Wnt activation disturbs cell competition and causes diffuse invasion of transformed cells through NF-κB-MMP21 pathway.

Normal epithelial cells exert their competitive advantage over RasV12-transformed cells and eliminate them into the apical lumen via cell competition. However, the internal or external factors that compromise cell competition and provoke carcinogenesis remain elusive. In this study, we examine the effect of sequential accumulation of gene mutations, mimicking multi-sequential carcinogenesis on RasV12-induced cell competition in intestinal epithelial tissues. Consequently, we find that the directionality of RasV12-cell extrusion in Wnt-activated epithelia is reversed, and transformed cells are delaminated into the basal lamina via non-cell autonomous MMP21 upregulation. Subsequently, diffusively infiltrating, transformed cells develop into highly invasive carcinomas. The elevated production of MMP21 is elicited partly through NF-κB signaling, blockage of which restores apical elimination of RasV12 cells. We further demonstrate that the NF-κB-MMP21 axis is significantly bolstered in early colorectal carcinoma in humans. Collectively, this study shows that cells with high mutational burdens exploit cell competition for their benefit by behaving as unfit cells, endowing them with an invasion advantage.

Autophagic perturbation caused by reduced lysosomal activity positively regulates cell competition.

Newly emerging transformed epithelial cells are recognized and apically removed by surrounding normal cells through a biological event termed "cell competition". However, little is known about the mechanisms underlying this process. In a recent study, we describe that RASG12V/RasV12-transformed cells surrounded by normal cells exhibit decreased lysosomal activity accompanied with accumulation of autophagosomes. Restoration of low lysosomal activity or inhibition of autophagosome formation significantly antagonizes apical extrusion of RASG12V cells, suggesting that non-degradable autophagosomes are required for cell competition. Notably, analysis of a cell competition mouse model demonstrates that macroautophagy/autophagy-ablated RASG12V cells are less readily eliminated by cell competition, and remaining transformed cells destroy ductal integrity, leading to chronic pancreatitis. Thus, our findings illuminate a critical role for non-degradable autophagosomes in cell competition and reveal a homeostasis-preserving role of autophagy upon emergence of transformed cells.

Non-degradable autophagic vacuoles are indispensable for cell competition.

Cell competition is a process by which unwanted cells are eliminated from tissues. Apical extrusion is one mode whereby normal epithelial cells remove transformed cells, but it remains unclear how this process is mechanically effected. In this study, we show that autophagic and endocytic fluxes are attenuated in RasV12-transformed cells surrounded by normal cells due to lysosomal dysfunction, and that chemical manipulation of lysosomal activity compromises apical extrusion. We further find that RasV12 cells deficient in autophagy initiation machinery are resistant to elimination pressure exerted by normal cells, suggesting that non-degradable autophagic vacuoles are required for cell competition. Moreover, in vivo analysis revealed that autophagy-ablated RasV12 cells are less readily eliminated by cell competition, and remaining transformed cells destroy ductal integrity, leading to chronic pancreatitis. Collectively, our findings illuminate a positive role for autophagy in cell competition and reveal a homeostasis-preserving function of autophagy upon emergence of transformed cells.

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.

Basal extrusion of single-oncogenic mutant cells induces dome-like structures with altered microenvironments.

At the initial stage of carcinogenesis, oncogenic transformation occurs in single cells within epithelial layers. However, the behavior and fate of the newly emerging transformed cells remain enigmatic. Here, using originally established mouse models, we investigate the fate of RasV12-transformed cells that appear in a mosaic manner within epithelial tissues. In the lung bronchial epithelium, most majority of RasV12-transformed cells are apically extruded, whereas noneliminated RasV12 cells are often basally delaminated leading to various noncell-autonomous changes in surrounding environments; macrophages and activated fibroblasts are accumulated, and normal epithelial cells overlying RasV12 cells overproliferate and form a convex multilayer, which is termed a 'dome-like structure'. In addition, basally extruded RasV12 cells acquire certain features of epithelial-mesenchymal transition (EMT). Furthermore, the expression of COX-2 is profoundly elevated in RasV12 cells in dome-like structures, and treatment with the COX inhibitor ibuprofen suppresses the recruitment of activated fibroblasts and moderately diminishes the formation of dome-like structures. Therefore, basal extrusion of single-oncogenic mutant cells can induce a tumor microenvironment and EMT and generate characteristic precancerous lesions, providing molecular insights into the earlier steps of cancer development.

