p75 neurotrophin receptor cleavage by α- and γ-secretases is required for neurotrophin-mediated proliferation of brain tumor-initiating cells

LM11a-31 Inhibits p75 Neurotrophin Receptor (p75 NTR ) Cleavage and is Neuroprotective in a Cell Culture Model of Parkinson's Disease

The p75 Neurotrophin Receptor (p75 NTR ) is a multifunctional transmembrane protein that mediates neuronal responses to pathological conditions in specific regions of the nervous system. In many biological contexts, p75 NTR signaling is initiated through sequential cleavage of the receptor by α- and γ-secretases, which releases receptor fragments for downstream signaling. Our previous work demonstrated that proteolytic processing of p75 NTR in this manner is stimulated by oxidative stress in Lund Human Mesencephalic (LUHMES) cells, a dopaminergic neuronal cell line derived from human mesencephalic tissue. Considering the vulnerability of dopaminergic neurons in the ventral mesencephalon to oxidative stress and neurodegeneration associated with Parkinson's disease (PD), we investigated the role of this signaling cascade in neurodegeneration and explored cellular processes that govern oxidative stress-induced p75 NTR signaling. In the present study, we provide evidence that oxidative stress induces cleavage of p75 NTR by promoting c-Jun N-terminal Kinase (JNK)-dependent internalization of p75 NTR from the cell surface. This activation of p75 NTR signaling is counteracted by tropomyosin-related kinase (Trk) receptor signaling; however, oxidative stress leads to Trk receptor downregulation, thereby enhancing p75 NTR processing. Importantly, we demonstrate that this pathway can be inhibited by LM11a-31, a small molecule modulator of p75 NTR , thereby conferring protection against neurodegeneration. Treatment with LM11a-31 significantly reduced p75 NTR cleavage and neuronal death associated with oxidative stress. These findings reveal novel mechanisms underlying activation of p75 NTR in response to oxidative stress, underscore a key role for p75 NTR in dopaminergic neurodegeneration, and highlight p75 NTR as a potential therapeutic target for reducing neurodegeneration in PD.

Neurotrophin-3 Facilitates Stemness Properties and Associates with Poor Survival in Lung Cancer

INTRODUCTION

Cancer stem cells (CSCs) shape the tumor microenvironment via neuroendocrine signaling and orchestrate drug resistance and metastasis. Cytokine antibody array demonstrated the upregulation of neurotrophin-3 (NT-3) in lung CSCs. This study aims to dissect the role of NT-3 in lung CSCs during tumor innervation.

METHODS

Western blotting, quantitative reverse transcription-PCR, and flow cytometry were used to determine the expression of the NT-3 axis in lung CSCs. NT-3-knockdown and NT-3-overexpressed cells were derived lung CSCs, followed by examining the stemness gene expression, tumorsphere formation, transwell migration and invasion, drug resistance, soft agar colony formation, and in vivo tumorigenicity. Human lung cancer tissue microarray and bioinformatic databases were used to investigate the clinical relevance of NT-3 in lung cancer.

RESULTS

NT-3 and its receptor tropomyosin receptor kinase C (TrkC) were augmented in lung tumorspheres. NT-3 silencing (shNT-3) suppressed the migration and anchorage-independent growth of lung cancer cells. Further, shNT-3 abolished the sphere-forming capability, chemo-drug resistance, invasion, and in vivo tumorigenicity of lung tumorspheres with a decreased expression of CSC markers. Conversely, NT-3 overexpression promoted migration and anchorage-independent growth and fueled tumorsphere formation by upregulating the expression of CSC markers. Lung cancer tissue microarray analysis revealed that NT-3 increased in patients with advanced-stage, lymphatic metastasis and positively correlated with Sox2 expression. Bioinformatic databases confirmed a co-expression of NT-3/TrkC-axis and demonstrated that NT-3, NT-3/TrkC, NT-3/Sox2, and NT-3/CD133 worsen the survival of lung cancer patients.

CONCLUSION

NT-3 conferred the stemness features in lung cancer during tumor innervation, which suggests that NT-3-targeting is feasible in eradicating lung CSCs.

Nerve Growth Factor and the Role of Inflammation in Tumor Development

Nerve growth factor (NGF) plays a dual role both in inflammatory states and cancer, acting both as a pro-inflammatory and oncogenic factor and as an anti-inflammatory and pro-apoptotic mediator in a context-dependent way based on the signaling networks and its interaction with diverse cellular components within the microenvironment. This report aims to provide a summary and subsequent review of the literature on the role of NGF in regulating the inflammatory microenvironment and tumor cell growth, survival, and death. The role of NGF in inflammation and tumorigenesis as a component of the inflammatory system, its interaction with the various components of the respective microenvironments, its ability to cause epigenetic changes, and its role in the treatment of cancer have been highlighted in this paper.

Exploring the Vital Link Between Glioma, Neuron, and Neural Activity in the Context of Invasion

Because of their ability to infiltrate normal brain tissue, gliomas frequently evade microscopic surgical excision. The histologic infiltrative property of human glioma has been previously characterized as Scherer secondary structures, of which the perivascular satellitosis is a prospective target for anti-angiogenic treatment in high-grade gliomas. However, the mechanisms underlying perineuronal satellitosis remain unclear, and therapy remains lacking. Our knowledge of the mechanism underlying Scherer secondary structures has improved over time. New techniques, such as laser capture microdissection and optogenetic stimulation, have advanced our understanding of glioma invasion mechanisms. Although laser capture microdissection is a useful tool for studying gliomas that infiltrate the normal brain microenvironment, optogenetics and mouse xenograft glioma models have been extensively used in studies demonstrating the unique role of synaptogenesis in glioma proliferation and identification of potential therapeutic targets. Moreover, a rare glioma cell line is established that, when transplanted in the mouse brain, can replicate and recapitulate the human diffuse invasion phenotype. This review discusses the primary molecular causes of glioma, its histopathology-based invasive mechanisms, and the importance of neuronal activity and interactions between glioma cells and neurons in the brain microenvironment. It also explores current methods and models of gliomas.

ProNGF Expression and Targeting in Glioblastoma Multiforme

Glioblastoma multiforme (GBM) is the most lethal adult brain cancer. Temozolomide (TMZ), the standard chemotherapeutic drug used in GBM, has limited benefit and alternate therapies are needed to improve GBM treatment. Nerve growth factor (NGF) and its precursor proNGF are increasingly recognized as stimulators of human tumor progression. The expression and stimulatory effect of NGF on GBM cell growth has previously been reported, but the status of proNGF in GBM is unreported. In this study, we have investigated proNGF expression and biological activity in GBM. A clinical cohort of GBM (n = 72) and low-grade glioma (n = 20) was analyzed by immunohistochemistry for proNGF and digital quantification. ProNGF expression was significantly increased in GBM compared to low grade gliomas and proNGF was also detected in patient plasma samples. ProNGF was also detected in most GBM cell lines by Western blotting. Although anti-proNGF blocking antibodies inhibited cell growth in GBM cells with methylated MGMT gene promoter, targeting proNGF could not potentiate the efficacy of TMZ. In subcutaneous xenograft of human GBM cells, anti-proNGF antibodies slightly reduced tumor volume but had no impact on TMZ efficacy. In conclusion, this data reveals that proNGF is overexpressed in GBM and can stimulate cancer cell growth. The potential of proNGF as a clinical biomarker and therapeutic target warrants further investigations.

The effects of CHF6467, a new mutated form of NGF, on cell models of human glioblastoma. A comparison with wild-type NGF

CHF6467 is a mutated form of human recombinant nerve growth factor (NGF). The mutation selectively disrupts the binding of NGF to its p75NTR receptor while maintaining the affinity toward TrkA receptor. Because of such different profile of receptor interaction, CHF6467 maintains unaltered the neurotrophic and neuroprotective properties of wild-type NGF but shows reduced algogenic activity.In this study, we investigated the effects of CHF6467 on mortality, proliferation, cell-damage and migration in three human glioblastoma cell lines (U87MG, T98G, LN18), and in the rat astrocytoma C6 cells. Both CHF6467 and wild-type NGF, given in the range 1-50 ng/ml, did not modify cell proliferation, metabolism and migration, as well as the number of live/dead cells.The present in vitro data are predictive of a lack of tumorigenic activity by both wild-type NGF and CHF6467 on these cell types in vivo, and warrant for CHF6467 further clinical development.

