neuroblastomas, and 2 desmoplastic small round cell tumors (DSRCTs) were analyzed. The detection of the EWS-FLI1 (20/25) and EWS-ERG (4/25) fusion transcripts resolved 24 of 25 cases of Ewing sarcoma/PNET. The PAX3/7-FKHR fusion transcript was detected in 2 of 4 cases of alveolar rhabdomyosarcoma and the EWS-WT1 transcript in both cases of DSRCT. Tyrosine hydroxylase and 3,4-dihydroxyphenylalanine (dopa) decarboxylase transcripts were demonstrated in 10 of 13 cases of neuroblastoma. In comparison, immunocytochemical analysis resolved 19 (76%) of 25 Ewing sarcomas, 9 (82%) of 11 rhabdomyosarcomas, 6 (46%) of 13 neuroblastomas, and 1 (50%) of 2 DSRCTs. Overall, RT-PCR resolved 38 (86%) of 44 vs 35 (69%) of 51 cases by immunocytochemical analysis. RT-PCR is easily applied to fine-needle aspirates of SBRCT and greatly facilitates accurate tumor typing.

Identification of a novel nonsense mutation on the Pax3 gene in ENU-derived white belly spotting mice and its genetic interaction with c-Kit

In the course of a large-scale screening program of N-ethyl-N-nitrosourea mutagenesis, we isolated two semidominant mutation lines with white belly spotting, named as wps and wbs. Direct sequencing detected a nucleotide G-to-A transversion in exon 2 of the c-Kit gene in wps, which resulted in a missense D60N mutation. Another mutant, wbs, was mapped to chromosome 1 by genome-wide linkage analysis. In 93 meioses, the wbs locus was confined to a 5.2-Mb region between D1Mit380 and D1Mit215, including the Pax3 gene. A nonsense mutation K107X on the Pax3 coding region in wbs mice was identified, causing the loss of Pax3 protein in the homozygous mutant. We further demonstrated that Pax3 exhibited genetic interaction with c-Kit by intercrossing the wps and wbs mice. Further, Pax3 transactivated the c-Kit promoter in different cell lines. However, electrophoretic mobility shift assays showed that Pax3 did not bind to the c-Kit promoter, indicating that Pax3 may interact with c-Kit in an indirect way. This expands our understanding of the intricate regulatory network governing the melanocyte development.

Selective upregulation of interleukin-8 by human rhabdomyosarcomas in response to hypoxia: therapeutic implications

Rhabdomyosarcoma (RMS) is the most common soft-tissue sarcoma of adolescence and childhood. Because RMS tumors are highly vascularized, we sought to determine which factors secreted by RMS cells are crucial in stimulating angiogenesis in response to hypoxia. To address this issue, we evaluated expression of several proangiogenic factors [interleukin (IL)-8, vascular endothelial growth factor (VEGF), fibroblast growth factor (FGF)-2, stromal-derived factor (SDF)-1, hepatocyte growth factor (HGF) and leukemia inhibitory factor (LIF)] in 8 human RMS cell lines in both normal steady-state and hypoxic conditions. We found by real-time quantitative polymerase chain reaction (RQ-PCR) and confirmed by enzyme-linked immunosorbent assay (ELISA) that from all the factors evaluated, IL-8, whose expression is very low in normoxia, had been very highly expressed and secreted by RMS cells lines during hypoxic conditions ( approximately 40-170 times). Interestingly, this upregulation was not affected by knocking down hypoxia-inducible factor (HIF)-1alpha, but was inhibited by mitogen-activated protein kinase (MAPK)p42/44 and phosphatidylinositaol 3-kinase (PI3K)/AKT pathway inhibitors. This suggests that IL-8 expression is regulated in an activating protein (AP)-1- and nuclear factor (NF)-kappaB-dependent manner. Furthermore, we found that conditioned media (CM) harvested from RMS cells exposed to hypoxia activated and stimulated chemotactic responses in human umbilical vein endothelial cells (HUVECs) and that IL-8 was responsible for hypoxia-related effects. Finally, by employing shRNA, the expression of IL-8 in human RH-30 cells was downregulated. We noticed that such RMS cells, if injected into skeletal muscles of immunodeficient mice, have a reduced ability for tumor formation. We conclude that IL-8 is a pivotal proangiogenic factor released by human RMS cells in hypoxic conditions and that the targeting of IL-8 may prove to be a novel and efficient strategy for inhibiting RMS growth.

