Therapeutic targeting approach on epithelial-mesenchymal plasticity to combat cancer metastasis

Epithelial-mesenchymal plasticity (EMP) is a process in which epithelial cells lose their characteristics and acquire mesenchymal properties, leading to increased motility and invasiveness, which are key factors in cancer metastasis. Targeting EMP has emerged as a promising therapeutic approach to combat cancer metastasis. Various strategies have been developed to target EMP, including inhibition of key signaling pathways, such as TGF-β, Wnt/β-catenin, and Notch, that regulate EMP, as well as targeting specific transcription factors, such as Snail, Slug, and Twist, that promote EMP. Additionally, targeting the tumor microenvironment, which plays a critical role in promoting EMP, has also shown promise. Several preclinical and clinical studies have demonstrated the efficacy of EMP-targeting therapies in inhibiting cancer metastasis. However, further research is needed to optimize these strategies and improve their clinical efficacy. Overall, therapeutic targeting of EMP represents a promising approach for the development of novel cancer therapies that can effectively inhibit metastasis, a major cause of cancer-related mortality.

Novel plasma exosome biomarkers for prostate cancer progression in co-morbid metabolic disease

Comorbid Type 2 diabetes (T2D), a metabolic complication of obesity, associates with worse cancer outcomes for prostate, breast, head and neck, colorectal and several other solid tumors. However, the molecular mechanisms remain poorly understood. Emerging evidence shows that exosomes carry miRNAs in blood that encode the metabolic status of originating tissues and deliver their cargo to target tissues to modulate expression of critical genes. Exosomal communication potentially connects abnormal metabolism to cancer progression. Here, we hypothesized that T2D plasma exosomes induce epithelial-mesenchymal transition (EMT) and immune checkpoints in prostate cancer cells. We demonstrate that plasma exosomes from subjects with T2D induce EMT features in prostate cancer cells and upregulate the checkpoint genes CD274 and CD155. We demonstrate that specific exosomal miRNAs that are differentially abundant in plasma of T2D adults compared to nondiabetic controls (miR374a-5p, miR-93-5p and let-7b-3p) are delivered to cancer cells, thereby regulating critical target genes. We build on our previous reports showing BRD4 controls migration and dissemination of castration-resistant prostate cancer, and transcription of key EMT genes, to show that T2D exosomes require BRD4 to drive EMT and immune ligand expression. We validate our findings with gene set enrichment analysis of human prostate tumor tissue in TGCA genomic data. These results suggest novel, non-invasive approaches to evaluate and potentially block progression of prostate and other cancers in patients with comorbid T2D.

ERK2 signaling regulates cell-cell adhesion of epithelial cells and enhances growth factor-induced cell scattering

The ERK signaling pathway, consisting of core protein kinases Raf, MEK and effector kinases ERK1/2, regulates various biological outcomes such as cell proliferation, differentiation, apoptosis, or cell migration. Signal transduction through the ERK signaling pathway is tightly controlled at all levels of the pathway. However, it is not well understood whether ERK pathway signaling can be modulated by the abundance of ERK pathway core kinases. In this study, we investigated the effects of low-level overexpression of the ERK2 isoform on the phenotype and scattering of cuboidal MDCK epithelial cells growing in discrete multicellular clusters. We show that ERK2 overexpression reduced the vertical size of lateral membranes that contain cell-cell adhesion complexes. Consequently, ERK2 overexpressing cells were unable to develop cuboidal shape, remained flat with increased spread area and intercellular adhesive contacts were present only on the basal side. Interestingly, ERK2 overexpression was not sufficient to increase phosphorylation of multiple downstream targets including transcription factors and induce global changes in gene expression, namely to increase the expression of pro-migratory transcription factor Fra1. However, ERK2 overexpression enhanced HGF/SF-induced cell scattering as these cells scattered more rapidly and to a greater extent than parental cells. Our results suggest that an increase in ERK2 expression primarily reduces cell-cell cohesion and that weakened intercellular adhesion synergizes with upstream signaling in the conversion of the multicellular epithelium into single migrating cells. This mechanism may be clinically relevant as the analysis of clinical data revealed that in one type of cancer, pancreatic adenocarcinoma, ERK2 overexpression correlates with a worse prognosis.