Pilot Investigation on p75ICD Expression in Laryngeal Squamous Cell Carcinoma

We investigated the p75 Neurotrophin Receptor (p75NTR) expression and cleavage product p75NTR Intracellular Domain (p75ICD) as potential oncogenic and metastatic markers in human Laryngeal Squamous Cell Carcinoma (LSCC). p75NTR is highly expressed in Cancer Stem Cells (CSCs) of the laryngeal epithelia and it has been proposed as a marker for stemness, cell migration, and chemo-resistance in different squamous carcinomas. To investigate the clinical significance of p75NTR cleavage products in solid tumors, full-length and cleaved p75NTR expression was analyzed in laryngeal primary tumors from different-stage LSCC patients, diagnosed at the Policlinico Umberto I Hospital. Molecular and histological techniques were used to detect the expressions of p75NTR and p75ICD, and ATP Binding Cassette Subfamily G Member 2 (ABCG2), a CSC marker. We found regulated p75NTR cleavage during squamous epithelial tumor progression and tissue invasion. Our preliminary investigation suggests p75ICD expression and localization as possible features of tumorigenesis and metastaticity. Its co-localization with ABCG2 in squamous cells in the parenchyma invaded by the tumor formation allows us to hypothesize p75NTR and p75ICD roles in tumor invasion and CSC spreading in LSCC patients. These data might represent a starting point for a comprehensive analysis of p75NTR cleavage and of its clinical relevance as a potential molecular LSCC signature, possibly helping diagnosis, and improving prognosis and personalized therapy.

Astrocytic p75NTR expression provoked by ischemic stroke exacerbates the blood-brain barrier disruption

The disruption of the blood-brain barrier (BBB) plays a critical role in the pathology of ischemic stroke. p75 neurotrophin receptor (p75NTR ) contributes to the disruption of the blood-retinal barrier in retinal ischemia. However, whether p75NTR influences the BBB permeability after acute cerebral ischemia remains unknown. The present study investigated the role and underlying mechanism of p75NTR on BBB integrity in an ischemic stroke mouse model, middle cerebral artery occlusion (MCAO). After 24 h of MCAO, astrocytes and endothelial cells in the infarct-affected brain area up-regulated p75NTR . Genetic p75NTR knockdown (p75NTR+/- ) or pharmacological inhibition of p75NTR using LM11A-31, a selective inhibitor of p75NTR , both attenuated brain damage and BBB leakage in MCAO mice. Astrocyte-specific conditional knockdown of p75NTR mediated with an adeno-associated virus significantly ameliorated BBB disruption and brain tissue damage, as well as the neurological functions after stroke. Further molecular biological examinations indicated that astrocytic p75NTR activated NF-κB and HIF-1α signals, which upregulated the expression of MMP-9 and vascular endothelial growth factor (VEGF), subsequently leading to tight junction degradation after ischemia. As a result, increased leukocyte infiltration and microglia activation exacerbated brain injury after stroke. Overall, our results provide novel insight into the role of astrocytic p75NTR in BBB disruption after acute cerebral ischemia. The p75NTR may therefore be a potential therapeutic target for the treatment of ischemic stroke.

LMO1 Plays an Oncogenic Role in Human Glioma Associated With NF-kB Pathway

Background

LIM domain only protein1(LMO1), a nuclear transcription coregulator, is implicated in the pathogenesis of T-cell acute lymphoblastic leukemia and neuroblastoma. However, the clinical significance and potential mechanism of LMO1 in human gliomas remain to be determined.

Methods

In this study, expression level data and clinical information were obtained via three databases. The Cox proportional hazards regression model was used to predict outcomes for glioma patients. In vitro and in vivo assays were used to explore the function of LMO1 in human glioma. Gene set enrichment analysis (GSEA), RNA-seq and western blot were used to explore the potential molecular mechanisms. A prognostic model was built for predicting the overall survival(OS) of human glioma patients.

Results

High LMO1 expression was associated with a high tumor grade and a poor prognosis in patients. High levels of LMO1 mRNA were correlated with poor prognosis in patients with isocitrate dehydrogenase (IDH)-wild-type (wt) and 1p/19q non-codeletion gliomas. Gene silencing of LMO1 significantly inhibited tumor growth, invasion and migration in vitro. In contrast, LMO1 over-expression promoted tumor growth, invasion and migration. Mechanically, LMO1 may positively regulate the level of NGFR mRNA and protein. NGFR mediated the regulation between LMO1 and NF-kB activation. Consistently, the nude mice study further confirmed that knockdown of LMO1 blocked tumor growth via NGFR-NF-kB axis. Finally, The nomogram based on the LMO1 signature for overall survival (OS) prediction in human glioma patients exhibited good performance in the individual mortality risk.

Conclusion

This study provides new insights and evidences that high level expression of LMO1 is significantly correlated with progression and prognosis in human gliomas. LMO1 played a critical role in tumorigenesis and progression. The present study first investigated the LMO1–NGFR–NF-kB axis regulate cell growth and invasion in human glioma cells, whereby targeting this pathway may be a therapeutic target for glioma.

Brothers in arms: proBDNF/BDNF and sAPPα/Aβ-signaling and their common interplay with ADAM10, TrkB, p75NTR, sortilin, and sorLA in the progression of Alzheimer's disease

Brain-derived neurotrophic factor (BDNF) is an important modulator for a variety of functions in the central nervous system (CNS). A wealth of evidence, such as reduced mRNA and protein level in the brain, cerebrospinal fluid (CSF), and blood samples of Alzheimer's disease (AD) patients implicates a crucial role of BDNF in the progression of this disease. Especially, processing and subcellular localization of BDNF and its receptors TrkB and p75 are critical determinants for survival and death in neuronal cells. Similarly, the amyloid precursor protein (APP), a key player in Alzheimer's disease, and its cleavage fragments sAPPα and Aβ are known for their respective roles in neuroprotection and neuronal death. Common features of APP- and BDNF-signaling indicate a causal relationship in their mode of action. However, the interconnections of APP- and BDNF-signaling are not well understood. Therefore, we here discuss dimerization properties, localization, processing by α- and γ-secretase, relevance of the common interaction partners TrkB, p75, sorLA, and sortilin as well as shared signaling pathways of BDNF and sAPPα.

Bone Morphogenetic Protein 7 Effect on Human Glioblastoma Cell Transmigration and Migration

Glioblastoma, World Health Organization—grade IV, is the most malignant glioma type and it is still an incurable tumor due to the high level of heterogeneity and uncontrolled metastatic nature. In addition to the tumorigenicity-suppressing activity, bone morphogenetic protein 7 (BMP7) has recently been found for its invasion-promoting role in glioblastoma. However, the detailed and precise mechanism in this issue should have more elucidation. Thus, in this study, we determined the BMP7 effect on glioblastoma transmigration and migration regulations and the underlying mechanisms. Human LN18/LN229 glioblastoma cells were used in this study. Our results showed a higher BMP7/pSmad5 level in human malignant glioma tissues compared to healthy brain tissues. In addition, it was demonstrated that endogenous and exogenous BMP7 stimulation could increase the transmigration and migration capabilities of human LN18/LN229 glioblastoma cells. Moreover, this event is regulated by Smad5 and p75 neurotrophin receptor (p75NTR) signaling. Furthermore, unexpected data are that the Smad1 gene knockdown could lead to the cell death of human LN18 glioblastoma cells. Overall, the present study finds that the invasion-promoting activity of BMP7 might be an autocrine stimulation of glioblastoma and this effect could be regulated by Smad5-p75NTR signaling.