Oncogenic mutations of PIK3CA in human cancers

The involvement of the PIK3CA gene product p110α, the catalytic subunit of phosphatidylinositol 3-kinase (PI3K), in human cancer has been suggested for over 15 years, and support for this proposal had been provided by both genetic and functional studies, including most recently the discovery of common activating missense mutations of PIK3CA in a wide variety of common human tumor types. This chapter will focus on the discovery of these mutations and describes their relevance to a wide range of common human tumor types.Of note, the identification and functional analysis of the PIK3CA gene are reviewed in other chapters in this book. However, a brief mention will be made here of its general properties as background to our focus on the discovery of its cancer-specific mutations.

Regulation of expression of stromal-derived factor-1 receptors: CXCR4 and CXCR7 in human rhabdomyosarcomas

Rhabdomyosarcomas (RMS) express CXCR4 and CXCR7 receptors that bind prometastatic alpha-chemokine stromal-derived factor-1 (SDF-1). In this report, we analyzed the activity of both promoters in a model of less metastatic human embryonal-RMS cell line (RD) and more metastatic alveolar-like RMS (RD cells transduced with paired box gene 3/forkhead homologue; PAX3-FKHR fusion gene). First, CXCR4 is barely detectable in RD and becomes upregulated in RD/PAX3-FKHR cells. In contrast, CXCR7 highly expressed in RD becomes downregulated in RD/PAX3-FKHR cells. Next, promoter deletion and mutation studies revealed that whereas (a) expression of CXCR4 in RD and RD/PAX3-FKHR cells required nuclear respiratory factor-1 (NRF-1) binding site and (b) was additionally upregulated by direct interaction of NRF-1 with PAX3-FKHR, CXCR7 promoter activity required a proximal nuclear factor-kappaB-binding motif. The requirement of these factors for CXCR4 and CXCR7 promoter activities was additionally supported after blocking NRF-1 and nuclear factor-kappaB. Furthermore, CXCR4 expression in PAX3-FKHR(+) RMS cells seems to be enhanced because of the interaction of PAX3-FKHR and NRF-1 proteins in the proximal part of the promoter that prevents access of the negative regulator of transcription YY1 to its binding site. Finally, although hypoxia enhances CXCR4 and CXCR7 promoter activity and receptor expression in RD cells, it inhibits CXCR7 expression in RD/PAX3-FKHR cells. In conclusion, SDF-1 binding receptors CXCR4 and CXCR7 are differently regulated in RMS cells. The upregulation of CXCR4 and downregulation of CXCR7 expression by PAX3-FKHR or hypoxia may give SDF-1 an advantage to better engage the CXCR4 receptor, thus increasing RMS motility.

Small cell tumors of bone

Bone tumors are fortunately rare, but small cell tumors of bone are a relatively common subset of these lesions. They comprise of a diverse group of primary and metastatic neoplasms in both children and adults. The most common small cell tumors of bone include Ewing sarcoma/primitive neuroectodermal tumor, small cell osteosarcoma, multiple myeloma, lymphoma, leukemia, neuroblastoma, rhabdomyosarcoma, and Langerhans cell histiocytosis. Although each entity has its distinctive features, the differential diagnosis of this group of tumors is still challenging because they are all "small, blue, and round cell tumors", histologically. The correct diagnosis of small cell tumors of bone depends on an evaluation of clinical, radiologic, pathologic, and genetic features. Patients' age and sex are very important, as are the signs and symptoms at presentation. Radiologically, which bone is involved, the specific portion of the bone (epiphysis, metaphysis, or diaphysis; cortex vs. medulla) involved, and the radiographic manifestations (lytic, blastic, or mixed lytic and blastic) are also often critical parameters for the diagnosis. In recent years, with a better understanding of the molecular and cytogenetic background of several small cell tumors, more accurate diagnoses have been supported by the clinicopathologic criteria and by a panel of immunohistochemical studies. In this review we will provide an overview of the clinical, radiologic, pathologic, and genetic characteristics of these tumors.

