Epithelial defense against cancer (EDAC)

Epithelial cell extrusion at a glance

The robustness and plasticity of epithelial tissues rely on the capacity of such tissues to eliminate cells without affecting their sealing. This is achieved by epithelial cell extrusion - a well-orchestrated series of remodelling steps involving the eliminated cell and its neighbours - which ensures the constant maintenance of mechanical and chemical barrier properties while allowing cell expulsion. In this Cell Science at a Glance and the accompanying poster, we describe the remodelling steps that take place within dying or extruding cells, as well as neighbouring cells, outlining the commonalities and variations between tissues and organisms. These steps include reorganization of the cytoskeleton and remodelling of cell-cell junctions that alters their contribution to mechanical coupling and mechanotransduction. We also discuss larger-scale coordination between cells and the contribution of cell extrusion to tissue morphogenesis, epithelial surveillance mechanisms, and pathologies such as cancer and chronic inflammation. Altogether, we outline the complexity and plasticity of this minimalist morphogenetic process.

Imperfect wound healing sets the stage for chronic diseases

Although the age of the genome gave us much insight about how our organs fail with disease, it also suggested that diseases do not arise from mutations alone; rather, they develop as we age. In this Review, we examine how wound healing might act to ignite disease. Wound healing works well when we are younger, repairing damage from accidents, environmental assaults, and battles with pathogens. Yet, with age and accumulation of mutations and tissue damage, the repair process can devolve, leading to inflammation, fibrosis, and neoplastic signaling. We discuss healthy wound responses and how our bodies might misappropriate these pathways in disease. Although we focus predominantly on epithelial-based (lung and skin) diseases, similar pathways might operate in cardiac, muscle, and neuronal diseases.

Autocrine glutamate signaling drives cell competition in Drosophila

Cell competition is an evolutionarily conserved quality control process that eliminates suboptimal or potentially dangerous cells. Although differential metabolic states act as direct drivers of competition, how these are measured across tissues is not understood. Here, we demonstrate that vesicular glutamate transporter (VGlut) and autocrine glutamate signaling are required for cell competition and Myc-driven super-competition in the Drosophila epithelia. We find that the loss of glutamate-stimulated VGlut>NMDAR>CaMKII>CrebB signaling triggers loser status and cell death under competitive settings via the autocrine induction of TNF. This in turn drives TNFR>JNK activation, triggering loser cell elimination and PDK/LDH-dependent metabolic reprogramming. Inhibiting caspases or preventing loser cells from transferring lactate to their neighbors nullifies cell competition. Further, in a Drosophila model for premalignancy, Myc-overexpressing clones co-opt this signaling circuit to acquire super-competitor status. Targeting glutamate signaling converts Myc "super-competitor" clones into "losers," highlighting new therapeutic opportunities to restrict the evolution of fitter clones.

Entosis implicates a new role for P53 in microcephaly pathogenesis, beyond apoptosis

Entosis, a form of cell cannibalism, is a newly discovered pathogenic mechanism leading to the development of small brains, termed microcephaly, in which P53 activation was found to play a major role. Microcephaly with entosis, found in Pals1 mutant mice, displays P53 activation that promotes entosis and apoptotic cell death. This previously unappreciated pathogenic mechanism represents a novel cellular dynamic in dividing cortical progenitors which is responsible for cell loss. To date, various recent models of microcephaly have bolstered the importance of P53 activation in cell death leading to microcephaly. P53 activation caused by mitotic delay or DNA damage manifests apoptotic cell death which can be suppressed by P53 removal in these animal models. Such genetic studies attest P53 activation as quality control meant to eliminate genomically unfit cells with minimal involvement in the actual function of microcephaly associated genes. In this review, we summarize the known role of P53 activation in a variety of microcephaly models and introduce a novel mechanism wherein entotic cell cannibalism in neural progenitors is triggered by P53 activation.

Crk mediates Csk-Hippo signaling independently of Yap tyrosine phosphorylation to induce cell extrusion

Src family kinases (SFKs), including Src, Fyn and Yes, play important roles in development and cancer. Despite being first discovered as the Yes-associated protein, the regulation of Yap by SFKs remains poorly understood. Here, through single-cell analysis and genetic lineage tracing, we show that the pan-epithelial ablation of C-terminal Src kinase (Csk) in the lacrimal gland unleashes broad Src signaling but specifically causes extrusion and apoptosis of acinar progenitors at a time when they are shielded by myoepithelial cells from the basement membrane. Csk mutants can be phenocopied by constitutively active Yap and rescued by deleting Yap or Taz, indicating a significant functional overlap between Src and Yap signaling. Although Src-induced tyrosine phosphorylation has long been believed to regulate Yap activity, we find that mutating these tyrosine residues in both Yap and Taz fails to perturb mouse development or alleviate the Csk lacrimal gland phenotype. In contrast, Yap loses Hippo signaling-dependent serine phosphorylation and translocates into the nucleus in Csk mutants. Further chemical genetics studies demonstrate that acute inhibition of Csk enhances Crk/CrkL phosphorylation and Rac1 activity, whereas removing Crk/CrkL or Rac1/Rap1 ameliorates the Csk mutant phenotype. These results show that Src controls Hippo-Yap signaling through the Crk/CrkL-Rac/Rap axis to promote cell extrusion.

