PKCepsilon regulation of an alpha5 integrin-ZO-1 complex controls lamellae formation in migrating cancer cells

Dynamic behavior of cell-cell adhesion factors in collective cell migration

Collective cell migration is a fundamental process underlying various biological phenomena, including embryonic development and cancer cell invasion. The cohesive yet flexible movement of cell collectives largely depends on the coordinated regulation of cell-cell and cell-substrate adhesions. In this review, we summarize the regulation of key cell-cell junction components, such as cadherins and zonula occludens proteins during collective cell migration, with a particular focus on the recently discovered multifaceted roles of ZO-1 in both cell-cell and cell-substrate interactions.

Cell-cell junctional proteins in cancer

A hallmark change during carcinogenesis is disruption or dysregulation of cell-cell junctions. It enables a transformed cell to adopt mesenchymal phenotype and acquire higher potential to migrate and invade. This ultimately leads to cancer metastasis. During this process, junctional proteins undergo remarkable changes in terms of their expressional pattern, localization, and activity. De-localized junctional proteins may adopt atypical roles which might act to either suppress tumorigenesis or facilitate cancer development, depending on several factors. In this chapter, the authors attempt to know the expression pattern of junctional proteins in different types of cancer, understand its significance, and gather knowledge about the mechanisms by which they regulate tumorigenesis and cancer development.

Turn-on protein switches for controlling actin binding in cells

Within a shared cytoplasm, filamentous actin (F-actin) plays numerous and critical roles across the cell body. Cells rely on actin-binding proteins (ABPs) to organize F-actin and to integrate its polymeric characteristics into diverse cellular processes. Yet, the multitude of ABPs that engage with and shape F-actin make studying a single ABP's influence on cellular activities a significant challenge. Moreover, without a means of manipulating actin-binding subcellularly, harnessing the F-actin cytoskeleton for synthetic biology purposes remains elusive. Here, we describe a suite of designed proteins, Controllable Actin-binding Switch Tools (CASTs), whose actin-binding behavior can be controlled with external stimuli. CASTs were developed that respond to different external inputs, providing options for turn-on kinetics and enabling orthogonality and multiplexing. Being genetically encoded, we show that CASTs can be inserted into native protein sequences to control F-actin association locally and engineered into structures to control cell and tissue shape and behavior.

ZO-1 regulates the migration of mesenchymal stem cells in cooperation with α-catenin in response to breast tumor cells

Mesenchymal stem cells are recruited from the bone marrow into breast tumors, contributing to the creation of a tumor microenvironment that fosters tropism for breast tumors. However, the intrinsic mechanisms underlying the recruitment of bone marrow-derived mesenchymal stem cells (MSCs) into the breast tumor microenvironment are still under investigation. Our discoveries identified zonula occludens-1 (ZO-1) as a specific intrinsic molecule that plays a vital role in mediating the collective migration of MSCs towards breast tumor cells and transforming growth factor beta (TGF-β), which is a crucial factor secreted by breast tumor cells. Upon migration in response to MDA-MB-231 cells and TGF-β, MSCs showed increased formation of adherens junction-like structures (AJs) expressing N-cadherin and α-catenin at their cell-cell contacts. ZO-1 was found to be recruited into the AJs at the cell-cell contacts between MSCs. Additionally, ZO-1 collaborated with α-catenin to regulate AJ formation, dependently on the SH3 and GUK domains of the ZO-1 protein. ZO-1 knockdown led to the impaired migration of MSCs in response to the stimuli and subsequent downregulation of AJs formation at the cell-cell contacts during MSCs migration. Overall, our study highlights the novel role of ZO-1 in guiding MSC migration towards breast tumor cells, suggesting its potential as a new strategy for controlling and re-engineering the breast tumor microenvironment.

Identifying General Tumor and Specific Lung Cancer Biomarkers by Transcriptomic Analysis

The bioinformatic pipeline previously developed in our research laboratory is used to identify potential general and specific deregulated tumor genes and transcription factors related to the establishment and progression of tumoral diseases, now comparing lung cancer with other two types of cancer. Twenty microarray datasets were selected and analyzed separately to identify hub differentiated expressed genes and compared to identify all the deregulated genes and transcription factors in common between the three types of cancer and those unique to lung cancer. The winning DEGs analysis allowed to identify an important number of TFs deregulated in the majority of microarray datasets, which can become key biomarkers of general tumors and specific to lung cancer. A coexpression network was constructed for every dataset with all deregulated genes associated with lung cancer, according to DAVID’s tool enrichment analysis, and transcription factors capable of regulating them, according to oPOSSUM´s tool. Several genes and transcription factors are coexpressed in the networks, suggesting that they could be related to the establishment or progression of the tumoral pathology in any tissue and specifically in the lung. The comparison of the coexpression networks of lung cancer and other types of cancer allowed the identification of common connectivity patterns with deregulated genes and transcription factors correlated to important tumoral processes and signaling pathways that have not been studied yet to experimentally validate their role in lung cancer. The Kaplan–Meier estimator determined the association of thirteen deregulated top winning transcription factors with the survival of lung cancer patients. The coregulatory analysis identified two top winning transcription factors networks related to the regulatory control of gene expression in lung and breast cancer. Our transcriptomic analysis suggests that cancer has an important coregulatory network of transcription factors related to the acquisition of the hallmarks of cancer. Moreover, lung cancer has a group of genes and transcription factors unique to pulmonary tissue that are coexpressed during tumorigenesis and must be studied experimentally to fully understand their role in the pathogenesis within its very complex transcriptomic scenario. Therefore, the downstream bioinformatic analysis developed was able to identify a coregulatory metafirm of cancer in general and specific to lung cancer taking into account the great heterogeneity of the tumoral process at cellular and population levels.

Extracellular ATP promotes angiogenesis and adhesion of TNBC cells to endothelial cells via up-regulation of CTGF

Our previous works have indicated that extracellular ATP is an important prometastasis factor. However, the molecular mechanism involved needs to be further studied. We demonstrated that extracellular ATP treatment could upregulate the expression of connective tissue growth factor (CTGF) in both triple‐negative breast cancer (TNBC) cells and endothelial cells (ECs). Extracellular ATP stimulated the migration of TNBC cells and ECs, and angiogenesis of ECs via the P2Y2––YAP‐CTGF axis. Furthermore, we demonstrated that adenosine triphosphate (ATP) stimulated TNBC cell adhesion to ECs and transmigration through the EC layer via CTGF by upregulation of integrin β1 on TNBC cells and VCAM‐1 on ECs. Both apyrase (ATP‐diphosphohydrolase) and CTGF shRNA treatments could inhibit the metastasis of inoculated tumors to lung and liver in a mouse model, and these treated tumors had fewer blood vessels. Collectively, our data indicated that extracellular ATP promotes tumor angiogenesis and the interactions between TNBC cells and ECs through upregulation of CTGF, thereby stimulating TNBC metastasis. The pleiotropic effects of ATP in angiogenesis and cell adhesion suggest that extracellular ATP or CTGF could be an effective target for TNBC therapy.

