ETVs dictate hPSC differentiation by tuning biophysical properties

Stem cells maintain a dynamic dialog with their niche, integrating biochemical and biophysical cues to modulate cellular behavior. Yet, the transcriptional networks that regulate cellular biophysical properties remain poorly defined. Here, we leverage human pluripotent stem cells (hPSCs) and two morphogenesis models - gastruloids and pancreatic differentiation - to establish ETV transcription factors as critical regulators of biophysical parameters and lineage commitment. Genetic ablation of ETV1 or ETV1/ETV4/ETV5 in hPSCs enhances cell-cell and cell-ECM adhesion, leading to aberrant multilineage differentiation including disrupted germ-layer organization, ectoderm loss, and extraembryonic cell overgrowth in gastruloids. Furthermore, ETV1 loss abolishes pancreatic progenitor formation. Single-cell RNA sequencing and follow-up assays reveal dysregulated mechanotransduction via the PI3K/AKT signaling. Our findings highlight the importance of transcriptional control over cell biophysical properties and suggest that manipulating these properties may improve in vitro cell and tissue engineering strategies.

Physical biology of cell-substrate interactions under cyclic stretch

Mechanosensitive focal adhesion (FA) complexes mediate dynamic interactions between cells and substrates and regulate cellular function. Integrins in FA complexes link substrate ligands to stress fibers (SFs) and aid load transfer and traction generation. We developed a one-dimensional, multi-scale, stochastic finite element model of a fibroblast on a substrate that includes calcium signaling, SF remodeling, and FA dynamics. We linked stochastic dynamics, describing the formation and clustering of integrins to substrate ligands via motor-clutches, to a continuum level SF contractility model at various locations along the cell length. We quantified changes in cellular responses with substrate stiffness, ligand density, and cyclic stretch. Results show that tractions and integrin recruitments varied along the cell length; tractions were maximum at lamellar regions and reduced to zero at the cell center. Optimal substrate stiffness, based on maximum tractions exerted by the cell, shifted toward stiffer substrates at high ligand densities. Mean tractions varied biphasically with substrate stiffness and peaked at the optimal substrate stiffness. Cytosolic calcium increased monotonically with substrate stiffness and accumulated near lamellipodial regions. Cyclic stretch increased the cytosolic calcium, integrin concentrations, and tractions at lamellipodial and intermediate regions on compliant substrates. The optimal substrate stiffness under stretch shifted toward compliant substrates for a given ligand density. Stretch also caused cell deadhesions beyond a critical substrate stiffness. FA's destabilized on stiff substrates under cyclic stretch. An increase in substrate stiffness and cyclic stretch resulted in higher fibroblast contractility. These results show that chemomechanical coupling is essential in mechanosensing responses underlying cell-substrate interactions.

Mena regulates nesprin-2 to control actin-nuclear lamina associations, trans-nuclear membrane signalling and gene expression

Interactions between cells and the extracellular matrix, mediated by integrin adhesion complexes, play key roles in fundamental cellular processes, including the sensing and transduction of mechanical cues. Here, we investigate systems-level changes in the integrin adhesome in patient-derived cutaneous squamous cell carcinoma cells and identify the actin regulatory protein Mena as a key node in the adhesion complex network. Mena is connected within a subnetwork of actin-binding proteins to the LINC complex component nesprin-2, with which it interacts and co-localises at the nuclear envelope. Moreover, Mena potentiates the interactions of nesprin-2 with the actin cytoskeleton and the nuclear lamina. CRISPR-mediated Mena depletion causes altered nuclear morphology, reduces tyrosine phosphorylation of the nuclear membrane protein emerin and downregulates expression of the immunomodulatory gene PTX3 via the recruitment of its enhancer to the nuclear periphery. We uncover an unexpected role for Mena at the nuclear membrane, where it controls nuclear architecture, chromatin repositioning and gene expression. Our findings identify an adhesion protein that regulates gene transcription via direct signalling across the nuclear envelope.

