The fibronectin-binding integrins alpha5beta1 and alphavbeta3 differentially modulate RhoA-GTP loading, organization of cell matrix adhesions, and fibronectin fibrillogenesis

Calcium levels modulate platelet function, platelet-cancer cell interaction, and cancer cell invasion

Platelet-cancer cell interactions play a significant role in metastasis. Indeed, they interact via a plethora of receptors, including integrins (e.g. ⍺IIbβ3 and ⍺vβ3), and calcium is essential for both their stability and function. Additionally, calcium plays a significant role in the coagulation cascade, and the implication of calcium level changes on metastatic dissemination and cancer-associated thrombosis are not fully understood. A significant proportion of cancer patients suffer from hypercalcemia and have a worse prognosis. We hypothesized that calcium levels are important for platelet-cancer cell interactions that are mediated via integrins, thus this can be leveraged to disrupt platelet support to the metastatic process. In this study, we assessed the detection of integrins ⍺IIbβ3 and ⍺vβ3 on platelets and cancer cells, platelet function, and the respective receptors implicated in platelet function, while modulating calcium levels. The effect of calcium levels on platelet-cancer cell interactions and cancer cell invasion in vitro was also assessed. Our data demonstrates that calcium levels affect surface integrins, and receptors involved in platelet-cancer cell interactions. In addition, calcium levels significantly affect platelet activation and aggregation. In our experimental scenarios, calcium depletion modulates platelet-cancer cell interaction with MDA-MB-231 breast cancer cells, while hypercalcemic environments did not affect interaction. Meanwhile, hypercalcemia leads to enhanced cancer cell invasion for both MDA-MB-231 and A549 cells in the presence of platelets. Thus, this study provides a greater understanding of the dynamics associated with the effects of calcium and platelet-cancer cell interactions mediated by integrins.

Integrins in Cardiovascular Health and Disease: Molecular Mechanisms and Therapeutic Opportunities

Cardiovascular diseases, including atherosclerosis, hypertension, and heart failure, remain the leading cause of global mortality, with endothelial dysfunction and vascular remodeling as critical contributors. Integrins, as transmembrane adhesion proteins, are central regulators of cell adhesion, migration, and signaling, playing a pivotal role in maintaining vascular homeostasis and mediating pathological processes such as inflammation, angiogenesis, and extracellular matrix remodeling. This article comprehensively examines the role of integrins in the pathogenesis of cardiovascular diseases, focusing on their dysfunction in endothelial cells and interactions with inflammatory mediators, such as TNF-α. Molecular mechanisms of integrin action are discussed, including their involvement in mechanotransduction, leukocyte adhesion, and signaling pathways that regulate vascular integrity. The review also highlights experimental findings, such as the use of specific integrin-targeting plasmids and immunofluorescence to elucidate integrin functions under inflammatory conditions. Additionally, potential therapeutic strategies are explored, including the development of integrin inhibitors, monoclonal antibodies, and their application in regenerative medicine. These approaches aim not only to mitigate pathological vascular remodeling but also to promote tissue repair and angiogenesis. By bridging insights from molecular studies with their translational potential, this work underscores the promise of integrin-based therapies in advancing the management and treatment of cardiovascular diseases.

Integrins as Key Mediators of Metastasis

Metastasis is currently becoming a major clinical concern, due to its potential to cause therapeutic resistance. Its development involves a series of phases that describe the metastatic cascade: preparation of the pre-metastatic niche, epithelial-mesenchymal transition, dissemination, latency and colonization of the new tissue. In the last few years, new therapeutic targets, such as integrins, are arising to face this disease. Integrins are transmembrane proteins found in every cell that have a key role in the metastatic cascade. They intervene in adhesion and intracellular signaling dependent on the extracellular matrix and cytokines found in the microenvironment. In this case, integrins can initiate the epithelial-mesenchymal transition, guide the formation of the pre-metastatic niche and increase tumor migration and survival. Integrins also take part in the tumor vascularization process necessary to sustain metastasis. This fact emphasizes the importance of inhibitory therapies capable of interfering with the function of integrins in metastasis.

Targeting Pancreatic Cancer Cell Stemness by Blocking Fibronectin-Binding Integrins on Cancer-Associated Fibroblasts

SIGNIFICANCE

Simultaneous targeting of two integrins that function as receptors for FN, a protumor ECM protein, can prevent fibroblasts from supporting the malignant behavior of pancreatic cancer cells.

Cilengitide sensitivity is predicted by overall integrin expression in breast cancer

BACKGROUND

Treatment options for triple-negative breast cancer (TNBC) are limited and patients face a poor prognosis. Here, we sought to identify drugs that target TNBC vulnerabilities and understand the biology underlying these responses. We analyzed the Broad Institute DepMap to identify recurrent TNBC vulnerabilities and performed a 45-compound screen on vulnerability-related pathways on a set of up to 8 TNBC cell lines. We identified a subset of cell lines with an ITGAV vulnerability and a differential sensitivity to cilengitide, an integrin inhibitor targeting ITGAV:ITGB3 and ITGAV:ITGB5. Next, we sought to understand cilengitide resistance and response biomarkers. Clinical trials targeting integrins continue enrolling patients, necessitating an understanding of how these drugs affect tumors.

METHODS

We combined in vitro assays with computational approaches to systematically explore the differential sensitivity to cilengitide and resistance mechanisms. We tested an additional pan-ITGAV inhibitor (GLPG0187) to determine how generalizable our findings on cilengitide sensitivity might be to integrin inhibition. ITGB4, ITGA3, and ITGA6 knockdown experiments assessed the importance of integrin monomers in cell attachment during cilengitide treatment. Additionally, we explored the role of extracellular matrix (ECM) proteins in cilengitide response by performing cell replating experiments and by culturing on collagen, fibronectin, or laminin coated plates.

RESULTS

We discovered that cell-derived ECM modulates cilengitide sensitivity and exogenous fibronectin addition conferred resistance to all sensitive TNBC cell lines, though fibronectin expression did not correlate with sensitivity. Instead, elevated overall integrin protein levels, not specific integrins, in TNBC cells positively correlated with resistance. This suggested that high pan-integrin expression promotes cilengitide resistance. Thus, we tested cilengitide in six luminal breast cancer cell lines (which have low integrin levels); all were sensitive. Also, pan-ITGAV inhibitor, GLPG0187, showed the same sensitivity profile across our TNBC cell lines, suggesting our findings apply to other integrin inhibitors.

CONCLUSIONS

Integrin inhibitors are appealing candidates to pursue as anti-cancer drugs because they are generally well-tolerated, but their efficacy is mixed, possibly due to the absence of predictive markers. Cilengitide induces death in breast cancer cells with low integrin abundance, where complementary ECM promotes survival. Thus, integrin inhibition in breast cancer warrants further study.

Self-assembled Arginine-Glycine-Aspartic Acid Mimic Peptide Hydrogels as Multifunctional Biomaterials for Wound Healing

Clinical management of nonhealing ulcers requires advanced materials that can enhance wound closure rates without relying on the release of drugs or other growth factors to obviate systemic deleterious side effects. In our previous work, we synthesized an integrin-binding cell adhesive MNH2 {Fmoc-FFβAR(K)βA-NH2 consisting of an RGD mimic, [R(K)], with an amide terminus}, MOH {Fmoc-FFβAR(K)βA-OH consisting of an RGD mimic, [R(K)], with acid terminus}, and MR (Fmoc-FFβARGDβA-NH2 consisting of an RGD peptide, reference) with multifunctional activity. Here, we reported the synthesis, characterization, and performance of a reversed derivative, R-MNH2 (Fmoc-FFβA(K)RβA-NH2 consisting of an RGD mimic, [K(R)], with an amide terminus) of an antimicrobial cell adhesive peptide, MNH2. Both peptides (MNH2 and R-MNH2) were found to interact with αvβ3 integrin, as shown by docking studies; however, they differed in cell adhesive properties, hydrogel formation, and antimicrobial efficacy. Later, the wound healing ability of a series of RGD/RGD peptide mimics (MR, R-MNH2, MNH2, and MOH) was studied in a methicillin-resistant Staphylococcus aureus (MRSA)-infected Balb/c mouse model. All studied peptides showed cell adhesion and wound healing properties; however, only the amide-terminal RGD peptide mimic, MNH2, and its reversed derivative, R-MNH2, showed antimicrobial activity in both in vitro and in vivo studies. Of these, MNH2 showed the highest integrin-mediated spreading, migration, and proliferation of dermal cells in vitro as well as in vivo. Therefore, the MNH2 peptide mimic represents a paradigm shift in the development of dermoconductive strategies to treat chronic wounds.