The adaptive transition of glioblastoma stem cells and its implications on treatments

Glioblastoma is the most malignant tumor occurring in the human central nervous system with overall median survival time <14.6 months. Current treatments such as chemotherapy and radiotherapy cannot reach an optimal remission since tumor resistance to therapy remains a challenge. Glioblastoma stem cells are considered to be responsible for tumor resistance in treating glioblastoma. Previous studies reported two subtypes, proneural and mesenchymal, of glioblastoma stem cells manifesting different sensitivity to radiotherapy or chemotherapy. Mesenchymal glioblastoma stem cells, as well as tumor cells generate from which, showed resistance to radiochemotherapies. Besides, two metabolic patterns, glutamine or glucose dependent, of mesenchymal glioblastoma stem cells also manifested different sensitivity to radiochemotherapies. Glutamine dependent mesenchymal glioblastoma stem cells are more sensitive to radiotherapy than glucose-dependent ones. Therefore, the transition between proneural and mesenchymal subtypes, or between glutamine-dependent and glucose-dependent, might lead to tumor resistance to radiochemotherapies. Moreover, neural stem cells were also hypothesized to participate in glioblastoma stem cells mediated tumor resistance to radiochemotherapies. In this review, we summarized the basic characteristics, adaptive transition and implications of glioblastoma stem cells in glioblastoma therapy.

The p75NTR and its carboxyl-terminal fragment exert opposing effects on melanoma cell proliferation and apoptosis via modulation of the NF-κB pathway

The p75 neurotrophin receptor (p75NTR ), a member of the tumor necrosis factor superfamily of receptors, is sensitive to proteolysis and has been observed to be expressed in various cancers. However, the roles of p75NTR and its proteolytic fragments in tumorigenesis remain incompletely understood. Here, we report that the proportion of the p75NTR carboxyl-terminal fragment (p75NTR -CTF) is much higher than that of the full-length p75NTR (p75NTR -FL) in melanoma cells. Whereas p75NTR -FL positively regulates apoptosis, p75NTR -CTF promotes cell proliferation and survival, as well as increasing sorafenib resistance in vivo and in vitro. Moreover, p75NTR -CTF activates the nuclear factor kappa B pathway and enhances the mRNA and protein levels of its downstream genes c-IAP1/2, FLIP, bFGF, IL8 and VEGF. On the contrary, p75NTR -FL inhibits these processes. Taken together, these findings demonstrate that p75NTR -CTF and p75NTR -FL have opposing functions in melanoma cells, suggesting that the ratio of the two proteins affects the balance between cell death and survival. The presence of distinct p75NTR proteolytic fragments may affect biological outcomes in tumor cells.

Metformin inhibits proliferation of oral squamous cell carcinoma cells by suppressing proteolysis of nerve growth factor receptor

OBJECTIVE

We aimed to explore the effects of metformin on oral squamous cell carcinoma (OSCC) cell proliferation and the associated molecular mechanisms.

METHODS

We established an OSCC model in SCC15 cells overexpressing nerve growth factor receptor (NGFR) or the N-terminal region (aa 1-250; NGFR-N), and assessed cell proliferation by CCK-8 assay, colony formation assay, and cell cycle analysis. Levels of NGFR and related genes and proteins were detected by qPCR and western blotting, and NGFR and NGFR-N affinity for p53 was assessed by immunoprecipitation assay. Additionally, the effects of NGFR and NGFR-N on p53 binding with its downstream gene promoters were analyzed by chromatin immunoprecipitation.

RESULTS

Metformin inhibited OSCC cell proliferation and blocked NGFR proteolysis, thereby reducing the generation of its intracellular domain and NGFR-N. Moreover, compared with NGFR, NGFR-N showed higher affinity for p53 and more strongly inactivated p53 to promote cell proliferation. Furthermore, upregulation of NGFR-N downregulated levels of p53-specific downstream transcripts and proteins, whereas these levels were significantly upregulated in metformin-treated cells overexpressing NGFR.

CONCLUSIONS

These results showed that metformin inhibited cell proliferation by suppressing NGFR proteolysis, thereby promoting its antitumor effect in OSCC and offering novel insight into a role for metformin in OSCC treatment.

Exportin 1 Inhibition Induces Nerve Growth Factor Receptor Expression to Inhibit the NF-κB Pathway in Preclinical Models of Pediatric High-Grade Glioma

High-grade glioma (HGG) is the leading cause of cancer-related death among children. Selinexor, an orally bioavailable, reversible inhibitor of the nuclear export protein, exportin 1, is in clinical trials for a range of cancers, including HGG. It inhibits the NF-κB pathway and strongly induces the expression of nerve growth factor receptor (NGFR) in preclinical cancer models. We hypothesized that selinexor inhibits NF-κB via upregulation of NGFR. In HGG cells, sensitivity to selinexor correlated with increased induction of cell surface NGFR expression. Knocking down NGFR in HGG cells increased proliferation, anchorage-independent growth, stemness markers, and levels of transcriptionally available nuclear NF-κB not bound to IκB-α, while decreasing apoptosis and sensitivity to selinexor. Increasing IκB-α levels in NGFR knockdown cells restored sensitivity to selinexor. Overexpression of NGFR using cDNA reduced levels of free nuclear NF-κB, decreased stemness markers, and increased markers of cellular differentiation. In all HGG lines tested, selinexor decreased phosphorylation of NF-κB at serine 536 (a site associated with increased transcription of proliferative and inflammatory genes). Because resistance to selinexor monotherapy occurred in our in vivo model, we screened selinexor with a panel of FDA-approved anticancer agents. Bortezomib, a proteasome inhibitor that inhibits the NF-κB pathway through a different mechanism than selinexor, showed synergy with selinexor against HGG in vitro Our results help elucidate selinexor's mechanism of action and identify NGFR as a potential biomarker of its effect in HGG and in addition suggest a combination therapy strategy for these challenging tumors.

Cancer stem cells-driven tumor growth and immune escape: the Janus face of neurotrophins

Cancer Stem Cells (CSCs) are self-renewing cancer cells responsible for expansion of the malignant mass in a dynamic process shaping the tumor microenvironment. CSCs may hijack the host immune surveillance resulting in typically aggressive tumors with poor prognosis.In this review, we focus on neurotrophic control of cellular substrates and molecular mechanisms involved in CSC-driven tumor growth as well as in host immune surveillance. Neurotrophins have been demonstrated to be key tumor promoting signaling platforms. Particularly, Nerve Growth Factor (NGF) and its specific receptor Tropomyosin related kinase A (TrkA) have been implicated in initiation and progression of many aggressive cancers. On the other hand, an active NGF pathway has been recently proven to be critical to oncogenic inflammation control and in promoting immune response against cancer, pinpointing possible pro-tumoral effects of NGF/TrkA-inhibitory therapy.A better understanding of the molecular mechanisms involved in the control of tumor growth/immunoediting is essential to identify new predictive and prognostic intervention and to design more effective therapies. Fine and timely modulation of CSCs-driven tumor growth and of peripheral lymph nodes activation by the immune system will possibly open the way to precision medicine in neurotrophic therapy and improve patient's prognosis in both TrkA- dependent and independent cancers.

Regulation of BACE1 expression after injury is linked to the p75 neurotrophin receptor

BACE1 is a transmembrane aspartic protease that cleaves various substrates and it is required for normal brain function. BACE1 expression is high during early development, but it is reduced in adulthood. Under conditions of stress and injury, BACE1 levels are increased; however, the underlying mechanisms that drive BACE1 elevation are not well understood. One mechanism associated with brain injury is the activation of injurious p75 neurotrophin receptor (p75), which can trigger pathological signals. Here we report that within 72 h after controlled cortical impact (CCI) or laser injury, BACE1 and p75 are increased and tightly co-expressed in cortical neurons of mouse brain. Additionally, BACE1 is not up-regulated in p75 null mice in response to focal cortical injury, while p75 over-expression results in BACE1 augmentation in HEK-293 and SY5Y cell lines. A luciferase assay conducted in SY5Y cell line revealed that BACE1 expression is regulated at the transcriptional level in response to p75 transfection. Interestingly, this effect does not appear to be dependent upon p75 ligands including mature and pro-neurotrophins. In addition, BACE1 activity on amyloid precursor protein (APP) is enhanced in SY5Y-APP cells transfected with a p75 construct. Lastly, we found that the activation of c-jun n-terminal kinase (JNK) by p75 contributes to BACE1 up-regulation. This study explores how two injury-induced molecules are intimately connected and suggests a potential link between p75 signaling and the expression of BACE1 after brain injury.

