Malignant transformation of neurofibromas in neurofibromatosis 1 is associated with CDKN2A/p16 inactivation

Gene expression profiling reveals unique molecular subtypes of Neurofibromatosis Type I-associated and sporadic malignant peripheral nerve sheath tumors

Malignant peripheral nerve sheath tumors (MPNSTs) are highly aggressive Schwann cell neoplasms that are frequently associated with Type I Neurofibromatosis (NF1) and respond poorly to current therapeutic regimens. To better understand the molecular heterogeneity of these tumors, we performed gene expression profiling on 25 NF1-associated and 17 sporadic MPNSTs using oligonucleotide microarrays representing approximately 8100 unique human gene transcripts. Using several previously reported statistical approaches, we were unable to identify a molecular signature that could reliably distinguish between NF1-associated and sporadic MPNSTs in independent training and test sample sets. However, using an unsupervised clustering approach, we identified an extensive gene expression signature that distinguished 9 of the 42 tumors analyzed. This signature corresponded to relative overexpression of transcripts associated with neuroglial differentiation (NCAM, MBP, L1CAM, P1P) and relative down-regulation of proliferation and growth factor associated transcripts (IGF2, FGFR1, MDK, Ki67). All tumors with this gene expression signature lacked expression of EGFR and all but one tumor were derived from patients with NF1. However, there were no other obvious associations with histological grade, tumor site, metastasis, recurrence, age, or patient survival. We conclude that distinct molecular classes of MPNST exist and that the ability to stratify these tumors based on unique and biologically relevant gene expression profiles may be important for future targeted therapeutics.

Molecular profiling of malignant peripheral nerve sheath tumors associated with neurofibromatosis type 1, based on large-scale real-time RT-PCR

Background

Neurofibromatosis type 1 (NF1) is an autosomal dominant disorder with a complex range of clinical symptoms. 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 (MPNSTs), and the underlying molecular mechanisms are largely unknown.

Results

To obtain further insight into the molecular pathogenesis of MPNSTs, we used real-time quantitative RT-PCR to quantify the mRNA expression of 489 selected genes in MPNSTs, in comparison with plexiform neurofibromas.

The expression of 28 (5.7%) of the 489 genes was significantly different between MPNSTs and plexiform neurofibromas; 16 genes were upregulated and 12 were downregulated in MPNSTs.

The altered genes were mainly involved in cell proliferation (MKI67, TOP2A, CCNE2), senescence (TERT, TERC), apoptosis (BIRC5/Survivin, TP73) and extracellular matrix remodeling (MMP13, MMP9, TIMP4, ITGB4). More interestingly, other genes were involved in the Ras signaling pathway (RASSF2, HMMR/RHAMM) and the Hedgehog-Gli signaling pathway (DHH, PTCH2). Several of the down-regulated genes were Schwann cell-specific (L1CAM, MPZ, S100B, SOX10, ERBB3) or mast cell-specific (CMA1, TPSB), pointing to a depletion and/or dedifferentiation of Schwann cells and mast cells during malignant transformation of plexiform neurofibromas.

Conclusion

These data suggest that a limited number of signaling pathways, and particularly the Hedgehog-Gli signaling pathway, may be involved in malignant transformation of plexiform neurofibromas. Some of the relevant genes or their products warrant further investigation as potential therapeutic targets in NF1.

Genetic and phenotypic characterization of tumor cells derived from malignant peripheral nerve sheath tumors of neurofibromatosis type 1 patients

Neurofibromatosis type 1 (NF1) patients have an 8-13% lifetime risk of developing malignant peripheral nerve sheath tumors (MPNST) which have a very poor prognosis. In this study, cells from eight MPNSTs (six primary and two recurrences) of six clinically and genetically well-characterized NF1 patients were taken into culture. Tracing of loss of heterozygosity (LOH) of the NF1, p53, and p16 gene regions or of abnormal karyotypes enabled identification of tumor cells from five MPNSTs. In two other MPNST-derived cell cultures, LOH of the relevant regions in the original tumors could not be detected, indicating that the obtained cells were nonneoplastic cells. Cells from most MPNSTs grew only under standard culture conditions but not under conditions optimized for Schwann cells. These cells were S100-negative and did not exhibit spindle shape which is a characteristic of Schwann cells. Drastically increased proliferation rates were found for most of the MPNST cells in comparison to Schwann cells derived from benign neurofibromas. Our study demonstrates that genetic analysis is effective and essential for verification of MPNST tumor cells in culture. These verified MPNST cells are valuable for further investigations of the biology and pathogenesis of this malignancy as well as for in vitro pharmacologic studies essential for the development of new therapies.

