Long-term culture and characterization of human neurofibroma-derived Schwann cells

Existing and Developing Preclinical Models for Neurofibromatosis Type 1-Related Cutaneous Neurofibromas

Neurofibromatosis type 1 (NF1) is caused by a nonfunctional copy of the NF1 tumor suppressor gene that predisposes patients to the development of cutaneous neurofibromas (cNFs), the skin tumor that is the hallmark of this condition. Innumerable benign cNFs, each appearing by an independent somatic inactivation of the remaining functional NF1 allele, form in nearly all patients with NF1. One of the limitations in developing a treatment for cNFs is an incomplete understanding of the underlying pathophysiology and limitations in experimental modeling. Recent advances in preclinical in vitro and in vivo modeling have substantially enhanced our understanding of cNF biology and created unprecedented opportunities for therapeutic discovery. We discuss the current state of cNF preclinical in vitro and in vivo model systems, including two- and three-dimensional cell cultures, organoids, genetically engineered mice, patient-derived xenografts, and porcine models. We highlight the models' relationship to human cNFs and how they can be used to gain insight into cNF development and therapeutic discovery.

Modeling iPSC-derived human neurofibroma-like tumors in mice uncovers the heterogeneity of Schwann cells within plexiform neurofibromas

Plexiform neurofibromas (pNFs) are developmental tumors that appear in neurofibromatosis type 1 individuals, constituting a major source of morbidity and potentially transforming into a highly metastatic sarcoma (MPNST). pNFs arise after NF1 inactivation in a cell of the neural crest (NC)-Schwann cell (SC) lineage. Here, we develop an iPSC-based NC-SC in vitro differentiation system and construct a lineage expression roadmap for the analysis of different 2D and 3D NF models. The best model consists of generating heterotypic spheroids (neurofibromaspheres) composed of iPSC-derived differentiating NF1(-/-) SCs and NF1(+/-) pNF-derived fibroblasts (Fbs). Neurofibromaspheres form by maintaining highly proliferative NF1(-/-) cells committed to the NC-SC axis due to SC-SC and SC-Fb interactions, resulting in SC linage cells at different maturation points. Upon engraftment on the mouse sciatic nerve, neurofibromaspheres consistently generate human NF-like tumors. Analysis of expression roadmap genes in human pNF single-cell RNA-seq data uncovers the presence of SC subpopulations at distinct differentiation states.

Modeling tumors of the peripheral nervous system associated with Neurofibromatosis type 1: Reprogramming plexiform neurofibroma cells

Plexiform neurofibromas (pNFs) are benign tumors of the peripheral nervous system (PNS) that can progress towards a deadly soft tissue sarcoma termed malignant peripheral nerve sheath tumor (MPNST). pNFs appear during development in the context of the genetic disease Neurofibromatosis type 1 (NF1) due to the complete loss of the NF1 tumor suppressor gene in a cell of the neural crest (NC) - Schwann cell (SC) axis of differentiation. NF1(-/-) cells from pNFs can be reprogrammed into induced pluripotent stem cells (iPSCs) that exhibit an increased proliferation rate and maintain full iPSC properties. Efficient protocols for iPSC differentiation towards NC and SC exist and thus NC cells can be efficiently obtained from NF1(-/-) iPSCs and further differentiated towards SCs. In this review, we will focus on the iPSC modeling of pNFs, including the reprogramming of primary pNF-derived cells, the properties of pNF-derived iPSCs, the capacity to differentiate towards the NC-SC lineage, and how well iPSC-derived NF1(-/-) SC spheroids recapitulate pNF-derived primary SCs. The potential uses of NF1(-/-) iPSCs in pNF modeling and a future outlook are discussed.

NF1 patient missense variants predict a role for ATM in modifying neurofibroma initiation

In Neurofibromatosis type 1, NF1 gene mutations in Schwann cells (SC) drive benign plexiform neurofibroma (PNF), and no additional SC changes explain patient-to-patient variability in tumor number. Evidence from twin studies suggests that variable expressivity might be caused by unidentified modifier genes. Whole exome sequencing of SC and fibroblast DNA from the same resected PNFs confirmed biallelic SC NF1 mutations; non-NF1 somatic SC variants were variable and present at low read number. We identified frequent germline variants as possible neurofibroma modifier genes. Genes harboring variants were validated in two additional cohorts of NF1 patients and by variant burden test. Genes including CUBN, CELSR2, COL14A1, ATR and ATM also showed decreased gene expression in some neurofibromas. ATM-relevant DNA repair defects were also present in a subset of neurofibromas with ATM variants, and in some neurofibroma SC. Heterozygous ATM G2023R or homozygous S707P variants reduced ATM protein expression in heterologous cells. In mice, genetic Atm heterozygosity promoted Schwann cell precursor self-renewal and increased tumor formation in vivo, suggesting that ATM variants contribute to neurofibroma initiation. We identify germline variants, rare in the general population, overrepresented in NF1 patients with neurofibromas. ATM and other identified genes are candidate modifiers of PNF pathogenesis.

