Distinct biophysical mechanisms of focal adhesion kinase mechanoactivation by different extracellular matrix proteins

Focal adhesion kinase signaling - tumor vulnerabilities and clinical opportunities

Focal adhesion kinase (FAK; encoded by PTK2) was discovered over 30 years ago as a cytoplasmic protein tyrosine kinase that is localized to cell adhesion sites, where it is activated by integrin receptor binding to extracellular matrix proteins. FAK is ubiquitously expressed and functions as a signaling scaffold for a variety of proteins at adhesions and in the cell cytoplasm, and with transcription factors in the nucleus. FAK expression and intrinsic activity are essential for mouse development, with molecular connections to cell motility, cell survival and gene expression. Notably, elevated FAK tyrosine phosphorylation is common in tumors, including pancreatic and ovarian cancers, where it is associated with decreased survival. Small molecule and orally available FAK inhibitors show on-target inhibition in tumor and stromal cells with effects on chemotherapy resistance, stromal fibrosis and tumor microenvironment immune function. Herein, we discuss recent insights regarding mechanisms of FAK activation and signaling, its roles as a cytoplasmic and nuclear scaffold, and the tumor-intrinsic and -extrinsic effects of FAK inhibitors. We also discuss results from ongoing and advanced clinical trials targeting FAK in low- and high-grade serous ovarian cancers, where FAK acts as a master regulator of drug resistance. Although FAK is not known to be mutationally activated, preventing FAK activity has revealed multiple tumor vulnerabilities that support expanding clinical combinatorial targeting possibilities.

TiO2 Nano-Biopatterning Reveals Optimal Ligand Presentation for Cell-Matrix Adhesion Formation

Nanoscale organization of transmembrane receptors is critical for cellular functions, enabled by the nanoscale engineering of bioligand presentation. Previously, a spatial threshold of ≤60 nm for integrin binding ligands in cell-matrix adhesion is demonstrated using monoliganded gold nanoparticles. However, the ligand geometric arrangement is limited to hexagonal arrays of monoligands, while plasmonic quenching limits further investigation by fluorescence-based high-resolution imaging. Here, these limitations are overcome with dielectric TiO2 nanopatterns, eliminating fluorescence quenching, thus enabling super-resolution fluorescence microscopy on nanopatterns. By dual-color super-resolution imaging, high precision and consistency among nanopatterns, bioligands, and integrin nanoclusters are observed, validating the high quality and integrity of both nanopattern functionalization and passivation. By screening TiO2 nanodiscs with various diameters, an increase in fibroblast cell adhesion, spreading area, and Yes-associated protein (YAP) nuclear localization on 100 nm diameter compared with smaller diameters was observed. Focal adhesion kinase is identified as the regulatory signal. These findings explore the optimal ligand presentation when the minimal requirements are sufficiently fulfilled in the heterogenous extracellular matrix network of isolated binding regions with abundant ligands. Integration of high-fidelity nano-biopatterning with super-resolution imaging allows precise quantitative studies to address early signaling events in response to receptor clustering and their nanoscale organization.

Shaping Oncogenic Microenvironments: Contribution of Fibronectin

The extracellular matrix (ECM) is a complex network of proteins and glycans, dynamically remodeled and specifically tailored to the structure/function of each organ. The malignant transformation of cancer cells is determined by both cell intrinsic properties, such as mutations, and extrinsic variables, such as the mixture of surrounding cells in the tumor microenvironment and the biophysics of the ECM. During cancer progression, the ECM undergoes extensive remodeling, characterized by disruption of the basal lamina, vascular endothelial cell invasion, and development of fibrosis in and around the tumor cells resulting in increased tissue stiffness. This enhanced rigidity leads to aberrant mechanotransduction and further malignant transformation potentiating the de-differentiation, proliferation and invasion of tumor cells. Interestingly, this fibrotic microenvironment is primarily secreted and assembled by non-cancerous cells. Among them, the cancer-associated fibroblasts (CAFs) play a central role. CAFs massively produce fibronectin together with type I collagen. This review delves into the primary interactions and signaling pathways through which fibronectin can support tumorigenesis and metastasis, aiming to provide critical molecular insights for better therapy response prediction.

Culture substrate stiffness impacts human myoblast contractility-dependent proliferation and nuclear envelope wrinkling

Understanding how biophysical and biochemical microenvironmental cues together influence the regenerative activities of muscle stem cells and their progeny is crucial in strategizing remedies for pathological dysregulation of these cues in aging and disease. In this study, we investigated the cell-level influences of extracellular matrix (ECM) ligands and culture substrate stiffness on primary human myoblast contractility and proliferation within 16 h of plating and found that tethered fibronectin led to stronger stiffness-dependent responses compared to laminin and collagen. A proteome-wide analysis further uncovered cell metabolism, cytoskeletal and nuclear component regulation distinctions between cells cultured on soft and stiff substrates. Interestingly, we found that softer substrates increased the incidence of myoblasts with a wrinkled nucleus, and that the extent of wrinkling could predict Ki67 (also known as MKI67) expression. Nuclear wrinkling and Ki67 expression could be controlled by pharmacological manipulation of cellular contractility, offering a potential cellular mechanism. These results provide new insights into the regulation of human myoblast stiffness-dependent contractility response by ECM ligands and highlight a link between myoblast contractility and proliferation.

Decoding the forces that shape muscle stem cell function

Skeletal muscle is a force-producing organ composed of muscle tissues, connective tissues, blood vessels, and nerves, all working in synergy to enable movement and provide support to the body. While robust biomechanical descriptions of skeletal muscle force production at the body or tissue level exist, little is known about force application on microstructures within the muscles, such as cells. Among various cell types, skeletal muscle stem cells reside in the muscle tissue environment and play a crucial role in driving the self-repair process when muscle damage occurs. Early evidence indicates that the fate and function of skeletal muscle stem cells are controlled by both biophysical and biochemical factors in their microenvironments, but much remains to accomplish in quantitatively describing the biophysical muscle stem cell microenvironment. This book chapter aims to review current knowledge on the influence of biophysical stresses and landscape properties on muscle stem cells in heath, aging, and diseases.

Polarized focal adhesion kinase activity within a focal adhesion during cell migration

Focal adhesion kinase (FAK) relays integrin signaling from outside to inside cells and contributes to cell adhesion and motility. However, the spatiotemporal dynamics of FAK activity in single FAs is unclear due to the lack of a robust FAK reporter, which limits our understanding of these essential biological processes. Here we have engineered a genetically encoded FAK activity sensor, dubbed FAK-separation of phases-based activity reporter of kinase (SPARK), which visualizes endogenous FAK activity in living cells and vertebrates. Our work reveals temporal dynamics of FAK activity during FA turnover. Most importantly, our study unveils polarized FAK activity at the distal tip of newly formed single FAs in the leading edge of a migrating cell. By combining FAK-SPARK with DNA tension probes, we show that tensions applied to FAs precede FAK activation and that FAK activity is proportional to the strength of tension. These results suggest tension-induced polarized FAK activity in single FAs, advancing the mechanistic understanding of cell migration.

