Neurofibromin regulates G protein-stimulated adenylyl cyclase activity.

Neurofibromatosis type 1 (NF1) is a dominant genetic disorder characterized by multiple benign and malignant nervous system tumors, and by learning defects in 45% of children with NF1 mutations. Studies of neurofibromin, the protein encoded by NF1, have focused on its functions in tumorigenesis and regulation of Ras activity; however, Drosophila NF1 regulates both Ras and cyclic AMP (cAMP) pathways. Expression of a human NF1 transgene rescued cAMP-related phenotypes in NF1 mutant flies (small body size and G protein-stimulated adenylyl cyclase (AC) activity defects), and neuropeptide- and G protein-stimulated AC activity were lower in Nf1-/- as compared to Nf1+/- mouse brains, demonstrating that neurofibromin regulates AC activity in both mammals and flies.     

Neurofibromin regulates somatic growth through the hypothalamic-pituitary axis

To study the role of the neurofibromatosis-1 (NF1) gene in mammalian brain development, we recently generated mice in which Nf1 gene inactivation occurs in neuroglial progenitor cells using the brain lipid binding protein (BLBP) promoter. We found that Nf1(BLBP)CKO mice exhibit significantly reduced body weights and anterior pituitary gland sizes. We further demonstrate that the small anterior pituitary size reflects loss of neurofibromin expression in the hypothalamus, leading to reduced growth hormone releasing hormone, pituitary growth hormone (GH) and liver insulin-like growth factor-1 (IGF1) production. Since neurofibromin both negatively regulates Ras activity and positively modulates cAMP levels, we examined the signaling pathway responsible for these abnormalities. While BLBP-mediated expression of an activated Ras molecule did not recapitulate the body weight and hypothalamic/pituitary defects, treatment of Nf1(BLBP)CKO mice with rolipram to increase cAMP levels resulted in a partial restoration of the body weight phenotype. Furthermore, conditional expression of the Ras regulatory GAP domain of neurofibromin also did not rescue the body weight or Igf1 mRNA defects in Nf1(BLBP)CKO mice. Collectively, these data demonstrate a critical role for neurofibromin in hypothalamic-pituitary axis function and provide further insights into the short stature and GH deficits seen in children with NF1.     

Nf1+/- mice have increased neointima formation via hyperactivation of a Gleevec sensitive molecular pathway

Neurofibromatosis type I (NF1) is a genetic disorder caused by mutations in the NF1 tumor suppressor gene. Neurofibromin is encoded by NF1 and functions as a negative regulator of Ras activity. Somatic mutations in the residual normal NF1 allele within cancers of NF1 patients is consistent with NF1 functioning as a tumor-suppressor. However, the prevalent non-malignant manifestations of NF1, including learning and bone disorders emphasize the importance of dissecting the cellular and biochemical effects of NF1 haploinsufficiency in multiple cell lineages. One of the least studied complications of NF1 involves cardiovascular disorders, including arterial occlusions that result in cerebral and visceral infarcts. NF1 vasculopathy is characterized by vascular smooth muscle cell (VSMC) accumulation in the intima area of vessels resulting in lumen occlusion. We recently showed that Nf1 haploinsufficiency increases VSMC proliferation and migration via hyperactivation of the Ras-Erk pathway, which is a signaling axis directly linked to neointima formation in diverse animal models of vasculopathy. Given this observation, we tested whether heterozygosity of Nf1 would lead to vaso-occlusive disease in genetically engineered mice in vivo. Strikingly, Nf1+/- mice have increased neointima formation, excessive vessel wall cell proliferation and Erk activation after vascular injury in vivo. Further, this effect is directly dependent on a Gleevec sensitive molecular pathway. Therefore, these studies establish an Nf1 model of vasculopathy, which mirrors features of human NF1 vaso-occlusive disease, identifies a potential therapeutic target and provides a platform to further dissect the effect of Nf1 haploinsufficiency in cardiovascular disease.     

