Mechanisms of integration of cells and extracellular matrices by integrins

Influence of the Surface Topography of Titanium Dental Implants on the Behavior of Human Amniotic Stem Cells

The dental implant surface plays a crucial role in osseointegration. The topography and physicochemical properties will affect the cellular functions. In this research, four distinct titanium surfaces have been studied: machined acting (MACH), acid etched (AE), grit blasting (GBLAST), and a combination of grit blasting and subsequent acid etching (GBLAST + AE). Human amniotic mesenchymal (hAMSCs) and epithelial stem cells (hAECs) isolated from the amniotic membrane have attractive stem-cell properties. They were cultured on titanium surfaces to analyze their impact on biological behavior. The surface roughness, microhardness, wettability, and surface energy were analyzed using interferometric microscopy, Vickers indentation, and drop-sessile techniques. The GBLAST and GBLAST + AE surfaces showed higher roughness, reduced hydrophilicity, and lower surface energy with significant differences. Increased microhardness values for GBLAST and GBLAST + AE implants were attributed to surface compression. Cell viability was higher for hAMSCs, particularly on GBLAST and GBLAST + AE surfaces. Alkaline phosphatase activity enhanced in hAMSCs cultured on GBLAST and GBLAST + AE surfaces, while hAECs showed no mineralization signals. Osteogenic gene expression was upregulated in hAMSCs on GBLAST surfaces. Moreover, α2 and β1 integrin expression enhanced in hAMSCs, suggesting a surface-integrin interaction. Consequently, hAMSCs would tend toward osteoblastic differentiation on grit-blasted surfaces conducive to osseointegration, a phenomenon not observed in hAECs.

Integrins in the Immunity of Insects: A Review

Integrins are a large group of cell-surface proteins that are classified as transmembrane proteins. Integrins are classified into different types based on sequence variations, leading to structural and functional diversity. They are broadly distributed in animals and have a wide range of biological functions such as cell-to-cell communication, intracellular cytoskeleton organization, cellular signaling, immune responses, etc. Integrins are among the most abundant cell surface proteins in insects, exhibiting their indispensability in insect physiology. Because of their critical biological involvement in physiological processes, they appear to be a novel target for designing effective pest control strategies. In the current literature review, we first discuss the discovery and expression responses of integrins against various types of pathogens. Secondly, we examine the specific biological roles of integrins in controlling microbial pathogens, such as phagocytosis, encapsulation, nodulation, immune signaling, and so on. Finally, we describe the possible uses of integrins to control agricultural insect pests.

Borax induces osteogenesis by stimulating NaBC1 transporter via activation of BMP pathway

The intrinsic properties of mesenchymal stem cells (MSCs) make them ideal candidates for tissue engineering applications. Efforts have been made to control MSC behavior by using material systems to engineer synthetic extracellular matrices and/or include soluble factors in the media. This work proposes a simple approach based on ion transporter stimulation to determine stem cell fate that avoids the use of growth factors. Addition of borax alone, transported by the NaBC1-transporter, enhanced MSC adhesion and contractility, promoted osteogenesis and inhibited adipogenesis. Stimulated-NaBC1 promoted osteogenesis via the BMP canonical pathway (comprising Smad1/YAP nucleus translocation and osteopontin expression) through a mechanism that involves simultaneous NaBC1/BMPR1A and NaBC1/α₅β₁/α_vβ₃ co-localization. We describe an original function for NaBC1 transporter, besides controlling borate homeostasis, capable of stimulating growth factor receptors and fibronectin-binding integrins. Our results open up new biomaterial engineering approaches for biomedical applications by a cost-effective strategy that avoids the use of soluble growth factors.

Rico et al. propose a simple approach based on borax stimulation of NaBC1 transporter, which enhances FN-binding integrin-dependent mesenchymal stem cell adhesion and contractility, promotes osteogenesis and inhibits adipogenesis. Osteogenic differentiation depends on activation of the BMP pathway through a mechanism that involves simultaneous co-localization of NaBC1 with FN-binding integrins and BMPR1A.

Cell-surface heparan sulfate proteoglycans as multifunctional integrators of signaling in cancer

Proteoglycans (PGs) represent a large proportion of the components that constitute the extracellular matrix (ECM). They are a diverse group of glycoproteins characterized by a covalent link to a specific glycosaminoglycan type. As part of the ECM, heparan sulfate (HS)PGs participate in both physiological and pathological processes including cell recruitment during inflammation and the promotion of cell proliferation, adhesion and motility during development, angiogenesis, wound repair and tumor progression. A key function of HSPGs is their ability to modulate the expression and function of cytokines, chemokines, growth factors, morphogens, and adhesion molecules. This is due to their capacity to act as ligands or co-receptors for various signal-transducing receptors, affecting pathways such as FGF, VEGF, chemokines, integrins, Wnt, notch, IL-6/JAK-STAT3, and NF-κB. The activation of those pathways has been implicated in the induction, progression, and malignancy of a tumor. For many years, the study of signaling has allowed for designing specific drugs targeting these pathways for cancer treatment, with very positive results. Likewise, HSPGs have become the subject of cancer research and are increasingly recognized as important therapeutic targets. Although they have been studied in a variety of preclinical and experimental models, their mechanism of action in malignancy still needs to be more clearly defined. In this review, we discuss the role of cell-surface HSPGs as pleiotropic modulators of signaling in cancer and identify them as promising markers and targets for cancer treatment.

