Involvement of caveolin-1 in low shear stress-induced breast cancer cell motility and adhesion: Roles of FAK/Src and ROCK/p-MLC pathways

The impact of tumor microenvironment: unraveling the role of physical cues in breast cancer progression

Metastasis accounts for the vast majority of breast cancer-related fatalities. Although the contribution of genetic and epigenetic modifications to breast cancer progression has been widely acknowledged, emerging evidence underscores the pivotal role of physical stimuli in driving breast cancer metastasis. In this review, we summarize the changes in the mechanics of the breast cancer microenvironment and describe the various forces that impact migrating and circulating tumor cells throughout the metastatic process. We also discuss the mechanosensing and mechanotransducing molecules responsible for promoting the malignant phenotype in breast cancer cells. Gaining a comprehensive understanding of the mechanobiology of breast cancer carries substantial potential to propel progress in prognosis, diagnosis, and patient treatment.

Hydrodynamic shear stress' impact on mammalian cell properties and its applications in 3D bioprinting

As an effective cell assembly method, three-dimensional bioprinting has been widely used in building organ models and tissue repair over the past decade. However, different shear stresses induced throughout the entire printing process can cause complex impacts on cell integrity, including reducing cell viability, provoking morphological changes and altering cellular functionalities. The potential effects that may occur and the conditions under which these effects manifest are not clearly understood. Here, we review systematically how different mammalian cells respond under shear stress. We enumerate available experimental apparatus, and we categorise properties that can be affected under disparate stress patterns. We also summarise cell damaging mathematical models as a predicting reference for the design of bioprinting systems. We concluded that it is essential to quantify specific cell resistance to shear stress for the optimisation of bioprinting systems. Besides, as substantial positive impacts, including inducing cell alignment and promoting cell motility, can be generated by shear stress, we suggest that we find the proper range of shear stress and actively utilise its positive influences in the development of future systems.

Recent progress of mechanosensitive mechanism on breast cancer

The mechanical environment is important for tumorigenesis and progression. Tumor cells can sense mechanical signals by mechanosensitive receptors, and these mechanical signals can be converted to biochemical signals to regulate cell behaviors, such as cell differentiation, proliferation, migration, apoptosis, and drug resistance. Here, we summarized the effects of the mechanical microenvironment on breast cancer cell activity, and mechanotransduction mechanism from cellular microenvironment to cell membrane, and finally to the nucleus, and also relative mechanosensitive proteins, ion channels, and signaling pathways were elaborated, therefore the mechanical signal could be transduced to biochemical or molecular signal. Meanwhile, the mechanical models commonly used for biomechanics study in vitro and some quantitative descriptions were listed. It provided an essential theoretical basis for the occurrence and development of mechanosensitive breast cancer, and also some potential drug targets were proposed to treat such disease.

Biophysics in tumor growth and progression: from single mechano-sensitive molecules to mechanomedicine

Evidence from physical sciences in oncology increasingly suggests that the interplay between the biophysical tumor microenvironment and genetic regulation has significant impact on tumor progression. Especially, tumor cells and the associated stromal cells not only alter their own cytoskeleton and physical properties but also remodel the microenvironment with anomalous physical properties. Together, these altered mechano-omics of tumor tissues and their constituents fundamentally shift the mechanotransduction paradigms in tumorous and stromal cells and activate oncogenic signaling within the neoplastic niche to facilitate tumor progression. However, current findings on tumor biophysics are limited, scattered, and often contradictory in multiple contexts. Systematic understanding of how biophysical cues influence tumor pathophysiology is still lacking. This review discusses recent different schools of findings in tumor biophysics that have arisen from multi-scale mechanobiology and the cutting-edge technologies. These findings range from the molecular and cellular to the whole tissue level and feature functional crosstalk between mechanotransduction and oncogenic signaling. We highlight the potential of these anomalous physical alterations as new therapeutic targets for cancer mechanomedicine. This framework reconciles opposing opinions in the field, proposes new directions for future cancer research, and conceptualizes novel mechanomedicine landscape to overcome the inherent shortcomings of conventional cancer diagnosis and therapies.

Shear stress regulation of nanoparticle uptake in vascular endothelial cells

Nanoparticles (NPs) hold tremendous targeting potential in cardiovascular disease and regenerative medicine, and exciting clinical applications are coming into light. Vascular endothelial cells (ECs) exposure to different magnitudes and patterns of shear stress (SS) generated by blood flow could engulf NPs in the blood. However, an unclear understanding of the role of SS on NP uptake is hindering the progress in improving the targeting of NP therapies. Here, the temporal and spatial distribution of SS in vascular ECs and the effect of different SS on NP uptake in ECs are highlighted. The mechanism of SS affecting NP uptake through regulating the cellular ROS level, endothelial glycocalyx and membrane fluidity is summarized, and the molecules containing clathrin and caveolin in the engulfment process are elucidated. SS targeting NPs are expected to overcome the current bottlenecks and change the field of targeting nanomedicine. This assessment on how SS affects the cell uptake of NPs and the marginalization of NPs in blood vessels could guide future research in cell biology and vascular targeting drugs.

