NF1 Loss Research Articles

Highlights from Recent Cancer Literature

Highlights from Recent Cancer Literature

Most Human Non-GCIMP Glioblastoma Subtypes Evolve from a Common Proneural-like Precursor Glioma

To understand the relationships between the non-GCIMP glioblastoma (GBM) subgroups, we performed mathematical modeling to predict the temporal sequence of driver events during tumorigenesis. The most common order of evolutionary events is 1) chromosome (chr) 7 gain and chr10 loss, followed by 2) CDKN2A loss and/or TP53 mutation, and 3) alterations canonical for specific subtypes. We then developed a computational methodology to identify drivers of broad copy number changes, identifying PDGFA (chr7) and PTEN (chr10) as driving initial nondisjunction events. These predictions were validated using mouse modeling, showing that PDGFA is sufficient to induce proneural-like gliomas and that additional NF1 loss converts proneural to the mesenchymal subtype. Our findings suggest that most non-GCIMP mesenchymal GBMs arise as, and evolve from, a proneural-like precursor.

Combined MEK inhibition and BMP2 treatment promotes osteoblast differentiation and bone healing in Nf1Osx -/- mice.

Neurofibromatosis type I (NF1) is an autosomal dominant disease with an incidence of 1/3000, caused by mutations in the NF1 gene, which encodes the RAS/GTPase-activating protein neurofibromin. Non-bone union after fracture (pseudarthrosis) in children with NF1 remains a challenging orthopedic condition to treat. Recent progress in understanding the biology of neurofibromin suggested that NF1 pseudarthrosis stems primarily from defects in the bone mesenchymal lineage and hypersensitivity of hematopoietic cells to TGFβ. However, clinically relevant pharmacological approaches to augment bone union in these patients remain limited. In this study, we report the generation of a novel conditional mutant mouse line used to model NF1 pseudoarthrosis, in which Nf1 can be ablated in an inducible fashion in osteoprogenitors of postnatal mice, thus circumventing the dwarfism associated with previous mouse models where Nf1 is ablated in embryonic mesenchymal cell lineages. An ex vivo-based cell culture approach based on the use of Nf1(flox/flox) bone marrow stromal cells showed that loss of Nf1 impairs osteoprogenitor cell differentiation in a cell-autonomous manner, independent of developmental growth plate-derived or paracrine/hormonal influences. In addition, in vitro gene expression and differentiation assays indicated that chronic ERK activation in Nf1-deficient osteoprogenitors blunts the pro-osteogenic property of BMP2, based on the observation that only combination treatment with BMP2 and MEK inhibition promoted the differentiation of Nf1-deficient osteoprogenitors. The in vivo preclinical relevance of these findings was confirmed by the improved bone healing and callus strength observed in Nf1osx (-/-) mice receiving Trametinib (a MEK inhibitor) and BMP2 released locally at the fracture site via a novel nanoparticle and polyglycidol-based delivery method. Collectively, these results provide novel evidence for a cell-autonomous role of neurofibromin in osteoprogenitor cells and insights about a novel targeted approach for the treatment of NF1 pseudoarthrosis.