Thy-1 (CD90)-regulated cell adhesion and migration of mesenchymal cells: insights into adhesomes, mechanical forces, and signaling pathways

Cell adhesion and migration depend on the assembly and disassembly of adhesive structures known as focal adhesions. Cells adhere to the extracellular matrix (ECM) and form these structures via receptors, such as integrins and syndecans, which initiate signal transduction pathways that bridge the ECM to the cytoskeleton, thus governing adhesion and migration processes. Integrins bind to the ECM and soluble or cell surface ligands to form integrin adhesion complexes (IAC), whose composition depends on the cellular context and cell type. Proteomic analyses of these IACs led to the curation of the term adhesome, which is a complex molecular network containing hundreds of proteins involved in signaling, adhesion, and cell movement. One of the hallmarks of these IACs is to sense mechanical cues that arise due to ECM rigidity, as well as the tension exerted by cell-cell interactions, and transduce this force by modifying the actin cytoskeleton to regulate cell migration. Among the integrin/syndecan cell surface ligands, we have described Thy-1 (CD90), a GPI-anchored protein that possesses binding domains for each of these receptors and, upon engaging them, stimulates cell adhesion and migration. In this review, we examine what is currently known about adhesomes, revise how mechanical forces have changed our view on the regulation of cell migration, and, in this context, discuss how we have contributed to the understanding of signaling mechanisms that control cell adhesion and migration.

Matrix stiffness, endothelial dysfunction and atherosclerosis

Atherosclerosis (AS) is the leading cause of the human cardiovascular diseases (CVDs). Endothelial dysfunction promotes the monocytes infiltration and inflammation that participate fundamentally in atherogenesis. Endothelial cells (EC) have been recognized as mechanosensitive cells and have different responses to distinct mechanical stimuli. Emerging evidence shows matrix stiffness-mediated EC dysfunction plays a vital role in vascular disease, but the underlying mechanisms are not yet completely understood. This article aims to summarize the effect of matrix stiffness on the pro-atherosclerotic characteristics of EC including morphology, rigidity, biological behavior and function as well as the related mechanical signal. The review also discusses and compares the contribution of matrix stiffness-mediated phagocytosis of macrophages and EC to AS progression. These advances in our understanding of the relationship between matrix stiffness and EC dysfunction open the avenues to improve the prevention and treatment of now-ubiquitous atherosclerotic diseases.

Growth factors and mechano-regulated reciprocal crosstalk with extracellular matrix tune the keratocyte-fibroblast/myofibroblast transition

Improper healing of the cornea after injury, infections or surgery can lead to corneal scar formation, which is associated with the transition of resident corneal keratocytes into activated fibroblasts and myofibroblasts (K-F/M). Myofibroblasts can create an extracellular matrix (ECM) niche in which fibrosis is promoted and perpetuated, resulting in progressive tissue opacification and vision loss. As a reversion back to quiescent keratocytes is essential to restore corneal transparency after injury, we characterized how growth factors with demonstrated profibrotic effects (PDGF, FGF, FBS, TGFβ1) induce the K-F/M transition, and whether their withdrawal can revert it. Indeed, the upregulated expression of αSMA and the associated changes in cytoskeletal architecture correlated with increases in cell contractility, fibronectin (Fn) and collagen matrix density and Fn fiber strain, as revealed by 2D cell culture, nanopillar cellular force mapping and a FRET-labeled Fn tension probe. Substrate mechanosensing drove a more complete K-F/M transition reversal following growth factor withdrawal on nanopillar arrays than on planar glass substrates. Using decellularized ECM scaffolds, we demonstrated that the K-F/M transition was inhibited in keratocytes reseeded onto myofibroblast-assembled, and/or collagen-1-rich ECM. This supports the presence of a myofibroblast-derived ECM niche that contains cues favoring tissue homeostasis rather than fibrosis.

Sculpting with stiffness: rigidity as a regulator of morphogenesis

From a physical perspective, morphogenesis of tissues results from interplay between their material properties and the mechanical forces exerted on them. The importance of mechanical forces in influencing cell behaviour is widely recognised, whereas the importance of tissue material properties in vivo, like stiffness, has only begun to receive attention in recent years. In this mini-review, we highlight key themes and concepts that have emerged related to how tissue stiffness, a fundamental material property, guides various morphogenetic processes in living organisms.

The role of single protein elasticity in mechanobiology

In addition to biochemical signals and genetic considerations, mechanical forces are rapidly emerging as a master regulator of human physiology. Yet the molecular mechanisms that regulate force-induced functionalities across a wide range of scales, encompassing the cell, tissue or organ levels, are comparatively not so well understood. With the advent, development and refining of single molecule nanomechanical techniques, enabling to exquisitely probe the conformational dynamics of individual proteins under the effect of a calibrated force, we have begun to acquire a comprehensive knowledge on the rich plethora of physicochemical principles that regulate the elasticity of single proteins. Here we review the major advances underpinning our current understanding of how the elasticity of single proteins regulates mechanosensing and mechanotransduction. We discuss the present limitations and future challenges of such a prolific and burgeoning field.

OVOL2 impairs RHO GTPase signaling to restrain mitosis and aggressiveness of Anaplastic Thyroid Cancer

Background

Anaplastic Thyroid Cancer (ATC) is an undifferentiated and aggressive tumor that often originates from well-Differentiated Thyroid Carcinoma (DTC) through a trans-differentiation process. Epithelial-to-Mesenchymal Transition (EMT) is recognized as one of the major players of this process. OVOL2 is a transcription factor (TF) that promotes epithelial differentiation and restrains EMT during embryonic development. OVOL2 loss in some types of cancers is linked to aggressiveness and poor prognosis. Here, we aim to clarify the unexplored role of OVOL2 in ATC.

Methods

Gene expression analysis in thyroid cancer patients and cell lines showed that OVOL2 is mainly associated with epithelial features and its expression is deeply impaired in ATC. To assess OVOL2 function, we established an OVOL2-overexpression model in ATC cell lines and evaluated its effects by analyzing gene expression, proliferation, invasion and migration abilities, cell cycle, specific protein localization through immunofluorescence staining. RNA-seq profiling showed that OVOL2 controls a complex network of genes converging on cell cycle and mitosis regulation and Chromatin Immunoprecipitation identified new OVOL2 target genes.

Results

Coherently with its reported function, OVOL2 re-expression restrained EMT and aggressiveness in ATC cells. Unexpectedly, we observed that it caused G2/M block, a consequent reduction in cell proliferation and an increase in cell death. This phenotype was associated to generalized abnormalities in the mitotic spindle structure and cytoskeletal organization. By RNA-seq experiments, we showed that many pathways related to cytoskeleton and migration, cell cycle and mitosis are profoundly affected by OVOL2 expression, in particular the RHO-GTPase pathway resulted as the most interesting. We demonstrated that RHO GTPase pathway is the central hub of OVOL2-mediated program in ATC and that OVOL2 transcriptionally inhibits RhoU and RhoJ. Silencing of RhoU recapitulated the OVOL2-driven phenotype pointing to this protein as a crucial target of OVOL2 in ATC.

Conclusions

Collectively, these data describe the role of OVOL2 in ATC and uncover a novel function of this TF in inhibiting the RHO GTPase pathway interlacing its effects on EMT, cytoskeleton dynamics and mitosis.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13046-022-02316-2.

Exploring the difference in the mechanics of vascular smooth muscle cells from wild-type and apolipoprotein-E knockout mice

Atherosclerosis-related cardiovascular diseases are a leading cause of mortality worldwide. Vascular smooth muscle cells (VSMCs) comprise the medial layer of the arterial wall and undergo phenotypic switching during atherosclerosis to a synthetic phenotype capable of proliferation and migration. The surrounding environment undergoes alterations in extracellular matrix (ECM) stiffness and composition and an increase in cholesterol content. Using an atherosclerotic murine model, we analyzed how the mechanics of VSMCs isolated from Western diet-fed apolipoprotein-E knockout (ApoE-/-) and wild-type (WT) mice were altered during atherosclerosis. Increased stiffness of ApoE-/- VSMCs correlated with a greater degree of stress fiber alignment, as evidenced by atomic force microscopy (AFM)-generated force maps and stress fiber topography images. On type-1 collagen (COL1)-coated polyacrylamide (PA) gels (referred to as substrate) of varying stiffness, ApoE-/- VSMCs had lower adhesion forces to COL1 and N-cadherin (N-Cad) compared with WT cells. ApoE-/- VSMC stiffness was significantly greater than that of WT cells. Cell stiffness increased with increasing substrate stiffness for both ApoE-/- and WT VSMCs. In addition, ApoE-/- VSMCs showed an enhanced migration capability on COL1-coated substrates and a general decreasing trend in migration capacity with increasing substrate stiffness, correlating with lowered adhesion forces as compared with WT VSMCs. Altogether, these results demonstrate the potential contribution of the alteration in VSMC mechanics in the development of atherosclerosis.