CD44-independent hepatocyte growth factor/c-Met autocrine loop promotes malignant peripheral nerve sheath tumor cell invasion in vitro

Malignant peripheral nerve sheath tumors (MPNSTs) are invasive peripheral nerve neoplasms that express both the receptor tyrosine kinase c-Met and its ligand hepatocyte growth factor (HGF). The combined expression of these proteins has been implicated in tumor cell growth and metastasis. However, HGF/c-Met autocrine activity requires the presence of a serine protease, the HGF activator (HGFA), and, in some cells, the CD44 transmembrane glycoprotein. Here, we found that HGFA, HGF, c-Met, and CD44 are coexpressed in MPNSTs but their localization did not correlate with increased cell proliferation. The ST8814 MPNST cell line also expresses all of these proteins, can convert pro-HGF to active HGF, and exhibits constitutive c-Met phosphorylation. Blocking c-Met activity or expression inhibits the invasive behavior of these cells but not their proliferation. Interestingly, although a CD44 splice variant contributes to MPNST cell invasion and interacts with c-Met and HGF in ST8814 cells, it is not required for c-Met activation. These data indicate that an HGF/c-Met autocrine loop can promote MPNST invasion through a CD44-independent mechanism and suggest that c-Met, HGFA, and HGF are potential molecular targets to inhibit MPNST metastasis.

Topoisomerase-II alpha is upregulated in malignant peripheral nerve sheath tumors and associated with clinical outcome

PURPOSE

To identify target genes of clinical significance for patients with malignant peripheral-nerve sheath tumor (MPNST), an aggressive cancer for which no consensus therapy exists.

MATERIALS AND METHODS

Biopsies and clinical data from 51 patients with MPNST were included in this study. Based on our previous research implicating chromosome arm 17q amplification in MPNST, we performed gene expression analyses of 14 MPNSTs using chromosome 17-specific cDNA microarrays. Copy numbers of selected gene probes and centromere probes were then determined by interphase fluorescence in situ hybridization in 16 MPNSTs. Finally, we generated a tissue microarray containing 79 samples from 44 MPNSTs, on which in situ protein expressions of candidate genes were examined and related to clinical end points.

RESULTS

Among several deregulated genes found by cDNA microarray analyses, topoisomerase II alpha (TOP2A) was the most overexpressed gene in MPNSTs compared with benign neurofibromas. Excess copies of the TOP2A were also seen at the DNA level in 10 of 16 cases, and high expression of the TOP2A protein was seen in 83% of the tumors on the tissue microarray. The TOP2A-expressing tumors were associated with poor cancer-specific survival and presence of metastases.

CONCLUSION

We have identified TOP2A as a target gene in MPNST, using a focused gene expression profiling followed by a DNA copy number evaluation and clinical validation of the encoded protein using a tissue microarray. This study is the first to suggest that TOP2A expression may be a predictive factor for adverse outcome in MPNST.

Characterization of the somatic mutational spectrum of the neurofibromatosis type 1 (NF1) gene in neurofibromatosis patients with benign and malignant tumors

One of the main features of neurofibromatosis type 1 (NF1) is benign neurofibromas, 10-20% of which become transformed into malignant peripheral nerve sheath tumors (MPNSTs). The molecular basis of NF1 tumorigenesis is, however, still unclear. Ninety-one tumors from 31 NF1 patients were screened for gross changes in the NF1 gene using microsatellite/restriction fragment length polymorphism (RFLP) markers; loss of heterozygosity (LOH) was found in 17 out of 91 (19%) tumors (including two out of seven MPNSTs). Denaturing high performance liquid chromatography (DHPLC) was then used to screen 43 LOH-negative and 10 LOH-positive tumors for NF1 microlesions at both RNA and DNA levels. Thirteen germline and 12 somatic mutations were identified, of which three germline (IVS7-2A>G, 3731delT, 6117delG) and eight somatic (1888delG, 4374-4375delCC, R2129S, 2088delG, 2341del18, IVS27b-5C>T, 4083insT, Q519P) were novel. A mosaic mutation (R2429X) was also identified in a neurofibroma by DHPLC analysis and cloning/sequencing. The observed somatic and germline mutational spectra were similar in terms of mutation type, relative frequency of occurrence, and putative underlying mechanisms of mutagenesis. Tumors lacking mutations were screened for NF1 gene promoter hypermethylation but none were found. Microsatellite instability (MSI) analysis revealed MSI in five out of 11 MPNSTs as compared to none out of 70 neurofibromas (p=1.8 x 10(-5)). The screening of seven MPNSTs for subtle mutations in the CDKN2A and TP53 genes proved negative, although the screening of 11 MPNSTs detected LOH involving either the TP53 or the CDKN2A gene in a total of four tumors. These findings are consistent with the view that NF1 tumorigenesis is a complex multistep process involving a variety of different types of genetic defect at multiple loci.