Hepatocyte growth factor derived from senescent cells attenuates cell competition-induced apical elimination of oncogenic cells.

Cellular senescence and cell competition are important tumor suppression mechanisms that restrain cells with oncogenic mutations at the initial stage of cancer development. However, the link between cellular senescence and cell competition remains unclear. Senescent cells accumulated during the in vivo aging process contribute toward age-related cancers via the development of senescence-associated secretory phenotype (SASP). Here, we report that hepatocyte growth factor (HGF), a SASP factor, inhibits apical extrusion and promotes basal protrusion of Ras-mutated cells in the cell competition assay. Additionally, cellular senescence induced by a high-fat diet promotes the survival of cells with oncogenic mutations, whereas crizotinib, an inhibitor of HGF signaling, provokes the removal of mutated cells from mouse livers and intestines. Our study provides evidence that cellular senescence inhibits cell competition-mediated elimination of oncogenic cells through HGF signaling, suggesting that it may lead to cancer incidence during aging.

Extracellular ATP facilitates cell extrusion from epithelial layers mediated by cell competition or apoptosis.

For the maintenance of epithelial homeostasis, various aberrant or dysfunctional cells are actively eliminated from epithelial layers. This cell extrusion process mainly falls into two modes: cell-competition-mediated extrusion and apoptotic extrusion. However, it is not clearly understood whether and how these processes are governed by common molecular mechanisms. In this study, we demonstrate that the reactive oxygen species (ROS) levels are elevated within a wide range of epithelial layers around extruding transformed or apoptotic cells. The downregulation of ROS suppresses the extrusion process. Furthermore, ATP is extracellularly secreted from extruding cells, which promotes the ROS level and cell extrusion. Moreover, the extracellular ATP and ROS pathways positively regulate the polarized movements of surrounding cells toward extruding cells in both cell-competition-mediated and apoptotic extrusion. Hence, extracellular ATP acts as an "extrude me" signal and plays a prevalent role in cell extrusion, thereby sustaining epithelial homeostasis and preventing pathological conditions or disorders.

Cell competition-induced apical elimination of transformed cells, EDAC, orchestrates the cellular homeostasis.

Newly emerging transformed cells are often eliminated from the epithelium via cell competition with the surrounding normal cells. A number of recent studies using mammalian cell competition systems have demonstrated that cells with various types of oncogenic insults are extruded from the tissue in a cell death-dependent or -independent manner. Cell competition-mediated elimination of transformed cells, called EDAC (epithelial defense against cancer), represents an intrinsic anti-tumor activity within the epithelial cell society to reduce the risk of oncogenesis. Here we delineate roles and molecular mechanisms of this homeostatic process, especially focusing on mammalian models.

GPR30-Expressing Gastric Chief Cells Do Not Dedifferentiate But Are Eliminated via PDK-Dependent Cell Competition During Development of Metaplasia.

BACKGROUND & AIMS: Gastric chief cells, a mature cell type that secretes digestive enzymes, have been proposed to be the origin of metaplasia and cancer through dedifferentiation or transdifferentiation. However, studies supporting this claim have had technical limitations, including issues with the specificity of chief cell markers and the toxicity of drugs used. We therefore sought to identify genes expressed specifically in chief cells and establish a model to trace these cells. METHODS: We performed transcriptome analysis of Mist1-CreERT-traced cells, with or without chief cell depletion. Gpr30-rtTA mice were generated and crossed to TetO-Cre mice, and lineage tracing was performed after crosses to R26-TdTomato mice. Additional lineage tracing experiments were performed using Mist1-CreERT, Kitl-CreERT, Tff1-Cre, and Tff2-Cre mice crossed to reporter mice. Mice were given high-dose tamoxifen or DMP-777 or were infected with Helicobacter pylori to induce gastric metaplasia. We studied mice that expressed mutant forms of Ras in gastric cells, using TetO-KrasG12D, LSL-KrasG12D, and LSL-HrasG12V mice. We analyzed stomach tissues from GPR30-knockout mice. Mice were given dichloroacetate to inhibit pyruvate dehydrogenase kinase (PDK)-dependent cell competition. RESULTS: We identified GPR30, the G-protein-coupled form of the estrogen receptor, as a cell-specific marker of chief cells in gastric epithelium of mice. Gpr30-rtTA mice crossed to TetO-Cre;R26-TdTomato mice had specific expression of GPR30 in chief cells, with no expression noted in isthmus stem cells or lineage tracing of glands. Expression of mutant Kras in GPR30+ chief cells did not lead to the development of metaplasia or dysplasia but, instead, led to a reduction in labeled numbers of chief cells and a compensatory expansion of neck lineage, which was derived from upper Kitl+ clones. Administration of high-dose tamoxifen, DMP-777, or H pylori decreased the number of labeled chief cells. Chief cells were eliminated from epithelia via GPR30- and PDK-dependent cell competition after metaplastic stimuli, whereas loss of GRP30 or inhibition of PDK activity preserved chief cell numbers and attenuated neck lineage cell expansion. CONCLUSIONS: In tracing studies of mice, we found that most chief cells are lost during metaplasia and therefore are unlikely to contribute to gastric carcinogenesis. Expansion of cells that coexpress neck and chief lineage markers, known as spasmolytic polypeptide-expressing metaplasia, does not occur via dedifferentiation from chief cells but, rather, through a compensatory response from neck progenitors to replace the eliminated chief cells.