New insights into FAK structure and function in focal adhesions

Focal adhesion kinase (FAK; also known as PTK2) was discovered three decades ago and is now recognised as a key player in the regulation of cell-matrix adhesion and mesenchymal cell migration. Although it is essential during development, FAK also drives invasive cancer progression and metastasis. On a structural level, the basic building blocks of FAK have been described for some time. However, a picture of how FAK integrates into larger assemblies in various cellular environments, including one of its main cellular locations, the focal adhesion (FA) complex, is only beginning to emerge. Nano-resolution data from cellular studies, as well as atomic structures from reconstituted systems, have provided first insights, but also point to challenges that remain for obtaining a full structural understanding of how FAK is integrated in the FA complex and the structural changes occurring at different stages of FA maturation. In this Review, we discuss the known structural features of FAK, the interactions with its partners within the FA environment on the cell membrane and propose how its initial assembly in nascent FAs might change during FA maturation under force.

Extracellular matrix regulates force transduction at VE-cadherin junctions

Increased tension on VE-cadherin (VE-cad) complexes activates adaptive cell stiffening and local cytoskeletal reinforcement--two key signatures of intercellular mechanotransduction. Here we demonstrate that tugging on VE-cad receptors initiates a cascade that results in downstream integrin activation. The formation of new integrin adhesions potentiates vinculin and actin recruitment to mechanically reinforce stressed cadherin adhesions. This cascade differs from documented antagonistic effects of integrins on intercellular junctions. We identify focal adhesion kinase, Abl kinase, and RhoA GTPase as key components of the positive feedback loop. Results further show that a consequence of integrin involvement is the sensitization of intercellular force transduction to the extracellular matrix (ECM) not by regulating junctional tension but by altering signal cascades that reinforce cell-cell adhesions. On type 1 collagen or fibronectin substrates, integrin subtypes α2β1 and α5β1, respectively, differentially control actin remodeling at VE-cad adhesions. Specifically, ECM-dependent differences in VE-cad force transduction mirror differences in the rigidity sensing mechanisms of α2β1 and α5β1 integrins. The findings verify the role of integrins in VE-cad force transduction and uncover a previously unappreciated mechanism by which the ECM impacts the mechanical reinforcement of interendothelial junctions.

Decreased FAK activity and focal adhesion dynamics impair proper neurite formation of medium spiny neurons in Huntington's disease

Huntington's disease (HD) is a neurodegenerative disorder caused by a polyglutamine expansion in the protein huntingtin (HTT) [55]. While the final pathological consequence of HD is the neuronal cell death in the striatum region of the brain, it is still unclear how mutant HTT (mHTT) causes synaptic dysfunctions at the early stage and during the progression of HD. Here, we discovered that the basal activity of focal adhesion kinase (FAK) is severely reduced in a striatal HD cell line, a mouse model of HD, and the human post-mortem brains of HD patients. In addition, we observed with a FRET-based FAK biosensor [59] that neurotransmitter-induced FAK activation is decreased in HD striatal neurons. Total internal reflection fluorescence (TIRF) imaging revealed that the reduced FAK activity causes the impairment of focal adhesion (FA) dynamics, which further leads to the defect in filopodial dynamics causing the abnormally increased number of immature neurites in HD striatal neurons. Therefore, our results suggest that the decreased FAK and FA dynamics in HD impair the proper formation of neurites, which is crucial for normal synaptic functions [52]. We further investigated the molecular mechanism of FAK inhibition in HD and surprisingly discovered that mHTT strongly associates with phosphatidylinositol 4,5-biphosphate, altering its normal distribution at the plasma membrane, which is crucial for FAK activation [14, 60]. Therefore, our results provide a novel molecular mechanism of FAK inhibition in HD along with its pathological mechanism for synaptic dysfunctions during the progression of HD.

Optical regulation of endogenous RhoA reveals selection of cellular responses by signal amplitude

How protein signaling networks respond to different input strengths is an important but poorly understood problem in cell biology. For example, RhoA can promote focal adhesion (FA) growth or disassembly, but how RhoA activity mediates these opposite outcomes is not clear. Here, we develop a photoswitchable RhoA guanine nucleotide exchange factor (GEF), psRhoGEF, to precisely control endogenous RhoA activity. Using this optical tool, we discover that peak FA disassembly selectively occurs upon activation of RhoA to submaximal levels. We also find that Src activation at FAs selectively occurs upon submaximal RhoA activation, identifying Src as an amplitude-dependent RhoA effector. Finally, a pharmacological Src inhibitor reverses the direction of the FA response to RhoA activation from disassembly to growth, demonstrating that Src functions to suppress FA growth upon RhoA activation. Thus, rheostatic control of RhoA activation by psRhoGEF reveals that cells can use signal amplitude to produce multiple responses to a single biochemical signal.

Interplay between mechanics and signalling in regulating cell fate

Mechanical signalling affects multiple biological processes during development and in adult organisms, including cell fate transitions, cell migration, morphogenesis and immune responses. Here, we review recent insights into the mechanisms and functions of two main routes of mechanical signalling: outside-in mechanical signalling, such as mechanosensing of substrate properties or shear stresses; and mechanical signalling regulated by the physical properties of the cell surface itself. We discuss examples of how these two classes of mechanical signalling regulate stem cell function, as well as developmental processes in vivo. We also discuss how cell surface mechanics affects intracellular signalling and, in turn, how intracellular signalling controls cell surface mechanics, generating feedback into the regulation of mechanosensing. The cooperation between mechanosensing, intracellular signalling and cell surface mechanics has a profound impact on biological processes. We discuss here our understanding of how these three elements interact to regulate stem cell fate and development.

Truncated O-Glycan-Bearing MUC16 Enhances Pancreatic Cancer Cells Aggressiveness via α4β1 Integrin Complexes and FAK Signaling

Elevated levels of Mucin-16 (MUC16) in conjunction with a high expression of truncated O-glycans is implicated in playing crucial roles in the malignancy of pancreatic ductal adenocarcinoma (PDAC). However, the mechanisms by which such aberrant glycoforms present on MUC16 itself promote an increased disease burden in PDAC are yet to be elucidated. This study demonstrates that the CRISPR/Cas9-mediated genetic deletion of MUC16 in PDAC cells decreases tumor cell migration. We found that MUC16 enhances tumor malignancy by activating the integrin-linked kinase and focal adhesion kinase (ILK/FAK)-signaling axis. These findings are especially noteworthy in truncated O-glycan (Tn and STn antigen)-expressing PDAC cells. Activation of these oncogenic-signaling pathways resulted in part from interactions between MUC16 and integrin complexes (α4β1), which showed a stronger association with aberrant glycoforms of MUC16. Using a monoclonal antibody to functionally hinder MUC16 significantly reduced the migratory cascades in our model. Together, these findings suggest that truncated O-glycan containing MUC16 exacerbates malignancy in PDAC by activating FAK signaling through specific interactions with α4 and β1 integrin complexes on cancer cell membranes. Targeting these aberrant glycoforms of MUC16 can aid in the development of a novel platform to study and treat metastatic pancreatic cancer.