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

Altered expression of proteins in the dystrophin-associated glycoprotein complex results in muscular dystrophy and has more recently been implicated in a number of forms of cancer. Here we show that loss of either of two members of this complex, dystrophin in mdx mice or alpha sarcoglycan in Sgca(-/-) mice, results in the spontaneous development of muscle-derived embryonal rhabdomyosarcoma (RMS) after 1 year of age. Many mdx and Sgca(-/-) tumors showed increased expression of insulin-like growth factor 2, retinoblastoma protein, and phosphorylated Akt and decreased expression of phosphatase and tensin homolog gene, much as is found in a human RMS. Further, all mdx and Sgca(-/-) RMS analyzed had increased expression of p53 and murine double minute (mdm)2 protein and contained missense p53 mutations previously identified in human cancers. The mdx RMS also contained missense mutations in Mdm2 or alternatively spliced Mdm2 transcripts that lacked an exon encoding a portion of the p53-binding domain. No Pax3:Fkhr or Pax7:Fkhr translocation mRNA products were evident in any tumor. Expression of natively glycosylated alpha dystroglycan and alpha sarcoglycan was reduced in mdx RMS, whereas dystrophin expression was absent in almost all human RMS, both for embryonal and alveolar RMS subtypes. These studies show that absence of members of the dystrophin-associated glycoprotein complex constitutes a permissive environment for spontaneous development of embryonal RMS associated with mutation of p53 and mutation or altered splicing of Mdm2.

Diabetes and apoptosis: neural crest cells and neural tube

Birth defects resulting from diabetic pregnancy are associated with apoptosis of a critical mass of progenitor cells early during the formation of the affected organ(s). Insufficient expression of genes that regulate viability of the progenitor cells is responsible for the apoptosis. In particular, maternal diabetes inhibits expression of a gene, Pax3, that encodes a transcription factor which is expressed in neural crest and neuroepithelial cells. As a result of insufficient Pax3, cardiac neural crest and neuroepithelial cells undergo apoptosis by a process dependent on the p53 tumor suppressor protein. This, then provides a cellular explanation for the cardiac outflow tract and neural tube and defects induced by diabetic pregnancy.

Polycomb group proteins: navigators of lineage pathways led astray in cancer

The Polycomb group (PcG) proteins are transcriptional repressors that regulate lineage choices during development and differentiation. Recent studies have advanced our understanding of how the PcG proteins regulate cell fate decisions and how their deregulation potentially contributes to cancer. In this Review we discuss the emerging roles of long non-coding RNAs (ncRNAs) and a subset of transcription factors, which we call cell fate transcription factors, in the regulation of PcG association with target genes. We also speculate about how their deregulation contributes to tumorigenesis.

PAX3 is expressed in the stromal compartment of the developing kidney and in Wilms tumors with myogenic phenotype

Wilms tumor (WT) is the most frequent renal neoplasm of childhood; a myogenic component is observed in 5% to 10% of tumors. We demonstrate for the first time that myogenic WTs are associated with expression of PAX3, a transcription factor known to specify myoblast cell fate during muscle development. In a panel of 20 WTs, PAX3 was identified in 13 of 13 tumor samples with myogenic histopathology but was absent in 7 of 7 tumors lacking a myogenic component. Furthermore, we show that PAX3 is expressed in the metanephric mesenchyme and stromal compartment of developing mouse kidney. Modulation of endogenous PAX3 expression in human embryonic kidney (HEK293) cells influenced cell migration in in vitro assays. Mutations of WT1 were consistently associated with PAX3 expression in WTs, and modulation of WT1 expression in HEK293 cells was inversely correlated with the level of endogenous PAX3 protein. We demonstrate abundant PAX3 and absence of PAX2 expression in a novel cell line (WitP3) isolated from the stromal portion of a WT bearing a homozygous deletion of the WT1 gene. We hypothesize that PAX3 sets stromal cell fate in developing kidney but is normally suppressed by WT1 during the mesenchyme-to-epithelium transition leading to nephrogenesis. Loss of WT1 permits aberrant PAX3 expression in a subset of WTs with myogenic phenotype.