TJP1, a Membrane-Expressed Protein, is a Potential Therapeutic and Prognostic Target for Lung Cancer

Objective: Lung cancer is a malignant tumor with the highest mortality rate in the world. It is necessary to develop effective biomarkers for diagnosis or prognostic treatment to improve the survival rate of patients. In this prospective study, we identified a membrane-expressed protein Tight Junction Protein 1 (TJP1), which is an ideal therapeutic target for lung cancer, and demonstrated its role in invasion, migration, and proliferation of lung cancer. Methods: High-throughput monoclonal antibody microarrays were used to screen for differential expression of monoclonal antibodies (mAbs) in lung cancer and normal lung tissue. Differentially expressed antibodies were used to immunoprecipitate their cellular targets to be identified by mass spectrometry. The identified target TJP1 was knocked down to observe the effect of reduced gene expression on lung cancer cell function. Immunohistochemistry on human tumor tissues and The Cancer Genome Atlas (TCGA) database was used to explore the relationship between TJP1 expression in multiple cancer types and patient prognosis. Results: The antibody CL007473 was overexpressed in tumor tissue and its target protein was identified by mass spectrometry and immunofluorescence as TJP1, a membrane-expressed protein. Knockdown of TJP1 in lung cancer cell lines showed that reduced expression of TJP1 could inhibit the invasion and migration of lung cancer cells and inhibit the proliferation of cancer cells, suggesting that membrane-expressed protein TJP1 may be used as a therapeutic target for lung cancer. TCGA database analysis showed that TJP1 was highly expressed in pancreatic cancer (PAAD) tissues compared with normal tissues, and low expression was more beneficial to the prognosis and survival of PAAD patients. Conclusion: Membrane-expressed protein TJP1 may be a good therapeutic and prognostic target for lung cancer and has the potential to be a prognostic biomarker in pancreatic cancer.

TJP1 Contributes to Tumor Progression through Supporting Cell-Cell Aggregation and Communicating with Tumor Microenvironment in Leiomyosarcoma

Leiomyosarcoma (LMS) is a mesenchymal malignancy with a complex karyotype. Despite accumulated evidence, the factors contributing to the development of LMS are unclear. Here, we investigated the role of tight-junction protein 1 (TJP1), a membrane-associated intercellular barrier protein during the development of LMS and the tumor microenvironment. We orthotopically transplanted SK-LMS-1 cells and their derivatives in terms of TJP1 expression by intramuscular injection, such as SK-LMS-1 Sh-Control cells and SK-LMS-1 Sh-TJP1. We observed robust tumor growth in mice transplanted with LMS cell lines expressing TJP1 while no tumor mass was found in mice transplanted with SK-LMS-1 Sh-TJP1 cells with silenced TJP1 expression. Tissues from mice were stained and further analyzed to clarify the effects of TJP1 expression on tumor development and the tumor microenvironment. To identify the TJP1-dependent factors important in the development of LMS, genes with altered expression were selected in SK-LMS-1 cells such as cyclinD1, CSF1 and so on. The top 10% of highly expressed genes in LMS tissues were obtained from public databases. Further analysis revealed two clusters related to cell proliferation and the tumor microenvironment. Furthermore, integrated analyses of the gene expression networks revealed correlations among TJP1, CSF1 and CTLA4 at the mRNA level, suggesting a possible role for TJP1 in the immune environment. Taken together, these results imply that TJP1 contributes to the development of sarcoma by proliferation through modulating cell-cell aggregation and communication through cytokines in the tumor microenvironment and might be a beneficial therapeutic target.

Moxifloxacin induces random migration in human corneal fibroblasts via the protein kinase C epsilon/zonula occludens-1 signaling pathway

Moxifloxacin (MOX) suppresses cell movement in human corneal fibroblasts (HCFs). Zonula occludens-1 (ZO-1) is localized to the leading edge of migrating HCFs. This study explored the role of ZO-1 in MOX-suppressed cell migration in HCFs. A single-cell trajectory analysis revealed that MOX negatively regulated the migratory properties of HCFs including migration distance, migration velocity, and directionality (P < 0.001, P < 0.001, and P = 0.018, respectively). MOX increased endogenous ZO-1 in HCFs in a concentration-dependent manner (P = 0.083, P = 0.005, and P = 0.001 at 10, 50, and 100 μg/ml, respectively), but decreased the phosphorylation of endogenous ZO-1 at serines, threonines, and tyrosines. In contrast, MOX did not alter the expression of protein kinase C epsilon (PKCε), Rac-1, Cdc42, and MRCKβ. However, MOX did also reduce the phosphorylation level of PKCε at serines and threonines (P < 0.001 at 100 μg/ml). In addition, MOX increased the phosphorylation level of Rac-1 in a concentration-dependent manner (P < 0.001 at 100 μg/ml). Compared with the mock cells, the directionality of cell movement increased significantly in ZO-1-expressing HCFs (P = 0.012) and decreased significantly in ZO-1-silenced HCFs (P = 0.002). The directionality did not change significantly in Rac-1-silenced HCFs. ZO-1-expressing HCFs moved faster than mock cells. PKCε, Cdc42, Rac-1, and phosphorylated Rac-1 were decreased in ZO-1-overexpressing HCFs, but increased in ZO-1-silenced HCFs. Finally, silencing ZO-1 blocked MOX hyperactivation of Rac-1. These suggest that MOX might trigger random migration in human corneal stromal cells through PKCε-modulated ZO-1 inactivation and Rac-1 hyperactivation.

PLP2 drives collective cell migration via ZO-1-mediated cytoskeletal remodeling at the leading edge in human colorectal cancer cells

Collective cell migration (CCM), in which cell-cell integrity remains preserved during movement, plays an important role in the progression of cancer. However, studies describing CCM in cancer progression are majorly focused on the effects of extracellular tissue components on moving cell plasticity. The molecular and cellular mechanisms of CCM during cancer progression remain poorly explored. Here, we report that proteolipid protein 2 (PLP2), a colonic epithelium-enriched transmembrane protein, plays a vital role in the CCM of invasive human colorectal cancer (CRC) epithelium by modulating leading-edge cell dynamics in 2D. The extracellular pool of PLP2, secreted via exosomes, was also found to contribute to the event. During CCM, the protein was found to exist in association with ZO-1 (also known as TJP1) and to be involved in the positioning of the latter at the migrating edge. PLP2-mediated positioning of ZO-1 at the leading edge further alters actin cytoskeletal organization that involves Rac1 activation. Taken together, our findings demonstrate that PLP2, via its association with ZO-1, drives CCM in CRC epithelium by modulating the leading-edge actin cytoskeleton, thereby opening up new avenues of cancer research. This article has an associated First Person interview with the first author of the paper.

The PKC universe keeps expanding: From cancer initiation to metastasis

Classical and novel protein kinase C (PKC) isozymes (c/nPKCs), members of the PKC family that become activated by the lipid second messenger diacylglycerol (DAG) and phorbol esters, exert a myriad of cellular effects that impact proliferative and motile cellular responses. While c/nPKCs have been indisputably associated with tumor promotion, their roles exceed by far their sole involvement as promoter kinases. Indeed, this original dogma has been subsequently redefined by the introduction of several new concepts: the identification of tumor suppressing roles for c/nPKCs, and their participation in early and late stages of carcinogenesis. This review dives deep into the intricate roles of c/nPKCs in cancer initiation as well as in the different stages of the metastatic cascade, with great emphasis in their involvement in cancer cell motility via regulation of small Rho GTPases, the production of extracellular matrix (ECM)-degrading proteases, and the epithelial-to-mesenchymal transition (EMT) program required for the acquisition of highly invasive traits. Here, we highlight functional interplays between either PKCα or PKCε and mesenchymal features that may ultimately contribute to anticancer drug resistance in cellular and animal models. We also introduce the novel hypothesis that c/nPKCs may be implicated in the control of immune evasion through the regulation of immune checkpoint protein expression. In summary, dissecting the colossal complexity of c/nPKC signaling in the wide spectrum of cancer progression may bring new opportunities for the development of meaningful tools aiding for cancer prognosis and therapy.

The Prospect of Identifying Resistance Mechanisms for Castrate-Resistant Prostate Cancer Using Circulating Tumor Cells: Is Epithelial-to-Mesenchymal Transition a Key Player?