Fibroblast integrin α11β1 is a collagen assembly receptor in mechanoregulated fibrillar adhesions

Solid epithelial cancers with significant desmoplasia are characterized by an excessive deposition of collagen-based matrix, which often supports tumor progression. However, the mechanism of how collagen receptors mediate collagen fibrillogenesis still remains mostly unclear. We show that the collagen-binding integrin α11β1 can co-localize with tensin-1 and deposited collagen I in human pancreatic ductal adenocarcinoma (PDAC) stroma. In addition to the canonical fibrillar adhesion integrin α5β1 expressed by human PDAC cancer-associated fibroblasts (CAFs), tensin-1-positive fibrillar adhesions contained α11β1 but lacked α1β1 and α2β1. CAFs lacking α5β1 expression displayed mechanoregulated and tensin-1 dependent α11β1 fibrillar adhesions, suggesting independent roles of the two integrins with regards to fibrillar adhesions-based de novo fibrillogenesis. Further, we demonstrate that cell surface-associated collagen I assembly necessitated α11β1, but not α5β1 expression. In summary, α11β1 integrin is a novel component of fibrillar adhesions, which is strategically positioned to mediate de novo collagen fibrillogenesis at the cell surface under pro-fibrotic conditions.

Proteins Derived From MRL/MpJ Tendon Provisional Extracellular Matrix and Secretome Promote Pro-Regenerative Tenocyte Behavior

Tendinopathies are prevalent musculoskeletal conditions that have no effective therapies to attenuate scar formation. In contrast to other adult mammals, the tendons of Murphy Roths Large (MRL/MpJ) mice possess a superior healing capacity following acute and overuse injuries. Here, we hypothesized that the application of biological cues derived from the local MRL/MpJ tendon environment would direct otherwise scar-mediated tenocytes towards a pro-regenerative MRL/MpJ-like phenotype. We identified soluble factors enriched in the secretome of MRL/MpJ tenocytes using bioreactor systems and quantitative proteomics. We then demonstrated that the combined administration of structural and soluble constituents isolated from decellularized MRL/MpJ tendon provisional ECM (dPECM) and the secretome stimulate scar-mediated rodent tenocytes towards enhanced mechanosensitivity, proliferation, intercellular communication, and ECM deposition associated with MRL/MpJ cell behavior. Our findings highlight key biological mechanisms that drive MRL/MpJ tenocyte activity and their interspecies utility to be harnessed for therapeutic strategies that promote pro-regenerative healing outcomes.

Teaser

Proteins enriched in a super-healer mouse strain elicit interspecies utility in promoting pro-regenerative tenocyte behavior.

A proteomics approach to isolating neuropilin-dependent α5 integrin trafficking pathways: neuropilin 1 and 2 co-traffic α5 integrin through endosomal p120RasGAP to promote polarised fibronectin fibrillogenesis in endothelial cells

Integrin trafficking to and from membrane adhesions is a crucial mechanism that dictates many aspects of a cell's behaviour, including motility, polarisation, and invasion. In endothelial cells (ECs), the intracellular traffic of α5 integrin is regulated by both neuropilin 1 (NRP1) and neuropilin 2 (NRP2), yet the redundancies in function between these co-receptors remain unclear. Moreover, the endocytic complexes that participate in NRP-directed traffic remain poorly annotated. Here we identify an important role for the GTPase-activating protein p120RasGAP in ECs, promoting the recycling of α5 integrin from early endosomes. Mechanistically, p120RasGAP enables transit of endocytosed α5 integrin-NRP1-NRP2 complexes to Rab11+ recycling endosomes, promoting cell polarisation and fibronectin (FN) fibrillogenesis. Silencing of both NRP receptors, or p120RasGAP, resulted in the accumulation of α5 integrin in early endosomes, a loss of α5 integrin from surface adhesions, and attenuated EC polarisation. Endothelial-specific deletion of both NRP1 and NRP2 in the postnatal retina recapitulated our in vitro findings, severely impairing FN fibrillogenesis and polarised sprouting. Our data assign an essential role for p120RasGAP during integrin traffic in ECs and support a hypothesis that NRP receptors co-traffic internalised cargoes. Importantly, we utilise comparative proteomics analyses to isolate a comprehensive map of NRP1-dependent and NRP2-dependent α5 integrin interactions in ECs.

Omental preadipocytes stimulate matrix remodeling and IGF signaling to support ovarian cancer metastasis

Ovarian cancer can metastasize to the omentum, which is associated with a complex tumor microenvironment. Omental stromal cells facilitate ovarian cancer colonization by secreting cytokines and growth factors. Improved understanding of the tumor supportive functions of specific cell populations in the omentum could identify strategies to prevent and treat ovarian cancer metastasis. Here, we showed that omental preadipocytes enhance the tumor initiation capacity of ovarian cancer cells. Secreted factors from preadipocytes supported cancer cell viability during nutrient and isolation stress and enabled prolonged proliferation. Co-culturing with pre-adipocytes led to upregulation of genes involved in extracellular matrix (ECM) organization, cellular response to stress, and regulation of insulin-like growth factor (IGF) signaling in ovarian cancer cells. IGF-1 induced ECM genes and increased alternative NF-κB signaling by activating RelB. Inhibiting the IGF-1 receptor (IGF1R) initially increased tumor omental adhesion but decreased growth of established preadipocyte-induced subcutaneous tumors as well as established intraperitoneal tumors. Together, this study shows that omental preadipocytes support ovarian cancer progression, which has implications for targeting metastasis.

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.

Force-Regulated Spontaneous Conformational Changes of Integrins α5β1 and αVβ3

Integrins are cell surface nanosized receptors crucial for cell motility and mechanosensing of the extracellular environment, which are often targeted for the development of biomaterials and nanomedicines. As a key feature of integrins, their activity, structure and behavior are highly mechanosensitive, which are regulated by mechanical forces down to pico-Newton scale. Using single-molecule biomechanical approaches, we compared the force-modulated ectodomain bending/unbending conformational changes of two integrin species, α5β1 and αVβ3. It was found that the conformation of integrin α5β1 is determined by a threshold head-to-tail tension. By comparison, integrin αVβ3 exhibits bistability even without force and can spontaneously transition between the bent and extended conformations with an apparent transition time under a wide range of forces. Molecular dynamics simulations observed almost concurrent disruption of ∼2 hydrogen bonds during integrin α5β1 unbending, but consecutive disruption of ∼7 hydrogen bonds during integrin αVβ3 unbending. Accordingly, we constructed a canonical energy landscape for integrin α5β1 with a single energy well that traps the integrin in the bent state until sufficient force tilts the energy landscape to allow the conformational transition. In contrast, the energy landscape of integrin αVβ3 conformational changes was constructed with hexa-stable intermediate states and intermediate energy barriers that segregate the conformational change process into multiple small steps. Our study elucidates the different biomechanical inner workings of integrins α5β1 and αVβ3 at the submolecular level, helps understand their mechanosignaling processes and how their respective functions are facilitated by their distinctive mechanosensitivities, and provides useful design principles for the engineering of protein-based biomechanical nanomachines.

Epithelial homelessness: an atypical form of anoikis triggered by Leishmania interaction with epithelial cells

Aim: Leishmaniasis is characterized by a spectrum of diseases with two main clinical forms, cutaneous and visceral, caused by Leishmania tropica and Leishmania donovani, respectively. Studying Leishmania's interaction with the epithelial barrier at the initial site of a bite is crucial to understanding the establishment of the disease. Materials & methods: To discern parasite-host epithelial interaction, we developed in vitro cellular models involving co-cultures of Leishmania and MDCK epithelial cells. Results: Both L. donovani-MDCK and L. tropica-MDCK co-culture models demonstrated a phenomenon known as atypical anoikis apoptosis, typically identified by distinctive 'flipping in' of cell membranes and disordered cytoskeletal frameworks. Conclusion: This study bridges the gap in the fundamental understanding of the intricate latticework involving vector-Leishmania-host and may inform drug development strategies.

Stiffness-dependent MSC homing and differentiation into CAFs - implications for breast cancer invasion

Cellular heterogeneity and extracellular matrix (ECM) stiffening have been shown to be drivers of breast cancer invasiveness. Here, we examine how stiffness-dependent crosstalk between cancer cells and mesenchymal stem cells (MSCs) within an evolving tumor microenvironment regulates cancer invasion. By analyzing previously published single-cell RNA sequencing datasets, we establish the existence of a subpopulation of cells in primary tumors, secondary sites and circulatory tumor cell clusters of highly aggressive triple-negative breast cancer (TNBC) that co-express MSC and cancer-associated fibroblast (CAF) markers. By using hydrogels with stiffnesses of 0.5, 2 and 5 kPa to mimic different stages of ECM stiffening, we show that conditioned medium from MDA-MB-231 TNBC cells cultured on 2 kPa gels, which mimic the pre-metastatic stroma, drives efficient MSC chemotaxis and induces stable differentiation of MSC-derived CAFs in a TGFβ (TGFB1)- and contractility-dependent manner. In addition to enhancing cancer cell proliferation, MSC-derived CAFs on 2 kPa gels maximally boost local invasion and confer resistance to flow-induced shear stresses. Collectively, our results suggest that homing of MSCs at the pre-metastatic stage and their differentiation into CAFs actively drives breast cancer invasion and metastasis in TNBC.