Viscoelastic Biomaterials for Tissue Regeneration

The extracellular matrix (ECM) mechanical properties regulate key cellular processes in tissue development and regeneration. The majority of scientific investigation has focused on ECM elasticity as the primary mechanical regulator of cell and tissue behavior. However, all living tissues are viscoelastic, exhibiting both solid- and liquid-like mechanical behavior. Despite increasing evidence regarding the role of ECM viscoelasticity in directing cellular behavior, this aspect is still largely overlooked in the design of biomaterials for tissue regeneration. Recently, with the emergence of various bottom-up material design strategies, new approaches can deliver unprecedented control over biomaterial properties at multiple length scales, thus enabling the design of viscoelastic biomaterials that mimic various aspect of the native tissue ECM microenvironment. This review describes key considerations for the design of viscoelastic biomaterials for tissue regeneration. We provide an overview of the role of matrix viscoelasticity in directing cell behavior towards regenerative outcomes, highlight recent strategies utilizing viscoelastic hydrogels for regenerative therapies, and outline remaining challenges, potential solutions, and emerging applications for viscoelastic biomaterials in tissue engineering and regenerative medicine.

Phosphorylated paxillin and phosphorylated FAK constitute subregions within focal adhesions

Integrin-mediated adhesions are convergence points of multiple signaling pathways. Their inner structure and their diverse functions can be studied with super-resolution microscopy. Here, we examined the spatial organization within focal adhesion by analyzing several adhesion proteins with structured illumination microscopy (SIM). We found that phosphorylated paxillin (pPax) and phosphorylated focal adhesion kinase (pFAK) form spot-like, spatially defined clusters within adhesions in several cell lines and confirmed these findings with additional super-resolution techniques. These clusters showed a more regular separation from each other compared to more randomly distributed labels of general FAK or paxillin. Mutational analysis indicated that the active (open) FAK conformation is a prerequisite for the pattern formation of pFAK. Live-cell super-resolution imaging revealed that organization in clusters is preserved over time for FAK constructs; however, distance between clusters is dynamic for FAK, while paxillin is more stable. Combined, these data introduce spatial clusters of pPax and pFAK as substructures in adhesions and highlight the relevance of paxillin-FAK binding for establishing a regular substructure in focal adhesions.

Substrate rigidity modulates traction forces and stoichiometry of cell–matrix adhesions

In cell–matrix adhesions, integrin receptors and associated proteins provide a dynamic coupling of the extracellular matrix (ECM) to the cytoskeleton. This allows bidirectional transmission of forces between the ECM and the cytoskeleton, which tunes intracellular signaling cascades that control survival, proliferation, differentiation, and motility. The quantitative relationships between recruitment of distinct cell–matrix adhesion proteins and local cellular traction forces are not known. Here, we applied quantitative super-resolution microscopy to cell–matrix adhesions formed on fibronectin-stamped elastomeric pillars and developed an approach to relate the number of talin, vinculin, paxillin, and focal adhesion kinase (FAK) molecules to the local cellular traction force. We find that FAK recruitment does not show an association with traction-force application, whereas a ∼60 pN force increase is associated with the recruitment of one talin, two vinculin, and two paxillin molecules on a substrate with an effective stiffness of 47 kPa. On a substrate with a fourfold lower effective stiffness, the stoichiometry of talin:vinculin:paxillin changes to 2:12:6 for the same ∼60 pN traction force. The relative change in force-related vinculin recruitment indicates a stiffness-dependent switch in vinculin function in cell–matrix adhesions. Our results reveal a substrate-stiffness-dependent modulation of the relationship between cellular traction-force and the molecular stoichiometry of cell–matrix adhesions.

Morphological Phenotyping of Organotropic Brain- and Bone-Seeking Triple Negative Metastatic Breast Tumor Cells

Triple negative breast cancer (TNBC) follows a non-random pattern of metastasis to the bone and brain tissue. Prior work has found that brain-seeking breast tumor cells display altered proteomic profiles, leading to alterations in pathways related to cell signaling, cell cycle, metabolism, and extracellular matrix remodeling. Given the unique microenvironmental characteristics of brain and bone tissue, we hypothesized that brain- or bone-seeking TNBC cells may have altered morphologic or migratory phenotypes from each other, or from the parental TNBC cells, as a function of the biochemical or mechanical microenvironment. In this study, we utilized TNBC cells (MDA-MB-231) that were conditioned to metastasize solely to brain (MDA-BR) or bone (MDA-BO) tissue. We quantified characteristics such as cell morphology, migration, and stiffness in response to cues that partially mimic their final metastatic niche. We have shown that MDA-BO cells have a distinct protrusive morphology not found in MDA-P or MDA-BR. Further, MDA-BO cells migrate over a larger area when on a collagen I (abundant in bone tissue) substrate when compared to fibronectin (abundant in brain tissue). However, migration in highly confined environments was similar across the cell types. Modest differences were found in the stiffness of MDA-BR and MDA-BO cells plated on collagen I vs. fibronectin-coated surfaces. Lastly, MDA-BO cells were found to have larger focal adhesion area and density in comparison with the other two cell types. These results initiate a quantitative profile of mechanobiological phenotypes in TNBC, with future impacts aiming to help predict metastatic propensities to organ-specific sites in a clinical setting.

New Insights on the Nuclear Functions and Targeting of FAK in Cancer

Focal adhesion kinase (FAK) is a non-receptor tyrosine kinase over-expressed and activated in both adult and pediatric cancers, where it plays important roles in the regulation of pathogenesis and progression of the malignant phenotype. FAK exerts its functions in cancer by two different ways: a kinase activity in the cytoplasm, mainly dependent on the integrin signaling, and a scaffolding activity into the nucleus by networking with different gene expression regulators. For this reason, FAK has to be considered a target with high therapeutic values. Indeed, evidence suggests that FAK targeting could be effective, either alone or in combination, with other already available treatments. Here, we propose an overview of the novel insights about FAK’s structure and nuclear functions, with a special focus on the recent findings concerning the roles of this protein in cancer. Additionally, we provide a recent update on FAK inhibitors that are currently in clinical trials for patients with cancer, and discuss the challenge and future directions of drug-based anti-FAK targeted therapies.

Viscoelasticity, Like Forces, Plays a Role in Mechanotransduction

Viscoelasticity and its alteration in time and space has turned out to act as a key element in fundamental biological processes in living systems, such as morphogenesis and motility. Based on experimental and theoretical findings it can be proposed that viscoelasticity of cells, spheroids and tissues seems to be a collective characteristic that demands macromolecular, intracellular component and intercellular interactions. A major challenge is to couple the alterations in the macroscopic structural or material characteristics of cells, spheroids and tissues, such as cell and tissue phase transitions, to the microscopic interferences of their elements. Therefore, the biophysical technologies need to be improved, advanced and connected to classical biological assays. In this review, the viscoelastic nature of cytoskeletal, extracellular and cellular networks is presented and discussed. Viscoelasticity is conceptualized as a major contributor to cell migration and invasion and it is discussed whether it can serve as a biomarker for the cells' migratory capacity in several biological contexts. It can be hypothesized that the statistical mechanics of intra- and extracellular networks may be applied in the future as a powerful tool to explore quantitatively the biomechanical foundation of viscoelasticity over a broad range of time and length scales. Finally, the importance of the cellular viscoelasticity is illustrated in identifying and characterizing multiple disorders, such as cancer, tissue injuries, acute or chronic inflammations or fibrotic diseases.

FAK in Cancer: From Mechanisms to Therapeutic Strategies

Focal adhesion kinase (FAK), a non-receptor tyrosine kinase, is overexpressed and activated in many cancer types. FAK regulates diverse cellular processes, including growth factor signaling, cell cycle progression, cell survival, cell motility, angiogenesis, and the establishment of immunosuppressive tumor microenvironments through kinase-dependent and kinase-independent scaffolding functions in the cytoplasm and nucleus. Mounting evidence has indicated that targeting FAK, either alone or in combination with other agents, may represent a promising therapeutic strategy for various cancers. In this review, we summarize the mechanisms underlying FAK-mediated signaling networks during tumor development. We also summarize the recent progress of FAK-targeted small-molecule compounds for anticancer activity from preclinical and clinical evidence.

