Rho-stimulated contractility contributes to the fibroblastic phenotype of Ras-transformed epithelial cells

Exploiting differential effects of actomyosin contractility to control cell sorting among breast cancer cells

In order to gain a greater understanding of the factors that drive spatial organization in multicellular aggregates of cancer cells, we investigate the segregation patterns of 6 breast cell lines of varying degree of mesenchymal character during formation of mixed aggregates. Cell sorting is considered in the context of available adhesion proteins and cellular contractility. It is found that the primary compaction mediator (cadherins or integrins) for a given cell type in isolation plays an important role in compaction speed, which in turn is the major factor dictating preference for interior or exterior position within mixed aggregates. In particular, cadherin-deficient, invasion-competent cells tend to position towards the outside of aggregates, facilitating access to extracellular matrix. Reducing actomyosin contractility is found to have a differential effect on spheroid formation depending on compaction mechanism. Inhibition of contractility has a significant stabilizing effect on cell-cell adhesions in integrin-driven aggregation and a mildly destabilizing effect in cadherin-based aggregation. This differential response is exploited to statically control aggregate organization and dynamically rearrange cells in pre-formed aggregates. Sequestration of invasive cells in the interior of spheroids provides a physical barrier that reduces invasion in three-dimensional culture, revealing a potential strategy for containment of invasive cell types.

Generation of anisotropic strain dysregulates wild-type cell division at the interface between host and oncogenic tissue

Epithelial tissues are highly sensitive to anisotropies in mechanical force, with cells altering fundamental behaviors, such as cell adhesion, migration, and cell division.1-5 It is well known that, in the later stages of carcinoma (epithelial cancer), the presence of tumors alters the mechanical properties of a host tissue and that these changes contribute to disease progression.6-9 However, in the earliest stages of carcinoma, when a clonal cluster of oncogene-expressing cells first establishes in the epithelium, the extent to which mechanical changes alter cell behavior in the tissue as a whole remains unclear. This is despite knowledge that many common oncogenes, such as oncogenic Ras, alter cell stiffness and contractility.10-13 Here, we investigate how mechanical changes at the cellular level of an oncogenic cluster can translate into the generation of anisotropic strain across an epithelium, altering cell behavior in neighboring host tissue. We generated clusters of oncogene-expressing cells within otherwise normal in vivo epithelium, using Xenopus laevis embryos. We find that cells in kRasV12, but not cMYC, clusters have increased contractility, which introduces radial stress in the tissue and deforms surrounding host cells. The strain imposed by kRasV12 clusters leads to increased cell division and altered division orientation in neighboring host tissue, effects that can be rescued by reducing actomyosin contractility specifically in the kRasV12 cells. Our findings indicate that some oncogenes can alter the mechanical and proliferative properties of host tissue from the earliest stages of cancer development, changes that have the potential to contribute to tumorigenesis.

You Talking to Me? Cadherin and Integrin Crosstalk in Biomaterial Design

While much work has been done in the design of biomaterials to control integrin-mediated adhesion, less emphasis has been put on functionalization of materials with cadherin ligands. Yet, cell-cell contacts in combination with cell-matrix interactions are key in driving embryonic development, collective cell migration, epithelial to mesenchymal transition, and cancer metastatic processes, among others. This review focuses on the incorporation of both cadherin and integrin ligands in biomaterial design, to promote what is called the "adhesive crosstalk." First, the structure and function of cadherins and their role in eliciting mechanotransductive processes, by themselves or in combination with integrin mechanosensing, are introduced. Then, biomaterials that mimic cell-cell interactions, and recent applications to get insights in fundamental biology and tissue engineering, are critically discussed.

The Expression of the Cancer-Associated lncRNA Snhg15 Is Modulated by EphrinA5-Induced Signaling

The Eph receptor tyrosine kinases and their respective ephrin-ligands are an important family of membrane receptors, being involved in developmental processes such as proliferation, migration, and in the formation of brain cancer such as glioma. Intracellular signaling pathways, which are activated by Eph receptor signaling, are well characterized. In contrast, it is unknown so far whether ephrins modulate the expression of lncRNAs, which would enable the transduction of environmental stimuli into our genome through a great gene regulatory spectrum. Applying a combination of functional in vitro assays, RNA sequencing, and qPCR analysis, we found that the proliferation and migration promoting stimulation of mouse cerebellar granule cells (CB) with ephrinA5 diminishes the expression of the cancer-related lncRNA Snhg15. In a human medulloblastoma cell line (DAOY) ephrinA5 stimulation similarly reduced SNHG15 expression. Computational analysis identified triple-helix-mediated DNA-binding sites of Snhg15 in promoters of genes found up-regulated upon ephrinA5 stimulation and known to be involved in tumorigenic processes. Our findings propose a crucial role of Snhg15 downstream of ephrinA5-induced signaling in regulating gene transcription in the nucleus. These findings could be potentially relevant for the regulation of tumorigenic processes in the context of glioma.

The Regulation of Intestinal Mucosal Barrier by Myosin Light Chain Kinase/Rho Kinases

The intestinal epithelial apical junctional complex, which includes tight and adherens junctions, contributes to the intestinal barrier function via their role in regulating paracellular permeability. Myosin light chain II (MLC-2), has been shown to be a critical regulatory protein in altering paracellular permeability during gastrointestinal disorders. Previous studies have demonstrated that phosphorylation of MLC-2 is a biochemical marker for perijunctional actomyosin ring contraction, which increases paracellular permeability by regulating the apical junctional complex. The phosphorylation of MLC-2 is dominantly regulated by myosin light chain kinase- (MLCK-) and Rho-associated coiled-coil containing protein kinase- (ROCK-) mediated pathways. In this review, we aim to summarize the current state of knowledge regarding the role of MLCK- and ROCK-mediated pathways in the regulation of the intestinal barrier during normal homeostasis and digestive diseases. Additionally, we will also suggest potential therapeutic targeting of MLCK- and ROCK-associated pathways in gastrointestinal disorders that compromise the intestinal barrier.

ILK supports RhoA/ROCK-mediated contractility of human intestinal epithelial crypt cells by inducing the fibrillogenesis of endogenous soluble fibronectin during the spreading process

BACKGROUND

Fibronectin (FN) assembly into an insoluble fibrillar matrix is a crucial step in many cell responses to extracellular matrix (ECM) properties, especially with regards to the integrin-related mechanosensitive signaling pathway. We have previously reported that the silencing of expression of integrin-linked kinase (ILK) in human intestinal epithelial crypt (HIEC) cells causes significant reductions in proliferation and spreading through concomitantly acquired impairment of soluble FN deposition. These defects in ILK-depleted cells are rescued by growth on exogenous FN. In the present study we investigated the contribution of ILK in the fibrillogenesis of FN and its relation to integrin-actin axis signaling and organization.