Epithelial plasticity in COPD results in cellular unjamming due to an increase in polymerized actin

The airway epithelium is subjected to insults such as cigarette smoke (CS), a primary cause of chronic obstructive pulmonary disease (COPD) and serves as an excellent model to study cell plasticity. Here, we show that both CS-exposed and COPD-patient derived epithelia (CHBE) display quantitative evidence of cellular plasticity, with loss of specialized apical features and a transcriptional profile suggestive of partial epithelial-to-mesenchymal transition (pEMT), albeit with distinct cell motion indicative of cellular unjamming. These injured/diseased cells have an increased fraction of polymerized actin, due to loss of the actin-severing protein cofilin-1. We observed that decreasing polymerized actin restores the jammed state in both CHBE and CS-exposed epithelia, indicating that the fraction of polymerized actin is critical in unjamming the epithelia. Our kinetic energy spectral analysis suggests that loss of cofilin-1 results in unjamming, similar to that seen with both CS exposure and in CHBE cells. The findings suggest that in response to chronic injury, although epithelial cells display evidence of pEMT, their movement is more consistent with cellular unjamming. Inhibitors of actin polymerization rectify the unjamming features of the monolayer. This article has an associated First Person interview with the first author of the paper.

Role of Secretoglobin+ (club cell) NFκB/RelA-TGFβ signaling in aero-allergen-induced epithelial plasticity and subepithelial myofibroblast transdifferentiation

Repetitive aeroallergen exposure is linked to sensitization and airway remodeling through incompletely understood mechanisms. In this study, we examine the dynamic mucosal response to cat dander extract (CDE), a ubiquitous aero-allergen linked to remodeling, sensitization and asthma. We find that daily exposure of CDE in naïve C57BL/6 mice activates innate neutrophilic inflammation followed by transition to a lymphocytic response associated with waves of mucosal transforming growth factor (TGF) isoform expression. In parallel, enhanced bronchiolar Smad3 expression and accumulation of phospho-SMAD3 was observed, indicating paracrine activation of canonical TGFβR signaling. CDE exposure similarly triggered epithelial cell plasticity, associated with expression of mesenchymal regulatory factors (Snai1 and Zeb1), reduction of epithelial markers (Cdh1) and activation of the NFκB/RelA transcriptional activator. To determine whether NFκB functionally mediates CDE-induced growth factor response, mice were stimulated with CDE in the absence or presence of a selective IKK inhibitor. IKK inhibition substantially reduced the level of CDE-induced TGFβ1 expression, pSMAD3 accumulation, Snai1 and Zeb1 expression. Activation of epithelial plasticity was demonstrated by flow cytometry in whole lung homogenates, where CDE induces accumulation of SMA⁺Epcam⁺ population. Club cells are important sources of cytokine and growth factor production. To determine whether Club cell innate signaling through NFκB/RelA mediated CDE induced TGFβ signaling, we depleted RelA in Secretoglobin (Scgb1a1)-expressing bronchiolar cells. Immunofluorescence-optical clearing light sheet microscopy showed a punctate distribution of Scgb1a1 progenitors throughout the small airway. We found that RelA depletion in Secretoglobin⁺ cells results in inhibition of the mucosal TGFβ response, blockade of EMT and reduced subepithelial myofibroblast expansion. We conclude that the Secretoglobin—derived bronchiolar cell is central to coordinating the innate response required for mucosal TGFβ1 response, EMT and myofibroblast expansion. These data have important mechanistic implications for how aero-allergens trigger mucosal injury response and remodeling in the small airway.