Tumor initiation and early tumorigenesis: molecular mechanisms and interventional targets

Tumorigenesis is a multistep process, with oncogenic mutations in a normal cell conferring clonal advantage as the initial event. However, despite pervasive somatic mutations and clonal expansion in normal tissues, their transformation into cancer remains a rare event, indicating the presence of additional driver events for progression to an irreversible, highly heterogeneous, and invasive lesion. Recently, researchers are emphasizing the mechanisms of environmental tumor risk factors and epigenetic alterations that are profoundly influencing early clonal expansion and malignant evolution, independently of inducing mutations. Additionally, clonal evolution in tumorigenesis reflects a multifaceted interplay between cell-intrinsic identities and various cell-extrinsic factors that exert selective pressures to either restrain uncontrolled proliferation or allow specific clones to progress into tumors. However, the mechanisms by which driver events induce both intrinsic cellular competency and remodel environmental stress to facilitate malignant transformation are not fully understood. In this review, we summarize the genetic, epigenetic, and external driver events, and their effects on the co-evolution of the transformed cells and their ecosystem during tumor initiation and early malignant evolution. A deeper understanding of the earliest molecular events holds promise for translational applications, predicting individuals at high-risk of tumor and developing strategies to intercept malignant transformation.

Exploring the Enigma: The Role of the Epithelial Protein Lost in Neoplasm in Normal Physiology and Cancer Pathogenesis

The cytoskeleton plays a pivotal role in maintaining the epithelial phenotype and is vital to several hallmark processes of cancer. Over the past decades, researchers have identified the epithelial protein lost in neoplasm (EPLIN, also known as LIMA1) as a key regulator of cytoskeletal dynamics, cytoskeletal organization, motility, as well as cell growth and metabolism. Dysregulation of EPLIN is implicated in various aspects of cancer progression, such as tumor growth, invasion, metastasis, and therapeutic resistance. Its altered expression levels or activity can disrupt cytoskeletal dynamics, leading to aberrant cell motility and invasiveness characteristic of malignant cells. Moreover, the involvement of EPLIN in cell growth and metabolism underscores its significance in orchestrating key processes essential for cancer cell survival and proliferation. This review provides a comprehensive exploration of the intricate roles of EPLIN across diverse cellular processes in both normal physiology and cancer pathogenesis. Additionally, this review discusses the possibility of EPLIN as a potential target for anticancer therapy in future studies.

A mismatch in the expression of cell surface molecules induces tissue-intrinsic defense against aberrant cells

Tissue-intrinsic error correction enables epithelial cells to detect abnormal neighboring cells and facilitate their removal from the tissue. One of these pathways, "interface surveillance," is triggered by cells with aberrant developmental and cell-fate-patterning pathways. It remains unknown which molecular mechanisms provide cells with the ability to compare fate between neighboring cells. We demonstrate that Drosophila imaginal discs express an array of cell surface molecules previously implicated in neuronal axon guidance processes. They include members of the Robo, Teneurin, Ephrin, Toll-like, or atypical cadherin families. Importantly, a mismatch in expression levels of these cell surface molecules between adjacent cells is sufficient to induce interface surveillance, indicating that differences in expression levels between neighboring cells, rather than their absolute expression levels, are crucial. Specifically, a mismatch in Robo2 and Robo3, but not Robo1, induces enrichment of actin, myosin II, and Ena/Vasp, as well as activation of JNK and apoptosis at clonal interfaces. Moreover, Robo2 can induce interface surveillance independently of its cytosolic domain and without the need for the Robo-ligand Slit. The expression of Robo2 and other cell surface molecules, such as Teneurins or the Ephrin receptor is regulated by fate-patterning pathways intrinsic and extrinsic to the wing disc, as well as by expression of oncogenic RasV12. Combined, we demonstrate that neighboring cells respond to a mismatch in surface code patterns mediated by specific transmembrane proteins and reveal a novel function for these cell surface proteins in cell fate recognition and removal of aberrant cells during development and homeostasis of epithelial tissues.

Cell competition: emerging signaling and unsolved questions

Multicellular communities have an intrinsic mechanism that optimizes their structure and function via cell-cell communication. One of the driving forces for such self-organization of the multicellular system is cell competition, the elimination of viable unfit or deleterious cells via cell-cell interaction. Studies in Drosophila and mammals have identified multiple mechanisms of cell competition caused by different types of mutations or cellular changes. Intriguingly, recent studies have found that different types of "losers" of cell competition commonly show reduced protein synthesis. In Drosophila, the reduction in protein synthesis levels in loser cells is caused by phosphorylation of the translation initiation factor eIF2α via a bZip transcription factor Xrp1. Given that a variety of cellular stresses converge on eIF2α phosphorylation and thus global inhibition of protein synthesis, cell competition may be a machinery that optimizes multicellular fitness by removing stressed cells. In this review, we summarize and discuss emerging signaling mechanisms and critical unsolved questions, as well as the role of protein synthesis in cell competition.

Mutual communication between radiosensitive and radioresistant esophageal cancer cells modulates their radiosensitivity

Radiotherapy is an important treatment modality for patients with esophageal cancer; however, the response to radiation varies among different tumor subpopulations due to tumor heterogeneity. Cancer cells that survive radiotherapy (i.e., radioresistant) may proliferate, ultimately resulting in cancer relapse. However, the interaction between radiosensitive and radioresistant cancer cells remains to be elucidated. In this study, we found that the mutual communication between radiosensitive and radioresistant esophageal cancer cells modulated their radiosensitivity. Radiosensitive cells secreted more exosomal let-7a and less interleukin-6 (IL-6) than radioresistant cells. Exosomal let-7a secreted by radiosensitive cells increased the radiosensitivity of radioresistant cells, whereas IL-6 secreted by radioresistant cells decreased the radiosensitivity of radiosensitive cells. Although the serum levels of let-7a and IL-6 before radiotherapy did not vary significantly between patients with radioresistant and radiosensitive diseases, radiotherapy induced a more pronounced decrease in serum let-7a levels and a greater increase in serum IL-6 levels in patients with radioresistant cancer compared to those with radiosensitive cancer. The percentage decrease in serum let-7a and the percentage increase in serum IL-6 levels at the early stage of radiotherapy were inversely associated with tumor regression after radiotherapy. Our findings suggest that early changes in serum let-7a and IL-6 levels may be used as a biomarker to predict the response to radiotherapy in patients with esophageal cancer and provide new insights into subsequent treatments.