Nf1-/- Schwann cell-conditioned medium modulates mast cell degranulation by c-Kit-mediated hyperactivation of phosphatidylinositol 3-kinase

Neurofibromatosis type 1 (NF1) is a common genetic disorder and is characterized by both malignant and nonmalignant neurofibromas, which are composed of Schwann cells, degranulating mast cells, fibroblasts, and extracellular matrix. We and others have previously shown that hyperactivation of the c-Kit pathway in an Nf1 haploinsufficient microenvironment is required for both tumor formation and progression. Mast cells play a key role in both tumorigenesis and neoangiogenesis via the production of matrix metalloproteinases, heparin, and a range of different growth factors. In the present study, we show that tumorigenic Schwann cells derived from Nf1(-/-) embryos promote increased degranulation of Nf1(+/-) mast cells compared with wild-type mast cells via the secretion of the Kit ligand. Furthermore, we used genetic intercrosses as well as pharmacological agents to link the hyperactivation of the p21(Ras)-phosphatidylinositol 3-kinase (PI3K) pathway to the increased degranulation of Nf1(+/-) mast cells both in vitro and in vivo. These studies identify the p21(Ras)-PI3K pathway as a major regulator of the gain in Nf1(+/-) mast cell degranulation in neurofibromas. Collectively, these studies identify both c-Kit and PI3K as molecular targets that modulate mast cell functions in cases of NF1.     

Neurofibroma-associated growth factors activate a distinct signaling network to alter the function of neurofibromin-deficient endothelial cells

Genetic inactivation of tumor suppressor genes initiates human cancers. However, interaction of accessory cells with the tumor-initiating cell within the microenvironment is often required for tumor progression. This paradigm is relevant to understanding neurofibroma development in neurofibromatosis type I patients. Somatic inactivation of the Nf1 tumor suppressor gene, which encodes neurofibromin, is necessary but not sufficient to initiate neurofibroma development. In contrast, neurofibromas occur with high penetrance in mice in which Nf1 is ablated in Schwann cells in the context of a heterozygous mutant (Nf1+/-) microenvironment. Neurofibromas are highly vascularized, and recent studies suggest that Nf1+/- mice have increased angiogenesis in vivo. However, the function of neurofibromin in human endothelial cells (ECs) and the biochemical mechanism by which neurofibromin regulates neoangiogenesis are not known. Utilizing Nf1+/- mice, primary human ECs and endothelial progenitor cells harvested from NF1 patients, we identified a discrete Ras effector pathway, which alters the proliferation and migration of neurofibromin-deficient ECs in response to neurofibroma-derived growth factors both in vitro and in vivo. Thus, these studies identify a unique biochemical pathway in Nf1+/- ECs as a potential therapeutic target in the neurofibroma microenvironment.     

Reduced growth of Drosophila neurofibromatosis 1 mutants reflects a non-cell-autonomous requirement for GTPase-Activating Protein activity in larval neurons

Neurofibromatosis type 1 (NF1) is among the most common genetic disorders of humans and is caused by loss of neurofibromin, a large and highly conserved protein whose only known function is to serve as a GTPase-Activating Protein (GAP) for Ras. However, most Drosophila NF1 mutant phenotypes, including an overall growth deficiency, are not readily modified by manipulating Ras signaling strength, but are rescued by increasing signaling through the cAMP-dependent protein kinase A pathway. This has led to suggestions that NF1 has distinct Ras- and cAMP-related functions. Here we report that the Drosophila NF1 growth defect reflects a non-cell-autonomous requirement for NF1 in larval neurons that express the R-Ras ortholog Ras2, that NF1 is a GAP for Ras1 and Ras2, and that a functional NF1-GAP catalytic domain is both necessary and sufficient for rescue. Moreover, a Drosophila p120RasGAP ortholog, when expressed in the appropriate cells, can substitute for NF1 in growth regulation. Our results show that loss of NF1 can give rise to non-cell-autonomous developmental defects, implicate aberrant Ras-mediated signaling in larval neurons as the primary cause of the NF1 growth deficiency, and argue against the notion that neurofibromin has separable Ras- and cAMP-related functions.     

