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PubMed1995

Identification of neurofibromatosis 1 (NF1) homologous loci by direct sequencing, fluorescence in situ hybridization, and PCR amplification of somatic cell hybrids.

Using fluorescence in situ hybridization (FISH), we have identified seven NF1-related loci, two separate loci on chromosome 2, at bands 2q21 and 2q33-q34, and one locus each on five other chromosomes at bands 14q11.2, 15q11.2, 18p11.2, 21q11.2-q21, and 22q11.2. Application of PCR using NF1 primer pairs and genomic DNA from somatic cell hybrids confirmed the above loci, identified additional loci on chromosomes 12 and 15, and showed that the various loci do not share homology beyond NF1 exon 27b. Sequenced PCR products representing segments corresponding to NF1 exons from these loci demonstrated greater than 95% sequence identity with the NF1 locus. We used sequence differences between bona fide NF1 and NF1-homologous loci to strategically design primer sets to specifically amplify 30 of 36 exons within the 5' end of the NF1 gene. These developments have facilitated mutation analysis at the NF1 locus using genomic DNA as template.

Animals↗
PubMed1991

Neurofibromatosis type 1 (NF1) gene: implication in neuroectodermal differentiation and genesis of brain tumors.

The gene responsible for neurofibromatosis type 1 (NF1), a common autosomal dominantly inherited disease, has been isolated. A region of NF1 gene product has been demonstrated to share structural and functional similarities with the mammalian GTPase activating protein (GAP) and the yeast IRA proteins. Thus, the NF1 protein is thought to play a role in signal transduction by stimulating the conversion of the Ras protein from a GTP-bound active form to a GDP-bound inactive form. The increased risk of malignant tumors in neuroectodermal tissues of NF1 patients may be caused by disruption of growth and differentiation regulatory functions of the NF1 gene. A second type of the NF1-GAP related domain (NF1-GRD) transcript, which has an extra 21-amino-acid insert in the center of the previously reported first type transcript, has been described. This insert significantly changes the hydrophilicity and secondary structure of the central region of NF1-GRD, therefore, suggesting it also changes its function. Alternative splicing is the most likely mechanism by which these two types of transcripts arise. The NF1-GRD alternative splicing has been shown to be intimately involved in differentiation of neuroectodermal tissues. Aberrant regulation of the alternative splicing may contribute to tumor formation in neuroectodermal tissue.

Amino Acid Sequence↗
PubMed2005

The effect of extracellular calcium concentration on calcium-mediated cell signaling in NF1 tumor suppressor-deficient keratinocytes.

Capacitative calcium entry and calcium wave propagation were studied in keratinocytes from healthy volunteers and patients with type 1 neurofibromatosis (NF1) in calcium-depleted and in low calcium culture medium. In previous studies, we found evidence that mutations of the NF1 tumor suppressor gene can lead to altered calcium-mediated cell signaling in keratinocytes cultured in the presence of a high extracellular calcium concentration. The present study demonstrated that the differences between normal and NF1 keratinocytes were dependent on extracellular calcium concentration. Specifically, when keratinocytes were exposed to thapsigargin under calcium-depleted culture conditions the subsequent increase in free intracellular calcium concentration was moderate in NF1 keratinocytes compared to controls. The finding indicates lowered endoplasmic calcium stores in NF1 which may also in part explain the reduced activation signal for capacitative calcium influx and the wound-induced intracellular Ca2+ transient observed in NF1 keratinocytes maintained in culture medium containing 0.05 mM calcium. The differences between control and NF1 keratinocytes were most pronounced when the cells were cultured in the presence of a high (1.8 mM) calcium concentration. Since elevated extracellular calcium levels induce keratinocytes to form cellular contacts and lead to terminal differentiation, markedly aberrant responses of NF1 keratinocytes in the presence of a high calcium concentration may help to explain previous findings on impaired formation of cellular junctions and differentiation in NF1 deficient cells.

Adult↗
PubMed1996

Sex differences in mutational rate and mutational mechanism in the NF1 gene in neurofibromatosis type 1 patients.