Cancer drug resistance induced by EMT: novel therapeutic strategies

Over the last decade, important clinical benefits have been achieved in cancer patients by using drug-targeting strategies. Nevertheless, drug resistance is still a major problem in most cancer therapies. Epithelial-mesenchymal plasticity (EMP) and tumour microenvironment have been described as limiting factors for effective treatment in many cancer types. Moreover, epithelial-to-mesenchymal transition (EMT) has also been associated with therapy resistance in many different preclinical models, although limited evidence has been obtained from clinical studies and clinical samples. In this review, we particularly deepen into the mechanisms of which intermediate epithelial/mesenchymal (E/M) states and its interconnection to microenvironment influence therapy resistance. We also describe how the use of bioinformatics and pharmacogenomics will help to figure out the biological impact of the EMT on drug resistance and to develop novel pharmacological approaches in the future.

Induction of Epithelial-mesenchymal Transition in MDCK II Cells

Epithelial-mesenchymal transition (EMT) is a reversible process of epithelial cell transdifferentiation into a mesenchymal cell, that enables initiation of cell migration. EMT plays an important role in embryonic development, tissue repair and cancer metastasis. Better understanding of cellular and molecular events during EMT will not only provide novel insights on how mammalian organism develops and how epithelial tissues regenerate, but also can identify novel therapeutic targets for cancer therapy. Here we aim to provide a detailed protocol on how to induce EMT in Madin-Darby Canine Kidney (MDCK) II epithelial cell line and perform immunofluorescent staining on EMT-induced cells.

Bittersweet tumor development and progression: Emerging roles of epithelial plasticity glycosylations

Altered metabolism is one of the hallmarks of cancer. The best-known cancer metabolic anomaly is an increase in aerobic glycolysis, which generates ATP and other basic building blocks, such as nucleotides, lipids, and proteins to support tumor cell growth and survival. Epithelial plasticity (EP) programs such as the epithelial-mesenchymal transition (EMT) and mesenchymal-epithelial transition (MET) are evolutionarily conserved processes that are essential for embryonic development. EP also plays an important role during tumor progression toward metastasis and treatment resistance, and new roles in the acceleration of tumorigenesis have been found. Recent evidence has linked EMT-related transcriptomic alterations with metabolic reprogramming in cancer cells, which include increased aerobic glycolysis. More recent studies have revealed a novel connection between EMT and altered glycosylation in tumor cells, in which EMT drives an increase in glucose uptake and flux into the hexosamine biosynthetic pathway (HBP). The HBP is a side-branch pathway from glycolysis which generates the end product uridine-5'-diphosphate-N-acetylglucosamine (UDP-GlcNAc). A key downstream utilization of UDP-GlcNAc is for the post-translational modification O-GlcNAcylation which involves the attachment of the GlcNAc moiety to Ser/Thr/Asn residues of proteins. Global changes in protein O-GlcNAcylation are emerging as a general characteristic of cancer cells. In our recent study, we demonstrated that the EMT-HBP-O-GlcNAcylation axis drives the O-GlcNAcylation of key proteins such as c-Myc, which previous studies have shown to suppress oncogene-induced senescence (OIS) and contribute to accelerated tumorigenesis. Here, we review the HBP and O-GlcNAcylation and their putative roles in driving EMT-related cancer processes with examples to illuminate potential new therapeutic targets for cancer.

Face morphogenesis is promoted by Pbx-dependent EMT via regulation of Snail1 during frontonasal prominence fusion

Human cleft lip with or without cleft palate (CL/P) is a common craniofacial abnormality caused by impaired fusion of the facial prominences. We have previously reported that, in the mouse embryo, epithelial apoptosis mediates fusion at the seam where the prominences coalesce. Here, we show that apoptosis alone is not sufficient to remove the epithelial layers. We observed morphological changes in the seam epithelia, intermingling of cells of epithelial descent into the mesenchyme and molecular signatures of epithelial-mesenchymal transition (EMT). Utilizing mouse lines with cephalic epithelium-specific Pbx loss exhibiting CL/P, we demonstrate that these cellular behaviors are Pbx dependent, as is the transcriptional regulation of the EMT driver Snail1. Furthermore, in the embryo, the majority of epithelial cells expressing high levels of Snail1 do not undergo apoptosis. Pbx1 loss- and gain-of-function in a tractable epithelial culture system revealed that Pbx1 is both necessary and sufficient for EMT induction. This study establishes that Pbx-dependent EMT programs mediate murine upper lip/primary palate morphogenesis and fusion via regulation of Snail1. Of note, the EMT signatures observed in the embryo are mirrored in the epithelial culture system.