Neurofibromin is a novel regulator of RAS-induced signals in primary vascular smooth muscle cells

Neurofibromatosis type I (NF1) is a genetic disorder caused by mutations in the NF1 tumor suppressor gene. Neurofibromin is encoded by NF1 and functions as a negative regulator of Ras activity. NF1 patients develop renal artery stenosis and arterial occlusions resulting in cerebral and visceral infarcts. Further, NF1 patients develop vascular neurofibromas where tumor vessels are invested in a dense pericyte sheath. Although it is well established that aberrations in Ras signaling lead to human malignancies, emerging data generated in genetically engineered mouse models now implicate perturbations in the Ras signaling axis in vascular smooth muscular cells (VSMCs) as central to the initiation and progression of neointimal hyperplasia and arterial stenosis. Despite these observations, the function of neurofibromin in regulating VSMC function and how Ras signals are terminated in VSMCs is virtually unknown. Utilizing VSMCs harvested from Nf1+/- mice and primary human neurofibromin-deficient VSMCs, we identify a discrete Ras effector pathway, which is tightly regulated by neurofibromin to limit VSMC proliferation and migration. Thus, these studies identify neurofibromin as a novel regulator of Ras activity in VSMCs and provide a framework for understanding cardiovascular disease in NF1 patients and a mechanism by which Ras signals are attenuated for maintaining VSMC homeostasis in blood vessel walls.     

Mice lacking Nf1 in osteochondroprogenitor cells display skeletal dysplasia similar to patients with neurofibromatosis type I

Mutations in NF1 cause neurofibromatosis type I (NF1), a disorder characterized, among other clinical manifestations, by generalized and focal bony lesions. Dystrophic scoliosis and tibial pseudoarthrosis are the most severe skeletal manifestations for which treatment is not satisfactory, emphasizing the dearth of knowledge related to the biology of NF1 in bone cells. Using reporter mice, we report here that the mouse Col2α1-Cre promoter (collagen, type II, alpha 1) is active not only in chondrocytes but also in adult bone marrow osteoprogenitors giving rise to osteoblasts. Based on this finding, we crossed the Col2α1-Cre transgenic and Nf1(flox/flox) mice to determine whether loss of Nf1 in axial and appendicular osteochondroprogenitors recapitulates the skeletal abnormalities of NF1 patients. By microtomographic and X-rays studies, we show that Nf1(Col2)(-/-) mice display progressive scoliosis and kyphosis, tibial bowing and abnormalities in skull and anterior chest wall formation. These defects were accompanied by a low bone mass phenotype, high bone cortical porosity, osteoidosis, increased osteoclastogenesis and decreased osteoblast number, as quantified by histomorphometry and 3D-microtomography. Loss of Nf1 in osteochondroprogenitors also caused severe short stature and intervertebral disc defects. Blockade of the RAS/ERK activation characteristic of Nf1(-/-) osteoprogenitors by lovastatin during embryonic development could attenuate the increased cortical porosity observed in mutant pups. These data and the skeletal similarities between this mouse model and NF1 patients thus suggest that activation of the RAS/ERK pathway by Nf1 loss-of-function in osteochondroprogenitors is responsible for the vertebral and tibia lesions in NF1 patients, and that this molecular signature may represent a good therapeutic target.     