Differential Ire1 determines loser cell fate in tumor-suppressive cell competition

Tumor-suppressive cell competition (TSCC) is a conserved surveillance mechanism in which neighboring cells actively eliminate oncogenic cells. Despite overwhelming studies showing that the unfolded protein response (UPR) is dysregulated in various tumors, it remains debatable whether the UPR restrains or promotes tumorigenesis. Here, using Drosophila eye epithelium as a model, we uncover a surprising decisive role of the Ire1 branch of the UPR in regulating cell polarity gene scribble (scrib) loss-induced TSCC. Both mutation and hyperactivation of Ire1 accelerate elimination of scrib clones via inducing apoptosis and autophagy, respectively. Unexpectedly, relative Ire1 activity is also crucial for determining loser cell fate, as dysregulating Ire1 signaling in the surrounding healthy cells reversed the "loser" status of scrib clones by decreasing their apoptosis. Furthermore, we show that Ire1 is required for cell competition in mammalian cells. Together, these findings provide molecular insights into scrib-mediated TSCC and highlight Ire1 as a key determinant of loser cell fate.

Apoptotic extracellular vesicle formation via local phosphatidylserine exposure drives efficient cell extrusion

Cell extrusion is a universal mode of cell removal from tissues, and it plays an important role in regulating cell numbers and eliminating unwanted cells. However, the underlying mechanisms of cell delamination from the cell layer are unclear. Here, we report a conserved execution mechanism of apoptotic cell extrusion. We found extracellular vesicle (EV) formation in extruding mammalian and Drosophila cells at a site opposite to the extrusion direction. Lipid-scramblase-mediated local exposure of phosphatidylserine is responsible for EV formation and is crucial for executing cell extrusion. Inhibition of this process disrupts prompt cell delamination and tissue homeostasis. Although the EV has hallmarks of an apoptotic body, its formation is governed by the mechanism of microvesicle formation. Experimental and mathematical modeling analysis illustrated that EV formation promotes neighboring cells' invasion. This study showed that membrane dynamics play a crucial role in cell exit by connecting the actions of the extruding cell and neighboring cells.

Characterization of LIMA1 and its emerging roles and potential therapeutic prospects in cancers

Actin is the most abundant and highly conserved cytoskeletal protein present in all eukaryotic cells. Remodeling of the actin cytoskeleton is controlled by a variety of actin-binding proteins that are extensively involved in biological processes such as cell motility and maintenance of cell shape. LIM domain and actin-binding protein 1 (LIMA1), as an important actin cytoskeletal regulator, was initially thought to be a tumor suppressor frequently downregulated in epithelial tumors. Importantly, the deficiency of LIMA1 may be responsible for dysregulated cytoskeletal dynamics, altered cell motility and disrupted cell-cell adhesion, which promote tumor proliferation, invasion and migration. As research progresses, the roles of LIMA1 extend from cytoskeletal dynamics and cell motility to cell division, gene regulation, apical extrusion, angiogenesis, cellular metabolism and lipid metabolism. However, the expression of LIMA1 in malignant tumors and its mechanism of action have not yet been elucidated, and many problems and challenges remain to be addressed. Therefore, this review systematically describes the structure and biological functions of LIMA1 and explores its expression and regulatory mechanism in malignant tumors, and further discusses its clinical value and therapeutic prospects.

Clonal interactions in cancer: integrating quantitative models with experimental and clinical data

Tumors consist of different genotypically distinct subpopulations-or subclones-of cells. These subclones can influence neighboring clones in a process called "clonal interaction." Conventionally, research on driver mutations in cancer has focused on their cell-autonomous effects that lead to an increase in fitness of the cells containing the driver. Recently, with the advent of improved experimental and computational technologies for investigating tumor heterogeneity and clonal dynamics, new studies have shown the importance of clonal interactions in cancer initiation, progression, and metastasis. In this review we provide an overview of clonal interactions in cancer, discussing key discoveries from a diverse range of approaches to cancer biology research. We discuss common types of clonal interactions, such as cooperation and competition, its mechanisms, and the overall effect on tumorigenesis, with important implications for tumor heterogeneity, resistance to treatment, and tumor suppression. Quantitative models-in coordination with cell culture and animal model experiments-have played a vital role in investigating the nature of clonal interactions and the complex clonal dynamics they generate. We present mathematical and computational models that can be used to represent clonal interactions and provide examples of the roles they have played in identifying and quantifying the strength of clonal interactions in experimental systems. Clonal interactions have proved difficult to observe in clinical data; however, several very recent quantitative approaches enable their detection. We conclude by discussing ways in which researchers can further integrate quantitative methods with experimental and clinical data to elucidate the critical-and often surprising-roles of clonal interactions in human cancers.

Pleiotropic effects of cell competition between normal and transformed cells in mammalian cancers

PURPOSE

In the course of tumor progression, cancer clones interact with host normal cells, and these interactions make them under selection pressure all the time. Cell competition, which can eliminate suboptimal cells and optimize organ development via comparison of cell fitness information, is found to take place between host cells and transformed cells in mammals and play important roles in different phases of tumor progression. The aim of this study is to summarize the current knowledge about the roles and corresponding mechanisms of different cell competition interactions between host normal cells and transformed cells involved in mammalian tumor development.

METHODS

We reviewed the published relevant articles in the Pubmed.

RESULTS

So far, the role of several cell competition interactions have been well described in the different phases of mammalian tumor genesis and development. While cell competitions for trophic factors and epithelial defense against cancer (EDAC) prevent the emergence of transformed cells and suppress carcinogenesis, fitness-fingerprints-comparison system and Myc supercompetitors promote the local expansion of transformed cells after the early tumor lesion is formatted. In addition, various preclinical tumor-suppression models which based on the molecular mechanisms of these competition interactions show potential clinical value of boosting the fitness of host normal cells.