CELL INTRINSIC SEXUAL DIMORPHISM IN THE RB AND P21 PATHWAYS UNDERLIES MALE PREDOMINANCE IN GBM

BACKGROUND: Male prevalence across histological subtypes of brain tumors is well known but unexplained. The effects of sex on human disease frequently result from acute actions of circulating sex hormones on cellular physiology and immune function. However, differences in brain tumor rates between males and females are comparable in prepubertal children, and pre and post-menopausal adults, suggesting that alternate mechanisms may underlie this disparity. Here we show that sex-specific differences exist in thresholds for malignant transformation within the astrocyte lineage and that this can contribute to male predominance in the most common brain tumor, glioblastoma (GBM). METHODS: Analysis of three publically accessible databases was utilized to determine whether sex differences are equally present in each of the four molecular subtypes of GBM. Stepwise transformation was modeled for Mesenchymal GBM in separate male and female murine astrocyte cultures by sequential inactivation of neurofibromin (NF1) and p53. Thresholds for transformation were measured in soft agar assays and with in vivo tumorigenesis assays. The molecular basis for differences in thresholds for transformation between male and female astrocytes was investigated in evaluations of stem cell induction, Rb inactivation and p21 activation. RESULTS: Significant male predominance was consistently observed in Proneural and Mesenchymal subtypes of GBM. We modeled Mesenchymal subtype GBM with combined loss of Nf1 and p53 function through cre-mediated knock-out of Nf1 (Nf1-/-) and expression of a dominant negative p53 construct (DNp53). These changes induced a subpopulation of cells with clonogenic, stem cell function in male but not female astrocytes. Male Nf1-/-,DNp53 astrocytes exhibited significantly greater growth compared to female Nf1-/-,DNp53 astrocytes. In addition, male but not female Nf1-/-,DNp53 astrocytes were transformed with either EGF treatment or in vivo implantation. Male Nf1-/-,DNp53 astrocytes exhibited greater in vivo tumorigencitiy regardless of the sex of the recipient mouse. Induced intracranial tumors were diagnosed as grade 4 astrocytomas based on standard histological features. Enhanced stem cell function and tumorigenicity in male Nf1-/-,DNp53 astrocytes was associated with greater inactivation of Rb and less p21 activation compared to female Nf1-/-,DNp53 astrocytes. CONCLUSIONS: Sex differences in cancer, including GBM can involve cell intrinsic sexual dimorphism in tumor suppressor pathways resulting in different thresholds for transformation in males and females. These results suggest that tumor suppressor and oncogene mechanisms should be evaluated in a sex-specific fashion and that screening and treatment of GBM and other cancers may need to be sex-specific. SECONDARY CATEGORY: n/a.

Loss of NF1 in Cutaneous Melanoma Is Associated with RAS Activation and MEK Dependence

Melanoma is a disease characterized by lesions that activate ERK. Although 70% of cutaneous melanomas harbor activating mutations in the BRAF and NRAS genes, the alterations that drive tumor progression in the remaining 30% are largely undefined. Vemurafenib, a selective inhibitor of RAF kinases, has clinical utility restricted to BRAF-mutant tumors. MEK inhibitors, which have shown clinical activity in NRAS-mutant melanoma, may be effective in other ERK pathway-dependent settings. Here, we investigated a panel of melanoma cell lines wild type for BRAF and NRAS to determine the genetic alteration driving their transformation and their dependence on ERK signaling in order to elucidate a candidate set for MEK inhibitor treatment. A cohort of the BRAF/RAS wild type cell lines with high levels of RAS-GTP had loss of NF1, a RAS GTPase activating protein. In these cell lines, the MEK inhibitor PD0325901 inhibited ERK phosphorylation, but also relieved feedback inhibition of RAS, resulting in induction of pMEK and a rapid rebound in ERK signaling. In contrast, the MEK inhibitor trametinib impaired the adaptive response of cells to ERK inhibition, leading to sustained suppression of ERK signaling and significant antitumor effects. Notably, alterations in NF1 frequently co-occurred with RAS and BRAF alterations in melanoma. In the setting of BRAF(V600E), NF1 loss abrogated negative feedback on RAS activation, resulting in elevated activation of RAS-GTP and resistance to RAF, but not MEK, inhibitors. We conclude that loss of NF1 is common in cutaneous melanoma and is associated with RAS activation, MEK-dependence, and resistance to RAF inhibition.

Deciphering root causes of intrinsic BRAF inhibitor resistance in melanoma: ushering in a new genomics case reports feature for Annals of Oncology

Deciphering root causes of intrinsic BRAF inhibitor resistance in melanoma: ushering in a new genomics case reports feature for Annals of Oncology

Proteomic screening identifies a YAP-driven signaling network linked to tumor cell proliferation in human schwannomas