Ras-Mek-Erk Signaling Regulates Nf1 Heterozygous Neointima Formation

Neurofibromatosis type 1 (NF1) results from mutations in the NF1 tumor-suppressor gene, which encodes neurofibromin, a negative regulator of diverse Ras signaling cascades. Arterial stenosis is a nonneoplastic manifestation of NF1 that predisposes some patients to debilitating morbidity and sudden death. Recent murine studies demonstrate that Nf1 heterozygosity (Nf1^+/−) in monocytes/macrophages significantly enhances intimal proliferation after arterial injury. However, the downstream Ras effector pathway responsible for this phenotype is unknown. Based on in vitro assays demonstrating enhanced extracellular signal-related kinase (Erk) signaling in Nf1^+/− macrophages and vascular smooth muscle cells and in vivo evidence of Erk amplification without alteration of phosphatidylinositol 3-kinase signaling in Nf1^+/− neointimas, we tested the hypothesis that Ras-Erk signaling regulates intimal proliferation in a murine model of NF1 arterial stenosis. By using a well-established in vivo model of inflammatory cell migration and standard cell culture, neurofibromin-deficient macrophages demonstrate enhanced sensitivity to growth factor stimulation in vivo and in vitro, which is significantly diminished in the presence of PD0325901, a specific inhibitor of Ras-Erk signaling in phase 2 clinical trials for cancer. After carotid artery injury, Nf1^+/− mice demonstrated increased intimal proliferation compared with wild-type mice. Daily administration of PD0325901 significantly reduced Nf1^+/− neointima formation to levels of wild-type mice. These studies identify the Ras-Erk pathway in neurofibromin-deficient macrophages as the aberrant pathway responsible for enhanced neointima formation.Neurofibromatosis type 1 (NF1) results from mutations in the NF1 tumor-suppressor gene, which encodes the protein neurofibromin. Neurofibromin negatively regulates Ras activity in multiple cell types by accelerating the hydrolysis of active Ras-GTP to its inactive diphosphate conformation.¹ These loss-of-function mutations accelerate Ras signaling and sensitize vessel wall cells and circulating hematopoietic cells, particularly myeloid progenitors and their differentiated progeny, to growth factors implicated in maintaining vascular wall homeostasis and disease pathogenesis.^1–4 Some patients with NF1 are predisposed to intimal proliferation, termed neointima, leading to debilitating arterial stenosis and tissue ischemia that contribute significantly to the premature mortality observed in this population.⁵Nf1 heterozygous (Nf1^+/−) mice display increased neointima formation, characterized by proliferating vascular smooth muscle cells (VSMCs) and infiltration of bone marrow–derived macrophages after arterial ligation, which is reminiscent of patients with NF1.^5,6 Neurofibromin-deficient endothelial cells, VSMCs, and bone marrow–derived myeloid cells demonstrate preferential activation of the Ras-Erk signaling pathway, without corresponding alterations in Ras–phosphatidylinositol 3-kinase signaling, in response to multiple growth factors in vitro.^2–4,7 This is an interesting observation because lineage-restricted inactivation of a single Nf1 gene in endothelial cells and/or VSMCs does not replicate the striking neointima observed in Nf1 heterozygous mice. However, we recently demonstrated that lineage-specific inactivation of a single Nf1 gene copy in monocytes/macrophages is sufficient to reproduce the enhanced neointima formation observed in Nf1 heterozygous mice compared with wild-type (WT) mice.⁸Based on these observations, we used in vitro and in vivo systems of macrophage function to test the hypothesis that Nf1 heterozygous macrophage function and mobilization to sites of inflammation are directly controlled by Ras-Erk signaling and that use of a specific and long-acting inhibitor of Ras-Erk signaling, under evaluation in multiple phase 1 and 2 clinical trials for cancer and preclinical models of NF1 malignancy,^1,9–12 will reduce neointima formation after mechanical injury.     