CONCLUSION

Cell competition between host and transformed cells has pleiotropic effects in mammalian tumor genesis and development. The clarification of specific molecular mechanisms shed light on novel ideas for the prevention and treatment of cancer.

To not love thy neighbor: mechanisms of cell competition in stem cells and beyond

Cell competition describes the process in which cells of greater fitness are capable of sensing and instructing elimination of lesser fit mutant cells. Since its discovery in Drosophila, cell competition has been established as a critical regulator of organismal development, homeostasis, and disease progression. It is therefore unsurprising that stem cells (SCs), which are central to these processes, harness cell competition to remove aberrant cells and preserve tissue integrity. Here, we describe pioneering studies of cell competition across a variety of cellular contexts and organisms, with the ultimate goal of better understanding competition in mammalian SCs. Furthermore, we explore the modes through which SC competition takes place and how this facilitates normal cellular function or contributes to pathological states. Finally, we discuss how understanding of this critical phenomenon will enable targeting of SC-driven processes, including regeneration and tumor progression.

Bilateral JNK activation is a hallmark of interface surveillance and promotes elimination of aberrant cells

Tissue-intrinsic defense mechanisms eliminate aberrant cells from epithelia and thereby maintain the health of developing tissues or adult organisms. 'Interface surveillance' comprises one such distinct mechanism that specifically guards against aberrant cells which undergo inappropriate cell fate and differentiation programs. The cellular mechanisms which facilitate detection and elimination of these aberrant cells are currently unknown. We find that in Drosophila imaginal discs, clones of cells with inappropriate activation of cell fate programs induce bilateral JNK activation at clonal interfaces, where wild type and aberrant cells make contact. JNK activation is required to drive apoptotic elimination of interface cells. Importantly, JNK activity and apoptosis are highest in interface cells within small aberrant clones, which likely supports the successful elimination of aberrant cells when they arise. Our findings are consistent with a model where clone size affects the topology of interface contacts and thereby the strength of JNK activation in wild type and aberrant interface cells. Bilateral JNK activation is unique to 'interface surveillance' and is not observed in other tissue-intrinsic defense mechanisms, such as classical 'cell-cell competition'. Thus, bilateral JNK interface signaling provides an independent tissue-level mechanism to eliminate cells with inappropriate developmental fate but normal cellular fitness. Finally, oncogenic Ras-expressing clones activate 'interface surveillance' but evade elimination by bilateral JNK activation. Combined, our work establishes bilateral JNK interface signaling and interface apoptosis as a new hallmark of interface surveillance and highlights how oncogenic mutations evade tumor suppressor function encoded by this tissue-intrinsic surveillance system.

An entosis-like process induces mitotic disruption in Pals1 microcephaly pathogenesis

Entosis is cell cannibalism utilized by tumor cells to engulf live neighboring cells for pro- or anti-tumorigenic purposes. It is unknown whether this extraordinary cellular event can be pathogenic in other diseases such as microcephaly, a condition characterized by a smaller than normal brain at birth. We find that mice mutant for the human microcephaly-causing gene Pals1, which exhibit diminished cortices due to massive cell death, also exhibit nuclei enveloped by plasma membranes inside of dividing cells. These cell-in-cell (CIC) structures represent a dynamic process accompanied by lengthened mitosis and cytokinesis abnormalities. As shown in tumor cells, ROCK inhibition completely abrogates CIC structures and restores the normal length of mitosis. Moreover, genetic elimination of Trp53 produces a remarkable rescue of cortical size along with substantial reductions of CIC structures and cell death. These results provide a novel pathogenic mechanism by which microcephaly is produced through entotic cell cannibalism.

The role of RAS oncogenes in controlling epithelial mechanics

Mutations in RAS are key oncogenic drivers and therapeutic targets. Oncogenic Ras proteins activate a network of downstream signalling pathways, including extracellular signal-regulated kinase (ERK) and phosphatidylinositol 3-kinase (PI3K), promoting cell proliferation and survival. However, there is increasing evidence that RAS oncogenes also alter the mechanical properties of both individual malignant cells and transformed tissues. Here we discuss the role of oncogenic RAS in controlling mechanical cell phenotypes and how these mechanical changes promote oncogenic transformation in single cells and tissues. RAS activation alters actin organisation and actomyosin contractility. These changes alter cell rheology and impact mechanosensing through changes in substrate adhesion and YAP/TAZ-dependent mechanotransduction. We then discuss how these changes play out in cell collectives and epithelial tissues by driving large-scale tissue deformations and the expansion of malignant cells. Uncovering how RAS oncogenes alter cell mechanics will lead to a better understanding of the morphogenetic processes that underlie tumour formation in RAS-mutant cancers.

Somatic variation in normal tissues: friend or foe of cancer early detection?

BACKGROUND

Seemingly normal tissues progressively become populated by mutant clones over time. Most of these clones bear mutations in well-known cancer genes but only rarely do they transform into cancer. This poses questions on what triggers cancer initiation and what implications somatic variation has for cancer early detection.

DESIGN

We analysed recent mutational screens of healthy and cancer-free diseased tissues to compare somatic drivers and the causes of somatic variation across tissues. We then reviewed the mechanisms of clonal expansion and their relationships with age and diseases other than cancer. We finally discussed the relevance of somatic variation for cancer initiation and how it can help or hinder cancer detection and prevention.

RESULTS

The extent of somatic variation is highly variable across tissues and depends on intrinsic features, such as tissue architecture and turnover, as well as the exposure to endogenous and exogenous insults. Most somatic mutations driving clonal expansion are tissue-specific and inactivate tumor suppressor genes involved in chromatin modification and cell growth signaling. Some of these genes are more frequently mutated in normal tissues than cancer, indicating a context-dependent cancer promoting or protective role. Mutant clones can persist over a long time or disappear rapidly, suggesting that their fitness depends on the dynamic equilibrium with the environment. The disruption of this equilibrium is likely responsible for their transformation into malignant clones and knowing what triggers this process is key for cancer prevention and early detection. Somatic variation should be considered in liquid biopsy, where it may contribute cancer-independent mutations, and in the identification of cancer drivers, since not all mutated genes favoring clonal expansion also drive tumorigenesis.

