Disease relevance of NF1

• The neurofibromatosis type 1 (NF1) protein contains a region of significant sequence similarity to ras p21 GTPase-activating protein (GAP) and the yeast IRA1 gene product [1].
• We describe an amino acid substitution in the NF1 GRD, altering Lys-1423, that has occurred in three tumor types: colon adenocarcinoma, myelodysplastic syndrome, and anaplastic astrocytoma, and in one family with neurofibromatosis 1 [2].
• Defects in the NF1 gene have been implicated in the inherited disorder neurofibromatosis type 1, which is characterized by several developmental abnormalities including an increased frequency of benign and malignant tumours of neural crest origin (neurofibromas and neurofibrosarcomas respectively) [3].
• Although pheochromocytoma susceptibility may be associated with germline mutations in the tumor-suppressor genes VHL and NF1 and in the proto-oncogene RET, the genetic basis for most cases of nonsyndromic familial pheochromocytoma is unknown [4].
• Neurofibromatosis type 1 (NF1) is a common familial tumour syndrome with multiple clinical features such as neurofibromas, café-au-lait spots (CLS), iris Lisch nodules, axillary freckling, optic glioma, specific bone lesions and an increased risk of malignant tumours [5].

Psychiatry related information on NF1

• In children, brain symptoms cause most of the morbidity in TSC, and nerve sheath and nervous system tumors as well as learning disabilities cause major morbidity in NF1 [6].
• Large deletions of the NF1 locus occur in 5 to 10% of patients with neurofibromatosis and are commonly associated with specific additional abnormalities characterized by mental retardation, dysmorphic features, and intellectual impairment [7].
• Comorbid affective disorders, anxiety disorders, and suicide are frequently observed during NF1 [8].
• Those with NF1 and ADHD were rated significantly poorer on the Child Behavior Checklist (CBCL) than were the NF1 control group [9].
• There were increased numbers of children with NF1 achieving scores in the borderline and abnormal range for ratings of peer problems (p < 0.001), hyperactivity (p < 0.001), emotional symptoms (p < 0.001), and conduct disorder (p < 0.05) [10].

High impact information on NF1

• We present a detailed study of genetic variation and underlying recombination processes in two copies of an LCR (NF1REPa and NF1REPc) on chromosome 17 involved in the generation of NF1 microdeletions and in a third copy (REP19) on chromosome 19 from which the others originated over 6.7 million years ago [11].
• Mitotic recombination effects homozygosity for NF1 germline mutations in neurofibromas [12].
• By comparing molecular and fluorescent in situ hybridization analysis of these cells, we demonstrate mitotic recombination is the mechanism underlying this type of loss of heterozygosity leading to reduction to homozygosity of NF1 germline mutation [12].
• NF1 tumor suppressor gene function: narrowing the GAP [13].
• Pure populations of neurofibroma-derived Schwann cells bearing both NF1 mutated alleles (NF1-/-) have been isolated from different neurofibromas showing loss of heterozygosity of nearly the entire 17q chromosome [12].

Chemical compound and disease context of NF1

• C-->U RNA editing of neurofibromatosis 1 (NF1) mRNA changes an arginine (CGA) to a UGA translational stop codon, predicted to result in translational termination of the edited mRNA [14].
• Also, this PP1/GL-2003 combination therapy has been proven to be very effective to suppress the estrogen-independent growth of an NF1-deficient multidrug/FK228-resistant human breast cancer (MDA-MB-231) xenograft in mice [15].
• The group of pheochromocytoma susceptibility genes includes, along with the tumor suppressor genes VHL and NF1, the proto-oncogene RET and the genes encoding succinate dehydrogenase subunit D and succinate dehydrogenase subunit B. Whether there is a common pathway among these different genes is still a matter of debate [16].
• The motor protein kinesin-1 links neurofibromin and merlin in a common cellular pathway of neurofibromatosis [17].
• Neurofibromin-deficient Schwann cells have increased lysophosphatidic acid dependent survival and migration-implications for increased neurofibroma formation during pregnancy [18].

Biological context of NF1

• Numerous point mutations found in NF1 patients or derived from genetic screening protocols can be analysed on the basis of the three-dimensional structural model, which also allows identification of the site where structural changes in a differentially spliced isoform are to be expected [19].
• Missense mutations found in NF1 patients map to NF1GRD, underscoring its importance for pathogenesis [19].
• To elucidate the extent of microheterogeneity at the deletion boundaries, we used single-copy DNA fragments from the extreme ends of the deleted segment to perform FISH on metaphase chromosomes from eight patients with NF1 who had large deletions [20].
• The analysis of neurofibromin transcripts from different neurofibromatosis type 1 (NF1) patients revealed the skipping of exons containing PTCs [21].
• Finally, adenovirus-mediated transfection of HepG2 cells revealed induction of editing of apoB RNA, along with preferential editing of NF1 transcripts containing exon 23A [14].