RESULTS

We show that de novo fibrillogenesis of endogenous soluble FN is ILK-dependent. This function seemingly induces the assembly of an ECM that supports increased cytoskeletal tension and the development of a fully spread contractile cell phenotype. We observed that HIEC cell adhesion to exogenous FN or collagen-I (Col-I) is sufficient to restore fibrillogenesis of endogenous FN in ILK-depleted cells. We also found that optimal engagement of the Ras homolog gene family member A (RhoA) GTPase/Rho-associated kinase (ROCK-1, ROCK-2)/myosin light chain (MLC) pathway, actin ventral stress fiber formation, and integrin adhesion complex (IAC) maturation rely primarily upon the cell's capacity to execute FN fibrillogenesis, independent of any significant ILK input. Lastly, we confirm the integrin α5β1 as the main integrin responsible for FN assembly, although in ILK-depleted cells αV-class integrins expression is needed to allow the rescue of FN fibrillogenesis on exogenous substrate.

CONCLUSION

Our study demonstrates that ILK specifically induces the initiation of FN fibrillogenesis during cell spreading, which promotes RhoA/ROCK-dependent cell contractility and maturation of the integrin-actin axis structures. However, the fibrillogenesis process and its downstream effect on RhoA signaling, cell contractility and spreading are ILK-independent in human intestinal epithelial crypt cells.

The Myosin Family of Mechanoenzymes: From Mechanisms to Therapeutic Approaches

Myosins are among the most fascinating enzymes in biology. As extremely allosteric chemomechanical molecular machines, myosins are involved in myriad pivotal cellular functions and are frequently sites of mutations leading to disease phenotypes. Human β-cardiac myosin has proved to be an excellent target for small-molecule therapeutics for heart muscle diseases, and, as we describe here, other myosin family members are likely to be potentially unique targets for treating other diseases as well. The first part of this review focuses on how myosins convert the chemical energy of ATP hydrolysis into mechanical movement, followed by a description of existing therapeutic approaches to target human β-cardiac myosin. The next section focuses on the possibility of targeting nonmuscle members of the human myosin family for several diseases. We end the review by describing the roles of myosin in parasites and the therapeutic potential of targeting them to block parasitic invasion of their hosts.

Polycomb-mediated repression of EphrinA5 promotes growth and invasion of glioblastoma

Glioblastoma (GBM) is the most common and most aggressive intrinsic brain tumour in adults. Integrated transcriptomic and epigenomic analyses of glioblastoma initiating cells (GIC) in a mouse model uncovered a novel epigenetic regulation of EfnA5. In this model, Bmi1 enhances H3K27me3 at the EfnA5 locus and reinforces repression of selected target genes in a cellular context-dependent fashion. EfnA5 mediates Bmi1-dependent proliferation and invasion in vitro and tumour formation in an allograft model. Importantly, we show that this novel Polycomb feed-forward loop is also active in human GIC and we provide pre-clinical evidence of druggability of the EFNA5 signalling pathway in GBM xenografts overexpressing Bmi1.

Suppression of focal adhesion formation may account for the suppression of cell migration, invasion and growth of non-small cell lung cancer cells following treatment with polyisoprenylated cysteinyl amide inhibitors

Migratory cells form extracellular matrix attachments called focal-adhesions. Focal adhesion assembly and disassembly are regulated by the Rho family of small GTPases. We previously reported that polyisoprenylated cysteinyl amide inhibitors (PCAIs) suppress Rho protein levels, disrupting F-actin cytoskeleton remodeling in the formation of lamellipodia and filopodia. In this study, we investigated whether these observations effect focal adhesion formation, which involves cell surface receptors known as integrins and several signaling/adaptor proteins such as vinculin, α-actinin, Rock kinases and phospho-Myosin Light Chain-2 (p-MLC-2), that foster the linkage of the actin cytoskeleton to the extracellular matrix. We observed that treatment of H1299 cells with 5 μM PCAIs for 24 h markedly diminished the level of full-length integrin α4 by at least 24% relative to controls. PCAIs at 5 μM, diminished the levels of vinculin by at least 50%. Immunofluorescent analysis showed at least a 76% decrease in the number of vinculin-focal adhesion punctates. In addition, PCAIs diminished Rock1 levels by 25% and its substrate, p-MLC-2 by 75%. PCAIs did not significantly alter the levels of integrin β5, α-actinin, and Rock2, suggesting that the effects of the PCAIs are target specific. Our data indicate that the PCAIs alter the levels of the Rho proteins and their effectors to abrogate their functions in cytoskeleton remodeling thereby suppressing focal adhesion formation. This in turn results in a PCAIs-induced decrease in cell invasion, thus making the PCAIs propitious agents for the inhibition of cancer growth and metastasis.

Effect of metastasis suppressor 1 on H1299 cells and its clinical significance in non-small cell lung cancer

The present study aimed to investigate the effect of metastasis suppressor 1 (MTSS1) on the proliferation, migration and invasion of human H1299 non-small cell lung cancer cells and its clinical significance in non‑small cell lung cancer. The target gene MTSS1-overexpressing lentivirus (LV-MTSS1) was transfected into H1299 cells and expression of MTSS1 was detected at the mRNA and protein levels. Cell Counting Kit-8, wound healing and Transwell assays revealed that the migration and invasion activities were significantly suppressed by MTSS1, but that it had no effect on cell proliferation. In addition, MTSS1 expression in tissue microarrays including samples from 223 cases of non-small cell lung cancer was tested by immunohistochemistry to explore the correlation between MTSS1 and clinicopathological characteristics and prognosis. MTSS1 suppressed H1299 cell migration and invasion, and its expression level can be used as a new independent factor for determining the prognosis of non-small cell lung cancer.

Non-muscle myosin II in disease: mechanisms and therapeutic opportunities

The actin motor protein non-muscle myosin II (NMII) acts as a master regulator of cell morphology, with a role in several essential cellular processes, including cell migration and post-synaptic dendritic spine plasticity in neurons. NMII also generates forces that alter biochemical signaling, by driving changes in interactions between actin-associated proteins that can ultimately regulate gene transcription. In addition to its roles in normal cellular physiology, NMII has recently emerged as a critical regulator of diverse, genetically complex diseases, including neuronal disorders, cancers and vascular disease. In the context of these disorders, NMII regulatory pathways can be directly mutated or indirectly altered by disease-causing mutations. NMII regulatory pathway genes are also increasingly found in disease-associated copy-number variants, particularly in neuronal disorders such as autism and schizophrenia. Furthermore, manipulation of NMII-mediated contractility regulates stem cell pluripotency and differentiation, thus highlighting the key role of NMII-based pharmaceuticals in the clinical success of stem cell therapies. In this Review, we discuss the emerging role of NMII activity and its regulation by kinases and microRNAs in the pathogenesis and prognosis of a diverse range of diseases, including neuronal disorders, cancer and vascular disease. We also address promising clinical applications and limitations of NMII-based inhibitors in the treatment of these diseases and the development of stem-cell-based therapies.