Coupling of Fibrin Reorganization and Fibronectin Patterning by Corneal Fibroblasts in Response to PDGF BB and TGFβ1

We previously reported that corneal fibroblasts within 3D fibrin matrices secrete, bind, and organize fibronectin into tracks that facilitate cell spreading and migration. Other cells use these fibronectin tracks as conduits, which leads to the development of an interconnected cell/fibronectin network. In this study, we investigate how cell-induced reorganization of fibrin correlates with fibronectin track formation in response to two growth factors present during wound healing: PDGF BB, which stimulates cell spreading and migration; and TGFβ1, which stimulates cellular contraction and myofibroblast transformation. Both PDGF BB and TGFβ1 stimulated global fibrin matrix contraction (p < 0.005); however, the cell and matrix patterning were different. We found that, during PDGF BB-induced cell spreading, fibronectin was organized simultaneously with the generation of tractional forces at the leading edge of pseudopodia. Over time this led to the formation of an interconnected network consisting of cells, fibronectin and compacted fibrin tracks. Following culture in TGFβ1, cells were less motile, produced significant local fibrin reorganization, and formed fewer cellular connections as compared to PDGF BB (p < 0.005). Although bands of compacted fibrin tracks developed in between neighboring cells, fibronectin labeling was not generally present along these tracks, and the correlation between fibrin and fibronectin labeling was significantly less than that observed in PDGF BB (p < 0.001). Taken together, our results show that cell-induced extracellular matrix (ECM) reorganization can occur independently from fibronectin patterning. Nonetheless, both events seem to be coordinated, as corneal fibroblasts in PDGF BB secrete and organize fibronectin as they preferentially spread along compacted fibrin tracks between cells, producing an interconnected network in which cells, fibronectin and compacted fibrin tracks are highly correlated. This mechanism of patterning could contribute to the formation of organized cellular networks that have been observed following corneal injury and refractive surgery.

Adhesion molecules in gamete transport, fertilization, early embryonic development, and implantation-role in establishing a pregnancy in cattle: A review

Cell-cell adhesion molecules have critically important roles in the early events of reproduction including gamete transport, sperm-oocyte interaction, embryonic development, and implantation. Major adhesion molecules involved in reproduction include cadherins, integrins, and disintegrin and metalloprotease domain-containing (ADAM) proteins. ADAMs on the surface of sperm adhere to integrins on the oocyte in the initial stages of sperm-oocyte interaction and fusion. Cadherins act in early embryos to organize the inner cell mass and trophectoderm. The trophoblast and uterine endometrial epithelium variously express cadherins, integrins, trophinin, and selectin, which achieve apposition and attachment between the elongating conceptus and uterine epithelium before implantation. An overview of the major cell-cell adhesion molecules is presented and this is followed by examples of how adhesion molecules help shape early reproductive events. The argument is made that a deeper understanding of adhesion molecules and reproduction will inform new strategies that improve embryo survival and increase the efficiency of natural mating and assisted breeding in cattle.

Biomechanical Forces and Oxidative Stress: Implications for Pulmonary Vascular Disease

Significance: Oxidative stress in the cell is characterized by excessive generation of reactive oxygen species (ROS). Superoxide (O₂^-) and hydrogen peroxide (H₂O₂) are the main ROS involved in the regulation of cellular metabolism. As our fundamental understanding of the underlying causes of lung disease has increased it has become evident that oxidative stress plays a critical role. Recent Advances: A number of cells in the lung both produce, and respond to, ROS. These include vascular endothelial and smooth muscle cells, fibroblasts, and epithelial cells as well as the cells involved in the inflammatory response, including macrophages, neutrophils, eosinophils. The redox system is involved in multiple aspects of cell metabolism and cell homeostasis. Critical Issues: Dysregulation of the cellular redox system has consequential effects on cell signaling pathways that are intimately involved in disease progression. The lung is exposed to biomechanical forces (fluid shear stress, cyclic stretch, and pressure) due to the passage of blood through the pulmonary vessels and the distension of the lungs during the breathing cycle. Cells within the lung respond to these forces by activating signal transduction pathways that alter their redox state with both physiologic and pathologic consequences. Future Directions: Here, we will discuss the intimate relationship between biomechanical forces and redox signaling and its role in the development of pulmonary disease. An understanding of the molecular mechanisms induced by biomechanical forces in the pulmonary vasculature is necessary for the development of new therapeutic strategies.