Differential regulation of fibronectin expression and fibrillogenesis by autocrine TGF-β1 signaling in malignant and benign mammary epithelial cells

Remodeling of the extracellular matrix (ECM) is a key hallmark of cancer progression. A critical component of ECM remodeling is the assembly of the glycoprotein fibronectin (FN) into insoluble fibrils, which provide a scaffold for invading vascular endothelial cells and escaping cancer cells, as well as a framework for collagen deposition and oncogenic cytokine tethering. FN fibril assembly is induced by Transforming Growth Factor-β1 (TGF-β1), which was originally identified for its role in malignant transformation. Addition of exogenous TGF-β1 drives FN fibril assembly while also upregulating endogenous TGF-β1 expression and autocrine signaling. In the current study, we sought to determine if autocrine TGF-β1 signaling plays a role in FN fibril formation in either MCF10A mammary epithelial cells, which behave similarly to healthy epithelia, or malignant MDA- MB-231 breast cancer cells. Our results show two interesting findings: first, malignant MDA-MB- 231 cells assemble less FN into fibrils, despite expressing and secreting more soluble FN; second, autocrine TGF-β1 signaling is required for FN fibril formation in MCF10A epithelial cells, even in the presence of exogenous, active TGF-β1. This suggests that autocrine TGF-β1 is signaling through distinct pathways from active exogenous TGF-β1. We hypothesized that this signaling was mediated by interactions between the TGF-β1 latency associated peptide (LAP) and αv integrins; indeed, incubating MCF10As with soluble LAP, even in the absence of the active TGF-β1 ligand, partially recovered FN fibril assembly. Taken together, these data suggests that autocrine TGF-β1 plays a critical role in FN fibril assembly, and this interaction is mediated by LAP-integrin signaling.

β1 integrin signaling governs necroptosis via the chromatin-remodeling factor CHD4

Fibrosis, characterized by sustained activation of myofibroblasts and excessive extracellular matrix (ECM) deposition, is known to be associated with chronic inflammation. Receptor-interacting protein kinase 3 (RIPK3), the central kinase of necroptosis signaling, is upregulated in fibrosis and contributes to tumor necrosis factor (TNF)-mediated inflammation. In bile-duct-ligation-induced liver fibrosis, we found that myofibroblasts are the major cell type expressing RIPK3. Genetic ablation of β1 integrin, the major profibrotic ECM receptor in fibroblasts, not only abolished ECM fibrillogenesis but also blunted RIPK3 expression via a mechanism mediated by the chromatin-remodeling factor chromodomain helicase DNA-binding protein 4 (CHD4). While the function of CHD4 has been conventionally linked to the nucleosome-remodeling deacetylase (NuRD) and CHD4-ADNP-HP1(ChAHP) complexes, we found that CHD4 potently repressed a set of genes, including Ripk3, with high locus specificity but independent of either the NuRD or the ChAHP complex. Thus, our data uncover that β1 integrin intrinsically links fibrotic signaling to RIPK3-driven inflammation via a novel mode of action of CHD4.

Intrinsic self-organization of integrin nanoclusters within focal adhesions is required for cellular mechanotransduction

Upon interaction with the extracellular matrix, the integrin receptors form nanoclusters as a first biochemical response to ligand binding. Here, we uncover a critical biodesign principle where these nanoclusters are spatially self-organized, facilitating effective mechanotransduction. Mouse Embryonic Fibroblasts (MEFs) with integrin β3 nanoclusters organized themselves with an intercluster distance of ∼550 nm on uniformly coated fibronectin substrates, leading to larger focal adhesions. We determined that this spatial organization was driven by cell-intrinsic factors since there was no pre-existing pattern on the substrates. Altering this spatial organization using cyclo-RGD functionalized Titanium nanodiscs (of 100 nm, corroborating to the integrin nanocluster size) spaced at intervals of 300 nm (almost half), 600 nm (normal) or 1000 nm (almost double) resulted in abrogation in mechanotransduction, indicating that a new parameter i.e., an optimal intercluster distance is necessary for downstream function. Overexpression of α-actinin, which induces a kink in the integrin tail, disrupted the establishment of the optimal intercluster distance, while simultaneous co-overexpression of talin head with α-actinin rescued it, indicating a concentration-dependent competition, and that cytoplasmic activation of integrin by talin head is required for the optimal intercluster organization. Additionally, talin head-mediated recruitment of FHOD1 that facilitates local actin polymerization at nanoclusters, and actomyosin contractility were also crucial for establishing the optimal intercluster distance and a robust mechanotransduction response. These findings demonstrate that cell-intrinsic machinery plays a vital role in organizing integrin receptor nanoclusters within focal adhesions, encoding essential information for downstream mechanotransduction signalling.

Upregulation of fibronectin and its integrin receptors - an adaptation to isolation stress that facilitates tumor initiation

Tumor initiation at either primary or metastatic sites is an inefficient process in which tumor cells must fulfill a series of conditions. One critical condition involves the ability of individual tumor-initiating cells to overcome 'isolation stress', enabling them to survive within harsh isolating microenvironments that can feature nutrient stress, hypoxia, oxidative stress and the absence of a proper extracellular matrix (ECM). In response to isolation stress, tumor cells can exploit various adaptive strategies to develop stress tolerance and gain stemness features. In this Opinion, we discuss how strategies such as the induction of certain cell surface receptors and deposition of ECM proteins enable tumor cells to endure isolation stress, thereby gaining tumor-initiating potential. As examples, we highlight recent findings from our group demonstrating how exposure of tumor cells to isolation stress upregulates the G-protein-coupled receptor lysophosphatidic acid receptor 4 (LPAR4), its downstream target fibronectin and two fibronectin-binding integrins, α5β1 and αvβ3. These responses create a fibronectin-rich niche for tumor cells, ultimately driving stress tolerance, cancer stemness and tumor initiation. We suggest that approaches to prevent cancer cells from adapting to stress by suppressing LPAR4 induction, blocking its downstream signaling or disrupting fibronectin-integrin interactions hold promise as potential strategies for cancer treatment.

RNA-binding protein-regulated fibronectin is essential for EGFR-activated metastasis of head and neck squamous cell carcinoma

There is a higher expression level of epidermal growth factor receptor (EGFR) in up to 90% of advanced head and neck squamous cell carcinoma (HNSCC) tissue than in normal surrounding tissues. However, the role of RNA-binding proteins (RBPs) in EGFR-associated metastasis of HNSCC remains unclear. In this study, we reveal that RBPs, specifically nucleolin (NCL) and heterogeneous nuclear ribonucleoprotein A2/B1 (hnRNPA2B1), correlated with the mesenchymal phenotype of HNSCC. The depletion of RBPs significantly attenuated EGF-induced HNSCC metastasis. Intriguingly, the EGF-induced EMT markers, such as fibronectin, were regulated by RBPs through the ERK and NF-κB pathway, followed by the enhancement of mRNA stability of fibronectin through the 5' untranslated region (5'-UTR) of the gene. The upregulation of fibronectin triggered the integrin signaling activation to enhance tumor cells' attachment to endothelial cells and increase endothelial permeability. In addition, the concurrence of EGFR and RBPs or EGFR and fibronectin was associated with overall survival and disease-free survival of HNSCC. The in vivo study showed that depletion of NCL, hnRNPA2B1, and fibronectin significantly inhibited EGF-promoted extravasation of tumor cells into lung tissues. The depletion of fibronectin or treatment with integrin inhibitors dramatically attenuated EGF-induced HNSCC metastatic nodules in the lung. Our data suggest that the RBPs/fibronectin axis is essential for EGF-induced tumor-endothelial cell interactions to enhance HNSCC cell metastasis.

Imaging and quantitative analysis of integrin-dependent cell-matrix adhesions

Integrin-dependent cell-extracellular matrix adhesion is essential for wound healing, embryonic development, immunity, and tissue organization. Here, we present a protocol for the imaging and quantitative analysis of integrin-dependent cell-matrix adhesions. We describe steps for cell culture; virus preparation; lentiviral transduction; imaging with widefield, confocal, and total internal reflection fluorescence microscopy; and using a script for their quantitative analysis. We then detail procedures for analyzing adhesion dynamics by live-cell imaging and fluorescence recovery after photobleaching (FRAP). For complete details on the use and execution of this protocol, please refer to Margadant et al. (2012),1 van der Bijl et al. (2020),2 Amado-Azevedo et al. (2021).3.