The Effect of Matrix Stiffness on Human Hepatocyte Migration and Function-An In Vitro Research

The extracellular matrix (ECM) regulates cellular function through the dynamic biomechanical and biochemical interplay between the resident cells and their microenvironment. Pathologically stiff ECM promotes phenotype changes in hepatocytes during liver fibrosis. To investigate the effect of ECM stiffness on hepatocyte migration and function, we designed an easy fabricated polyvinyl alcohol (PVA) hydrogel in which stiffness can be controlled by changing the concentration of glutaraldehyde. Three stiffnesses of hydrogels corresponding to the health of liver tissue, early stage, and end stage of fibrosis were selected. These were 4.8 kPa (soft), 21 kPa (moderate), and 45 kPa (stiff). For hepatocytes attachment, the hydrogel was coated with fibronectin. To evaluate the optimal concentration of fibronectin, hydrogel was coated with 0.1 mg/mL, 0.01 mg/mL, 0.005 mg/mL, or 0.003 mg/mL fibronectin, and the migratory behavior of single hepatocyte cultured on different concentrations of fibronectin was analyzed. To further explore the effect of substrate stiffness on hepatocyte migration, we used a stiffness controllable commercial 3D collagen gel, which has similar substrate stiffness to that of PVA hydrogel. Our result confirmed the PVA hydrogel biocompatibility with high hepatocytes survival. Fibronectin (0.01 mg/mL) promoted optimal migratory behavior for single hepatocytes. However, for confluent hepatocytes, a stiff substrate promoted hepatocellular migration compared with the soft and moderate groups via enhancing the formation of actin- and tubulin-rich structures. The gene expression analysis and protein expression analysis showed that the stiff substrate altered the phenotype of hepatocytes and induced apoptosis. Hepatocytes in stiff 3D hydrogel showed a higher proportion of cell death and expression of filopodia.

Insights and perspectives on calcium channel functions in the cockpit of cancerous space invaders

Development of metastasis causes the most serious clinical consequences of cancer and is responsible for over 90 % of cancer-related deaths. Hence, a better understanding of the mechanisms that drive metastasis formation appears critical for drug development designed to prevent the spread of cancer and related mortality. Metastasis dissemination is a multistep process supported by the increased motility and invasiveness capacities of tumor cells. To succeed in overcoming the mechanical constraints imposed by the basement membrane and surrounding tissues, cancer cells reorganize their focal adhesions or extend acto-adhesive cellular protrusions, called invadosomes, that can both contact the extracellular matrix and tune its degradation through metalloprotease activity. Over the last decade, accumulating evidence has demonstrated that altered Ca²⁺ channel activities and/or expression promote tumor cell-specific phenotypic changes, such as exacerbated migration and invasion capacities, leading to metastasis formation. While several studies have addressed the molecular basis of Ca²⁺ channel-dependent cancer cell migration, we are still far from having a comprehensive vision of the Ca²⁺ channel-regulated mechanisms of migration/invasion. This is especially true regarding the specific context of invadosome-driven invasion. This review aims to provide an overview of the current evidence supporting a central role for Ca²⁺ channel-dependent signaling in the regulation of these dynamic degradative structures. It will present available data on the few Ca²⁺ channels that have been studied in that specific context and discuss some potential interesting actors that have not been fully explored yet.

Effects of Electrical Stimulation on Stem Cells

Recent interest in developing new regenerative medicine- and tissue engineering-based treatments has motivated researchers to develop strategies for manipulating stem cells to optimize outcomes in these potentially, game-changing treatments. Cells communicate with each other, and with their surrounding tissues and organs via electrochemical signals. These signals originate from ions passing back and forth through cell membranes and play a key role in regulating cell function during embryonic development, healing, and regeneration. To study the effects of electrical signals on cell function, investigators have exposed cells to exogenous electrical stimulation and have been able to increase, decrease and entirely block cell proliferation, differentiation, migration, alignment, and adherence to scaffold materials. In this review, we discuss research focused on the use of electrical stimulation to manipulate stem cell function with a focus on its incorporation in tissue engineering-based treatments.

Filopodia and focal adhesions: An integrated system driving branching morphogenesis in neuronal pathfinding and angiogenesis

Single cell branching during development in vertebrates is typified by neuronal branching to form neurites and vascular branches formed by sprouting angiogenesis. Neurons and endothelial tip cells possess subcellular protrusions that share many common features from the morphological to the molecular level. Both systems utilize filopodia as their cellular protrusion organelles and depend on specific integrin-mediated adhesions to the local extracellular matrix for guidance in their pathfinding. We discuss the similar molecular machineries involved in these two types of cell branch formation and use their analogy to propose a new mechanism for angiogenic filopodia function, namely as adhesion assembly sites. In support of this model we provide primary data of angiogenesis in zebrafish in vivo showing that the actin assembly factor VASP participates in both filopodia formation and adhesion assembly at the base of the filopodia, enabling forward progress of the tip cell. The use of filopodia and their associated adhesions provide a common mechanism for neuronal and endothelial pathfinding during development in response to extracellular matrix cues.

