Integrated transcriptomics uncovers an enhanced association between the prion protein gene expression and vesicle dynamics signatures in glioblastomas.

BACKGROUND: Glioblastoma (GBM) is an aggressive brain tumor that exhibits resistance to current treatment, making the identification of novel therapeutic targets essential. In this context, cellular prion protein (PrPC) stands out as a potential candidate for new therapies. Encoded by the PRNP gene, PrPC can present increased expression levels in GBM, impacting cell proliferation, growth, migration, invasion and stemness. Nevertheless, the exact molecular mechanisms through which PRNP/PrPC modulates key aspects of GBM biology remain elusive. METHODS: To elucidate the implications of PRNP/PrPC in the biology of this cancer, we analyzed publicly available RNA sequencing (RNA-seq) data of patient-derived GBMs from four independent studies. First, we ranked samples profiled by bulk RNA-seq as PRNPhigh and PRNPlow and compared their transcriptomic landscape. Then, we analyzed PRNP+ and PRNP- GBM cells profiled by single-cell RNA-seq to further understand the molecular context within which PRNP/PrPC might function in this tumor. We explored an additional proteomics dataset, applying similar comparative approaches, to corroborate our findings. RESULTS: Functional profiling revealed that vesicular dynamics signatures are strongly correlated with PRNP/PrPC levels in GBM. We found a panel of 73 genes, enriched in vesicle-related pathways, whose expression levels are increased in PRNPhigh/PRNP+ cells across all RNA-seq datasets. Vesicle-associated genes, ANXA1, RAB31, DSTN and SYPL1, were found to be upregulated in vitro in an in-house collection of patient-derived GBM. Moreover, proteome analysis of patient-derived samples reinforces the findings of enhanced vesicle biogenesis, processing and trafficking in PRNPhigh/PRNP+ GBM cells. CONCLUSIONS: Together, our findings shed light on a novel role for PrPC as a potential modulator of vesicle biology in GBM, which is pivotal for intercellular communication and cancer maintenance. We also introduce GBMdiscovery, a novel user-friendly tool that allows the investigation of specific genes in GBM biology.

Extracellular vesicles throughout development: A potential roadmap for emerging glioblastoma therapies.

Extracellular vesicles (EVs) are membrane-delimited vesicular bodies carrying different molecules, classified according to their size, density, cargo, and origin. Research on this topic has been actively growing through the years, as EVs are associated with critical pathological processes such as neurodegenerative diseases and cancer. Despite that, studies exploring the physiological functions of EVs are sparse, with particular emphasis on their role in organismal development, initial cell differentiation, and morphogenesis. In this review, we explore the topic of EVs from a developmental perspective, discussing their role in the earliest cell-fate decisions and neural tissue morphogenesis. We focus on the function of EVs through development to highlight possible conserved or novel processes that can impact disease progression. Specifically, we take advantage of what was learned about their role in development so far to discuss EVs impact on glioblastoma, a particular brain tumor of stem-cell origin and poor prognosis, and how their function can be hijacked to improve current therapies.

Unconventional Protein Secretion in Brain Tumors Biology: Enlightening the Mechanisms for Tumor Survival and Progression.

Non-canonical secretion pathways, collectively known as unconventional protein secretion (UPS), are alternative secretory mechanisms usually associated with stress-inducing conditions. UPS allows proteins that lack a signal peptide to be secreted, avoiding the conventional endoplasmic reticulum-Golgi complex secretory pathway. Molecules that generally rely on the canonical pathway to be secreted may also use the Golgi bypass, one of the unconventional routes, to reach the extracellular space. UPS studies have been increasingly growing in the literature, including its implication in the biology of several diseases. Intercellular communication between brain tumor cells and the tumor microenvironment is orchestrated by various molecules, including canonical and non-canonical secreted proteins that modulate tumor growth, proliferation, and invasion. Adult brain tumors such as gliomas, which are aggressive and fatal cancers with a dismal prognosis, could exploit UPS mechanisms to communicate with their microenvironment. Herein, we provide functional insights into the UPS machinery in the context of tumor biology, with a particular focus on the secreted proteins by alternative routes as key regulators in the maintenance of brain tumors.

Multifaceted WNT Signaling at the Crossroads Between Epithelial-Mesenchymal Transition and Autophagy in Glioblastoma.

Tumor cells can employ epithelial-mesenchymal transition (EMT) or autophagy in reaction to microenvironmental stress. Importantly, EMT and autophagy negatively regulate each other, are able to interconvert, and both have been shown to contribute to drug-resistance in glioblastoma (GBM). EMT has been considered one of the mechanisms that confer invasive properties to GBM cells. Autophagy, on the other hand, may show dual roles as either a GBM-promoter or GBM-suppressor, depending on microenvironmental cues. The Wingless (WNT) signaling pathway regulates a plethora of developmental and biological processes such as cellular proliferation, adhesion and motility. As such, GBM demonstrates deregulation of WNT signaling in favor of tumor initiation, proliferation and invasion. In EMT, WNT signaling promotes induction and stabilization of different EMT activators. WNT activity also represses autophagy, while nutrient deprivation induces ß-catenin degradation via autophagic machinery. Due to the importance of the WNT pathway to GBM, and the role of WNT signaling in EMT and autophagy, in this review we highlight the effects of the WNT signaling in the regulation of both processes in GBM, and discuss how the crosstalk between EMT and autophagy may ultimately affect tumor biology.

A New Take on Prion Protein Dynamics in Cellular Trafficking.

The mobility of cellular prion protein (PrPC) in specific cell membrane domains and among distinct cell compartments dictates its molecular interactions and directs its cell function. PrPC works in concert with several partners to organize signaling platforms implicated in various cellular processes. The scaffold property of PrPC is able to gather a molecular repertoire to create heterogeneous membrane domains that favor endocytic events. Dynamic trafficking of PrPC through multiple pathways, in a well-orchestrated mechanism of intra and extracellular vesicular transport, defines its functional plasticity, and also assists the conversion and spreading of its infectious isoform associated with neurodegenerative diseases. In this review, we highlight how PrPC traffics across intra- and extracellular compartments and the consequences of this dynamic transport in governing cell functions and contributing to prion disease pathogenesis.

Prion Protein at the Leading Edge: Its Role in Cell Motility.

Cell motility is a central process involved in fundamental biological phenomena during embryonic development, wound healing, immune surveillance, and cancer spreading. Cell movement is complex and dynamic and requires the coordinated activity of cytoskeletal, membrane, adhesion and extracellular proteins. Cellular prion protein (PrPC) has been implicated in distinct aspects of cell motility, including axonal growth, transendothelial migration, epithelial-mesenchymal transition, formation of lamellipodia, and tumor migration and invasion. The preferential location of PrPC on cell membrane favors its function as a pivotal molecule in cell motile phenotype, being able to serve as a scaffold protein for extracellular matrix proteins, cell surface receptors, and cytoskeletal multiprotein complexes to modulate their activities in cellular movement. Evidence points to PrPC mediating interactions of multiple key elements of cell motility at the intra- and extracellular levels, such as integrins and matrix proteins, also regulating cell adhesion molecule stability and cell adhesion cytoskeleton dynamics. Understanding the molecular mechanisms that govern cell motility is critical for tissue homeostasis, since uncontrolled cell movement results in pathological conditions such as developmental diseases and tumor dissemination. In this review, we discuss the relevant contribution of PrPC in several aspects of cell motility, unveiling new insights into both PrPC function and mechanism in a multifaceted manner either in physiological or pathological contexts.