RhoGAPs and Rho GTPases in platelets

Platelet cytoskeletal reorganization is essential for platelet adhesion and thrombus formation in hemostasis and thrombosis. The Rho GTPases RhoA, Rac1 and Cdc42 are the main players in cytoskeletal dynamics of platelets responsible for the formation of filopodia and lamellipodia to strongly increase the platelet surface upon activation. They are involved in platelet activation and aggregate formation including platelet secretion, integrin activation and arterial thrombus formation. The activity of Rho GTPases is tightly controlled by different proteins such as GTPase-activating proteins (GAPs). GAPs stimulate GTP hydrolysis to terminate Rho signaling. The role and impact of GAPs in platelets is not well-defined and many of the RhoGAPs identified are not known to be present in platelets or to have any function in platelets. The recently identified RhoGAPs Oligophrenin1 (OPHN1) and Nadrin regulate the activity of RhoA, Rac1 and Cdc42 and subsequent platelet cytoskeletal reorganization, platelet activation and thrombus formation. In the last years, the analysis of genetically modified mice helped to gain the understanding of Rho GTPases and their regulators in cytoskeletal rearrangements and other Rho mediated cellular processes in platelets.

Spinal cord regeneration

Three theories of regeneration dominate neuroscience today, all purporting to explain why the adult central nervous system (CNS) cannot regenerate. One theory proposes that Nogo, a molecule expressed by myelin, prevents axonal growth. The second theory emphasizes the role of glial scars. The third theory proposes that chondroitin sulfate proteoglycans (CSPGs) prevent axon growth. Blockade of Nogo, CSPG, and their receptors indeed can stop axon growth in vitro and improve functional recovery in animal spinal cord injury (SCI) models. These therapies also increase sprouting of surviving axons and plasticity. However, many investigators have reported regenerating spinal tracts without eliminating Nogo, glial scar, or CSPG. For example, many motor and sensory axons grow spontaneously in contused spinal cords, crossing gliotic tissue and white matter surrounding the injury site. Sensory axons grow long distances in injured dorsal columns after peripheral nerve lesions. Cell transplants and treatments that increase cAMP and neurotrophins stimulate motor and sensory axons to cross glial scars and to grow long distances in white matter. Genetic studies deleting all members of the Nogo family and even the Nogo receptor do not always improve regeneration in mice. A recent study reported that suppressing the phosphatase and tensin homolog (PTEN) gene promotes prolific corticospinal tract regeneration. These findings cannot be explained by the current theories proposing that Nogo and glial scars prevent regeneration. Spinal axons clearly can and will grow through glial scars and Nogo-expressing tissue under some circumstances. The observation that deleting PTEN allows corticospinal tract regeneration indicates that the PTEN/AKT/mTOR pathway regulates axonal growth. Finally, many other factors stimulate spinal axonal growth, including conditioning lesions, cAMP, glycogen synthetase kinase inhibition, and neurotrophins. To explain these disparate regenerative phenomena, I propose that the spinal cord has evolved regenerative mechanisms that are normally suppressed by multiple extrinsic and intrinsic factors but can be activated by injury, mediated by the PTEN/AKT/mTOR, cAMP, and GSK3b pathways, to stimulate neural growth and proliferation.

Validation of the effects of TGF-β1 on tumor recurrence and prognosis through tumor retrieval and cell mechanical properties

Background

In vivo, the transforming growth factor-beta1 (TGF-β1)-induced epithelial to mesenchymal transition (EMT) occurs in seconds during cancer cells intravasation and extravasation. Although it has been established that cellular stiffness can change as a cancer cell transformed, the precise relationship between TGF-β1-induced mesenchymal stem cell mechanics and cancer prognosis remains unclear. Accordingly, it is hard to define the effects of EMT on cell mechanical properties (CMs), tumor recurrence and metastasis risks. This study bridges physical and pathological disciplines to reconcile single-cell mechanical measurements of tumor cells.

Methods and results

We developed a microplate measurement system (MMS) and revealed the intrinsic divergent tumor composition of retrieval cells by cell stiffness and adhesion force and flow cytometry analysis. After flow cytometry sorting, we could measure the differences in CMs of the Sca-1⁺-CD44⁺ (mesenchymal-stem-cell-type) and the other subgroups. As well as the stiffer and heterogeneous compositions among tumor tissues with higher recurrence risk were depicted by MMS and atomic force microscopy (AFM). An in vitro experiment validated that Lewis lung carcinoma (LLC) cells acquired higher CMs and motility after EMT, but abrogated by SB-505124 inhibition. Concomitantly, the CD31, MMP13 and TGF-β1 enriched micro-environment in the tumor was associated with higher recurrence and distal lung metastasis risks. Furthermore, we report a comprehensive effort to correlate CMs to tumor-prognosis indicators, in which a decreased body weight gain ratio (BWG) and increased tumor weight (TW) were correlated with increased CMs.

Conclusions

Together, we determined that TGF-β1 was significantly associated with malignant tumor progressing. In terms of clinical applications, local tumor excision followed by MMS analysis offers an opportunity to predict tumor recurrence and metastasis risks.

Mutant B-RAF regulates a Rac-dependent cadherin switch in melanoma

The ability of cells to invade into the dermis is a critical event in the development of cutaneous melanoma and ultimately an indicator of poor prognosis. However, the molecular events surrounding the acquisition of this invasive phenotype remain incompletely understood. Mutations in B-RAF are frequent in melanoma and are known to regulate the invasive phenotype. In this study, we sought to determine the molecular mechanisms controlling melanoma invasion. We found that mutant B-RAF signaling regulates a cadherin switch. In melanoma cells expressing mutant B-RAF we observed high levels of N-cadherin and low levels of E-cadherin. Depletion of mutant B-RAF, by siRNA, caused a decrease in the levels of N-cadherin and an increase in the levels of E-cadherin. Mechanistically, we found that this cadherin switch required the activity of Rac1 and its GEF, Tiam1, both of which show suppressed activity in the presence of mutant B-RAF. Consistent with the work of others, we found that depletion of mutant B-RAF decreased the invasive capacity of the melanoma cells. However, simultaneous depletion of B-RAF and Rac or Tiam1 resulted in invasive capacity similar to that of control cells. Taken together, our results suggest that mutant B-RAF signaling downregulates Tiam1/Rac activity resulting in an increase in N-cadherin levels and a decrease in E-cadherin levels and ultimately enhanced invasion.