Biophysical cues to improve the immunomodulatory capacity of mesenchymal stem cells: The progress and mechanisms

Mesenchymal stem cells (MSCs) can maintain immune homeostasis and many preclinical trials with MSCs have been carried out around the world. In vitro culture of MSCs has been found to result in the decline of immunomodulatory capacity, migration and proliferation. To address these problems, simulating the extracellular environment for preconditioning of MSCs is a promising and inexpensive method. Biophysical cues in the external environment that MSCs are exposed to have been shown to affect MSC migration, residency, differentiation, secretion, etc. We review the main ways in which MSCs exert their immunomodulatory ability, and summarize recent advances in mechanical preconditioning of MSCs to enhance immunomodulatory capacity and related mechanical signal sensing and transduction mechanisms.

Caveolae Mechanotransduction at the Interface between Cytoskeleton and Extracellular Matrix

The plasma membrane (PM) is subjected to multiple mechanical forces, and it must adapt and respond to them. PM invaginations named caveolae, with a specific protein and lipid composition, play a crucial role in this mechanosensing and mechanotransduction process. They respond to PM tension changes by flattening, contributing to the buffering of high-range increases in mechanical tension, while novel structures termed dolines, sharing Caveolin1 as the main component, gradually respond to low and medium forces. Caveolae are associated with different types of cytoskeletal filaments, which regulate membrane tension and also initiate multiple mechanotransduction pathways. Caveolar components sense the mechanical properties of the substrate and orchestrate responses that modify the extracellular matrix (ECM) according to these stimuli. They perform this function through both physical remodeling of ECM, where the actin cytoskeleton is a central player, and via the chemical alteration of the ECM composition by exosome deposition. Here, we review mechanotransduction regulation mediated by caveolae and caveolar components, focusing on how mechanical cues are transmitted through the cellular cytoskeleton and how caveolae respond and remodel the ECM.

Cell response to mechanical microenvironment cues via Rho signaling: From mechanobiology to mechanomedicine

Mechanical cues in the cell microenvironment such as those from extracellular matrix properties, stretching, compression and shear stress, play a critical role in maintaining homeostasis. Upon sensing mechanical stimuli, cells can translate these external forces into intracellular biochemical signals to regulate their cellular behaviors, but the specific mechanisms of mechanotransduction at the molecular level remain elusive. As a subfamily of the Ras superfamily, Rho GTPases have been recognized as key intracellular mechanotransduction mediators that can regulate multiple cell activities such as proliferation, migration and differentiation as well as biological processes such as cytoskeletal dynamics, metabolism, and organ development. However, the upstream mechanosensors for Rho proteins and downstream effectors that respond to Rho signal activation have not been well illustrated. Moreover, Rho-mediated mechanical signals in previous studies are highly context-dependent. In this review, we systematically summarize the types of mechanical cues in the cell microenvironment and provide recent advances on the roles of the Rho-based mechanotransduction in various cell activities, physiological processes and diseases. Comprehensive insights into the mechanical roles of Rho GTPase partners would open a new paradigm of mechanomedicine for a variety of diseases. STATEMENT OF SIGNIFICANCE: In this review, we highlight the critical role of Rho GTPases as signal mediators to respond to physical cues in microenvironment. This article will add a distinct contribution to this set of knowledge by intensively addressing the relationship between Rho signaling and mechanobiology/mechanotransduction/mechanomedcine. This topic has not been discussed by the journal, nor has it yet been developed by the field. The comprehensive picture that will develop, from molecular mechanisms and engineering methods to disease treatment strategies, represents an important and distinct contribution to the field. We hope that this review would help researchers in various fields, especially clinicians, oncologists and bioengineers, who study Rho signal pathway and mechanobiology/mechanotransduction, understand the critical role of Rho GTPase in mechanotransduction.

Shear stress enhances anoikis resistance of cancer cells through ROS and NO suppressed degeneration of Caveolin-1

Circulating tumor cells (CTCs) acquire enhanced anti-anoikis abilities after experiencing flow shear stress in the circulatory system. Our previous study demonstrated that low shear stress (LSS) promotes anoikis resistance of human breast carcinoma cells via caveolin-1 (Cav-1)-dependent extrinsic and intrinsic apoptotic pathways. However, the underlying mechanism how LSS enhanced Cav-1 expression in suspended cancer cells remains unclear. Herein, we found that LSS induced redox signaling was involved in the regulation of Cav-1 level and anoikis resistance in suspension cultured cancer cells. Exposure of human breast carcinoma MDA-MB-231 cells to LSS (2 dyn/cm²) markedly induced ROS and ^•NO generation, which promoted the cell viability and reduced the cancer cell apoptosis. Furthermore, ROS and ^•NO scavenging inhibited the upregulation of Cav-1 by interfering ubiquitination, and suppressed the anoikis resistance of suspended tumor cells. These findings provide new insight into the mechanism by which LSS-stimulated ROS and ^•NO generation increases Cav-1 stabilization in suspended cancer cells through inhibition of ubiquitination and proteasomal degradation, which could be a potential target for therapy of metastatic tumors.

Functions and clinical significance of mechanical tumor microenvironment: cancer cell sensing, mechanobiology and metastasis

Dynamic and heterogeneous interaction between tumor cells and the surrounding microenvironment fuels the occurrence, progression, invasion, and metastasis of solid tumors. In this process, the tumor microenvironment (TME) fractures cellular and matrix architecture normality through biochemical and mechanical means, abetting tumorigenesis and treatment resistance. Tumor cells sense and respond to the strength, direction, and duration of mechanical cues in the TME by various mechanotransduction pathways. However, far less understood is the comprehensive perspective of the functions and mechanisms of mechanotransduction. Due to the great therapeutic difficulties brought by the mechanical changes in the TME, emerging studies have focused on targeting the adverse mechanical factors in the TME to attenuate disease rather than conventionally targeting tumor cells themselves, which has been proven to be a potential therapeutic approach. In this review, we discussed the origins and roles of mechanical factors in the TME, cell sensing, mechano‐biological coupling and signal transduction, in vitro construction of the tumor mechanical microenvironment, applications and clinical significance in the TME.

