Entosis Is Induced by Glucose Starvation

Determinants of nutrient limitation in cancer

Proliferation requires that cells accumulate sufficient biomass to grow and divide. Cancer cells within tumors must acquire a variety of nutrients, and tumor growth slows or stops if necessary metabolites are not obtained in sufficient quantities. Importantly, the metabolic demands of cancer cells can be different from those of untransformed cells, and nutrient accessibility in tumors is different than in many normal tissues. Thus, cancer cell survival and proliferation may be limited by different metabolic factors than those that are necessary to maintain noncancerous cells. Understanding the variables that dictate which nutrients are critical to sustain tumor growth may identify vulnerabilities that could be used to treat cancer. This review examines the various cell-autonomous, local, and systemic factors that determine which nutrients are limiting for tumor growth.

Canine oral primary melanoma cells exhibit shift to mesenchymal phenotype and phagocytic behaviour

Canine oral malignant melanoma (COMM) is a potentially lethal cancer disease. We established primary cell lines from mostly amelanotic primary COMM and metastases and assessed lesions and derived cells for Melan A, PNL2 and CD146 expression. Then, migration and invasion of CD146-enriched vs -depleted COMM cells were analysed. Epithelial-to-mesenchymal transition (EMT) was addressed by Vimentin-staining and MMP2/MMP9 zymography. Phagocytic behaviour was analysed by histopathological examination and phagocytosis assay. While Melan A- and PNL2-staining yielded inconsistent data, 100% of COMM sections and primary cells showed CD146 expression, suggesting that this protein may serve as a prognostic marker. An overall correlation between CD146-expression and migration/invasion was not observed. All primary cell lines consistently expressed Vimentin and secreted biologically active MMP2, indicating that they had undergone EMT. Importantly, COMM sections exhibited cell-in-cell structures, and all primary cell lines exhibited phagocytic activity, supporting the concept that cell cannibalism may have a role in COMM progression.

Heterotypic cell-in-cell structures in colon cancer can be regulated by IL-6 and lead to tumor immune escape

Heterotypic CICs (cell-in-cell structures) have been found between tumor cells and various immune cells in a variety of cancer tissues. The frequency of CICs has been found to correlate with tumor malignancy in some studies but not in others. Herein, we examined in depth the CICs observed in colon cancer to determine their potential significance in disease progression. Heterotypic CICs were observed by histochemistry between epithelial cells and lymphocytes in an expanded spectrum of colon tissue from colitis to cancer and in vitro studies were performed using the colonic tumor cell line HCT8 and human peripheral blood lymphocytes. Our data revealed that the CICs formed by colonic epithelial cells and infiltrated lymphocytes not only positively correlated with tumor malignancy but also were upregulated by the inflammatory cytokine IL-6. In addition, we observed that colon cancer cells could initiate autophagy for survival after cytotoxic lymphocyte internalization and that IL-6 could also be involved in this process to promote the death of lymphocytes in CIC structures. Furthermore, certain changes were observed in tumor cells after experiencing CICs. Our findings suggest that CICs formed by colon cancer cells and lymphocytes contribute to tumor escape from immune surveillance, which could be facilitated by IL-6, and might represent a previously undescribed pathway for tumor cells to adapt and evade host immune defense.

Mechanisms of oncogenic cell competition-Paths of victory

Cancer is a multistep process. In the early phases of this disease, mutations in oncogenes and tumor suppressors are thought to promote clonal expansion. These mutations can increase cell competitiveness, allowing tumor cells to grow within the tissue by eliminating wild type host cells. Recent studies have shown that cell competition can also function in later phases of cancer. Here, we examine the existing evidence linking cell competition and tumorigenesis. We focus on the mechanisms underlying cell competition and their contribution to disease pathogenesis.