Knockdown of HMGA2 regulates the level of autophagy via interactions between MSI2 and Beclin1 to inhibit NF1-associated malignant peripheral nerve sheath tumour growth

Background

Malignant peripheral nerve sheath tumours (MPNSTs) are sarcomas of Schwann cell lineage origin that occur sporadically or in association with the inherited syndrome, neurofibromatosis type 1 (NF1). This study aimed to examine the function of High mobility group protein A2 (HMGA2) in NF1 MPNST progression and the underlying molecular mechanism.

Methods

Immunohistochemistry (IHC) was used to detect HMGA2 expression in MPNST and neurofibroma patient samples. Cell Cycle Kit-8 (CCK-8) and 5-ethynyl-20-deoxyuridine (EdU) assays, terminal deoxynucleotidyl transferase-mediated nick end labelling, and transmission electron microscopy were performed to reveal HMGA2 functions in NF1 MPNST cells in vitro and in vivo. Chromatin immunoprecipitation sequencing (ChIP-Seq) and RNA sequencing (RNA-Seq) were used to detect HMGA2-modulated genes regulating autophagy and growth in NF1 MPNSTs in vitro and in vivo.

Results

NF1 MPNST samples exhibit higher HMGA2 positivity rates (13/16) than sporadic MPNST (16/41) and neurofibroma (0/7) patient samples. High HMGA2 expression is correlated with poor prognosis. Neurofibromin 1 (NF1)-deficient MPNST cells display elevated HMGA2 expression. Functional experiments revealed that HMGA2 knockdown inhibits NF1 MPNST cell growth in vitro and in vivo. In addition to promoting cell cycle arrest and apoptosis, HMGA2 knockdown inhibits autophagy, favouring cell death. RNA-Seq and ChIP-Seq revealed that HMGA2 directly activates the Musashi-2 (MSI2) promoter region, and MSI2 overexpression reverses autophagy and growth in shHMGA2-transfected cells. MSI2 interacts with Beclin1, and Beclin1 blockade inhibits autophagy, thereby inhibiting cell proliferation.

Conclusions

HMGA2 knockdown regulates autophagy via MSI2-Beclin1 interactions to inhibit NF1 MPNST growth, revealing potential therapeutic targets for these untreatable tumours.

Electronic supplementary material

The online version of this article (10.1186/s13046-019-1183-2) contains supplementary material, which is available to authorized users.

The role of nerve microenvironment for neurofibroma development

Deregulation of RAS signaling in Neurofibromatosis type 1 (NF1) results in the development of multiple neurofibromas, complex tumor of the peripheral nerves with no effective medical treatment. There is increasing evidences that neurofibroma initiates through loss of NF1 function in the Schwann cell lineage, followed by a cascade of interactions with other cell types in the surrounding tumor microenvironment. In NF1 patients, neurofibromas always develop along peripheral nerves and do not migrate to distant organs, including the central nervous system. In this study, we sought to identify the contributions of these peripheral nerves in neurofibroma formation. Using in vivo and in vitro three-dimensional (3D) culturing system, we show that peripheral nerves are absolutely required for neurofibroma tumorigenesis and report a novel 3D skin raft culture system for neurofibroma formation in vitro to decipher tumor pathogenesis. This interaction between neoplastic Schwann cells and their surrounding neural microenvironment has important implications for understanding early cellular events that dictate tumorigenesis. It also provides fertile ground for the elucidation of intrinsic and extrinsic factors within the nerve microenvironment that likely play essential roles in neurofibroma development and, therefore, viable therapeutic targets in neurofibroma therapy.

CK2 blockade causes MPNST cell apoptosis and promotes degradation of β-catenin

Malignant peripheral nerve sheath tumors (MPNSTs) are soft tissue sarcomas that are a major cause of mortality of Neurofibromatosis type 1 (NF1) patients. MPNST patients have few therapeutic options available and only complete surgical resection can be curative. MPNST formation and survival are dependent on activated β-catenin signaling. The goal of this study was to determine if inhibition of the CK2 enzyme can be therapeutically exploited in MPNSTs, given CK2's role in mainta ining oncogenic phenotypes including stabilization of β-catenin. We found that CK2α is over-expressed in MPNSTs and is critical for maintaining cell survival, as the CK2 inhibitor, CX-4945 (Silmitasertib), and shRNA targeting CK2α each significantly reduce MPNST cell viability. These effects were preceded by loss of critical signaling pathways in MPNSTs, including destabilization of β-catenin and TCF8. CX-4945 administration in vivo slowed tumor growth and extends survival time. We conclude that CK2 inhibition is a promising approach to blocking β-catenin in MPNST cells, although combinatorial therapies may be required for maximal efficacy.

MEK inhibitors enhance therapeutic response towards ATRA in NF1 associated malignant peripheral nerve sheath tumors (MPNST) in-vitro

OBJECTIVE

Neurofibromatosis type 1 (NF1) is a hereditary tumor syndrome characterized by an increased risk of malignant peripheral nerve sheath tumors (MPNST). Chemotherapy of MPNST is still insufficient. In this study, we investigated whether human tumor Schwann cells derived from NF1 associated MPNST respond to all-trans retinoic acid (ATRA). We analyzed effects of ATRA and MEK inhibitor (MEKi) combination therapy.