Malignant peripheral nerve sheath tumor: a comparison of grade, immunophenotype, and cell cycle/growth activation marker expression in sporadic and neurofibromatosis 1-related lesions

This study investigates differences in expression of the cell cycle/growth activation markers p53, p16, and p27, and their relationship with nerve sheath cell and proliferation markers among plexiform neurofibromas (PNF), NF1-related and non-NF1 MPNSTs of different histologic grades and between benign-appearing and malignant areas in the MPNSTs associated with PNFs. Formalin-fixed, paraffin-embedded archival tissue from PNFs and MPNSTs were immunostained using the avidin-biotin-complex method with antibodies to S-100 protein (S-100), Leu7 (CD57), CD34, p16, p27, p53, Mib-1, and topoisomerase II-alpha (TopoIIalpha), with appropriate controls. All PNFs and most low-grade MPNSTs displayed diffuse or focal reactivity for S-100, Leu7, CD34, p16, and p27 and negative reactivity for p53, Mib-1, and TopoIIalpha. Most high-grade MPNSTs displayed decreased or negative reactivity to S-100, Leu7, CD34, p16, and p27 but increased reactivity to p53 (59%), Mib-1 (72%), and TopoIIalpha (72%). In addition, combined nuclear and cytoplasmic (nucleocytoplasmic) p27 staining, which was not seen in the PNF or low-grade MPNST, was observed in 33% of high-grade MPNSTs. These findings suggest that p53, p16, and p27 may be involved in tumor progression in the PNF-MPNST sequence. However, alterations in p53, p16, and p27 do not distinguish between low-grade MPNST and PNF, including PNF adjacent to high-grade MPNST. Although p53, p16, and p27 are unlikely to be reliable markers for early detection of tumor progression in MPNST, p53 reactivity was more frequent in NF1-associated high-grade MPNST and appeared to be a marker for high tumor grade. Combining immunohistochemical stains with histologic grading with careful examination of mitotic activity may provide insight into the progression of peripheral nerve sheath tumors.

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.

Hypertrophic neuropathies and malignant peripheral nerve sheath tumors in transgenic mice overexpressing glial growth factor beta3 in myelinating Schwann cells

The neuregulin-1 (NRG-1) family of growth and differentiation factors exerts a variety of effects on Schwann cells and their precursors during nervous system development; however, NRG-1 effects on adult Schwann cells are poorly defined. Several lines of evidence suggest that NRG-1 actions on adult Schwann cells are distinct from those observed during development. To test this hypothesis, we generated transgenic mice overexpressing the NRG-1 isoform glial growth factor beta3 (GGFbeta3) in myelinating Schwann cells [protein zero (P0)GGFbeta3 mice]. P0-GGFbeta3 mice develop resting tremors, gait abnormalities, decreased hindlimb strength, and paralysis by approximately 7 months of age. Sciatic nerves from these animals show a hypertrophic neuropathy characterized by demyelination, remyelination, and "onion bulb" formation. Development of this hypertrophic neuropathy is preceded by Schwann cell hyperplasia that is prominent in 1-month-old mice and present but decreased in 2- and 4-month-old animals. P0-GGFbeta3 mice also develop peripheral ganglion-associated malignant peripheral nerve sheath tumors. Motor, sensory, and sympathetic ganglia from 1-, 2-, and 4-month-old P0-GGFbeta3 mice uniformly contain intraganglionic, likely preneoplastic, Schwann cell proliferations. Examination of bromodeoxyuridine incorporation and caspase-3 activation in sciatic nerves and trigeminal ganglia indicates that Schwann cell hyperplasia in P0-GGFbeta3 mice reflects increased proliferation rather than decreased apoptosis. These observations are consistent with the hypothesis that GGFbeta3 induces proliferation of adult Schwann cells and demyelination of peripheral nerve axons. Furthermore, overexpression of this NRG-1 isoform frequently induces neoplastic Schwann cell proliferation within PNS ganglia, suggesting that NRG-1 may contribute to human Schwann cell neoplasia.