Neurofibromatosis type 1 (NF1) is an autosomal dominant disorder with a prevalence of around 1 in 3500, affecting all ethnic groups. The clinical manifestations of the disease are variable, even among members of the same family, and affect a variety of tissues and cell types, including skin, iris, central and peripheral nervous systems and skeletal system. It has been reported that the majority of sporadic mutations in NF1 arise in paternally inherited alleles. We present here a collaborative study of the parental origin and type of mutation in individuals with de novo NF1, who account for up to a half of all cases of clinically diagnosed NF1. We have studied intragenic and extragenic markers in 470 NF1 families. In 32 of these families it was possible to assess the parental origin of a de novo NF1 mutation either by linkage analysis (in families with three generations) or by the detection of an intragenic deletion in a sporadic NF1 case. Eleven of these 32 families have three generations (the second and third generation being affected), with the mutation (not a large deletion) being of paternal origin in 82% of them (P < 0.05). In the other 21 families an intragenic deletion was detected, in 76% being in the maternal chromosome and in 24% in the paternal one (P < 0.05). Our results suggest that in NF1 the majority of deletions occur in oogenesis, while other types of mutations should account for the paternally derived NF1 mutations.

Chromosome Mapping↗
PubMed1997

Identification of de novo deletions at the NF1 gene: no preferential paternal origin and phenotypic analysis of patients.

Neurofibromatosis type 1 (NF1) is a common autosomal dominant disorder. To date, a relatively small number of NF1 mutations have been characterized, thus precluding genotype-phenotype correlations. By genotyping 75 NF1 families, we have detected six hemizygous patients (two of whom are members of the same family). The five presumed deletions were confirmed by two quantitative methods of analysis of NF1 copy number: Southern hybridization with cDNA probes and a single-strand conformation polymorphism analysis that discriminates between the NF1 gene and the pseudogene sequences. The five deletions remove most of the NF1 gene, at least 225 kb, from exon 9 to the 3' end of the coding sequence. The origin of de novo mutations in the NF1 gene has been reported to be mainly paternal but we have determined that four of the de novo deletions involved the maternal chromosome and one the paternal chromosome. The six patients with deletions exhibited precocious, multiple clinical features of the disease. The incidence of tumor complications, particularly plexiform neurofibromas and intracranial tumors, among this group of patients is higher than the observed incidence in our NF1 population, suggesting that NF1 haploinsufficiency may cause a more severe phenotype with regard to tumor development. In contrast to other reports that associated large deletions with mildly dysmorphic facies, mental retardation and a large number of cutaneous neurofibromas, only one out of our six patients presented this phenotype.

Adolescent↗
PubMed2006

Histopathology and clinical outcome of NF1-associated vs. sporadic malignant peripheral nerve sheath tumors.

The differences in the clinical course and histopathology of sporadic and neurofibromatosis type 1 (NF1)-associated malignant peripheral nerve sheath tumors (MPNST) were investigated retrospectively. The collective comprised 38 NF1 patients and 14 sporadic patients. NF1 patients were significantly younger at diagnosis (p<0.001) and had a significantly shorter survival time than sporadic patients (median survival 17 months vs. 42 months, Breslow p<0.05). The time interval to local recurrence and metastatic spread was also significantly shorter in NF1 patients (9.4 months vs. 30.0 months, p<0.01; 9.1 months vs. 33.2 months, p<0.001, respectively). In patients with the original histopathological data available (22 NF1 patients, 14 sporadic cases), NF1-associated MPNST showed a significantly higher cellularity compared to sporadic tumors (p<0.001) whereas sporadic MPNST featured a significantly higher pleomorphism (p<0.01). Most importantly, while histopathological variables correlated with French Fédération Nationale des Centres de Lutte Contre le Cancer grading in sporadic MPNST, this was not the case for NF1-associated tumors. The differences between NF1-associated and sporadic MPNST in regard to the clinical course and histopathology may reflect some fundamental differences in biology and pathomechanism of the two tumor groups. Our findings indicate the necessity for a separate grading scheme which takes into account the genetic background in NF1 patients.