Hernia and Cancer: The Points Where the Roads Intersect

Introduction: This review aimed to present common points, intersections, and potential interactions or mutual effects for hernia and cancer. Besides direct relationships, indirect connections, and possible involvements were searched. Materials and Methods: A literature search of PubMed database was performed in July 2018 as well as a search of relevant journals and reference lists. The total number of screened articles was 1,422. Some articles were found in multiple different searches. A last PubMed search was performed during manuscript writing in December 2018 to update the knowledge. Eventually 427 articles with full text were evaluated, and 264 included, in this review. Results: There is no real evidence for a possible common etiology for abdominal wall hernias and any cancer type. The two different diseases had been found to have some common points in the studies on genes, integrins, and biomarkers, however, to date no meaningful relationship has been identified between these points. There is also some, albeit rather conflicting, evidence for inguinal hernia being a possible risk factor for testicular cancer. Neoadjuvant or adjuvant therapeutic modalities like chemotherapy and radiotherapy may cause postoperative herniation with their adverse effects on tissue repair. Certain specific substances like bevacizumab may cause more serious complications and interfere with hernia repair. There are only two articles in PubMed directly related to the topic of "hernia and cancer." In one of these the authors claimed that there was no association between cancer development and hernia repair with mesh. The other article reported two cases of squamous-cell carcinoma developed secondary to longstanding mesh infections. Conclusion: As expected, the relationship between abdominal wall hernias and cancer is weak. Hernia repair with mesh does not cause cancer, there is only one case report on cancer development following a longstanding prosthetic material infections. However, there are some intersection points between these two disease groups which are worthy of research in the future.

Basement Membrane Defects in Genetic Kidney Diseases

The glomerular basement membrane (GBM) is a specialized structure with a significant role in maintaining the glomerular filtration barrier. This GBM is formed from the fusion of two basement membranes during development and its function in the filtration barrier is achieved by key extracellular matrix components including type IV collagen, laminins, nidogens, and heparan sulfate proteoglycans. The characteristics of specific matrix isoforms such as laminin-521 (α5β2γ1) and the α3α4α5 chain of type IV collagen are essential for the formation of a mature GBM and the restricted tissue distribution of these isoforms makes the GBM a unique structure. Detailed investigation of the GBM has been driven by the identification of inherited abnormalities in matrix proteins and the need to understand pathogenic mechanisms causing severe glomerular disease. A well-described hereditary GBM disease is Alport syndrome, associated with a progressive glomerular disease, hearing loss, and lens defects due to mutations in the genes COL4A3, COL4A4, or COL4A5. Other proteins associated with inherited diseases of the GBM include laminin β2 in Pierson syndrome and LMX1B in nail patella syndrome. The knowledge of these genetic mutations associated with GBM defects has enhanced our understanding of cell-matrix signaling pathways affected in glomerular disease. This review will address current knowledge of GBM-associated abnormalities and related signaling pathways, as well as discussing the advances toward disease-targeted therapies for patients with glomerular disease.

Fibroblast-fibronectin patterning and network formation in 3D fibrin matrices

PURPOSE

We previously reported that fibroblasts migrating within 3-D collagen matrices move independently, whereas fibroblasts within 3-D fibrin matrices form an interconnected network. Similar networks have been identified previously during in vivo corneal wound healing. In this study, we investigate the role of fibronectin in mediating this mechanism of collective cell spreading, migration and patterning.

METHODS

To assess cell spreading, corneal fibroblasts were plated within fibrillar collagen or fibrin matrices. To assess migration, compacted cell-populated collagen matrices were nested inside cell-free fibrin matrices. Constructs were cultured in serum-free media containing PDGF, with or without RGD peptide, anti-α5 or anti-fibronectin blocking antibodies. In some experiments, LifeAct and fluorescent fibronectin were used to allow dynamic assessment of cell-induced fibronectin reorganization. 3-D and 4-D imaging were used to assess cell mechanical behavior, connectivity, F-actin, α5 integrin and fibronectin organization.

RESULTS

Corneal fibroblasts within 3-D fibrin matrices formed an interconnected network that was lined with cell-secreted fibronectin. Live cell imaging demonstrated that fibronectin tracks were formed at the leading edge of spreading and migrating cells. Furthermore, fibroblasts preferentially migrated through fibronectin tracks laid down by other cells. Interfering with cell-fibronectin binding with RGD, anti α5 integrin or anti fibronectin antibodies inhibited cell spreading and migration through fibrin, but did not affect cell behavior in collagen.

CONCLUSIONS

In this study, a novel mode of cell patterning was identified in which corneal fibroblasts secrete and attach to fibronectin via α5β1 integrin to facilitate spreading and migration within 3-D fibrin matrices, resulting in the formation of localized fibronectin tracks. Other cells use these fibronectin tracks as conduits, resulting in an interconnected cell-fibronectin network.

Quantitative Studies of Endothelial Cell Fibronectin and Filamentous Actin (F-Actin) Coalignment in Response to Shear Stress

Both fibronectin (FN) and filamentous actin (F-actin) fibers play a critical role for endothelial cells (ECs) in responding to shear stress and modulating cell alignment and functions. FN is dynamically coupled to the F-actin cytoskeleton via focal adhesions. However, it is unclear how ECs cooperatively remodel their subcellular FN matrix and intracellular F-actin cytoskeleton in response to shear stress. Current studies are hampered by the lack of a reliable and sensitive quantification method of FN orientation. In this study, we developed a MATLAB-based feature enhancement method to quantify FN and F-actin orientation. The role of F-actin in FN remodeling was also studied by treating ECs with cytochalasin D. We have demonstrated that FN and F-actin codistributed and coaligned parallel to the flow direction, and that F-actin alignment played an essential role in regulating FN alignment in response to shear stress. Our findings offer insight into how ECs cooperatively remodel their subcellular ECM and intracellular F-actin cytoskeleton in response to mechanical stimuli, and are valuable for vascular tissue engineering.