Micronuclei and Genome Chaos: Changing the System Inheritance

Micronuclei research has regained its popularity due to the realization that genome chaos, a rapid and massive genome re-organization under stress, represents a major common mechanism for punctuated cancer evolution. The molecular link between micronuclei and chromothripsis (one subtype of genome chaos which has a selection advantage due to the limited local scales of chromosome re-organization), has recently become a hot topic, especially since the link between micronuclei and immune activation has been identified. Many diverse molecular mechanisms have been illustrated to explain the causative relationship between micronuclei and genome chaos. However, the newly revealed complexity also causes confusion regarding the common mechanisms of micronuclei and their impact on genomic systems. To make sense of these diverse and even conflicting observations, the genome theory is applied in order to explain a stress mediated common mechanism of the generation of micronuclei and their contribution to somatic evolution by altering the original set of information and system inheritance in which cellular selection functions. To achieve this goal, a history and a current new trend of micronuclei research is briefly reviewed, followed by a review of arising key issues essential in advancing the field, including the re-classification of micronuclei and how to unify diverse molecular characterizations. The mechanistic understanding of micronuclei and their biological function is re-examined based on the genome theory. Specifically, such analyses propose that micronuclei represent an effective way in changing the system inheritance by altering the coding of chromosomes, which belongs to the common evolutionary mechanism of cellular adaptation and its trade-off. Further studies of the role of micronuclei in disease need to be focused on the behavior of the adaptive system rather than specific molecular mechanisms that generate micronuclei. This new model can clarify issues important to stress induced micronuclei and genome instability, the formation and maintenance of genomic information, and cellular evolution essential in many common and complex diseases such as cancer.

The molecular machinery of regulated cell death

Cells may die from accidental cell death (ACD) or regulated cell death (RCD). ACD is a biologically uncontrolled process, whereas RCD involves tightly structured signaling cascades and molecularly defined effector mechanisms. A growing number of novel non-apoptotic forms of RCD have been identified and are increasingly being implicated in various human pathologies. Here, we critically review the current state of the art regarding non-apoptotic types of RCD, including necroptosis, pyroptosis, ferroptosis, entotic cell death, netotic cell death, parthanatos, lysosome-dependent cell death, autophagy-dependent cell death, alkaliptosis and oxeiptosis. The in-depth comprehension of each of these lethal subroutines and their intercellular consequences may uncover novel therapeutic targets for the avoidance of pathogenic cell loss.

Biological relevance of cell-in-cell in cancers

Cell-in-cell (CIC) is a term used to describe the presence of one, usually living, cell inside another cell that is typically considered non-phagocytic. Examples of this include tumour cells inside tumour cells (homotypic), mesenchymal stem cells inside tumour cells (heterotypic) or immune cells inside tumour cells (heterotypic). CIC formation can occur in cell lines and in tissues and it has been most frequently observed during inflammation and in cancers. Over the past 10 years, many researchers have studied CIC structures and a few different models have been proposed through which they can be formed, including entosis, cannibalism and emperipolesis among others. Recently, our laboratory discovered a role for mutant p53 in facilitating the formation of CIC and promoting genomic instability. These data and research by many others have uncovered a variety of molecules involved in CIC formation and have started to give us an idea of why they are formed and how they could contribute to oncogenic processes. In this perspective, we summarise current literature and speculate on the role of CIC in cancer biology.

Macropinocytosis and autophagy crosstalk in nutrient scavenging

Adaptive strategies used by cells to scavenge and recycle essential nutrients are important for survival in nutrient-depleted environments such as cancer tissues. Autophagy and macropinocytosis are two major mechanisms that promote nutrient recycling and scavenging, which share considerable, yet poorly understood, cross-regulation. Here we review recent findings that connect these starvation response mechanisms and discuss the implications of their crosstalk. This article is part of the Theo Murphy meeting issue 'Macropinocytosis'.