Intrinsic Mechanical Cues and Their Impact on Stem Cells and Embryogenesis

Although understanding how soluble cues direct cellular processes revolutionised the study of cell biology in the second half of the 20th century, over the last two decades, new insights into how mechanical cues similarly impact cell fate decisions has gained momentum. During development, extrinsic cues such as fluid flow, shear stress and compressive forces are essential for normal embryogenesis to proceed. Indeed, both adult and embryonic stem cells can respond to applied forces, but they can also detect intrinsic mechanical cues from their surrounding environment, such as the stiffness of the extracellular matrix, which impacts differentiation and morphogenesis. Cells can detect changes in their mechanical environment using cell surface receptors such as integrins and focal adhesions. Moreover, dynamic rearrangements of the cytoskeleton have been identified as a key means by which forces are transmitted from the extracellular matrix to the cell and vice versa. Although we have some understanding of the downstream mechanisms whereby mechanical cues are translated into changes in cell behaviour, many of the signalling pathways remain to be defined. This review discusses the importance of intrinsic mechanical cues on adult cell fate decisions, the emerging roles of cell surface mechano-sensors and the cytoskeleton in enabling cells to sense its microenvironment, and the role of intracellular signalling in translating mechanical cues into transcriptional outputs. In addition, the contribution of mechanical cues to fundamental processes during embryogenesis such as apical constriction and convergent extension is discussed. The continued development of tools to measure the biomechanical properties of soft tissues in vivo is likely to uncover currently underestimated contributions of these cues to adult stem cell fate decisions and embryogenesis, and may inform on regenerative strategies for tissue repair.

Mechanics-driven nuclear localization of YAP can be reversed by N-cadherin ligation in mesenchymal stem cells

Mesenchymal stem cells adopt differentiation pathways based upon cumulative effects of mechanosensing. A cell's mechanical microenvironment changes substantially over the course of development, beginning from the early stages in which cells are typically surrounded by other cells and continuing through later stages in which cells are typically surrounded by extracellular matrix. How cells erase the memory of some of these mechanical microenvironments while locking in memory of others is unknown. Here, we develop a material and culture system for modifying and measuring the degree to which cells retain cumulative effects of mechanosensing. Using this system, we discover that effects of the RGD adhesive motif of fibronectin (representative of extracellular matrix), known to impart what is often termed "mechanical memory" in mesenchymal stem cells via nuclear YAP localization, are erased by the HAVDI adhesive motif of the N-cadherin (representative of cell-cell contacts). These effects can be explained by a motor clutch model that relates cellular traction force, nuclear deformation, and resulting nuclear YAP re-localization. Results demonstrate that controlled storage and removal of proteins associated with mechanical memory in mesenchymal stem cells is possible through defined and programmable material systems.

Striated muscle proteins are regulated both by mechanical deformation and by chemical post-translational modification

All cells sense force and build their cytoskeleton to optimize function. How is this achieved? Two major systems are involved. The first is that load deforms specific protein structures in a proportional and orientation-dependent manner. The second is post-translational modification of proteins as a consequence of signaling pathway activation. These two processes work together in a complex way so that local subcellular assembly as well as overall cell function are controlled. This review discusses many cell types but focuses on striated muscle. Detailed information is provided on how load deforms the structure of proteins in the focal adhesions and filaments, using α-actinin, vinculin, talin, focal adhesion kinase, LIM domain-containing proteins, filamin, myosin, titin, and telethonin as examples. Second messenger signals arising from external triggers are distributed throughout the cell causing post-translational or chemical modifications of protein structures, with the actin capping protein CapZ and troponin as examples. There are numerous unanswered questions of how mechanical and chemical signals are integrated by muscle proteins to regulate sarcomere structure and function yet to be studied. Therefore, more research is needed to see how external triggers are integrated with local tension generated within the cell. Nonetheless, maintenance of tension in the sarcomere is the essential and dominant mechanism, leading to the well-known phrase in exercise physiology: "use it or lose it."

Mechanical Loading Disrupts Focal Adhesion Kinase Activation in Mandibular Fibrochondrocytes During Murine Temporomandibular Joint Osteoarthritis

PURPOSE

Mechanical overloading is a key initiating condition for temporomandibular joint (TMJ) osteoarthritis (OA). The integrin-focal adhesion kinase (FAK) signaling axis is implicated in the mechanobiological response of cells through phosphorylation at Tyr397 (pFAK) but poorly defined in TMJ health and disease. We hypothesize that mechanical overloading disrupts TMJ homeostasis through dysregulation of FAK signaling.

MATERIALS AND METHODS

To assess if FAK and pFAK are viable clinical targets for TMJ OA, peri-articular tissues were collected from patients with TMJ OA receiving a total TMJ replacement. To compare clinical samples with preclinical in vivo studies of TMJ OA, the joints of c57/bl6 mice were surgically destabilized and treated with and without inhibitor of pFAK (iFAK). FAK signaling and TMJ OA progression was evaluated and compared using RT-PCR, western blot, immunohistochemistry, and histomorphometry. To evaluate mechanical overloading in vitro, primary murine mandibular fibrochondrocytes were seeded in a 4% agarose-collagen scaffold and loaded in a compression bioreactor with and without iFAK.

RESULTS

FAK/pFAK was mostly absent from the articular cartilage layer in the clinical sample and suppressed on the central condyle and elevated on the lateral and medial condyle in murine TMJ OA. In vitro, compressive loading lowered FAK/pFAK levels and elevated the expression of TGFβ, NG2, and MMP-13. iFAK treatment suppressed MMP13 and Col6 and elevated TGFβ, NG2, and ACAN in a load independent manner. In vivo, iFAK treatment moderately attenuated OA progression and increased collagen maturation.

CONCLUSION

These data illustrate that FAK/pFAK is implicated in the signaled dysfunction of excessive mechanical loading during TMJ OA and that iFAK treatment can moderately attenuate the progression of cartilage degeneration in the mandibular condyle.

Kinases of the Focal Adhesion Complex Contribute to Cardiomyocyte Specification

Differentiation of pluripotent stem cells to cardiomyocytes is influenced by culture conditions including the extracellular matrices or similar synthetic scaffolds on which they are grown. However, the molecular mechanisms that link the scaffold with differentiation outcomes are not fully known. Here, we determined by immunofluorescence staining and mass spectrometry approaches that extracellular matrix (ECM) engagement by mouse pluripotent stem cells activates critical components of canonical wingless/integrated (Wnt) signaling pathways via kinases of the focal adhesion to drive cardiomyogenesis. These kinases were found to be differentially activated depending on type of ECM engaged. These outcomes begin to explain how varied ECM composition of in vivo tissues with development and in vitro model systems gives rise to different mature cell types, having broad practical applicability for the design of engineered tissues.