Activation mechanisms of αVβ3 integrin by binding to fibronectin: A computational study

Integrin αVβ3 plays an important role in regulating cellular activities and in human diseases. Although the structure of αVβ3 has been studied by crystallography and electron microscopy, the detailed activation mechanism of integrin αVβ3 induced by fibronectin remains unclear. In this study, we investigated the conformational and dynamical motion changes of Mn2+ -bound integrin αVβ3 by binding to fibronectin with molecular dynamics simulations. Results showed that fibronectin binding to integrin αVβ3 caused the changes of the conformational flexibility of αVβ3 domains, the essential mode of motion for the domains of αV subunit and β3 subunit and the degrees of correlated motion of residues between the domains of αV subunit and β3 subunit of integrin αVβ3. The angle of Propeller domain with respect to the Calf-2 domain of αV subunit and the angle of Hybrid domain with respect to βA domain of β3 subunit significantly increased when integrin αVβ3 was bound to fibronectin. These changes could result in the conformational change tendency of αVβ3 from a bend conformation to an extended conformation and lead to the open swing of Hybrid domain relative to βA domain of β3 subunit, which have demonstrated their importance for αVβ3 activation. Fibronectin binding to integrin αVβ3 significantly decreased the relative position of α1 helix to βA domain and that to metal ion-dependent adhesion site, stabilized Mn2+ ions binding in integrin αVβ3 and changed fibronectin conformation, which are important for αVβ3 activation. Results from this study provide important molecular insight into the "outside-in" activation mechanism of integrin αVβ3 by binding to fibronectin.

Hereditary Dentin Defects

By the Shields classification, articulated over 30 years ago, inherited dentin defects are divided into 5 types: 3 types of dentinogenesis imperfecta (DGI), and 2 types of dentin dysplasia (DD). DGI type I is osteogenesis imperfecta (OI) with DGI. OI with DGI is caused, in most cases, by mutations in the 2 genes encoding type I collagen. Many genes are required to generate the enzymes that catalyze collagen’s diverse post-translational modifications and its assembly into fibers, fibrils, bundles, and networks. Rare inherited diseases of bone are caused by defects in these genes, and some are occasionally found to include DGI as a feature. Appreciation of the complicated genetic etiology of DGI associated with bony defects splintered the DGI type I description into a multitude of more precisely defined entities, all with their own designations. In contrast, DD-II, DGI-II, and DGI-III, each with its own pattern of inherited defects limited to the dentition, have been found to be caused by various defects in DSPP (dentin sialophosphoprotein), a gene encoding the major non-collagenous proteins of dentin. Only DD-I, an exceedingly rare condition featuring short, blunt roots with obliterated pulp chambers, remains untouched by the revolution in genetics, and its etiology is still a mystery. A major surprise in the characterization of genes underlying inherited dentin defects is the apparent lack of roles played by the genes encoding the less-abundant non-collagenous proteins in dentin, such as dentin matrix protein 1 ( DMP1), integrin-binding sialoprotein ( IBSP), matrix extracellular phosphoglycoprotein ( MEPE), and secreted phosphoprotein-1, or osteopontin ( SPP1, OPN). This review discusses the development of the dentin extracellular matrix in the context of its evolution, and discusses the phenotypes and clinical classifications of isolated hereditary defects of tooth dentin in the context of recent genetic data respecting their genetic etiologies.

Dynamic interplay between adhesion surfaces in carcinomas: Cell-cell and cell-matrix crosstalk

Cell-cell and cell-matrix signaling and communication between adhesion sites involve mechanisms which are required for cellular functions during normal development and homeostasis; however these cellular functions and mechanisms are often deregulated in cancer. Aberrant signaling at cell-cell and cell-matrix adhesion sites often involves downstream mediators including Rho GTPases and tyrosine kinases. This review discusses these molecules as putative mediators of cellular crosstalk between cell-cell and cell-matrix adhesion sites, in addition to their attractiveness as therapeutic targets in cancer. Interestingly, inter-junctional crosstalk mechanisms are frequently typified by the way in which bacterial and viral pathogens opportunistically infect or intoxicate mammalian cells. This review therefore also discusses the concept of learning from pathogen-host interaction studies to better understand coordinated communication between cell-cell and cell-matrix adhesion sites, in addition to highlighting the potential therapeutic usefulness of exploiting pathogens or their products to tap into inter-junctional crosstalk. Taken together, we feel that increased knowledge around mechanisms of cell-cell and cell-matrix adhesion site crosstalk and consequently a greater understanding of their therapeutic targeting offers a unique opportunity to contribute to the emerging molecular revolution in cancer biology.

Heparan Sulfate Proteoglycans May Promote or Inhibit Cancer Progression by Interacting with Integrins and Affecting Cell Migration

The metastatic disease is one of the main consequences of tumor progression, being responsible for most cancer-related deaths worldwide. This review intends to present and discuss data on the relationship between integrins and heparan sulfate proteoglycans in health and cancer progression. Integrins are a family of cell surface transmembrane receptors, responsible for cell-matrix and cell-cell adhesion. Integrins' main functions include cell adhesion, migration, and survival. Heparan sulfate proteoglycans (HSPGs) are cell surface molecules that play important roles as cell receptors, cofactors, and overall direct or indirect contributors to cell organization. Both molecules can act in conjunction to modulate cell behavior and affect malignancy. In this review, we will discuss the different contexts in which various integrins, such as α5, αV, β1, and β3, interact with HSPGs species, such as syndecans and perlecans, affecting tissue homeostasis.