The raft cytoskeleton binding protein complexes personate functional regulators in cell behaviors

Several cytoskeleton proteins interact with raft proteins to form raft-cytoskeleton binding protein complexes (RCPCs) that control cell migration and adhesion. The purpose of this paper is to review the latest research on the modes and mechanisms by which a RCPC controls different cellular functions. This paper discusses RCPC composition and its role in cytoskeleton reorganization, as well as the latest developments in molecular mechanisms that regulate cell adhesion and migration under normal conditions. In addition, the role of some external stimuli (such as stress and chemical signals) in this process is further debated, and meanwhile potential mechanisms for RCPC to regulate lipid raft fluidity is proposed. Thus, this review mainly contributes to the understanding of RCPC signal transduction in cells. Additionally, the targeted signal transduction of RCPC and its mechanism connection with cell behaviors will provide a logical basis for the development of unified interventions to combat metastasis related dysfunction and diseases.

Non-muscle myosin II isoforms orchestrate substrate stiffness sensing to promote cancer cell contractility and migration

The stiffening of the extracellular matrix (ECM) during tumor progression results in an increase in cancer cell motility. In cell migration, two major isoforms of non-muscle myosin II (NMII), NMIIA and NMIIB, are expressed and assembled into the cytoskeleton. However, the isoform-specific regulatory roles of NMIIA and NMIIB as well as the underlying mechanisms in response to mechanical cues of the ECM are still elusive. Here, based on polyacrylamide (PAA) gels with tunable elastic modulus, we mimicked the mechanical properties of tumor tissue at different stages of breast cancer in vitro and investigated the distinct roles of NMII isoforms in the regulation of substrate stiffness. We demonstrate that NMIIA is engaged in establishing cell polarity by facilitating lamellipodia formation, focal adhesion turnover, and actin polymerization at the cell leading edge, while NMIIB is recruited to the cell perinuclear region and contributes to traction force generation and polarized distribution, both in a substrate stiffness-dependent manner. We further validated that substrate stiffness modulates the distribution and activation of NMII isoforms via the Rac1/p-PAK1/pS1916-NMIIA and PKCζ/pS1935-NMIIB signaling pathways in a site- and kinase-specific phosphoregulation manner. Our study is helpful for understanding the mechanotransduction of cancer cells and provides inspiration for molecular targets in antimetastatic therapy.

Mechanobiology of Pulmonary Diseases: A Review of Engineering Tools to Understand Lung Mechanotransduction

Cells within the lung micro-environment are continuously subjected to dynamic mechanical stimuli which are converted into biochemical signaling events in a process known as mechanotransduction. In pulmonary diseases, the abrogated mechanical conditions modify the homeostatic signaling which influences cellular phenotype and disease progression. The use of in vitro models has significantly expanded our understanding of lung mechanotransduction mechanisms. However, our ability to match complex facets of the lung including three-dimensionality, multicellular interactions, and multiple simultaneous forces is limited and it has proven difficult to replicate and control these factors in vitro. The goal of this review is to (a) outline the anatomy of the pulmonary system and the mechanical stimuli that reside therein, (b) describe how disease impacts the mechanical micro-environment of the lung, and (c) summarize how existing in vitro models have contributed to our current understanding of pulmonary mechanotransduction. We also highlight critical needs in the pulmonary mechanotransduction field with an emphasis on next-generation devices that can simulate the complex mechanical and cellular environment of the lung. This review provides a comprehensive basis for understanding the current state of knowledge in pulmonary mechanotransduction and identifying the areas for future research.

Shear stress triggered circular dorsal ruffles formation to facilitate cancer cell migration

Circular dorsal ruffles (CDRs) are a kind of special ring-shaped membrane structure rich in F-actin, it is highly involved in the invasion-metastasis of tumor. Shear stress is one of the biophysical elements that affects the fate of tumor cells. However, how shear stress contributes to the CDRs formation is still unclear. In this study, we found that shear stress stimulated the formation of CDRs and promoted the migration of human breast MDA-MB-231 carcinoma cells. Integrin-linked kinase (ILK) mediated the recruiting of ADP-ribosylation factors (ARAP1/Arf1) to CDRs. Meanwhile, the transfection of ARAP1 or Arf1 mutant decreased the number of cells with CDRs, the CDRs areas and perimeters, thus blocked the cancer cell migration. This indicated that the ARAP1/Arf1 were necessary for the CDRs formation and cancer cell migration. Further study revealed that shear stress could stimulate the formation of intracellular macropinocytosis (MPS) thus promoted the ARAP1/Arf1 transportation to early endosome to regulate cancer cell migration after the depolymerization of CDRs. Our study elucidates that the CDRs formation is essential in shear stress-induced breast cancer cell migration, which provides a new research target for exploring the cytoskeletal mechanisms of breast cancer malignance.