Inactivation of the NF2 gene predisposes to neurofibromatosis type II and the development of schwannomas. In vitro studies have shown that loss of NF2 leads to the induction of mitogenic signaling mediated by receptor tyrosine kinases (RTKs), MAP kinase, AKT, or Hippo pathways. The goal of our study was to evaluate the expression and activity of these signaling pathways in human schwannomas in order to identify new potential therapeutic targets. Large sets of human schwannomas, totaling 68 tumors, were analyzed using complementary proteomic approaches. RTK arrays identified the most frequently activated RTKs. The correlation between the expression and activity of signaling pathways and proliferation of tumor cells using Ki67 marker was investigated by reverse-phase protein array (RRPA). Finally, immunohistochemistry was used to evaluate the expression pattern of signaling effectors in the tumors. We showed that Her2, Her3, PDGFRß, Axl, and Tie2 are frequently activated in the tumors. Furthermore, RRPA demonstrated that Ki67 levels are linked to YAP, p-Her3, and PDGFRß expression levels. In addition, Her2, Her3, and PDGFRß are transcriptional targets of Yes-associated protein (YAP) in schwannoma cells in culture. Finally, we observed that the expression of these signaling effectors is very variable between tumors. Tumor cell proliferation in human schwannomas is linked to a signaling network controlled by the Hippo effector YAP. Her2, Her3, PDGFRß, Axl, and Tie2, as well as YAP, represent potentially valuable therapeutic targets. However, the variability of their expression between tumors may result in strong differences in the response to targeted therapy.

Acquired Resistance to Dasatinib in Lung Cancer Cell Lines Conferred byDDR2Gatekeeper Mutation andNF1Loss

The treatment of non-small cell lung cancer has evolved dramatically over the past decade with the adoption of widespread use of effective targeted therapies in patients with distinct molecular alterations. In lung squamous cell carcinoma (lung SqCC), recent studies have suggested that DDR2 mutations are a biomarker for therapeutic response to dasatinib and clinical trials are underway testing this hypothesis. Although targeted therapeutics are typically quite effective as initial therapy for patients with lung cancer, nearly all patients develop resistance with long-term exposure to targeted drugs. Here, we use DDR2-dependent lung cancer cell lines to model acquired resistance to dasatinib therapy. We perform targeted exome sequencing to identify two distinct mechanisms of acquired resistance: acquisition of the T654I gatekeeper mutation in DDR2 and loss of NF1. We show that NF1 loss activates a bypass pathway, which confers ERK dependency downstream of RAS activation. These results indicate that acquired resistance to dasatinib can occur via both second-site mutations in DDR2 and by activation of bypass pathways. These data may help to anticipate mechanisms of resistance that may be identified in upcoming clinical trials of anti-DDR2 therapy in lung cancer and suggest strategies to overcome resistance.

Rapid target gene validation in complex cancer mouse models using re‐derived embryonic stem cells

Human cancers modeled in Genetically Engineered Mouse Models (GEMMs) can provide important mechanistic insights into the molecular basis of tumor development and enable testing of new intervention strategies. The inherent complexity of these models, with often multiple modified tumor suppressor genes and oncogenes, has hampered their use as preclinical models for validating cancer genes and drug targets. In our newly developed approach for the fast generation of tumor cohorts we have overcome this obstacle, as exemplified for three GEMMs; two lung cancer models and one mesothelioma model. Three elements are central for this system; (i) The efficient derivation of authentic Embryonic Stem Cells (ESCs) from established GEMMs, (ii) the routine introduction of transgenes of choice in these GEMM-ESCs by Flp recombinase-mediated integration and (iii) the direct use of the chimeric animals in tumor cohorts. By applying stringent quality controls, the GEMM-ESC approach proofs to be a reliable and effective method to speed up cancer gene assessment and target validation. As proof-of-principle, we demonstrate that MycL1 is a key driver gene in Small Cell Lung Cancer.

Stroke Literature Synopses: Basic Science

<i>Stroke</i> Literature Synopses: Basic Science

Neuregulin-1 overexpression and Trp53 haploinsufficiency cooperatively promote de novo malignant peripheral nerve sheath tumor pathogenesis

