The paracaspase MALT1 controls cholesterol homeostasis in glioblastoma stem-like cells through lysosome proteome shaping

Lysosomal damage due to cholesterol accumulation triggers immunogenic cell death

Cholesterol serves as a vital lipid that regulates numerous physiological processes. Nonetheless, its role in regulating cell death processes remains incompletely understood. In this study, we investigated the role of cholesterol trafficking in immunogenic cell death. Through cell-based drug screening, we identified two antidepressants, sertraline and indatraline, as potent inducers of the nuclear translocation of TFEB (transcription factor EB). Activation of TFEB was mediated through the autophagy-independent lipidation of MAP1LC3/LC3 (microtubule associated protein 1 light chain 3). Both compounds promoted cholesterol accumulation within lysosomes, resulting in lysosomal membrane permeabilization, disruption of autophagy and cell death that could be reversed by cholesterol depletion. Molecular docking analysis indicated that sertraline and indatraline have the potential to inhibit cholesterol binding to the lysosomal cholesterol transporters, NPC1 (NPC intracellular cholesterol transporter 1) and NPC2. This inhibitory effect might be further enhanced by the upregulation of NPC1 and NPC2 expression by TFEB. Both antidepressants also upregulated PLA2G15 (phospholipase A2 group XV), an enzyme that elevates lysosomal cholesterol. In cancer cells, sertraline and indatraline elicited immunogenic cell death, converting dying cells into prophylactic vaccines that were able to confer protection against tumor growth in mice. In a therapeutic setting, a single dose of each compound was sufficient to significantly reduce the outgrowth of established tumors in a T-cell-dependent manner. These results identify sertraline and indatraline as immunostimulatory agents for cancer treatment. More generally, this research shed light on novel therapeutic avenues harnessing lysosomal cholesterol transport to regulate immunogenic cell death.Abbreviation: ATG5: autophagy related 5; ATG13: autophagy related 13; DKO: double knockout; ICD: immunogenic cell death; KO: knockout; LAMP1: lysosomal associated membrane protein 1; LAMP2: lysosomal associated membrane protein 2; LGALS3: galectin 3; LDL: low-density lipoprotein; LMP: lysosomal membrane permeabilization; MAP1LC3/LC3: microtubule associated protein 1 light chain 3; MTX: mitoxantrone; NPC1: NPC intracellular cholesterol transporter 1; NPC2: NPC intracellular cholesterol transporter 2; TFE3: transcription factor E3; TFEB: transcription factor EB; ULK1: unc-51 like autophagy activating kinase 1.

SREBP2 as a central player in cancer progression: potential for targeted therapeutics

Recent studies have identified the reprogramming of lipid metabolism as a critical hallmark of malignancy. Enhanced cholesterol uptake and increased cholesterol biosynthesis significantly contribute to the rapid growth of tumors, with cholesterol also playing essential roles in cellular signaling pathways. Targeting cholesterol metabolism has emerged as a promising therapeutic strategy in oncology. The sterol regulatory element-binding protein-2 (SREBP2) serves as a primary transcriptional regulator of genes involved in cholesterol biosynthesis and is crucial for maintaining cholesterol homeostasis. Numerous studies have reported the upregulation of SREBP2 across various cancers, facilitating tumor progression. This review aims to provide a comprehensive overview of the structure, biological functions, and regulatory mechanisms of SREBP2. Furthermore, we summarize that SREBP2 plays a crucial role in various cancers and tumor microenvironment primarily by regulating cholesterol, as well as through several non-cholesterol pathways. We also particularly emphasize therapeutic agents targeting SREBP2 that are currently under investigation. This review seeks to enhance our understanding of SREBP2's involvement in cancer and provide theoretical references for cancer therapies that target SREBP2.

A coregulatory influence map of glioblastoma heterogeneity and plasticity

We present GBM-cRegMap, an online resource providing a comprehensive coregulatory influence network perspective on glioblastoma (GBM) heterogeneity and plasticity. Using representation learning algorithms, we derived two components of this resource: GBM-CoRegNet, a highly specific coregulatory network of tumor cells, and GBM-CoRegMap, a unified network influence map based on 1612 tumors from 16 studies. As a widely applicable closed-loop system connecting cellular models and tumors, GBM-cRegMap will provide the GBM research community with an easy-to-use web tool ( https://gbm.cregmap.com ) that maps any existing or newly generated transcriptomic "query" data to a reference coregulatory network and a large-scale manifold of disease heterogeneity. Using GBM-cRegMap, we demonstrated the synergy between the two components by refining the molecular classification of GBM, identifying potential key regulators, and aligning the transcriptional profiles of tumors and in vitro models. Through the amalgamation of a vast dataset, we validated the proneural (PN)-mesenchymal (MES) axis and identified three subclasses of classical (CL) tumors: astrocyte-like (CL-A), epithelial basal-like (CL-B), and cilium-rich (CL-C). We revealed the CL-C subclass, an intermediate state demonstrating the plasticity of GBM cells along the PN-MES axis under chemotherapy. We identified key regulators, such as PAX8, and NKX2.5, potentially involved in temozolomide (TMZ) resistance. Notably, NKX2.5, more expressed in higher-grade gliomas, negatively impacts patient survival, and regulates genes involved in glucose metabolism.