Adolescent↗
PubMed1995

Genomic organization of the neurofibromatosis 1 gene (NF1).

Neurofibromatosis 1 maps to chromosome band 17q11.2, and the NF1 locus has been partially characterized. Even though the full-length NF1 cDNA has been sequenced, the complete genomic structure of the NF1 gene has not been elucidated. The 5' end of NF1 is embedded in a CpG island containing a NotI restriction site, and the remainder of the gene lies in the adjacent 350-kb NotI fragment. In our efforts to develop a comprehensive screen for NF1 mutations, we have isolated genomic DNA clones that together harbor the entire NF1 cDNA sequence. We have identified all intron-exon boundaries of the coding region and established that it is composed of 59 exons. Furthermore, we have defined the 3'-untranslated region (3'-UTR) of the NF1 gene; it spans approximately 3.5 kb of genomic DNA sequence and is continuous with the stop codon. Oligonucleotide primer pairs synthesized from exon-flanking DNA sequences were used in the polymerase chain reaction with cloned, chromosome 17-specific genomic DNA as template to amplify NF1 exons 1 through 27b and the exon containing the 3'-UTR separately. This information should be useful for implementing a comprehensive NF1 mutation screen using genomic DNA as template.

Amino Acid Sequence↗
PubMed2002

NF1 tumor suppressor mRNA is targeted to the cell-cell contact zone in Ca(2+)-induced keratinocyte differentiation.

SUMMARY: We have previously shown that NF1 (type 1 neurofibromatosis) p21ras GTPase-activating tumor suppressor protein undergoes major relocalization during the formation of cell-cell junctions in differentiating keratinocytes in vitro. This prompted us to study the distribution of NF1 mRNA under the same conditions by in situ hybridization. In differentiating keratinocytes, the NF1 mRNA signal intensified within the cell cytoplasm within the first 0.5 to 2 hours after induction of cellular differentiation. First, the hybridization signal was evenly distributed throughout the cytoplasm. Subsequently, NF1 mRNA was gradually polarized to the cellular periphery at the side of cell-cell junctions and finally disappeared. Reappearance of NF1 mRNA was found in migrating keratinocytes forming a bilayered culture. Disruption of microfibrillar cytoskeleton, but not microtubules, caused a marked change in the subcellular distribution of NF1 mRNA. This data may suggest that intact actin microfilaments are essential for transport of NF1 mRNA to the cell periphery. This is the first study demonstrating that NF1, or any tumor suppressor mRNA, belongs to a rare group of mRNAs not targeted to free polysomes or ribosomes of the rough endoplasmic reticulum. This finding recognizes a potential way for post-transcriptional modification of NF1 expression.

Adult↗
PubMed2002

Neurofibromin and NF1 gene analysis in composite pheochromocytoma and tumors associated with von Recklinghausen's disease.

Composite tumor of pheochromocytoma and neuroblastoma, or ganglioneuroma, or ganglioneuroblastoma (composite pheochromocytoma), also known as mixed neuroendocrine and neural tumor, are sometimes combined with neurofibromatosis type 1 (NF1). To better understand the relationship between NF1 and composite pheochromocytoma, an immunohistochemical study using anti-neuro-fibromin that is an NF1 gene product and DNA sequence of NF1 Exon 31 were carried out in five cases of composite pheochromocytoma and in various tumors from five patients with NF1. Neurofibromin was not expressed in Schwann cells and sustentacular cells of composite pheochromocytomas and was very weakly or negatively expressed in neurofibroma of NF1 patients. However, it was strongly expressed in ganglionic cells and pheochromocytoma cells of the composite pheochromocytomas and also in mucosal ganglioneuromas, a gangliocytic paraganglioma, and in pheochromocytomas from the patients with NF1. Although there was no mutation in NF1 Exon 31, it could not be ruled out that there were mutations in other sites of the NF1 gene. Neurofibromin insufficiency may induce abnormal proliferation of Schwann cells in composite pheochromocytomas as well as in neurofibromatosis.