Malignant peripheral nerve sheath tumors (MPNSTs) are Schwann cell-derived malignancies that arise from plexiform neurofibromas in patients with mutation of the neurofibromin 1 (NF1) gene. We have shown that the growth factor neuregulin-1 (NRG1) also contributes to human neurofibroma and MPNST pathogenesis and that outbred C57BL/6J × SJL/J transgenic mice overexpressing NRG1 in Schwann cells (P0-GGFβ3 mice) recapitulate the process of neurofibroma-MPNST progression. However, it is unclear whether NRG1 acts predominantly within NF1-regulated signaling cascades or instead activates other essential cascades that cooperate with NF1 loss to promote tumorigenesis. We now report that tumorigenesis is suppressed in inbred P0-GGFβ3 mice on a C57BL/6J background. To determine whether NRG1 overexpression interacts with reduced Nf1 or Trp53 gene dosage to "unmask" tumorigenesis in these animals, we followed cohorts of inbred P0-GGFβ3;Nf1+/−, P0-GGFβ3;Trp53+/− and control (P0-GGFβ3, Nf1+/− and Trp53+/−) mice for 1 year. We found no reduction in survival or tumors in control and P0-GGFβ3;Nf1+/− mice. In contrast, P0-GGFβ3;Trp53+/− mice died on average at 226 days, with MPNSTs present in 95 % of these mice. MPNSTs in inbred P0-GGFβ3;Trp53+/− mice arose de novo from micro-MPNSTs that uniformly develop intraganglionically. These micro-MPNSTs are of lower grade (WHO grade II-III) than the major MPNSTs (WHO grade III-IV); array comparative genomic hybridization showed that lower grade MPNSTs also had fewer genomic abnormalities. Thus, P0-GGFβ3;Trp53+/− mice represent a novel model of low- to high-grade MPNST progression. We further conclude that NRG1 promotes peripheral nervous system neoplasia predominantly via its effects on the signaling cascades affected by Nf1 loss.

Abstract C138: Loss of NF1 in melanoma cell lines is associated with active Ras and dependence on MEK even in the absence of BRAF or NRAS mutation.

Abstract Though two-thirds of cutaneous melanomas harbor activating mutations in the BRAF and NRAS genes, the alterations that drive tumor progression in the roughly 30% of melanoma tumors wild-type for BRAF and NRAS remain largely uncharacterized. The selective RAF inhibitors vemurafenib and dabrafenib inhibit MAPK pathway activity only in BRAF mutant cells, thus their clinical utility is restricted to patients with BRAF mutant tumors. MEK inhibitors, which have broader antitumor activity and have shown promising activity in NRAS mutant melanoma, may be effective in a broader range of MAPK pathway-dependent tumors. We performed a functional and genomic analysis of melanoma cell lines wild-type for BRAF and NRAS to determine whether occult mutations in RAS signaling were present. Elevated RAS-GTP was common in BRAF/NRAS wild-type melanoma cell lines, a subset of which exhibited total loss of NF1 protein expression. The proliferation of NF1-null melanoma cells was dependent upon MEK, though the cellular potency of several allosteric MEK inhibitors that are currently in clinical testing (PD0325901, AZD6244, MEK162 and trametinib) varied widely in NF1-null melanoma cells. The greatest antitumor activity was noted with trametinib, a MEK inhibitor that also blocks RAF mediated phosphorylation of MEK. Notably, alterations in NF1 also co-occurred with RAS and BRAF mutations in both cell lines and human melanomas. In the setting of BRAF co-mutation, loss of NF1 abrogated upstream negative feedback on RAS activation resulting in constitutive expression of RAS-GTP and resistance to RAF but not MEK inhibition. In summary, NF1 loss is a common event in cutaneous melanoma that is associated with RAS activation, MEK dependence and RAF inhibitor resistance. Citation Information: Mol Cancer Ther 2013;12(11 Suppl):C138. Citation Format: Moriah H. Nissan, Christine Pratilas, Alexis Jones, Helen Won, Li Kong, Zhan Yao, Taha Merghoub, Antoni Ribas, Paul Chapman, Rona Yaeger, Barry Taylor, Nikolaus Shultz, Michael F. Berger, Neal Rosen, David B. Solit. Loss of NF1 in melanoma cell lines is associated with active Ras and dependence on MEK even in the absence of BRAF or NRAS mutation. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2013 Oct 19-23; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2013;12(11 Suppl):Abstract nr C138.

Abstract B14: Deciphering individual roles of p53 and NF1 in suppressing gliomagenesis