Prostate cancer (PCa) is initially driven by excessive androgen receptor (AR) signaling with androgen deprivation therapy (ADT) being a major therapeutic approach to its treatment. However, the development of drug resistance is a significant limitation on the effectiveness of both first-line and more recently developed second-line ADTs. There is a need then to study AR signaling within the context of other oncogenic signaling pathways that likely mediate this resistance. This review focuses on interactions between AR signaling, the well-known phosphatidylinositol-3-kinase/AKT pathway, and an emerging mediator of these pathways, the Hippo/YAP1 axis in metastatic castrate-resistant PCa, and their involvement in the regulation of epithelial-mesenchymal transition (EMT), a feature of disease progression and ADT resistance. Analysis of these pathways in circulating tumor cells (CTCs) may provide an opportunity to evaluate their utility as biomarkers and address their importance in the development of resistance to current ADT with potential to guide future therapies.

Tight Junctions in Cell Proliferation

Tight junction (TJ) proteins form a continuous intercellular network creating a barrier with selective regulation of water, ion, and solutes across endothelial, epithelial, and glial tissues. TJ proteins include the claudin family that confers barrier properties, members of the MARVEL family that contribute to barrier regulation, and JAM molecules, which regulate junction organization and diapedesis. In addition, the membrane-associated proteins such as MAGUK family members, i.e., zonula occludens, form the scaffold linking the transmembrane proteins to both cell signaling molecules and the cytoskeleton. Most studies of TJ have focused on the contribution to cell-cell adhesion and tissue barrier properties. However, recent studies reveal that, similar to adherens junction proteins, TJ proteins contribute to the control of cell proliferation. In this review, we will summarize and discuss the specific role of TJ proteins in the control of epithelial and endothelial cell proliferation. In some cases, the TJ proteins act as a reservoir of critical cell cycle modulators, by binding and regulating their nuclear access, while in other cases, junctional proteins are located at cellular organelles, regulating transcription and proliferation. Collectively, these studies reveal that TJ proteins contribute to the control of cell proliferation and differentiation required for forming and maintaining a tissue barrier.

ΔNp63α suppresses cells invasion by downregulating PKCγ/Rac1 signaling through miR-320a

ΔNp63α, a member of the p53 family of transcription factors, is overexpressed in a number of cancers and plays a role in proliferation, differentiation, migration, and invasion. ΔNp63α has been shown to regulate several microRNAs that are involved in development and cancer. We identified miRNA miR-320a as a positively regulated target of ΔNp63α. Previous studies have shown that miR-320a is downregulated in colorectal cancer and targets the small GTPase Rac1, leading to a reduction in noncanonical WNT signaling and EMT, thereby inhibiting tumor metastasis and invasion. We showed that miR-320a is a direct target of ΔNp63α. Knockdown of ΔNp63α in HaCaT and A431 cells downregulates miR-320a levels and leads to a corresponding elevation in PKCγ transcript and protein levels. Rac1 phosphorylation at Ser71 was increased in the absence of ΔNp63α, whereas overexpression of ΔNp63α reversed S71 phosphorylation of Rac1. Moreover, increased PKCγ levels, Rac1 phosphorylation and cell invasion observed upon knockdown of ΔNp63α was reversed by either overexpressing miR-320a mimic or Rac1 silencing. Finally, silencing PKCγ or treatment with the PKC inhibitor Gö6976 reversed increased Rac1 phosphorylation and cell invasion observed upon silencing ΔNp63α. Taken together, our data suggest that ΔNp63α positively regulates miR-320a, thereby inhibiting PKCγ expression, Rac1 phosphorylation, and cancer invasion.

Gold Nanorod Photothermal Therapy Alters Cell Junctions and Actin Network in Inhibiting Cancer Cell Collective Migration

Most cancer-related deaths come from metastasis. It was recently discovered that nanoparticles could inhibit cancer cell migration. Whereas most researchers focus on single-cell migration, the effect of nanoparticle treatment on collective cell migration has not been explored. Collective migration occurs commonly in many types of cancer metastasis, where a group of cancer cells move together, which requires the contractility of the cytoskeleton filaments and the connection of neighboring cells by the cell junction proteins. Here, we demonstrate that gold nanorods (AuNRs) and the introduction of near-infrared light could inhibit the cancer cell collective migration by altering the actin filaments and cell junctions with significantly triggered phosphorylation changes of essential proteins, using mass spectrometry-based phosphoproteomics. Further observation using super-resolution stochastic optical reconstruction microscopy (STORM) showed the actin cytoskeleton filament bundles were disturbed, which is difficult to differentiate under a normal fluorescence microscope. The decreased expression level of N-cadherin junctions and morphological changes of tight junction protein zonula occludens 2 were also observed. All of these results indicate possible functions of the AuNR treatments in regulating and remodeling the actin filaments and cell junction proteins, which contribute to decreasing cancer cell collective migration.

Every step of the way: integrins in cancer progression and metastasis

Cell adhesion to the extracellular matrix is fundamental to tissue integrity and human health. Integrins are the main cellular adhesion receptors that through multifaceted roles as signalling molecules, mechanotransducers and key components of the cell migration machinery are implicated in nearly every step of cancer progression from primary tumour development to metastasis. Altered integrin expression is frequently detected in tumours, where integrins have roles in supporting oncogenic growth factor receptor (GFR) signalling and GFR-dependent cancer cell migration and invasion. In addition, integrins determine colonization of metastatic sites and facilitate anchorage-independent survival of circulating tumour cells. Investigations describing integrin engagement with a growing number of versatile cell surface molecules, including channels, receptors and secreted proteins, continue to lead to the identification of novel tumour-promoting pathways. Integrin-mediated sensing, stiffening and remodelling of the tumour stroma are key steps in cancer progression supporting invasion, acquisition of cancer stem cell characteristics and drug resistance. Given the complexity of integrins and their adaptable and sometimes antagonistic roles in cancer cells and the tumour microenvironment, therapeutic targeting of these receptors has been a challenge. However, novel approaches to target integrins and antagonism of specific integrin subunits in stringently stratified patient cohorts are emerging as potential ways forward.

Proteomic screening identifies the zonula occludens protein ZO-1 as a new partner for ADAM12 in invadopodia-like structures

The epithelial mesenchymal transition (EMT) is a key process for cancer cell invasion and migration. This complex program whereby epithelial tumor cells loose polarity and acquire mesenchymal phenotype is driven by the regulation of cell-cell adhesion and cell-substrate interactions. We recently described the association of ADAM12 with EMT and we now use immunoprecipitation and proteomic approaches to identify interacting partners for ADAM12 during EMT. We identify twenty proteins that are involved in molecular mechanisms associated with adhesion/invasion processes. Integrative network analyses point out the zonula occludens protein ZO-1, as a new potential partner for ADAM12. In silico screening demonstrates that ZO-1 and ADAM12 are coexpressed in breast cancer cell lines sharing EMT signature. We validate the interaction between ZO-1 and ADAM12 in invasive breast cancer cell lines and show that ZO-1 and ADAM12 co-localize in actin- and cortactin-rich structures. Silencing either ADAM12 or ZO-1 inhibits gelatin degradation demonstrating that both proteins are required for matrix degradation. We further show that matrix metalloprotease 14, known to mediate degradation of collagen in invadopodia-like structures interacts with ZO-1. Depletion of PKCε that regulates the recruitment of ADAM12 and ZO-1 to cell membranes induces a decrease in ADAM12 and ZO-1 at invadopodia-like structures and degradation activity. Together our data provide evidence for a new interaction between ADAM12, a mesenchymal marker induced during TGF-β-dependent EMT and ZO-1, a scaffolding protein expressed in tight junctions of epithelial cells, both proteins being redistributed at the invadopodia-like structures of mesenchymal invasive cells to promote PKCε-dependent matrix degradation.

Control of Mechanotransduction by Molecular Clutch Dynamics

The linkage of cells to their microenvironment is mediated by a series of bonds that dynamically engage and disengage, in what has been conceptualized as the molecular clutch model. Whereas this model has long been employed to describe actin cytoskeleton and cell migration dynamics, it has recently been proposed to also explain mechanotransduction (i.e., the process by which cells convert mechanical signals from their environment into biochemical signals). Here we review the current understanding on how cell dynamics and mechanotransduction are driven by molecular clutch dynamics and its master regulator, the force loading rate. Throughout this Review, we place a specific emphasis on the quantitative prediction of cell response enabled by combined experimental and theoretical approaches.