The Early Adhesion Effects of Human Gingival Fibroblasts on Bovine Serum Albumin Loaded Hydrogenated Titanium Nanotube Surface

The soft tissue sealing at the transmucal portion of implants is vital for the long-term stability of implants. Hydrogenated titanium nanotubes (H₂-TNTs) as implant surface treatments were proved to promote the adhesion of human gingival fibroblasts (HGFs) and have broad usage as drug delivery systems. Bovine serum albumin (BSA) as the most abundant albumin in body fluid was crucial for cell adhesion and was demonstrated as a normal loading protein. As the first protein arriving on the surface of the implant, albumin plays an important role in initial adhesion of soft tissue cells, it is also a common carrier, transferring and loading different endogenous and exogenous substances, ions, drugs, and other small molecules. The aim of the present work was to investigate whether BSA-loaded H₂-TNTs could promote the early adhesion of HGFs; H₂-TNTs were obtained by hydrogenated anodized titanium dioxide nanotubes (TNTs) in thermal treatment, and BSA was loaded in the nanotubes by vacuum drying; our results showed that the superhydrophilicity of H₂-TNTs is conducive to the loading of BSA. In both hydrogenated titanium nanotubes and non-hydrogenated titanium nanotubes, a high rate of release was observed over the first hour, followed by a period of slow and sustained release; however, BSA-loading inhibits the early adhesion of human gingival fibroblasts, and H₂-TNTs has the best promoting effect on cell adhesion. With the release of BSA after 4 h, the inhibitory effect of BSA on cell adhesion was weakened.

Epidermal ROCK2 induces AKT1/GSK3β/β-catenin, NFκB and dermal tenascin C; but enhanced differentiation and p53/p21 inhibit papilloma

ROCK2 roles in epidermal differentiation and carcinogenesis have been investigated in mice expressing an RU486-inducible, 4HT-activated ROCK2 transgene (K14.creP/lslROCKer). RU486/4HT-mediated ROCKer activation induced epidermal hyperplasia similar to cutaneous oncogenic rasHa (HK1.ras); however ROCKer did not elicit papillomas. Instead, anomalous basal-layer ROCKer expression corrupted normal ROCK2 roles underlying epidermal rigidity/stiffness and barrier maintanance, resulting in premature keratin K1, loricrin and filaggrin expression. Also, hyperproliferative/stress-associated keratin K6 was reduced; possibly reflecting altered ROCK2 roles in epidermal rigidity and keratinocyte flexibility/migration during wound healing. Consistent with increased proliferation, K14.creP/lslROCKer hyperplasia displayed supra-basal-to-basal increases in activated p-AKT1, inactivated p-GSK3β ser9 and membranous/nuclear β-catenin expression together with weak NFκB, which were absent in equivalent HK1.ras hyperplasia. Furthermore, ROCKer-mediated increases in epidermal rigidity via p-MypT1 inactivation/elevated MLC, coupled to anomalous β-catenin expression, induced tenascin C-positive dermal fibroblasts. Alongside an altered ECM, these latent tenascin C-positive dermal fibroblasts may become putative pre-cancer-associated fibroblasts (pre-CAFs) and establish a susceptibility that subsequently contributes to tumour progression. However, anomalous differentiation was also accompanied by an immediate increase in basal-layer p53/p21 expression; suggesting that while ROCK2/AKT1/β-catenin activation increased keratinocyte proliferation resulting in hyperplasia, compensatory p53/p21 and accelerated differentiation helped inhibit papillomatogenesis.

Integrin Adhesion Complex Organization in Sheep Myometrium Reflects Changing Mechanical Forces during Pregnancy and Postpartum

Simple Summary

IACs assemble within the sheep myometrium during early-to-mid gestation in response to increased stretch of the uterine wall and continue to increase as pregnancy progresses. Fibronectin (FN1) is important in its ability to attach to IACs in myometrial cells to generate force to sustain powerful contractions during labor. After parturition, IACs are disassembled but the integrin subunits ITGA5 and ITGB1 remain expressed at the protein level at least two weeks postpartum.

Abstract

Cells respond to extracellular mechanical forces through the assembly of integrin adhesion complexes (IACs) that provide a scaffold through which cells sense and transduce responses to those forces. IACs are composed of transmembrane integrin receptors that bind to extracellular matrix (ECM) proteins externally and connect with the actomyosin cytoskeleton internally. Myometrial smooth muscle cells respond to forces that arise due to increases in fetal growth/weight, placental fluid volumes, and blood flow. As a result, the uterus transforms into an organ that can forcefully expel the fetus and placental membranes during parturition. While earlier studies focused on IAC expression in the myometrial compartment of rodents and humans to explore pregnancy-associated responses, the present study examines IAC assembly in ovine myometrium where mechanical forces are expected to be amplified in a manner similar to humans. Results indicate that the ITGA5 and ITGB1 heterodimers associate with the ECM protein FN1 externally, and with VCL and TLN1 internally, to form IACs in myometrial cells during the first trimester of pregnancy. These IACs become increasingly ordered until parturition. This ordered structure is lost by one day postpartum; however, the abundance of the integrin proteins remains elevated for at least two weeks postpartum. Implications of the present study are that sheep are similar to humans regarding the assembly of IACs in the pregnant myometrium and suggest that IACs may form much earlier in human gestation than was previously implied by the rat model. Results highlight the continued value of the sheep model as a flagship gynecological model for understanding parturition in humans.

Cytoskeletal prestress: The cellular hallmark in mechanobiology and mechanomedicine

Increasing evidence demonstrates that mechanical forces, in addition to soluble molecules, impact cell and tissue functions in physiology and diseases. How living cells integrate mechanical signals to perform appropriate biological functions is an area of intense investigation. Here, we review the evidence of the central role of cytoskeletal prestress in mechanotransduction and mechanobiology. Elevating cytoskeletal prestress increases cell stiffness and reinforces cell stiffening, facilitates long-range cytoplasmic mechanotransduction via integrins, enables direct chromatin stretching and rapid gene expression, spurs embryonic development and stem cell differentiation, and boosts immune cell activation and killing of tumor cells whereas lowering cytoskeletal prestress maintains embryonic stem cell pluripotency, promotes tumorigenesis and metastasis of stem cell-like malignant tumor-repopulating cells, and elevates drug delivery efficiency of soft-tumor-cell-derived microparticles. The overwhelming evidence suggests that the cytoskeletal prestress is the governing principle and the cellular hallmark in mechanobiology. The application of mechanobiology to medicine (mechanomedicine) is rapidly emerging and may help advance human health and improve diagnostics, treatment, and therapeutics of diseases.

TRPV4-Rho signaling drives cytoskeletal and focal adhesion remodeling in trabecular meshwork cells

Intraocular pressure (IOP) is dynamically regulated by the trabecular meshwork (TM), a mechanosensitive tissue that protects the eye from injury through dynamic regulation of aqueous humor flow. TM compensates for mechanical stress impelled by chronic IOP elevations through increased actin polymerization, tissue stiffness, and contractility. This process has been associated with open angle glaucoma; however, the mechanisms that link mechanical stress to pathological cytoskeletal remodeling downstream from the mechanotransducers remain poorly understood. We used fluorescence imaging and biochemical analyses to investigate cytoskeletal and focal adhesion remodeling in human TM cells stimulated with physiological strains. Mechanical stretch promoted F-actin polymerization, increased the number and size of focal adhesions, and stimulated the activation of the Rho-associated protein kinase (ROCK). Stretch-induced activation of the small GTPase Ras homolog family member A (RhoA), and tyrosine phosphorylations of focal adhesion proteins paxillin, focal adhesion kinase (FAK), vinculin, and zyxin were time dependently inhibited by ROCK inhibitor trans-4-[(1R)-1-aminoethyl]-N-4-pyridinylcyclohexanecarboxamide dihydrochloride (Y-27632), and by HC-067047, an antagonist of transient receptor potential vanilloid 4 (TRPV4) channels. Both TRPV4 and ROCK activation were required for zyxin translocation and increase in the number/size of focal adhesions in stretched cells. Y-27632 blocked actin polymerization without affecting calcium influx induced by membrane stretch and the TRPV4 agonist GSK1016790A. These results reveal that mechanical tuning of TM cells requires parallel activation of TRPV4, integrins, and ROCK, with chronic stress leading to sustained remodeling of the cytoskeleton and focal complexes.