Mechanobiology of Autophagy: The Unexplored Side of Cancer

Proper execution of cellular function, maintenance of cellular homeostasis and cell survival depend on functional integration of cellular processes and correct orchestration of cellular responses to stresses. Cancer transformation is a common negative consequence of mismanagement of coordinated response by the cell. In this scenario, by maintaining the balance among synthesis, degradation, and recycling of cytosolic components including proteins, lipids, and organelles the process of autophagy plays a central role. Several environmental stresses activate autophagy, among those hypoxia, DNA damage, inflammation, and metabolic challenges such as starvation. In addition to these chemical challenges, there is a requirement for cells to cope with mechanical stresses stemming from their microenvironment. Cells accomplish this task by activating an intrinsic mechanical response mediated by cytoskeleton active processes and through mechanosensitive protein complexes which interface the cells with their mechano-environment. Despite autophagy and cell mechanics being known to play crucial transforming roles during oncogenesis and malignant progression their interplay is largely overlooked. In this review, we highlight the role of physical forces in autophagy regulation and their potential implications in both physiological as well as pathological conditions. By taking a mechanical perspective, we wish to stimulate novel questions to further the investigation of the mechanical requirements of autophagy and appreciate the extent to which mechanical signals affect this process.

Tyrosine phosphorylation of tumor cell caveolin-1: impact on cancer progression

Caveolin-1 (CAV1) has long been implicated in cancer progression, and while widely accepted as an oncogenic protein, CAV1 also has tumor suppressor activity. CAV1 was first identified in an early study as the primary substrate of Src kinase, a potent oncoprotein, where its phosphorylation correlated with cellular transformation. Indeed, CAV1 phosphorylation on tyrosine-14 (Y14; pCAV1) has been associated with several cancer-associated processes such as focal adhesion dynamics, tumor cell migration and invasion, growth suppression, cancer cell metabolism, and mechanical and oxidative stress. Despite this, a clear understanding of the role of Y14-phosphorylated pCAV1 in cancer progression has not been thoroughly established. Here, we provide an overview of the role of Src-dependent phosphorylation of tumor cell CAV1 in cancer progression, focusing on pCAV1 in tumor cell migration, focal adhesion signaling and metabolism, and in the cancer cell response to stress pathways characteristic of the tumor microenvironment. We also discuss a model for Y14 phosphorylation regulation of CAV1 effector protein interactions via the caveolin scaffolding domain.

Microfluidic Systems with Embedded Cell Culture Chambers for High-Throughput Biological Assays

The ability to generate chemical and mechanical gradients on chips is important for either creating biomimetic designs or enabling high-throughput assays. However, there is still a significant knowledge gap in the generation of mechanical and chemical gradients in a single device. In this study, we developed gradient-generating microfluidic circuits with integrated microchambers to allow cell culture and to introduce chemical and mechanical gradients to cultured cells. A chemical gradient is generated across the microchambers, exposing cells to a uniform concentration of drugs. The embedded microchamber also produces a mechanical gradient in the form of varied shear stresses induced upon cells among different chambers as well as within the same chamber. Cells seeded within the chambers remain viable and show a normal morphology throughout the culture time. To validate the effect of different drug concentrations and shear stresses, doxorubicin is flowed into chambers seeded with skin cancer cells at different flow rates (from 0 to 0.2 μL/min). The experimental results show that increasing doxorubicin concentration (from 0 to 30 μg/mL) within chambers not only prohibits cell growth but also induces cell death. In addition, the increased shear stress (0.005 Pa) at high flow rates poses a synergistic effect on cell viability by inducing cell damage and detachment. Moreover, the ability of the device to seed cells in a 3D microenvironment was also examined and confirmed. Collectively, the study demonstrates the potential of microchamber-embedded microfluidic gradient generators in 3D cell culture and high-throughput drug screening.

Caveolin-1 promotes trophoblast cell invasion through the focal adhesion kinase (FAK) signalling pathway during early human placental development

Normal implantation and placental development depend on the appropriate differentiation and invasion of trophoblast cells. Inadequate trophoblast cell invasion results in pregnancy-related disorders, which endanger both mother and fetus; however, the mechanism of early placental development has not been fully explained. In this study we conducted gene expression profile analysis using mouse placental tissues at different developmental stages (embryonic day (E)7.5, E14.5 and E19.5) using series tests of cluster (STC) and Kyoto Encyclopaedia of Genes and Genomes (KEGG) pathway analyses. Focal adhesion kinase (FAK) signalling pathway-related gene expression levels were verified using quantitative reverse transcription polymerase chain reaction and western blot. The results showed that caveolin-1 (Cav1) was downregulated in the placenta of unexplained spontaneous abortion subjects compared with that of induced abortion. Furthermore, by modulating CAV1 expression levels, CAV1 was shown to promote human trophoblast cell proliferation, migration and invasion by activating the FAK signalling pathway. These results indicate that CAV1 and the FAK signalling pathway are crucial for early placental development, which sheds new light on our understanding of the mechanisms of human trophoblast cell invasion and early development of the placenta.

Biophysical signal transduction in cancer cells: Understanding its role in cancer pathogenesis and treatment

Signaling between cells can promote both the development and progression of cancer. It has been found that chemical and physical signals, together with extracellular factors, can influence cancer progression. In this review, we focus on the physical microenvironment of cancer cells and examine the action of mechanical, electromagnetic, thermal, and acoustic signals on cancer cells, which may provide new directions for cancer research and treatment.