Matrix stiffness controls megakaryocyte adhesion, fibronectin fibrillogenesis, and proplatelet formation through Itgβ3

Megakaryocytes (MKs) are the precursor cells of platelets, located in the bone marrow (BM). Once mature, they extend elongated projections named proplatelets through sinusoid vessels, emerging from the marrow stroma into the circulating blood. Not all signals from the microenvironment that regulate proplatelet formation are understood, particularly those from the BM biomechanics. We sought to investigate how MKs perceive and adapt to modifications of the stiffness of their environment. Although the BM is one of the softest tissue of the body, its rigidification results from excess fibronectin (FN), and other matrix protein deposition occur upon myelofibrosis. Here, we have shown that mouse MKs are able to detect the stiffness of a FN-coated substrate and adapt their morphology accordingly. Using a polydimethylsiloxane substrate with stiffness varying from physiological to pathological marrow, we found that a stiff matrix favors spreading, intracellular contractility, and FN fibrils assembly at the expense of proplatelet formation. Itgb3, but not Itgb1, is required for stiffness sensing, whereas both integrins are involved in fibrils assembly. In contrast, soft substrates promote proplatelet formation in an Itgb3-dependent manner, consistent with the ex vivo decrease in proplatelet formation and the in vivo decrease in platelet number in Itgb3-deficient mice. Our findings demonstrate the importance of environmental stiffness for MK functions with potential pathophysiological implications during pathologies that deregulate FN deposition and modulate stiffness in the marrow.

Reticular adhesions are assembled at flat clathrin lattices and opposed by active integrin α5β1

Reticular adhesions (RAs) consist of integrin αvβ5 and harbor flat clathrin lattices (FCLs), long-lasting structures with similar molecular composition as clathrin-mediated endocytosis (CME) carriers. Why FCLs and RAs colocalize is not known. Here, we show that RAs are assembled at FCLs in a process controlled by fibronectin (FN) and its receptor, integrin α5β1. We observed that cells on FN-rich matrices displayed fewer FCLs and RAs. CME machinery inhibition abolished RAs and live-cell imaging showed that RA establishment requires FCL coassembly. The inhibitory activity of FN was mediated by the activation of integrin α5β1 at Tensin1-positive fibrillar adhesions. Conventionally, endocytosis disassembles cellular adhesions by internalizing their components. Our results present a novel paradigm in the relationship between these two processes by showing that endocytic proteins can actively function in the assembly of cell adhesions. Furthermore, we show this novel adhesion assembly mechanism is coupled to cell migration via unique crosstalk between cell-matrix adhesions.

SEMA7a primes integrin α5β1 engagement instructing fibroblast mechanotransduction, phenotype and transcriptional programming

Integrins are cellular receptors that bind the extracellular matrix (ECM) and facilitate the transduction of biochemical and biophysical microenvironment cues into cellular responses. Upon engaging the ECM, integrin heterodimers must rapidly strengthen their binding with the ECM, resulting in the assembly of force-resistant and force-sensitive integrin associated complexes (IACs). The IACs constitute an essential apparatus for downstream signaling and fibroblast phenotypes. During wound healing, integrin signaling is essential for fibroblast motility, proliferation, ECM reorganization and, ultimately, restoration of tissue homeostasis. Semaphorin 7A (SEMA7a) has been previously implicated in post-injury inflammation and tissue fibrosis, yet little is known about SEMA7a's role in directing stromal cell, particularly fibroblast, behaviors. We demonstrate that SEMA7a regulates integrin signaling through cis-coupling with active integrin α5β1 on the plasma membrane, enabling rapid integrin adhesion strengthening to fibronectin (Fn) and normal downstream mechanotransduction. This molecular function of SEMA7a potently regulates fibroblast adhesive, cytoskeletal, and migratory phenotype with strong evidence of downstream alterations in chromatin structure resulting in global transcriptomic reprogramming such that loss of SEMA7a expression is sufficient to impair the normal migratory and ECM assembly phenotype of fibroblasts resulting in significantly delayed tissue repair in vivo.

CSK-mediated signalling by integrins in cancer

Cancer progression and metastasis are processes heavily controlled by the integrin receptor family. Integrins are cell adhesion molecules that constitute the central components of mechanosensing complexes called focal adhesions, which connect the extracellular environment with the cell interior. Focal adhesions act as key players in cancer progression by regulating biological processes, such as cell migration, invasion, proliferation, and survival. Src family kinases (SFKs) can interplay with integrins and their downstream effectors. SFKs also integrate extracellular cues sensed by integrins and growth factor receptors (GFR), transducing them to coordinate metastasis and cell survival in cancer. The non-receptor tyrosine kinase CSK is a well-known SFK member that suppresses SFK activity by phosphorylating its specific negative regulatory loop (C-terminal Y⁵²⁷ residue). Consequently, CSK may play a pivotal role in tumour progression and suppression by inhibiting SFK oncogenic effects in several cancer types. Remarkably, CSK can localise near focal adhesions when SFKs are activated and even interact with focal adhesion components, such as phosphorylated FAK and Paxillin, among others, suggesting that CSK may regulate focal adhesion dynamics and structure. Even though SFK oncogenic signalling has been extensively described before, the specific role of CSK and its crosstalk with integrins in cancer progression, for example, in mechanosensing, remain veiled. Here, we review how CSK, by regulating SFKs, can regulate integrin signalling, and focus on recent discoveries of mechanotransduction. We additionally examine the cross talk of integrins and GFR as well as the membrane availability of these receptors in cancer. We also explore new pharmaceutical approaches to these signalling pathways and analyse them as future therapeutic targets.

Early committed polarization of intracellular tension in response to cell shape determines the osteogenic differentiation of mesenchymal stromal cells

Within the heterogeneous tissue architecture, a comprehensive understanding of how cell shapes regulate cytoskeletal mechanics by adjusting focal adhesions (FAs) signals to correlate with the lineage commitment of mesenchymal stromal cells (MSCs) remains obscure. Here, via engineered extracellular matrices, we observed that the development of mature FAs, coupled with a symmetrical pattern of radial fiber bundles, appeared at the right-angle vertices in cells with square shape. While circular cells aligned the transverse fibers parallel to the cell edge, and moved them centripetally in a counter-clockwise direction, symmetrical bundles of radial fibers at the vertices of square cells disrupted the counter-clockwise swirling and bridged the transverse fibers to move centripetally. In square cells, the contractile force, generated by the myosin IIA-enriched transverse fibers, were concentrated and transmitted outwards along the symmetrical bundles of radial fibers, to the extracellular matrix through FAs, and thereby driving FA organization and maturation. The symmetrical radial fiber bundles concentrated the transverse fibers contractility inward to the linkage between the actin cytoskeleton and the nuclear envelope. The tauter cytoskeletal network adjusted the nuclear-actomyosin force balance to cause nuclear deformability and to increase nuclear translocation of the transcription co-activator YAP, which in turn modulated the switch in MSC commitment. Thus, FAs dynamically respond to geometric cues and remodel actin cytoskeletal network to re-distribute intracelluar tension towards the cell nucleus, and thereby controlling YAP mechanotransduction signaling in regulating MSC fate decision. STATEMENT OF SIGNIFICANCE: We decipher how cellular mechanics is self-organized depending on extracellular geometric features to correlate with mesenchymal stromal cell lineage commitment. In response to geometry constrains on cell morphology, symmetrical radial fiber bundles are assembled and clustered depending on the maturation state of focal adhesions and bridge with the transverse fibers, and thereby establishing the dynamic cytoskeletal network. Contractile force, generated by the myosin-IIA-enriched transverse fibers, is transmitted and dynamically drives the retrograde movement of the actin cytoskeletal network, which appropriately adjusts the nuclear-actomyosin force balance and deforms the cell nucleus for YAP mechano-transduction signaling in regulating mesenchymal stromal cell fate decision.

Lfc subcellular localization and activity is controlled by αv-class integrin

Fibronectin (FN)-binding integrins control a variety of cellular responses through Rho GTPases. The FN-binding integrins, αvβ3 and α5β1, are known to induce different effects on cell morphology and motility. Here, we report that FN-bound αvβ3 integrin, but not FN-bound α5β1 integrin, triggers the dissociation of the RhoA GEF Lfc (also known as GEF-H1 and ARHGEF2 in humans) from microtubules (MTs), leading to the activation of RhoA, formation of stress fibres and maturation of focal adhesions (FAs). Conversely, loss of Lfc expression decreases RhoA activity, stress fibre formation and FA size, suggesting that Lfc is the major GEF downstream of FN-bound αvβ3 that controls RhoA activity. Mechanistically, FN-engaged αvβ3 integrin activates a kinase cascade involving MARK2 and MARK3, which in turn leads to phosphorylation of several phospho-sites on Lfc. In particular, S151 was identified as the main site involved in the regulation of Lfc localization and activity. Our findings indicate that activation of Lfc and RhoA is orchestrated in FN-adherent cells in an integrin-specific manner.