Abstract Cancer is difficult to treat because it is a disease caused by multiple genetic alterations. Understanding how individual mutations contribute to pathogenesis and how they cooperate to aid malignancy offers deep insights of tumorigenic mechanisms that will facilitate the design of effective treatment. However, conventional methods, including most mouse cancer models, do not offer the temporal and spatial resolution required to study tumorigenesis in great details, especially because single gene mutations rarely lead to detectable malignancy. To resolve this issue, our lab uses a novel mouse model termed MADM (Mosaic Analysis with Double Markers) to analyze the contribution of individual mutations to aberrant behaviors of tumor cell of origin during pre-transforming stages. Starting with a mouse heterozygous for a TSG, MADM can generate sparse mutant cells that are null for the TSG via Cre-loxP mediated inter-chromosomal mitotic recombination. Concurrently, MADM unambiguously labels mutant cells with GFP and their wild-type sibling cells with RFP, allowing us to precisely analyze behavioral changes of green mutant cells, using their sibling red cells as the internal control. Using MADM to model glioblastoma, the most common and aggressive malignant primary brain tumor, our lab previously demonstrated that oligodendrocyte precursor cell (OPC) is the cell of origin. Using MADM to generate p53 and NF1 double-null OPCs, we found that mutant OPCs dramatically over-expanded at the pre-transforming stage compared to WT sibling cells. Further analysis indicated that mutant OPCs manifest augmented proliferative activities and halted differentiation processes. However, it is still unknown what is the individual contribution of the loss of p53 and NF1 and how their cooperativity leads to malignant transformation. Utilizing MADM, we generated genetic mosaic mice with individual loss of either p53 or NF1 in OPCs and determined the cellular property changes of mutant cells, including proliferative rate, differentiation ability, overall expansion, and malignant transformation. We found that, while the mosaic loss of NF1 alone is sufficient to lead to increased proliferation and impaired differentiation of mutant cells, it is insufficient to lead to malignancy even though mutant cells overwhelm the mouse brain, suggesting that p53 plays critical gatekeeping roles in gliomagenesis. On the other hand, when we examined brains containing p53-null OPCs, we were surprised to find that the loss of p53 alone had no detectable effect on cell number, proliferation and differentiation of mutant cells. We reasoned that the tumor suppressing functions of p53 may only be manifested in an NF1 mutant background, and thus generated a new mosaic model in which all OPCs are NF1-null while green cells are p53 null and red ones are p53 WT. Surprisingly, we still found no differences in cell number, proliferation, or differentiation between green and red cells, suggesting that p53 suppress gliomagenesis through some unknown mechanisms. In summary, our data suggested that NF1 loss leads to glioma initiation by promoting proliferation and inhibiting differentiation of OPCs while p53 loss only contributes to later stage of glioma progressions, and that an effective treatment paradigm would need to address all these mechanisms to halt malignancy. Citation Format: Phillippe Gonzalez, Chong Liu, Hui Zong. Deciphering individual roles of p53 and NF1 in suppressing gliomagenesis. [abstract]. In: Proceedings of the Third AACR International Conference on Frontiers in Basic Cancer Research; Sep 18-22, 2013; National Harbor, MD. Philadelphia (PA): AACR; Cancer Res 2013;73(19 Suppl):Abstract nr B14.

Injury Signals Cooperate with Nf1 Loss to Relieve the Tumor-Suppressive Environment of Adult Peripheral Nerve

Schwann cells are highly plastic cells that dedifferentiate to a progenitor-like state following injury. However, deregulation of this plasticity, may be involved in the formation of neurofibromas, mixed-cell tumors of Schwann cell (SC) origin that arise upon loss ofNF1. Here, we show that adult myelinating SCs (mSCs) are refractory to Nf1 loss. However, in thecontext of injury, Nf1-deficient cells display opposing behaviors along the wounded nerve; distal totheinjury, Nf1(-/-) mSCs redifferentiate normally, whereas at the wound site Nf1(-/-) mSCs give rise toneurofibromas in both Nf1(+/+) and Nf1(+/-) backgrounds. Tracing experiments showed that distinct cell types within the tumor derive from Nf1-deficient SCs. This model of neurofibroma formation demonstrates that neurofibromas can originate from adult SCs and that the nerve environment can switch from tumor suppressive to tumor promoting at a site of injury. These findings have implications for both the characterization and treatment of neurofibromas.

New strategies in pediatric gliomas: molecular advances in pediatric low-grade gliomas as a model.

Pediatric low-grade gliomas (pLGG) account for more brain tumors in children than any other histologic subtype. While surgery, chemotherapy and radiation remain the mainstay of upfront treatment, recent advances in molecular interrogation of pLGG have shown a small number of recurring genetic mutations in these tumors that might be exploited therapeutically. Notable findings include abnormalities in the RAS/MAP kinase pathway such as NF-1 loss or BRAF activation and mTOR activation. Recent identification of activating re-arrangements in c-MYB and MYBL1 in pediatric diffuse astrocytoma also provide candidates for therapeutic intervention. Targeting these molecularly identified pathways may allow for improved outcomes for patients as pediatric oncology moves into the era of biology-driven medicine.