A novel integrin function in innate immunity from Chinese mitten crab (Eriocheir sinensis)

Integrins belong to a superfamily of conserved α β heterodimeric cell surface receptors that have critical function in cell migration, differentiation, and survival. In this study, an integrin called EsIntegrin was identified from Chinese mitten crab Eriocheir sinensis. EsIntegrin cDNA is 4415 bp long with a 2457 bp open reading frame that encodes an 818 amino acid protein. EsIntegrin contains a signal peptide, an integrin beta subunit (N-terminal portion of extracellular region) INB domain, an epidermal growth factor (hEGF) domain, an integrin B tail domain, a transmembrane region, and an integrin b cyt domain. EsIntegrin was mainly expressed in hemocytes and the heart, with a relatively lower expression level in gills, nerves, intestine, hepatopancreas, muscles, and eyestalk. When healthy crabs were challenged with LPS, PGN, Staphyloccocus aureus, or Vibrio parahaemolyticus, EsIntegrin expression level was upregulated significantly. Recombinant EsIntegrin has agglutination activity to Gram-positive (e.g., S. aureus and Bacillus subtilis) and Gram-negative bacteria (e.g., V. parahaemolyticus and Aeromonas hydrophila) in the presence of calcium. Furthermore, rEsIntegrin could not only bind to various bacteria such as S. aureus, Micrococcus luteus, B. subtilis, Bacillus megaterium, Bacillus thuringiensis, V. parahaemolyticus, Vibrio anguillarum, A. hydrophila, Vibrio natriegens, and Escherichia coli, but this compound also helped crabs in clearing virulent Gram-negative bacterium, V. parahaemolyticus, in vivo. These data suggested that EsIntegrin might function as cellular receptor that is involved in anti-bacterial immunity from E. sinensis.

Integrin β subunit and its RNA interference in immune and developmental processes of the Oriental tobacco budworm, Helicoverpa assulta

Integrins are cell surface heterodimeric proteins interacting with the extracellular matrix and mediating environmental signals through cell membranes. A full-length cDNA sequence of the integrin β1 subunit gene (HaITGb1) was cloned from the Oriental tobacco budworm, Helicoverpa assulta, and analyzed for its physiological role in both immune response and development. HaITGb1 was expressed in all developmental stages from egg to adult and in all tested larval tissues of hemocytes, fat body, gut, and epidermis. Utilizing an RNA interference (RNAi) approach, injection of a specific double-stranded RNA (dsRNA) in larvae suppressed HaITGb1 transcript levels and significantly impaired hemocytes in their extracellular matrix adherence properties. Furthermore, the RNAi treatment significantly suppressed hemocyte nodule formation in response to bacterial challenge, which resulted in significantly enhanced susceptibility to both pathogenic and non-pathogenic bacteria. The RNAi treatment also interfered with H. assulta larval and pupal development. These results suggest that the extensive and constitutive expression of HaITGb1 is necessary for H. assulta to perform an efficient immune response against microbial pathogens and undergo normal immature development.

Effects of Blocking αvβ₃ integrin by a recombinant RGD disintegrin on remodeling of wound healing after induction of incisional hernia in rats

PURPOSE

Incisional hernia (IH) is characterized by defective wound healing process. Disba-01, a αvb₃ integrin blocker has shown to control the rate of wound repair and therefore it could be a target for new wound healing therapies.The objective of the study was to determine the changes induced by Disba-01 on repair of wound healing after induced IH in rats.

METHODS

Thirty two male albino rats were submitted to IH and divided into 4 experimental groups: G1, placebo control; G2, DisBa-01-treated; G3, anti-αvβ₃ antibodies-treated and G4, anti-α₂ antibodies-treated. Histological. biochemical and extracellular matrix remodeling analysis of abdominal wall were evaluated.

RESULTS

After 14 days, 100% of the G2 did not present hernia, and the hernia ring was closed by a thin membrane. In contrast, all groups maintained incisional hernia. DisBa-01 also increased the number macrophages and fibroblasts and induced the formation of new vessels. Additionally, MMP-2 was strongly activated only in G2 (P<0.05). Anti- αvβ₃-integrin antibodies produced similar results than Disba-01 but not anti-α₂ integrin blocking antibodies.

CONCLUSION

These results strongly indicate that Disba-01 has an important role in the control of wound healing and the blocking of this integrin may be an interesting therapeutical strategy in IH.

β Integrins mediate FAK Y397 autophosphorylation of resistance arteries during eutrophic inward remodeling in hypertension

Human essential hypertension is characterized by eutrophic inward remodeling of the resistance arteries with little evidence of hypertrophy. Upregulation of αVβ3 integrin is crucial during this process. In order to investigate the role of focal adhesion kinase (FAK) activation in this process, the level of FAK Y397 autophosphorylation was studied in small blood vessels from young TGR(mRen2)27 animals as blood pressure rose and eutrophic inward remodeling took place. Between weeks 4 and 5, this process was completed and accompanied by a significant increase in FAK phosphorylation compared with normotensive control animals. Phosphorylated (p)FAK Y397 was coimmunoprecipitated with both β1- and β3-integrin-specific antibodies. In contrast, only a fraction (<10-fold) was coprecipitated with the β3 integrin subunit in control vessels. Inhibition of eutrophic remodeling by cRGDfV treatment of TGR(mRen2)27 rats resulted in the development of smooth-muscle-cell hypertrophy and a significant further enhancement of FAK Y397 phosphorylation, but this time with exclusive coassociation of pFAK Y397 with integrin β1. We established that phosphorylation of FAK Y397 with association with β1 and β3 integrins occurs with pressure-induced eutrophic remodeling. Inhibiting this process leads to an adaptive hypertrophic vascular response induced by a distinct β1-mediated FAK phosphorylation pattern.