Contact Guidance of Connective Tissue Fibroblasts on Submicrometer Anisotropic Topographical Cues Is Dependent on Tissue of Origin, β1 Integrins, and Tensin-1 Recruitment

The substratum topography of both natural and synthetic materials is a prominent regulator of cell behaviors including adhesion, migration, matrix fibrillogenesis, and cell phenotype. Connective tissue fibroblasts are known to respond to repeating groove topographical modifications by aligning and exhibiting directed migration, a phenomenon termed contact guidance. Although both reside in collagen rich connective tissues, dermal and gingival fibroblasts are known to exhibit differences in phenotype during wound healing, with gingival tissue showing a fetal-like scarless response. Differences in adhesion formation and maturation are known to underlie both a scarring phenotype and cell response to topographical features. Utilizing repeating groove substrates with periodicities of 600, 900, and 1200 nm (depth, 100 nm), we investigated the roles of integrins αvβ3 and β1 associated adhesions on contact guidance of human gingival (HGFs) and dermal fibroblasts (HDFs). HGFs showed a higher degree of orientation with the groove long axis than HDFs, with alignment of both vinculin and tensin-1 evident on 600 and 900 nm periodicities in both cell types. Orientation with grooves of any periodicity in HGFs and HDFs did not alter the adhesion number or area compared to smooth control surfaces. Growth of both cell types on all periodicities reduced fibronectin fibrillogenesis compared to control surfaces. Independent inhibition of integrin αvβ3 and β1 in both cell types induced changes in spreading up to 6 h and reduced alignment with the groove long axis. At 24 h post-seeding with blocking antibodies, HGFs recovered orientation, but in HDFs, blocking of β1, but not αvβ3 integrins, inhibited alignment. Blocking of β1 and αvβ3 in HDFs, but not HGFs, inhibited tensin-1-associated fibrillar adhesion formation. Furthermore, inhibition of β1 integrins in HDFs, but not HGFs, resulted in recruitment of tensin-1 to αvβ3 focal adhesions, preventing HDFs from aligning with the groove long axis. Our work demonstrates that tensin-1 localization with specific integrins in adhesion sites is an important determinant of contact guidance. This work emphasizes further the need for tissue-specific biomaterials, when integration into host tissues is required.

Astrocyte-associated fibronectin promotes the proinflammatory phenotype of astrocytes through β1 integrin activation

Astrocytes are key players in neuroinflammation. In response to central nervous system (CNS) injury or disease, astrocytes undergo reactive astrogliosis, which is characterized by increased proliferation, migration, and glial fibrillary acidic protein (GFAP) expression. Activation of the transcription factor nuclear factor-κB (NF-κB) and upregulation of downstream proinflammatory mediators in reactive astrocytes induce a proinflammatory phenotype in astrocytes, thereby exacerbating neuroinflammation by establishing an inflammatory loop. In this study, we hypothesized that excessive fibronectin (FN) derived from reactive astrocytes would induce this proinflammatory phenotype in astrocytes in an autocrine manner. We exogenously treated astrocytes with monomer FN, which can be incorporated into the extracellular matrix (ECM), to mimic plasma FN extravasated through a compromised blood-brain barrier in neuroinflammation. We also induced de novo synthesis and accumulation of astrocyte-derived FN through tumor necrosis factor-α (TNF-α) stimulation. The excessive FN deposition resulting from both treatments initiated reactive astrogliosis and triggered NF-κB signaling in the cultured astrocytes. In addition, inhibition of FN accumulation in the ECM by the FN inhibitor pUR4 strongly attenuated the FN- and TNF-α-induced GFAP expression, NF-κB activation, and proinflammatory mediator production of astrocytes by interrupting FN-β1 integrin coupling and thus the inflammatory loop. In an in vivo experiment, intrathecal injection of pUR4 considerably ameliorated FN deposition, GFAP expression, and NF-κB activation in inflamed spinal cord, suggesting the therapeutic potential of pUR4 for attenuating neuroinflammation and promoting neuronal function restoration.

Heparin-mimicking polymer-based hydrogel matrix regulates macrophage polarization by controlling cell adhesion

The physicochemical properties of biomaterials influence cell adhesion, shape, and polarization of macrophages. In this study, we aimed to evaluate the polarization of macrophages in terms of the regulation of cell adhesion and how synthetic mimics for heparin and poly(sodium-4-styrenesulfonate) can regulate macrophage polarization by modulating cell shape, focal adhesion, cell traction force, and intracellular tension. Our initial findings showed that macrophages cultured with heparin-mimicking polymer-based hydrogel matrix showed reduced expression of cell adhesion markers such as integrins, vinculin, RhoA, and ROCK1/2 and reduced cell shape, elongation, cell-matrix traction force, and intracellular tension. Furthermore, we observed a significant decrease in cell adhesion in cells cultured on the hydrogel, resulting in the promotion of M1 polarization. These findings offer insights into the important roles of cell-matrix interactions in macrophage polarization and offer a platform for heparin-mimicking polymer-based hydrogel matrices to induce M1 polarization by inducing cell adhesion without classical activators.

Force-regulated spontaneous conformational changes of integrins α 5 β 1 and α V β 3

Force can modulate the properties and functions of macromolecules by inducing conformational changes, such as coiling/uncoiling, zipping/unzipping, and folding/unfolding. Here we compared force-modulated bending/unbending of two purified integrin ectodomains, α 5 β 1 and α V β 3 , using single-molecule approaches. Similar to previously characterized mechano-sensitive macromolecules, the conformation of α 5 β 1 is determined by a threshold head-to-tail tension, suggesting a canonical energy landscape with a deep energy well that traps the integrin in the bent state until sufficient force tilts the energy landscape to accelerate transition to the extended state. By comparison, α V β 3 exhibits bi-stability even without force and can spontaneously transition between the bent and extended conformations in a wide range of forces without energy supplies. Molecular dynamics simulations revealed consecutive formation and disruption of 7 hydrogen bonds during α V β 3 bending and unbending, respectively. Accordingly, we constructed an energy landscape with hexa-stable intermediate states to break down the energy barrier separating the bent and extended states into smaller ones, making it possible for the thermal agitation energy to overcome them sequentially and to be accumulated and converted into mechanical work required for α V β 3 to bend against force. Our study elucidates the different inner workings of α 5 β 1 and α V β 3 at the sub-molecular level, sheds lights on how their respectively functions are facilitated by their distinctive mechano-sensitivities, helps understand their signal initiation processes, and provides critical concepts and useful design principles for engineering of protein-based biomechanical nanomachines.

Alterations of Cytoskeleton Networks in Cell Fate Determination and Cancer Development

Cytoskeleton proteins have been long recognized as structural proteins that provide the necessary mechanical architecture for cell development and tissue homeostasis. With the completion of the cancer genome project, scientists were surprised to learn that huge numbers of mutated genes are annotated as cytoskeletal or associated proteins. Although most of these mutations are considered as passenger mutations during cancer development and evolution, some genes show high mutation rates that can even determine clinical outcomes. In addition, (phospho)proteomics study confirms that many cytoskeleton-associated proteins, e.g., β-catenin, PIK3CA, and MB21D2, are important signaling mediators, further suggesting their biofunctional roles in cancer development. With emerging evidence to indicate the involvement of mechanotransduction in stemness formation and cell differentiation, mutations in these key cytoskeleton components may change the physical/mechanical properties of the cells and determine the cell fate during cancer development. In particular, tumor microenvironment remodeling triggered by such alterations has been known to play important roles in autophagy, metabolism, cancer dormancy, and immune evasion. In this review paper, we will highlight the current understanding of how aberrant cytoskeleton networks affect cancer behaviors and cellular functions through mechanotransduction.

Aspirin Inhibits Fibronectin Expression and Reverses Fibronectin-Mediated Cell Invasiveness by Activating Akt Signaling in Preeclampsia

Preeclampsia is a severe gestational hypertensive disorder that may lead to maternal multiple organ dysfunction and adverse fetal outcomes. Aspirin provides a protective effect by reducing the risk of preeclampsia; however, its mechanism of action is unclear. Fibronectin (FN) is a key factor in cell motility and is associated with preeclampsia. Here, we demonstrated that cellular FN expression was elevated in the placenta of preeclamptic patients. The functional roles of plasma and cellular FN in trophoblasts were investigated by treating HTR-8/SVneo cells with exogenous recombinant human FN protein (rhFN) and siRNA, respectively. Trophoblast migration and invasion were inhibited by rhFN and facilitated by FN knockdown. Moreover, rhFN activated ERK and Akt signaling in trophoblasts, and FN-suppressed cell motility was rescued by ERK and/or Akt inhibitors. In this study, aspirin suppressed trophoblast cellular FN expression and reversed FN-mediated cell functions, including cell migration, invasion, and ERK/Akt signal changes. Taken together, the results of this study revealed the effects of FN on trophoblast motility and signaling; aspirin inhibits FN expression and reverses FN-mediated trophoblast biology. These results provide a drug mechanism for disease prevention and a target for preeclampsia intervention.