Inhibition of TRPC6 reduces non-small cell lung cancer cell proliferation and invasion

Recent studies indicate that the transient receptor potential canonical 6 (TRPC6) channel is highly expressed in several types of cancer cells. However, it remains unclear whether TRPC6 contributes to the malignancy of human non-small cell lung cancer (NSCLC). We used a human NSCLC A549 cell line as a model and found that pharmacological blockade or molecular knockdown of TRPC6 channel inhibited A549 cell proliferation by arresting cell cycle at the S-G2M phase and caused a significant portion of cells detached and rounded-up, but did not induce any types of cell death. Western blot and cell cycle analysis show that the detached round cells at the S-G2M phase expressed more TRPC6 than the still attached polygon cells at the G1 phase. Patch-clamp data also show that TRPC whole-cell currents in the detached cells were significantly higher than in the still attached cells. Inhibition of Ca²⁺-permeable TRPC6 channels significantly reduced intracellular Ca²⁺ in A549 cells. Interestingly, either blockade or knockdown of TRPC6 strongly reduced the invasion of this NSCLC cell line and decreased the expression of an adherent protein, fibronectin, and a tight junction protein, zonula occluden protein-1 (ZO-1). These data suggest that TRPC6-mediated elevation of intracellular Ca²⁺ stimulates NSCLC cell proliferation by promoting cell cycle progression and that inhibition of TRPC6 attenuates cell proliferation and invasion. Therefore, further in vivo studies may lead to a consideration of using a specific TRPC6 blocker as a complement to treat NSCLC.

E-cadherin cleavage by MT2-MMP regulates apical junctional signaling and epithelial homeostasis in the intestine

Cadherin-based intercellular adhesions are essential players in epithelial homeostasis, but their dynamic regulation during tissue morphogenesis and remodeling remain largely undefined. Here, we characterize an unexpected role for the membrane-anchored metalloproteinase MT2-MMP in regulating epithelial cell quiescence. Following co-immunoprecipitation and mass spectrometry, the MT2-MMP cytosolic tail was found to interact with the zonula occludens protein-1 (ZO-1) at the apical junctions of polarized epithelial cells. Functionally, MT2-MMP localizes in the apical domain of epithelial cells where it cleaves E-cadherin and promotes epithelial cell accumulation, a phenotype observed in 2D polarized cells as well as 3D cysts. MT2-MMP-mediated cleavage subsequently disrupts apical E-cadherin-mediated cell quiescence resulting in relaxed apical cortical tension favoring cell extrusion and re-sorting of Src kinase activity to junctional complexes, thereby promoting proliferation. Physiologically, MT2-MMP loss of function alters E-cadherin distribution, leading to impaired 3D organoid formation by mouse colonic epithelial cells ex vivo and reduction of cell proliferation within intestinal crypts in vivo Taken together, these studies identify an MT2-MMP-E-cadherin axis that functions as a novel regulator of epithelial cell homeostasis in vivo.

Making Heads or Tails of It: Cell-Cell Adhesion in Cellular and Supracellular Polarity in Collective Migration

Collective cell migration is paramount to morphogenesis and contributes to the pathogenesis of cancer. To migrate directionally and reach their site of destination, migrating cells must distinguish a front and a rear. In addition to polarizing individually, cell-cell interactions in collectively migrating cells give rise to a higher order of polarity, which allows them to move as a supracellular unit. Rather than just conferring adhesion, emerging evidence indicates that cadherin-based adherens junctions intrinsically polarize the cluster and relay mechanical signals to establish both intracellular and supracellular polarity. In this review, we discuss the various functions of adherens junctions in polarity of migrating cohorts.

Clustering of integrin α5 at the lateral membrane restores epithelial polarity in invasive colorectal cancer cells

Apicobasolateral polarity is a fundamental property of epithelial cells, and its loss is a hallmark of cancer. Integrin-mediated contact with the extracellular matrix defines the basal surface, setting in motion E-cadherin-mediated cell-cell contact, which establishes apicobasolateral polarity. Role(s) for lateral integrins in this polarization process and the consequences of their disruption are incompletely understood. We show that addition of an integrin β1-activating monoclonal antibody, P4G11, to invasive colorectal cancer cells in three-dimensional type 1 collagen reverts the invasive phenotype and restores apicobasolateral polarity. P4G11 induces clustering of integrin α5β1 at lateral, intercellular surfaces. This leads to deposition and polymerization of fibronectin and recruitment of paxillin to sites of lateral integrin α5β1 clustering and is followed by tight junction formation, as determined by ZO-1 localization. Inducible elimination of integrin α5 abrogates the epithelial-organizing effects of P4G11. In addition, polymerization of fibronectin is required for the effects of P4G11, and addition of polymerized superfibronectin is sufficient to induce tight junction formation and apicobasolateral polarization. In the normal human colon, we show that integrin α5 localizes to the lateral membrane of terminally differentiated colonocytes and that integrin α5 staining may be reduced in colorectal cancer. Thus we propose a novel role for integrin α5β1 in regulating epithelial morphogenesis.

Binding of ZO-1 to α5β1 integrins regulates the mechanical properties of α5β1-fibronectin links

Fundamental processes in cell adhesion, motility, and rigidity adaptation are regulated by integrin-mediated adhesion to the extracellular matrix (ECM). The link between the ECM component fibronectin (fn) and integrin α5β1 forms a complex with ZO-1 in cells at the edge of migrating monolayers, regulating cell migration. However, how this complex affects the α5β1-fn link is unknown. Here we show that the α5β1/ZO-1 complex decreases the resistance to force of α5β1-fn adhesions located at the edge of migrating cell monolayers while also increasing α5β1 recruitment. Consistently with a molecular clutch model of adhesion, this effect of ZO-1 leads to a decrease in the density and intensity of adhesions in cells at the edge of migrating monolayers. Taken together, our results unveil a new mode of integrin regulation through modification of the mechanical properties of integrin-ECM links, which may be harnessed by cells to control adhesion and migration.

Tight junction protein ZO-1 controls organic cation/carnitine transporter OCTN2 (SLC22A5) in a protein kinase C-dependent way

OCTN2 (SLC22A5) is an organic cation/carnitine transporter belonging to the solute carrier transporters (SLC) family. OCTN2 is ubiquitously expressed and its presence was shown in various brain cells, including the endothelial cells forming blood-brain barrier, where it was mainly detected at abluminal membrane and in proximity of tight junctions (TJ). Since OCTN2 contains a PDZ-binding domain, the present study was focused on a possible role of transporter interaction with a TJ-associated protein ZO-1, containing PDZ domains and detected in rat Octn2 proteome. We showed previously that activation of protein kinase C (PKC) in rat astrocytes regulates Octn2 surface presence and activity. Regulation of a wild type Octn2 and its deletion mutant without a PDZ binding motif were studied in heterologous expression system in HEK293 cells. Plasma membrane presence of overexpressed Octn2 did not depend on either PKC activation or presence of PDZ-binding motif, anyhow, as assayed in proximity ligation assay, the truncation of PDZ binding motif resulted in a strongly diminished Octn2/ZO-1 interaction and in a decreased transporter activity. The same effects on Octn2 activity were detected upon PKC activation, what correlated with ZO-1 phosphorylation. It is postulated that ZO-1, when not phosphorylated by PKC, keeps Octn2 in an active state, while elimination of this binding in ΔPDZ mutant or after ZO-1 phosphorylation leads to diminution of Octn2 activity.