Adrenal Gland Neoplasms↗
PubMed1999

Haploinsufficiency for the neurofibromatosis 1 (NF1) tumor suppressor results in increased astrocyte proliferation.

Individuals affected with neurofibromatosis 1 (NF1) harbor increased numbers of GFAP-immunoreactive cerebral astrocytes and develop astrocytomas that can lead to blindness and death. Mice heterozygous for a targeted Nf1 mutation (Nf1+/-) were employed as a model for the human disease to evaluate the hypothesis that reduced NF1 protein (neurofibromin) expression may confer a growth advantage for astrocytes, such that inactivation of only one NF1 allele is sufficient for abnormal astrocyte proliferation. Here, we report that Nf17+/- mice have increased numbers of cerebral astrocytes and increased astrocyte proliferation compared to wild-type littermates. Intriguingly, primary Nf1+/- astrocyte cultures failed to demonstrate a cell-autonomous growth advantage unless they were cocultured with C17 neuronal cells. This C17 neuronal cell-induced Nf1+/- increase in proliferation was blocked by MEK inhibition (PD98059), suggesting a p21-ras-dependent effect. Furthermore, mice heterozygous for a targeted mutation in another GAP molecule, p120-GAP, demonstrated no increases in cerebral astrocyte number. These findings suggest that reduced NF1 expression results in a cell context-dependent increase in astrocyte proliferation that may be sufficient for the development of astrocytic growth abnormalities in patients with NF1.

Animals↗
PubMed2006

Nf1 haploinsufficiency augments angiogenesis.

Mutations in the NF1 tumor-suppressor gene underlie neurofibromatosis type 1 (NF1), in which patients are predisposed to certain tumors such as neurofibromas and may associate with vascular disorder. Plexiform neurofibromas are slow growing benign tumors that are highly vascular and can progress to malignancy. The development of neurofibromas requires loss of both Nf1 alleles in Schwann cells destined to become neoplastic and may be exacerbated by Nf1 heterozygosity in other non-neoplastic cells. This study tested the hypothesis that Nf1 heterozygosity exaggerates angiogenesis. We found that Nf1 heterozygous mice showed increased neovascularization in both the retina and cornea in response to hypoxia and bFGF, respectively, compared to their wild-type littermates. The increase in corneal neovascularization was associated with heightened endothelial cell proliferation and migration, and increased infiltration of inflammatory cells. In addition, Nf1 heterozygous endothelial cell cultures showed an exaggerated proliferative response to angiogenic factors, particularly to bFGF. These findings support the conclusion that Nf1 heterozygosity in endothelial cells and perhaps inflammatory cells augments angiogenesis, which may promote neurofibroma formation in NF1.

Animals↗
PubMed2005

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.

Animals↗
PubMed1995

Inhibition of Ras/Raf interaction by anti-oncogenic mutants of neurofibromin, the neurofibromatosis type 1 (NF1) gene product, in cell-free systems.

The neurofibromatosis type 1 (NF1) gene encodes a protein, neurofibromin, containing GTPase-activating protein-related domain (GRD) that stimulates intrinsic GTPase activity of Ras protein. By screening a randomly mutagenized NF1-GRD library in Saccharomyces cerevisiae, we isolated two NF1-GRD mutants (NF201 and NF204) with single amino acid substitutions, which suppress the heat shock-sensitive phenotype of the RAS2(G19V) mutant. The NF1-GRD mutants also suppress the oncogenic Ras-induced transformation of NIH 3T3 mouse fibroblasts (Nakafuku, M., Nagamine, M., Ohtoshi, A., Tanaka, K., Toh-e, A., and Kaziro, Y. (1993) Proc. Natl. Acad. Sci. U.S.A. 90, 6706-6710). In this paper, we investigated the molecular mechanism of inhibition of the transforming Ras-specific function by the NF1-GRD mutants in mammalian cells. In human embryonic kidney (HEK) 293 cells, the mutant NF1-GRDs attenuated the stimulation of mitogen-activated protein kinase by Ras(G12V), but not by platelet-derived growth factor. In cell-free systems, purified recombinant NF1-GRD mutants showed an inhibitory effect on the association of Ras.guanosine 5'-O-(3-thiotriphosphate) (GTP gamma S) with Raf at several times lower concentrations than the wild type. Furthermore, it was revealed that the binding affinity of the mutant NF1-GRDs toward Ras.GTP gamma S is approximately 5-10 times higher than the wild type. These results suggest that the mutant NF1-GRDs tightly bind to an oncogenic Ras in its GTP-bound active conformation and block the interaction between Ras and its effector, Raf.