An Anti-tumorigenic Role of the Warburg Effect at Emergence of Transformed Cells.

The Warburg effect is one of the hallmarks of cancer cells, characterized by enhanced aerobic glycolysis. Despite intense research efforts, its functional relevance or biological significance to facilitate tumor progression is still debatable. Hence the question persists when and how the Warburg effect contributes to carcinogenesis. Especially, the role of metabolic changes at a very early stage of tumorigenesis has received relatively little attention, and how aerobic glycolysis impacts tumor incidence remains largely unknown. Here we discuss a novel paradigm for the effect of the Warburg effect that provides a suppressive role in oncogenesis.Key words: Warburg effect, aerobic glycolysis, cell competition, EDAC.

Mutant p53-Expressing Cells Undergo Necroptosis via Cell Competition with the Neighboring Normal Epithelial Cells.

p53 is a tumor suppressor protein, and its missense mutations are frequently found in human cancers. During the multi-step progression of cancer, p53 mutations generally accumulate at the mid or late stage, but not in the early stage, and the underlying mechanism is still unclear. In this study, using mammalian cell culture and mouse ex vivo systems, we demonstrate that when p53R273H- or p53R175H-expressing cells are surrounded by normal epithelial cells, mutant p53 cells undergo necroptosis and are basally extruded from the epithelial monolayer. When mutant p53 cells alone are present, cell death does not occur, indicating that necroptosis results from cell competition with the surrounding normal cells. Furthermore, when p53R273H mutation occurs within RasV12-transformed epithelia, cell death is strongly suppressed and most of the p53R273H-expressing cells remain intact. These results suggest that the order of oncogenic mutations in cancer development could be dictated by cell competition.

Physiological and pathological relevance of cell competition in fly to mammals.

In multicellular organisms, incidentally emerging suboptimal cells are removed to maintain homeostasis of tissues. The unfavorable cells are excluded by a process termed cell competition whereby the resident normal cells actively eliminate the unfit cells of the identical lineage. Although the phenomenon of cell competition was originally discovered in Drosophila, a number of recent studies have provided implications of cell competition in tissue regeneration, development and oncogenesis in mammals. Here the roles of cell competition in fly to mammals are discussed.

Cell competition with normal epithelial cells promotes apical extrusion of transformed cells through metabolic changes.

Recent studies have revealed that newly emerging transformed cells are often apically extruded from epithelial tissues. During this process, normal epithelial cells can recognize and actively eliminate transformed cells, a process called epithelial defence against cancer (EDAC). Here, we show that mitochondrial membrane potential is diminished in RasV12-transformed cells when they are surrounded by normal cells. In addition, glucose uptake is elevated, leading to higher lactate production. The mitochondrial dysfunction is driven by upregulation of pyruvate dehydrogenase kinase 4 (PDK4), which positively regulates elimination of RasV12-transformed cells. Furthermore, EDAC from the surrounding normal cells, involving filamin, drives the Warburg-effect-like metabolic alteration. Moreover, using a cell-competition mouse model, we demonstrate that PDK-mediated metabolic changes promote the elimination of RasV12-transformed cells from intestinal epithelia. These data indicate that non-cell-autonomous metabolic modulation is a crucial regulator for cell competition, shedding light on the unexplored events at the initial stage of carcinogenesis.