Cadherins in collective cell migration of mesenchymal cells

Immunity, embryogenesis and tissue repair rely heavily on cell migration. Cells can be seen migrating as individuals or large groups. In the latter case, collectiveness emerges via cell-cell interactions. In migratory epithelial cell sheets, classic Cadherins are critical to maintain tissue integrity, to promote coordination and establish cell polarity. However, recent evidence indicates that mesenchymal cells, migrating in streams such as neural crest or cancer cells, also exhibit collective migration. Here we will explore the idea that Cadherins play an essential role during collective migration of mesenchymal cells.

From mechanical force to RhoA activation

Throughout their lives, all cells constantly experience and respond to various mechanical forces. These frequently originate externally but can also arise internally as a result of the contractile actin cytoskeleton. Mechanical forces trigger multiple signaling pathways. Several converge and result in the activation of the GTPase RhoA. In this review, we focus on the pathways by which mechanical force leads to RhoA regulation, especially when force is transmitted via cell adhesion molecules that mediate either cell-matrix or cell-cell interactions. We discuss both the upstream signaling events that lead to activation of RhoA and the downstream consequences of this pathway. These include not only cytoskeletal reorganization and, in a positive feedback loop, increased myosin-generated contraction but also profound effects on gene expression and differentiation.

Rac1 and RhoA GTPases have antagonistic functions during N-cadherin-dependent cell-cell contact formation in C2C12 myoblasts

BACKGROUND INFORMATION

N-cadherin, a member of the Ca(2+)-dependent cell-cell adhesion molecule family, plays an essential role in the induction of the skeletal muscle differentiation programme. However, the molecular mechanisms which govern the formation of N-cadherin-dependent cell-cell contacts in myoblasts remain unexplored.

RESULTS

In the present study, we show that N-cadherin-dependent cell contact formation in myoblasts is defined by two stages. In the first phase, N-cadherin is highly mobile in the lamellipodia extensions between the contacting cells. The second stage corresponds to the formation of mature N-cadherin-dependent cell contacts, characterized by the immobilization of a pool of N-cadherin which appears to be clustered in the interdigitated membrane structures that are also membrane attachment sites for F-actin filaments. We also demonstrated that the formation of N-cadherin-dependent cell-cell contacts requires a co-ordinated and sequential activity of Rac1 and RhoA. Rac1 is involved in the first stage and facilitates N-cadherin-dependent cell-cell contact formation, but it is not absolutely required. Conversely, RhoA is necessary for N-cadherin-dependent cell contact formation, since, via ROCK (Rho-associated kinase) signalling and myosin 2 activation, it allows the stabilization of N-cadherin at the cell-cell contact sites.

CONCLUSIONS

We have shown that Rac1 and RhoA have opposite effects on N-cadherin-dependent cell-cell contact formation in C2C12 myoblasts and act sequentially to allow its formation.

Adherens junctions and cancer

Cadherins and catenins are the central cell-cell adhesion molecules in adherens junctions (AJs). This chapter reviews the knowledge concerning the role of cadherins and catenins in epithelial cancer and examines the published literature demonstrating the changes in the expression and function of these proteins in human cancer and the association of these changes with patient outcomes. The chapter also covers the mechanistic studies aiming at uncovering the significance of changes in cadherin and catenin expression in cancer and potential molecular mechanisms responsible for the causal role of AJs in cancer initiation and progression.

Integrins and cadherins join forces to form adhesive networks

Cell-cell and cell-extracellular-matrix (cell-ECM) adhesions have much in common, including shared cytoskeletal linkages, signaling molecules and adaptor proteins that serve to regulate multiple cellular functions. The term 'adhesive crosstalk' is widely used to indicate the presumed functional communication between distinct adhesive specializations in the cell. However, this distinction is largely a simplification on the basis of the non-overlapping subcellular distribution of molecules that are involved in adhesion and adhesion-dependent signaling at points of cell-cell and cell-substrate contact. The purpose of this Commentary is to highlight data that demonstrate the coordination and interdependence of cadherin and integrin adhesions. We describe the convergence of adhesive inputs on cell signaling pathways and cytoskeletal assemblies involved in regulating cell polarity, migration, proliferation and survival, differentiation and morphogenesis. Cell-cell and cell-ECM adhesions represent highly integrated networks of protein interactions that are crucial for tissue homeostasis and the responses of individual cells to their adhesive environments. We argue that the machinery of adhesion in multicellular tissues comprises an interdependent network of cell-cell and cell-ECM interactions and signaling responses, and not merely crosstalk between spatially and functionally distinct adhesive specializations within cells.

Forcing form and function: biomechanical regulation of tumor evolution

Cancer cells exist in a constantly evolving tissue microenvironment of diverse cell types within a proteinaceous extracellular matrix. As tumors evolve, the physical forces within this complex microenvironment change, with pleiotropic effects on both cell- and tissue-level behaviors. Recent work suggests that these biomechanical factors direct tissue development and modulate tissue homeostasis, and, when altered, crucially influence tumor evolution. In this review, we discuss the biomechanical regulation of cell and tissue homeostasis from the molecular, cellular and tissue levels, including how modifications of this physical dialogue could contribute to cancer etiology. Because of the broad impact of biomechanical factors on cell and tissue functions, an understanding of tumor evolution from the biomechanical perspective should improve risk assessment, clinical diagnosis and the efficacy of cancer treatment.

Downregulation of metastasis suppressor 1(MTSS1) is associated with nodal metastasis and poor outcome in Chinese patients with gastric cancer

Background

The putative tumor metastasis suppressor 1(MTSS1) is an actin-binding scaffold protein that has been implicated to play an important role in carcinogenesis and cancer metastasis, yet its role in the development of gastric cancer has not been well illustrated. In this study, we detected MTSS1 expression and explored its clinical significance in gastric cancer.

Methods

Immunohistochemistry was performed using tissue microarrays containing gastric adenocarcinoma specimens from 1,072 Chinese patients with normal adjacent mucosa, primary gastric cancer and lymph node (LN) metastasis and specific antibody against MTSS1. MTSS1 mRNA and protein expression were detected by reverse transcription-polymerase chain reaction and Western blotting. The clinical follow-up was done in the 669 patients living in Shanghai that was chose from the 1072 cases.

Results

Complete loss of MTSS1 expression was observed in 751 cases (70.1%) of the 1,072 primary tumors and 103 (88%) of 117 nodal metastases; and loss of MTSS1 expression was significantly associated with poorly differentiated tumors, large tumor size, deep invasion level, the presence of nodal metastases and advanced disease stage. Moreover, multivariate analysis demonstrated that loss of MTSS1 expression correlated significantly with poor survival rates (RR = 0.194, 95% CI = 0.144-0.261, P < 0.001).