Reciprocal Signaling between Glioblastoma Stem Cells and Differentiated Tumor Cells Promotes Malignant Progression

Glioblastoma is the most lethal primary brain tumor; however, the crosstalk between glioblastoma stem cells (GSCs) and their supportive niche is not well understood. Here, we interrogated reciprocal signaling between GSCs and their differentiated glioblastoma cell (DGC) progeny. We found that DGCs accelerated GSC tumor growth. DGCs preferentially expressed brain-derived neurotrophic factor (BDNF), whereas GSCs expressed the BDNF receptor NTRK2. Forced BDNF expression in DGCs augmented GSC tumor growth. To determine molecular mediators of BDNF-NTRK2 paracrine signaling, we leveraged transcriptional and epigenetic profiles of matched GSCs and DGCs, revealing preferential VGF expression by GSCs, which patient-derived tumor models confirmed. VGF serves a dual role in the glioblastoma hierarchy by promoting GSC survival and stemness in vitro and in vivo while also supporting DGC survival and inducing DGC secretion of BDNF. Collectively, these data demonstrate that differentiated glioblastoma cells cooperate with stem-like tumor cells through BDNF-NTRK2-VGF paracrine signaling to promote tumor growth.

Death domain of p75 neurotrophin receptor: a structural perspective on an intracellular signalling hub

The death domain (DD) is a globular protein motif with a signature feature of an all-helical Greek-key motif. It is a primary mediator of a variety of biological activities, including apoptosis, cell survival and cytoskeletal changes, which are related to many neurodegenerative diseases, neurotrauma, and cancers. DDs exist in a wide range of signalling proteins including p75 neurotrophin receptor (p75^NTR ), a member of the tumour necrosis factor receptor superfamily. The specific signalling mediated by p75^NTR in a given cell depends on the type of ligand engaging the extracellular domain and the recruitment of cytosolic interactors to the intracellular domain, especially the DD, of the receptor. In solution, the p75^NTR -DDs mainly form a symmetric non-covalent homodimer. In response to extracellular signals, conformational changes in the p75^NTR extracellular domain (ECD) propagate to the p75^NTR -DD through the disulfide-bonded transmembrane domain (TMD) and destabilize the p75^NTR -DD homodimer, leading to protomer separation and exposure of binding sites on the DD surface. In this review, we focus on recent advances in the study of the structural mechanism of p75^NTR -DD signalling through recruitment of diverse intracellular interactors for the regulation and control of diverse functional outputs.

From Neural Crest Development to Cancer and Vice Versa: How p75NTR and (Pro)neurotrophins Could Act on Cell Migration and Invasion?

The p75 neurotrophin receptor (p75^NTR), also known as low-affinity nerve growth factor, belongs to the tumor necrosis factor family of receptors. p75^NTR is widely expressed in the nervous system during the development, as well as, in the neural crest population, since p75^NTR has been described as ubiquitously expressed and considered as a neural crest marker. Neural crest cells (NCCs) constitute an transient population accurately migrating and invading, with precision, defined sites of the embryo. During migration, NCCs are guided along distinct migratory pathways by specialized molecules present in the extracellular matrix or on the surfaces of those cells. Two main processes direct NCC migration during the development: (1) an epithelial-to-mesenchymal transition and (2) a process known as contact inhibition of locomotion. In adults, p75^NTR remains expressed by NCCs and has been identified in an increasing number of cancer cells. Nonetheless, the regulation of the expression of p75^NTR and the underlying mechanisms in stem cell biology or cancer cells have not yet been sufficiently addressed. The main objective of this review is therefore to analyze elements of our actual knowledge regarding p75^NTR roles during the development (mainly focusing on neural crest development) and see how we can transpose that information from development to cancer (and vice versa) to better understand the link between p75^NTR and cell migration and invasion. In this review, we successively analyzed the molecular mechanisms of p75^NTR when it interacts with several coreceptors and/or effectors. We then analyzed which signaling pathways are the most activated or linked to NCC migration during the development. Regarding cancer, we analyzed the described molecular pathways underlying cancer cell migration when p75^NTR was correlated to cancer cell migration and invasion. From those diverse sources of information, we finally summarized potential molecular mechanisms underlying p75^NTR activation in cell migration and invasion that could lead to new research areas to develop new therapeutic protocols.

Microglia/Astrocytes-Glioblastoma Crosstalk: Crucial Molecular Mechanisms and Microenvironmental Factors

In recent years, the functions of glial cells, namely, astrocytes and microglia, have gained prominence in several diseases of the central nervous system, especially in glioblastoma (GB), the most malignant primary brain tumor that leads to poor clinical outcomes. Studies showed that microglial cells or astrocytes play a critical role in promoting GB growth. Based on the recent findings, the complex network of the interaction between microglial/astrocytes cells and GB may constitute a potential therapeutic target to overcome tumor malignancy. In the present review, we summarize the most important mechanisms and functions of the molecular factors involved in the microglia or astrocytes-GB interactions, which is particularly the alterations that occur in the cell's extracellular matrix and the cytoskeleton. We overview the cytokines, chemokines, neurotrophic, morphogenic, metabolic factors, and non-coding RNAs actions crucial to these interactions. We have also discussed the most recent studies regarding the mechanisms of transportation and communication between microglial/astrocytes - GB cells, namely through the ABC transporters or by extracellular vesicles. Lastly, we highlight the therapeutic challenges and improvements regarding the crosstalk between these glial cells and GB.

Complexity and Selectivity of γ-Secretase Cleavage on Multiple Substrates: Consequences in Alzheimer's Disease and Cancer

The processing of the amyloid-β protein precursor (AβPP) by β- and γ-secretases is a pivotal event in the genesis of Alzheimer's disease (AD). Besides familial mutations on the AβPP gene, or upon its overexpression, familial forms of AD are often caused by mutations or deletions in presenilin 1 (PSEN1) and 2 (PSEN2) genes: the catalytic components of the proteolytic enzyme γ-secretase (GS). The "amyloid hypothesis", modified over time, states that the aberrant processing of AβPP by GS induces the formation of specific neurotoxic soluble amyloid-β (Aβ) peptides which, in turn, cause neurodegeneration. This theory, however, has recently evidenced significant limitations and, in particular, the following issues are debated: 1) the concept and significance of presenilin's "gain of function" versus "loss of function"; and 2) the presence of several and various GS substrates, which interact with AβPP and may influence Aβ formation. The latter consideration is suggestive: despite the increasing number of GS substrates so far identified, their reciprocal interaction with AβPP itself, even in the AD field, is significantly unexplored. On the other hand, GS is also an important pharmacological target in the cancer field; inhibitors or GS activity are investigated in clinical trials for treating different tumors. Furthermore, the function of AβPP and PSENs in brain development and in neuronal migration is well known. In this review, we focused on a specific subset of GS substrates that directly interact with AβPP and are involved in its proteolysis and signaling, by evaluating their role in neurodegeneration and in cell motility or proliferation, as a possible connection between AD and cancer.

Targetome Analysis Revealed Involvement of MiR-126 in Neurotrophin Signaling Pathway: A Possible Role in Prevention of Glioma Development

OBJECTIVES

For the first time, we used molecular signaling pathway enrichment analysis to determine possible involvement of miR-126 and IRS-1 in neurotrophin pathway.

MATERIALS AND METHODS

In this prospective study, Validated and predicted targets (targetome) of miR-126 were collected following searching miRtarbase (http://mirtarbase.mbc.nctu.edu.tw/) and miRWalk 2.0 databases, respectively. Then, approximate expression of miR-126 targeting in Glioma tissue was examined using UniGene database (http://www.ncbi. nlm.nih.gov/unigene). In silico molecular pathway enrichment analysis was carried out by DAVID 6.7 database (http://david. abcc.ncifcrf.gov/) to explore which signaling pathway is related to miR-126 targeting and how miR-126 attributes to glioma development.

RESULTS

MiR-126 exerts a variety of functions in cancer pathogenesis via suppression of expression of target gene including PI3K, KRAS, EGFL7, IRS-1 and VEGF. Our bioinformatic studies implementing DAVID database, showed the involvement of miR-126 target genes in several signaling pathways including cancer pathogenesis, neurotrophin functions, Glioma formation, insulin function, focal adhesion production, chemokine synthesis and secretion and regulation of the actin cytoskeleton.

CONCLUSIONS

Taken together, we concluded that miR-126 enhances the formation of glioma cancer stem cell probably via down regulation of IRS-1 in neurotrophin signaling pathway.