METHODS

MPNST cell lines S462, T265, NSF1 were treated with ATRA and MEKi U0126 and PD0325901. We assessed cell viability, proliferation, migration, apoptosis and differentiation as well as mRNA expression of RAR and RXR subtypes and ATRA target genes such as CRABP2, CYP26A1, RARB and PDK1. We also analyzed CRABP2 methylation in cell lines and performed immunohistochemistry of human MPNST specimens.

RESULTS

ATRA therapy reduced viability and proliferation in S462 and T265 cells, accompanied by differentiation, apoptosis and reduced migration. NSF1 cells which lacked RXRG expression did not respond to ATRA. We furthermore demonstrated that ATRA signaling was functional for common targets, and that mRNA expression of CRABP2 and its targets was raised by ATRA therapy, whereas alternative pathways via FABP5 were not induced. Finally, combination of ATRA and MEKi demonstrated additively reduced viability of T265 and S462 cells.

CONCLUSIONS

We observed therapeutic effects in two of three MPNST cell lines pronounced by combination therapy. These data point to a potentially successful treatment of MPNST by combined application of ATRA and MEK inhibitors such as U0126 or PD0325901.

Immortalization of human normal and NF1 neurofibroma Schwann cells

Neurofibromas, which are benign Schwann cell tumors, are the hallmark feature in the autosomal dominant condition neurofibromatosis 1 (NF1) and are associated with biallelic loss of NF1 gene function. There is a need for effective therapies for neurofibromas, particularly the larger, plexiform neurofibromas. Tissue culture is an important tool for research. However, it is difficult to derive enriched human Schwann cell cultures, and most enter replicative senescence after 6-10 passages, impeding cell-based research in NF1. Through exogenous expression of human telomerase reverse transcriptase and murine cyclin-dependent kinase (mCdk4), normal (NF1 wild-type), neurofibroma-derived Schwann cells heterozygous for NF1 mutation, and neurofibroma-derived Schwann cells homozygous for NF1 mutation were immortalized, including some matched samples from the same NF1 patient. Initial experiments employed retroviral vectors, while subsequent work utilized lentiviral vectors carrying these genes because of improved efficiency. Expression of both transgenes was required for immortalization. Molecular and immunohistochemical analysis indicated that these cell lines are of Schwann cell lineage and have a range of phenotypes, many of which are consistent with their primary cultures. This is the first report of immortalization and detailed characterization of multiple human NF1 normal nerve and neurofibroma-derived Schwann cell lines, which will be highly useful research tools to study NF1 and other Schwann tumor biology and conditions.

Soluble AXL: a possible circulating biomarker for neurofibromatosis type 1 related tumor burden

Neurofibromatosis type 1 (NF1) is the most common tumor predisposition disorder affecting 1/3500 worldwide. Patients are at risk of developing benign (neurofibromas) and malignant peripheral nerve sheath tumors (MPNST). The AXL receptor tyrosine kinase has been implicated in several kinds of cancers, but so far no studies have investigated the role of AXL in NF1 related tumorigenesis. Recently, the soluble fraction from the extracellular domain of AXL (sAXL) has been found in human plasma, and its level was correlated to poor prognosis in patients with renal cancer. Compared to normal human Schwann cells, a significantly high expression level of AXL was found in three of the four MPNST cell lines and two of the three primary MPNST tissues. Similarly, the level of sAXL in conditioned media corresponded to the protein and mRNA levels of AXL in the MPNST cell lines. Furthermore, in two different human MPNST xenograft models, the human sAXL could be detected in the mouse plasma. Its level was proportionate to the size of the xenograft tumors, while no human sAXL was detect prior to the formation of the tumors. Treatment with a newly developed photodynamic therapy, prevented further tumor growth and resulted in drastically reduced the levels of sAXL compared to that of the control group. Finally, the level of sAXL was significantly increased in patients with plexiform tumors compared to patients with only dermal neurofibromas, further supporting the role of sAXL as a marker for NF1 related tumor burden.

Neurofibroma of sinus maxillae

Neurofibroma is a benign tumour composed from Schwann cells. Localization in sinus maxillea is very rare. Authors presenting case which was treatment in Maxillo-Facial Surgery Clinic in Wrocław.

The activation of the WNT signaling pathway is a Hallmark in neurofibromatosis type 1 tumorigenesis

PURPOSE

The hallmark of neurofibromatosis type 1 (NF1) is the onset of dermal or plexiform neurofibromas, mainly composed of Schwann cells. Plexiform neurofibromas can transform into malignant peripheral nerve sheath tumors (MPNST) that are resistant to therapies.

EXPERIMENTAL DESIGN

The aim of this study was to identify an additional pathway in the NF1 tumorigenesis. We focused our work on Wnt signaling that is highly implicated in cancer, mainly in regulating the proliferation of cancer stem cells. We quantified mRNAs of 89 Wnt pathway genes in 57 NF1-associated tumors including dermal and plexiform neurofibromas and MPNSTs. Expression of two major stem cell marker genes and five major epithelial-mesenchymal transition marker genes was also assessed. The expression of significantly deregulated Wnt genes was then studied in normal human Schwann cells, fibroblasts, endothelial cells, and mast cells and in seven MPNST cell lines.