Hypertrophic neuropathies and malignant peripheral nerve sheath tumors in transgenic mice overexpressing glial growth factor beta3 in myelinating Schwann cells

The neuregulin-1 (NRG-1) family of growth and differentiation factors exerts a variety of effects on Schwann cells and their precursors during nervous system development; however, NRG-1 effects on adult Schwann cells are poorly defined. Several lines of evidence suggest that NRG-1 actions on adult Schwann cells are distinct from those observed during development. To test this hypothesis, we generated transgenic mice overexpressing the NRG-1 isoform glial growth factor beta3 (GGFbeta3) in myelinating Schwann cells [protein zero (P0)GGFbeta3 mice]. P0-GGFbeta3 mice develop resting tremors, gait abnormalities, decreased hindlimb strength, and paralysis by approximately 7 months of age. Sciatic nerves from these animals show a hypertrophic neuropathy characterized by demyelination, remyelination, and "onion bulb" formation. Development of this hypertrophic neuropathy is preceded by Schwann cell hyperplasia that is prominent in 1-month-old mice and present but decreased in 2- and 4-month-old animals. P0-GGFbeta3 mice also develop peripheral ganglion-associated malignant peripheral nerve sheath tumors. Motor, sensory, and sympathetic ganglia from 1-, 2-, and 4-month-old P0-GGFbeta3 mice uniformly contain intraganglionic, likely preneoplastic, Schwann cell proliferations. Examination of bromodeoxyuridine incorporation and caspase-3 activation in sciatic nerves and trigeminal ganglia indicates that Schwann cell hyperplasia in P0-GGFbeta3 mice reflects increased proliferation rather than decreased apoptosis. These observations are consistent with the hypothesis that GGFbeta3 induces proliferation of adult Schwann cells and demyelination of peripheral nerve axons. Furthermore, overexpression of this NRG-1 isoform frequently induces neoplastic Schwann cell proliferation within PNS ganglia, suggesting that NRG-1 may contribute to human Schwann cell neoplasia.

Constitutive activation of the neuregulin-1/ErbB receptor signaling pathway is essential for the proliferation of a neoplastic Schwann cell line

Neuregulin-1 (NRG-1) proteins promote Schwann cell survival, differentiation and proliferation during development. High levels of an NRG-like activity are also present in some human peripheral nerve sheath tumors, suggesting that NRG-1 isoforms may be involved in the development of these neoplasms. We examined the expression of NRG-1 and its receptors, the erbB membrane tyrosine kinases, in JS1 cells, a rapidly proliferating line derived from a chemically induced rat malignant peripheral nerve sheath tumor (MPNST). Relative to nontransformed Schwann cells, JS1 cells overexpress the NRG-1 receptor erbB3 and its erbB2 coreceptor; JS1 erbB2 transcripts show no evidence of the activating mutation commonly found in N-ethyl-N-nitrosourea-induced neoplasms. JS1 cells do not express the epidermal growth factor receptor (EGFR), a kinase implicated in the pathogenesis of a major subset of MPNSTs. JS1 cells also express mRNAs encoding multiple alpha and beta isoforms from the glial growth factor and sensory and motor neuron-derived factor NRG-1 subfamilies. Stimulation with NRG-1beta in the presence of forskolin produces a dose-dependent increase in JS1 DNA synthesis. Even in unstimulated JS1 cells, however, erbB2 and erbB3 are constitutively tyrosine phosphorylated. Reducing this constitutive phosphorylation with the specific erbB inhibitor PD158780 markedly impairs JS1 DNA synthesis. These observations support the hypothesis that NRG-1 isoforms and erbB kinases act in an autocrine and/or paracrine fashion to promote mitogenesis in JS1 cells. The absence of EGFR expression in JS1 cells suggests that constitutive activation of the NRG-1/erbB signaling pathway is an alternative means of inducing Schwann cell neoplasia.

Evaluation of F18-deoxyglucose positron emission tomography (FDG-PET) to assess the nature of neurogenic tumours

AIMS

Benign neurofibromas and malignant peripheral nerve sheath tumours (MPNST) commonly develop in patients with neurofibromatosis. Differentiation of benign from malignant tumours by conventional preoperative imaging is unreliable. FDG-PET is a non-invasive technique for biological tumour evaluation. The aim of this study was to assess the value of FDG-PET in patients with neurogenic tumours suspicious for MPNST.