Junctional proteins of the blood-brain barrier: New insights into function and dysfunction

The blood-brain barrier (BBB) is a highly complex and dynamic barrier. It is formed by an interdependent network of brain capillary endothelial cells, endowed with barrier properties, and perivascular cells (astrocytes and pericytes) responsible for inducing and maintaining those properties. One of the primary properties of the BBB is a strict regulation of paracellular permeability due to the presence of junctional complexes (tight, adherens and gap junctions) between the endothelial cells. Alterations in junction assembly and function significantly affect BBB properties, particularly barrier permeability. However, such alterations are also involved in remodeling the brain endothelial cell surface and regulating brain endothelial cell phenotype. This review summarizes the characteristics of brain endothelial tight, adherens and gap junctions and highlights structural and functional alterations in junctional proteins that may contribute to BBB dysfunction.

Tight junction protein 1 is regulated by transforming growth factor-β and contributes to cell motility in NSCLC cells

Tight junction protein 1 (TJP1), a component of tight junction, has been reported to play a role in protein networks as an adaptor protein, and TJP1 expression is altered during tumor development. Here, we found that TJP1 expression was increased at the RNA and protein levels in TGF-β-stimulated lung cancer cells, A549. SB431542, a type-I TGF-β receptor inhibitor, as well as SB203580, a p38 kinase inhibitor, significantly abrogated the effect of TGF-β on TJP1 expression. Diphenyleneiodonium, an NADPH oxidase inhibitor, also attenuated TJP1 expression in response to TGF-β in lung cancer cells. When TJP1 expression was reduced by shRNA lentiviral particles in A549 cells (A549-sh TJP1), wound healing was much lower than in cells infected with control viral particles. Taken together, these data suggest that TGF-β enhances TJP1 expression, which may play a role beyond structural support in tight junctions during cancer development.

Different effects of ZO-1, ZO-2 and ZO-3 silencing on kidney collecting duct principal cell proliferation and adhesion

Coordinated cell proliferation and ability to form intercellular seals are essential features of epithelial tissue function. Tight junctions (TJs) classically act as paracellular diffusion barriers. More recently, their role in regulating epithelial cell proliferation in conjunction with scaffolding zonula occludens (ZO) proteins has come to light. The kidney collecting duct (CD) is a model of tight epithelium that displays intense proliferation during embryogenesis followed by very low cell turnover in the adult kidney. Here, we examined the influence of each ZO protein (ZO-1, -2 and -3) on CD cell proliferation. We show that all 3 ZO proteins are strongly expressed in native CD and are present at both intercellular junctions and nuclei of cultured CD principal cells (mCCDcl1). Suppression of either ZO-1 or ZO-2 resulted in increased G0/G1 retention in mCCDcl1 cells. ZO-2 suppression decreased cyclin D1 abundance while ZO-1 suppression was accompanied by increased nuclear p21 localization, the depletion of which restored cell cycle progression. Contrary to ZO-1 and ZO-2, ZO-3 expression at intercellular junctions dramatically increased with cell density and relied on the presence of ZO-1. ZO-3 depletion did not affect cell cycle progression but increased cell detachment. This latter event partly relied on increased nuclear cyclin D1 abundance and was associated with altered β1-integrin subcellular distribution and decreased occludin expression at intercellular junctions. These data reveal diverging, but interconnected, roles for each ZO protein in mCCDcl1 proliferation. While ZO-1 and ZO-2 participate in cell cycle progression, ZO-3 is an important component of cell adhesion.

Functional proteomic biomarkers in cancer

Beyond penetrant germline and somatic mutations, there are substantial challenges in extrapolating phenotypes from linear DNA sequences and transcriptomics. This brings a molecular pathology emphasis to the properties of the main players responsible for executing actions, proteins. The proteomic attribute most frequently determined in pathology is (relative) content, but for many candidate biomarkers this is not the most important feature to understand. In keeping pace with the depth of knowledge of the mechanisms underlying pathologies, we need to ask more sophisticated questions about the state of proteins, for example, their oligomerization status, modification status, and location. This demands hitherto nonroutine approaches to proteomics, which we will discuss in this brief perspective.

Control of cell-cell forces and collective cell dynamics by the intercellular adhesome

Dynamics of epithelial tissues determine key processes in development, tissue healing and cancer invasion. These processes are critically influenced by cell-cell adhesion forces. However, the identity of the proteins that resist and transmit forces at cell-cell junctions remains unclear, and how these proteins control tissue dynamics is largely unknown. Here we provide a systematic study of the interplay between cell-cell adhesion proteins, intercellular forces and epithelial tissue dynamics. We show that collective cellular responses to selective perturbations of the intercellular adhesome conform to three mechanical phenotypes. These phenotypes are controlled by different molecular modules and characterized by distinct relationships between cellular kinematics and intercellular forces. We show that these forces and their rates can be predicted by the concentrations of cadherins and catenins. Unexpectedly, we identified different mechanical roles for P-cadherin and E-cadherin; whereas P-cadherin predicts levels of intercellular force, E-cadherin predicts the rate at which intercellular force builds up.

A multi-omics approach identifies key hubs associated with cell type-specific responses of airway epithelial cells to staphylococcal alpha-toxin

Responsiveness of cells to alpha-toxin (Hla) from Staphylococcus aureus appears to occur in a cell-type dependent manner. Here, we compare two human bronchial epithelial cell lines, i.e. Hla-susceptible 16HBE14o- and Hla-resistant S9 cells, by a quantitative multi-omics strategy for a better understanding of Hla-induced cellular programs. Phosphoproteomics revealed a substantial impact on phosphorylation-dependent signaling in both cell models and highlights alterations in signaling pathways associated with cell-cell and cell-matrix contacts as well as the actin cytoskeleton as key features of early rHla-induced effects. Along comparable changes in down-stream activity of major protein kinases significant differences between both models were found upon rHla-treatment including activation of the epidermal growth factor receptor EGFR and mitogen-activated protein kinases MAPK1/3 signaling in S9 and repression in 16HBE14o- cells. System-wide transcript and protein expression profiling indicate induction of an immediate early response in either model. In addition, EGFR and MAPK1/3-mediated changes in gene expression suggest cellular recovery and survival in S9 cells but cell death in 16HBE14o- cells. Strikingly, inhibition of the EGFR sensitized S9 cells to Hla indicating that the cellular capacity of activation of the EGFR is a major protective determinant against Hla-mediated cytotoxic effects.

NHE3 phosphorylation via PKCη marks the polarity and orientation of directionally migrating cells

Endogenous electric fields (EF) may provide an overriding cue for directional cell migration during wound closure. Perceiving a constant direction requires active sodium-hydrogen exchanger (pNHE3) at the leading edge of HEK 293 cells but its activation mechanism is not yet fully understood. Because protein kinase C (PKC) is required in electrotaxis, we asked whether NHE3 is activated by PKC during wound healing. Using pharmacological (pseudosubstrate and edelfosine) inhibition, we showed that inhibition of PKCη isoform impairs directional cell migration in HEK 293 cells in the presence of a persistent directional cue (0.25-0.3 V/mm of EF for 2 h). Further, we found that pNHE3 forms complexes with both PKCη and ɣ-tubulin, suggesting that these molecules may regulate the microtubule-organizing center. In addition, cellular pNHE3 content was reduced significantly when PKCη was inhibited during directional cell migration. Taken together, these data suggest that PKCη-dependent phosphorylation of NHE3 and the formation of pNHE3/PKCη/ɣ-tubulin complexes at the leading edge of the cell are required for directional cell migration in an EF.

Regulation of the cytokinesis cleavage furrow by PKCε

Cytokinesis is the final act of the cell cycle where the replicated DNA and cellular contents are finally split into two daughter cells. This process is very tightly controlled as DNA segregation errors and cytokinesis failure is commonly associated with aneuploidy and aggressive tumours. Protein kinase Cε (PKCε) is a lipid-activated serine/threonine kinase that is part of the PKC superfamily. PKCε plays a complex role in the regulation of migration, adhesion and cytokinesis and in the present article we discuss the interplay between these processes. Integrin-mediated interaction with the actin cytoskeleton is a known regulator of cell adhesion and migration and there is emerging evidence that this pathway may also be essential for cytokinesis. We discuss evidence that a known actin-binding region in PKCε is involved in PKCε-mediated regulation of cytokinesis, providing a link between integrin-mediated stabilization of the cytokinesis furrow and PKCε recruitment.