3T3 Cells↗
PubMed1998

Nf1 regulates hematopoietic progenitor cell growth and ras signaling in response to multiple cytokines.

Neurofibromin, the protein encoded by the NF1 tumor-suppressor gene, negatively regulates the output of p21(ras) (Ras) proteins by accelerating the hydrolysis of active Ras-guanosine triphosphate to inactive Ras-guanosine diphosphate. Children with neurofibromatosis type 1 (NF1) are predisposed to juvenile chronic myelogenous leukemia (JCML) and other malignant myeloid disorders, and heterozygous Nf1 knockout mice spontaneously develop a myeloid disorder that resembles JCML. Both human and murine leukemias show loss of the normal allele. JCML cells and Nf1-/- hematopoietic cells isolated from fetal livers selectively form abnormally high numbers of colonies derived from granulocyte-macrophage progenitors in cultures supplemented with low concentrations of granulocyte-macrophage colony stimulating factor (GM-CSF). Taken together, these data suggest that neurofibromin is required to downregulate Ras activation in myeloid cells exposed to GM-CSF. We have investigated the growth and proliferation of purified populations of hematopoietic progenitor cells isolated from Nf1 knockout mice in response to the cytokines interleukin (IL)-3 and stem cell factor (SCF), as well as to GM-CSF. We found abnormal proliferation of both immature and lineage-restricted progenitor populations, and we observed increased synergy between SCF and either IL-3 or GM-CSF in Nf1-/- progenitors. Nf1-/- fetal livers also showed an absolute increase in the numbers of immature progenitors. We further demonstrate constitutive activation of the Ras-Raf-MAP (mitogen-activated protein) kinase signaling pathway in primary c-kit+ Nf1-/- progenitors and hyperactivation of MAP kinase after growth factor stimulation. The results of these experiments in primary hematopoietic cells implicate Nf1 as playing a central role in regulating the proliferation and survival of primitive and lineage-restricted myeloid progenitors in response to multiple cytokines by modulating Ras output.

Animals↗
PubMed2005

NF1 gene mutations represent the major molecular event underlying neurofibromatosis-Noonan syndrome.

Neurofibromatosis type 1 (NF1) demonstrates phenotypic overlap with Noonan syndrome (NS) in some patients, which results in the so-called neurofibromatosis-Noonan syndrome (NFNS). From a genetic point of view, NFNS is a poorly understood condition, and controversy remains as to whether it represents a variable manifestation of either NF1 or NS or is a distinct clinical entity. To answer this question, we screened a cohort with clinically well-characterized NFNS for mutations in the entire coding sequence of the NF1 and PTPN11 genes. Heterozygous NF1 defects were identified in 16 of the 17 unrelated subjects included in the study, which provides evidence that mutations in NF1 represent the major molecular event underlying this condition. Lesions included nonsense mutations, out-of-frame deletions, missense changes, small inframe deletions, and one large multiexon deletion. Remarkably, a high prevalence of inframe defects affecting exons 24 and 25, which encode a portion of the GAP-related domain of the protein, was observed. On the other hand, no defect in PTPN11 was observed, and no lesion affecting exons 11-27 of the NF1 gene was identified in 100 PTPN11 mutation-negative subjects with NS, which provides further evidence that NFNS and NS are genetically distinct disorders. These results support the view that NFNS represents a variant of NF1 and is caused by mutations of the NF1 gene, some of which have been demonstrated to cause classic NF1 in other individuals.

Child↗
PubMed2001

Heterozygosity for the neurofibromatosis 1 (NF1) tumor suppressor results in abnormalities in cell attachment, spreading and motility in astrocytes.