ALK expression in rhabdomyosarcomas: correlation with histologic subtype and fusion status

Immunohistochemical staining for anaplastic lymphoma kinase (ALK) has been described in rhabdomyosarcomas (RMS), especially the alveolar subtype. Previous studies have yielded conflicting results regarding the pattern of staining (nuclear versus cytoplasmic), and there has been no correlation with PAX3-7/FKHR fusion status. This study was undertaken to evaluate ALK receptor protein expression in a large series of RMS; to correlate these results with fusion status; and to investigate the possibility of 2p23 amplification or translocation using fluorescence in situ hybridization (FISH). Sixty-nine cases of RMS were examined and classified as alveolar RMS (ARMS), embryonal RMS (ERMS), or unclassifiable RMS (URMS) subtypes. Anaplastic lymphoma kinase immunohistochemistry was performed using anti-human CD246 antibody; cases were considered positive when more than 50% of cells had moderate or intense cytoplasmic and/or nuclear staining. There were 30 ARMS, 37 ERMS, and 2 URMS subtypes. Reverse transcription-polymerase chain reaction for PAX3/PAX7-FKHR fusion analysis had been done in all cases of ARMS, in 27 of 37 cases of ERMS, and in both URMS cases. Anaplastic lymphoma kinase staining was positive in 16 of 30 ARMS (53%) and 9 of 39 nonalveolar RMS (23%) cases (P < 0.05). Of the 21 ARMS cases with PAX3-FKHR fusion, 10 of 21 (48%) were positive for ALK staining; of the 6 ARMS cases with PAX7-FKHR fusion, 3 of 6 (50%) were positive for ALK staining; and 3 of 3 (100%) of the fusion-negative ARMS were positive with ALK staining. When comparing each of the ARMS subtypes, statistical significance was not reached. All positive cases showed dot-like cytoplasmic staining; nuclear staining was not seen. Of a subset of 6 ALK-positive ARMS submitted for break-apart FISH for the ALK locus, there was no evidence of a translocation; 1 case had ALK amplification and 2 had low-level gains of the ALK gene. We conclude that there is ALK overexpression in RMS, more commonly in ARMS than in ERMS, most likely independent of fusion status. Amplification or upregulation of ALK may underlie ALK protein overexpression.

Engraftment of mesenchymal stem cells into dystrophin-deficient mice is not accompanied by functional recovery

Mesenchymal stem cell preparations have been proposed for muscle regeneration in musculoskeletal disorders. Although MSCs have great in vitro expansion potential and possess the ability to differentiate into several mesenchymal lineages, myogenesis has proven to be much more difficult to induce. We have recently demonstrated that Pax3, the master regulator of the embryonic myogenic program, enables the in vitro differentiation of a murine mesenchymal stem cell line (MSCB9-Pax3) into myogenic progenitors. Here we show that injection of these cells into cardiotoxin-injured muscles of immunodeficient mice leads to the development of muscle tumors, resembling rhabdomyosarcomas. We then extended these studies to primary human mesenchymal stem cells (hMSCs) isolated from bone marrow. Upon genetic modification with a lentiviral vector encoding PAX3, hMSCs activated the myogenic program as demonstrated by expression of myogenic regulatory factors. Upon transplantation, the PAX3-modified MSCs did not generate rhabdomyosarcomas but rather, resulted in donor-derived myofibers. These were found at higher frequency in PAX3-transduced hMSCs than in mock-transduced MSCs. Nonetheless, neither engraftment of PAX3-modified or unmodified MSCs resulted in improved contractility. Thus these findings suggest that limitations remain to be overcome before MSC preparations result in effective treatment for muscular dystrophies.