Tumor promoter PMA enhances kindlin-2 and decreases vimentin recruitment into cell adhesion sites

Phorbol diester PMA (phorbol 12-myristate 13-acetate) is a well-known promoter of tumor progression. PMA also regulates cell adhesion by several mechanisms including conformational activation of integrins and integrin clustering. Here, PMA was shown to induce lamellipodia formation and reorganization of the adhesion sites as well as actin and vimentin filaments independently of integrin preactivation. To further analyze the mechanism of PMA action, the protein composition in the α1β1 integrin/collagen IV adhesion sites was analyzed by mass spectrometry and proteomics. In four independent experiments we observed the reduced recruitment of vimentin in relation to integrin α1 subunit. This was in full agreement with the fact that we also detected the retraction of vimentin from cell adhesions by confocal microscopy. Furthermore, the accumulation of kindlin-2 into cell adhesions was significantly increased after PMA treatment. Kindlin-2 siRNA inhibited cell spreading as well as the formation of actin fibrils and cell adhesions, but did not prevent the effect of PMA on lamellipodia formation. Thus, kindlin-2 recruitment was considered to be a consequence rather than the primary cause for the loss of connection between vimentin and the adhesion sites.

Adhesion protein networks reveal functions proximal and distal to cell-matrix contacts

Cell adhesion to the extracellular matrix is generally mediated by integrin receptors, which bind to intracellular adhesion proteins that form multi-molecular scaffolding and signalling complexes. The networks of proteins, and their interactions, are dynamic, mechanosensitive and extremely complex. Recent efforts to characterise adhesions using a variety of technologies, including imaging, proteomics and bioinformatics, have provided new insights into their composition, organisation and how they are regulated, and have also begun to reveal unexpected roles for so-called adhesion proteins in other cellular compartments (for example, the nucleus or centrosomes) in diseases such as cancer. We believe this is opening a new chapter on understanding the wider functions of adhesion proteins, both proximal and distal to cell-matrix contacts.

Direct Interaction between TalinB and Rap1 is necessary for adhesion of Dictyostelium cells

Background

The small G-protein Rap1 is an important regulator of cellular adhesion in Dictyostelium, however so far the downstream signalling pathways for cell adhesion are not completely characterized. In mammalian cells talin is crucial for adhesion and Rap1 was shown to be a key regulator of talin signalling.

Results

In a proteomic screen we identified TalinB as a potential Rap1 effector in Dictyostelium. In subsequent pull-down experiments we demonstrate that the Ras association (RA) domain of TalinB interacts specifically with active Rap1. Studies with a mutated RA domain revealed that the RA domain is essential for TalinB-Rap1 interaction, and that this interaction contributes to cell-substrate adhesion during single-celled growth and is crucial for cell-cell adhesion during multicellular development.

Conclusions

Dictyostelium Rap1 directly binds to TalinB via the conserved RA domain. This interaction is critical for adhesion, which becomes essential for high adhesive force demanding processes, like morphogenesis during multicellular development of Dictyostelium. In mammalian cells the established Rap1-talin interaction is indirect and acts through the scaffold protein - RIAM. Interestingly, direct binding of mouse Rap1 to the RA domain of Talin1 has recently been demonstrated.

Electronic supplementary material

The online version of this article (doi:10.1186/s12860-015-0078-0) contains supplementary material, which is available to authorized users.

Regulator of Chromosome Condensation 2 Identifies High-Risk Patients within Both Major Phenotypes of Colorectal Cancer

PURPOSE

Colorectal cancer has high incidence and mortality worldwide. Patients with microsatellite instable (MSI) tumors have significantly better prognosis than patients with microsatellite stable (MSS) tumors. Considerable variation in disease outcome remains a challenge within each subgroup, and our purpose was to identify biomarkers that improve prediction of colorectal cancer prognosis.

EXPERIMENTAL DESIGN

Mutation analyses of 42 MSI target genes were performed in two independent MSI tumor series (n = 209). Markers that were significantly associated with prognosis in the test series were assessed in the validation series, followed by functional and genetic explorations. The clinical potential was further investigated by immunohistochemistry in a population-based colorectal cancer series (n = 903).