CONCLUSIONS

Somatic variation and the factors governing homeostasis of normal tissues should be taken into account when devising strategies for cancer prevention and early detection.

Clone wars: From molecules to cell competition in intestinal stem cell homeostasis and disease

The small intestine is among the fastest self-renewing tissues in adult mammals. This rapid turnover is fueled by the intestinal stem cells residing in the intestinal crypt. Wnt signaling plays a pivotal role in regulating intestinal stem cell renewal and differentiation, and the dysregulation of this pathway leads to cancer formation. Several studies demonstrate that intestinal stem cells follow neutral drift dynamics, as they divide symmetrically to generate other equipotent stem cells. Competition for niche space and extrinsic signals in the intestinal crypt is the governing mechanism that regulates stemness versus cell differentiation, but the underlying molecular mechanisms are still poorly understood, and it is not yet clear how this process changes during disease. In this review, we highlight the mechanisms that regulate stem cell homeostasis in the small intestine, focusing on Wnt signaling and its regulation by RNF43 and ZNRF3, key inhibitors of the Wnt pathway. Furthermore, we summarize the evidence supporting the current model of intestinal stem cell regulation, highlighting the principles of neutral drift at the basis of intestinal stem cell homeostasis. Finally, we discuss recent studies showing how cancer cells bypass this mechanism to gain a competitive advantage against neighboring normal cells.

Stem cells in the gut rapidly renew themselves through processes that cancer cells co-opt to trigger tumor development. Gabriele Colozza from the Institute of Molecular Biotechnology in Vienna, Austria, and colleagues review how a network of critical molecular signals and competition for limited space help to regulate the dynamics of stem cells in the intestines. The correct balance between self-renewal and differentiation is tightly controlled by the so-called Wnt signaling pathway and its inhibitors. Competition between dividing cells in the intestinal crypts, the locations between finger-like protrusions in the gut where stem cells are found, provides another protective mechanism against runaway stem cell growth. However, intestinal cancer cells, thanks to their activating mutations, bypass these safeguards to gain a survival advantage. Drugs that target these ‘super-competitive’ behaviors could therefore help combat tumor proliferation.

Cell Architecture-Dependent Constraints: Critical Safeguards to Carcinogenesis

Animal cells display great diversity in their shape. These morphological characteristics result from crosstalk between the plasma membrane and the force-generating capacities of the cytoskeleton macromolecules. Changes in cell shape are not merely byproducts of cell fate determinants, they also actively drive cell fate decisions, including proliferation and differentiation. Global and local changes in cell shape alter the transcriptional program by a multitude of mechanisms, including the regulation of physical links between the plasma membrane and the nuclear envelope and the mechanical modulation of cation channels and signalling molecules. It is therefore not surprising that anomalies in cell shape contribute to several diseases, including cancer. In this review, we discuss the possibility that the constraints imposed by cell shape determine the behaviour of normal and pro-tumour cells by organizing the whole interconnected regulatory network. In turn, cell behaviour might stabilize cells into discrete shapes. However, to progress towards a fully transformed phenotype and to acquire plasticity properties, pro-tumour cells might need to escape these cell shape restrictions. Thus, robust controls of the cell shape machinery may represent a critical safeguard against carcinogenesis.

Single-Cell RNA Sequencing Reveals the Role of Epithelial Cell Marker Genes in Predicting the Prognosis of Colorectal Cancer Patients

Single-cell RNA sequencing (scRNA-seq) is increasingly used in studies on gastrointestinal cancers. This study investigated the prognostic value of epithelial cell-associated biomarkers in colorectal cancer (CRC) using scRNA-seq data. We downloaded and analysed scRNA-seq data from four CRC samples from the Gene Expression Omnibus (GEO), and we identified marker genes of malignant epithelial cells (MECs) using CRC transcriptome and clinical data downloaded from The Cancer Genome Atlas (TCGA) and GEO as training and validation cohorts, respectively. In the TCGA training cohort, weighted gene correlation network analysis, univariate Cox proportional hazard model (Cox) analysis, and least absolute shrinkage and selection operator regression analysis were performed on the marker genes of MEC subsets to identify a signature of nine prognostic MEC-related genes (MECRGs) and calculate a risk score based on the signature. CRC patients were divided into high- and low-risk groups according to the median risk score. We found that the MECRG risk score was significantly correlated with the clinical features and overall survival of CRC patients, and that CRC patients in the high-risk group showed a significantly shorter survival time. The univariate and multivariate Cox regression analyses showed that the MECRG risk score can serve as an independent prognostic factor for CRC patients. Gene set enrichment analysis revealed that the MECRG signature genes are involved in fatty acid metabolism, p53 signalling, and other pathways. To increase the clinical application value, we constructed a MECRG nomogram by combining the MECRG risk score with other independent prognostic factors. The validity of the nomogram is based on receiver operating characteristics and calibration curves. The MECRG signature and nomogram models were well validated in the GEO dataset. In conclusion, we established an epithelial cell marker gene-based risk assessment model based on scRNA-seq analysis of CRC samples for predicting the prognosis of CRC patients.

Cell competition and the regulative nature of early mammalian development

The mammalian embryo exhibits a remarkable plasticity that allows it to correct for the presence of aberrant cells, adjust its growth so that its size is in accordance with its developmental stage, or integrate cells of another species to form fully functional organs. Here, we will discuss the contribution that cell competition, a quality control that eliminates viable cells that are less fit than their neighbors, makes to this plasticity. We will do this by reviewing the roles that cell competition plays in the early mammalian embryo and how they contribute to ensure normal development of the embryo.