PAX5 is expressed in small-cell lung cancer and positively regulates c-Met transcription

PAX5 is a nuclear transcription factor required for B cell development, and its expression was evaluated in upper aerodigestive malignancies and pancreatic cancer by immunoblotting. The PAX5 protein expression was relatively strong in small-cell lung cancer (SCLC, 11/12); however, its expression was not detected in non-SCLC (NSCLC, n=13), mesothelioma (n=7), pancreatic (n=6), esophageal (n=6) and head and neck cancer cell lines (n=12). In comparison, PAX8 and PAX3 expressions were absent or non-detectable in SCLC cell lines; however, PAX8 was expressed in most of the tested NSCLC cell lines (13/13) and also frequently in all the other cell lines. We also detected frequent expressions of PAX2 and PAX9 protein in the various cell lines. Utilizing neuroendocrine tumor samples, we found that the frequency as well as the average intensity of the expression of PAX5 increased from pulmonary carcinoid (9%, moderate and strong PAX5 expression, n=44), to large-cell neuroendocrine carcinoma (LCNC, 27%, n=11) to SCLC (33%, n=76). FISH analysis revealed no translocations of the PAX5 gene, but polyploidy in some SCLC tumor tissues (6/37). We determined that PAX5 could regulate the transcription of c-Met using luciferase-coupled reporter and chromatin immunoprecipitation analysis. In addition, the phospho-c-Met (active form) and PAX5 were both localized to the same intra-nuclear compartment in hepatocyte growth factor treated SCLC cells and interacted with each other. Finally, we determined the therapeutic translational potential of PAX5 using PAX5 knockdown SCLC cells in conjunction with Topoisomerase 1 (SN38) and c-Met (SU11274) inhibitors. Loss of endogenous PAX5 significantly decreased the viability of SCLC cells, especially when combined with SN38 or SU11274, and maximum effect was seen when both inhibitors were used. Therefore, we propose that PAX5 could be an important regulator of c-Met transcription and a potential target for therapy in SCLC.

Integrated functions of Pax3 and Pax7 in the regulation of proliferation, cell size and myogenic differentiation

Pax3 and Pax7 are paired-box transcription factors with roles in developmental and adult regenerative myogenesis. Pax3 and Pax7 are expressed by postnatal satellite cells or their progeny but are down regulated during myogenic differentiation. We now show that constitutive expression of Pax3 or Pax7 in either satellite cells or C2C12 myoblasts results in an increased proliferative rate and decreased cell size. Conversely, expression of dominant-negative constructs leads to slowing of cell division, a dramatic increase in cell size and altered morphology. Similarly to the effects of Pax7, retroviral expression of Pax3 increases levels of Myf5 mRNA and MyoD protein, but does not result in sustained inhibition of myogenic differentiation. However, expression of Pax3 or Pax7 dominant-negative constructs inhibits expression of Myf5, MyoD and myogenin, and prevents differentiation from proceeding. In fibroblasts, expression of Pax3 or Pax7, or dominant-negative inhibition of these factors, reproduce the effects on cell size, morphology and proliferation seen in myoblasts. Our results show that in muscle progenitor cells, Pax3 and Pax7 function to maintain expression of myogenic regulatory factors, and promote population expansion, but are also required for myogenic differentiation to proceed.

Pigmentation PAX-ways: the role of Pax3 in melanogenesis, melanocyte stem cell maintenance, and disease

Transcription factors initiate programs of gene expression and are catalysts in downstream molecular cascades that modulate a variety of cellular processes. Pax3 is a transcription factor that is important in the melanocyte and influences melanocytic proliferation, resistance to apoptosis, migration, lineage specificity and differentiation. In this review, we focus on Pax3 and the molecular pathways that Pax3 is a part of during melanogenesis and in the melanocyte stem cell. These roles of Pax3 are emphasized during the development of diseases and syndromes resulting from either too much or too little Pax3 function. Due to its key task in melanocyte stem cells and tumors, the Pax3 pathway may provide an ideal target for either stem cell or cancer therapies.