Activation of cell migration via morphological changes in focal adhesions depends on shear stress in MYCN-amplified neuroblastoma cells

Neuroblastoma is the most common solid tumour of childhood, and it metastasizes to distant organs. However, the mechanism of metastasis, which generally depends on the cell motility of the neuroblastoma, remains unclear. In many solid tumours, it has been reported that shear stress promotes metastasis. Here, we investigated the relationship between shear stress and cell motility in the MYCN-amplified human neuroblastoma cell line IMR32, using a microfluidic device. We confirmed that most of the cells migrated downstream, and cell motility increased dramatically when the cells were exposed to a shear stress of 0.4 Pa, equivalent to that expected in vivo. We observed that the morphological features of focal adhesion were changed under a shear stress of 0.4 Pa. We also investigated the relationship between malignancy and the motility of IMR32 cells under shear stress. Decreasing the expression of MYCN in IMR32 cells via siRNA transfection inhibited cell motility by a shear stress of 0.4 Pa. These results suggest that MYCN-amplified neuroblastoma cells under high shear stress migrate to distant organs due to high cell motility, allowing cell migration to lymphatic vessels and venules.

Hypoxic induction of vasculogenic mimicry in hepatocellular carcinoma: role of HIF-1 α, RhoA/ROCK and Rac1/PAK signaling

BACKGROUND

Vasculogenic mimicry (VM), defined as a capability of aggressive tumor Cells to mimic embryonic vasculogenic networks, caused poor prognosis in hepatocellular carcinoma (HCC). Rho kinases (ROCK), p21-activated kinase (PAK), hypoxia or epithelial-mesenchymal transition (EMT) contributed to the VM potential. However, the details underlying these biological behaviors have not been completely elucidated.

METHODS

Kaplan-Meier analysis was conducted to predict relationship with hypoxia Inducible factor (HIF-1α), EMT related markers: Vimentin and patient prognosis. CD34/periodic acid-Schiff (PAS) double staining was examined to differentiate VM-positive (VM+) and VM-negative (VM-) samples. Cells were cultured under controlled hypoxic environments (1% O2) or normoxic conditions. The effect of hypoxia on RhoA/ROCK, Rac1/PAK and EMT were evaluated by real time-qPCR and western blot. HIF-1α small interfering RNA (siRNA), overexpressed or short hairpin RNA (shRNA) of ROCK and kinase inhibitors were used to explore the effect of HIF-1α, RhoA/ROCK, Rac1/PAK and Vimentin on VM.

RESULTS

HIF-1α or Vimentin was upregulated in VM+ HCC tissues, compared to non-cancerous tissues (P < 0.01), and patients with high expression of HIF-1α or Vimentin had worse prognosis (P < 0.001). We showed hypoxia induced RhoA/ROCK and Rac1/PAK signaling transduction, and EMT could be repressed by HIF-1α siRNA. Notably, RhoA/ROCK or Rac1/PAK stabilized HIF-1α in hypoxia, whereas HIF-1α did not significantly altered RhoA/ROCK or Rac1/PAK signaling in hypoxia. Moreover, we found distinct roles of ROCK1, ROCK2 and PAK in regulating Vimentin phosphorylation.

CONCLUSIONS

RhoA/ROCK and Rac/PAK signaling played crucial roles in hypoxia-induced VM via Ser72 and Ser56 Vimentin phosphorylation in HCC.

The role of polarisation of circulating tumour cells in cancer metastasis

Metastasis is the spread of cancer cells from a primary tumour to a distant site of the body. Metastasising tumour cells have to survive and readjust to different environments, such as heterogeneous solid tissues and liquid phase in lymph- or blood circulation, which they achieve through a high degree of plasticity that renders them adaptable to varying conditions. One defining characteristic of the metastatic process is the transition of tumour cells between different polarised phenotypes, ranging from differentiated epithelial polarity to migratory front-rear polarity. Here, we review the polarisation types adopted by tumour cells during the metastatic process and describe the recently discovered single-cell polarity in liquid phase observed in circulating tumour cells. We propose that single-cell polarity constitutes a mode of polarisation of the cell cortex that is uncoupled from the intracellular polarisation machinery, which distinguishes single-cell polarity from other types of polarity identified so far. We discuss how single-cell polarity can contribute to tumour metastasis and the therapeutic potential of this new discovery.

Leptin Promotes Expression of EMT-Related Transcription Factors and Invasion in a Src and FAK-Dependent Pathway in MCF10A Mammary Epithelial Cells

Leptin is one of the main adipokines secreted in breast tissue. Leptin promotes epithelial-mesenchymal transition (EMT), cell migration and invasion in epithelial breast cells, leading to tumor progression. Although, the molecular mechanisms that underlie these events are not fully understood, the activation of different signaling pathways appears to be essential. In this sense, the effects of leptin on the activation of kinases like Src and FAK, which regulate signaling pathways that activate the EMT program, are not completely described. Therefore, we investigated the involvement of these kinases using an in vitro model for leptin-induced EMT process in the non-tumorigenic MCF10A cell line. To this end, MCF10A cells were stimulated with leptin, and Src and FAK activation was assessed. Specific events occurring during EMT were also evaluated in the presence or absence of the kinases' chemical inhibitors PP2 and PF-573228. For instance, we tested the expression and subcellular localization of the EMT-related transcription factors Twist and β-catenin, by western blot and immunofluorescence. We also evaluated the secretion and activation of matrix metalloproteases (MMP-2 and MMP-9) by gelatin zymography. Invasiveness properties of leptin-stimulated cells were determined by invadopodia formation assays, and by the Transwell chamber method. Our results showed that leptin promotes EMT through Src and FAK activation, which leads to the secretion and activation of MMP-2 and MMP-9, invadopodia formation and cell invasion in MCF10A cells. In conclusion, our data suggest that leptin promotes an increase in the expression levels of Twist and β-catenin, the secretion of MMP-2, MMP-9, the invadopodia formation and invasion in MCF10A cells in a Src and FAK-dependent manner.