Trafficking in cancer: from gene deregulation to altered organelles and emerging biophysical properties

Intracellular trafficking supports all cell functions maintaining the exchange of material between membrane-bound organelles and the plasma membrane during endocytosis, cargo sorting, and exocytosis/secretion. Several proteins of the intracellular trafficking machinery are deregulated in diseases, particularly cancer. This complex and deadly disease stays a heavy burden for society, despite years of intense research activity. Here, we give an overview about trafficking proteins and highlight that in addition to their molecular functions, they contribute to the emergence of intracellular organelle landscapes. We review recent evidence of organelle landscape alterations in cancer. We argue that focusing on organelles, which represent the higher-order, cumulative behavior of trafficking regulators, could help to better understand, describe and fight cancer. In particular, we propose adopting a physical framework to describe the organelle landscape, with the goal of identifying the key parameters that are crucial for a stable and non-random organelle organization characteristic of healthy cells. By understanding these parameters, we may gain insights into the mechanisms that lead to a pathological organelle spatial organization, which could help explain the plasticity of cancer cells.

Protocol for qualitative analysis of lysosome immunoprecipitation from patient-derived glioblastoma stem-like cells

Lysosomes are critical for the sustenance of glioblastoma stem-like cells (GSCs) properties. We present a protocol to enrich and purify lysosomes from patient-derived GSCs in culture. We describe the steps required to stably express a tagged lysosomal protein in GSCs, mechanically lyse cells, magnetically immunopurify lysosomes, and qualitatively assess these organelles. We then detail the procedure for retrieving intact and purified lysosomes from GSCs. We also specify cell culture conditions, storage procedures, and sample preparation for immunoblotting. For complete details on the use and execution of this protocol, please refer to Maghe et al.1.

Drug-Induced Reorganisation of Lipid Metabolism Limits the Therapeutic Efficacy of Ponatinib in Glioma Stem Cells

The standard of care for glioblastoma (GBM) involves surgery followed by adjuvant radio- and chemotherapy, but often within months, patients relapse, and this has been linked to glioma stem cells (GSCs), self-renewing cells with increased therapy resistance. The identification of the epidermal growth factor receptor (EGFR) and platelet-derived growth factor receptor (PDGFR) as key players in gliomagenesis inspired the development of inhibitors targeting these tyrosine kinases (TKIs). However, results from clinical trials testing TKIs have been disappointing, and while the role of GSCs in conventional therapy resistance has been extensively studied, less is known about resistance of GSCs to TKIs. In this study, we have used compartmentalised proteomics to analyse the adaptive response of GSCs to ponatinib, a TKI with activity against PDGFR. The analysis of differentially expressed proteins revealed that GSCs respond to ponatinib by broadly rewiring lipid metabolism, involving fatty acid beta-oxidation, cholesterol synthesis, and sphingolipid degradation. Inhibiting each of these metabolic pathways overcame ponatinib adaptation of GSCs, but interrogation of patient data revealed sphingolipid degradation as the most relevant pathway in GBM. Our data highlight that targeting lipid metabolism, and particularly sphingolipid degradation in combinatorial therapies, could improve the outcome of TKI therapies using ponatinib in GBM.

Glioma Stem Cells-Features for New Therapy Design

On a molecular level, glioma is very diverse and presents a whole spectrum of specific genetic and epigenetic alterations. The tumors are unfortunately resistant to available therapies and the survival rate is low. The explanation of significant intra- and inter-tumor heterogeneity and the infiltrative capability of gliomas, as well as its resistance to therapy, recurrence and aggressive behavior, lies in a small subset of tumor-initiating cells that behave like stem cells and are known as glioma cancer stem cells (GCSCs). They are responsible for tumor plasticity and are influenced by genetic drivers. Additionally, GCSCs also display greater migratory abilities. A great effort is under way in order to find ways to eliminate or neutralize GCSCs. Many different treatment strategies are currently being explored, including modulation of the tumor microenvironment, posttranscriptional regulation, epigenetic modulation and immunotherapy.