Embryonal rhabdomyosarcoma with a novel t(2;6)(p23;p21.1)

Chromosomal translocations are infrequently encountered in embryonal rhabdomyosarcoma (E-RMS). Here, we present a case of an infant with a chest wall E-RMS in which t(2;6)(p23;p21.1) was detected. Despite the involvement of the 2p23 locus in the translocation, the tumor did not express ALK. The t(2;6)(p23;p21.1) is a novel finding in E-RMS that may provide insight into the pathogenesis of this relatively frequent childhood tumor.

Genomic analysis reveals Mycoplasma pneumoniae repetitive element 1-mediated recombination in a clinical isolate

Mycoplasmas are cell wall-less bacteria that evolved by drastic reduction of the genome size. Complete genome analysis of Mycoplasma pneumoniae revealed the presence of numerous copies of four distinct large M. pneumoniae repetitive elements (RepMPs). One copy each of RepMP2/3, RepMP4, and RepMP5 are localized within the P1 operon (MPN140 to MPN142 loci), and their involvement in sequence variation in adhesin P1 and adherence-related protein B/C has been documented. Here we analyzed a clinical strain of M. pneumoniae designated S1 isolated from a 1993 outbreak of respiratory infections in San Antonio, TX. Based on the type of RepMPs within the P1 operon, we classified clinical isolate S1 as type 2 with unique minor sequence variations. Hybridization with oligonucleotide arrays revealed sequence divergence in two previously unsuspected hypothetical genes (MPN137 and MPN138 loci). Closer inspection of this region revealed that the MPN137 and MPN138 loci harbored previously unrecognized unique RepMP1 sequences found only in M. pneumoniae. PCR and sequence analyses revealed a recombination event involving three RepMP1-containing genes that resulted in fusion of MPN137 and MPN138 reading frames and loss of all but a short fragment of another RepMP1-containing locus, MPN130. The multiple copies of unique RepMP1 elements spread throughout the chromosome could allow vast numbers of sequence variations in clinical strains. Comparisons of amino acid sequences showed the presence of leucine zipper motifs in MPN130 and MPN138 proteins in reference strain M129 and the absence of these motifs in the fused protein of S1. The presence of tandem leucine and other repeats points to possible regulatory functions of proteins encoded by RepMP1-containing genes.

Towards a new era of tissue-based diagnosis and research

Molecular investigation of tissue obtained from patients with many chronic illnesses is becoming increasingly important. Using the example of childhood cancer, we show how such investigations contribute in important ways to understanding the underlying pathophysiological basis of disease, determining optimal patient management, and identifying targets for potential new novel therapeutic approaches. Tissue banks are now recognized as an important resource for biomedical research in this area. Challenges for the future of tissue-banking include formalization of technical matters, including the generation of standard operating procedures and quality-control methods. More complex challenges attend the legal and ethical issues in tissue banking. Notwithstanding recent UK legislation, there are many legal uncertainties. Use of excised tissue in research is often claimed to raise a range of ethical issues, but it is not at all clear that public confidence and support for tissue-based research is as negative as some accounts in the socio-anthropological and ethical literature would suggest. Nonetheless, ensuring confidence and trust in tissue-banking will remain an important objective, and the possibilities of novel governance structures should be explored.

HSP90 antagonist, geldanamycin, inhibits proliferation, induces apoptosis and blocks migration of rhabdomyosarcoma cells in vitro and seeding into bone marrow in vivo

In this study, geldanamycin (GA) was found to have an antiproliferative effect on both embryonal and alveolar rhabdomyosarcoma (RMS) cell lines. The maximum level of inhibition reached 80% for both embryonal and alveolar RMS. After GA treatment, cells also became apoptotic as judged by Annexin V-positive staining, activation of caspase-3 pathway and poly(ADP ribose) polymerase cleavage. GA was responsible for the arrest of RMS cells in both G1 and G2/M phases of the cell cycle. G1 blockade, however, was transient and was seen only in the first 24 h of GA treatment. RMS often gives distant metastases to various organs including bone marrow. RMS cells express high levels of MET receptor and respond to hepatocyte growth factor with increased motility. In our study, we found that GA decreased the level of MET expression and inhibited the chemotaxis of RMS cells toward the hepatocyte growth factor gradient. GA also blocked the homing of RMS cells into bone marrow of severe combined immune deficient mice. In all our experiments embryonal RMS cell lines were significantly more sensitive, and lower concentrations of GA were sufficient to block embryonal RMS cell proliferation, induce apoptosis and inhibit motility. Our data show that the HSP90 inhibitor GA has the potential to become a new drug in RMS treatment. It blocks RMS proliferation, decreases cell survival and inhibits motility of RMS cells.