METHODS

Benign and malignant neurogenic soft tissue tumours were prospectively evaluated by computed tomography or magnetic resonance imaging. Three-dimensional qualitative and quantitative FDG-PET was performed. Standard uptake value (SUV) was analyzed with respect to histological diagnosis and follow-up data.

RESULTS

Twenty-five neurogenic soft tissue tumours were included. FDG-PET identified all primary (n=6) and recurrent MPNST (n=7). Benign lesions (n=12) did not demonstrate high FDG uptake. The SUV was significantly higher in MPNST (median 2.9; range 1.8-12.3), than in benign tumours (median 1.1; range 0.5-1.8) (p<0.001). At a cut-off value of 1.8 SUV measured 1 h post-injection FDG-PET distinguished between MPNST and benign neurogenic tumours with 100% sensitivity and 83% specificity.

CONCLUSIONS

FDG-PET allows discrimination of benign from malignant neurogenic tumours. This should be particularly useful in patients with neurofibromatosis as FDG-PET may help to avoid multiple surgical procedures for benign tumours.

Cytogenetic characterization of three malignant peripheral nerve sheath tumors

Malignant peripheral nerve sheath tumors (MPNST) are soft tissue sarcomas occurring frequently in patients with neurofibromatosis 1. We present three fully karyotyped cases of MPNST revealing aberrant near-triploid karyotypes. In all three cases we found deletions of chromosome arms or chromosomes 1p, 10q, 9, and 15, as well as gain of chromosome 7 in two NF1-associated cases and gain of chromosome 8 in an NF1-associated and a sporadic case. The chromosomal region of the NF1 gene was cytogenetically unchanged in all cases, whereas two MPNST cases showed losses of the region 22q harboring the locus of the NF2 gene.

Evidence for involvement of a tumor suppressor gene on 1p in malignant peripheral nerve sheath tumors

Malignant peripheral nerve sheath tumors (MPNST) are rare soft-tissue malignancies. The genetic basis of these tumors is still poorly understood. Cytogenetic analyses predominantly revealed complex karyotypes, precluding the identification of recurrent chromosomal changes. We report loss of 1p material in a near-diploid karyotype with few or no additional structural chromosome changes in two sporadic cases of MPNST, indicating an important role of 1p loss in MPNST development. In one of these two tumors, a distal 1p deletion (1p31.2 approximately pter) was detected suggesting involvement of a tumor suppressor gene located within this distal region of 1p. Further evidence for recurrent 1p loss in MPNST was obtained by interphase fluorescence in situ hybridization, which showed loss of 1p material in 3 out of 13 tumors. These findings together with data from the literature suggest that loss of a tumor suppressor gene located within distal 1p is implicated in the pathogenesis of MPNST.

Malignant peripheral nerve sheath tumor cell invasion is facilitated by Src and aberrant CD44 expression

Malignant peripheral nerve sheath tumors (MPNSTs) are aggressive malignancies that arise within peripheral nerves. These tumors occur with increased incidence in patients with neurofibromatosis type 1 (NF1), exhibiting increased Ras activity due to loss of the NF1 gene product, neurofibromin, and abnormal expression of the epidermal growth factor receptor (EGFR). We previously found that MPNSTs express increased levels of the CD44 family of transmembrane glycoproteins that have been implicated in tumor cell invasion and metastasis. In two MPNST cell lines, we have found that elevated CD44 expression and cell invasion are dependent on Src kinase activity but are independent of mitogen-activated protein kinases (MAPK) kinase (MEK) activity. In contrast, inhibition of Src kinase activity has no influence on MPNST cell proliferation. Reduction of CD44 levels, using antisense oligonucleotides, results in reduced MPNST cell invasion in vitro, suggesting that Src contributes in part to MPNST cell invasion by increasing CD44 levels. At least some of this increased CD44 expression results from elevated EGFR levels through a Src-dependent mechanism, consistent with the notion that EGFR promotes constitutive Src activation in MPNSTs. These data indicate that Src and CD44 are putative targets for the treatment of MPNST invasion and metastasis.

Intraparotid facial nerve neurofibromas

OBJECTIVES

To provide an awareness of intraparotid facial nerve neurofibroma as a cause of parotid masses and to describe their characteristics and management considerations.

STUDY DESIGN

Case report with literature review.