RESULTS

The expression of nine Wnt genes was significantly deregulated in plexiform neurofibromas in comparison with dermal neurofibromas. Twenty Wnt genes showed altered expression in MPNST biopsies and cell lines. Immunohistochemical studies confirmed the Wnt pathway activation in NF1-associated MPNSTs. We then confirmed that the knockdown of NF1 in Schwann cells but not in epithelial cells provoked the activation of Wnt pathway by functional transfection assays. Furthermore, we showed that the protein expression of active β-catenin was increased in NF1-silenced cell lines. Wnt pathway activation was strongly associated to both cancer stem cell reservoir and Schwann-mesenchymal transition.

CONCLUSION

We highlighted the implication of Wnt pathway in NF1-associated tumorigenesis.

EGFR-STAT3 signaling promotes formation of malignant peripheral nerve sheath tumors

Malignant peripheral nerve sheath tumors (MPNSTs) develop sporadically or in the context of neurofibromatosis type 1. Epidermal growth factor receptor (EGFR) overexpression has been implicated in MPNST formation, but its precise role and relevant signaling pathways remain unknown. We found that EGFR overexpression promotes mouse neurofibroma transformation to aggressive MPNST (GEM-PNST). Immunohistochemistry demonstrated phosphorylated STAT3 (Tyr705) in both human MPNST and mouse GEM-PNST. A specific JAK2/STAT3 inhibitor FLLL32 delayed MPNST formation in an MPNST xenograft nude mouse model. STAT3 knockdown by shRNA prevented MPNST formation in vivo. Finally, reducing EGFR activity strongly reduced pSTAT3 in vivo. Thus, an EGFR-STAT3 pathway is necessary for MPNST transformation and establishment of MPNST xenografts growth but not for tumor maintenance. Efficacy of the FLLL32 pharmacological inhibitor in delaying MPNST growth suggests that combination therapies targeting JAK/STAT3 might be useful therapeutics.

Partial Blindness to Submicron Topography in NF1 Haploinsufficient Cultured Fibroblasts Indicates a New Function of Neurofibromin in Regulation of Mechanosensoric

Cells sense physical properties of their extracellular environment and translate them into biochemical signals. In this study, cell responses to surfaces with submicron topographies were investigated in cultured human NF1 haploinsufficient fibroblasts. Age-matched fibroblasts from 8 patients with neurofibromatosis type 1 (NF1(+/-)) and 9 controls (NF1(+/+)) were cultured on surfaces with grooves of 200 nm height and lateral distance of 2 μm. As cellular response indicator, the mean cell orientation along microstructured grooves was systematically examined. The tested NF1 haploinsufficient fibroblasts were significantly less affected by the topography than those from healthy donors. Incubation of the NF1(+/-) fibroblasts with the farnesyltransferase inhibitor FTI-277 and other inhibitors of the neurofibromin pathway ameliorates significantly the cell orientation. These data indicate that NF1 haploinsufficiency results in an altered response to specific surface topography in fibroblasts. We suggest a new function of neurofibromin in the sensoric mechanism to topographies and a partial mechanosensoric blindness by NF1 haploinsufficiency.

Exploring the somatic NF1 mutational spectrum associated with NF1 cutaneous neurofibromas

Neurofibromatosis type-1 (NF1), caused by heterozygous inactivation of the NF1 tumour suppressor gene, is associated with the development of benign and malignant peripheral nerve sheath tumours (MPNSTs). Although numerous germline NF1 mutations have been identified, relatively few somatic NF1 mutations have been described in neurofibromas. Here we have screened 109 cutaneous neurofibromas, excised from 46 unrelated NF1 patients, for somatic NF1 mutations. NF1 mutation screening (involving loss-of-heterozygosity (LOH) analysis, multiplex ligation-dependent probe amplification and DNA sequencing) identified 77 somatic NF1 point mutations, of which 53 were novel. LOH spanning the NF1 gene region was evident in 25 neurofibromas, but in contrast to previous data from MPNSTs, it was absent at the TP53, CDKN2A and RB1 gene loci. Analysis of DNA/RNA from neurofibroma-derived Schwann cell cultures revealed NF1 mutations in four tumours whose presence had been overlooked in the tumour DNA. Bioinformatics analysis suggested that four of seven novel somatic NF1 missense mutations (p.A330T, p.Q519P, p.A776T, p.S1463F) could be of functional/clinical significance. Functional analysis confirmed this prediction for p.S1463F, located within the GTPase-activating protein-related domain, as this mutation resulted in a 150-fold increase in activated GTP-bound Ras. Comparison of the relative frequencies of the different types of somatic NF1 mutation observed with those of their previously reported germline counterparts revealed significant (P=0.001) differences. Although non-identical somatic mutations involving either the same or adjacent nucleotides were identified in three pairs of tumours from the same patients (P<0.0002), no association was noted between the type of germline and somatic NF1 lesion within the same individual.