Manipulation of Focal Adhesion Signaling by Pathogenic Microbes

Focal adhesions (FAs) serve as dynamic signaling hubs within the cell. They connect intracellular actin to the extracellular matrix (ECM) and respond to environmental cues. In doing so, these structures facilitate important processes such as cell-ECM adhesion and migration. Pathogenic microbes often modify the host cell actin cytoskeleton in their pursuit of an ideal replicative niche or during invasion to facilitate uptake. As actin-interfacing structures, FA dynamics are also intimately tied to actin cytoskeletal organization. Indeed, exploitation of FAs is another avenue by which pathogenic microbes ensure their uptake, survival and dissemination. This is often achieved through the secretion of effector proteins which target specific protein components within the FA. Molecular mimicry of the leucine-aspartic acid (LD) motif or vinculin-binding domains (VBDs) commonly found within FA proteins is a common microbial strategy. Other effectors may induce post-translational modifications to FA proteins through the regulation of phosphorylation sites or proteolytic cleavage. In this review, we present an overview of the regulatory mechanisms governing host cell FAs, and provide examples of how pathogenic microbes have evolved to co-opt them to their own advantage. Recent technological advances pose exciting opportunities for delving deeper into the mechanistic details by which pathogenic microbes modify FAs.

Abl and Canoe/Afadin mediate mechanotransduction at tricellular junctions

Epithelial structure is generated by the dynamic reorganization of cells in response to mechanical forces. Adherens junctions transmit forces between cells, but how cells sense and respond to these forces in vivo is not well understood. We identify a mechanotransduction pathway involving the Abl tyrosine kinase and Canoe/Afadin that stabilizes cell adhesion under tension at tricellular junctions in the Drosophila embryo. Canoe is recruited to tricellular junctions in response to actomyosin contractility, and this mechanosensitivity requires Abl-dependent phosphorylation of a conserved tyrosine in the Canoe actin-binding domain. Preventing Canoe tyrosine phosphorylation destabilizes tricellular adhesion, and anchoring Canoe at tricellular junctions independently of mechanical inputs aberrantly stabilizes adhesion, arresting cell rearrangement. These results identify a force-responsive mechanism that stabilizes tricellular adhesion under tension during epithelial remodeling.

Suspension state regulates epithelial-to-mesenchymal transition and stemness of breast tumor cells

OBJECTIVES

The mechanical forces on circulating tumor cells (CTCs) should not be ignored in blood and it is more essential that CTCs can overcome and utilize the mechanical interaction to acquire the ability of distant metastasis. At present there are few studies on how suspension mechanics regulates the behavior of tumor cells. The aim of the study was to explore the effects of suspension state on the epithelial-mesenchymal transition (EMT) and stemness of breast CTCs and the molecular mechanisms involved.

RESULTS

Suspension state could regulate the program of EMT in breast cancer cells, which supported the complex dynamic concept of EMT. It is that the Ras homolog family member A (RhoA)/Rho-associated coiled-coil containing protein kinase 1 (ROCK1) signaling pathway was activated by suspension state in MCF-7 cells instead of MDA-MB-231 cells. In addition, suspension state increased the stemness of breast cancer cells from different aspects.

CONCLUSION

The study highlighted the emergence of hybrid epithelial/mesenchymal (E/M) state during hematogenous metastasis and the plasticity of CTCs caused by cancer stem cells, further providing novel insights into clinical monitoring of CTCs and therapeutic strategies.

Squeezing through the microcirculation: survival adaptations of circulating tumour cells to seed metastasis

During metastasis, tumour cells navigating the vascular circulatory system-circulating tumour cells (CTCs)-encounter capillary beds, where they start the process of extravasation. Biomechanical constriction forces exerted by the microcirculation compromise the survival of tumour cells within capillaries, but a proportion of CTCs manage to successfully extravasate and colonise distant sites. Despite the profound importance of this step in the progression of metastatic cancers, the factors about this deadly minority of cells remain elusive. Growing evidence suggests that mechanical forces exerted by the capillaries might induce adaptive mechanisms in CTCs, enhancing their survival and metastatic potency. Advances in microfluidics have enabled a better understanding of the cell-survival capabilities adopted in capillary-mimicking constrictions. In this review, we will highlight adaptations developed by CTCs to endure mechanical constraints in the microvasculature and outline how these mechanical forces might trigger dynamic changes towards a more invasive phenotype. A better understanding of the dynamic mechanisms adopted by CTCs within the microcirculation that ultimately lead to metastasis could open up novel therapeutic avenues.

Manipulating the Tumor Microenvironment in Tumor Organoids Induces Phenotypic Changes and Chemoresistance

Tumors comprised a tightly surrounded tumor microenvironment, made up of non-cellular extracellular matrix (ECM) and stromal cells. Although treatment response is often attributed to tumor heterogeneity, progression and malignancy are profoundly influenced by tumor cell interactions with the surrounding ECM. Here, we used a tumor organoid model, consisting of hepatic stellate cells (HSCs) embedded in collagen type 1 (Col1) and colorectal cancer cell (HCT-116) spheroids, to determine the relationship between the ECM architecture, cancer cell malignancy, and chemoresistance. Exogenous transforming growth factor beta (TGF-β) used to activate the HSCs increased the remodeling and bundling of Col1 in the ECM around the cancer spheroid. A dense ECM architecture inhibited tumor cell growth, reversed their mesenchymal phenotype, preserved stem cell population, and reduced chemotherapy response. Overall, our results demonstrate that controlled biofabrication and manipulation of the ECM in tumor organoids results enables studying tumor cell-ECM interactions and better understand tumor cell response to chemotherapies.

Involvement of the FAK Network in Pathologies Related to Altered Mechanotransduction

Mechanotransduction is a physiological process in which external mechanical stimulations are perceived, interpreted, and translated by cells into biochemical signals. Mechanical stimulations exerted by extracellular matrix stiffness and cell–cell contacts are continuously applied to living cells, thus representing a key pivotal trigger for cell homeostasis, survival, and function, as well as an essential factor for proper organ development and metabolism. Indeed, a deregulation of the mechanotransduction process consequent to gene mutations or altered functions of proteins involved in perceiving cellular and extracellular mechanics can lead to a broad range of diseases, from muscular dystrophies and cardiomyopathies to cancer development and metastatization. Here, we recapitulate the involvement of focal adhesion kinase (FAK) in the cellular conditions deriving from altered mechanotransduction processes.

Integration of mechanical and ECM microenvironment signals in the determination of cancer stem cell states

Purpose of review

Cancer stem cells (CSCs) are increasingly understood to play a central role in tumor progression. Growing evidence implicates tumor microenvironments as a source of signals that regulate or even impose CSC states on tumor cells. This review explores points of integration for microenvironment-derived signals that are thought to regulate CSCs in carcinomas.

Recent findings

CSC states are directly regulated by the mechanical properties and extra cellular matrix (ECM) composition of tumor microenvironments that promote CSC growth and survival, which may explain some modes of therapeutic resistance. CSCs sense mechanical forces and ECM composition through integrins and other cell surface receptors, which then activate a number of intracellular signaling pathways. The relevant signaling events are dynamic and context-dependent.

Summary

CSCs are thought to drive cancer metastases and therapeutic resistance. Cells that are in CSC states and more differentiated states appear to be reversible and conditional upon the components of the tumor microenvironment. Signals imposed by tumor microenvironment are of a combinatorial nature, ultimately representing the integration of multiple physical and chemical signals. Comprehensive understanding of the tumor microenvironment-imposed signaling that maintains cells in CSC states may guide future therapeutic interventions.