CD271+ Cells Are Diagnostic and Prognostic and Exhibit Elevated MAPK Activity in SHH Medulloblastoma

The extensive heterogeneity both between and within the medulloblastoma subgroups underscores a critical need for variant-specific biomarkers and therapeutic strategies. We previously identified a role for the CD271/p75 neurotrophin receptor (p75NTR) in regulating stem/progenitor cells in the SHH medulloblastoma subgroup. Here, we demonstrate the utility of CD271 as a novel diagnostic and prognostic marker for SHH medulloblastoma using IHC analysis and transcriptome data across 763 primary tumors. RNA sequencing of CD271⁺ and CD271^- cells revealed molecularly distinct, coexisting cellular subsets, both in vitro and in vivo MAPK/ERK signaling was upregulated in the CD271⁺ population, and inhibiting this pathway reduced endogenous CD271 levels, stem/progenitor cell proliferation, and cell survival as well as cell migration in vitro Treatment with the MEK inhibitor selumetinib extended survival and reduced CD271 levels in vivo, whereas, treatment with vismodegib, a well-known smoothened (SMO) inhibitor currently in clinical trials for the treatment of recurrent SHH medulloblastoma, had no significant effect in our models. Our study demonstrates the clinical utility of CD271 as both a diagnostic and prognostic tool for SHH medulloblastoma tumors and reveals a novel role for MEK inhibitors in targeting CD271⁺ SHH medulloblastoma cells.Significance: This study identifies CD271 as a specific and novel biomarker of SHH-type medulloblastoma and that targeting CD271⁺ cells through MEK inhibition represents a novel therapeutic strategy for the treatment of SHH medulloblastoma. Cancer Res; 78(16); 4745-59. ©2018 AACR.

Expression of brain-derived neurotrophic factor and its receptor TrkB is associated with poor prognosis and a malignant phenotype in small cell lung cancer

OBJECTIVES

TrkB is a receptor for brain-derived neurotrophic factor (BDNF) and is highly expressed in various cancers, with BDNF-TrkB signaling having been implicated in tumor progression and metastasis. The role of the BDNF-TrkB system in small cell lung cancer (SCLC), a neuroendocrine cancer, has remained unclear, however. We examined BDNF and TrkB expression in SCLC patients as well as the function of BDNF-TrkB signaling in SCLC cell lines.

MATERIALS AND METHODS

BDNF and TrkB expression in tumor specimens of 58 SCLC patients and 20 non-small cell lung cancer (NSCLC) patients was examined by immunohistochemistry and was scored on the basis of the distribution and intensity of staining. TrkB-overexpressing SCLC (SBC5^TrkB) cells were established by retrovirus transduction and were examined for the effects of BDNF on intracellular signaling, cell proliferation, and cell migration in vitro.

RESULTS

The staining score for TrkB in NSCLC and SCLC specimens was 2.80 ± 0.19 and 3.60 ± 0.15, respectively, whereas that for BDNF was 1.95 ± 0.32 and 2.76 ± 0.14, respectively. High levels of both TrkB and BDNF expression in SCLC tumors were significantly associated with poor overall survival in multivariate analysis (hazard ratio = 1.821, P = 0.036). BDNF activated AKT and ERK signaling pathways in and promoted the migration of SBC5^TrkB cells, and these effects were attenuated by the pan-Trk inhibitor GNF-5837. GNF-5837 also inhibited the proliferation of SBC5^TrkB cells in the presence of BDNF.

CONCLUSION

Coexpression of BDNF and TrkB was associated with poor prognosis in SCLC patients, and BDNF promoted the migration of TrkB-overexpressing SCLC cells. TrkB is thus a potential therapeutic target for SCLC.

Genetic and molecular alterations in olfactory neuroblastoma: implications for pathogenesis, prognosis and treatment

Olfactory neuroblastoma (ONB, Esthesioneuroblastoma) is an infrequent neoplasm of the head and neck area derived from olfactory neuroepithelium. Despite relatively good prognosis a subset of patients shows recurrence, progression and/or metastatic disease, which requires additional treatment. However, neither prognostic nor predictive factors are well specified. Thus, we performed a literature search for the currently available data on disturbances in molecular pathways, cytogenetic changes and results gained by next generation sequencing (NGS) approaches in ONB in order to gain an overview of genetic alterations which might be useful for treating patients with ONB. We present briefly ONB molecular pathogenesis and propose potential therapeutic targets and prognostic factors. Possible therapeutic targets in ONB include: receptor tyrosine kinases (c-kit, PDGFR-b, TrkB; EGFR); somatostatin receptor; FGF-FGFR1 signaling; Sonic hedgehog pathway; apoptosis-related pathways (Bcl-2, TRAIL) and neoangiogenesis (VEGF; KDR). Furthermore, we compare high- and low-grade ONB, and describe its frequent mimicker: sinonasal neuroendocrine carcinoma. ONB is often a therapeutic challenge, so our goal should be the implementation of acquired knowledge into clinical practice, especially at pretreated, recurrent and metastatic stages. Moreover, the multicenter molecular studies are needed to increase the amount of available data.

Neurotrophin receptors in the pathogenesis, diagnosis and therapy of neurodegenerative diseases

In the last few years, exciting properties have emerged regarding the activation, signaling, mechanisms of action, and therapeutic targeting of the two types of neurotrophin receptors: the p75^NTR with its intracellular and extracellular peptides, the Trks, their precursors and their complexes. This review summarizes these new developments, with particular focus on neurodegenerative diseases. Based on the evolving knowledge, innovative concepts have been formulated regarding the pathogenesis of these diseases, especially the Alzheimer's and two other, the Parkinson's and Huntington's diseases. The medical progresses include original procedures of diagnosis, started from studies in mice and now investigated for human application, based on innovative classes of receptor agonists and blockers. In parallel, comprehensive studies have been and are being carried out for the development of drugs. The relevance of these studies is based on the limitations of the therapies employed until recently, especially for the treatment of Alzheimer's patients. Starting from well known drugs, previously employed for non-neurodegenerative diseases, the ongoing progress has lead to the development of small molecules that cross rapidly the blood-brain barrier. Among these molecules the most promising are specific blockers of the p75^NTR receptor. Additional drugs, that activate Trk receptors, were shown effective against synaptic loss and memory deficits. In the near future such approaches, coordinated with treatments with monoclonal antibodies and with developments in the microRNA field, are expected to improve the therapy of neurodegenerative diseases, and may be relevant also for other human disease conditions.

Differential Expression of Circular RNAs in Glioblastoma Multiforme and Its Correlation with Prognosis

OBJECTIVE: The present study aimed to explore the expression profiles of circular RNAs (circRNAs) in glioblastoma multiforme (GBM) in an attempt to identify potential core genes in the pathogenesis of this tumor. METHODS: Differentially expressed circRNAs were screened between tumor tissues from five GBM patients and five normal brain samples using Illumina Hiseq. Bioinformatics analysis was used to analyze their potential function. CircBRAF was further detected in different WHO grades glioma tissues and normal brain tissues. Kaplan-Meier curves and multivariate Cox's analysis were used to analyze the association between circBRAF expression level and prognosis of glioma patients. RESULTS: A total of 1411 differentially expressed circRNAs were identified in GBM patients including 206 upregulated circRNAs and 1205 downregulated circRNAs. Differential expression of circRNAs was closely associated with the biological process and molecular function. The downregulated circRNAs were mainly associated with ErbB and Neurotrophin signaling pathways. Moreover, the expression level of circBRAF in normal brain tissues was significantly higher than that in glioma tissues (P < .001). CircBRAF was significantly lower in glioma patients with high pathological grade (WHO III & IV) than those with low grade (WHO I & II) (P < .001). Cox analysis revealed that high circBRAF expression was an independent biomarker for predicting good progression-free survival and overall survival in glioma patients (HR = 0.413, 95% CI 0.201-0.849; HR = 0.299, 95% CI 0.135-0.661; respectively). CONCLUSION: The present study identified a profile of dysregulated circRNAs in GBM. Bioinformatics analysis showed that dysregulated circRNAs might be associated with tumorigenesis and development of GBM. In addition, circBRAF could severe as a biomarker for predicting pathological grade and prognosis in glioma patients.