Pax genes and neural tube defects in the mouse

The Pax genes encode a family of transcription factors that are expressed in restricted regions of the developing embryo. Several Pax genes are expressed in the developing nervous system where they are believed to regulate the morphogenesis of neural structures. Loss-of-function mutations in the Pax-3 gene have been identified in a number of alleles of the mouse mutant splotch. In homozygous splotch embryos closure of the neural tube is defective with embryos exhibiting spina bifida and/or exencephaly. Other structures in which Pax-3 is expressed are also affected, most notably those tissues derived from the neural crest and somites.

Characterization, anticancer drug susceptibility and atRA-induced growth inhibition of a novel cell line (HUMEMS) established from pleural effusion of alveolar rhabdomyosarcoma of breast tissue

We recently established a cell line derived from pleural effusion from a 13-year-old girl with primary alveolar rhabdomyosarcoma (RMS with a chromosomal translocation t[2;13]) in the breast tissue. The cell line was designated as HUMEMS. Cases of primary alveolar RMS swelling in the breast are extremely rare (about 0.2% of all RMSs). Therefore, the HUMEMS cell line is an important material for studying therapeutics for malignant tumors in children. The HUMEMS cell line we isolated consisted of two morphological subtypes. One type (SSN cells) is small in size and has a single nucleus. Another (LMN cells) is large in size and has two or more nuclei. Both SSN cells and LMN cells were immunohistochemically positive for desmin and slightly positive for myoglobin. Our data suggested LMN cells are well-differentiated SSN cells. Moreover, in some of the LMN cells, rapid cell contractions (1-5 times/10 sec) were observed. We investigated the anticancer drug susceptibility of the HUMEMS cell line with an oxygen electrode apparatus (Daikin, DOX-10, JPN) and effect of all-trans-retinoic acid (atRA) to the cell line. The atRA-treatment inhibited proliferation of the HUMEMS cells.

Correlation Between Histology and PAX/FKHR Fusion Status in Alveolar Rhabdomyosarcoma

At the molecular level, alveolar rhabdomyosarcomas (ARMS) are characterized by 3 mutually exclusive PAX/FKHR conditions: PAX3/FKHR fusion (present in 60% of cases), PAX7/FKHR fusion (present in 20%), and PAX/FKHR fusion-negativity (present in 20%). The possibility of morphologic variation among these molecular subtypes has not been investigated. We undertook a blinded retrospective study of 65 cases of ARMS (16 PAX/FKHR fusion-negative, 36 PAX3/FKHR-positive, and 13 PAX7/FKHR-positive by routine reverse transcription-polymerase chain reaction). We evaluated cytohistologic parameters such as microcyst formation, solid foci, differentiation, giant cell formation, anaplasia, nuclear grade, mitosis/karyorrhexis index, rosette formation, geographic necrosis, presence and amount of rhabdomyoblastic differentiation, and the presence of foci resembling embryonal rhabdomyosarcoma. We analyzed the results using a simple chi formula. Of these features, only totally solid alveolar architecture reached significance (P=0.00014), with 7 of 16 PAX/FKHR-negative cases lacking this feature, compared with 0 of 36 PAX3/FKHR cases and 2/13 PAX7/FKHR cases. These preliminary results indicate that in general, only totally solid alveolar architecture in ARMS may predict the absence of a PAX/FKHR fusion. No features seemed to predict the presence of a particular fusion type. Our results suggest that histologic assessment of ARMS has limited correlation with PAX/FKHR fusion status.