Drosophila DOCK family protein sponge regulates the JNK pathway during thorax development

The dedicator of cytokinesis (DOCK) family proteins that are conserved in a wide variety of species are known as DOCK1-DOCK11 in mammals. The Sponge (Spg) is a Drosophila counterpart to the mammalian DOCK3. Specific knockdown of spg by pannir-GAL4 or apterous-GAL4 driver in wing discs induced split thorax phenotype in adults. Reduction of the Drosophila c-Jun N-terminal kinase (JNK), basket (bsk) gene dose enhanced the spg knockdown-induced phenotype. Conversely, overexpression of bsk suppressed the split thorax phenotype. Monitoring JNK activity in the wing imaginal discs by immunostaining with anti-phosphorylated JNK (anti-pJNK) antibody together with examination of lacZ expression in a puckered-lacZ enhancer trap line revealed the strong reduction of the JNK activity in the spg knockdown clones. This was further confirmed by Western immunoblot analysis of extracts from wing discs of spg knockdown fly with anti-pJNK antibody. Furthermore, the Duolink in situ Proximity Ligation Assay method detected interaction signals between Spg and Rac1 in the wing discs. Taken together, these results indicate Spg positively regulates JNK pathway that is required for thorax development and the regulation is mediated by interaction with Rac1.

Targeting tight junctions during epithelial to mesenchymal transition in human pancreatic cancer

Pancreatic cancer continues to be a leading cause of cancer-related death worldwide and there is an urgent need to develop novel diagnostic and therapeutic strategies to reduce the mortality of patients with this disease. In pancreatic cancer, some tight junction proteins, including claudins, are abnormally regulated and therefore are promising molecular targets for diagnosis, prognosis and therapy. Claudin-4 and -18 are overexpressed in human pancreatic cancer and its precursor lesions. Claudin-4 is a high affinity receptor of Clostridium perfringens enterotoxin (CPE). The cytotoxic effects of CPE and monoclonal antibodies against claudin-4 are useful as novel therapeutic tools for pancreatic cancer. Claudin-18 could be a putative marker and therapeutic target with prognostic implications for patients with pancreatic cancer. Claudin-1, -7, tricellulin and marvelD3 are involved in epithelial to mesenchymal transition (EMT) of pancreatic cancer cells and thus might be useful as biomarkers during disease. Protein kinase C is closely related to EMT of pancreatic cancer and regulates tight junctions of normal human pancreatic duct epithelial cells and the cancer cells. This review focuses on the regulation of tight junctions via protein kinase C during EMT in human pancreatic cancer for the purpose of developing new diagnostic and therapeutic modalities for pancreatic cancer.

Talin regulates moesin-NHE-1 recruitment to invadopodia and promotes mammary tumor metastasis

Invadopodia are actin-rich protrusions that degrade the extracellular matrix and are required for stromal invasion, intravasation, and metastasis. The role of the focal adhesion protein talin in regulating these structures is not known. Here, we demonstrate that talin is required for invadopodial matrix degradation and three-dimensional extracellular matrix invasion in metastatic breast cancer cells. The sodium/hydrogen exchanger 1 (NHE-1) is linked to the cytoskeleton by ezrin/radixin/moesin family proteins and is known to regulate invadopodium-mediated matrix degradation. We show that the talin C terminus binds directly to the moesin band 4.1 ERM (FERM) domain to recruit a moesin-NHE-1 complex to invadopodia. Silencing talin resulted in a decrease in cytosolic pH at invadopodia and blocked cofilin-dependent actin polymerization, leading to impaired invadopodium stability and matrix degradation. Furthermore, talin is required for mammary tumor cell motility, intravasation, and spontaneous lung metastasis in vivo. Thus, our findings provide a novel understanding of how intracellular pH is regulated and a molecular mechanism by which talin enhances tumor cell invasion and metastasis.

Nongenomic thyroid hormone signaling occurs through a plasma membrane-localized receptor

Thyroid hormone (TH) is essential for vertebrate development and the homeostasis of most adult tissues, including bone. TH stimulates target gene expression through the nuclear thyroid receptors TRα and TRβ; however, TH also has rapid, transcription-independent (nongenomic) effects. We found a previously uncharacterized plasma membrane-bound receptor that was necessary and sufficient for nongenomic TH signaling in several cell types. We determined that this receptor is generated by translation initiation from an internal methionine of TRα, which produces a transcriptionally incompetent protein that is palmitoylated and associates with caveolin-containing plasma membrane domains. TH signaling through this receptor stimulated a pro-proliferative and pro-survival program by increasing the intracellular concentrations of calcium, nitric oxide (NO), and cyclic guanosine monophosphate (cGMP), which led to the sequential activation of protein kinase G II (PKGII), the tyrosine kinase Src, and extracellular signal-regulated kinase (ERK) and Akt signaling. Hypothyroid mice exhibited a cGMP-deficient state with impaired bone formation and increased apoptosis of osteocytes, which was rescued by a direct stimulator of guanylate cyclase. Our results link nongenomic TH signaling to a previously uncharacterized membrane-bound receptor, and identify NO synthase, guanylate cyclase, and PKGII as TH effectors that activate kinase cascades to regulate cell survival and proliferation.

Protein Kinase C (PKC) Isozymes and Cancer

Protein kinase C (PKC) is a family of phospholipid-dependent serine/threonine kinases, which can be further classified into three PKC isozymes subfamilies: conventional or classic, novel or nonclassic, and atypical. PKC isozymes are known to be involved in cell proliferation, survival, invasion, migration, apoptosis, angiogenesis, and drug resistance. Because of their key roles in cell signaling, PKC isozymes also have the potential to be promising therapeutic targets for several diseases, such as cardiovascular diseases, immune and inflammatory diseases, neurological diseases, metabolic disorders, and multiple types of cancer. This review primarily focuses on the activation, mechanism, and function of PKC isozymes during cancer development and progression.

The Multifunctional Protein Kinase C-ε in Cancer Development and Progression

The protein kinase C (PKC) family proteins are important signal transducers and have long been the focus of cancer research. PKCɛ, a member of this family, is overexpressed in most solid tumors and plays critical roles in different processes that lead to cancer development. Studies using cell lines and animal models demonstrated the transforming potential of PKCɛ. While earlier research established the survival functions of PKCɛ, recent studies revealed its role in cell migration, invasion and cancer metastasis. PKCɛ has also been implicated in epithelial to mesenchymal transition (EMT), which may be the underlying mechanism by which it contributes to cell motility. In addition, PKCɛ affects cell-extracellular matrix (ECM) interactions by direct regulation of the cytoskeletal elements. Recent studies have also linked PKCɛ signaling to cancer stem cell functioning. This review focuses on the role of PKCɛ in different processes that lead to cancer development and progression. We also discussed current literatures on the pursuit of PKCɛ as a target for cancer therapy.