The Role of Neurotrophin Signaling in Gliomagenesis: A Focus on the p75 Neurotrophin Receptor (p75NTR/CD271)

The p75 neurotrophin receptor (p75^NTR, a.k.a. CD271), a transmembrane glycoprotein and a member of the tumor necrosis family (TNF) of receptors, was originally identified as a nerve growth factor receptor in the mid-1980s. While p75^NTR is recognized to have important roles during neural development, its presence in both neural and nonneural tissues clearly supports the potential to mediate a broad range of functions depending on cellular context. Using an unbiased in vivo selection paradigm for genes underlying the invasive behavior of glioma, a critical characteristic that contributes to poor clinical outcome for glioma patients, we identified p75^NTR as a central regulator of glioma invasion. Herein we review the expanding role that p75^NTR plays in glioma progression with an emphasis on how p75^NTR may contribute to the treatment refractory nature of glioma. Based on the observation that p75^NTR is expressed and functional in two critical glioma disease reservoirs, namely, the highly infiltrative cells that evade surgical resection, and the radiation- and chemotherapy-resistant brain tumor-initiating cells (also referred to as brain tumor stem cells), we propose that p75^NTR and its myriad of downstream signaling effectors represent rationale therapeutic targets for this devastating disease. Lastly, we provide the provocative hypothesis that, in addition to the well-documented cell autonomous signaling functions, the neurotrophins, and their respective receptors, contribute in a cell nonautonomous manner to drive the complex cellular and molecular composition of the brain tumor microenvironment, an environment that fuels tumorigenesis.

Neurotrophin Trk Receptors: New Targets for Cancer Therapy

In the last few years, exciting reports have emerged regarding the role of the two types of neurotrophin receptors, p75^NTR and Trks, not only in neurons, where they were discovered, but also in non-neural cells and, especially, in numerous cancers, including breast, lung, colon-rectum, pancreas, prostate, glioblastoma, neuroblastoma, myeloma, and lymphoid tumors. Traditionally, p75^NTR, activated by all neurotrophins and their precursors, is an inhibitor. In various cancers, however, activated p75^NTR induces variable effects, from inhibition to stimulation of cell proliferation, dependent on their direct or coordinate/indirect mechanism(s) of action. TrkA, TrkB, and TrkC, activated by distinct neurotrophins, are high affinity stimulatory receptors. In cancers, activation of Trks, especially of TrkB, are stimulators of cell proliferation, aggressiveness, and metastases. In rare cancers, these processes are due not to receptor activation but to fusion or mutation of the encoding genes. A considerable panel of anti-Trk drugs, developed recently, has been investigated both in vitro and in living mice for their effects on cancer cells. Many such drugs protect from cancers by preventing cell proliferation and inducing apoptosis. At present, these drugs are under control by trials, to promote introduction in human therapy. Moreover, anti-Trk drugs have been employed also in combination with classical chemotherapeutic drugs. So far, studies in mice have been positive. The chemotherapeutic/anti-receptor combinations exhibited in fact increased potency and down-regulation of resistance, with no increase of side effects.

The brain-tumor related protein podoplanin regulates synaptic plasticity and hippocampus-dependent learning and memory

INTRODUCTION

Podoplanin is a cell-surface glycoprotein constitutively expressed in the brain and implicated in human brain tumorigenesis. The intrinsic function of podoplanin in brain neurons remains however uncharacterized.

MATERIALS AND METHODS

Using an established podoplanin-knockout mouse model and electrophysiological, biochemical, and behavioral approaches, we investigated the brain neuronal role of podoplanin.

RESULTS

Ex-vivo electrophysiology showed that podoplanin deletion impairs dentate gyrus synaptic strengthening. In vivo, podoplanin deletion selectively impaired hippocampus-dependent spatial learning and memory without affecting amygdala-dependent cued fear conditioning. In vitro, neuronal overexpression of podoplanin promoted synaptic activity and neuritic outgrowth whereas podoplanin-deficient neurons exhibited stunted outgrowth and lower levels of p-Ezrin, TrkA, and CREB in response to nerve growth factor (NGF). Surface Plasmon Resonance data further indicated a physical interaction between podoplanin and NGF.

DISCUSSION

This work proposes podoplanin as a novel component of the neuronal machinery underlying neuritogenesis, synaptic plasticity, and hippocampus-dependent memory functions. The existence of a relevant cross-talk between podoplanin and the NGF/TrkA signaling pathway is also for the first time proposed here, thus providing a novel molecular complex as a target for future multidisciplinary studies of the brain function in the physiology and the pathology. Key messages Podoplanin, a protein linked to the promotion of human brain tumors, is required in vivo for proper hippocampus-dependent learning and memory functions. Deletion of podoplanin selectively impairs activity-dependent synaptic strengthening at the neurogenic dentate-gyrus and hampers neuritogenesis and phospho Ezrin, TrkA and CREB protein levels upon NGF stimulation. Surface plasmon resonance data indicates a physical interaction between podoplanin and NGF. On these grounds, a relevant cross-talk between podoplanin and NGF as well as a role for podoplanin in plasticity-related brain neuronal functions is here proposed.

Structural Characterization of the p75 Neurotrophin Receptor: A Stranger in the TNFR Superfamily

Although p75 neurotrophin receptor (p75^NTR) was the founding member of the tumor necrosis factor (TNF) receptor superfamily (TNFRSF), it is an atypical TNFRSF protein. p75^NTR like TNF-R1 and Fas-R contain an extracellular domain with four cysteine-rich domains (CRD) and a death domain (DD) in the intracellular region. While TNFRSF proteins are activated by trimeric TNFSF ligands, p75^NTR forms dimers activated by dimeric neurotrophins that are structurally unrelated to TNFSF proteins. In addition, although p75^NTR shares with other members the interaction with the TNF receptor-associated factors to activate the NF-κB and cell death pathways, p75^NTR does not interact with the DD-containing proteins FADD, TRADD, or MyD88. By contrast, the DD of p75^NTR is able to recruit several protein interactors via a full catalog of DD interactions not described before in the TNFRSF. p75-DD forms homotypic symmetrical DD-DD complexes with itself and with the related p45-DD; forms heterotypic DD-CARD interactions with the RIP2-CARD domain, and forms a new interaction between a DD and RhoGDI. All these features, in addition to its promiscuous interactions with several ligands and coreceptors, its processing by α- and γ-secretases, the dimeric nature of its transmembrane domain and its "special" juxtamembrane region, make p75^NTR a truly stranger in the TNFR superfamily. In this chapter, I will summarize the known structural aspects of p75^NTR and I will analyze from a structural point of view, the similitudes and differences between p75^NTR and the other members of the TNFRSF.

Molecular Pathways: Receptor Ectodomain Shedding in Treatment, Resistance, and Monitoring of Cancer

Proteases known as sheddases cleave the extracellular domains of their substrates from the cell surface. The A Disintegrin and Metalloproteinases ADAM10 and ADAM17 are among the most prominent sheddases, being widely expressed in many tissues, frequently overexpressed in cancer, and promiscuously cleaving diverse substrates. It is increasingly clear that the proteolytic shedding of transmembrane receptors impacts pathophysiology and drug response. Receptor substrates of sheddases include the cytokine receptors TNFR1 and IL6R; the Notch receptors; type-I and -III TGFβ receptors; receptor tyrosine kinases (RTK) such as HER2, HER4, and VEGFR2; and, in particular, MET and TAM-family RTKs AXL and Mer (MerTK). Activation of receptor shedding by mechanical cues, hypoxia, radiation, and phosphosignaling offers insight into mechanisms of drug resistance. This particularly holds for kinase inhibitors targeting BRAF (such as vemurafenib and dabrafenib) and MEK (such as trametinib and cobimetinib), along with direct sheddase inhibitors. Receptor proteolysis can be detected in patient fluids and is especially relevant in melanoma, glioblastoma, lung cancer, and triple-negative breast cancer where RTK substrates, MAPK signaling, and ADAMs are frequently dysregulated. Translatable strategies to exploit receptor shedding include combination kinase inhibitor regimens, recombinant decoy receptors based on endogenous counterparts, and, potentially, immunotherapy. Clin Cancer Res; 23(3); 623-9. ©2016 AACR.