Role of epithelial to mesenchymal transition in hepatocellular carcinoma

The epithelial to mesenchymal transition (EMT) is a multistep biological process whereby epithelial cells change in plasticity by transient de-differentiation into a mesenchymal phenotype. EMT and its reversal, mesenchymal to epithelial transition (MET), essentially occur during embryogenetic morphogenesis and have been increasingly described in fibrosis and cancer during the last decade. In carcinoma progression, EMT plays a crucial role in early steps of metastasis when cells lose cell-cell contacts due to ablation of E-cadherin and acquire increased motility to spread into surrounding or distant tissues. Epithelial plasticity has become a hot issue in hepatocellular carcinoma (HCC), as strong inducers of EMT such as transforming growth factor-β are able to orchestrate both fibrogenesis and carcinogenesis, showing rising cytokine levels in cirrhosis and late stage HCC. In this review, we consider the significance of EMT-MET in malignant hepatocytes as well as changes in the plasticity of hepatic stellate cells for cellular heterogeneity of HCC, and further aim at explaining the current limiting insights into EMT by snapshot analyses of HCC tissues. Recent advances in the identification of clinically relevant mechanisms that impinge on important EMT-transcription factors, as well as on miRNAs causing EMT signatures and HCC progression are highlighted. In addition, we draw particular attention to framing EMT in the context of potential clinical relevance for HCC patients. We conclude that some aspects of EMT are still elusive and further studies are required to better link the clinical management of HCC with biomarkers and targeted therapies related to EMT.

Epithelial plasticity in urothelial carcinoma: Current advancements and future challenges

Urothelial carcinoma (UC) of the bladder is characterized by high recurrence rate where a subset of these cells undergoes transition to deadly muscle invasive disease and later metastasizes. Urothelial cancer stem cells (UroCSCs), a tumor subpopulation derived from transformation of urothelial stem cells, are responsible for heterogeneous tumor formation and resistance to systemic treatment in UC of the bladder. Although the precise reason for pathophysiologic spread of tumor is not clear, transcriptome analysis of microdissected cancer cells expressing multiple progenitor/stem cell markers validates the upregulation of genes that derive epithelial-to-mesenchymal transition. Experimental studies on human bladder cancer xenografts describe the mechanistic functions and regulation of epithelial plasticity for its cancer-restraining effects. It has been further examined to be associated with the recruitment of a pool of UroCSCs into cell division in response to damages induced by adjuvant therapies. This paper also discusses the various probable therapeutic approaches to attenuate the progressive manifestation of chemoresistance by co-administration of inhibitors of epithelial plasticity and chemotherapeutic drugs by abrogating the early tumor repopulation as well as killing differentiated cancer cells.

Epithelial plasticity in urothelial carcinoma: Current advancements and future challenges

Urothelial carcinoma (UC) of the bladder is characterized by high recurrence rate where a subset of these cells undergoes transition to deadly muscle invasive disease and later metastasizes. Urothelial cancer stem cells (UroCSCs), a tumor subpopulation derived from transformation of urothelial stem cells, are responsible for heterogeneous tumor formation and resistance to systemic treatment in UC of the bladder. Although the precise reason for pathophysiologic spread of tumor is not clear, transcriptome analysis of microdissected cancer cells expressing multiple progenitor/stem cell markers validates the upregulation of genes that derive epithelial-to-mesenchymal transition. Experimental studies on human bladder cancer xenografts describe the mechanistic functions and regulation of epithelial plasticity for its cancer-restraining effects. It has been further examined to be associated with the recruitment of a pool of UroCSCs into cell division in response to damages induced by adjuvant therapies. This paper also discusses the various probable therapeutic approaches to attenuate the progressive manifestation of chemoresistance by co-administration of inhibitors of epithelial plasticity and chemotherapeutic drugs by abrogating the early tumor repopulation as well as killing differentiated cancer cells.