The development of cutaneous neurofibromas

Cutaneous neurofibromas are the hallmarks of neurofibromatosis type 1 (NF1). They are composed of multiple cell types, and traditionally they are believed to arise from small nerve tributaries of the skin. A key finding in the context of this view has been that subpopulations of tumor Schwann cells harbor biallelic inactivation of the NF1 gene (NF1(-/-)). In the present study, our aim was to clarify further the pathogenesis of cutaneous neurofibromas. First, we detected cells expressing multipotency-associated biomarkers in cutaneous neurofibromas. Second, we developed a method for isolating and expanding multipotent neurofibroma-derived precursor cells (NFPs) from dissociated human cutaneous neurofibromas and used it to analyze their growth and differentiation potential. In analogy to solitary cells resident in neurofibromas, NFPs were found to express nestin and had the potential to differentiate to, at least, Schwann cells, neurons, epithelial cells, and adipocytes. Mutation analysis of the NFPs revealed that their genotype was NF1(+/-). The results led us to speculate that the development of cutaneous neurofibromas includes the recruitment of multipotent NF1(+/-) precursor cells. These cells may be derived from the multipotent cells of the hair roots, which often are intimately associated with microscopic neurofibromas.

Differential expression of CCN1/CYR61, CCN3/NOV, CCN4/WISP1, and CCN5/WISP2 in neurofibromatosis type 1 tumorigenesis

The hallmark of neurofibromatosis type 1 is the development of dermal and plexiform neurofibromas. Neurofibromatosis type 1 patients with plexiform neurofibromas are at risk of developing malignant peripheral nerve sheath tumors. We applied a 22,000-oligonucleotide microarray transcriptomic approach to a series of plexiform neurofibromas in comparison with dermal neurofibromas, and results were confirmed with real-time quantitative reverse transcription-polymerase chain reaction. Thirteen genes were upregulated and 10 were downregulated in plexiform neurofibromas. The upregulated genes mainly encode molecules involved in cell adhesion, extracellular matrix, fibrogenesis, and angiogenesis. Several CCN gene family members were dysregulated in neurofibromatosis type 1 tumorigenesis; the angiogenic gene CCN1/CYR61 was specifically upregulated in the plexiform neurofibromas; CCN4/WISP1 was upregulated, and CCN3/NOV and CCN5/WISP2 were downregulated in paired comparisons of plexiform neurofibroma and malignant peripheral nerve sheath tumor from the same patients. CCN1 and CCN3 proteins were detected by immunohistochemistry in neurofibromatosis type 1-associated tumors. Upregulation of S100A8, S100A9, and CD36 was also observed and suggests a role of this pathway in inflammation-associated genesis of plexiform neurofibromas. In summary, a limited number of pathways are potentially involved in plexiform neurofibroma development. Some of the genes identified, particularly CCN1, might be useful diagnostic or prognostic markers or form the basis for novel therapeutic strategies.

Pathogenesis of vestibular schwannoma in ring chromosome 22

Background

Ring chromosome 22 is a rare human constitutional cytogenetic abnormality. Clinical features of neurofibromatosis type 1 and 2 as well as different tumour types have been reported in patients with ring chromosome 22. The pathogenesis of these tumours is not always clear yet.

Methods

We report on a female patient with a ring chromosome 22 presenting with severe mental retardation, autistic behaviour, café-au-lait macules and facial dysmorphism. Peripheral blood lymphocytes were karyotyped and array CGH was performed on extracted DNA. At the age of 20 years she was diagnosed with a unilateral vestibular schwannoma. Tumour cells were analyzed by karyotyping, array CGH and NF2 mutation analysis.

Results

Karyotype on peripheral blood lymphocytes revealed a ring chromosome 22 in all analyzed cells. A 1 Mb array CGH experiment on peripheral blood DNA showed a deletion of 5 terminal clones on the long arm of chromosome 22. Genetic analysis of vestibular schwannoma tissue revealed loss of the ring chromosome 22 and a somatic second hit in the NF2 gene on the remaining chromosome 22.

Conclusion

We conclude that tumours can arise by the combination of loss of the ring chromosome and a pathogenic NF2 mutation on the remaining chromosome 22 in patients with ring chromosome 22. Our findings indicate that patients with a ring 22 should be monitored for NF2-related tumours starting in adolescence.

Class III beta-tubulin is a component of the mitotic spindle in multiple cell types

The findings of this study show that Class III beta-tubulin is a component of the mitotic spindle in multiple cell types. Class III beta-tubulin has been widely used as a neuron-specific marker, but it has been detected also in association with breast and pancreatic cancers. In this study, we describe a novel finding of Class III beta-tubulin in a subpopulation of cells in malignant peripheral nerve sheath tumor. The findings of this study also show that Class III beta-tubulin is expressed by normal mesenchymal and epithelial cells (fibroblasts and keratinocytes), two transitional cell carcinoma cell lines, and neurofibroma Schwann cells, as shown by immunolabeling and Western transfer analysis using two different Tuj-1 antibodies that are specific for Class III beta-tubulin. The corresponding mRNA was detected using RT-PCR and whole human genome microarrays. Both antibodies localized Class III beta-tubulin to the mitotic spindle and showed a colocalization with alpha-tubulin. The immunoreaction became visible in early prophase, and the most intense immunoreaction was detected during metaphase and anaphase when microtubules were connected to the kinetochores on chromosomes. Class III beta-tubulin-specific immunoreaction lasted to the point when the midbody of cytokinesis became detectable.