Material-driven fibronectin and vitronectin assembly enhances BMP-2 presentation and osteogenesis

Mesenchymal stem cell (MSC)-based tissue engineering strategies are of interest in the field of bone tissue regenerative medicine. MSCs are commonly investigated in combination with growth factors (GFs) and biomaterials to provide a regenerative environment for the cells. However, optimizing how biomaterials interact with MSCs and efficiently deliver GFs, remains a challenge. Here, via plasma polymerization, tissue culture plates are coated with a layer of poly (ethyl acrylate) (PEA), which is able to spontaneously permit fibronectin (FN) to form fibrillar nanonetworks. However, vitronectin (VN), another important extracellular matrix (ECM) protein forms multimeric globules on the polymer, thus not displaying functional groups to cells. Interestingly, when FN and VN are co-absorbed onto PEA surfaces, VN can be entrapped within the FN fibrillar nanonetwork in the monomeric form providing a heterogeneous, open ECM network. The combination of FN and VN promote MSC adhesion and leads to enhanced GF binding; here we demonstrate this with bone morphogenetic protein-2 (BMP2). Moreover, MSC differentiation into osteoblasts is enhanced, with elevated expression of osteopontin (OPN) and osteocalcin (OCN) quantified by immunostaining, and increased mineralization observed by von Kossa staining. Osteogenic intracellular signalling is also induced, with increased activity in the SMAD pathway. The study emphasizes the need of recapitulating the complexity of native ECM to achieve optimal cell-material interactions.

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Vitronectin can be incorporated within fibronectin fibril networks upon co-coating onto poly (ethyl acrylate) modified surfaces.

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Fibronectin and vitronectin networks promote mesenchymal stem cell adhesion and induce α5 integrin clustering.

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Fibronectin and vitronectin nanonetworks improve bone morphogenetic protein-2 presentation to mesenchymal stem cells and thus facilitates osteogenesis.

Peptides for Coating TiO2 Implants: An In Silico Approach

Titanium is usually used in the manufacturing of metal implants due to its biocompatibility and high resistance to corrosion. A structural and functional connection between the living bone and the surface of the implant, a process called osseointegration, is mandatory for avoiding prolonged healing, infections, and tissue loss. Therefore, osseointegration is crucial for the success of the implantation procedure. Osseointegration is a process mediated by bone-matrix progenitor cells' proteins, named integrins. In this study, we used an in silico approach to assemble and test peptides that can be strategically used in sensitizing TiO₂ implants in order to improve osseointegration. To do so, we downloaded PDB structures of integrins α5β1, αvβ3, and αIIbβ3; their biological ligands; and low-cost proteins from the Protein Data Bank, and then we performed a primary (integrin-protein) docking analysis. Furthermore, we modeled complex peptides with the potential to bind to the TiO₂ surface on the implant, as well as integrins in the bone-matrix progenitor cells. Then we performed a secondary (integrin-peptide) docking analysis. The ten most promising integrin-peptide docking results were further verified by molecular dynamics (MD) simulations. We recognized 82 peptides with great potential to bind the integrins, and therefore to be used in coating TiO₂ implants. Among them, peptides 1 (GHTHYHAVRTQTTGR), 3 (RKLPDATGR), and 8 (GHTHYHAVRTQTLKA) showed the highest binding stability during the MD simulations. This bioinformatics approach saves time and more effectively directs in vitro studies.

Force tuning through regulation of clathrin-dependent integrin endocytosis

Integrin endocytosis is essential for many fundamental cellular processes. Whether and how the internalization impacts cellular mechanics remains elusive. Whereas previous studies reported the contribution of the integrin activator, talin, in force development, the involvement of inhibitors is less documented. We identified ICAP-1 as an integrin inhibitor involved in mechanotransduction by co-working with NME2 to control clathrin-mediated endocytosis of integrins at the edge of focal adhesions (FA). Loss of ICAP-1 enables β3-integrin-mediated force generation independently of β1 integrin. β3-integrin-mediated forces were associated with a decrease in β3 integrin dynamics stemming from their reduced diffusion within adhesion sites and slow turnover of FA. The decrease in β3 integrin dynamics correlated with a defect in integrin endocytosis. ICAP-1 acts as an adaptor for clathrin-dependent endocytosis of integrins. ICAP-1 controls integrin endocytosis by interacting with NME2, a key regulator of dynamin-dependent clathrin-coated pits fission. Control of clathrin-mediated integrin endocytosis by an inhibitor is an unprecedented mechanism to tune forces at FA.

Cell–Fibronectin Interactions and Actomyosin Contractility Regulate the Segmentation Clock and Spatio-Temporal Somite Cleft Formation during Chick Embryo Somitogenesis

Fibronectin is essential for somite formation in the vertebrate embryo. Fibronectin matrix assembly starts as cells emerge from the primitive streak and ingress in the unsegmented presomitic mesoderm (PSM). PSM cells undergo cyclic waves of segmentation clock gene expression, followed by Notch-dependent upregulation of meso1 in the rostral PSM which induces somite cleft formation. However, the relevance of the fibronectin matrix for these molecular processes remains unknown. Here, we assessed the role of the PSM fibronectin matrix in the spatio-temporal regulation of chick embryo somitogenesis by perturbing (1) extracellular fibronectin matrix assembly, (2) integrin–fibronectin binding, (3) Rho-associated protein kinase (ROCK) activity and (4) non-muscle myosin II (NM II) function. We found that integrin–fibronectin engagement and NM II activity are required for cell polarization in the nascent somite. All treatments resulted in defective somitic clefts and significantly perturbed meso1 and segmentation clock gene expression in the PSM. Importantly, inhibition of actomyosin-mediated contractility increased the period of hairy1/hes4 oscillations from 90 to 120 min. Together, our work strongly suggests that the fibronectin–integrin–ROCK–NM II axis regulates segmentation clock dynamics and dictates the spatio-temporal localization of somitic clefts.

Gut homeostasis, injury, and healing: New therapeutic targets

The integrity of the gastrointestinal mucosa plays a crucial role in gut homeostasis, which depends upon the balance between mucosal injury by destructive factors and healing via protective factors. The persistence of noxious agents such as acid, pepsin, nonsteroidal anti-inflammatory drugs, or Helicobacter pylori breaks down the mucosal barrier and injury occurs. Depending upon the size and site of the wound, it is healed by complex and overlapping processes involving membrane resealing, cell spreading, purse-string contraction, restitution, differentiation, angiogenesis, and vasculogenesis, each modulated by extracellular regulators. Unfortunately, the gut does not always heal, leading to such pathology as peptic ulcers or inflammatory bowel disease. Currently available therapeutics such as proton pump inhibitors, histamine-2 receptor antagonists, sucralfate, 5-aminosalicylate, antibiotics, corticosteroids, and immunosuppressants all attempt to minimize or reduce injury to the gastrointestinal tract. More recent studies have focused on improving mucosal defense or directly promoting mucosal repair. Many investigations have sought to enhance mucosal defense by stimulating mucus secretion, mucosal blood flow, or tight junction function. Conversely, new attempts to directly promote mucosal repair target proteins that modulate cytoskeleton dynamics such as tubulin, talin, Ehm2, filamin-a, gelsolin, and flightless I or that proteins regulate focal adhesions dynamics such as focal adhesion kinase. This article summarizes the pathobiology of gastrointestinal mucosal healing and reviews potential new therapeutic targets.

Integrin Crosstalk and Its Effect on the Biological Functions of the Trabecular Meshwork/Schlemm’s Canal

Integrins are a family of heterodimeric receptors composed of an α- and β-subunit that mediate cell-adhesion to a number of extracellular matrix (ECM) proteins in the Trabecular Meshwork/Schlemm’s canal (TM/SC) of the eye. Upon binding an ECM ligand, integrins transmit signals that activate a number of signaling pathways responsible for regulating actin-mediated processes (i.e phagocytosis, cell contractility, and fibronectin fibrillogenesis) that play an important role in regulating intraocular pressure (IOP) and may be involved in glaucoma. An important function of integrin-mediated signaling events is that the activity of one integrin can affect the activity of other integrins in the same cell. This creates a crosstalk that allows TM/SC cells to respond to changes in the ECM presumably induced by the mechanical forces on the TM/SC, aging and disease. In this review, we discuss how integrin crosstalk influences the function of the human TM/SC pathway. In particular, we will discuss how different crosstalk pathways mediated by either the αvβ3 or α4β1 integrins can play opposing roles in the TM when active and therefore act as on/off switches to modulate the cytoskeleton-mediated processes that regulate the outflow of aqueous humor through the TM/SC.