The oncogenic transcription factor PAX3-FKHR can convert fibroblasts into contractile myotubes

PAX3-FKHR, the product of a rearrangement of PAX3 with FKHR is the pathogenetic marker for alveolar rhabdomyosarcoma, an aggressive form of childhood cancer. In this work we show that PAX3-FKHR, which is a stronger transcriptional activator relative to PAX3, can lead to two apparently irreconcilable outcomes: transformation and terminal myogenic differentiation. Fibroblasts (10T1/2, NIH3T3, and a newly established murine line named 'Plus') transduced by PAX3-FKHR acquire transformed features such as anchorage independence and loss of contact inhibition and concomitantly undergo various degrees of myogenic conversion depending on the host cells, including, in the case of the Plus line, terminal differentiation into contractile myotubes. This work highlights the potential of PAX3-FKHR to functionally operate as a deregulated Pangene and may have implications with regard to the identity of the precursor cell giving rise to alveolar rhabdomyosarcoma.

Leukemia inhibitory factor: a newly identified metastatic factor in rhabdomyosarcomas

Rhabdomyosarcoma frequently infiltrates bone marrow and this process involves the stromal-derived factor-1 (SDF-1)-CXCR4 axis. Because leukemia inhibitory factor (LIF), like SDF-1, is secreted by bone marrow stroma and directs the regeneration of skeletal muscles, we examined whether the LIF-LIF receptor (LIF-R) axis affects the biology of rhabdomyosarcoma cells. We found that in rhabdomyosarcoma cells, LIF stimulates the following: (a) phosphorylation of mitogen-activated protein kinase p42/44, AKT, and signal transducers and activators of transcription 3, (b) adhesion and chemotaxis, and (c) increased resistance to cytostatics. To compare the biological effects of LIF versus SDF-1, we examined the RH30 cell line, which is highly responsive to both ligands, and found that the chemotaxis of these cells is significantly reduced when the inhibitors of both receptors (T140 for CXCR4 and gp190 blocking antibody for LIF-R) are added simultaneously. Subsequently, by using repetitive chemotaxis to LIF or SDF-1, we selected from the RH30 line subpopulations of cells that respond to LIF but not SDF-1 (RH30-L) or to SDF-1 but not LIF (RH30-S). We found that (a) RH30-L cells seed better to the bone marrow, liver, and lymph nodes of immunodeficient mice than RH30-S cells and (b) mice inoculated i.m. with the RH30-L cells had more rhabdomyosarcoma cells in the bone marrow and lung after 6 weeks. Thus, we present the first evidence that the LIF-LIF-R axis may direct rhabdomyosarcoma metastasis. Further, because we showed that the in vivo metastasis of RH30 cells is inhibited by small interfering RNA against LIF-R, molecular targeting of this axis could become a new strategy to control the metastasis of rhabdomyosarcoma.

Dystrophin-deficient mdx mice display a reduced life span and are susceptible to spontaneous rhabdomyosarcoma

Duchenne muscular dystrophy (DMD) is the most common, lethal genetic disorder of children. A number of animal models of muscular dystrophy exist, but the most effective model for characterizing the structural and functional properties of dystrophin and therapeutic interventions has been the mdx mouse. Despite the approximately 20 years of investigations of the mdx mouse, the impact of the disease on the life span of mdx mice and the cause of death remain unresolved. Consequently, a life span study of the mdx mouse was designed that included cohorts of male and female mdx and wild-type C57BL/10 mice housed under specific pathogen-free conditions with deaths restricted to natural causes and with examination of the carcasses for pathology. Compared with wild-type mice, both mdx male and female mice had reduced life spans and displayed a progressively dystrophic muscle histopathology. Surprisingly, old mdx mice were prone to develop muscle tumors that resembled the human form of alveolar rhabdomyosarcoma, a cancer associated with poor prognosis. Rhabdomyosarcomas have not been observed previously in nontransgenic mice. The results substantiate the mdx mouse as an important model system for studies of the pathogenesis of and potential remedies for DMD.