Conclusions

MTSS1 expression decreased significantly as gastric cancer progressed and metastasized, suggesting MTSS1 may serve as a useful biomarker for the prediction of outcome of gastric cancer.

Vinculin potentiates E-cadherin mechanosensing and is recruited to actin-anchored sites within adherens junctions in a myosin II-dependent manner

Vinculin localizes to tension-bearing cell–cell junctions to help transmit signals from E-cadherin to the actin cytoskeleton in response to mechanical stress.

Cell surface receptors integrate chemical and mechanical cues to regulate a wide range of biological processes. Integrin complexes are the mechanotransducers between the extracellular matrix and the actomyosin cytoskeleton. By analogy, cadherin complexes may function as mechanosensors at cell–cell junctions, but this capacity of cadherins has not been directly demonstrated. Furthermore, the molecular composition of the link between E-cadherin and actin, which is needed to sustain such a function, is unresolved. In this study, we describe nanomechanical measurements demonstrating that E-cadherin complexes are functional mechanosensors that transmit force between F-actin and E-cadherin. Imaging experiments reveal that intercellular forces coincide with vinculin accumulation at actin-anchored cadherin adhesions, and nanomechanical measurements show that vinculin potentiates the E-cadherin mechanosensory response. These investigations directly demonstrate the mechanosensory capacity of the E-cadherin complex and identify a novel function for vinculin at cell–cell junctions. These findings have implications for barrier function, morphogenesis, cell migration, and invasion and may extend to all soft tissues in which classical cadherins regulate cell–cell adhesion.

Tetraspanin CD151 regulates RhoA activation and the dynamic stability of carcinoma cell-cell contacts

Tetraspanins regulate integrin-dependent tumor cell interactions with the extracellular matrix. Here we show that tetraspanin CD151, which plays critical roles in regulating the adhesion and motility of individual tumor cells, is also an important regulator of collective tumor cell migration. Near total silencing of CD151 destabilizes E-cadherin-dependent carcinoma cell-cell junctions and enhances the collective migration of intact tumor cell sheets. This effect does not depend on reduced E-cadherin cell-surface expression or intrinsic adhesivity, or on obvious disruptions in the E-cadherin regulatory complex. Instead, the loss of CD151 causes excessive RhoA activation, loss of actin organization at cell-cell junctions, and increased actin stress fibers at the basal cell surface. Cell-cell contacts within CD151-silenced monolayers display a nearly threefold increase in remodeling rate and a significant reduction in lifespan as compared to cell-cell contacts within wild-type monolayers. CD151 re-expression restores junctional stability, as does acute treatment of CD151-silenced cells with a cell-permeable RhoA inhibitor. However, a CD151 mutant with impaired association with α3β1 integrin fails to restore junctional organization. These data reveal that, in addition to its roles in regulating tumor cell-substrate interactions, CD151 is also an important regulator of the stability of tumor cell-cell interactions, potentially through its interaction with α3β1 integrin. This could help to explain the phenotypes in human patients and mice lacking CD151.

Restoration of E-cadherin cell-cell junctions requires both expression of E-cadherin and suppression of ERK MAP kinase activation in Ras-transformed breast epithelial cells

E-cadherin is a main component of the cell-cell adhesion junctions that play a principal role in maintaining normal breast epithelial cell morphology. Breast and other cancers that have up-regulated activity of Ras are often found to have down-regulated or mislocalized E-cadherin expression. Disruption of E-cadherin junctions and consequent gain of cell motility contribute to the process known as epithelial-to-mesenchymal transition (EMT). Enforced expression of E-cadherin or inhibition of Ras-signal transduction pathway has been shown to be effective in causing reversion of EMT in several oncogene-transformed and cancer-derived cell lines. In this study, we investigated MCF10A human breast epithelial cells and derivatives that were transformed with either activated H-Ras or N-Ras to test for the reversion of EMT by inhibition of Ras-driven signaling pathways. Our results demonstrated that inhibition of mitogen-activated protein kinase (MAPK) kinase, but not PI3-kinase, Rac, or myosin light chain kinase, was able to completely restore E-cadherin cell-cell junctions and epithelial morphology in cell lines with moderate H-Ras expression. In MCF10A cells transformed by a high-level expression of activated H-Ras or N-Ras, restoration of E-cadherin junction required both the enforced reexpression of E-cadherin and suppression of MAPK kinase. Enforced expression of E-cadherin alone did not induce reversion from the mesenchymal phenotype. Our results suggest that Ras transformation has at least two independent actions to disrupt E-cadherin junctions, with effects to cause both mislocalization of E-cadherin away from the cell surface and profound decrease in the expression of E-cadherin.

Metastasis suppressor 1 (MTSS1) demonstrates prognostic value and anti-metastatic properties in breast cancer

Metastasis suppressor 1 (MTSS1) may play an important role in cancer metastasis. Firstly, this study assessed MTSS1 expression levels within breast cancer patients to reveal any clinical relevance. Secondly, we aimed to clarify the cellular function of MTSS1 in breast cancer cells. MTSS1 expression levels were assessed in a cohort of breast cancer specimens (normal n=33; cancer n=127), through quantitative PCR analysis and immuno-histochemical techniques. The influence of MTSS1 was further examined via biological overexpression and knockdown within breast cancer cell lines. We report that patients with tumours expressing reduced levels of MTSS1 had a poorer prognosis (p=0.042). High levels of MTSS1 correlated with an increased patient overall survival (p=0.0108) and disease-free survival (p=0.012). Furthermore, overexpression of MTSS1 significantly suppressed (p<0.01) the invasive, migratory, growth and adherence properties of a human breast cancer cell line. In contrast, knockdown of MTSS1 dramatically enhanced these properties. We conclude that MTSS1 is a prognostic indicator of disease-free survival in breast cancer patients and demonstrates the ability to play a role in governing the metastatic nature of breast cancer cells.

Dual FGF-2 and intergrin alpha5beta1 signaling mediate GRAF-induced RhoA inactivation in a model of breast cancer dormancy

Interactions with the bone marrow stroma regulate dormancy and survival of breast cancer micrometastases. In an in vitro model of dormancy in the bone marrow, we previously demonstrated that estrogen-dependent breast cancer cells are partially re-differentiated by FGF-2, re-express integrin α5β1 lost with malignant transformation and acquire an activated PI3K/Akt pathway. Ligation of integrin α5β1 by fibronectin and activation of the PI3K pathway both contribute to survival of these dormant cells. Here, we investigated mechanisms responsible for the dormant phenotype. Experiments demonstrate that integrin α5β1 controls de novo cytoskeletal rearrangements, cell spreading, focal adhesion kinase rearrangement to the cell perimeter and recruitment of a RhoA GAP known as GRAF. This results in the inactivation of RhoA, an effect which is necessary for the stabilization of cortical actin. Experiments also demonstrate that activation of the PI3K pathway by FGF-2 is independent of integrin α5β1 and is also required for cortical actin reorganization, GRAF membrane relocalization and RhoA inactivation. These data suggest that GRAF-mediated RhoA inactivation and consequent phenotypic changes of dormancy depend on dual signaling by FGF-2-initiated PI3K activation and through ligation of integrin α5β1 by fibronectin.