Induction of entosis in prostate cancer cells by nintedanib and its therapeutic implications

Entosis is a homogeneous cell-in-cell phenomenon and a non-apoptotic cell death process. Tyrosine kinase inhibitors have been used in the treatment of prostate cancer and have already demonstrated efficacy in a clinical setting. The present study investigated the role of entosis in prostate cancer treated with the tyrosine kinase inhibitor nintedanib. Prostate cancer cells were treated with nintedanib in vitro and entosis was observed. Mice xenografts were created to evaluate whether nintedanib is able to induce entosis in vivo. The reverse transcription-quantitative polymerase chain reaction, western blotting and immunofluorescence were performed to investigate whether the entosis pathway is induced by nintedanib. It was also investigated whether entosis can contribute to cell survival and progression under nintedanib stress, and nintedanib was revealed to enhance prostate cancer cell entosis. Nintedanib-induced entosis in prostate cancer cells occurred through phosphoinositide 3-kinase/cell division cycle 42 (CDC42) inhibition, followed by the upregulation of epithelial (E-)cadherin and components of the Rho kinase (ROCK) signaling pathway. In addition, nintedanib-resistant cells exhibiting entosis had a higher invasive ability. In addition, in vivo treatment of mice xenografts with nintedanib also increased the expression of E-cadherin and components of the ROCK signaling pathway. Nintedanib can promote entosis during prostate cancer treatment by modulating the CDC42 pathway. Furthermore, prostate cancer cells acquired nintedanib resistance and survived by activating entosis.

Contractility kits promote assembly of the mechanoresponsive cytoskeletal network

Cellular contractility is governed by a control system of proteins that integrates internal and external cues to drive diverse shape change processes. This contractility controller includes myosin II motors, actin crosslinkers and protein scaffolds, which exhibit robust and cooperative mechanoaccumulation. However, the biochemical interactions and feedback mechanisms that drive the controller remain unknown. Here, we use a proteomics approach to identify direct interactors of two key nodes of the contractility controller in the social amoeba Dictyostelium discoideum: the actin crosslinker cortexillin I and the scaffolding protein IQGAP2. We highlight several unexpected proteins that suggest feedback from metabolic and RNA-binding proteins on the contractility controller. Quantitative in vivo biochemical measurements reveal direct interactions between myosin II and cortexillin I, which form the core mechanosensor. Furthermore, IQGAP1 negatively regulates mechanoresponsiveness by competing with IQGAP2 for binding the myosin II-cortexillin I complex. These myosin II-cortexillin I-IQGAP2 complexes are pre-assembled into higher-order mechanoresponsive contractility kits (MCKs) that are poised to integrate into the cortex upon diffusional encounter coincident with mechanical inputs.This article has an associated First Person interview with the first author of the paper.

Methods for the Study of Entotic Cell Death

Entosis is a mechanism of cell competition occurring in cancers that involves the engulfment and killing of neighboring cells. The death of ingested cells, called entotic cell death, usually occurs in a non-apoptotic, autophagy protein-dependent manner, where microtubule-associated protein light chain 3 (LC3) is lipidated onto entotic vacuoles. Here we present methods to quantify entotic cell death and its associated LC3 lipidation.

Cell-in-cell phenomena in cancer

Cell-in-cell structures are reported in numerous cancers, and their presence is an indicator for poor prognosis. Mechanistic studies have identified how cancer cells manage to ingest whole neighbouring cells to form such structures, and the consequences of cell-in-cell formation on cancer progression have been elucidated. In this Opinion article, we discuss how two related cell-in-cell processes, cell cannibalism and entosis, are regulated and how these mechanisms promote cancer progression. We propose that cannibalistic activity is a hallmark of cancer that results in part from selection by metabolic stress and serves to feed aggressive cancer cells.