Fluid shear stress stimulates breast cancer cells to display invasive and chemoresistant phenotypes while upregulating PLAU in a 3D bioreactor

Breast cancer cells experience a range of shear stresses in the tumor microenvironment (TME). However most current in vitro three-dimensional (3D) models fail to systematically probe the effects of this biophysical stimuli on cancer cell metastasis, proliferation, and chemoresistance. To investigate the roles of shear stress within the mammary and lung pleural effusion TME, a bioreactor capable of applying shear stress to cells within a 3D extracellular matrix was designed and characterized. Breast cancer cells were encapsulated within an interpenetrating network hydrogel and subjected to shear stress of 5.4 dynes cm^-2 for 72 hr. Finite element modeling assessed shear stress profiles within the bioreactor. Cells exposed to shear stress had significantly higher cellular area and significantly lower circularity, indicating a motile phenotype. Stimulated cells were more proliferative than static controls and showed higher rates of chemoresistance to the anti-neoplastic drug paclitaxel. Fluid shear stress-induced significant upregulation of the PLAU gene and elevated urokinase activity was confirmed through zymography and activity assay. Overall, these results indicate that pulsatile shear stress promotes breast cancer cell proliferation, invasive potential, chemoresistance, and PLAU signaling.

Src and ROCK Kinases Differentially Regulate Mineralization of Human Osteosarcoma Saos-2 Cells

Osteoblasts initiate bone mineralization by releasing matrix vesicles (MVs) into the extracellular matrix (ECM). MVs promote the nucleation process of apatite formation from Ca²⁺ and P_i in their lumen and bud from the microvilli of osteoblasts during bone development. Tissue non-specific alkaline phosphatase (TNAP) as well as annexins (among them, AnxA6) are abundant proteins in MVs that are engaged in mineralization. In addition, sarcoma proto-oncogene tyrosine-protein (Src) kinase and Rho-associated coiled-coil (ROCK) kinases, which are involved in vesicular transport, may also regulate the mineralization process. Upon stimulation in osteogenic medium containing 50 μg/mL of ascorbic acid (AA) and 7.5 mM of β-glycerophosphate (β-GP), human osteosarcoma Saos-2 cells initiated mineralization, as evidenced by Alizarin Red-S (AR-S) staining, TNAP activity, and the partial translocation of AnxA6 from cytoplasm to the plasma membrane. The addition of 4-amino-5-(4-chlorophenyl)-7-(t-butyl)pyrazolo [3,4-d] pyrimidine (PP2), which is an inhibitor of Src kinase, significantly inhibited the mineralization process when evaluated by the above criteria. In contrast, the addition of (R)-(+)-trans-4-(1-aminoethyl)-N-(4-pyridyl) cyclohexane carboxamide hydrochloride (Y-27632), which is an inhibitor of ROCK kinase, did not affect significantly the mineralization induced in stimulated Saos-2 cells as denoted by AR-S and TNAP activity. In conclusion, mineralization by human osteosarcoma Saos-2 cells seems to be differently regulated by Src and ROCK kinases.

Alteration in gene expression profiles of thymoma: Genetic differences and potential novel targets

BACKGROUND

This study was conducted to investigate the gene expression profiles associated with thymoma to better understand the molecular mechanism underlying the pathogenesis of thymoma.

METHODS

Eight patients with thymomas (type A, AB, B1, and B2) and four controls with thymic cysts were analyzed using microarray profiling to identify changes in gene expression.

RESULTS

Across all of our samples, 2319 messenger RNAs were upregulated and 2776 were downregulated in thymomas relative to thymic cysts. Gene ontology and pathway analyses revealed that a large number of genes participate in cellular functions, among which MHC class II protein complex assembly, assembly with peptide antigen, calcium activated phosphatidylcholine scrambling, and release of cytoplasmic sequestered NF-κB were dysregulated, whereas intestinal immune network for immunoglobulin A production, cytokine-cytokine receptor interaction, the calcium signaling pathway, and pathways related to autoimmune diseases were downregulated.

CONCLUSIONS

Our results revealed gene expression differences between thymomas and thymic cysts, and identified key candidate genes/pathways that might be used as diagnostic markers and potential therapeutic targets to treat cancer metastasis.

ROCK isoforms differentially modulate cancer cell motility by mechanosensing the substrate stiffness