Biological functionalities of transglutaminase 2 and the possibility of its compensation by other members of the transglutaminase family

Transglutaminase 2 (TG2) is the most widely distributed and most abundantly expressed member of the transglutaminase family of enzymes, a group of intracellular and extracellular proteins that catalyze the Ca²⁺-dependent posttranslational modification of proteins. It is a unique member of the transglutaminase family owing to its specialized biochemical, structural and functional elements, ubiquitous tissue distribution and subcellular localization, and substrate specificity. The broad substrate specificity of TG2 and its flexible interaction with numerous other gene products may account for its multiple biological functions. In addition to the classic Ca²⁺-dependent transamidation of proteins, which is a hallmark of transglutaminase enzymes, additional Ca²⁺-independent enzymatic and nonenzymatic activities of TG2 have been identified. Many such activities have been directly or indirectly implicated in diverse cellular physiological events, including cell growth and differentiation, cell adhesion and morphology, extracellular matrix stabilization, wound healing, cellular development, receptor-mediated endocytosis, apoptosis, and disease pathology. Given the wide range of activities of the transglutaminase gene family it has been suggested that, in the absence of active versions of TG2, its function could be compensated for by other members of the transglutaminase family. It is in the light of this assertion that we review, herein, TG2 activities and the possibilities and premises for compensation for its absence.

Biomimetic polyurethanes in nano and regenerative medicine

Nature's inspiration is a promising tool to design new biomaterials especially for frontier technological areas such as tissue engineering and nanomedicine.

Expression kinetics of β-integrin in Chinese shrimp (Fenneropenaeus chinensis) hemocytes following infection with white spot syndrome virus

Our previous study has demonstrated that an integrin β subunit of Chinese shrimp (Fenneropenaeus chinensis) (FcβInt) involved in WSSV infection. In order to further elucidate the potential role of the FcβInt in the WSSV infection, expression response of FcβInt to WSSV infection in shrimp hemocytes was investigated after intra-muscular injection with the virus. Following time-course hemocytes sampling, the expression variation of FcβInt in hemocytes was examined by flow cytometric immunofluorescence assay (FCIFA) and enzyme linked immunosorbent assay (ELISA) using the monoclonal antibody (Mab) 2C5 against FcβInt, which was successfully produced with recombinant partial FcβInt and exhibited binding to a 120 kDa hemocyte protein. Meanwhile, the dynamic state of FcβInt mRNA level and WSSV copies in hemocytes were determined by quantitative real-time PCR. The result of FCIFA showed that FcβInt was mainly expressed on the semi-granular and granular cells, which was down-regulated at 6 h post infection (p.i.), and significantly increased to the peak level at 12 h p.i., then decreased to the control level by 24 h. However, FcβInt on the hyaline cells was lowly expressed and didn't show active response to the viral infection. The variation of FcβInt concentrations in total hemocytes determined by ELISA was roughly in accordance with the changing tendency of FcβInt expressed on the semi-granular and granular cells. FcβInt mRNA level in total hemocytes was significantly up-regulated to the peak level at 12 h p.i. Moreover, the number of WSSV copies in hemocytes began to exhibit a significant increase at 24 h p.i. The present study demonstrated that WSSV infection would induce a differential regulation of FcβInt expression in different type hemocytes, which provided valuable evidences for the close correlation between FcβInt and WSSV infection.

Expression of caveolin-1 in the early phase of beta-TCP implanted in dog mandible

Caveolin is an essential and signature protein of caveolae. Caveolin-1 participates in signal transduction processes by acting as a scaffolding protein that concentrates, organizes and functional regulates signalling molecules within caveolar membranes. Beta-tricalcium phosphate (β-TCP) has been widely used for scaffold in tissue engineering due to its high biodegradability, osteoconductivity, easy manipulation, and lack of histotoxicity. To better understand the role of caveolin-1 in bone homeostasis and response to β-TCP scaffold, β-TCP was implanted into the dog mandible defects in beagle dogs, and gene expression profiles were examined focused on the molecular components involved in caveolin-1 regulation. Here we showed the quantitative imageology analysis characterized using in vivo micro-computed tomography (CT) images at 4 and 7 days after β-TCP implanted in dog mandibles. The bone reformation by using the β-TCP scaffolds began within 4 days of surgery, and was healing well at 7 days after surgery. Higher mRNA level of caveolin-1 was observed in β-TCP-implanted Beagle dog mandibles compared with controls at day 4 and day 7 post-surgery. The enhancement of caveolin-1 by β-TCP was further confirmed by immunohistochemistry and immunofluorescence analysis. We further revealed increased Smad7 and Phospho Stat3 expression in β-TCP-implanted specimens. Taken together, these results suggest that the enhancement of caveolin-1 play an important role in accelerating bone formation by β-TCP.