METHODS

The medical records of three patients with intraparotid facial nerve neurofibromas are reviewed, and data concerning the patient's presentations, treatment, and disease course are presented with a review of the world's literature on intraparotid facial nerve neurofibromas.

CONCLUSIONS

Tumors arising from the extratemporal course of the facial nerve are quite rare. The tumors arise from Schwann cells and include the schwannoma and the neurofibroma. The overwhelming benign nature of these lesions necessitates a conservative course of treatment. Histological diagnosis should be followed by a limited tumor excision with emphasis on retaining normal facial nerve function. Malignant lesions require wide excision with facial nerve grafting or facial nerve reanimation.

Pathogenesis of hereditary tumors: beyond the "two-hit" hypothesis

Knudson's 'two-hit' hypothesis has provided extremely important insights into the pathogenesis of tumors in autosomal dominant tumor predisposition syndromes, but recent evidence suggests that some such tumors may occur without a 'second hit' or require more than two mutations. Inactivation of both RB1 alleles appears to be insufficient by itself to cause malignancy in the tumors that develop in patients with hereditary retinoblastoma. On the other hand, certain tumors in patients with tuberous sclerosis complex appear to develop in haploinsufficient tissues that do not have 'second hit' mutations of a tuberous sclerosis gene. The molecular pathogenesis of certain other tumors in patients with tuberous sclerosis complex or neurofibromatosis 1 may not be fully explained by the 'two-hit' hypothesis either. Hereditary tumors, like non-hereditary tumors, may arise by a variety of molecular mechanisms, with loss of both alleles of a particular tumor suppressor gene being a frequent, but not invariably necessary or sufficient, event. Four models are presented to explain how various tumors may arise in patients with inherited tumor predisposition syndromes such as hereditary retinoblastoma, tuberous sclerosis complex or neurofibromatosis 1. Even tumors of one particular type may develop by more than one mechanism.

The molecular and genetic basis of neurological tumours

There are no effective therapies for many tumours of the nervous system. This is, in part, a consequence of their location within relatively inaccessible tissues. It is also likely, however, that the unique characteristics of the cells that give rise to these tumours create a set of conditions that facilitate tumour development. Here, we consider recent advances in molecular genetics, the development of mouse models and developmental neurobiology as they relate to tumours of neuroectodermal origin. It is likely that these advances will provide insight into underlying mechanisms and provide a rational framework for the development of effective interventions.

Neurofibromatosis 1

Neurofibromatosis 1 is one of the most common genetic conditions affecting the nervous system. Individuals with NF1 are predisposed to the development of peripheral nerve sheath tumors (neurofibromas and MPNSTs), astrocytomas (optic pathway gliomas), learning disabilities, seizures, strokes, macrocephaly, and vascular abnormalities. The NF1 tumor suppressor gene encodes a large protein (neurofibromin) that functions primarily as a RAS negative regulator, suggesting that targeted therapy for NF1 might derive from inhibition of the RAS signaling pathway.

Differential NF1, p16, and EGFR patterns by interphase cytogenetics (FISH) in malignant peripheral nerve sheath tumor (MPNST) and morphologically similar spindle cell neoplasms

Malignant peripheral nerve sheath tumors (MPNSTs) are diagnostically challenging neoplasms for which sensitive and specific immunohistochemical markers are lacking. Although limited to date, previous studies have suggested that NF1 (17q), NF2 (22q), p16 (9p), and EGFR (7p) alterations may be involved in MPNST tumorigenesis. To determine whether specific genetic changes differentiate between MPNST and morphologically similar neoplasms, we assessed these chromosomal regions in 22 MPNSTs (9 NF1-associated, 13 sporadic), 13 plexiform neurofibromas, 5 cellular schwannomas, 8 synovial sarcomas, 6 fibrosarcomas, and 13 hemangiopericytomas by 2-color FISH. NF1 deletions, often in the form of monosomy 17, were found in MPNSTs (76%). neurofibromas (31%), hemangiopericytomas (17%), and fibrosarcomas (17%), but not in synovial sarcomas or cellular schwannomas. NF1 losses were encountered more frequently in MPNSTs versus other sarcomas (p < 0.001), as were p16 homozygous deletions (45% vs 0%; p < 0.001), EGFR amplifications (26% vs 0%; p = 0.006), and polysomies for either chromosomes 7 (53% vs 12%; p = 0.003) or 22 (50% vs 4%; p < 0.001). Hemizygous or homozygous p16 deletions were detected in 75% of MPNSTs, but not in benign nerve sheath tumors (p < 0.001). Thus, FISH analysis identifies relatively specific genetic patterns that may be useful in selected cases, for which the differential diagnosis includes low- or high-grade MPNST.