I Spy in the Developing Fly a Multitude of Ways to Die

Cell proliferation and cell death are two opposing, yet complementary fundamental processes in development. Cell proliferation provides new cells, while developmental programmed cell death adjusts cell numbers and refines structures as an organism grows. Apoptosis is the best-characterized form of programmed cell death; however, there are many other non-apoptotic forms of cell death that occur throughout development. Drosophila is an excellent model for studying these varied forms of cell death given the array of cellular, molecular, and genetic techniques available. In this review, we discuss select examples of apoptotic and non-apoptotic cell death that occur in different tissues and at different stages of Drosophila development. For example, apoptosis occurs throughout the nervous system to achieve an appropriate number of neurons. Elsewhere in the fly, non-apoptotic modes of developmental cell death are employed, such as in the elimination of larval salivary glands and midgut during metamorphosis. These and other examples discussed here demonstrate the versatility of Drosophila as a model organism for elucidating the diverse modes of programmed cell death.

Nutrient scavenging in cancer

While cancer cell proliferation depends on access to extracellular nutrients, inadequate tumour perfusion means that glucose, amino acids and lipids are often in short supply. To overcome this obstacle to growth, cancer cells utilize multiple scavenging strategies, obtaining macromolecules from the microenvironment and breaking them down in the lysosome to produce substrates for ATP generation and anabolism. Recent studies have revealed four scavenging pathways that support cancer cell proliferation in low-nutrient environments: scavenging of extracellular matrix proteins via integrins, receptor-mediated albumin uptake and catabolism, macropinocytic consumption of multiple components of the tumour microenvironment and the engulfment and degradation of entire live cells via entosis. New evidence suggests that blocking these pathways alone or in combination could provide substantial benefits to patients with incurable solid tumours. Both US Food and Drug Administration (FDA)-approved drugs and several agents in preclinical or clinical development shut down individual or multiple scavenging pathways. These therapies may increase the extent and durability of tumour growth inhibition and/or prevent the development of resistance when used in combination with existing treatments. This Review summarizes the evidence suggesting that scavenging pathways drive tumour growth, highlights recent advances that define the oncogenic signal transduction pathways that regulate scavenging and considers the benefits and detriments of therapeutic strategies targeting scavenging that are currently under development.

Novel Methylselenoesters Induce Programed Cell Death via Entosis in Pancreatic Cancer Cells

Redox active selenium (Se) compounds have gained substantial attention in the last decade as potential cancer therapeutic agents. Several Se compounds have shown high selectivity and sensitivity against malignant cells. The cytotoxic effects are exerted by their biologically active metabolites, with methylselenol (CH₃SeH) being one of the key executors. In search of novel CH₃SeH precursors, we previously synthesized a series of methylselenoesters that were active (GI₅₀ < 10 µM at 72 h) against a panel of cancer cell lines. Herein, we refined the mechanism of action of the two lead compounds with the additional synthesis of new analogs (ethyl, pentyl, and benzyl derivatives). A novel mechanism for the programmed cell death mechanism for Se-compounds was identified. Both methylseleninic acid and the novel CH₃SeH precursors induced entosis by cell detachment through downregulation of cell division control protein 42 homolog (CDC42) and its downstream effector β1-integrin (CD29). To our knowledge, this is the first time that Se compounds have been reported to induce this type of cell death and is of importance in the characterization of the anticancerogenic properties of these compounds.

Visualising the dynamics of live pancreatic microtumours self-organised through cell-in-cell invasion

Pancreatic ductal adenocarcinoma (PDAC) reportedly progresses very rapidly through the initial carcinogenesis stages including DNA damage and disordered cell death. However, such oncogenic mechanisms are largely studied through observational diagnostic methods, partly because of a lack of live in vitro tumour imaging techniques. Here we demonstrate a simple live-tumour in vitro imaging technique using micro-patterned plates (micro/nanoplates) that allows dynamic visualisation of PDAC microtumours. When PDAC cells were cultured on a micro/nanoplate overnight, the cells self-organised into non-spheroidal microtumours that were anchored to the micro/nanoplate through cell-in-cell invasion. This self-organisation was only efficiently induced in small-diameter rough microislands. Using a time-lapse imaging system, we found that PDAC microtumours actively stretched to catch dead cell debris via filo/lamellipoedia and suction, suggesting that they have a sophisticated survival strategy (analogous to that of starving animals), which implies a context for the development of possible therapies for PDACs. The simple tumour imaging system visualises a potential of PDAC cells, in which the aggressive tumour dynamics reminds us of the need to review traditional PDAC pathogenesis.