Individuals with the neurofibromatosis 1 (NF1) tumor predisposition syndrome develop low-grade pilocytic astrocytomas at an increased frequency. Previously, we demonstrated that astrocytes from mice heterozygous for a targeted mutation in the Nf1 gene (Nf1+/- astrocytes) exhibit a cell autonomous growth advantage associated with increased RAS pathway activation. In this report, we extend our initial characterization of the effect of reduced Nf1 gene expression on astrocyte function by demonstrating that Nf1+/- astrocytes exhibit decreased cell attachment, actin cytoskeletal abnormalities during the initial phases of cell spreading, and increased cell motility. Whereas these cytoskeletal abnormalities were also observed in Nf1-/- astrocytes, astrocytes expressing a constitutively active RAS molecule showed increased cell motility and abnormal actin cytoskeleton organization during cell spreading, but exhibited normal cell attachment. Based on ongoing gene expression profiling experiments on human astrocytoma tumors, we demonstrate increased expression of two proteins implicated in cell attachment, spreading and motility (GAP43 and T-cadherin) in Nf1+/- and Nf1-/- astrocytes. These results support the emerging notion that tumor suppressor gene heterozygosity results in abnormalities in cell function that may contribute to the pathogenesis of non-tumor phenotypes in NF1.

Animals↗
PubMed2000

Schwann cells harbor the somatic NF1 mutation in neurofibromas: evidence of two different Schwann cell subpopulations.

Neurofibromas are one of the most characteristic features of neurofibromatosis type 1 (NF1), an inherited autosomal-dominant neurogenetic disorder affecting 1 in 3500 individuals worldwide. These benign tumors mainly consist of Schwann cells (SCs) and fibroblasts. Recent evidence demonstrates that somatic mutations at the NF1 gene are found in neurofibromas, but it has not been demonstrated whether SCs, fibroblasts and/or both cell types bear a somatic loss of NF1. We recently established a cell culture system that allows selective expansion of human SCs from neurofibromas. We cultured pure populations of SCs and fibroblasts derived from 10 neurofibromas with characterized NF1 mutations and found that SCs but not fibroblasts harbored a somatic mutation at the NF1 locus in all studied tumors. Furthermore, by culturing neurofibroma-derived SCs under different in vitro conditions we were able to obtain two genetically distinct SC subpopulations: NF1(-/-) and NF1(+/-). These data strongly support the idea that NF1 mutations in SCs, but not in fibroblasts, correlate to neurofibroma formation and demonstrate that only a portion of SCs in neurofibromas have mutations in both NF1 alleles.

Cell Division↗
PubMed2006

Molecular pathogenesis of multiple gastrointestinal stromal tumors in NF1 patients.

Gastrointestinal stromal tumors (GISTs) are the most common mesenchymal tumors of the gastrointestinal tract. KIT and PDGFRA activating mutations are the oncogenic mechanisms in most sporadic GISTs. In addition to sporadic occurrences, GISTs are increasingly being recognized in association with neurofibromatosis type 1 (NF1), yet the underlying pathogenic mechanism remains elusive. To gain an insight into the mechanisms underlying GIST formation in NF1 patients, we studied seven GISTs from three NF1 patients with a combination of different techniques: mutation analysis (KIT, PDGFRA and NF1), western blotting, array CGH and ex vivo imatinib response experiments. We demonstrate that (i) the NF1-related GISTs do not have KIT or PDGFRA mutations, (ii) the molecular event underlying GIST development in this patient group is a somatic inactivation of the wild-type NF1 allele in the tumor and (iii) inactivation of neurofibromin is an alternate mechanism to (hyper) activate the MAP-kinase pathway, while the JAK-STAT3 and PI3K-AKT pathways are less activated in NF1-related GIST compared with sporadic GISTs. In conclusion, we report for the first time the molecular pathogenesis of GISTs in NF1 individuals and demonstrate that this type of tumor clearly belongs to the spectrum of clinical symptoms in NF1.

Adult↗