Schwann cells from human neurofibromas show increased proliferation rates under the influence of progesterone

Neurofibromatosis type 1 (NF1) is a hereditary disease caused by mutations of the NF1 gene at 17q11.2. Loss of the NF1 gene product in Schwann cells leads to the development of benign nerve sheath tumors. These neurofibromas may occur at any time but tend to arise during periods of hormonal imbalance, suggesting that hormones influence neurofibroma growth. As steroid hormone levels rise during these times, we hypothesized that progesterone has proliferative effects on neurofibroma-derived Schwann cells. We chose specific medium conditions for selective proliferation of NF (+/-) and NF (-/-) cells from human neurofibromas. Genetic characterization was not performed, but former works have shown that under the conditions used (+/-) and (-/-) cells can be selected. Different progesterone concentrations were added at different days with BrdU-staining was performed to investigate proliferation rates and DAB-staining to identify a progesterone receptor. We could demonstrate that Schwann cells from human neurofibromas express progesterone receptors. These cells show elevated proliferation rates (highest in NF(-/-) cells) under progesterone, whereas normal human Schwann cells were not affected. These data suggest that progesterone plays an important role in the development of neurofibromas in NF1.

Molecular dissection of isolated disease features in mosaic neurofibromatosis type 1

Elucidation of the biological framework underlying the development of neurofibromatosis type 1 (NF1)-related symptoms has proved to be difficult. Complicating factors include the large size of the NF1 gene, the presence of several NF1 pseudogenes, the complex interactions between cell types, and the NF1-haploinsufficient state of all cells in the body. Here, we investigate three patients with distinct NF1-associated clinical manifestations (neurofibromas only, pigmentary changes only, and association of both symptoms). For each patient, various tissues and cell types were tested with comprehensive and quantitative assays capable of detecting low-percentage NF1 mutations. This approach confirmed the biallelic NF1 inactivation in Schwann cells in neurofibromas and, for the first time, demonstrated biallelic NF1 inactivation in melanocytes in NF1-related cafe-au-lait macules. Interestingly, both disease features arise even within a background of predominantly NF1 wild-type cells. Together, the data provide molecular evidence that (1) the distinct clinical picture of the patients is due to mosaicism for the NF1 mutation and (2) the mosaic phenotype reflects the embryonic timing and, accordingly, the neural crest-derived cell type involved in the somatic NF1 mutation. The study of the affected cell types provides important insight into developmental concepts underlying particular NF1-related disease features and opens avenues for improved diagnosis and genetic counseling of individuals with mosaic NF1.

Recent developments in neurofibromatosis type 1

PURPOSE OF REVIEW

This review summarizes the recent clinical and genetic developments in neurofibromatosis type 1 (NF1) and provides an insight into the possible underlying pathomechanisms.

RECENT FINDINGS

NF1, or von Recklinghausen disease, is one of the most common hereditary neurocutaneous disorders in humans. Clinically, NF1 is characterized by café-au-lait spots, freckling, skin neurofibroma, plexiform neurofibroma, bony defects, Lisch nodules and tumors of the central nervous system. The responsible gene, NF1, encodes a 2818 amino acid protein (neurofibromin). Pathological mutations range from single nucleotide substitutions to large-scale genomic deletions dispersed throughout the gene. In addition to the conventional mutation screening methods, a DNA chip microarray-based technology, combinational sequence-based hybridization, has been introduced to expedite mutation detection. Functional analysis has become more amenable following the development of the following: (1) primary Schwann cell cultures from NF1 patients; (2) mouse models; (3) proteomic technologies; and (4) mRNA silencing by RNA interference. These studies have shown that neurofibromin plays a role in adenylate cyclase and AKT-mTOR mediated pathways. It also appears to affect Ras-GTPase activating protein activity through the phosphorylation of protein kinase C which impacts on cell motility by binding with actin in the cytoskeleton.

SUMMARY

Recent advances in the clinical features and molecular genetics of NF1 will be discussed together with insights into the underlying pathomechanisms of NF1.

Microarray-Based Identification of Tenascin C and Tenascin XB, Genes Possibly Involved in Tumorigenesis Associated with Neurofibromatosis Type 1

PURPOSE

Neurofibromatosis type 1 (NF1) is an autosomal dominant disorder with a complex variety of clinical manifestations. The hallmark of NF1 is the onset of heterogeneous (dermal or plexiform) benign neurofibromas. Plexiform neurofibromas can give rise to malignant peripheral nerve sheath tumors, which are resistant to conventional therapies.

EXPERIMENTAL DESIGN

To identify new signaling pathways involved in the malignant transformation of plexiform neurofibromas, we applied a 22,000-oligonucleotide microarray approach to a series of plexiform neurofibromas and malignant peripheral nerve sheath tumors. Changes in the expression of selected genes were then confirmed by real-time quantitative reverse transcription-PCR.

RESULTS

We identified two tenascin gene family members that were significantly deregulated in both human NF1-associated tumors and NF1-deficient primary cells: Tenascin C (TNC) was up-regulated whereas tenascin XB (TNXB) was down-regulated during tumor progression. TNC activation is mainly due to the up-regulation of large TNC splice variants. Immunohistochemical studies showed that TNC transcripts are translated into TNC protein in TNC-overexpressing tumors. Aberrant transcriptional activation of TNC seems to be principally mediated by activator protein transcription factor complexes.