Kazrin regulates keratinocyte cytoskeletal networks, intercellular junctions and differentiation

Kazrin is an evolutionarily conserved protein that is upregulated during keratinocyte terminal differentiation. Kazrin localizes to desmosomes and binds the epidermal cornified envelope protein periplakin. Kazrin overexpression in human epidermal keratinocytes caused profound changes in cell shape, reduced filamentous actin, reorganized keratin filaments, and impaired assembly of intercellular junctions. These effects were attributable to decreased Rho activity in kazrin-overexpressing cells. Kazrin overexpression also stimulated terminal differentiation and reduced clonal growth in culture. Knockdown of kazrin decreased expression of differentiation markers and stimulated proliferation without changing total Rho activity. We conclude that kazrin is a dual regulator of intercellular adhesion and differentiation in keratinocytes and regulates these processes by Rho-dependent and -independent mechanisms.

PAK is required for the disruption of E-cadherin adhesion by the small GTPase Rac

E-cadherin cell-cell adhesion plays a major role in the maintenance of the morphology and function of epithelial tissues. Modulation of E-cadherin function is an important process in morphogenesis and tumour de-differentiation. We have previously shown that constitutively active Rac1 induces the disassembly of E-cadherin complexes from junctions in human keratinocytes. Here, we compare this activity in three members of the Rac subfamily (Rac1, Rac3 and Rac1b) and investigate the molecular mechanisms underlying Rac1-induced destabilization of junctions. We demonstrate that Rac3 shares with Rac1 the ability to interfere with cadherin-mediated adhesion. Rac1b is an alternative splice variant of Rac1 but, surprisingly, Rac1b cannot induce junction disassembly. Thus, Rac family members differ on their potential to perturb keratinocyte cell-cell contacts. The mechanism through which Rac promotes disassembly of cadherin-dependent adhesion does not involve an increase in contractility. Instead, activation of the Rac target PAK1 is necessary for destabilization of cell-cell contacts. Inhibition of PAK1 by dominant-negative constructs or depletion of endogenous PAK1 by RNA interference efficiently blocked Rac1-induced perturbation of junctions. Interestingly, PAK1 cannot be activated by Rac1b, suggesting that this may contribute to the inability of Rac1b to disrupt cell-cell contacts in keratinocytes. As PAK1 also plays a crucial role in lamellipodia formation, our data indicate that PAK1 is at the interface between junction destabilization and increased motility during morphogenetic events.

Clinicopathological significance of missing in metastasis B expression in hepatocellular carcinoma

Missing in metastasis (MIM) proteins are important regulators in controlling cell growth and development. There has been accumulating evidence suggesting a role of MIM-B in carcinogenesis, yet its role in the development of hepatocellular carcinoma has not been examined thus far. In this study, we investigated the clinicopathological significance of MIM-B in tumor and its matched adjacent nontumor tissue obtained from 40 patients with hepatocellular carcinoma. Increased MIM-B messenger RNA and protein expression, as detected by quantitative real-time polymerase chain reaction and Western blot, respectively, was found in hepatocellular carcinoma clinical samples; and its expression was significantly associated with early pathologic tumor-node-metastasis stage group (P = .007), presence of tumor encapsulation (P = .034), and absence of venous infiltration (P = .038). Higher levels of MIM-B expression were found to be associated with early stage disease. Elevated MIM-B expression may influence the development of hepatocellular carcinoma and may possibly be a powerful indicator for the disease at an early stage.

Hic-5 contributes to epithelial-mesenchymal transformation through a RhoA/ROCK-dependent pathway

Epithelial-mesenchymal transformation (EMT) in response to TGFbeta1 is a coordinated process of tissue morphogenesis that occurs during embryonic development as well as during certain pathologic events including kidney tubulointerstitial fibrosis. It is characterized by the disassembly of cell-cell junctions and dramatic alterations in the actin cytoskeleton that facilitates cell-matrix adhesion and stimulates migration. The focal adhesion adapter protein, Hic-5, has previously been reported to be upregulated during TGFbeta1-induced EMT in mouse mammary epithelial cells and the current study recapitulates this result in both mouse kidney proximal tubule epithelial, MCT, cells and human mammary epithelial, MCF10A, cells. To evaluate a causative role for Hic-5 in EMT, Hic-5 RNA interference (siRNA) was used to prevent Hic-5 expression in response to TGFbeta1 stimulation and was shown to suppress cell migration and actin stress fiber formation. It also resulted in the retention of a robust epithelial cell morphology characterized by elevated E-cadherin protein expression and well-organized adherens junctions. In addition, Hic-5 siRNA treatment led to the suppression of TGFbeta1 induction of RhoA activation. In contrast, forced expression of Hic-5 led to the formation of ROCK-dependent actin stress fibers. Furthermore, the induction of Hic-5 expression in response to TGFbeta1 was shown to be a RhoA/ROCK I-dependent process. Together, these data implicate Hic-5 as a key regulator of EMT and suggest that RhoA stimulated Hic-5 expression in response to TGFbeta1 may be functioning in a feed forward mechanism whereby Hic-5 maintains the mesenchymal phenotype through sustained RhoA activation and signaling.

Aberrant expression of X-linked genes RbAp46, Rsk4, and Cldn2 in breast cancer

The consequence of activation status or gain/loss of an X-chromosome in terms of the expression of tumor suppressor genes or oncogenes in breast cancer has not been clearly addressed. In this study, we investigated the activation status of the X-chromosomes in a panel of human breast cancer cell lines, human breast carcinoma, and adjacent mammary tissues and a panel of murine mammary epithelial sublines ranging from low to high invasive potentials. Results show that most human breast cancer cell lines were homozygous, but both benign cell lines were heterozygous for highly polymorphic X-loci (IDS and G6PD). On the other hand, 60% of human breast carcinoma cases were heterozygous for either IDS or G6PD markers. Investigation of the activation status of heterozygous cell lines revealed the presence of only one active X-chromosome, whereas most heterozygous human breast carcinoma cases had two active X-chromosomes. Furthermore, we determined whether or not an additional active X-chromosome affects expression levels of tumor suppressor genes and oncogenes. Reverse transcription-PCR data show high expression of putative tumor suppressor genes Rsk4 and RbAp46 in 47% and 79% of breast carcinoma cases, respectively, whereas Cldn2 was down-regulated in 52% of breast cancer cases compared with normal adjacent tissues. Consistent with mRNA expression, immunostaining for these proteins also showed a similar pattern. In conclusion, our data suggest that high expression of RbAp46 is likely to have a role in the development or progression of human breast cancer. The activation status of the X-chromosome may influence the expression levels of X-linked oncogenes or tumor suppressor genes.