Molecular biology of nervous system tumors

Many genetic alterations that contribute to CNS tumorigenesis and progression have been identified. One goal of such studies is to identify loci that would serve as diagnostic prognostic markers or both. A significant advance is the observation that chromosome 1p loss identified anaplastic oligodendroglioma and a subset of high-grade glioma patients who responded to chemotherapy and had longer survival times. Combined 1p and 19q loss was a predictor of prolonged survival of patients having pure oligodendrogliomas. Such markers eventually may be used to identify patients upfront who would benefit from treatment, while sparing patients who would not benefit. Although many molecular participants involved in the biologic pathways that promote proliferation, angiogenesis, and invasion have been elucidated, there are still many gaps in clinicians' knowledge. It is expected that the use of the human genome project information and databases such as SAGEmap, in combination with techniques such as cDNA arrays and proteomics, will facilitate greatly the identification of novel genes that contribute to CNS tumors. cDNA arrays and tissue arrays will permit the construction of CNS-specific screening tools that will permit the identification of tumor-specific mutations and alterations so that patient-specific therapies can be designed.

CDKN2A germline splicing mutation affecting both p16(ink4) and p14(arf) RNA processing in a melanoma/neurofibroma kindred

The CDKN2A locus encodes two tumor suppressor proteins, p16(ink4) and p14(arf), through use of alternative first exons. CDKN2A mutations detected in melanoma families are usually missense or nonsense changes which mainly impair p16(ink4) function. Large genomic deletions spanning the entire locus have been observed in two pedigrees with melanomas and nervous tumors. We have detected a novel splice site mutation in a family with melanomas, neurofibromas, and multiple dysplastic nevi. Both alternative mRNAs produced by the mutant allele lacked shared sequences from exon 2, which encodes a substantial portion (>50%) of both p16(ink4) and p14(arf) proteins. The development of neurofibromas can be explained by cooperative effects of combined inactivation of p16(ink4) and p14(arf) or, alternatively, of p14(arf) alone.

Rb and TP53 pathway alterations in sporadic and NF1-related malignant peripheral nerve sheath tumors

SUMMARY

Karyotypic complexities associated with frequent loss or rearrangement of a number of chromosome arms, deletions, and mutations affecting the TP53 region, and molecular alterations of the INK4A gene have been reported in sporadic and/or neurofibromatosis type I (NF1)-related malignant peripheral nerve sheath tumors (MPNSTs). However, no investigations addressing possible different pathogenetic pathways in sporadic and NF1-associated MPNSTs have been reported. This lack is unexpected because, despite similar morphologic and immunophenotypic features, NF1-related cases are, by definition, associated with NF1 gene defects. Thus, we investigated the occurrence of TP53 and p16(INK4A) gene deregulation and the presence of microsatellite alterations at markers located at 17p, 17q, 9p21, 22q, 11q, 1p, or 2q loci in MPNSTs and neurofibromas either related (14 cases) or unrelated (14 cases) to NF1. Our results indicate that, in MPNSTs, p16(INK4A) inactivation almost equally affects both groups. However, TP53 mutations and loss of heterozygosity involving the TP53 locus (43% versus 9%), and p53 wild type overexpression, related or not to mdm2 overexpression (71% versus 25%), seem to mainly be restricted to sporadic MPNSTs. In NF1-associated MPNSTs, our microsatellite results are consistent with the occurrence of somatic inactivation by loss of heterozygosity of the second NF1 allele.

Cancer-related gene expression profiles in NF1-associated pilocytic astrocytomas

BACKGROUND

Individuals affected with neurofibromatosis 1 (NF1) develop juvenile pilocytic astrocytomas (JPA) at an increased frequency, suggesting that the NF1 gene product, neurofibromin, functions as a negative growth regulator for astrocytes. Previously, the authors demonstrated that NF1-associated astrocytomas exhibit deletions and loss of NF1 gene expression on the DNA and protein levels. However, little is known about additional genetic events in clinically and radiographically progressive NF1-associated pilocytic astrocytomas.

OBJECTIVE/METHODS

To understand the potential role of cooperating genetic events in the development of these low-grade tumors, the authors used immunohistochemistry and selected confirmatory Western blots to examine nine symptomatic NF1-associated pilocytic astrocytomas for gene products whose expression patterns are altered in fibrillary astrocytomas.