Life, death and autophagy

Autophagy influences cell survival through maintenance of cell bioenergetics and clearance of protein aggregates and damaged organelles. Several lines of evidence indicate that autophagy is a multifaceted regulator of cell death, but controversy exists over whether autophagy alone can drive cell death under physiologically relevant circumstances. Here, we review the role of autophagy in cell death and examine how autophagy interfaces with other forms of cell death including apoptosis and necrosis.

Microenvironmental regulation of cancer cell metabolism: implications for experimental design and translational studies

Cancers have an altered metabolism, and there is interest in understanding precisely how oncogenic transformation alters cellular metabolism and how these metabolic alterations can translate into therapeutic opportunities. Researchers are developing increasingly powerful experimental techniques to study cellular metabolism, and these techniques have allowed for the analysis of cancer cell metabolism, both in tumors and in ex vivo cancer models. These analyses show that, while factors intrinsic to cancer cells such as oncogenic mutations, alter cellular metabolism, cell-extrinsic microenvironmental factors also substantially contribute to the metabolic phenotype of cancer cells. These findings highlight that microenvironmental factors within the tumor, such as nutrient availability, physical properties of the extracellular matrix, and interactions with stromal cells, can influence the metabolic phenotype of cancer cells and might ultimately dictate the response to metabolically targeted therapies. In an effort to better understand and target cancer metabolism, this Review focuses on the experimental evidence that microenvironmental factors regulate tumor metabolism, and on the implications of these findings for choosing appropriate model systems and experimental approaches.

Expression profiling identified IL-8 as a regulator of homotypic cell-in-cell formation

Homotypic cell-in-cell (CIC) structures forming between cancer cells were proposed to promote tumor evolution via entosis, a nonapoptotic cell death process. However, the mechanisms underlying their formation remained poorly understood. We performed a microarray analysis to identify genes associated with homotypic CIC formation. Cancer cells differing in their ability to form homotypic CIC structures were selected for the study. Association analysis identified 73 probe sets for 62 candidate genes potentially involved in CIC formation. Among them, twenty-one genes were downregulated while 41 genes were upregulated. Pathway analysis identified a gene interaction network centered on IL-8, which was upregulated in high CIC cells. Remarkably, CIC formation was significantly inhibited by IL-8 knockdown and enhanced upon recombinant IL-8 treatment, which correlated with altered cell-cell adhesion and expression of adhesive molecules such as P-cadherin and γ-catenin. Together, our work identified IL-8 as a positive regulator of homotypic CIC formation via enhancing intercellular adhesion. [BMB Reports 2018; 51(8): 412-417].

CDKN2A inhibits formation of homotypic cell-in-cell structures

Cell-in-cell (CIC) structures, characterized by enclosure of one or more cells within another cell, were extensively documented in human cancers. Although elevated CIC formation was found in cancers with CDKN2A inactivation, a causal link between them remains to be established. We reported here that inhibiting CDKN2A expression effectively promoted homotypic CIC formation, whereas ectopic overexpression of p16INK4a or p14ARF, two proteins encoded by CDKN2A gene, significantly suppressed CIC formation in MCF7 cells. The regulation of CIC formation by CDKN2A was tightly correlated with subcellular redistribution of E-cadherin, F-actin rearrangement and reduced phosphorylation of myosin light chain 2 (p-MLC2), consistent with which, CDKN2A expression imparted cells winner/outer identity in competition assay. Moreover, CIC formation negatively correlates with p16INK4a expression in human breast cancers. Thus, our work identifies CDKN2A as the first tumor suppressor whose inactivation promotes homotypic CIC formation in human cancer cells.