Analysis of Important Gene Ontology Terms and Biological Pathways Related to Pancreatic Cancer

Pancreatic cancer is a serious disease that results in more than thirty thousand deaths around the world per year. To design effective treatments, many investigators have devoted themselves to the study of biological processes and mechanisms underlying this disease. However, it is far from complete. In this study, we tried to extract important gene ontology (GO) terms and KEGG pathways for pancreatic cancer by adopting some existing computational methods. Genes that have been validated to be related to pancreatic cancer and have not been validated were represented by features derived from GO terms and KEGG pathways using the enrichment theory. A popular feature selection method, minimum redundancy maximum relevance, was employed to analyze these features and extract important GO terms and KEGG pathways. An extensive analysis of the obtained GO terms and KEGG pathways was provided to confirm the correlations between them and pancreatic cancer.

CD271 regulates the proliferation and motility of hypopharyngeal cancer cells

CD271 (p75 neurotrophin receptor) plays both positive and negative roles in cancer development, depending on the cell type. We previously reported that CD271 is a marker for tumor initiation and is correlated with a poor prognosis in human hypopharyngeal cancer (HPC). To clarify the role of CD271 in HPC, we established HPC cell lines and knocked down the CD271 expression using siRNA. We found that CD271-knockdown completely suppressed the cells’ tumor-forming capability both in vivo and in vitro. CD271-knockdown also induced cell-cycle arrest in G₀ and suppressed ERK phosphorylation. While treatment with an ERK inhibitor only partially inhibited cell growth, CDKN1C, which is required for maintenance of quiescence, was strongly upregulated in CD271-depleted HPC cells, and the double knockdown of CD271 and CDKN1C partially rescued the cells from G₀ arrest. In addition, either CD271 depletion or the inhibition of CD271-RhoA signaling by TAT-Pep5 diminished the in vitro migration capability of the HPC cells. Collectively, CD271 initiates tumor formation by increasing the cell proliferation capacity through CDKN1C suppression and ERK-signaling activation, and by accelerating the migration signaling pathway in HPC.

Intramuscular delivery of p75NTR ectodomain by an AAV vector attenuates cognitive deficits and Alzheimer's disease-like pathologies in APP/PS1 transgenic mice

The neurotrophin receptor p75 (p75NTR) is a receptor for amyloid-beta (Aβ) and mediates Aβ-induced neurodegenerative signals. The ectodomain of p75NTR (p75ECD) is a physiological protective factor against Aβ in Alzheimer's disease (AD). We have previously demonstrated that the shedding of p75ECD from the cell surface is down-regulated in AD brains and restoration of the p75ECD level in the brain, through intracranial administration of p75ECD by adeno-associated virus vectors, attenuates AD-like pathologies in an AD mouse model. In this study, we further investigated the feasibility and efficacy of peripheral administration of AAV-p75ECD on brain amyloid burden and associated pathogenesis. We found that intramuscular delivery of AAV-p75ECD increased the level of p75ECD in the blood, significantly improved the behavioral phenotype of amyloid precursor protein/PS1 transgenic mice, and reduced brain amyloid burden, attenuated Tau hyperphosphorylation, and neuroinflammation. Furthermore, intramuscular delivery of AAV-p75ECD was well tolerated. Our results indicate that peripheral delivery of p75ECD represents a safe and effective therapeutic strategy for AD. The ectodomain of p75NTR (p75ECD) is a physiological protective factor against amyloid-beta (Aβ) in Alzheimer's disease (AD). Intramuscular delivery of AAV-p75ECD increased the p75ECD levels in the blood, reduced brain amyloid burden through a 'peripheral sink' mechanism and alleviates AD-type pathologies. Peripheral delivery of p75ECD represents a promising therapeutic strategy for AD.

Nerve growth factor & TrkA as novel therapeutic targets in cancer

In the past 20years, nerve growth factor (NGF) and its receptors TrkA & p75NTR were recognized to be overexpressed in the overwhelming majority of human solid cancers. Recent studies discovered the presence of overactive TrkA signaling due to TrkA rearrangements or TrkA fusion products in frequent cancers like colorectal cancer, thyroid cancer, or acute myeloid leukemia. Thus, targeting TrkA/NGF via selective small-molecule-inhibitors or antibodies has gained enormous attention in the drug discovery sector. Clinical studies on the anti-cancer impact of NGF-blocking antibodies are likely to be accelerated after the recent removal of clinical holds on these agents by regulatory authorities. Based on these current developments, the present review provides not only a broad overview of the biological effects of NGF-TrkA-p75NTR on cancer cells and their microenvironment, but also explains why NGF and its receptors are going to evoke major interest as promising therapeutic anti-cancer targets in the coming decade.

Neurotrophin signaling in cancer stem cells

Cancer stem cells (CSCs), are thought to be at the origin of tumor development and resistance to therapies. Thus, a better understanding of the molecular mechanisms involved in the control of CSC stemness is essential to the design of more effective therapies for cancer patients. Cancer cell stemness and the subsequent expansion of CSCs are regulated by micro-environmental signals including neurotrophins. Over the years, the roles of neurotrophins in tumor development have been well established and regularly reviewed. Especially, nerve growth factor (NGF) and brain-derived neurotrophic factor (BDNF) are reported to stimulate tumor cell proliferation, survival, migration and/or invasion, and favors tumor angiogenesis. More recently, neurotrophins have been reported to regulate CSCs. This review briefly presents neurotrophins and their receptors, summarizes their roles in different cancers, and discusses the emerging evidence of neurotrophins-induced enrichment of CSCs as well as the involved signaling pathways.

Gamma-secretase-independent role for cadherin-11 in neurotrophin receptor p75 (p75(NTR)) mediated glioblastoma cell migration

The p75 neurotrophin receptor (p75(NTR)) undergoes γ-secretase-mediated regulated intramembrane proteolysis and is involved in glioblastoma cell migration and invasion. Consistent with previous reports, in this study we show that p75NTR increases U87-MG glioblastoma cell migration, which is reversed by inhibition of γ-secretase activity. However, we show that expression or stabilization of the γ-secretase-generated p75(NTR) intracellular domain (ICD) is not sufficient to induce U87-MG glioblastoma cell migration, and that exogenous expression of p75(NTR) ICD inhibits p75(NTR)-mediated glioblastoma cell (U87-MG and U373-MG) migration. To identify pathways and to determine how p75(NTR) mediates glioblastoma migration we utilized a microarray approach to assess differential gene expression profiles between parental U87-MG and cells stably expressing wild-type p75(NTR), a γ-secretase cleavage-resistant chimeric p75(NTR) mutant (p75FasTM) and the γ-secretase-generated p75(NTR)-ICD, which mimics constitutively cleaved p75(NTR) receptor. In our microarray data analysis we identified a subset of genes that were constitutively up-regulated in wild-type p75(NTR) cells, which were also repressed in p75(NTR) ICD expressing cells. Furthermore, our data revealed among the many differentially expressed genes, cadherin-11 (Cdh-11), matrix metalloproteinase 12 and relaxin/insulin-like family peptide receptor 2 as constitutively up-regulated in wild-type p75(NTR) cells, independent of γ-secretase activity. Consistent with a role in glioblastoma migration, we found that U87-p75(NTR) cells express higher levels of Cdh-11 protein and that siRNA-mediated knockdown of Cdh-11 resulted in a significant decrease in p75(NTR)-mediated glioblastoma cell migration. Therefore, we hypothesize that p75(NTR) can impact U87-MG glioblastoma cell migration in a γ-secretase-independent manner through modulation of specific genes, including Cdh-11, and that both γ-secretase-independent and -dependent mechanisms are involved in p75(NTR)-mediated U87-MG glioblastoma cell migration.

Characterization of novel biomarkers in selecting for subtype specific medulloblastoma phenotypes

Major research efforts have focused on defining cell surface marker profiles for characterization and selection of brain tumor stem/progenitor cells. Medulloblastoma is the most common primary malignant pediatric brain cancer and consists of 4 molecular subgroups: WNT, SHH, Group 3 and Group 4. Given the heterogeneity within and between medulloblastoma variants, surface marker profiles may be subtype-specific. Here, we employed a high throughput flow cytometry screen to identify differentially expressed cell surface markers in self-renewing vs. non-self-renewing SHH medulloblastoma cells. The top 25 markers were reduced to 4, CD271/p75NTR/NGFR, CD106/VCAM1, EGFR and CD171/NCAM-L1, by evaluating transcript levels in SHH tumors relative to samples representing the other variants. However, only CD271/p75NTR/NGFR and CD171/NCAM-L1 maintain differential expression between variants at the protein level. Functional characterization of CD271, a low affinity neurotrophin receptor, in cell lines and primary cultures suggested that CD271 selects for lower self-renewing progenitors or stem cells. Moreover, CD271 levels were negatively correlated with expression of SHH pathway genes. Our study reveals a novel role for CD271 in SHH medulloblastoma and suggests that targeting CD271 pathways could lead to the design of more selective therapies that lessen the broad impact of current treatments on developing nervous systems.