Sensory neurons from Nf1 haploinsufficient mice exhibit increased excitability

Neurofibromatosis type 1 (NF1) is a common genetic disorder characterized by tumor formation. People with NF1 also can experience more intense painful responses to stimuli, such as minor trauma, than normal. NF1 results from a heterozygous mutation of the NF1 gene, leading to decreased levels of neurofibromin, the protein product of the NF1 gene. Neurofibromin is a guanosine triphosphatase activating protein (GAP) for Ras and accelerates the conversion of active Ras-GTP to inactive Ras-GDP; therefore mutation of the NF1 gene frequently results in an increase in activity of the Ras transduction cascade. Using patch-clamp electrophysiological techniques, we examined the excitability of capsaicin-sensitive sensory neurons isolated from the dorsal root ganglia of adult mice with a heterozygous mutation of the Nf1 gene (Nf1+/-), analogous to the human mutation, in comparison to wildtype sensory neurons. Sensory neurons from adult Nf1+/- mice generated a more than twofold higher number of action potentials in response to a ramp of depolarizing current as wild-type neurons. Consistent with the greater number of action potentials, Nf1+/- neurons had lower firing thresholds, lower rheobase currents, and shorter firing latencies than wild-type neurons. Interestingly, nerve growth factor augmented the excitability of wild-type neurons in a concentration-related manner but did not further alter the excitability of the Nf1+/- sensory neurons. These data clearly suggest that GAPs, such as neurofibromin, can play a key role in the excitability of nociceptive sensory neurons. This increased excitability may explain the painful conditions experienced by people with NF1.     

Neurofibromin (NF1) genetic variant structure–function analyses using a full‐length mouse cDNA

Neurofibromatosis type 1 (NF1) is caused by pathogenic variants or mutations in the NF1 gene that encodes neurofibromin. We describe here a new approach to determining the functional consequences of NF1 genetic variants. We established a heterologous cell culture expression system using a full‐length mouse Nf1 cDNA (mNf1) and human cell lines. We demonstrate that the full‐length murine cDNA produces a > 250 kDa neurofibromin protein that is capable of modulating Ras signaling. We created mutant cDNAs representing NF1 patient variants with different clinically relevant phenotypes, and assessed their ability to produce mature neurofibromin and restore Nf1 activity in NF1^?/? cells. These cDNAs represent variants in multiple protein domains and various types of clinically relevant predicted variants. This approach will help advance research on neurofibromin structure and function, determine pathogenicity for missense variants, and allow for the development of activity assays and variant‐directed therapeutics.     

Neurofibromin (Nf1) is required for skeletal muscle development

Neurofibromatosis type 1 (NF1) is a multi-system disease caused by mutations in the NF1 gene encoding a Ras-GAP protein, neurofibromin, which negatively regulates Ras signaling. Besides neuroectodermal malformations and tumors, the skeletal system is often affected (e.g. scoliosis and long bone dysplasia) demonstrating the importance of neurofibromin for development and maintenance of the musculoskeletal system. Here, we focus on the role of neurofibromin in skeletal muscle development. Nf1 gene inactivation in the early limb bud mesenchyme using Prx1-cre (Nf1(Prx1)) resulted in muscle dystrophy characterized by fibrosis, reduced number of muscle fibers and reduced muscle force. This was caused by an early defect in myogenesis affecting the terminal differentiation of myoblasts between E12.5 and E14.5. In parallel, the muscle connective tissue cells exhibited increased proliferation at E14.5 and an increase in the amount of connective tissue as early as E16.5. These changes were accompanied by excessive mitogen-activated protein kinase pathway activation. Satellite cells isolated from Nf1(Prx1) mice showed normal self-renewal, but their differentiation was impaired as indicated by diminished myotube formation. Our results demonstrate a requirement of neurofibromin for muscle formation and maintenance. This previously unrecognized function of neurofibromin may contribute to the musculoskeletal problems in NF1 patients.     