RESULTS

We identified the cell-cycle gene regulator of chromosome condensation 2 (RCC2) as a cancer biomarker. We found a mutation in the 5' UTR region of RCC2 that in univariate and multivariate analyses was significantly associated with improved outcome in the MSI group. This mutation caused reduction of protein expression in dual luciferase gene reporter assays. siRNA knockdown in MSI colon cancer cells (HCT15) caused reduced cell proliferation, cell-cycle arrest, and increased apoptosis. Massive parallel sequencing revealed few RCC2 mutations in MSS tumors. However, weak RCC2 protein expression was significantly associated with poor prognosis, independent of clinical high-risk parameters, and stratifies clinically important patient subgroups with MSS tumors, including elderly patients (>75 years), stage II patients, and those with rectal cancer.

CONCLUSIONS

Impaired RCC2 affects functional and clinical endpoints of colorectal cancer. High-risk patients with either MSI or MSS tumors can be identified with cost-effective routine RCC2 assays.

Plasticity in the macromolecular-scale causal networks of cell migration

Heterogeneous and dynamic single cell migration behaviours arise from a complex multi-scale signalling network comprising both molecular components and macromolecular modules, among which cell-matrix adhesions and F-actin directly mediate migration. To date, the global wiring architecture characterizing this network remains poorly defined. It is also unclear whether such a wiring pattern may be stable and generalizable to different conditions, or plastic and context dependent. Here, synchronous imaging-based quantification of migration system organization, represented by 87 morphological and dynamic macromolecular module features, and migration system behaviour, i.e., migration speed, facilitated Granger causality analysis. We thereby leveraged natural cellular heterogeneity to begin mapping the directionally specific causal wiring between organizational and behavioural features of the cell migration system. This represents an important advance on commonly used correlative analyses that do not resolve causal directionality. We identified organizational features such as adhesion stability and adhesion F-actin content that, as anticipated, causally influenced cell migration speed. Strikingly, we also found that cell speed can exert causal influence over organizational features, including cell shape and adhesion complex location, thus revealing causality in directions contradictory to previous expectations. Importantly, by comparing unperturbed and signalling-modulated cells, we provide proof-of-principle that causal interaction patterns are in fact plastic and context dependent, rather than stable and generalizable.

Regulation of cell-matrix adhesion by OLA1, the Obg-like ATPase 1

Attachment of cells to the extracellular matrix induces clustering of membrane receptor integrins which in turn triggers the formation of focal adhesions (FAs). The adaptor/scaffold proteins in FAs provide linkage to actin cytoskeleton, whereas focal adhesion kinase (FAK) and other FA-associated kinases and phosphatases transduce integrin-mediated signaling cascades, promoting actin polymerization and progression of cell spreading. In this study, we explored the role of OLA1, a newly identified member of Obg-like ATPases, in regulating cell adhesion processes. We showed that in multiple human cell lines RNAi-mediated downregulation of OLA1 significantly accelerated cell adhesion and spreading, and conversely overexpression of OLA1 by gene transfection resulted in delayed cell adhesion and spreading. We further found that OLA1-deficient cells had elevated levels of FAK protein and decreased Ser3 phosphorylation of cofilin, an actin-binding protein and key regulator of actin filament dynamics, while OLA1-overexpressing cells exhibited the opposite molecular alterations in FAK and cofilin. These findings suggest that OLA1 plays an important negative role in cell adhesion and spreading, in part through the regulation of FAK expression and cofilin phosphorylation, and manipulation of OLA1 may lead to significant changes in cell adhesion and the associated phenotypes.

Comparative proteomic analysis of supportive and unsupportive extracellular matrix substrates for human embryonic stem cell maintenance

Human embryonic stem cells (hESCs) are pluripotent cells that have indefinite replicative potential and the ability to differentiate into derivatives of all three germ layers. hESCs are conventionally grown on mitotically inactivated mouse embryonic fibroblasts (MEFs) or feeder cells of human origin. In addition, feeder-free culture systems can be used to support hESCs, in which the adhesive substrate plays a key role in the regulation of stem cell self-renewal or differentiation. Extracellular matrix (ECM) components define the microenvironment of the niche for many types of stem cells, but their role in the maintenance of hESCs remains poorly understood. We used a proteomic approach to characterize in detail the composition and interaction networks of ECMs that support the growth of self-renewing hESCs. Whereas many ECM components were produced by supportive and unsupportive MEF and human placental stromal fibroblast feeder cells, some proteins were only expressed in supportive ECM, suggestive of a role in the maintenance of pluripotency. We show that identified candidate molecules can support attachment and self-renewal of hESCs alone (fibrillin-1) or in combination with fibronectin (perlecan, fibulin-2), in the absence of feeder cells. Together, these data highlight the importance of specific ECM interactions in the regulation of hESC phenotype and provide a resource for future studies of hESC self-renewal.