Anti-apoptotic role and clinical relevance of neurotrophins in diffuse large B-cell lymphomas

Background:

Diffuse large B-cell lymphoma (DLBCL) is a fatal malignancy that needs to identify new targets for additional therapeutic options. This study aimed to clarify the clinical and biological significance of endogenous neurotrophin (nerve growth factor (NGF) and brain-derived neurotrophic factor (BDNF)) in DLBCL biopsy samples and cell lines.

Methods:

We analysed expression of NGF, BDNF, and their receptors (Trk, p75^NTR) in 51 biopsies and cell lines by immunohistochemistry, immunofluorescence, and western blotting. To investigate the biological role of BDNF/TrkB/p75^NTR axis, effects of neurotrophin signalling inhibition were determined on tumour cell survival and vascular endothelial growth factor (VEGF) secretion. The pharmacological pan-Trk inhibitor K252a was used for in vitro and in vivo studies.

Results:

A BDNF/TrkB axis was expressed in all biopsies, which was independent of the germinal centre B-cell (GCB)/non-GCB profile. p75^NTR, TrkB, and BDNF tumour scores were significantly correlated and high NGF expression was significantly associated with MUM1/IRF4, and the non-GCB subtype. Diffuse large B-cell lymphoma cell lines co-expressed neurotrophins and their receptors. The full-length TrkB receptor was found in all cell lines, which was also phosphorylated at Tyr-817. p75^NTR was associated to Trk and not to its cell death co-receptor sortilin. In vitro, inhibition of neurotrophin signalling induced cell apoptosis. K252a caused cell apoptosis, decreased VEGF secretion, and potentiated rituximab effect, notably in less rituximab-sensitive cells. In vivo, K252a significantly reduced tumour growth and potentiated the effects of rituximab in a GCB-DLBCL xenograft model.

Conclusions:

This work argues for a pro-survival role of endogenous neurotrophins in DLBCLs and inhibition of Trk signalling might be a potential treatment strategy for rituximab resistant subgroups.

Enriched environment reduces glioma growth through immune and non-immune mechanisms in mice

Mice exposed to standard (SE) or enriched environment (EE) were transplanted with murine or human glioma cells and differences in tumour development were evaluated. We report that EE exposure affects: (i) tumour size, increasing mice survival; (ii) glioma establishment, proliferation and invasion; (iii) microglia/macrophage (M/Mφ) activation; (iv) natural killer (NK) cell infiltration and activation; and (v) cerebral levels of IL-15 and BDNF. Direct infusion of IL-15 or BDNF in the brain of mice transplanted with glioma significantly reduces tumour growth. We demonstrate that brain infusion of IL-15 increases the frequency of NK cell infiltrating the tumour and that NK cell depletion reduces the efficacy of EE and IL-15 on tumour size and of EE on mice survival. BDNF infusion reduces M/Mφ infiltration and CD68 immunoreactivity in tumour mass and reduces glioma migration inhibiting the small G protein RhoA through the truncated TrkB.T1 receptor. These results suggest alternative approaches for glioma treatment.

Circulating biomarker panels for targeted therapy in brain tumors

An important goal of oncology is the development of cancer risk-identifier biomarkers that aid early detection and target therapy. High-throughput profiling represents a major concern for cancer research, including brain tumors. A promising approach for efficacious monitoring of disease progression and therapy could be circulating biomarker panels using molecular proteomic patterns. Tailoring treatment by targeting specific protein-protein interactions and signaling networks, microRNA and cancer stem cell signaling in accordance with tumor phenotype or patient clustering based on biomarker panels represents the future of personalized medicine for brain tumors. Gathering current data regarding biomarker candidates, we address the major challenges surrounding the biomarker field of this devastating tumor type, exploring potential perspectives for the development of more effective predictive biomarker panels.

ShcC proteins: brain aging and beyond

To date, most studies of Shc family of signaling adaptor proteins have been focused on the near-ubiquitously expressed ShcA, indicating its relevance to age-related diseases and longevity. Although the role of the neuronal ShcC protein is much less investigated, accumulated evidence suggests its importance for neuroprotection against such aging-associated conditions as brain ischemia and oxidative stress. Here, we summarize more than decade of studies on the ShcC expression and function in normal brain, age-related brain pathologies and immune disorders with a focus on the interactions of ShcC with signaling proteins/pathways, and the possible implications of these interactions for changes associated with aging.

Neurotrophin signaling via TrkB and TrkC receptors promotes the growth of brain tumor-initiating cells

Neurotrophins and their receptors are frequently expressed in malignant gliomas, yet their functions are largely unknown. Previously, we have shown that p75 neurotrophin receptor is required for glioma invasion and proliferation. However, the role of Trk receptors has not been examined. In this study, we investigated the importance of TrkB and TrkC in survival of brain tumor-initiating cells (BTICs). Here, we show that human malignant glioma tissues and also tumor-initiating cells isolated from fresh human malignant gliomas express the neurotrophin receptors TrkB and TrkC, not TrkA, and they also express neurotrophins NGF, BDNF, and neurotrophin 3 (NT3). Specific activation of TrkB and TrkC receptors by ligands BDNF and NT3 enhances tumor-initiating cell viability through activation of ERK and Akt pathways. Conversely, TrkB and TrkC knockdown or pharmacologic inhibition of Trk signaling decreases neurotrophin-dependent ERK activation and BTIC growth. Further, pharmacological inhibition of both ERK and Akt pathways blocked BDNF, and NT3 stimulated BTIC survival. Importantly, attenuation of BTIC growth by EGFR inhibitors could be overcome by activation of neurotrophin signaling, and neurotrophin signaling is sufficient for long term BTIC growth as spheres in the absence of EGF and FGF. Our results highlight a novel role for neurotrophin signaling in brain tumor and suggest that Trks could be a target for combinatorial treatment of malignant glioma.

Neurotrophins are expressed in giant cell arteritis lesions and may contribute to vascular remodeling

Introduction

Giant cell arteritis (GCA) is characterized by intimal hyperplasia leading to ischaemic manifestations that involve large vessels. Neurotrophins (NTs) and their receptors (NTRs) are protein factors for growth, differentiation and survival of neurons. They are also involved in the migration of vascular smooth muscle cells (VSMCs). Our aim was to investigate whether NTs and NTRs are involved in vascular remodelling of GCA.

Methods

We included consecutive patients who underwent a temporal artery biopsy for suspected GCA. We developed an enzymatic digestion method to obtain VSMCs from smooth muscle cells in GCA patients and controls. Neurotrophin protein and gene expression and functional assays were studied from these VSMCs. Neurotrophin expression was also analysed by immunohistochemistry in GCA patients and controls.

Results

Whereas temporal arteries of both GCA patients (n = 22) and controls (n = 21) expressed nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), tropomyosin receptor kinase B (TrkB) and sortilin, immunostaining was more intense in GCA patients, especially in the media and intima, while neurotrophin-3 (NT-3) and P75 receptor (P75^NTR) were only detected in TA from GCA patients. Expression of TrkB, a BDNF receptor, was higher in GCA patients with ischaemic complications. Serum NGF was significantly higher in GCA patients (n = 28) vs. controls (n = 48), whereas no significant difference was found for BDNF and NT-3. NGF and BDNF enhanced GCA-derived temporal artery VSMC proliferation and BDNF facilitated migration of temporal artery VSMCs in patients with GCA compared to controls.

Conclusions

Our results suggest that NTs and NTRs are involved in vascular remodelling of GCA. In GCA-derived temporal artery VSMC, NGF promoted proliferation and BDNF enhanced migration by binding to TrkB and p75^NTR receptors. Further experiments are needed on a larger number of VSMC samples to confirm these results.

Electronic supplementary material

The online version of this article (doi:10.1186/s13075-014-0487-z) contains supplementary material, which is available to authorized users.