Tumors are characterized by extracellular matrix (ECM) remodeling and stiffening. The importance of ECM stiffness in cancer is well known. However, the biomechanical behavior of tumor cells and the underlying mechanotransduction pathways remain unclear. Here, we used polyacrylamide (PAA) substrates to simulate tissue stiffness at different progress stages of breast cancer in vitro, and we observed that moderate substrate stiffness promoted breast cancer cell motility. The substrate stiffness directly activated integrin β1 and focal adhesion kinase (FAK), which accelerate focal adhesion (FA) maturation and induce the downstream cascades of intracellular signals of the RhoA/ROCK pathway. Interestingly, the differential regulatory mechanism between two ROCK isoforms (ROCK1 and ROCK2) in cell motility and mechanotransduction was clearly identified. ROCK1 phosphorylated the myosin regulatory light chain (MRLC) and facilitated the generation of traction force, while ROCK2 phosphorylated cofilin and regulated the cytoskeletal remodeling by suppressing F-actin depolymerization. The ROCK isoforms differentially regulated the pathways of RhoA/ROCK1/p-MLC and RhoA/ROCK2/p-cofilin in a coordinate fashion to modulate breast cancer cell motility in a substrate stiffness-dependent manner through integrin β1-activated FAK signaling. Our findings provide new insights into the mechanisms of matrix mechanical property-induced cancer cell migration and malignant behaviors. STATEMENT OF SIGNIFICANCE: Here, we examined the relationship between substrate stiffness and tumor cellular motility by using polyacrylamide (PAA) substrates to simulate the stages in vivo of breast cancer. The results elucidated the different regulatory roles between the two ROCK isoforms in cell motility and demonstrated that stiff substrate (38 kPa) mediated RhoA/ROCK1/p-MLC and RhoA/ROCK2/p-cofilin pathways through integrin β1-FAK activation and eventually promoted directional migration. Our discoveries would have significant implications in the understanding of the interaction between cancer cells and tumor microenvironments, and hence, it might provide new insights into the metastasis inhibition, which could be an adjuvant way of cancer therapy.

Caveolin-1: a multifaceted driver of breast cancer progression and its application in clinical treatment

Human breast cancer is one of the most frequent cancer diseases and causes of death among female population worldwide. It appears at a high incidence and has a high malignancy, mortality, recurrence rate and poor prognosis. Caveolin-1 (Cav1) is the main component of caveolae and participates in various biological events. More and more experimental studies have shown that Cav1 plays a critical role in the progression of breast cancer including cell proliferation, apoptosis, autophagy, invasion, migration and breast cancer metastasis. Besides, Cav1 has been found to be involved in chemotherapeutics and radiotherapy resistance, which are still the principal problems encountered in clinical breast cancer treatment. In addition, stromal Cav1 may be a potential indicator for breast cancer patients' prognosis. In the current review, we cover the state-of-the-art study, development and progress on Cav1 and breast cancer, altogether describing the role of Cav1 in breast cancer progression and application in clinical treatment, in the hope of providing a basis for further research and promoting CAV1 gene as a potential target to diagnose and treat aggressive breast cancers.

FAK is Required for Tumor Metastasis-Related Fluid Microenvironment in Triple-Negative Breast Cancer

Cancer cell metastasis is the main cause of death in patients with cancer. Many studies have investigated the biochemical factors that affect metastasis; however, the role of physical factors such as fluid shear stress (FSS) in tumorigenesis and metastasis have been less investigated. Triple-negative breast cancer (TNBC) has a higher incidence of lymph node invasion and distant metastasis than other subtypes of breast cancer. In this study, we investigated the influence of FSS in regulating the malignant behavior of TNBC cells. Our data demonstrate that low FSS promotes cell migration, invasion, and drug resistance, while high FSS has the opposite results; additionally, we found that these phenomena were regulated through focal adhesion kinase (FAK). Using immunohistochemistry staining, we show that FAK levels correlate with the nodal stage and that FAK is a significant independent predictor of overall survival in patients. Altogether, these data implicate FAK as a fluid mechano-sensor that regulates the cell motility induced by FSS and provide a strong rationale for cancer treatments that combine the use of anti-cancer drugs and strategies to modulate tumor interstitial fluid flow.

Review: Mechanotransduction in ovarian cancer: Shearing into the unknown

Ovarian cancer remains a deadly diagnosis with an 85% recurrence rate and a 5-year survival rate of only 46%. The poor outlook of this disease has improved little over the past 50 years owing to the lack of early detection, chemoresistance and the complex tumor microenvironment. Within the peritoneal cavity, the presence of ascites stimulates ovarian tumors with shear stresses. The stiff environment found within the tumor extracellular matrix and the peritoneal membrane are also implicated in the metastatic potential and epithelial to mesenchymal transition (EMT) of ovarian cancer. Though these mechanical cues remain highly relevant to the understanding and treatment of ovarian cancers, our current knowledge of their biological processes and their clinical relevance is deeply lacking. Seminal studies on ovarian cancer mechanotransduction have demonstrated close ties between mechanotransduction and ovarian cancer chemoresistance, EMT, enhanced cancer stem cell populations, and metastasis. This review summarizes our current understanding of ovarian cancer mechanotransduction and the gaps in knowledge that exist. Future investigations on ovarian cancer mechanotransduction will greatly improve clinical outcomes via systematic studies that determine shear stress magnitude and its influence on ovarian cancer progression, metastasis, and treatment.

Shear stress promotes anoikis resistance of cancer cells via caveolin-1-dependent extrinsic and intrinsic apoptotic pathways

Circulating tumor cells (CTCs) need to acquire resistance to anoikis to survive after they experience fluid shear stress in the circulatory and lymphatic systems. However, the mechanism by which tumor cells resist anoikis under shear stress conditions remains unknown. Here, we found that the application of low shear stress (LSS; 2 dyn/cm² ) to human breast carcinoma cells (MDA-MB-231) resulted in increased anoikis resistance when tumor cells were grown under anchorage-independent conditions. Caveolin-1 (Cav-1), the major component of plasma membrane caveolae, was overexpressed in LSS-treated cells and prevented tumor cells from anoikis, while depletion of Cav-1 restored sensitivity to anoikis. LSS-induced dissociation of Cav-1-Fas inhibited formation of the death-inducing signaling complex, caspase-8 activation, and rendered tumor cells resistant to anoikis. Likewise, LSS blocked the mitochondrial pathway through promotion of integrin β1-focal adhesion kinase-mediated multicellular aggregation and suppression of truncated BID translocation mediated crosstalk between the extrinsic and intrinsic apoptotic pathways. Our findings provide insights into the mechanisms by which LSS induces anoikis resistance in breast carcinoma cells through inhibition of Cav-1-dependent extrinsic and intrinsic apoptotic pathways, and serves as a potential therapeutic target for CTCs and metastatic breast cancer.

