Upregulation of beta-amyloid precursor protein expression in glioblastoma multiforme

Insights into Dysregulated Neurological Biomarkers in Cancer

The link between neurodegenerative diseases (NDs) and cancer has generated greater interest in biomedical research, with decades of global studies investigating neurodegenerative biomarkers in cancer to better understand possible connections. Tau, amyloid-β, α-synuclein, SOD1, TDP-43, and other proteins associated with nervous system diseases have also been identified in various types of solid and malignant tumors, suggesting a potential overlap in pathological processes. In this review, we aim to provide an overview of current evidence on the role of these proteins in cancer, specifically examining their effects on cell proliferation, apoptosis, chemoresistance, and tumor progression. Additionally, we discuss the diagnostic and therapeutic implications of this interconnection, emphasizing the importance of further research to completely comprehend the clinical implications of these proteins in tumors. Finally, we explore the challenges and opportunities in targeting these proteins for the development of new targeted anticancer therapies, providing insight into how to integrate knowledge of NDs in oncology research.

Amyloids and brain cancer: molecular linkages and crossovers

Amyloids are high-order proteinaceous formations deposited in both intra- and extracellular spaces. These aggregates have tendencies to deregulate cellular physiology in multiple ways; for example, altered metabolism, mitochondrial dysfunctions, immune modulation, etc. When amyloids are formed in brain tissues, the endpoint often is death of neurons. However, interesting but least understood is a close connection of amyloids with another set of conditions in which brain cells proliferate at an extraordinary rate and form tumor inside brain. Glioblastoma is one such condition. Increasing number of evidence indicate a possible link between amyloid formation and depositions in brain tumors. Several proteins associated with cell cycle regulation and apoptotic pathways themselves have shown to possess high tendencies to form amyloids. Tumor suppressor protein p53 is one prominent example that mutate, oligomerize and form amyloids leading to loss- or gain-of-functions and cause increased cell proliferation and malignancies. In this review article, we present available examples, genetic links and common pathways that indicate that possibly the two distantly placed pathways: amyloid formation and developing cancers in the brain have similarities and are mechanistically intertwined together.

Molecular Characteristics of Amyloid Precursor Protein (APP) and Its Effects in Cancer

Amyloid precursor protein (APP) is a type 1 transmembrane glycoprotein, and its homologs amyloid precursor-like protein 1 (APLP1) and amyloid precursor-like protein 2 (APLP2) are highly conserved in mammals. APP and APLP are known to be intimately involved in the pathogenesis and progression of Alzheimer's disease and to play important roles in neuronal homeostasis and development and neural transmission. APP and APLP are also expressed in non-neuronal tissues and are overexpressed in cancer cells. Furthermore, research indicates they are involved in several cancers. In this review, we examine the biological characteristics of APP-related family members and their roles in cancer.

RNAi for contactin 2 inhibits proliferation of U87-glioma stem cells by downregulating AICD, EGFR, and HES1

Glioblastoma is the most common form of malignant brain tumors and has a poor prognosis. Glioma stem cells (GSCs) are thought to be responsible for the aberrant proliferation and invasion. Targeting the signaling pathways that promote proliferation in GSCs is one of the strategies for glioma treatment. In this study, we found increased expression of contactin 2 (CNTN2) and amyloid β precursor protein (APP) in U87-derived GSCs (U87-GSCs). RNA interference (RNAi) for CNTN2 downregulated the expression of APP intracellular domain (AICD), which is the proteolytic product of APP. Treatment with CNTN2 RNAi inhibited the proliferation of U87-GSCs. CNTN2 RNAi decreased the expression of epidermal growth factor receptor and HES1, which are potential targets of AICD. In summary, inhibition of the CNTN2/APP signaling pathway may repress the proliferation in U87-GSCs via downregulating the expression of HES1 and epidermal growth factor receptor. CNTN2/APP/AICD signaling pathway plays an important role in U87 glial tumorigenesis. Further studies are warranted to elucidate the role of these signaling pathways in other sources of GSCs. Depending on their role in proliferation in other sources of GSCs, members of the CNTN2/APP/AICD signaling pathway may provide novel targets for the development of therapy for glioblastomas.

Comprehensive proteome profiling of glioblastoma-derived extracellular vesicles identifies markers for more aggressive disease