Substrate Stiffness-Driven Membrane Tension Modulates Vesicular Trafficking via Caveolin-1

Liver fibrosis, a condition characterized by extensive deposition and cross-linking of extracellular matrix (ECM) proteins, is idiosyncratic in cases of chronic liver injury. The dysregulation of ECM remodeling by hepatic stellate cells (HSCs), the main mediators of fibrosis, results in an elevated ECM stiffness that drives the development of chronic liver disease such as cirrhosis and hepatocellular carcinoma. Tissue inhibitor of matrix metalloproteinase-1 (TIMP-1) is a key element in the regulation of ECM remodeling, which modulates the degradation and turnover of ECM components. We have previously reported that a rigid, fibrotic-like substrate can impact TIMP-1 expression at the protein level in HSCs without altering its mRNA expression. While HSCs are known to be highly susceptible to mechanical stimuli, the mechanisms through which mechanical cues regulate TIMP-1 at the post-translational level remain unclear. Here, we show a mechanism of regulation of plasma membrane tension by matrix stiffness. We found that this effect is orchestrated by the β1 integrin/RhoA axis and results in elevated exocytosis and secretion of TIMP-1 in a caveolin-1- and dynamin-2-dependent manner. We then show that TIMP-1 and caveolin-1 expression increases in cirrhosis and hepatocellular carcinoma. These conditions are associated with fibrosis, and this effect can be recapitulated in 3D fibrosis models consisting of hepatic stellate cells encapsulated in a self-assembling polypeptide hydrogel. This work positions stiffness-dependent membrane tension as a key regulator of enzyme secretion and function and a potential target for therapeutic strategies that aim at modulating ECM remodeling in chronic liver disease.

Canonical TGFβ signaling induces collective invasion in colorectal carcinogenesis through a Snail1- and Zeb1-independent partial EMT

Local invasion is the initial step towards metastasis, the main cause of cancer mortality. In human colorectal cancer (CRC), malignant cells predominantly invade as cohesive collectives and may undergo partial epithelial-mesenchymal transition (pEMT) at the invasive front. How this particular mode of stromal infiltration is generated is unknown. Here we investigated the impact of oncogenic transformation and the microenvironment on tumor cell invasion using genetically engineered organoids as CRC models. We found that inactivation of the Apc tumor suppressor combined with expression of oncogenic Kras^G12D and dominant-negative Trp53^R172H did not cell-autonomously induce invasion in vitro. However, oncogenic transformation primed organoids for activation of a collective invasion program upon exposure to the prototypical microenvironmental factor TGFβ1. Execution of this program co-depended on a permissive extracellular matrix which was further actively remodeled by invading organoids. Although organoids shed some epithelial properties particularly at the invasive edge, TGFβ1-stimulated organoids largely maintained epithelial gene expression while additionally implementing a mesenchymal transcription pattern, resulting in a pEMT phenotype that did not progress to a fully mesenchymal state. Notably, while TGFβ1 induced pEMT and promoted collective invasion, it abrogated self-renewal capacity of TKA organoids which correlated with the downregulation of intestinal stem cell (ISC) marker genes. Mechanistically, induction of the non-progressive pEMT required canonical TGFβ signaling mediated by Smad transcription factors (TFs), whereas the EMT master regulators Snail1 and Zeb1 were dispensable. Gene expression profiling provided further evidence for pEMT of TGFβ1-treated organoids and showed that their transcriptomes resemble those of human poor prognosis CMS4 cancers which likewise exhibit pEMT features. We propose that collective invasion in colorectal carcinogenesis is triggered by microenvironmental stimuli through activation of a novel, transcription-mediated form of non-progressive pEMT independently of classical EMT regulators.

Macrophage uptake of oxidized and acetylated low-density lipoproteins and generation of reactive oxygen species are regulated by linear stiffness of the growth surface

Macrophages are key players in the development of atherosclerosis: they scavenge lipid, transform into foam cells, and produce proinflammatory mediators. At the same time, the arterial wall undergoes profound changes in its mechanical properties. We recently showed that macrophage morphology and proinflammatory potential are regulated by the linear stiffness of the growth surface. Here we asked whether linear stiffness also regulates lipid uptake by macrophages. We cultured murine bone marrow-derived macrophages (BMMs) on polyacrylamide gels modeling stiffness of healthy (1kPa) and diseased (10-150kPa) blood vessels. In unprimed BMMs, increased linear stiffness increased uptake of oxidized (oxLDL) and acetylated (acLDL) low density lipoproteins and generation of reactive oxygen species, but did not alter phagocytosis of bacteria or silica particles. Macrophages adapted to stiff growth surfaces had increased mRNA and protein expression of two key lipoprotein receptors: CD36 and scavenger receptor b1. Regulation of the lipoprotein receptor, lectin-like receptor for ox-LDL, was more complex: mRNA expression decreased but surface protein expression increased with increased stiffness. Focal adhesion kinase was required for maximal uptake of oxLDL, but not of acLDL. Uptake of oxLDL and acLDL was independent of rho-associated coiled coil kinase. Through pharmacologic inhibition and genetic deletion, we found that transient receptor potential vanilloid 4 (TRPV4), a mechanosensitive ion channel, plays an inhibitory role in the uptake of acLDL, but not oxLDL. Together, these results implicate mechanical signaling in the uptake of acLDL and oxLDL, opening up the possibility of new pharmacologic targets to modulate lipid uptake by macrophages in vivo.

Developing biomaterials to mediate the spatial distribution of integrins

Innovation in material design to regulate cell behavior and function is one of the primary tasks in materials science. Integrins, a family of cell surface-adhesion receptors that mechanically connect the extracellular matrix (ECM) to the intracellular cytoskeleton, have long served as primary targets for the design of biomaterials because their activity is not only critical to a wide range of cell and tissue functions but also subject to very tight and complex regulations from the outside environment. To review the recent progress of material innovations targeting the spatial distribution of integrins, we first introduce the interaction mechanisms between cells and the ECM by highlighting integrin-based cell adhesions, describing how integrins respond to environmental stimuli, including variations in ligand presentation, mechanical cues, and topographical variations. Then, we overview the current development of soft materials in guiding cell behaviors and functions via spatial regulation of integrins. Finally, we discuss the current limitations of these technologies and the advances that may be achieved in the future. Undoubtedly, synthetic soft materials that mediate the spatial distribution of integrins play an important role in biomaterial innovations for advancing biomedical applications and addressing fundamental biological questions.

Cellular Tango: how extracellular matrix adhesion choreographs Rac-Rho signaling and cell movement

The small GTPases Rac and Rho are known to regulate eukaryotic cell shape, promoting front protrusion (Rac) or rear retraction (Rho) of the cell edge. Such cell deformation changes the contact and adhesion of cell to the extracellular matrix (ECM), while ECM signaling through integrin receptors also affects GTPase activity. We develop and investigate a model for this three-way feedback loop in 1D and 2D spatial domains, as well as in a fully deforming 2D cell shapes with detailed adhesion-bond biophysics. The model consists of reaction-diffusion equations solved numerically with open-source software, Morpheus, and with custom-built cellular Potts model simulations. We find a variety of patterns and cell behaviors, including persistent polarity, flipped front-back cell polarity oscillations, spiral waves, and random protrusion-retraction. We show that the observed spatial patterns depend on the cell shape, and vice versa.

EphA2 signaling within integrin adhesions regulates fibrillar adhesion elongation and fibronectin deposition

The multifunctional glycoprotein fibronectin influences several crucial cellular processes and contributes to multiple pathologies. While a link exists between fibronectin-associated pathologies and the receptor tyrosine kinase EphA2, the mechanism by which EphA2 promotes fibronectin matrix remodeling remains unknown. We previously demonstrated that EphA2 deletion reduces smooth muscle fibronectin deposition and blunts fibronectin deposition in atherosclerosis without influencing fibronectin expression. We now show that EphA2 expression is required for contractility-dependent elongation of tensin- and α5β1 integrin-rich fibrillar adhesions that drive fibronectin fibrillogenesis. Mechanistically, EphA2 localizes to integrin adhesions where focal adhesion kinase mediates ligand-independent Y772 phosphorylation, and mutation of this site significantly blunts fibrillar adhesion length. EphA2 deficiency decreases smooth muscle cell contractility by enhancing p190RhoGAP activation and reducing RhoA activity, whereas stimulating RhoA signaling in EphA2 deficient cells rescues fibrillar adhesion elongation. Together, these data identify EphA2 as a novel regulator of fibrillar adhesion elongation and provide the first data identifying a role for EphA2 signaling in integrin adhesions.