Fluid Shear Stress Induces Cell Cycle Arrest in Human Urinary Bladder Transitional Cell Carcinoma Through Bone Morphogenetic Protein Receptor-Smad1/5 Pathway

Introduction

Mechanical force generated from the interstitial fluid flow inside and surrounding tissue has been known to play a significant role in cancer pathophysiology. In this study, we aimed to investigate the role of laminar shear stress (LSS) in modulating the cell cycle of human bladder transitional carcinoma (BFTC-905) cells which are frequently stimulated by not only the interstitial fluid flow, but also the urine flow transported from kidney to bladder in the urinary tract.

Methods

The BFTC-905 cells were subjected to 0-12 dynes cm^-2 LSS for 1, 4, 8, or 12 h, respectively, followed by cellular and molecular assays for investigations of cell cycle regulation protein expressions, cell growth rates, and the potential mechanism.

Results

The results showed that the LSS with ≥ 8 dynes cm^-2 for ≥ 8 h significantly increased protein expressions of cyclin B1, Wee1, p21, and p-CDK1^(Tyr15) (p < 0.05 for each), but conversely decreased protein expressions of cyclin A2, D1, E1, and CDK-1, -2, -4, and -6 (p < 0.05 for each) in the BFTC-905 cells, indicating that a G₂/M cell cycle arrest was obtained after shearing stimulation. Furthermore, our data demonstrated that the LSS-induced G₂/M arrest and the corresponding changes in cell cycle regulatory protein expressions were modulated by bone morphogenetic protein (BMP) receptor-Smad1/5 signaling pathway.

Conclusions

Our findings provided evidences for the effect of mechanical microenvironment on urothelial cancer pathobiology and generated insights into mechanism of LSS-regulated bladder tumor cell cycle.

Feeling Stress: The Mechanics of Cancer Progression and Aggression

The tumor microenvironment is a dynamic landscape in which the physical and mechanical properties evolve dramatically throughout cancer progression. These changes are driven by enhanced tumor cell contractility and expansion of the growing tumor mass, as well as through alterations to the material properties of the surrounding extracellular matrix (ECM). Consequently, tumor cells are exposed to a number of different mechanical inputs including cell–cell and cell-ECM tension, compression stress, interstitial fluid pressure and shear stress. Oncogenes engage signaling pathways that are activated in response to mechanical stress, thereby reworking the cell's intrinsic response to exogenous mechanical stimuli, enhancing intracellular tension via elevated actomyosin contraction, and influencing ECM stiffness and tissue morphology. In addition to altering their intracellular tension and remodeling the microenvironment, cells actively respond to these mechanical perturbations phenotypically through modification of gene expression. Herein, we present a description of the physical changes that promote tumor progression and aggression, discuss their interrelationship and highlight emerging therapeutic strategies to alleviate the mechanical stresses driving cancer to malignancy.

MET Activation and Physical Dynamics of the Metastatic Process: The Paradigm of Cancers of Unknown Primary Origin

The molecular and cellular mechanisms which drive metastatic spread are the topic of constant debate and scientific research due to the potential implications for cancer patients' prognosis. In addition to genetics and environmental factors, mechanics of single cells and physical interaction with the surrounding environment play relevant role in defining invasive phenotype. Reconstructing the physical properties of metastatic clones may help to clarify still open issues in disease progression as well as to lead to new diagnostic and therapeutic approaches. In this perspective cancer of unknown primary origin (CUP) identify the ideal model to study physical interactions and forces involved in the metastatic process. We have previously demonstrated that MET oncogene is mutated with unexpected high frequency in CUPs. We here analyze and discuss how the MET activation by somatic mutation may affect physical properties in giving rise to such a highly malignant syndrome, as that defined by CUP.

MiR-199a/b-5p inhibits hepatocellular carcinoma progression by post-transcriptionally suppressing ROCK1

In this study, we explored the actions of miR-199a/b-5p during hepatocellular carcinoma (HCC) progression and its potential target genes. Through heatmap miRNA expression analysis of 15 matched HCC tumor and adjacent non-tumor liver tissues from the TCGA database, we detected 19 mRNAs that were upregulated and 13 that were downregulated specifically in HCC. Among these, miR-199 family members were downregulated in HCC tumors and cell lines, as compared to controls. Low miR-199a/b-5p expression was also associated with poor overall survival of HCC patients. miR-199a/b-5p overexpression in HCC cell lines inhibited cell proliferation, migration and invasion, both in vitro and in vivo. In addition, miR199-a/b-5p post-transcriptionally suppressed Rho-associated coiled-coil kinase 1 (ROCK1). This in turn led to inhibition of ROCK1/MLC and PI3K/Akt signaling, which is necessary for HCC proliferation and metastasis. These results indicate that miR-199a/b acts as tumor suppressors in HCC and represent promising therapeutic targets.