CONCLUSION

TNXB and TNC may be involved in the malignant transformation of plexiform neurofibromas. Anti-TNC antibodies, already used successfully in clinical trials to treat malignant human gliomas, may be an appropriate new therapeutic strategy for NF1.

Comprehensive NF1 screening on cultured Schwann cells from neurofibromas

Neurofibromatosis type 1 (NF1) is mainly characterized by the occurrence of benign peripheral nerve sheath tumors or neurofibromas. Thorough investigation of the somatic mutation spectrum has thus far been hampered by the large size of the NF1 gene and the considerable proportion of NF1 heterozygous cells within the tumors. We developed an improved somatic mutation detection strategy on cultured Schwann cells derived from neurofibromas and investigated 38 tumors from nine NF1 patients. Twenty-nine somatic NF1 lesions were detected which represents the highest NF1 somatic mutation detection rate described so far (76%). Furthermore, our data strongly suggest that the acquired second hit underlies reduced NF1 expression in Schwann cell cultures. Together, these data clearly illustrate that two inactivating NF1 mutations, in a subpopulation of the Schwann cells, are required for neurofibroma formation in NF1 tumorigenesis. The observed somatic mutation spectrum shows that intragenic NF1 mutations (26/29) are most prevalent, particularly frameshift mutations (12/29, 41%). We hypothesize that this mutation signature might reflect slightly reduced DNA repair efficiency as a trigger for NF1 somatic inactivation preceding tumorigenesis. Joint analysis of the current and previously published NF1 mutation data revealed a significant difference in the somatic mutation spectrum in patients with a NF1 microdeletion vs. non-microdeletion patients with respect to the prevalence of loss of heterozygosity events (0/15 vs. 41/81). Differences in somatic inactivation mechanism might therefore exist between NF1 microdeletion patients and the general NF1 population.

Malignant peripheral nerve sheath tumors with high and low Ras-GTP are permissive for oncolytic herpes simplex virus mutants

BACKGROUND

Malignant peripheral nerve sheath tumors (MPNSTs) occur most frequently in patients with neurofibromatosis type 1 and are often fatal. Current therapy relies upon radical surgical resection, which often fails to completely remove the tumor. To address the need for novel treatment approaches for this disease, we sought to determine if human MPNST-derived cell lines are sensitive to oncolytic Herpes simplex virus (oHSV) infection. Activation of the Ras pathway and its inhibitory effects on protein kinase R (PKR) activation have been shown to dictate cellular permissivity to oHSV mutants. Because NF-1-associated MPNSTs possess inherent hyperactive Ras, we hypothesized these tumors would be ideal therapeutic targets for oHSVs.

PROCEDURE

Human MPNST-derived cell lines were examined for sensitivity to oHSV-mediated gene transduction, virus replication, cytotoxicity, and apoptosis. These parameters were correlated with PKR activation following oHSV infection and compared with normal human Schwann cells (NHSCs) without hyperactive Ras.

RESULTS

MPNST-derived cell lines were efficiently transduced, supported virus replication and were killed by the oncolytic HSV mutants, including sporadic MPNSTs without hyperactive Ras. In contrast to the highly sensitive MPNST cell lines, NHSCs did not support mutant virus replication.

CONCLUSIONS

MPNSTs are susceptible to lysis by oncolytic HSV mutants, regardless of Ras status. Tumor-selective virus replication in MPNST cells appears to be mediated by both cellular expression of ribonucleotide reductase and prevention of eIF2alpha phosphorylation. Virus-induced cytotoxicity of MPNST cell lines was caused by both direct lysis and apoptosis. Our data suggest the use of oncolytic HSV mutants may represent a novel treatment approach for patients with MPNSTs.

Large-scale molecular comparison of human schwann cells to malignant peripheral nerve sheath tumor cell lines and tissues

Malignant peripheral nerve sheath tumors (MPNST) are highly invasive soft tissue sarcomas that arise within the peripheral nerve and frequently metastasize. To identify molecular events contributing to malignant transformation in peripheral nerve, we compared eight cell lines derived from MPNSTs and seven normal human Schwann cell samples. We found that MPNST lines are heterogeneous in their in vitro growth rates and exhibit diverse alterations in expression of pRb, p53, p14(Arf), and p16(INK4a) proteins. All MPNST cell lines express the epidermal growth factor receptor and lack S100beta protein. Global gene expression profiling using Affymetrix oligonucleotide microarrays identified a 159-gene molecular signature distinguishing MPNST cell lines from normal Schwann cells, which was validated in Affymetrix microarray data generated from 45 primary MPNSTs. Expression of Schwann cell differentiation markers (SOX10, CNP, PMP22, and NGFR) was down-regulated in MPNSTs whereas neural crest stem cell markers, SOX9 and TWIST1, were overexpressed in MPNSTs. Previous studies have implicated TWIST1 in apoptosis inhibition, resistance to chemotherapy, and metastasis. Reducing TWIST1 expression in MPNST cells using small interfering RNA did not affect apoptosis or chemoresistance but inhibited cell chemotaxis. Our results highlight the use of gene expression profiling in identifying genes and molecular pathways that are potential biomarkers and/or therapeutic targets for treatment of MPNST and support the use of the MPNST cell lines as a primary analytic tool.