RESULTS

The authors demonstrate that p53, p16, retinoblastoma (RB), epidermal growth factor receptor (EGFR), cyclin-dependent kinase 4 (CDK4), platelet-derived growth factor A (PDGF-A) and PDGF receptor alpha (PDGF-Ralpha) protein expression profiles are not altered in NF1-associated pilocytic astrocytomas. Similar to their sporadic counterparts, NF1-associated JPA also strongly expressed PEN5, a marker of post-O2A stage oligodendroglial precursor cells.

CONCLUSIONS

These results suggest that NF1-associated pilocytic astrocytomas lack the genetic changes typically associated with the more clinically aggressive fibrillary astrocytomas and lay the foundation for future studies to identify NF1 JPA-specific alterations.

Neurofibromatosis 1 (NF1) heterozygosity results in a cell-autonomous growth advantage for astrocytes

Individuals with neurofibromatosis 1 (NF1) develop low-grade astrocytomas at an increased frequency. To gain insight into the function of the Nf1 gene product as a growth regulator for astrocytes, we examined mice heterozygous for a targeted Nf1 mutation. In our previous studies, we demonstrated increased numbers of proliferating astrocytes in Nf1 heterozygote (Nf1+/-) mice in vivo. We now show that cultured Nf1+/- astrocytes exhibit a cell-autonomous growth advantage in vitro associated with increased p21-ras pathway activation. Furthermore, we demonstrate that Nf1+/-;wild-type N-ras mice have a similar astrocyte growth advantage in vitro and in vivo as either oncogenic N-ras or Nf1+/-; oncogenic N-ras mice. Lastly, mice heterozygous for targeted defects in both Nf1 and p53 as well as Nf1 and Rb exhibit 3- and 2.5-fold increases in astrocyte proliferation in vivo, respectively, suggesting that abnormalities in Nf1- and p53/Rb-regulated pathways cooperate in the heterozygous state to confer a growth advantage for brain astrocytes. Collectively, these results provide evidence for a cell-autonomous growth advantage in Nf1+/- astrocytes and suggest that some of the brain pathology in individuals with NF1 might result from reduced, but not absent, NF1 gene function.

Molecular genetics in pediatric dermatology

The field of pediatric dermatology continues to be enriched by the insights offered through molecular genetics. For some genetic skin disorders, including neurofibromatosis, tuberous sclerosis complex, and several forms of epidermolysis bullosa, genetic research has resulted in an evolving understanding of the relationship between genotype and phenotype, with the ability to predict some of the features of these disorders on the basis of the genetic defect. However, widespread use of molecular genetics for diagnostic testing of these disorders has not been possible because of genetic heterogeneity, limited availability, and reduced sensitivity. The appropriate use of genetic services is emphasized in this, the molecular era.

Gains in chromosomes 7, 8q, 15q and 17q are characteristic changes in malignant but not in benign peripheral nerve sheath tumors from patients with Recklinghausen's disease

In order to investigate typical genomic alterations in patients with Recklinghausen's disease (NF1) we studied one from each of the six patients with NF1 several benign and/or malignant tumors. By means of comparative genomic hybridization (CGH) gained results from six benign neurofibromas and 14 malignant peripheral nerve sheath tumors (MPNSTs) were compared with four benign peripheral nerve sheath tumors (BPNSTs) from patients without NF1. In all 14 MPNSTs DNA sequence copy number changes were detected with a mean value of 13.5 imbalances per sample. The most frequent gains were in 8q, 17q (12 tumors each), 7p, 15q (ten tumors each), and 7q (nine tumors). We found ten high-level amplifications in nine of the 14 samples. In two cases, the high-level amplification involved 7p14-pter and 17q24-qter as well. The most frequent loss was in 17p (seven tumors). The benign neurofibromas from NF1-patients and the sporadic BPNSTs revealed only partially DNA sequence copy number changes without any distinct pattern. The gains of #7, 8q, 15q, and 17q were found exclusively in MPNSTs but not in neurofibromas and are supposed to be associated with malignant tumor progression. In comparison of the results of the 14 MPNSTs from NF1-patients with the results of previously published 20 sporadic MPNSTs, we found that the gain of 8q occurs most frequently in both tumor groups. Of course additionally in the sporadic MPNSTs there were more frequent gains of 5p, #6, and statistically significant gains of 20q. On the other hand in the MPNSTs from NF1-patients the most frequent gains were found in #7, and statistically significant in 15q, and 17q.