A shared molecular mechanism underlies the human rasopathies Legius syndrome and Neurofibromatosis-1

The Ras/mitogen-activated protein kinase (MAPK) pathway plays a critical role in transducing mitogenic signals from receptor tyrosine kinases. Loss-of-function mutations in one feedback regulator of Ras/MAPK signaling, SPRED1 (Sprouty-related protein with an EVH1 domain), cause Legius syndrome, an autosomal dominant human disorder that resembles Neurofibromatosis-1 (NF1). Spred1 functions as a negative regulator of the Ras/MAPK pathway; however, the underlying molecular mechanism is poorly understood. Here we show that neurofibromin, the NF1 gene product, is a Spred1-interacting protein that is necessary for Spred1's inhibitory function. We show that Spred1 binding induces the plasma membrane localization of NF1, which subsequently down-regulates Ras-GTP levels. This novel mechanism for the regulation of neurofibromin provides a molecular bridge for understanding the overlapping pathophysiology of NF1 and Legius syndrome.     

Dynamic regulation of the Ras pathway via proteolysis of the NF1 tumor suppressor

Mutations in the NF1 tumor suppressor underlie the familial tumor predisposition syndrome neurofibromatosis type I. Although its encoded protein, neurofibromin, functions as a Ras-GTPase activating protein (GAP), nothing is known about how it is normally regulated or its precise role in controlling Ras signaling pathways. We show here that neurofibromin is dynamically regulated by the ubiquitin-proteasome pathway. Degradation is rapidly triggered in response to a variety of growth factors and requires sequences adjacent to the catalytic GAP-related domain of neurofibromin. However, whereas degradation is rapid, neurofibromin levels are re-elevated shortly after growth factor treatment. Accordingly, Nf1-deficient mouse embryonic fibroblasts (MEFs) exhibit an enhanced activation of Ras, prolonged Ras and ERK activities, and proliferate in response to subthreshold levels of growth factors. Thus, the dynamic proteasomal regulation of neurofibromin represents an important mechanism of controlling both the amplitude and duration of Ras-mediated signaling. Furthermore, this previously unrecognized Ras regulatory mechanism may be exploited therapeutically.     

Neurofibromatosis type 1 (Nf1)‐mutant mice exhibit increased sleep fragmentation

Neurofibromatosis type 1 (NF1) is a neurodevelopmental disorder in which affected children and adults are at a higher risk of sleep disorders. In an effort to identify potential sleep disturbances in a small animal model, we used a previously reported Nf1 conditional knockout (Nf1^CKO) mouse strain. In contrast to Nf1 mutant flies, the distribution of vigilance states was intact in Nf1^CKO mice. However, Nf1^CKO mice exhibited increased non‐REM sleep (NREM)‐to‐wake and wake‐to‐NREM transitions. This sleep disruption was accompanied by decreased bout durations during awake and NREM sleep states under both light and dark conditions. Moreover, Nf1^CKO mice have higher percentage delta power during awake and NREM sleep states under all light conditions. Taken together, Nf1^CKO mice phenocopy some of the sleep disturbances observed in NF1 patients and provide a tractable platform to explore the molecular mechanisms governing sleep abnormalities in NF1.     

Trio's Rho-specific GEF domain is the missing Galpha q effector in C. elegans

The Galpha(q) pathway is essential for animal life and is a central pathway for driving locomotion, egg laying, and growth in Caenorhabditis elegans, where it exerts its effects through EGL-8 (phospholipase Cbeta [PLCbeta]) and at least one other effector. To find the missing effector, we performed forward genetic screens to suppress the slow growth and hyperactive behaviors of mutants with an overactive Galpha(q) pathway. Four suppressor mutations disrupted the Rho-specific guanine-nucleotide exchange factor (GEF) domain of UNC-73 (Trio). The mutations produce defects in neuronal function, but not neuronal development, that cause sluggish locomotion similar to animals lacking EGL-8 (PLCbeta). Strains containing null mutations in both EGL-8 (PLCbeta) and UNC-73 (Trio RhoGEF) have strong synthetic phenotypes that phenocopy the arrested growth and near-complete paralysis of Galpha(q)-null mutants. Using cell-based and biochemical assays, we show that activated C. elegans Galpha(q) synergizes with Trio RhoGEF to activate RhoA. Activated Galpha(q) and Trio RhoGEF appear to be part of a signaling complex, because they coimmunoprecipitate when expressed together in cells. Our results show that Trio's Rho-specific GEF domain is a major Galpha(q) effector that, together with PLCbeta, mediates the Galpha(q) signaling that drives the locomotion, egg laying, and growth of the animal.     