Somatic loss of wild typeNF1 allele in neurofibromas: Comparison ofNF1 microdeletion and non-microdeletion patients

Neurofibromatosis type I (NF1) is an autosomal dominant familial tumor syndrome characterized by the presence of multiple benign neurofibromas. In 95% of NF1 individuals, a mutation is found in the NF1 gene, and in 5% of the patients, the germline mutation consists of a microdeletion that includes the NF1 gene and several flanking genes. We studied the frequency of loss of heterozygosity (LOH) in the NF1 region as a mechanism of somatic NF1 inactivation in neurofibromas from NF1 patients with and without a microdeletion. There was a statistically significant difference between these two patient groups in the proportion of neurofibromas with LOH. None of the 40 neurofibromas from six different NF1 microdeletion patients showed LOH, whereas LOH was observed in 6/28 neurofibromas from five patients with an intragenic NF1 mutation (P = 0.0034, Fisher's exact). LOH of the NF1 microdeletion region in NF1 microdeletion patients would de facto lead to a nullizygous state of the genes located in the deletion region and might be lethal. The mechanisms leading to LOH were further analyzed in six neurofibromas. In two out of six neurofibromas, a chromosomal microdeletion was found; in three, a mitotic recombination was responsible for the observed LOH; and in one, a chromosome loss with reduplication was present. These data show an important difference in the mechanisms of second hit formation in the 2 NF1 patient groups. We conclude that NF1 is a familial tumor syndrome in which the type of germline mutation influences the type of second hit in the tumors.

The NF1 tumor suppressor critically regulates TSC2 and mTOR

Loss-of-function mutations in the NF1 tumor suppressor gene underlie the familial cancer syndrome neurofibromatosis type I (NF1). The NF1-encoded protein, neurofibromin, functions as a Ras-GTPase activating protein (RasGAP). Accordingly, deregulation of Ras is thought to contribute to NF1 development. However, the critical effector pathways involved in disease pathogenesis are still unknown. We show here that the mTOR pathway is tightly regulated by neurofibromin. mTOR is constitutively activated in both NF1-deficient primary cells and human tumors in the absence of growth factors. This aberrant activation depends on Ras and PI3 kinase, and is mediated by the phosphorylation and inactivation of the TSC2-encoded protein tuberin by AKT. Importantly, tumor cell lines derived from NF1 patients, and a genetically engineered cell system that requires Nf1-deficiency for transformation, are highly sensitive to the mTOR inhibitor rapamycin. Furthermore, while we show that the activation of endogenous Ras leads to constitutive mTOR signaling in this disease state, we also demonstrate that in normal cells Ras is differentially required for mTOR signaling in response to various growth factors. Thus, these findings identify the NF1 tumor suppressor as an indispensable regulator of TSC2 and mTOR. Furthermore, our results also demonstrate that Ras plays a critical role in the activation of mTOR in both normal and tumorigenic settings. Finally, these data suggest that rapamycin, or its derivatives, may represent a viable therapy for NF1.

La neurofibromatose 1 (NF1) ou maladie de Von Recklinghausen

OBJECTIVES

Neurofibromatosis 1(NF1) is one of the most common genetic diseases. NF1 is an autosomal dominant genetic disorder and half of affected individuals have NF1 as the result of a new gene NF1 mutation. The offspring of an affected individual have a 50% risk of inheriting the altered NF1 gene. The disease manifestations are extremely variable, even within a family. NF1 is characterized by multiple cafe au lait spots, axillary and inguinal freckling, multiple discrete dermal neurofibromas, and iris Lisch nodules. Learning disabilities are frequent. Less common but potentially more serious manifestations include plexiform neurofibromas, optic and other central nervous system gliomas, malignant peripheral nerve sheath tumors, vasculopathy, and osseous lesions.

CURRENT KNOWLEDGES AND KEY POINTS

Since the original National Institutes of Health consensus Development Conference in 1987, there have been significant progress toward a more complete understanding of the molecular-bases for neurofibromatosis 1 and the routine follow-up for the care of the NF1 patients. The authors review the present data on the clinical and molecular aspects of the neurofibromatosis 1.

FUTURE PROSPECTS AND PROJECTS

NF1 requires life-long management adapted to age and multidisciplinary structures are particularly well adapted to the diversity of the manifestations of this pathology. The French NF-France Network has been created in 2001 to federate the French multidisciplinary structures for neurofibromatosis and harmonize the follow-up of NF1 patients in France.

Genetics of Neurofibromatosis 1-Associated Peripheral Nerve Sheath Tumors

Neurofibromatosis 1, an inherited disorder that affects 1/3500 individuals worldwide, predisposes to the development of benign and malignant peripheral nerve sheath tumors. The disorder results from inactivation of one of the NFI genes. The second NFI gene is typically inactivated in Schwann cells during tumor formation. This article reviews the different types of genetic alterations in NFI in both constitutional and tumor tissues and genetic alterations of other genes that may affect tumorigenesis. These studies have provided insight into the genetic basis of both the variable expression of the disorder and of benign and malignant peripheral nerve sheath tumorigenesis.