Rap1 GTPase is required for mouse lens epithelial maintenance and morphogenesis

Rap1, a Ras-like small GTPase, plays a crucial role in cell-matrix adhesive interactions, cell-cell junction formation, cell polarity and migration. The role of Rap1 in vertebrate organ development and tissue architecture, however, remains elusive. We addressed this question in a mouse lens model system using a conditional gene targeting approach. While individual germline deficiency of either Rap1a or Rap1b did not cause overt defects in mouse lens, conditional double deficiency (Rap1 cKO) prior to lens placode formation led to an ocular phenotype including microphthalmia and lens opacification in embryonic mice. The embryonic Rap1 cKO mouse lens exhibited striking defects including loss of E-cadherin- and ZO-1-based cell-cell junctions, disruption of paxillin and β1-integrin-based cell adhesive interactions along with abnormalities in cell shape and apical-basal polarity of epithelium. These epithelial changes were accompanied by increased levels of α-smooth muscle actin, vimentin and N-cadherin, and expression of transcriptional suppressors of E-cadherin (Snai1, Slug and Zeb2), and a mesenchymal metabolic protein (Dihydropyrimidine dehydrogenase). Additionally, while lens differentiation was not overtly affected, increased apoptosis and dysregulated cell cycle progression were noted in epithelium and fibers in Rap1 cKO mice. Collectively these observations uncover a requirement for Rap1 in maintenance of lens epithelial phenotype and morphogenesis.

Development of a method to isolate circulating tumor cells using mesenchymal-based capture

Epithelial tumor cells can become mesenchymal cells and vice versa via phenotypic transitions, a process known as epithelial plasticity. We postulate that during the process of metastasis, circulating tumor cells (CTCs) lose their epithelial phenotype and acquire a mesenchymal phenotype that may not be sufficiently captured by existing epithelial-based CTC technologies. We report here on the development of a novel CTC capture method, based on the biology of epithelial plasticity, which isolates cells based on OB-cadherin cell surface expression. Using this mesenchymal-based assay, OB-cadherin cellular events are detectable in men with metastatic prostate cancer and are less common in healthy volunteers. This method may complement existing epithelial-based methods and may be particularly useful in patients with bone metastases.

The relevance of the TGF-β Paradox to EMT-MET programs

The role of transforming growth factor-β (TGF-β) during tumorigenesis is complex and paradoxical, reflecting its ability to function as a tumor suppressor in normal and early-stage cancers, and as a tumor promoter in their late-stage counterparts. The switch in TGF-β function is known as the "TGF-β Paradox," whose manifestations are intimately linked to the initiation of epithelial-mesenchymal transition (EMT) programs in developing and progressing carcinomas. Indeed, as carcinoma cells emerge from EMT programs stimulated by TGF-β, they readily display a variety of acquired phenotypes that provide a selective advantage to growing carcinomas, including (i) enhanced cell migration and invasion; (ii) heightened resistance to cytotoxic agents, targeted chemotherapeutic, and radiation treatments; and (iv) boosted expansion of cancer-initiating and stem-like cell populations that underlie tumor metastasis and disease recurrence. At present, the molecular, cellular, and microenvironmental mechanisms that enable post-EMT and metastatic carcinoma cells to hijack the oncogenic activities of TGF-β remain incompletely understood. Additionally, the molecular mechanisms that counter EMT programs and limit the aggressiveness of late-stage carcinomas, events that transpire via mesenchymal-epithelial transition (MET) reactions, also need to be further elucidated. Here we review recent advances that provide new insights into how TGF-β promotes EMT programs in late-stage carcinoma cells, as well as how these events are balanced by MET programs during the development and metastatic progression of human carcinomas.