Optimal intensity shock wave promotes the adhesion and migration of rat osteoblasts via integrin β1-mediated expression of phosphorylated focal adhesion kinase

To search for factors promoting bone fracture repair, we investigated the effects of extracorporeal shock wave (ESW) on the adhesion, spreading, and migration of osteoblasts and its specific underlying cellular mechanisms. After a single period of stimulation by 10 kV (500 impulses) of shock wave (SW), the adhesion rate was increased as compared with the vehicle control. The data from both wound healing and transwell tests confirmed an acceleration in the migration of osteoblasts by SW treatment. RT-PCR, flow cytometry, and Western blotting showed that SW rapidly increased the surface expression of α5 and β1 subunit integrins, indicating that integrin β1 acted as an early signal for ESW-induced osteoblast adhesion and migration. It has also been found that a significant elevation occurred in the expression of phosphorylated β-catenin and focal adhesion kinase (FAK) at the site of tyrosine 397 in response to SW stimulation after the increasing expression of the integrin β1 molecule. When siRNAs of integrin α5 and β1 subunit were added, the level of FAK phosphorylation elevated by SW declined. Interestingly, the adhesion and migration of osteoblasts were decreased when these siRNA reagents as well as the ERK1/2 signaling pathway inhibitors, U0126 and PD98059, were present. Further studies demonstrated that U0126 could inhibit the downstream integrin-dependent signaling pathways, such as the FAK signaling pathway, whereas it had no influence on the synthesis of integrin β1 molecule. In conclusion, these data suggest that ESW promotes the adhesion and migration of osteoblasts via integrin β1-mediated expression of phosphorylated FAK at the Tyr-397 site; in addition, ERK1/2 are also important for osteoblast adhesion, spreading, migration, and integrin expression.

Regulation of TGFβ in the immune system: an emerging role for integrins and dendritic cells

Regulation of an immune response requires complex crosstalk between cells of the innate and adaptive immune systems, via both cell–cell contact and secretion of cytokines. An important cytokine with a broad regulatory role in the immune system is transforming growth factor-β (TGF-β). TGF-β is produced by and has effects on many different cells of the immune system, and plays fundamental roles in the regulation of immune responses during homeostasis, infection and disease. Although many cells can produce TGFβ, it is always produced as an inactive complex that must be activated to bind to the TGFβ receptor complex and promote downstream signalling. Thus, regulation of TGFβ activation is a crucial step in controlling TGFβ function. This review will discuss how TGFβ controls diverse immune responses and how TGFβ function is regulated, with a focus on recent work highlighting a critical role for the integrin αvβ8 expressed by dendritic cells in activating TGFβ.

Cardiomyocytes in vitro adhesion is actively influenced by biomimetic synthetic peptides for cardiac tissue engineering

Scaffolds for tissue engineering must be designed to direct desired events such as cell attachment, growth, and differentiation. The incorporation of extracellular matrix-derived peptides into biomaterials has been proposed to mimic biochemical signals. In this study, three synthetic fragments of fibronectin, vitronectin, and stromal-derived factor-1 were investigated for the first time as potential adhesive sequences for cardiomyocytes (CMs) compared to smooth muscle cells. CMs are responsive to all peptides to differing degrees, demonstrating the existence of diverse adhesion mechanisms. The pretreatment of nontissue culture well surfaces with the (Arginine-Glycine-Aspartic Acid) RGD sequence anticipated the appearance of CMs' contractility compared to the control (fibronectin-coated well) and doubled the length of cell viability. Future prospects are the inclusion of these sequences into biomaterial formulation with the improvement in cell adhesion that could play an important role in cell retention during dynamic cell seeding.

A target-specific feeding toxicity of β(1) integrin dsRNA against diamondback moth, Plutella xylostella

Integrin is a cell-surface protein consisting of α and β heterodimers. A predicted amino acid sequence of an integrin subunit of the diamondback moth, Plutella xylostella, was highly homologous to other lepidopteran β1 subunits and possessed essential functional domains. The β1 integrin of P. xylostella (βPx1) was expressed in all developmental stages of P. xylostella. It was also expressed in all tested tissues including hemocyte, fat body, gut, and epidermis of last instar. When βPx1 expression was suppressed by injection of dsRNA specific to βPx1 (dsRNA(βPx1)), the treated larvae exhibited significant suppression in immune response and also suffered significant larval mortality. When dsRNA(βPx1) was orally fed to young larvae, it suppressed the expression of âPx1 and resulted in a significant mortality. By contrast, a dsRNA specific to β1 subunit of Spodoptera exigua gave little adverse effects on βPx1 expression and larval development when it was treated by injection or oral administration, though these two genes showed 71% sequence homology. These results suggest a target-specific RNA interference of dsRNA(βPx1), which causes significant mortality to P. xylostella by feeding treatment.