Src activation in lipid rafts confers epithelial cells with invasive potential to escape from apical extrusion during cell competition

Abnormal/cancerous cells within healthy epithelial tissues undergo apical extrusion to protect against carcinogenesis, although they acquire invasive capacity once carcinogenesis progresses. However, the molecular mechanisms by which cancer cells escape from apical extrusion and invade surrounding tissues remain elusive. In this study, we demonstrate a molecular mechanism for cell fate switching during epithelial cell competition. We found that during competition within epithelial cell layers, Src transformation promotes maturation of focal adhesions and degradation of extracellular matrix. Src-transformed cells underwent basal delamination by Src activation within sphingolipid/cholesterol-enriched membrane microdomains/lipid rafts, whereas they were apically extruded when Src was outside of lipid rafts. A comparative analysis of contrasting phenotypes revealed that activation of the Src-STAT3-MMP axis through lipid rafts was required for basal delamination. CUB-domain-containing protein 1 (CDCP1) was identified as an Src-activating scaffold and as a Met regulator in lipid rafts, and its overexpression induced basal delamination. In renal cancer models, CDCP1 promoted epithelial-mesenchymal transition-mediated invasive behavior by activating the Src-STAT3-MMP axis through Met activation. Overall, these results suggest that spatial activation of Src signaling in lipid rafts confers resistance to apical extrusion and invasive potential on epithelial cells to promote carcinogenesis.

Ageing and cancer: a research gap to fill

The complex mechanisms of ageing biology are increasingly understood. Interventions to reduce or delay ageing‐associated diseases are emerging. Cancer is one of the diseases promoted by tissue ageing. A clockwise mutational signature is identified in many tumours. Ageing might be a modifiable cancer risk factor. To reduce the incidence of ageing‐related cancer and to detect the disease at earlier stages, we need to understand better the links between ageing and tumours. When a cancer is established, geriatric assessment and measures of biological age might help to generate evidence‐based therapeutic recommendations. In this approach, patients and caregivers would include the respective weight to give to the quality of life and survival in the therapeutic choices. The increasing burden of cancer in older patients requires new generations of researchers and geriatric oncologists to be trained, to properly address disease complexity in a multidisciplinary manner, and to reduce health inequities in this population of patients. In this review, we propose a series of research challenges to tackle in the next few years to better prevent, detect and treat cancer in older patients while preserving their quality of life.

TUMOR CELL MALIGNANCY: A COMPLEX TRAIT BUILT THROUGH RECIPROCAL INTERACTIONS BETWEEN TUMORS AND TISSUE-BODY SYSTEM

Since the discovery of oncogenes and tumor suppressor genes in the late past century, cancer research has been overwhelmingly focused on the genetics and biology of tumor cells and hence has addressed mostly cell-autonomous processes with emphasis on traditional driver/passenger genetic models. Nevertheless, over that same period, multiple seminal observations have accumulated highlighting the role of non-cell autonomous effectors in tumor growth and metastasis. However, given that cell autonomous and non-autonomous events are observed together at the time of diagnosis, it is in fact impossible to know whether the malignant transformation is initiated by cell autonomous oncogenic events or by non-cell autonomous conditions generated by alterations of the tissue-body ecosystem. This review aims at addressing this issue by taking the option of defining malignancy as a complex genetic trait incorporating genetically determined reciprocal interactions between tumor cells and tissue-body ecosystem.

Lima1 mediates the pluripotency control of membrane dynamics and cellular metabolism

Lima1 is an extensively studied prognostic marker of malignancy and is also considered to be a tumour suppressor, but its role in a developmental context of non-transformed cells is poorly understood. Here, we characterise the expression pattern and examined the function of Lima1 in mouse embryos and pluripotent stem cell lines. We identify that Lima1 expression is controlled by the naïve pluripotency circuit and is required for the suppression of membrane blebbing, as well as for proper mitochondrial energetics in embryonic stem cells. Moreover, forcing Lima1 expression enables primed mouse and human pluripotent stem cells to be incorporated into murine pre-implantation embryos. Thus, Lima1 is a key effector molecule that mediates the pluripotency control of membrane dynamics and cellular metabolism.

Cell competition: Clonal competition protects against early tumorigenesis

Aging tissues accumulate somatic mutations, yet cancer occurrence is relatively rare. A new study provides compelling evidence for why this may be the case and reveals that competition between mutant clones in oesophageal tissues protects against early tumorigenesis.

Clone competition as a mechanism to reduce tumor formation

With age, clones carrying somatic mutations in well-known cancer driver genes progressively populate adult tissues, yet cancer transformation is rare. In a recent issue of Nature, Colom et al. showed that competition between mutated clones with different fitness could act as a tumor-protective mechanism.

Struggle within: evolution and ecology of somatic cell populations

The extent to which normal (nonmalignant) cells of the body can evolve through mutation and selection during the lifetime of the organism has been a major unresolved issue in evolutionary and developmental studies. On the one hand, stable multicellular individuality seems to depend on genetic homogeneity and suppression of evolutionary conflicts at the cellular level. On the other hand, the example of clonal selection of lymphocytes indicates that certain forms of somatic mutation and selection are concordant with the organism-level fitness. Recent DNA sequencing and tissue physiology studies suggest that in addition to adaptive immune cells also neurons, epithelial cells, epidermal cells, hematopoietic stem cells and functional cells in solid bodily organs are subject to evolutionary forces during the lifetime of an organism. Here we refer to these recent studies and suggest that the expanding list of somatically evolving cells modifies idealized views of biological individuals as radically different from collectives.