Rab5-regulated endocytosis plays a crucial role in apical extrusion of transformed cells.

Newly emerging transformed cells are often eliminated from epithelial tissues. Recent studies have revealed that this cancer-preventive process involves the interaction with the surrounding normal epithelial cells; however, the molecular mechanisms underlying this phenomenon remain largely unknown. In this study, using mammalian cell culture and zebrafish embryo systems, we have elucidated the functional involvement of endocytosis in the elimination of RasV12-transformed cells. First, we show that Rab5, a crucial regulator of endocytosis, is accumulated in RasV12-transformed cells that are surrounded by normal epithelial cells, which is accompanied by up-regulation of clathrin-dependent endocytosis. Addition of chlorpromazine or coexpression of a dominant-negative mutant of Rab5 suppresses apical extrusion of RasV12 cells from the epithelium. We also show in zebrafish embryos that Rab5 plays an important role in the elimination of transformed cells from the enveloping layer epithelium. In addition, Rab5-mediated endocytosis of E-cadherin is enhanced at the boundary between normal and RasV12 cells. Rab5 functions upstream of epithelial protein lost in neoplasm (EPLIN), which plays a positive role in apical extrusion of RasV12 cells by regulating protein kinase A. Furthermore, we have revealed that epithelial defense against cancer (EDAC) from normal epithelial cells substantially impacts on Rab5 accumulation in the neighboring transformed cells. This report demonstrates that Rab5-mediated endocytosis is a crucial regulator for the competitive interaction between normal and transformed epithelial cells in mammals.

A role of the sphingosine-1-phosphate (S1P)-S1P receptor 2 pathway in epithelial defense against cancer (EDAC).

At the initial step of carcinogenesis, transformation occurs in single cells within epithelia, where the newly emerging transformed cells are surrounded by normal epithelial cells. A recent study revealed that normal epithelial cells have an ability to sense and actively eliminate the neighboring transformed cells, a process named epithelial defense against cancer (EDAC). However, the molecular mechanism of this tumor-suppressive activity is largely unknown. In this study, we investigated a role for the sphingosine-1-phosphate (S1P)-S1P receptor 2 (S1PR2) pathway in EDAC. First, we show that addition of the S1PR2 inhibitor significantly suppresses apical extrusion of RasV12-transformed cells that are surrounded by normal cells. In addition, knockdown of S1PR2 in normal cells induces the same effect, indicating that S1PR2 in the surrounding normal cells plays a positive role in the apical elimination of the transformed cells. Of importance, not endogenous S1P but exogenous S1P is involved in this process. By using FRET analyses, we demonstrate that S1PR2 mediates Rho activation in normal cells neighboring RasV12-transformed cells, thereby promoting accumulation of filamin, a crucial regulator of EDAC. Collectively these data indicate that S1P is a key extrinsic factor that affects the outcome of cell competition between normal and transformed epithelial cells.

The cell competition-based high-throughput screening identifies small compounds that promote the elimination of RasV12-transformed cells from epithelia.

Recent studies have revealed that cell competition can occur between normal and transformed epithelial cells; normal epithelial cells recognize the presence of the neighboring transformed cells and actively eliminate them from epithelial tissues. Here, we have established a brand-new high-throughput screening platform that targets cell competition. By using this platform, we have identified Rebeccamycin as a hit compound that specifically promotes elimination of RasV12-transformed cells from the epithelium, though after longer treatment it shows substantial cytotoxic effect against normal epithelial cells. Among several Rebeccamycin-derivative compounds, we have found that VC1-8 has least cytotoxicity against normal cells but shows the comparable effect on the elimination of transformed cells. This cell competition-promoting activity of VC1-8 is observed both in vitro and ex vivo. These data demonstrate that the cell competition-based screening is a promising tool for the establishment of a novel type of cancer preventive medicine.

EPLIN is a crucial regulator for extrusion of RasV12-transformed cells.