Extracellular vesicles (EVs) play key roles in glioblastoma (GBM) biology and represent novel sources of biomarkers that are detectable in the peripheral circulation. Despite this notionally non-invasive approach to assess GBM tumours in situ, a comprehensive GBM EV protein signature has not been described. Here, EVs secreted by six GBM cell lines were isolated and analysed by quantitative high-resolution mass spectrometry. Overall, 844 proteins were identified in the GBM EV proteome, of which 145 proteins were common to EVs secreted by all cell lines examined; included in the curated EV compendium (Vesiclepedia_559; http://microvesicles.org). Levels of 14 EV proteins significantly correlated with cell invasion (invadopodia production; r² > 0.5, p < 0.05), including several proteins that interact with molecules responsible for regulating invadopodia formation. Invadopodia, actin-rich membrane protrusions with proteolytic activity, are associated with more aggressive disease and are sites of EV release. Gene levels corresponding to invasion-related EV proteins showed that five genes (annexin A1, actin-related protein 3, integrin-β1, insulin-like growth factor 2 receptor and programmed cell death 6-interacting protein) were significantly higher in GBM tumours compared to normal brain in silico, with common functions relating to actin polymerisation and endosomal sorting. We also show that Cavitron Ultrasonic Surgical Aspirator (CUSA) washings are a novel source of brain tumour-derived EVs, demonstrated by particle tracking analysis, TEM and proteome profiling. Quantitative proteomics corroborated the high levels of proposed invasion-related proteins in EVs enriched from a GBM compared to low-grade astrocytoma tumour. Large-scale clinical follow-up of putative biomarkers, particularly the proposed survival marker annexin A1, is warranted.

Interleukin-1β and transforming growth factor-β cooperate to induce neurosphere formation and increase tumorigenicity of adherent LN-229 glioma cells

INTRODUCTION

Glioma stem cells (GSCs) have the property of self-renewal and appear to be a driving force for the initiation and recurrence of gliomas. We recently found that the human tumorigenic LN-229 glioma cell line failed to form neurospheres in serum-free conditions and generated mostly small tumors in vivo, suggesting that either LN-229 GSCs are not active in these conditions or GSCs are absent in the LN-229 cell line.

METHODS

Using self-renewal assay, soft-agar colony assay, cell proliferation assay, invasion assay, real time PCR analysis, ELISA and in vivo tumorigenic assay, we investigated the effects of interleukin (IL)-1β and transforming growth factor (TGF)-β on the development of GSCs from LN-229 cells.

RESULTS

Here, we demonstrate that the combination of IL-1β and TGF-β can induce LN-229 cells to form neurospheres in serum-free medium. IL-1β/TGF-β-induced neurospheres display up-regulated expression of stemness factor genes (nestin, Bmi-1, Notch-2 and LIF), and increased invasiveness, drug resistance and tumor growth in vivo: hallmarks of GSCs. These results indicate that IL-1β and TGF-β cooperate to induce a GSC phenotype in the LN-229 cell line. Induction of nestin, LIF and Notch-2 by IL-1β/TGF-β can be reverted after cytokine withdrawal. Remarkably, however, up-regulated Bmi-1 levels remained unchanged after cytokine withdrawal; and the cytokine-withdrawn cells maintained strong clonogenicity, suggesting that Bmi-1 may play a crucial role in tumorigenesis.

CONCLUSIONS

Our finding indicates that glioma cells without self-renewal capability in standard conditions could also contribute to glioma malignancy when cytokines, such as IL-1β and TGF-β, are present in the tumor environment. Targeting GSC-promoting cytokines that are highly expressed in glioblastomas may contribute to the development of more effective glioma therapies.

Critical role of cPLA2 in Aβ oligomer-induced neurodegeneration and memory deficit

Soluble beta-amyloid (Aβ) oligomers are considered to putatively play a critical role in the early synapse loss and cognitive impairment observed in Alzheimer's disease. We previously demonstrated that Aβ oligomers activate cytosolic phospholipase A(2) (cPLA(2)), which specifically releases arachidonic acid from membrane phospholipids. We here observed that cPLA(2) gene inactivation prevented the alterations of cognitive abilities and the reduction of hippocampal synaptic markers levels noticed upon a single intracerebroventricular injection of Aβ oligomers in wild type mice. We further demonstrated that the Aβ oligomer-induced sphingomyelinase activation was suppressed and that phosphorylation of Akt/protein kinase B (PKB) was preserved in neuronal cells isolated from cPLA(2)(-/-) mice. Interestingly, expression of the Aβ precursor protein (APP) was reduced in hippocampus homogenates and neuronal cells from cPLA(2)(-/-) mice, but the relationship with the resistance of these mice to the Aβ oligomer toxicity requires further investigation. These results therefore show that cPLA(2) plays a key role in the Aβ oligomer-associated neurodegeneration, and as such represents a potential therapeutic target for the treatment of Alzheimer's disease.

Functions of Aβ, sAPPα and sAPPβ : similarities and differences

Amyloid peptide (Aβ) is derived from the cleavage of amyloid precursor protein (APP), which also generates the soluble peptide APPβ (sAPPβ). An antagonist and major APP metabolic pathway involves cleavage by alpha secretase, which releases sAPPα. Although soluble Aβ oligomers are neurotoxic, Aβ monomers share similar properties with sAPPα. These include neurotrophic and neuroprotective effects, as well as stimulation of neural-progenitor proliferation. The properties of Aβ monomers and the neurotrophic capacity of sAPPβ to stimulate axonal outgrowth suggest that Aβ production is not deleterious per se. Consequently, therapeutic strategies for Alzheimer's disease that are targeted at Aβ-cleaving enzymes should modulate rather than inhibit Aβ generation. These strategies should focus on the factors that induce the conversion of Aβ monomers into toxic soluble oligomers. Another interesting therapeutic approach is to focus on the mechanisms of the different properties of sAPPα. Indeed, increasing sAPPα levels could shift proliferating cells towards tumorigenesis. In contrast to its neuroprotective effects, sAPPα is also able to activate microglia, leading to neurotoxicity. Understanding the mechanisms that underlie the different properties of sAPPα could therefore lead to the development of therapeutic strategies against Alzheimer's disease, which could be curative as well as preventive.