A ZO-1/α5β1-integrin complex regulates cytokinesis downstream of PKCε in NCI-H460 cells plated on fibronectin

Recently, we demonstrated that integrin adhesion to the extracellular matrix at the cleavage furrow is essential for cytokinesis of adherent cells. Here, we report that tight junction protein ZO-1 (Zonula Occludens-1) is required for successful cytokinesis in NCI-H460 cells plated on fibronectin. This function of ZO-1 involves interaction with the cytoplasmic domain of α5-integrin to facilitate recruitment of active fibronectin-binding integrins to the base of the cleavage furrow. In the absence of ZO-1, or a functional ZO-1/α5β1-integrin complex, proper actin-dependent constriction between daughter cells is impaired and cells fail cytokinesis. Super-resolution microscopy reveals that in ZO-1 depleted cells the furrow becomes delocalized from the matrix. We also show that PKCε-dependent phosphorylation at Serine168 is required for ZO-1 localization to the furrow and successful cell division. Altogether, our results identify a novel regulatory pathway involving the interplay between ZO-1, α5-integrin and PKCε in the late stages of mammalian cell division.

p38δ mitogen-activated protein kinase regulates the expression of tight junction protein ZO-1 in differentiating human epidermal keratinocytes

Increasing evidence has recognized tight junctions (TJs) as the lower epidermal inside-out diffusion barrier located in granular cell layers of the epidermis. However, little is known about the regulation of TJ components in epidermis. p38 pathway is one of the mitogen-activated protein kinase pathways, which controls cell growth, differentiation, and apoptosis. We have investigated the role of p38 signaling pathway in the regulation of selected desmosomal, adherens and TJ components in human primary keratinocytes during Ca(2+)-induced differentiation, as well as in cultured squamous cell carcinoma cell lines. p38 signaling pathway was inhibited in cultured keratinocytes and cutaneous squamous cell carcinoma cells using recombinant adenoviruses, small inhibitory RNAs (siRNA) and chemical inhibitors. Expression of intercellular junction proteins was investigated using Western analysis and indirect immunofluorescence (IIF). The results showed that inhibition of p38δ function by siRNA or adenovirally delivered dominant negative mutant led to markedly decreased levels of Zonula occludens-1 (ZO-1) protein in keratinocytes, while the expression of other junctional proteins studied was not altered. Immunolocalization of ZO-1 revealed that intercellular junction areas were depleted from ZO-1. Inhibition of ZO-1 by siRNA silencing did not however result in an altered expression or subcellular localization of other TJ components studied. The expression of ZO-1 in carcinoma cells was also regulated by p38. The results indicate that ZO-1 is regulated by p38δ while the other junction proteins studied are not. Since ZO-1 is an integral component of functional TJs, various pathological processes affecting signaling via p38δ may also interfere with epithelial maturation and the formation and function of TJs.

p120 catenin is a key effector of a Ras-PKCɛ oncogenic signaling axis

Within the family of protein kinase C (PKC) molecules, the novel isoform PRKCE (PKCɛ) acts as a bona fide oncogene in in vitro and in vivo models of tumorigenesis. Previous studies have reported expression of PKCɛ in breast, prostate and lung tumors above that of normal adjacent tissue. Data from the cancer genome atlas suggest increased copy number of PRKCE in triple negative breast cancer (TNBC). We find that overexpression of PKCɛ in a non-tumorigenic breast epithelial cell line is sufficient to overcome contact inhibition and results in the formation of cellular foci. Correspondingly, inhibition of PKCɛ in a TNBC cell model results in growth defects in two-dimensional (2D) and three-dimensional (3D) culture conditions and orthotopic xenografts. Using stable isotope labeling of amino acids in a cell culture phosphoproteomic approach, we find that CTNND1/p120ctn phosphorylation at serine 268 (P-S268) occurs in a strictly PKCɛ-dependent manner, and that loss of PKCɛ signaling in TNBC cells leads to reversal of mesenchymal morphology and signaling. In a model of Ras activation, inhibition of PKCɛ is sufficient to block mesenchymal cell morphology. Finally, treatment with a PKCɛ ATP mimetic inhibitor, PF-5263555, recapitulates genetic loss of function experiments impairing p120ctn phosphorylation as well as compromising TNBC cell growth in vitro and in vivo. We demonstrate PKCɛ as a tractable therapeutic target for TNBC, where p120ctn phosphorylation may serve as a readout for monitoring patient response.

Trop-2 promotes prostate cancer metastasis by modulating β(1) integrin functions

The molecular mechanisms underlying metastatic dissemination are still not completely understood. We have recently shown that β(1) integrin-dependent cell adhesion to fibronectin and signaling is affected by a transmembrane molecule, Trop-2, which is frequently upregulated in human carcinomas. Here, we report that Trop-2 promotes metastatic dissemination of prostate cancer cells in vivo and is abundantly expressed in metastasis from human prostate cancer. We also show here that Trop-2 promotes prostate cancer cell migration on fibronectin, a phenomenon dependent on β(1) integrins. Mechanistically, we demonstrate that Trop-2 and the α(5)β(1) integrin associate through their extracellular domains, causing relocalization of α(5)β(1) and the β(1)-associated molecule talin from focal adhesions to the leading edges. Trop-2 effect is specific as this molecule does not modulate migration on vitronectin, does not associate with the major vitronectin receptor, α(v)β(3) integrin, and does not affect localization of α(v)β(3) integrin as well as vinculin in focal adhesions. We show that Trop-2 enhances directional prostate cancer cell migration, through modulation of Rac1 GTPase activity. Finally, we show that Trop-2 induces activation of PAK4, a kinase that has been reported to mediate cancer cell migration. In conclusion, we provide the first evidence that β(1) integrin-dependent migratory and metastatic competence of prostate cancer cells is enhanced by Trop-2.

Lumican expression, localization and antitumor activity in prostate cancer

The stromal reaction surrounding tumors leads to the formation of a tumor-specific microenvironment, which may play either a restrictive role or a supportive role in the growth and progression of the tumors. Lumican, a small leucine-rich proteoglycan (SLRP) of the extracellular matrix (ECM), regulates collagen fibrillogenesis. Recently, lumican has also been shown to regulate cell behavior during embryonic development, tissue repair and tumor progression. The role of lumican in cancer varies according to the type of tumor. In this study we analyze the role of lumican in the pathogenesis of prostate cancer both in vivo and in vitro. Overall lumican up-regulation was observed in the primary tumors analyzed through both real-time PCR and immunostaining. The increase in lumican expression was observed in the reactive stroma surrounding prostate primary tumors with fibrotic deposition surrounding the acinar glands. In vitro analysis demonstrated that lumican inhibited both the migration and invasion of metastatic prostate cancer cells isolated from lymph node, bone and brain. Moreover, prostate cancer cells seeded on lumican presented a decrease in the formation of cellular projections, lamellipodia detected by a decreased rearrangement in ZO-1, keratin 8/18, integrin β1 and MT1-MMP, and invadopodia detected by disruption of α-smooth muscle actin, cortactin and N-WASP. Moreover, a significant increase in prostate cancer cell invasion was observed through the peritoneum of lumican knockout mice, further demonstrating the restrictive role lumican present in the ECM has on prostate cancer invasion. In conclusion, lumican present in the reactive stroma surrounding prostate primary tumors plays a restrictive role on cancer progression, and we therefore postulate that lumican could be a valuable marker in prostate cancer staging.

Hepatocyte growth factor stimulates the migration of gastric epithelial cells by altering the subcellular localization of the tight junction protein ZO-1

BACKGROUND

Hepatocyte growth factor (HGF) is essential for epithelial restitution, a process in which epithelial cells rapidly migrate to cover desquamated epithelium after mucosal injury in the gastrointestinal tract. In this study, we aimed to elucidate the molecular mechanisms of the HGF-mediated reconstitution of gastric epithelial structures by analyzing the expression and subcellular dynamics of tight junction proteins.

METHODS

We treated human gastric epithelial MKN74 cells with HGF, and examined the effects of HGF on cell migration and proliferation, and the expression and subcellular dynamics of tight junction proteins; as well, we investigated the effect of HGF on paracellular permeability to macromolecules (using fluorescein isothiocyanate [FITC]-dextran).