Collective behaviours in organoids

Collective behaviour emerges from interacting units within communities, such as migrating herds, swimming fish schools, and cells within tissues. At the microscopic level, collective behaviours include collective cell migration in development and cancer invasion, rhythmic gene expression in pattern formation, cell competition in homeostasis and cancer, force generation and mechano-sensing in morphogenesis. Studying the initiation and the maintenance of collective cell behaviours is key to understand the principles of development, regeneration and disease. However, the manifold influences of contributing factors in in vivo environments challenge the dissection of causalities in animal models. As an alternative model that has emerged to overcome this difficulty, in vitro three-dimensional organoid cultures provide a reductionist approach yet retain similarities with the in vivo tissue in cellular composition and tissue organisation. Here, we focus on recent progresses in studying collective behaviours in different organoid systems and discuss their advantages and the possibility of improvement for future applications.

The role of tissue maturity and mechanical state in controlling cell extrusion

Epithelia remove dying or excess cells by extrusion, a process that seamlessly squeezes cells out of the layer without disrupting their barrier function. New studies shed light into the intricate relationship between extrusion, tissue mechanics, and development. They emphasize the importance of whole tissue-mechanics, rather than single cell-mechanics in controlling extrusion. Tissue compaction, stiffness, and cell-cell adhesion can impact the efficiency of cell extrusion and mechanisms that drive it, to adapt to different conditions during development or disease.

The Duality of Caspases in Cancer, as Told through the Fly

Caspases, a family of cysteine-aspartic proteases, have an established role as critical components in the activation and initiation of apoptosis. Alongside this a variety of non-apoptotic caspase functions in proliferation, differentiation, cellular plasticity and cell migration have been reported. The activity level and context are important factors in determining caspase function. As a consequence of their critical role in apoptosis and beyond, caspases are uniquely situated to have pathological roles, including in cancer. Altered caspase function is a common trait in a variety of cancers, with apoptotic evasion defined as a "hallmark of cancer". However, the role that caspases play in cancer is much more complex, acting both to prevent and to promote tumourigenesis. This review focuses on the major findings in Drosophila on the dual role of caspases in tumourigenesis. This has major implications for cancer treatments, including chemotherapy and radiotherapy, with the activation of apoptosis being the end goal. However, such treatments may inadvertently have adverse effects on promoting tumour progression and acerbating the cancer. A comprehensive understanding of the dual role of caspases will aid in the development of successful cancer therapeutic approaches.

Cell competition between anaplastic thyroid cancer and normal thyroid follicular cells exerts reciprocal stress response defining tumor suppressive effects of normal epithelial tissue

The microenvironment of an early-stage tumor, in which a small number of cancer cells is surrounded by a normal counterpart milieu, plays a crucial role in determining the fate of initiated cells. Here, we examined cell competition between anaplastic thyroid cancer cells and normal thyroid follicular cells using co-culture method. Cancer cells were grown until they formed small clusters, to which normal cells were added to create high-density co-culture condition. We found that co-culture with normal cells significantly suppressed the growth of cancer cell clusters through the activation of Akt-Skp2 pathway. In turn, cancer cells triggered apoptosis in the neighboring normal cells through local activation of ERK1/2. A bi-directional cell competition provides a suppressive mechanism of anaplastic thyroid cancer progression. Since the competitive effect was negated by terminal growth arrest caused by radiation exposure to normal cells, modulation of reciprocal stress response in vivo could be an intrinsic mechanism associated with tumor initiation, propagation, and metastasis.

Mutant p53 in cell-cell interactions

In this review, Pilley et al. examine the impact of different p53 mutations and focus on how heterogeneity of p53 status can affect relationships between cells within a tumor.

p53 is an important tumor suppressor, and the complexities of p53 function in regulating cancer cell behaviour are well established. Many cancers lose or express mutant forms of p53, with evidence that the type of alteration affecting p53 may differentially impact cancer development and progression. It is also clear that in addition to cell-autonomous functions, p53 status also affects the way cancer cells interact with each other. In this review, we briefly examine the impact of different p53 mutations and focus on how heterogeneity of p53 status can affect relationships between cells within a tumor.

Spreading of Isolated Ptch Mutant Basal Cell Carcinoma Precursors Is Physiologically Suppressed and Counteracts Tumor Formation in Mice

Basal cell carcinoma (BCC) originate from Hedgehog/Patched signaling-activated epidermal stem cells. However, the chemically induced tumorigenesis of mice with a CD4Cre-mediated biallelic loss of the Hedgehog signaling repressor Patched also induces BCC formation. Here, we identified the cellular origin of CD4Cre-targeted BCC progenitors as rare Keratin 5⁺ epidermal cells and show that wildtype Patched offspring of these cells spread over the hair follicle/skin complex with increasing mouse age. Intriguingly, Patched mutant counterparts are undetectable in age-matched untreated skin but are getting traceable upon applying the chemical tumorigenesis protocol. Together, our data show that biallelic Patched depletion in rare Keratin 5⁺ epidermal cells is not sufficient to drive BCC development, because the spread of these cells is physiologically suppressed. However, bypassing the repression of Patched mutant cells, e.g., by exogenous stimuli, leads to an accumulation of BCC precursor cells and, finally, to tumor development.

Cell competition in liver carcinogenesis

Cell competition is now a well-established quality control strategy to optimize cell and tissue fitness in multicellular organisms. While pursuing this goal, it is also effective in selecting against altered/defective cells with putative (pre)-neoplastic potential, thereby edging the risk of cancer development. The flip side of the coin is that the molecular machinery driving cell competition can also be co-opted by neoplastic cell populations to expand unchecked, outside the boundaries of tissue homeostatic control. This review will focus on information that begins to emerge regarding the role of cell competition in liver physiology and pathology. Liver repopulation by normal transplanted hepatocytes is an interesting field of investigation in this regard. The biological coordinates of this process share many features suggesting that cell competition is a driving force for the clearance of endogenous damaged hepatocytes by normal donor-derived cells, as previously proposed. Intriguing analogies between liver repopulation and carcinogenesis will be briefly discussed and the potential dual role of cell competition, as a barrier or a spur to neoplastic development, will be considered. Cell competition is in essence a cooperative strategy organized at tissue level. One facet of such cooperative attitude is expressed in the elimination of altered cells which may represent a threat to the organismal community. On the other hand, the society of cells can be disrupted by the emergence of selfish clones, exploiting the molecular bar codes of cell competition, thereby paving their way to uncontrolled growth.