Retinal amyloid peptides and complement factor H in transgenic models of Alzheimer's disease

Murine transgenic models of Alzheimer's disease (Tg-AD) have been useful to analyze the contribution of β-amyloid precursor protein (βAPP), Aβ42 peptide deposition, and the proinflammatory mechanisms that characterize Alzheimer-type neuropathology. In this report, we have studied the levels of βAPP, Aβ40 and Aβ42 peptide, as well as the innate immune and inflammatory response-regulator complement factor H in the brain and retina in four different Tg-AD models including Tg2576, PSAPP, 3xTg-AD, and 5xFAD. Aged, symptomatic 5xFAD mice showed the highest retinal abundance of Aβ42 peptides and the highest deficits in complement factor H. This may be a useful model to study the mechanisms of amyloid-mediated inflammatory degeneration. The superior colliculus and retina obtained from late-stage Alzheimer's disease revealed upregulated amyloidogenic and inflammatory signaling along the anteroposterior axis of the retinal-primary visual cortex pathway.

Micro-RNA-128 (miRNA-128) down-regulation in glioblastoma targets ARP5 (ANGPTL6), Bmi-1 and E2F-3a, key regulators of brain cell proliferation

High density micro-RNA (miRNA) arrays, fluorescent-reporter miRNA assay and Northern miRNA dot-blot analysis show that a brain-enriched miRNA-128 is significantly down-regulated in glioblastoma multiforme (GBM) and in GBM cell lines when compared to age-matched controls. The down-regulation of miRNA-128 was found to inversely correlate with WHO tumor grade. Three bioinformatics-verified miRNA-128 targets, angiopoietin-related growth factor protein 5 (ARP5; ANGPTL6), a transcription suppressor that promotes stem cell renewal and inhibits the expression of known tumor suppressor genes involved in senescence and differentiation, Bmi-1, and a transcription factor critical for the control of cell-cycle progression, E2F-3a, were found to be up-regulated. Addition of exogenous miRNA-128 to CRL-1690 and CRL-2610 GBM cell lines (a) restored 'homeostatic' ARP5 (ANGPTL6), Bmi-1 and E2F-3a expression, and (b) significantly decreased the proliferation of CRL-1690 and CRL-2610 cell lines. Our data suggests that down-regulation of miRNA-128 may contribute to glioma and GBM, in part, by coordinately up-regulating ARP5 (ANGPTL6), Bmi-1 and E2F-3a, resulting in the proliferation of undifferentiated GBM cells.

Induction of terminal differentiation in melanoma cells on downregulation of beta-amyloid precursor protein

The incidence of melanoma, the most aggressive type of skin cancer, is increasing dramatically, and an effective treatment for patients with advanced disease is as yet unavailable. Greater insight into the molecular features of primary and metastatic melanoma is required, particularly the identification of key regulatory genes that shield the tumor cells from terminal differentiation and apoptosis. The beta-amyloid precursor protein (APP) is a cell surface receptor and the transmembrane precursor of the Abeta-peptide, which has an important role in Alzheimer's disease. The study presented here provides evidence that APP is expressed at high levels in advanced-stage melanomas, and that the cells cleave APP and secrete sAPP. We show that blocking the expression of APP by RNA interference impairs the proliferation of metastatic melanoma cells and leads to their terminal and irreversible differentiation. In addition, suppressing APP expression in a metastatic melanoma cell line renders the cells susceptible to several chemotherapeutic agents. Targeting APP may thus constitute a new approach to the treatment of this disease.

Up-regulation of micro-RNA-221 (miRNA-221; chr Xp11.3) and caspase-3 accompanies down-regulation of the survivin-1 homolog BIRC1 (NAIP) in glioblastoma multiforme (GBM)

Glioblastoma multiforme (GBM) represents a class of malignant gliomas which rapidly proliferate, invade and destroy surrounding brain tissues. This study examined micro-RNA (miRNA) speciation and miRNA effects on gene expression in six ATCC glioma and GBM cell lines and in 14 glioma and GBM samples obtained from human brain biopsy. We observed selective up-regulation of miRNA-221 and down-regulation of a miRNA-221 messenger RNA target encoding the survivin-1 homolog BIRC1, a neuronal inhibitor of apoptosis protein (NIAP) and marker for neurodegeneration. The expression of BIRC5 (survivin-1) and caspase-3 were found to be significantly up-regulated, particularly in stage IV GBM. These studies suggest that the abundance and speciation of the BIRC family of neural cell fate regulators are differentially regulated in glioma and GBM, and may contribute to progressive changes in apoptotic signaling and altered neural cell cycling functions.