Oxidized/deamidated-ceruloplasmin dysregulates choroid plexus epithelial cells functionality and barrier properties via RGD-recognizing integrin binding

Choroid plexus epithelial cells (CPEpiCs) determine the composition of cerebrospinal fluid (CSF) and constitute the blood-CSF barrier (BCSFB), functions that are altered in neurodegenerative diseases. In Parkinson's disease (PD) the pathological environment oxidizes and deamidates the ceruloplasmin, a CSF-resident ferroxidase, which undergoes a gain of RGD-recognizing integrin binding property, that may result in signal transduction. We investigated the effects that oxidized/deamidated ceruloplasmin (Cp-ox/de) may exert on CPEpiCs functions. Through RGD-recognizing integrins binding, Cp-ox/de mediates CPEpiCs adhesion and intracellular signaling, resulting in cell proliferation inhibition and alteration of the secretome profile in terms of proteins related to cell-extracellular matrix interaction. Oxidative conditions, comparable to those found in the CSF of PD patients, induced CPEpiCs barrier leakage, allowing Cp-ox/de to cross it, transducing integrins-mediated signal that further worsens BCSFB integrity. This mechanism might contribute to PD pathological processes altering CSF composition and aggravating the already compromised BCSFB function.

Binding of the Andes Virus Nucleocapsid Protein to RhoGDI Induces the Release and Activation of the Permeability Factor RhoA

Andes virus (ANDV) nonlytically infects pulmonary microvascular endothelial cells (PMECs), causing acute pulmonary edema termed hantavirus pulmonary syndrome (HPS). In HPS patients, virtually every PMEC is infected; however, the mechanism by which ANDV induces vascular permeability and edema remains to be resolved. The ANDV nucleocapsid (N) protein activates the GTPase RhoA in primary human PMECs, causing VE-cadherin internalization from adherens junctions and PMEC permeability. We found that ANDV N protein failed to bind RhoA but coprecipitates RhoGDI (Rho GDP dissociation inhibitor), the primary RhoA repressor that normally sequesters RhoA in an inactive state. ANDV N protein selectively binds the RhoGDI C terminus (residues 69 to 204) but fails to form ternary complexes with RhoA or inhibit RhoA binding to the RhoGDI N terminus (residues 1 to 69). However, we found that ANDV N protein uniquely inhibits RhoA binding to an S34D phosphomimetic RhoGDI mutant. Hypoxia and vascular endothelial growth factor (VEGF) increase RhoA-induced PMEC permeability by directing protein kinase Cα (PKCα) phosphorylation of S34 on RhoGDI. Collectively, ANDV N protein alone activates RhoA by sequestering and reducing RhoGDI available to suppress RhoA. In response to hypoxia and VEGF-activated PKCα, ANDV N protein additionally directs the release of RhoA from S34-phosphorylated RhoGDI, synergistically activating RhoA and PMEC permeability. These findings reveal a fundamental edemagenic mechanism that permits ANDV to amplify PMEC permeability in hypoxic HPS patients. Our results rationalize therapeutically targeting PKCα and opposing protein kinase A (PKA) pathways that control RhoGDI phosphorylation as a means of resolving ANDV-induced capillary permeability, edema, and HPS. IMPORTANCE HPS-causing hantaviruses infect pulmonary endothelial cells (ECs), causing vascular leakage, pulmonary edema, and a 35% fatal acute respiratory distress syndrome (ARDS). Hantaviruses do not lyse or disrupt the endothelium but dysregulate normal EC barrier functions and increase hypoxia-directed permeability. Our findings reveal a novel underlying mechanism of EC permeability resulting from ANDV N protein binding to RhoGDI, a regulatory protein that normally maintains edemagenic RhoA in an inactive state and inhibits EC permeability. ANDV N sequesters RhoGDI and enhances the release of RhoA from S34-phosphorylated RhoGDI. These findings indicate that ANDV N induces the release of RhoA from PKC-phosphorylated RhoGDI, synergistically enhancing hypoxia-directed RhoA activation and PMEC permeability. Our data suggest inhibiting PKC and activating PKA phosphorylation of RhoGDI as mechanisms of inhibiting ANDV-directed EC permeability and therapeutically restricting edema in HPS patients. These findings may be broadly applicable to other causes of ARDS.

In vitro maturation using an agarose matrix with incorporated extracellular matrix proteins improves porcine oocyte developmental competence by enhancing cytoplasmic maturation

Here, we present a novel in vitro maturation (IVM) system comprising an agarose matrix supplemented with extracellular matrix (ECM) proteins for enhanced maturation of immature oocytes within cumulus-oocyte complexes (COCs) derived from porcine medium antral follicles (MAFs). Immunocytochemical analyses of integrin subunit α₂ , α₅ , α₆ , β₁ , and β₄ expression suggested that integrin α₂ β₁ , α₅ β₁ , α₆ β₁ , and α₆ β₄ play pivotal roles in IVM of porcine immature oocytes. Combinatorial supplementation of fibronectin interacting with integrin α₅ β₁ , collagen interacting with integrin α₂ β₁ , and laminin interacting with integrin α₆ β₁ and α₆ β₄ to the agarose matrix had no significant effect on nuclear maturation. However, the number of parthenogenetic embryos that developed into blastocysts increased when oocytes were matured using agarose IVM matrices supplemented with fibronectin, collagen, or laminin. Furthermore, significant increases in cytoplasmic maturation-related parameters (BMP15 level, cumulus cell expansion score, intra-oocyte ATP level, and index of cortical granule distribution) were observed in COCs matured in vitro using ECM protein-incorporated agarose matrices. Our data suggest that mature porcine oocytes with enhanced developmental competence and high-quality cytoplasm can be generated via IVM using agarose matrices supplemented with fibronectin, collagen, or laminin.

Integrin intra-heterodimer affinity inversely correlates with integrin activatability

Integrins are heterodimeric cell surface receptors composed of an α and β subunit that mediate cell adhesion to extracellular matrix proteins such as fibronectin. We previously studied integrin α5β1 activation during zebrafish somitogenesis, and in the present study, we characterize the integrin αV fibronectin receptors. Integrins are activated via a conformational change, and we perform single-molecule biophysical measurements of both integrin activation via fluorescence resonance energy transfer (FRET)-fluorescence lifetime imaging microscopy (FLIM) and integrin intra-heterodimer stability via fluorescence cross-correlation spectroscopy (FCCS) in living embryos. We find that integrin heterodimers that exhibit robust cell surface expression, including αVβ3, αVβ5, and αVβ6, are never activated in this in vivo context, even in the presence of fibronectin matrix. In contrast, activatable integrins, such as integrin αVβ1, and alleles of αVβ3, αVβ5, αVβ6 that are biased to the active conformation exhibit poor cell surface expression and have a higher intra-heterodimer dissociation constant (KD). These observations suggest that a weak integrin intra-heterodimer affinity decreases integrin cell surface stability and increases integrin activatability.

Vav3 Mediates Pseudomonas aeruginosa Adhesion to the Cystic Fibrosis Airway Epithelium

Pseudomonas aeruginosa (Pa) represents the leading cause of airway infection in cystic fibrosis (CF). Early airways colonization can be explained by enhanced adhesion of Pa to the respiratory epithelium. RNA sequencing (RNA-seq) on fully differentiated primary cultures of airway epithelial cells from CF and non-CF donors predict that VAV3, β1 INTEGRIN, and FIBRONECTIN genes are significantly enriched in CF. Indeed, Vav3 is apically overexpressed in CF, associates with active β1 integrin luminally exposed, and increases fibronectin deposition. These luminal microdomains, rich in fibronectin and β1 integrin and regulated by Vav3, mediate the increased Pa adhesion to the CF epithelium. Interestingly, Vav3 inhibition normalizes the CF-dependent fibronectin and β1-integrin ectopic expression, improves the CF epithelial integrity, and prevents the enhanced Pa trapping to the CF epithelium. Through its capacity to promote a luminal complex with active β1 integrin and fibronectin that favors bacteria trapping, Vav3 may represent a new target in CF.

The Role of Cell Adhesion and Cytoskeleton Dynamics in the Pathogenesis of the Ehlers-Danlos Syndromes and Hypermobility Spectrum Disorders

The Ehlers-Danlos syndromes (EDS) are a group of 13 disorders, clinically defined through features of joint hypermobility, skin hyperextensibility, and tissue fragility. Most subtypes are caused by mutations in genes affecting the structure or processing of the extracellular matrix (ECM) protein collagen. The Hypermobility Spectrum Disorders (HSDs) are clinically indistinguishable disorders, but are considered to lack a genetic basis. The pathogenesis of all these disorders, however, remains poorly understood. Genotype-phenotype correlations are limited, and findings of aberrant collagen fibrils are inconsistent and associate poorly with the subtype and severity of the disorder. The defective ECM, however, also has consequences for cellular processes. EDS/HSD fibroblasts exhibit a dysfunctional phenotype including impairments in cell adhesion and cytoskeleton organization, though the pathological significance of this has remained unclear. Recent advances in our understanding of fibroblast mechanobiology suggest these changes may actually reflect features of a pathomechanism we herein define. This review departs from the traditional view of EDS/HSD, where pathogenesis is mediated by the structurally defective ECM. Instead, we propose EDS/HSD may be a disorder of membrane-bound collagen, and consider how aberrations in cell adhesion and cytoskeleton dynamics could drive the abnormal properties of the connective tissue, and be responsible for the pathogenesis of EDS/HSD.