Emerging mechanisms of cell competition

The growth and survival of cells within tissues can be affected by 'cell competition' between different cell clones. This phenomenon was initially recognized between wild-type cells and cells with mutations in ribosomal protein (Rp) genes in Drosophila melanogaster. However, competition also affects D. melanogaster cells with mutations in epithelial polarity genes, and wild-type cells exposed to 'super-competitor' cells with mutation in the Salvador-Warts-Hippo tumour suppressor pathway or expressing elevated levels of Myc. More recently, cell competition and super-competition were recognized in mammalian development, organ homeostasis and cancer. Genetic and cell biological studies have revealed that mechanisms underlying cell competition include the molecular recognition of 'different' cells, signalling imbalances between distinct cell populations and the mechanical consequences of differential growth rates; these mechanisms may also involve innate immune proteins, p53 and changes in translation.

Spatial competition shapes the dynamic mutational landscape of normal esophageal epithelium

During aging, progenitor cells acquire mutations, which may generate clones that colonize the surrounding tissue. By middle age, normal human tissues, including the esophageal epithelium (EE), become a patchwork of mutant clones. Despite their relevance for understanding aging and cancer, the processes that underpin mutational selection in normal tissues remain poorly understood. Here, we investigated this issue in the esophageal epithelium of mutagen-treated mice. Deep sequencing identified numerous mutant clones with multiple genes under positive selection, including Notch1, Notch2 and Trp53, which are also selected in human esophageal epithelium. Transgenic lineage tracing revealed strong clonal competition that evolved over time. Clone dynamics were consistent with a simple model in which the proliferative advantage conferred by positively selected mutations depends on the nature of the neighboring cells. When clones with similar competitive fitness collide, mutant cell fate reverts towards homeostasis, a constraint that explains how selection operates in normal-appearing epithelium.

Inflammatory Responses during Tumour Initiation: From Zebrafish Transgenic Models of Cancer to Evidence from Mouse and Man

The zebrafish is now an important model organism for cancer biology studies and provides unique and complementary opportunities in comparison to the mammalian equivalent. The translucency of zebrafish has allowed in vivo live imaging studies of tumour initiation and progression at the cellular level, providing novel insights into our understanding of cancer. Here we summarise the available transgenic zebrafish tumour models and discuss what we have gleaned from them with respect to cancer inflammation. In particular, we focus on the host inflammatory response towards transformed cells during the pre-neoplastic stage of tumour development. We discuss features of tumour-associated macrophages and neutrophils in mammalian models and present evidence that supports the idea that these inflammatory cells promote early stage tumour development and progression. Direct live imaging of tumour initiation in zebrafish models has shown that the intrinsic inflammation induced by pre-neoplastic cells is tumour promoting. Signals mediating leukocyte recruitment to pre-neoplastic cells in zebrafish correspond to the signals that mediate leukocyte recruitment in mammalian tumours. The activation state of macrophages and neutrophils recruited to pre-neoplastic cells in zebrafish appears to be heterogenous, as seen in mammalian models, which provides an opportunity to study the plasticity of innate immune cells during tumour initiation. Although several potential mechanisms are described that might mediate the trophic function of innate immune cells during tumour initiation in zebrafish, there are several unknowns that are yet to be resolved. Rapid advancement of genetic tools and imaging technologies for zebrafish will facilitate research into the mechanisms that modulate leukocyte function during tumour initiation and identify targets for cancer prevention.

The COX-2/PGE2 pathway suppresses apical elimination of RasV12-transformed cells from epithelia

At the initial stage of carcinogenesis, when RasV12-transformed cells are surrounded by normal epithelial cells, RasV12 cells are apically extruded from epithelia through cell competition with the surrounding normal cells. In this study, we demonstrate that expression of cyclooxygenase (COX)-2 is upregulated in normal cells surrounding RasV12-transformed cells. Addition of COX inhibitor or COX-2-knockout promotes apical extrusion of RasV12 cells. Furthermore, production of Prostaglandin (PG) E2, a downstream prostanoid of COX-2, is elevated in normal cells surrounding RasV12 cells, and addition of PGE2 suppresses apical extrusion of RasV12 cells. In a cell competition mouse model, expression of COX-2 is elevated in pancreatic epithelia harbouring RasV12-exressing cells, and the COX inhibitor ibuprofen promotes apical extrusion of RasV12 cells. Moreover, caerulein-induced chronic inflammation substantially suppresses apical elimination of RasV12 cells. These results indicate that intrinsically or extrinsically mediated inflammation can promote tumour initiation by diminishing cell competition between normal and transformed cells.

Ovarian Cancer Dissemination-A Cell Biologist's Perspective

Epithelial ovarian cancer (EOC) comprises multiple disease states representing a variety of distinct tumors that, irrespective of tissue of origin, genetic aberrations and pathological features, share common patterns of dissemination to the peritoneal cavity. EOC peritoneal dissemination is a stepwise process that includes the formation of malignant outgrowths that detach and establish widespread peritoneal metastases through adhesion to serosal membranes. The cell biology associated with outgrowth formation, detachment, and de novo adhesion is at the nexus of diverse genetic backgrounds that characterize the disease. Development of treatment for metastatic disease will require detailed characterization of cellular processes involved in each step of EOC peritoneal dissemination. This article offers a review of the literature that relates to the current stage of knowledge about distinct steps of EOC peritoneal dissemination, with emphasis on the cell biology aspects of the process.