Nf1 Loss and Ras Hyperactivation in Oligodendrocytes Induce NOS-Driven Defects in Myelin and Vasculature

SUMMARYPatients with neurofibromatosis type 1 (NF1) and Costello syndrome Rasopathy have behavioral deficits. In NF1 patients, these may correlate with white matter enlargement and aberrant myelin. To model these features, we induced Nf1 loss or HRas hyperactivation in mouse oligodendrocytes. Enlarged brain white matter tracts correlated with myelin decompaction, downregulation of claudin-11, and mislocalization of connexin-32. Surprisingly, non-cell-autonomous defects in perivascular astrocytes and the blood-brain barrier (BBB) developed, implicating a soluble mediator. Nitric oxide (NO) can disrupt tight junctions and gap junctions, and NO and NO synthases (NOS1–NOS3) were upregulated in mutant white matter. Treating mice with the NOS inhibitor NG-nitro-L-arginine methyl ester or the antioxidant N-acetyl cysteine corrected cellular phenotypes. CNP-HRasG12V mice also displayed locomotor hyperactivity, which could be rescued by antioxidant treatment. We conclude that Nf1/Ras regulates oligodendrocyte NOS and that dysregulated NO signaling in oligodendrocytes can alter the surrounding vasculature. The data suggest that anti-oxidants may improve some behavioral deficits in Rasopathy patients.

Global Profiling in Vestibular Schwannomas Shows Critical Deregulation of MicroRNAs and Upregulation in Those Included in Chromosomal Region 14q32

BackgroundVestibular schwannomas are benign tumors that arise from Schwann cells in the VIII cranial pair and usually present NF2 gene mutations and/or loss of heterozygosity on chromosome 22q. Deregulation has also been found in several genes, such as ERBB2 and NRG1. MicroRNAs are non-coding RNAs approximately 21 to 23 nucleotides in length that regulate mRNAs, usually by degradation at the post-transcriptional level.MethodsWe used microarray technology to test the deregulation of miRNAs and other non-coding RNAs present in GeneChip miRNA 1.0 (Affymetrix) over 16 vestibular schwannomas and 3 control-nerves, validating 10 of them by qRT-PCR.FindingsOur results showed the deregulation of 174 miRNAs, including miR-10b, miR-206, miR-183 and miR-204, and the upregulation of miR-431, miR-221, miR-21 and miR-720, among others. The results also showed an aberrant expression of other non-coding RNAs. We also found a general upregulation of the miRNA cluster located at chromosome 14q32.ConclusionOur results suggest that several miRNAs are involved in tumor formation and/or maintenance and that global upregulation of the 14q32 chromosomal site contains miRNAs that may represent a therapeutic target for this neoplasm.

Abstract 355: Generation of a murine model of Neurofibromatosis Type 2 that accurately recapitulates the spontaneous development of vestibular and spinal schwannomas found in NF2 patients.