RESULTS

HGF significantly stimulated the migration of MKN74 cells, but not their proliferation, in a dose-dependent manner. HGF did not affect the expression of tight junction proteins, including claudin-1, -3, -4 and -7; occludin; and zonula occludens (ZO)-1. However, fluorescence immunostaining revealed that, in the cell membrane, the levels of ZO-1, but not those of occludin or claudin-4, were transiently decreased 1 h after HGF treatment. The results were further confirmed by western blotting: HGF reduced the amount of ZO-1 protein in the cell membrane fraction concomitantly with an increase in cytoplasmic ZO-1. Furthermore, HGF reduced the interaction between ZO-1 and occludin, and induced the tyrosine phosphorylation of occludin, whereas the phosphorylation status of ZO-1 was not affected by exposure to HGF. Despite a decrease in the ZO-1/occludin interaction, HGF did not affect paracellular permeability to macromolecules.

CONCLUSIONS

HGF alters the subcellular localization of ZO-1, probably through the tyrosine phosphorylation of occludin, which may induce cell dispersion during epithelial restitution.

Claudin-1 expression confers resistance to anoikis in colon cancer cells in a Src-dependent manner

Denial of the appropriate cell-matrix interaction in epithelial cells induces apoptosis and is called 'anoikis'. Cancer cells are resistant to anoikis and it is believed that the resistance to anoikis helps promote tumor malignancy especially metastasis. We and others have demonstrated that the expression of tight junction protein claudin-1 is highly upregulated in colorectal cancer (CRC) and helps promote tumor progression and metastasis. However, molecular mechanism/s underlying claudin-1-dependent regulation of CRC progression remains poorly understood. In current study, we have determined that claudin-1 expression modulates anoikis in colon cancer cells to influence colon cancer invasion and thus metastasis. We have further provided data that claudin-1 modulates anoikis in a Src-Akt-Bcl-2-dependent manner. Importantly, claudin-1 physically associates with Src/p-Src in a multiprotein complex that also includes ZO-1, a PDZ-binding tight junction protein. Taken together, our data support the role of claudin-1 in the regulation of CRC progression and suggest that the regulation of anoikis may serve as a key regulatory mechanism in claudin-1-dependent regulation of CRC progression. Our findings are of direct clinical relevance and may open new therapeutic opportunity in colon cancer treatment and/or management.

β1 integrins restrict the growth of foci and spheroids

Extracellular matrices (ECM) have important roles for tissue architecture, both as structural and signaling components. Members of the integrin family are the main regulators of ECM assembly and transmitters of signals from the ECM to cells. In this study, we have analyzed the role of integrin subunit β1 in two-dimensional (2D) and three-dimensional (3D) cell cultures using integrin β1 null cells (MEFβ1(-/-) and GD25) and their β1 integrin-expressing counterparts. GD25 and GD25β1 cells proliferated with similar kinetics in sub-confluent 2D cultures, whereas GD25 cells attained higher cell numbers in confluent culture and formed foci with fivefold higher frequency than GD25β1 cells. Fibronectin fibrils were abundantly deposited throughout the GD25β1 colonies but strictly limited to the central multilayered area (focus) of GD25 colonies. During 3D growth as spheroids, GD25 continuously increased in size for >21 days while the growth of GD25β1 spheroids ceased after 14 days. Similarly, MEFβ1(-/-) cells formed foci and grew as spheroids, while the β1 integrin-expressing MEF did not. Expression levels of the cell cycle markers Ki67, PCNA, and histone H3-pSer10 were similar between GD25β1 and GD25 spheroids. Apoptotic cells accumulated earlier in GD25 spheroids; however, cell death increased with spheroid volumes in both spheroid types. In both cell systems, the presence of β1 integrins resulted in higher levels of active myosin light chain and inactive myosin light chain phosphatase, and a more compact spheroid structure. In conclusion, our results reveal that regulation of 3D growth in spheroids and foci is dependent on the β1 subfamily of integrins, and suggest that myosin-based spheroid contraction in combination with cell death limits the growth of β1-expressing spheroids.

Non-small cell lung carcinoma cell motility, rac activation and metastatic dissemination are mediated by protein kinase C epsilon

Background

Protein kinase C (PKC) ε, a key signaling transducer implicated in mitogenesis, survival, and cancer progression, is overexpressed in human primary non-small cell lung cancer (NSCLC). The role of PKCε in lung cancer metastasis has not yet been established.

Principal Findings

Here we show that RNAi-mediated knockdown of PKCε in H358, H1299, H322, and A549 NSCLC impairs activation of the small GTPase Rac1 in response to phorbol 12-myristate 13-acetate (PMA), serum, or epidermal growth factor (EGF). PKCε depletion markedly impaired the ability of NSCLC cells to form membrane ruffles and migrate. Similar results were observed by pharmacological inhibition of PKCε with εV1-2, a specific PKCε inhibitor. PKCε was also required for invasiveness of NSCLC cells and modulated the secretion of extracellular matrix proteases and protease inhibitors. Finally, we found that PKCε-depleted NSCLC cells fail to disseminate to lungs in a mouse model of metastasis.

Conclusions

Our results implicate PKCε as a key mediator of Rac signaling and motility of lung cancer cells, highlighting its potential as a therapeutic target.

A functional genetic screen reveals new regulators of β1-integrin activity

β1 integrins constitute a large group of widely distributed adhesion receptors, which regulate the ability of cells to interact with their surroundings. This regulation of the expression and activity of integrins is crucial for tissue homeostasis and development and contributes to inflammation and cancer. We report an RNA interference screen to uncover genes involved in the regulation of β1-integrin activity using cell spot microarray technology in cancer cell lines. Altogether, ten cancer and two normal cell lines were used to identify regulators of β1 integrin activity. Cell biological analysis of the identified β1-integrin regulatory genes revealed that modulation of integrin activity can influence cell invasion in a three-dimensional matrix. We demonstrate with loss-of-function and rescue experiments that CD9 activates and MMP8 inactivates β1 integrins and that both proteins associate with β1 integrins in cells. Furthermore, CD9 and MMP8 regulate cancer cell extravasation in vivo. Our discovery of new regulators of β1-integrin activity highlight the complexity of integrin activity regulation and provide a set of new genes involved in regulation of integrin function.

Systematic knockdown of epigenetic enzymes identifies a novel histone demethylase PHF8 overexpressed in prostate cancer with an impact on cell proliferation, migration and invasion

Our understanding of key epigenetic regulators involved in specific biological processes and cancers is still incomplete, despite great progress in genome-wide studies of the epigenome. Here, we carried out a systematic, genome-wide analysis of the functional significance of 615 epigenetic proteins in prostate cancer (PrCa) cells. We used the high-content cell-spot microarray technology and siRNA silencing of PrCa cell lines for functional screening of cell proliferation, survival, androgen receptor (AR) expression, histone methylation and acetylation. Our study highlights subsets of epigenetic enzymes influencing different cancer cell phenotypes. Plant homeo domain (PHD) finger proteins have a key role in cell survival and histone methylation, whereas histone deacetylases were primarily involved in regulating AR expression. In contrast, JumonjiC-domain (JmjC) containing histone lysine demethylases (KDMs) mainly had an impact on cell proliferation. Our results show that the KDMs JARID1B, PHF8, KDM3A, KDM3B and KDM4A were highly expressed in clinical PrCa samples. The PHD-finger protein 8 (PHF8), a transcriptional coactivator with both PHD- and JmjC-domains, was moderately to strongly expressed in 80% of clinical PrCa samples, whereas 76% of normal and benign samples were negative or only showed weak PHF8 expression. Strong PHF8 expression correlated significantly with high Gleason grade and was borderline significant for poor prognosis. The results of functional PHF8 knockdown implicate a role in cell migration and invasion, as shown by cell motility and 3-D invasion assays. Our study suggests that various cellular phenotypes are regulated by distinct subsets of epigenetic enzymes. Proteins interpreting and modifying histone methylation, such as JmjC-domain and particularly PHD-finger proteins like PHF8, are activated in subsets of PrCa's and promote cancer relevant phenotypes.