Cellular Plasticity during Metastasis: New Insights Provided by Intravital Microscopy

Metastasis is a highly dynamic process during which cancer and microenvironmental cells undergo a cascade of events required for efficient dissemination throughout the body. During the metastatic cascade, tumor cells can change their state and behavior, a phenomenon commonly defined as cellular plasticity. To monitor cellular plasticity during metastasis, high-resolution intravital microscopy (IVM) techniques have been developed and allow us to visualize individual cells by repeated imaging in animal models. In this review, we summarize the latest technological advancements in the field of IVM and how they have been applied to monitor metastatic events. In particular, we highlight how longitudinal imaging in native tissues can provide new insights into the plastic physiological and developmental processes that are hijacked by cancer cells during metastasis.

The stiffness-controlled release of interleukin-6 by cardiac fibroblasts is dependent on integrin α2β1

Cardiac fibroblasts are able to sense the rigidity of their environment. The present study examines whether the stiffness of the substrate in cardiac fibroblast culture can influence the release of interleukin‐6 (IL‐6), interleukin‐11 (IL‐11) and soluble receptor of IL‐6 (sIL‐6R). It also examines the roles of integrin α2β1 activation and intracellular signalling in these processes. Cardiac fibroblasts were cultured on polyacrylamide gels and grafted to collagen, with an elasticity of E = 2.23 ± 0.8 kPa (soft gel) and E = 8.28 ± 1.06 kPa (stiff gel, measured by Atomic Force Microscope). Flow cytometry and ELISA demonstrated that the fibroblasts cultured on the soft gel demonstrated higher expression of the α2 integrin subunit and increased α2β1 integrin count and released higher levels of IL‐6 and sIL‐6R than those on the stiff gel. Substrate elasticity did not modify fibroblast IL‐11 content. The silencing of the α2 integrin subunit decreased the release of IL‐6. Similar effects were induced by TC‐I 15 (an α2β1 integrin inhibitor). The IL‐6 levels in the serum and heart were markedly lower in α2 integrin‐deficient mice B6.Cg‐Itga2^{tm1.1Tkun/tm1.1Tkun} than wild type. Inhibition of Src kinase by AZM 475271 modifies the IL‐6 level. sIL‐6R secretion is not dependent on α2β1 integrin. Conclusion: The elastic properties of the substrate influence the release of IL‐6 by cardiac fibroblasts, and this effect is dependent on α2β1 integrin and kinase Src activation.

Structural basis of Focal Adhesion Kinase activation on lipid membranes

Focal adhesion kinase (FAK) is a key component of the membrane proximal signaling layer in focal adhesion complexes, regulating important cellular processes, including cell migration, proliferation, and survival. In the cytosol, FAK adopts an autoinhibited state but is activated upon recruitment into focal adhesions, yet how this occurs or what induces structural changes is unknown. Here, we employ cryo-electron microscopy to reveal how FAK associates with lipid membranes and how membrane interactions unlock FAK autoinhibition to promote activation. Intriguingly, initial binding of FAK to the membrane causes steric clashes that release the kinase domain from autoinhibition, allowing it to undergo a large conformational change and interact itself with the membrane in an orientation that places the active site toward the membrane. In this conformation, the autophosphorylation site is exposed and multiple interfaces align to promote FAK oligomerization on the membrane. We show that interfaces responsible for initial dimerization and membrane attachment are essential for FAK autophosphorylation and resulting cellular activity including cancer cell invasion, while stable FAK oligomerization appears to be needed for optimal cancer cell proliferation in an anchorage-independent manner. Together, our data provide structural details of a key membrane bound state of FAK that is primed for efficient autophosphorylation and activation, hence revealing the critical event in integrin mediated FAK activation and signaling at focal adhesions.

Disruption of ruminal homeostasis by malnutrition involved in systemic ruminal microbiota-host interactions in a pregnant sheep model

BACKGROUND

Undernutrition is a prevalent and spontaneous condition in animal production which always affects microbiota-host interaction in gastrointestinal tract. However, how undernutrition affects crosstalk homeostasis is largely unknown. Here, we discover how undernutrition affects microbial profiles and subsequently how microbial metabolism affects the signal transduction and tissue renewal in ruminal epithelium, clarifying the detrimental effect of undernutrition on ruminal homeostasis in a pregnant sheep model.

RESULTS

Sixteen pregnant ewes (115 days of gestation) were randomly and equally assigned to the control (CON) and severe feed restriction (SFR) groups. Ewes on SFR treatment were restricted to a 30% level of ad libitum feed intake while the controls were fed normally. After 15 days, all ewes were slaughtered to collect ruminal digesta for 16S rRNA gene and metagenomic sequencing and ruminal epithelium for transcriptome sequencing. Results showed that SFR diminished the levels of ruminal volatile fatty acids and microbial proteins and repressed the length, width, and surface area of ruminal papillae. The 16S rRNA gene analysis indicated that SFR altered the relative abundance of ruminal bacterial community, showing decreased bacteria about saccharide degradation (Saccharofermentans and Ruminococcus) and propionate genesis (Succiniclasticum) but increased butyrate producers (Pseudobutyrivibrio and Papillibacter). Metagenome analysis displayed that genes related to amino acid metabolism, acetate genesis, and succinate-pathway propionate production were downregulated upon SFR, while genes involved in butyrate and methane genesis and acrylate-pathway propionate production were upregulated. Transcriptome and real-time PCR analysis of ruminal epithelium showed that downregulated collagen synthesis upon SFR lowered extracellular matrix-receptor interaction, inactivated JAK3-STAT2 signaling pathway, and inhibited DNA replication and cell cycle.

CONCLUSIONS

Generally, undernutrition altered rumen bacterial community and function profile to decrease ruminal energy retention, promoted epithelial glucose and fatty acid catabolism to elevate energy supply, and inhibited the proliferation of ruminal epithelial cells. These findings provide the first insight into the systemic microbiota-host interactions that are involved in disrupting the ruminal homeostasis under a malnutrition pattern. Video Abstract.

Actin cytoskeleton in mesenchymal-to-amoeboid transition of cancer cells

During development of metastasis, tumor cells migrate through different tissues and encounter different extracellular matrices. An ability of cells to adapt mechanisms of their migration to these diverse environmental conditions, called migration plasticity, gives tumor cells an advantage over normal cells for long distant dissemination. Different modes of individual cell motility-mesenchymal and amoeboid-are driven by different molecular mechanisms, which largely depend on functions of the actin cytoskeleton that can be modulated in a wide range by cellular signaling mechanisms in response to environmental conditions. Various triggers can switch one motility mode to another, but regulations of these transitions are incompletely understood. However, understanding of the mechanisms driving migration plasticity is instrumental for finding anti-cancer treatment capable to stop cancer metastasis. In this review, we discuss cytoskeletal features, which allow the individually migrating cells to switch between mesenchymal and amoeboid migrating modes, called mesenchymal-to-amoeboid transition (MAT). We briefly describe main characteristics of different cell migration modes, and then discuss the triggering factors that initiate MAT with special attention to cytoskeletal features essential for migration plasticity.

Integrins as biomechanical sensors of the microenvironment

Integrins, and integrin-mediated adhesions, have long been recognized to provide the main molecular link attaching cells to the extracellular matrix (ECM) and to serve as bidirectional hubs transmitting signals between cells and their environment. Recent evidence has shown that their combined biochemical and mechanical properties also allow integrins to sense, respond to and interact with ECM of differing properties with exquisite specificity. Here, we review this work first by providing an overview of how integrin function is regulated from both a biochemical and a mechanical perspective, affecting integrin cell-surface availability, binding properties, activation or clustering. Then, we address how this biomechanical regulation allows integrins to respond to different ECM physicochemical properties and signals, such as rigidity, composition and spatial distribution. Finally, we discuss the importance of this sensing for major cell functions by taking cell migration and cancer as examples.