The musculoskeletal phenotype of the RASopathies

The Ras/MAPK signal transduction pathway is critical for the regulation of proliferation and differentiation of multiple cell types. Neurofibromatosis type 1 (NF1) is caused by inactivating mutations in the NF1 gene resulting in an increased Ras signaling cascade. Subsequently, additional syndromes with some overlapping physical manifestations such as Noonan syndrome, Costello syndrome, and cardiofaciocutaneous (CFC) syndrome were also shown to be due in many cases to mutations in genes encoding for proteins interacting with the Ras/MAPK pathway. Although neurocutaneous manifestations have been considered hallmark features for these disorders, multiple organ systems including the musculoskeletal system are affected. Some of the overlapping musculoskeletal phenotypes include scoliosis, kyphosis, anterior chest wall anomalies, pes planus, osteopenia, and hand anomalies. However, there are also discordant skeletal phenotypes such as sphenoid wing dysplasia and tibial pseudarthrosis seen only in NF1. We provide an overview of the concordant and discordant musculoskeletal manifestations in the RASopathies.     

未知酪氨酸激酶对骨髓瘤细胞中IL—6诱导Ras／MAPK／NF—IL—6途径活化的调节作用

目的 研究两条主要的IL-6信号转导途径-JAK/STAT和Ras/MAPK/NFG-IL-6在人骨髓瘤细胞系KM-3中的诱导活化情况和调控机制。方法 首先分别采用凝胶阻滞电泳（EMSA）和免疫沉淀（IP）方法检测参与 IL-6信号转导功能的转录因子（STAT3、NF-IL-6）和蛋白激酶（JAK1、MAPK）在KM-3细胞中的诱导活化情况。然后采用特异性酢氨酸蛋白激酶 抑制剂Genistein作用于KM-3细胞,观察酢氨酸磷酸化作用对KM-3细胞中IL-6信号转导功能的影响。结果 IL-6刺激后,KM-3细胞中只出现了Ras/MAPK/NF-IL-6信号转导途径的诱导激活,而JAK/STAT途径则不参与IL-6在KM-3细胞中的信号转导功能。Gwenistein的作用可明显抑制Ras/MAPK/NF-IL-6途径的活化。结论 一种目前尚无法确定的非JAK1酪氨酸蛋白激酶可参与并调节Ras/MAPK/NF-IL-6信号转导途径在KM-3细胞中的诱导活化。     

Lens induction requires attenuation of ERK signaling by Nf1

Aphakia (lack of lens) is a rare human congenital disorder with its genetic etiology largely unknown. Even in model organisms, very few mutations are known to result in such a drastic ocular defect. In this study, we have shown that homozygous deletion of Nf1, the Ras GTPase gene underlying human neurofibromatosis type 1 syndrome, causes lens dysgenesis in mouse. Although early lens specification proceeded normally in Nf1 mutants, lens induction was disrupted due to deficient cell proliferation. Further analysis showed that extracellular signal-regulated kinase (ERK) signaling was initially elevated in the invaginating lens placode, but by the lens vesicle stage, ERK phosphorylation was significantly reduced. Only after intraperitoneal treatment of U0126, an inhibitor of ERK phosphorylation, was lens development restored in Nf1 mutants. Hyperactive Ras-mitogen-activated protein kinase (MAPK) signaling is known to cause neuro-cardiofacial-cutaneous (NCFC) syndromes in humans. As a member of NCFC family genes, Nf1 represents the first example that attenuation of Ras-MAPK kinase signaling pathway is essential for normal lens development.