Defining the extracellular matrix using proteomics

The cell microenvironment has a profound influence on the behaviour, growth and survival of cells. The extracellular matrix (ECM) provides not only mechanical and structural support to cells and tissues but also binds soluble ligands and transmembrane receptors to provide spatial coordination of signalling processes. The ability of cells to sense the chemical, mechanical and topographical features of the ECM enables them to integrate complex, multiparametric information into a coherent response to the surrounding microenvironment. Consequently, dysregulation or mutation of ECM components results in a broad range of pathological conditions. Characterization of the composition of ECM derived from various cells has begun to reveal insights into ECM structure and function, and mechanisms of disease. Proteomic methodologies permit the global analysis of subcellular systems, but extracellular and transmembrane proteins present analytical difficulties to proteomic strategies owing to the particular biochemical properties of these molecules. Here, we review advances in proteomic approaches that have been applied to furthering our understanding of the ECM microenvironment. We survey recent studies that have addressed challenges in the analysis of ECM and discuss major outcomes in the context of health and disease. In addition, we summarize efforts to progress towards a systems-level understanding of ECM biology.

Polarity and stratification of the epidermis

Polarity is a fundamental property of epithelial cells. In this review, we discuss our current knowledge of the polarity of a stratified epithelium, the epidermis, focusing on similarities and differences with simple epithelial models. We highlight how the differences in tissue architecture and physiology result in alterations in some aspects of cell polarity. In addition, we discuss one of the most prominent uses for cell polarity in the epidermis-orienting the mitotic spindle to drive the stratification and differentiation of this tissue during development.

Proteomic analysis of α4β1 integrin adhesion complexes reveals α-subunit-dependent protein recruitment

Integrin adhesion receptors mediate cell-cell and cell-extracellular matrix interactions, which control cell morphology and migration, differentiation, and tissue integrity. Integrins recruit multimolecular adhesion complexes to their cytoplasmic domains, which provide structural and mechanosensitive signaling connections between the extracellular and intracellular milieux. The different functions of specific integrin heterodimers, such as α4β1 and α5β1, have been attributed to distinct signal transduction mechanisms that are initiated by selective recruitment of adhesion complex components to integrin cytoplasmic tails. Here, we report the isolation of ligand-induced adhesion complexes associated with wild-type α4β1 integrin, an activated α4β1 variant in the absence of the α cytoplasmic domain (X4C0), and a chimeric α4β1 variant with α5 leg and cytoplasmic domains (α4Pα5L), and the cataloguing of their proteomes by MS. Using hierarchical clustering and interaction network analyses, we detail the differential recruitment of proteins and highlight enrichment patterns of proteins to distinct adhesion complexes. We identify previously unreported components of integrin adhesion complexes and observe receptor-specific enrichment of molecules with previously reported links to cell migration and cell signaling processes. Furthermore, we demonstrate colocalization of MYO18A with active integrin in migrating cells. These datasets provide a resource for future studies of integrin receptor-specific signaling events.

Structure of bradavidin-C-terminal residues act as intrinsic ligands

Bradavidin is a homotetrameric biotin-binding protein from Bradyrhizobium japonicum, a nitrogen fixing and root nodule-forming symbiotic bacterium of the soybean. Wild-type (wt) bradavidin has 138 amino acid residues, whereas the C-terminally truncated core-bradavidin has only 118 residues. We have solved the X-ray structure of wt bradavidin and found that the C-terminal amino acids of each subunit were uniquely bound to the biotin-binding pocket of an adjacent subunit. The biotin-binding pocket occupying peptide (SEKLSNTK) was named “Brad-tag” and it serves as an intrinsic stabilizing ligand in wt bradavidin. The binding of Brad-tag to core-bradavidin was analysed by isothermal titration calorimetry and a binding affinity of ∼25 µM was measured. In order to study the potential of Brad-tag, a green fluorescent protein tagged with Brad-tag was prepared and successfully concentrated from a bacterial cell lysate using core-bradavidin-functionalized Sepharose resin.

A hitchhiker's guide to mechanobiology

More than a century ago, it was proposed that mechanical forces could drive tissue formation. However, only recently with the advent of enabling biophysical and molecular technologies are we beginning to understand how individual cells transduce mechanical force into biochemical signals. In turn, this knowledge of mechanotransduction at the cellular level is beginning to clarify the role of mechanics in patterning processes during embryonic development. In this perspective, we will discuss current mechanotransduction paradigms, along with the technologies that have shaped the field of mechanobiology.