At the initial stage of carcinogenesis, a mutation occurs in a single cell within a normal epithelial layer. We have previously shown that RasV12-transformed cells are apically extruded from the epithelium when surrounded by normal cells. However, the molecular mechanisms underlying this phenomenon remain elusive. Here, we demonstrate that Cav-1-containing microdomains and EPLIN (also known as LIMA1) are accumulated in RasV12-transformed cells that are surrounded by normal cells. We also show that knockdown of Cav-1 or EPLIN suppresses apical extrusion of RasV12-transformed cells, suggesting their positive role in the elimination of transformed cells from epithelia. EPLIN functions upstream of Cav-1 and affects its enrichment in RasV12-transformed cells that are surrounded by normal cells. Furthermore, EPLIN regulates non-cell-autonomous activation of myosin-II and protein kinase A (PKA) in RasV12-transformed cells. In addition, EPLIN substantially affects the accumulation of filamin A, a vital player in epithelial defense against cancer (EDAC), in the neighboring normal cells, and vice versa. These results indicate that EPLIN is a crucial regulator of the interaction between normal and transformed epithelial cells.

The Arf GTPase-activating protein SMAP1 promotes transferrin receptor endocytosis and interacts with SMAP2.

Arf GTPase-activating proteins (Arf GAP) play important roles in the formation of the membrane vesicles that traffic between subcellular membranous organelles. The small Arf GTPase-activating protein (SMAP) subfamily of Arf GAPs has two members, SMAP1 and SMAP2, in mammals. The present study investigated whether these two proteins may have an overlapping function in addition to their previously reported distinct functions. Results showed that the presence of either SMAP1 or SMAP2 was sufficient for endocytosis of the transferrin receptor, and that transferrin incorporation was impaired only by the absence of both SMAP1 and SMAP2. This suggests the involvement of both SMAP1 and SMAP2 in transferrin endocytosis. Results also demonstrated a physical association between SMAP1 and SMAP2, which might serve as a basis for a functional interaction, and identified the intramolecular domains responsible for this association.

Altered trafficking of mutated growth factor receptors and their associated molecules: implication for human cancers.

Ligand-stimulated receptor tyrosine kinases (RTKs) are phosphorylated/ubiquitinated, endocytosed and transported to the lysosomes via endosomes/multivesicular bodies, resulting in the attenuation of signal transmission. If this physiological mechanism of RTK signal downregulation is perturbed, signal transduction persists and may contribute to cellular transformation. This article presents several such examples. In some cases, endocytosis is impaired, and the activated RTK remains on the plasma membrane. In other cases, the activated RTK is endocytosed into endosomes/multivesicular bodies, but not subsequently sorted to the lysosomes for degradation. The latter cases indicate that even endocytosed RTKs can transmit signals. Transport of RTKs is accomplished via the formation and movement of membrane vesicles. Blockage or delay of endocytosis/trafficking can be caused by genetic alterations in the RTK itself or by mutations in CBL, Arf GAPs, or other components involved in internalization and vesicle transport. A survey of the literature indicates that, in some cases, even RTKs synthesized de novo can initiate signaling at the endoplasmic reticulum/Golgi before reaching the plasma membrane. The spectrum of molecules targeted by the signal is likely to be different between cell surface- and endoplasmic reticulum/Golgi-localized RTKs.

T-cell receptor signaling induces proximal Runx1 transactivation via a calcineurin-NFAT pathway.

Runx1 transcription factor is a key player in the development and function of T cells. Runx1 transcripts consist of two closely related isoforms (proximal and distal Runx1) whose expressions are regulated by different promoters. Which Runx1 isoform is expressed appears to be tightly regulated. The regulatory mechanism for differential transcription is, however, not fully understood. In this study, we investigated the regulation of the proximal Runx1 promoter in T cells. We showed that proximal Runx1 was expressed at a low level in naïve T cells from C57BL/6 mice, but its expression was remarkably induced upon T-cell activation. In the promoter of proximal Runx1, a highly conserved region was identified which spans from -412 to the transcription start site and harbors a NFAT binding site. In a luciferase reporter assay, this region was found to be responsive to T-cell activation through Lck and calcineurin pathways. Mutagenesis studies and chromatin immunoprecipitation assay indicated that the NFAT site was essential for NFAT binding and transactivation of the proximal Runx1 promoter. Furthermore, TCR signaling-induced expression of proximal Runx1 was blocked by treatment of cells with cyclosporin A. Together, these results demonstrate that the calcineurin-NFAT pathway regulates proximal Runx1 transcription upon TCR stimulation.