Abstract Neurofibromatosis type 2 (NF2) is a genetic disease resulting from germline loss of the NF2 tumor suppressor gene. The hallmark of NF2 is hearing and vestibular loss of function in young adults caused by the development of vestibular schwannomas, which occur bilaterally in nearly all patients and are associated with homozygous loss of NF2. Individuals affected with NF2 also acquire schwannomas of other cranial, spinal and peripheral nerves. Importantly, non-familial schwannomas, the most common tumor of the peripheral nervous system, are also caused by bi-allelic loss of NF2 gene function. A major limitation in the identification of genetic and pharmacologic targets for schwannomas has been the lack of a robust preclinical model that accurately recapitulates human NF2 disease. In order to develop a more robust model, we intercrossed a mouse expressing Cre Recombinase under the control of the 3.9PeriCre promoter with an Nf2 conditional knockout mouse previously generated by Dr. Marco Giovannini to conditionally ablate Nf2 in neural crest-derived cell populations. Histological analysis of the dorsal root ganglion (DRG) and proximal spinal nerves of 3.9PeriCre+;Nf2flox/flox mice revealed that intercrossed mice spontaneously develop tumors between 8 and 10 months at every single spinal level. Microscopic analysis implicated these tumors as schwannomas, as they display a dense pattern of cellularity consistent with the established criteria of GEM schwannoma, including S100β1 positivity. Quantitation of the DRG volume indicated that 3.9PeriCre+ mice have a statistically significant increase when compared to 3.9PeriCre- littermates. FDG-PET studies corroborated this finding, as comparative studies showed an increase in the metabolic activity of paraspinal tumors found in 3.9PeriCre+ mice. Auditory Brainstem Response testing has revealed that 3.9PeriCre+ mice acquire an age-dependent increase in hearing threshold by 8 months when compared to age-matched 3.9PeriCre- controls. Histological analysis of Cranial Nerve VIII confirmed that the hearing loss was directly associated with the development of vestibular schwannomas. To test for concomitant vestibular loss of function, three different behavioral studies (contact righting, trunk curl, and swim) were performed to isolate and test the integrity of the vestibular sense in 3.9PeriCre;Nf2flox/flox mice. These studies indicated that 3.9PeriCre+ mice develop vestibular deficits, as all three studies identified highly significant differences between the two genotypes. Collectively, these genetically engineered mice acquire a physiologic phenotype that closely recapitulates important features of human NF2 disease and provides opportunities for testing putative therapeutic targets using genetic intercrosses or novel small molecule inhibitors. Citation Format: Jeff R. Gehlhausen, Su Jung Park, Matthew Shew, Wade Clapp, Charles Yates. Generation of a murine model of Neurofibromatosis Type 2 that accurately recapitulates the spontaneous development of vestibular and spinal schwannomas found in NF2 patients. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 355. doi:10.1158/1538-7445.AM2013-355

Abstract 358: Nf1 inactivation in NG2-cells is not sufficient for murine optic glioma formation.

Abstract Individuals with the tumor predisposition syndrome, neurofibromatosis 1 (NF1), are prone to development of low-grade astrocytomas (gliomas). These tumors frequently include optic pathway gliomas predominantly arising in young children. We have previously developed several Nf1 genetically-engineered mouse (GEM) strains that form optic gliomas similar to those that occur in children with NF1. However, in the optic nerve, there are two types of potential neuroglial progenitors, GFAP+ and NG2+ cells. This latter population has been shown to represent a potential cell of origin for rat malignant gliomas, suggesting that NG2+ progenitors may represent the initiating cell for Nf1 optic glioma. In this study, we employed a complementary series of in vitro and in vivo approaches to determine whether NG2+ cells could give rise to Nf1 optic glioma. First, we demonstrate that Nf1 loss in NG2+ cells does not increase glial cell proliferation in vitro. Second, NG2-Cre-expressing cells give rise to all three macroglial lineages (astrocytes, NG2+ cells, and oligodendrocytes) in vivo, similar to GFAP-Cre-expressing cells that drive Nf1 optic glioma formation. Third, in striking contrast to the GFAP-Cre strain, Nf1 loss in NG2+ progenitor cells in vivo is insufficient for optic gliomagenesis. Together, these data exclude NG2+ cells as the likely cell of origin for NF1-associated optic glioma and establish a model of gliomagenesis in which Nf1 loss occurs in specific neuroglial progenitors during embryonic development. Citation Format: Anne C. Solga, Scott M. Gianino, David H. Gutmann. Nf1 inactivation in NG2-cells is not sufficient for murine optic glioma formation. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 358. doi:10.1158/1538-7445.AM2013-358

Neurofibromin interacts with the cytoplasmic Dynein Heavy Chain 1 in melanosomes of human melanocytes

Neurofibromin (NF1) is encoded by the NF1 tumour suppressor gene. Mutations result in a disorder known as Neurofibromatosis Type 1 (NF-1), and patients are often diagnosed due to the presence of unusual pigmentary patterns that include Café au lait macules (CALMs). Little is known about how loss of NF1 results in pigmentary defects in melanocytes. We sought to identify novel NF1 interacting proteins and elucidate the molecular mechanisms underlying the pigmentary defects. The cytoplasmic Dynein Heavy Chain 1 (DHC) was found to interact with NF1 along microtubules in vesicular structures identified to be melanosomes. Our studies suggest that NF1 is involved in melanosomal localization, and that disruptions in NF1–DHC interactions may contribute to the abnormal pigmentary features commonly associated with this debilitating syndrome.