Engineered Cell-Adhesive Nanoparticles Nucleate Extracellular Matrix Assembly

Tissue engineering aims to regenerate new biological tissue for replacing diseased or injured tissues. We propose a new approach to accelerate the deposition of cell-secreted matrix proteins into extracellular matrix fibrils. We examined whether dynamic substrates with nanoscale ligand features allowing for alpha5beta1 integrin recruiting, cellular tension generation, and alpha5beta1 integrin mobility would enhance fibronectin matrix assembly in a ligand model system that is routinely not sufficient for its induction. To this end, we developed biodynamic substrates consisting of cell adhesive fragment from the 9th and 10th type repeats of fibronectin (FNf ) functionalized to 100 nm prefabricated albumin nanoparticles (ANPs). FNf-ANPs modulated cellular spreading processes, promoting the development of stellate or dendritic morphologies. Concomitant with the spreading, FNf-ANPs rapidly recruited beta1 integrins to focal contacts and promoted the migration of beta1 integrins centripetally from the cell periphery toward the center. FNf-ANPs stimulated the deposition of secreted fibronectin into matrix fibrils; FNf, the key ligand alone, was not sufficient for fibronectin fibrillogenesis. When FNf-ANPs were displayed from "immobilized" substrates, abolishing any mobility of ligated beta1 integrins, fibronectin matrix assembly was abrogated, implicating the role of dynamic matrix display on matrix assembly. Receptor ligation of FNf-ANPs via noncontractile adhesions was not sufficient to stimulate fibrillogenesis, and Rho-kinase inhibitors abolished fibronectin matrix deposition. Our approach highlights the possibility of engineering integrin-based extracellular matrix assembly using nanotechnology, which may have implications for improved biomaterials for wound repair and basic understanding of matrix remodeling within pathogenesis and biomedicine.

p120-ctn: A nexus for contextual signaling via Rho GTPases

p120 catenin (p120) is the prototypic member of a subfamily of armadillo repeat domain proteins involved in intercellular adhesion. Recent evidence indicates that p120 associates with classical cadherins and regulates their stability. Ectopic p120 expression results in a variety of morphological effects, and promotes cell migration. There is now strong evidence that p120 acts, at least in part, through regulation of Rho GTPases. The data suggest that p120 may act as a signaling nexus, conveying messages from the cellular micro- and macro-environment to the cell's interior. By regulating Rho GTPases in a context-dependent manner p120 can exert profound effects on cellular responses from synaptic plasticity to vesicle trafficking, as well as regulate the motile vs. sessile, and possibly the proliferative vs. quiescent phenotype of epithelial cells. Here, we review the new evidence on the relationship of p120 to Rho GTPases, and discuss potential roles for the p120-Rho connection in normal and malignant cells.

Cell Adhesion, Cellular Tension, and Cell Cycle Control

Cooperative signaling between growth factor receptor tyrosine kinases, integrins, and the actin cytoskeleton is required for activation of the G1-phase cyclin-dependent kinases and progression through G1-phase. Increasing evidence suggests that there is cell type specificity in these cooperative interactions and that the compliance of the underlying substratum can strongly affect adhesion-dependent signaling to the cell cycle. This chapter reviews our current methods for studying how cell type specificity and changes in substratum compliance can contribute to G1-phase cell cycle control. We also describe several of our current analytical procedures.

Contraction of myofibroblasts in granulation tissue is dependent on Rho/Rho kinase/myosin light chain phosphatase activity

During wound healing and fibrocontractive diseases fibroblasts acquire a smooth muscle cell-like phenotype by differentiating into contractile force generating myofibroblasts. We examined whether regulation of myofibroblast contraction in granulation tissue is dominated by Ca2+-induced phosphorylation of myosin light chain kinase or by Rho/Rho kinase (ROCK)-mediated inhibition of myosin light chain phosphatase, similar to that of cultured myofibroblasts. Strips of granulation tissue obtained from rat granuloma pouches were stimulated with endothelin-1 (ET-1), serotonin, and angiotensin-II and isometric force generation was measured. We here investigated ET-1 in depth, because it was the only agonist that produced a long-lasting and strong response. The ROCK inhibitor Y27632 completely inhibited ET-1-promoted contraction and the phosphatase inhibitor calyculin elicited contraction in the absence of any other agonists, suggesting that activation of the Rho/ROCK/myosn light chain phosphatase pathway is critical in regulating in vivo myofibroblast contraction. Membrane depolarization with K+ also stimulated a long-lasting contraction of granulation tissue; however, the amount of force generated was significantly less compared to ET-1. Moreover, K+-induced contraction was inhibited by Y27632. These results are consistent with inhibition of myosin light chain phosphatase by the Rho/ROCK signaling pathway, which would account for the long-duration contraction of myofibroblasts necessary for wound closure.

Confirmation of a linkage between H-Ras and MMP-13 expression as well as MMP-9 by chemical genomic approach

As farnesylation of the Ras protein by farnesyl transferase is a critical step for the Ras functional activity, the farnesyl transferase inhibitor could affect H-Ras functions and the inhibitors such as arteminolide, SCH66336 and LB42908 completely inhibited Ras-farnesylation. However, they did not induce apoptosis of H-Ras-transformed cells with concentration for blocking H-Ras farnesylation. To determine the antitumor effects of the inhibitors, it was analyzed through the expression profile of genes, regulated by activated H-Ras or FTIs by using cDNA microarray. On the basis of the results, the relationship between H-Ras and MMPs expression was confirmed by RT-PCR, Western bolt, zymographic analysis and angiogenesis assay. Our results suggested that activation of MMP-13 as well as MMP-9 induced by H-Ras is involved in angiogenesis and with farnesyl transferase inhibitors, in part, exerts their anticancer effects. We confirmed that MMP-13 is a critical H-Ras target gene through chemical genomic approaches with farnesyl transferase inhibitors.