Anatomical context of NF1

• We used a genetic approach to test the hypothesis that NF1 negatively regulates myeloid cell growth through its effect on Ras [22].
• Neurofibromatosis type 1 (NF1) is a common genetic disorder which predisposes affected individuals to a variety of clinical features including tumors of the central and peripheral nervous systems [23].
• Loss of neurofibromin expression in NF1 patients is associated with elevated Ras activity and increased cell proliferation, predisposing to a variety of tumors of the peripheral and central nervous systems [24].
• NF1 siRNA induces characteristic morphological changes, such as excessive actin stress fiber formation, with elevated negative phosphorylation levels of cofilin, which regulates actin cytoskeletal reorganization by depolymerizing and severing actin filaments [24].
• Here we describe the identification of growth factors that are upregulated in NF1-/- mouse Schwann cells and are potential regulators of angiogenesis and cell growth [25].

Associations of NF1 with chemical compounds

• Intron 1, which is 100-140 kb long in humans, spans 2575 bp in the Fugu NF1 gene [26].
• Comparison of the primary sequences of RasGAPs shows two invariant arginine residues (Arg1276 and Arg1391 of neurofibromin) [27].
• Ras proteins are guanine-nucleotide binding proteins that have a low intrinsic GTPase activity that is enhanced 10(5)-fold by the GTPase-activating proteins (GAPs) p120-GAP and neurofibromin [27].
• In this study, site-directed mutagenesis was used to change each of these residues in the catalytic domain of neurofibromin (NF1-334) to alanine [27].
• We now show that, in response to EGF, neurofibromin is in vivo phosphorylated on serine residues by PKC-alpha, in human, rat, and avian CNS cells and cell lines [28].
• Primary AML blasts without functional NF1, unlike blasts with functional NF1, displayed sensitivity to rapamycin-induced apoptosis, thus identifying a dependence on mammalian target of rapamycin (mTOR) signaling for survival [29].

Physical interactions of NF1

• Neurofibromatosis type 1 (NF1) and tuberous sclerosis complex (TSC) represent two neurocutaneous disorders in which affected individuals develop tumors at an increased frequency [30].
• Moreover, neurofibromin exists in a complex with syndecan and CASK in vivo, as evidenced by their coimmunoprecipitation from rat brain [31].
• Footprinting and gel retardation analysis indicated that the transcription factor Sp1 binds to the NF-1 promoter [32].
• Transcription of the rat p53 gene is mediated by factor binding to two recognition motifs of NF1-like protein [33].
• NF1 binding correlated with the disappearance of ANT2 transcripts in quiescent cells [34].

Enzymatic interactions of NF1

• Calmodulin kinase II (CAMKII) is phosphorylated in response to PDGF-BB in the NF1 MPNST cell lines, whereas no phosphorylation of CAMKII was observed in nhSCs [35].

Regulatory relationships of NF1

• In addition, the exogenous expression of the NF1-GTPase-activating protein-related domain suppressed the NF1 siRNA-induced phenotypes [24].
• There may be a neurofibromin-induced and p21ras-mediated differentiation pathway of neuronal stem cells that is blocked in PNET [36].
• The GTPase of wild-type ras p21 was stimulated by NF1 GRD, but oncogenic mutants of ras p21 (Asp-12 and Val-12) were unaffected, and the GTPase of an effector mutant (Ala-38) was only weakly stimulated [1].
• CONCLUSIONS: These results depict an early fetal period when the NF1 tumor suppressor is abundantly expressed in epidermis and associated with cytokeratin filaments [37].
• We now describe a sequence upstream of and partially overlapping the NF1 site that activates the MBP promoter in oligodendrocytes, but not in Cos-7 cells [38].

Other interactions of NF1

• When expressed in non-mammalian systems, the region of the NF1 gene homologous to p120GAP produces a protein with GAP-like activity [3].
• We mapped the MenX locus to the distal part of rat chromosome 4, excluding the homologs of the genes responsible for the MEN syndromes (RET and MEN1) and syndromes with an endocrine tumor component (VHL and NF1) [39].
• Taken together, the data support the hypothesis that C-->U RNA editing of the NF1 transcript occurs both in a subset of PNSTs and in an alternatively spliced form containing a downstream exon, presumably an optimal configuration for enzymatic deamination by apobec-1 [14].
• Genetic analysis is consistent with the hypothesis that NF1 limits myeloid cell growth through p21ras [22].
• These results point to kinesin-1 as a common denominator between NF1 and NF2 [17].

Analytical, diagnostic and therapeutic context of NF1

• The genomic structure of the Neurofibromatosis Type1 (NF1) gene of Fugu rubripes was investigated by sequence analysis of two overlapping cosmids [26].
• Further, RT-PCR analysis demonstrated the absence of expression of NF1 mRNA type I isoform only in the MB-231 cell lines [40].
• METHODS: The expression of NF1 protein was studied in developing human epidermis using western transfer analysis, indirect immunofluorescence, confocal laser scanning microscopy, immunoelectron microscopy, and in situ hybridization [37].
• EGF-induced PKC phosphorylation was prominent in the cysteine/serine-rich domain (CSRD) of neurofibromin, which lies in the N-terminus and upstream of the Ras-GAP domain (GRD), and this modification significantly increased the association of neurofibromin with actin in co-immunoprecipitations [28].
• In order to characterize the NF1 gene product, now called neurofibromin, we raised polyclonal antibodies against C- and N-terminal regions of neurofibromin and analyzed the protein by Western blot analysis and immunohistochemical studies of rat brain [41].

References