Antifungal Peptides of the AFP Family Revisited: Are These Cannibal Toxins?

The emergence and spread of pathogenic fungi resistant to currently used antifungal drugs represents a serious challenge for medicine and agriculture. The use of smart antimicrobials, so-called “dirty drugs” which affect multiple cellular targets, is one strategy to prevent resistance. Of special interest is the exploitation of the AFP family of antimicrobial peptides, which include its founding member AFP from Aspergillus giganteus. This latter is a highly potent inhibitor of chitin synthesis and affects plasma membrane integrity in many human and plant pathogenic fungi. A transcriptomic meta-analysis of the afp-encoding genes in A. giganteus and A. niger predicts a role for these proteins during asexual sporulation, autophagy, and nutrient recycling, suggesting that AFPs are molecules important for the survival of A. niger and A. giganteus under nutrient limitation. In this review, we discuss parallels which exist between AFPs and bacterial cannibal toxins and provide arguments that the primary function of AFPs could be to kill genetically identical siblings. We hope that this review inspires computational and experimental biologists studying alternative explanations for the nature and function of antimicrobial peptides beyond the general assumption that they are mere defense molecules to fight competitors.

Cancer cell cannibalism: Multiple triggers emerge for entosis

Entosis is a form of epithelial cell engulfment and cannibalism prevalent in human cancer. Until recently, the only known trigger for entosis was loss of attachment to the extracellular matrix, as often occurs in the tumour microenvironment. However, two new studies now reveal that entosis can also occur among adherent epithelial cells, induced by mitosis or glucose starvation. Together, these findings point to the intriguing notion that certain hallmark properties of cancer cells, including anchorage independence, aberrant proliferation and metabolic stress, can converge on the induction of cell cannibalism, a phenomenon so frequently observed in tumours. In this review, we explore the molecular, cellular and biophysical mechanisms underlying entosis and discuss the impact of cell cannibalism on tumour biology.

Avenues to molecular imaging of dying cells: Focus on cancer

Successful treatment of cancer patients requires balancing of the dose, timing, and type of therapeutic regimen. Detection of increased cell death may serve as a predictor of the eventual therapeutic success. Imaging of cell death may thus lead to early identification of treatment responders and nonresponders, and to “patient‐tailored therapy.” Cell death in organs and tissues of the human body can be visualized, using positron emission tomography or single‐photon emission computed tomography, although unsolved problems remain concerning target selection, tracer pharmacokinetics, target‐to‐nontarget ratio, and spatial and temporal resolution of the scans. Phosphatidylserine exposure by dying cells has been the most extensively studied imaging target. However, visualization of this process with radiolabeled Annexin A5 has not become routine in the clinical setting. Classification of death modes is no longer based only on cell morphology but also on biochemistry, and apoptosis is no longer found to be the preponderant mechanism of cell death after antitumor therapy, as was earlier believed. These conceptual changes have affected radiochemical efforts. Novel probes targeting changes in membrane permeability, cytoplasmic pH, mitochondrial membrane potential, or caspase activation have recently been explored. In this review, we discuss molecular changes in tumors which can be targeted to visualize cell death and we propose promising biomarkers for future exploration.

Nutrient Sensing in Cancer

Cell-intrinsic mechanisms of nutrient sensing are intimately linked to adaptive metabolic responses, and these pathways play critical roles in the complex and dynamic nutrient environment of a growing tumor. Nutrient-responsive transcription factors (e.g., HIF, SREBP, ATF4) and signaling pathways (e.g., mTORC1, AMPK) allow tumor cells to tune their metabolic output and strategies to fluctuations in nutrient availability, thus balancing tumor cell proliferation and survival with a combination of anabolic and adaptive responses. Coupling these nutrient-sensing mechanisms to the control of recycling and scavenging processes, such as autophagy and macropinocytosis, further enhances the adaptability to nutrients within tumors. Here, we discuss the key nutrient-sensing pathways active in cancer cells, how oncogenic events influence these pathways, and their likely contributions to tumor growth and survival. A better understanding of nutrient-sensing strategies and metabolic adaptations within the tumor microenvironment is critical to defining and targeting metabolic vulnerabilities in cancer.