Regulation of cell adhesion by protein-tyrosine phosphatases: II. Cell-cell adhesion

Cell-cell adhesion is critical to the development and maintenance of multicellular organisms. The stability of many adhesions is regulated by protein tyrosine phosphorylation of cell adhesion molecules and their associated components, with high levels of phosphorylation promoting disassembly. The level of tyrosine phosphorylation reflects the balance between protein-tyrosine kinase and protein-tyrosine phosphatase activity. Many protein-tyrosine phosphatases associate with the cadherin-catenin complex, directly regulating the phosphorylation of these proteins, thereby affecting their interactions and the integrity of cell-cell junctions. Tyrosine phosphatases can also affect cell-cell adhesions indirectly by regulating the signaling pathways that control the activities of Rho family G proteins. In addition, receptor-type tyrosine phosphatases can mediate outside-in signaling through both ligand binding and dimerization of their extracellular domains. This review will discuss the role of protein-tyrosine phosphatases in cell-cell interactions, with an emphasis on cadherin-mediated adhesions.

Analysis of activated GAPs and GEFs in cell lysates

An assay was developed that allows the precipitation of the active pools of Rho-GEFs, Rho-GAPs, or effectors from cell or tissue lysates. This assay can be used to identify GEFs, GAPs, and effectors involved in specific cellular pathways to determine their GTPase specificity and to monitor the temporal activation of GEFs and GAPs in response to upstream signals.

Tight junctions: molecular architecture and function

Tight junctions are the most apical component of the epithelial junctional complex and are crucial for the formation and functioning of epithelial and endothelial barriers. They regulate selective diffusion of ions and solutes along the paracellular pathway and restrict apical/basolateral intramembrane diffusion of lipids. Research over the past years provided much insight into the molecular composition of tight junctions, and we are starting to understand the mechanisms that permit selective paracellular diffusion. Moreover, a complex network of proteins has been identified at tight junctions that is based on cytoskeleton-linked adaptors that recruit and thereby often regulate different types of signaling components that regulate epithelial proliferation, differentiation, and polarization.

Src and FAK signalling controls adhesion fate and the epithelial-to-mesenchymal transition

Src kinase controls cellular adhesions, including cadherin-based intercellular adhesions and integrin-mediated cell-matrix adhesions. In epithelial cells, Src activation, or increased signalling from migratory growth factor receptors via Src, induces an adhesion switch that enhances dynamic cell-matrix adhesions and migratory capacity while suppressing intercellular contact. Moreover, Src and the associated tyrosine kinase FAK are at the heart of the recently identified crosstalk between integrin- and cadherin-mediated adhesions of epithelial cells, particularly during the epithelial-to-mesenchymal transition.

Integrin-dependent actomyosin contraction regulates epithelial cell scattering

The scattering of Madin-Darby canine kidney cells in vitro mimics key aspects of epithelial-mesenchymal transitions during development, carcinoma cell invasion, and metastasis. Scattering is induced by hepatocyte growth factor (HGF) and is thought to involve disruption of cadherin-dependent cell-cell junctions. Scattering is enhanced on collagen and fibronectin, as compared with laminin1, suggesting possible cross talk between integrins and cell-cell junctions. We show that HGF does not trigger any detectable decrease in E-cadherin function, but increases integrin-mediated adhesion. Time-lapse imaging suggests that tension on cell-cell junctions may disrupt cell-cell adhesion. Varying the density and type of extracellular matrix proteins shows that scattering correlates with stronger integrin adhesion and increased phosphorylation of the myosin regulatory light chain. To directly test the role of integrin-dependent traction forces, substrate compliance was varied. Rigid substrates that produce high traction forces promoted scattering, in comparison to more compliant substrates. We conclude that integrin-dependent actomyosin traction force mediates the disruption of cell-cell adhesion during epithelial cell scattering.

Actin at cell-cell junctions is composed of two dynamic and functional populations

The ability of epithelial cells to polarize requires cell-cell adhesion mediated by cadherin receptors. During cell-cell contact, the mechanism via which a flat, spread cell shape is changed into a tall, cuboidal epithelial morphology is not known. We found that cadherin-dependent adhesion modulates actin dynamics by triggering changes in actin organization both locally at junctions and within the rest of the cell. Upon induction of cell-cell contacts, two spatial actin populations are distinguishable: junctional actin and peripheral thin bundles. With time, the relative position of these two populations changes and becomes indistinguishable to form a cortical actin ring that is characteristic of mature, fully polarized epithelial cells. Junctional actin and thin actin bundles differ in their actin dynamics and mechanism of formation, and interestingly, have distinct roles during epithelial polarization. Whereas junctional actin stabilizes clustered cadherin receptors at cell-cell contacts, contraction of peripheral actin bundle is essential for an increase in the maximum height at the lateral domain during polarization (cuboidal morphology). Thus, both junctional actin and thin bundles are necessary, and cooperate with each other to generate a polarized epithelial morphology.

Flow cytometry: a new approach for the molecular profiling of breast cancer

The established method in prognosis of breast cancer includes detection of molecular markers, such as the estrogen receptor (ER), progesterone receptor (PR), and HER-2/neu. These markers are routinely checked via immunohistochemistry (IHC). HER-2/neu is also detected by fluorescent in situ hybridization (FISH). Flow cytometric analysis has not yet been used for detection of such markers. Flow cytometry was performed on four established breast cancer cell lines: MCF7, T47D, BT474, MDA-MB-231, and on one normal breast epithelial cell line: MCF10A. Flow cytometric analysis was used for the detection of ER, PR, HER-2/neu, epidermal growth factor receptor (EGFR), and E-cadherin. Currently, EGFR and E-cadherin are not standard predictive factors in determining survival of breast cancer patients, but both may be beneficial to prognosis. Cells undergoing flow cytometric analysis lost marker expression with increasing passage number. The highest expression was found at cells passaged 0-1 times. MCF7, T47D, and BT474 all had similar marker expression patterns. E-cadherin demonstrated a strongly positive pattern with marker expression of 85-92% among the three cell lines. ER, PR, and HER-2/neu demonstrated a weakly positive expression pattern when compared with E-cadherin. Marker expression ranged from 15 to 61%. These three cell lines were almost negative for expression of EGFR where expression ranged from 0 to 6%. MDA-MB-231 had almost no expression of all 5 markers, with positive values ranging from 0 to 5%. MCF10A had weak positive to almost negative expression values of ER, PR, HER-2/neu, and E-cadherin, which ranged from 3 to 13%. EGFR, both surface and cytoplasmic markers, again were not expressed in MCF10A cells with an expression value of <1%. We found that ER, PR, and HER-2/neu marker expressions in 5 out of 5 cell lines were consistent with established expression patterns. EGFR and E-cadherin expression in 4 out of 5 cell lines were also consistent with established expression patterns. We have shown that flow cytometry provides quantitative data on expression patterns of important prognostic markers in breast cancer.