Molecular mechanisms of cell death: recommendations of the Nomenclature Committee on Cell Death 2018

Over the past decade, the Nomenclature Committee on Cell Death (NCCD) has formulated guidelines for the definition and interpretation of cell death from morphological, biochemical, and functional perspectives. Since the field continues to expand and novel mechanisms that orchestrate multiple cell death pathways are unveiled, we propose an updated classification of cell death subroutines focusing on mechanistic and essential (as opposed to correlative and dispensable) aspects of the process. As we provide molecularly oriented definitions of terms including intrinsic apoptosis, extrinsic apoptosis, mitochondrial permeability transition (MPT)-driven necrosis, necroptosis, ferroptosis, pyroptosis, parthanatos, entotic cell death, NETotic cell death, lysosome-dependent cell death, autophagy-dependent cell death, immunogenic cell death, cellular senescence, and mitotic catastrophe, we discuss the utility of neologisms that refer to highly specialized instances of these processes. The mission of the NCCD is to provide a widely accepted nomenclature on cell death in support of the continued development of the field.

The impact of non-genetic heterogeneity on cancer cell death

The goal of cancer chemotherapy is to induce homogeneous cell death within the population of targeted cancer cells. However, no two cells are exactly alike at the molecular level, and sensitivity to drug-induced cell death, therefore, varies within a population. Genetic alterations can contribute to this variability and lead to selection for drug resistant clones. However, there is a growing appreciation for the role of non-genetic variation in producing drug-tolerant cellular states that exhibit reduced sensitivity to cell death for extended periods of time, from hours to weeks. These cellular states may result from individual variation in epigenetics, gene expression, metabolism, and other processes that impact drug mechanism of action or the execution of cell death. Such population-level non-genetic heterogeneity may contribute to treatment failure and provide a cellular "substrate" for the emergence of genetic alterations that confer frank drug resistance.

Cholesterol inhibits entotic cell-in-cell formation and actomyosin contraction

Cell-in-cell structure is prevalent in human cancer, and associated with several specific pathophysiological phenomena. Although cell membrane adhesion molecules were found critical for cell-in-cell formation, the roles of other membrane components, such as lipids, remain to be explored. In this study, we attempted to investigate the effects of cholesterol and phospholipids on the formation of cell-in-cell structures by utilizing liposome as a vector. We found that Lipofectamine-2000, the reagent commonly used for routine transfection, could significantly reduce entotic cell-in-cell formation in a cell-specific manner, which is correlated with suppressed actomyosin contraction as indicated by reduced β-actin expression and myosin light chain phosphorylation. The influence on cell-in-cell formation was likely dictated by specific liposome components as some liposomes affected cell-in-cell formation while some others didn't. Screening on a limited number of lipids, the major components of liposome, identified phosphatidylethanolamine (PE), stearamide (SA), lysophosphatidic acid (LPA) and cholesterol (CHOL) as the inhibitors of cell-in-cell formation. Importantly, cholesterol treatment significantly inhibited myosin light chain phosphorylation, which resembles the effect of Lipofectamine-2000, suggesting cholesterol might be partially responsible for liposomes' effects on cell-in-cell formation. Together, our findings supporting a role of membrane lipids and cholesterol in cell-in-cell formation probably via regulating actomyosin contraction.

In the Hunger Games, the Winner Takes Everything

Entosis is an atypical form of cell death that occurs when a cell engulfs and kills another cell. A recent article by Overholtzer and colleagues indicates that glucose deprivation promotes entosis. AMP-activated protein kinase (AMPK) activation in the loser cells triggers their engulfment and elimination by winner cells, which endure starvation.