RNA interference of β1 integrin subunit impairs development and immune responses of the beet armyworm, Spodoptera exigua

Integrin is a cell surface protein that is composed of α and β heterodimer and mediates cell interaction with extracellular matrix or other cells including microbial pathogens. A full length cDNA sequence (2862 bp) of a β1 subunit integrin (βSe1) was cloned from the beet armyworm, Spodoptera exigua. Phylogenetic analysis showed that βSe1 was clustered with other insect β integrin subunits with the highest amino acid sequence identity (98.3%) to β1 of Spodoptera litura. Structural analysis of the deduced amino acid sequence indicated that βSe1 possessed all functional domains known in other insect β1 integrins. RT-PCR analysis showed that βSe1 was expressed in all developmental stages and all tested tissues of S. exigua. Its expression was further upregulated in hemocytes by injections of various microbes from quantitative RT-PCR analysis. Injection of double-stranded βSe1 RNA (dsRNA(βSe1)) into late instar S. exigua suppressed βSe1 expression and resulted in significant reduction in pupal weight. The dsRNA(βSe1) injection significantly impaired hemocyte-spreading and nodule formation of S. exigua in response to bacterial challenge. Furthermore, oral ingestion of dsRNA(βSe1) induced reduction of βSe1 expression in midgut and resulted in significant mortality of S. exigua during immature development. These results suggest that βSe1 plays crucial roles in performing cellular immune responses as well as larval development in S. exigua.

Baicalein inhibits the migration and invasive properties of human hepatoma cells

Flavonoids have been demonstrated to exert health benefits in humans. We investigated whether the flavonoid baicalein would inhibit the adhesion, migration, invasion, and growth of human hepatoma cell lines, and we also investigated its mechanism of action. The separate effects of baicalein and baicalin on the viability of HA22T/VGH and SK-Hep1 cells were investigated for 24h. To evaluate their invasive properties, cells were incubated on matrigel-coated transwell membranes in the presence or absence of baicalein. We examined the effect of baicalein on the adhesion of cells, on the activation of matrix metalloproteinases (MMPs), protein kinase C (PKC), and p38 mitogen-activated protein kinase (MAPK), and on tumor growth in vivo. We observed that baicalein suppresses hepatoma cell growth by 55%, baicalein-treated cells showed lower levels of migration than untreated cells, and cell invasion was significantly reduced to 28%. Incubation of hepatoma cells with baicalein also significantly inhibited cell adhesion to matrigel, collagen I, and gelatin-coated substrate. Baicalein also decreased the gelatinolytic activities of the matrix metalloproteinases MMP-2, MMP-9, and uPA, decreased p50 and p65 nuclear translocation, and decreased phosphorylated I-kappa-B (IKB)-β. In addition, baicalein reduced the phosphorylation levels of PKCα and p38 proteins, which regulate invasion in poorly differentiated hepatoma cells. Finally, when SK-Hep1 cells were grown as xenografts in nude mice, intraperitoneal (i.p.) injection of baicalein induced a significant dose-dependent decrease in tumor growth. These results demonstrate the anticancer properties of baicalein, which include the inhibition of adhesion, invasion, migration, and proliferation of human hepatoma cells in vivo.

Endorepellin, the angiostatic module of perlecan, interacts with both the α2β1 integrin and vascular endothelial growth factor receptor 2 (VEGFR2): a dual receptor antagonism

Endorepellin, the C-terminal module of perlecan, negatively regulates angiogenesis counter to its proangiogenic parental molecule. Endorepellin (the C-terminal domain V of perlecan) binds the α2β1 integrin on endothelial cells and triggers a signaling cascade that leads to disruption of the actin cytoskeleton. Here, we show that both perlecan and endorepellin bind directly and with high affinity to both VEGF receptors 1 and 2, in a region that differs from VEGFA-binding site. In both human and porcine endothelial cells, this interaction evokes a physical down-regulation of both the α2β1 integrin and VEGFR2, with concurrent activation of the tyrosine phosphatase SHP-1 and downstream attenuation of VEGFA transcription. We demonstrate that endorepellin requires both the α2β1 integrin and VEGFR2 for its angiostatic activity. Endothelial cells that express α2β1 integrin but lack VEGFR2, do not respond to endorepellin treatment. Thus, we provide a new paradigm for the activity of an antiangiogenic protein and mechanistically explain the specificity of endorepellin for endothelial cells, the only cells that simultaneously express both receptors. We hypothesize that a mechanism such as dual receptor antagonism could operate for other angiostatic fragments.

Caveolin-1 and integrin β1 regulate embryonic stem cell proliferation via p38 MAPK and FAK in high glucose

The involvement of caveolin-1 (Cav-1) and integrin β1 (IN β1) in regulation of embryonic stem (ES) cell growth by high glucose is by no means clear cut. Therefore, the aim of this study was to examine the influence of high glucose on Cav-1 and IN β1 expression in mouse ES cells and their signaling pathways to modulate proliferation. High glucose significantly increased Cav-1 and IN β1 expression. In addition, increased IN β1 expression was inhibited by Cav-1 small interfering RNA (siRNA). High glucose caused reactive oxygen species generation and p38 mitogen-activated protein kinase (MAPK) phosphorylation. Inhibition of p38 MAPK blocked high glucose-induced Cav-1 and fibronectin (FN) expression. Moreover, phosphorylation of both Src and focal adhesion kinase (FAK) were increased by high glucose, which were inhibited by IN β1 antibody. In addition, high glucose increased the expression levels of PINCH1/2, integrin-linked kinase (ILK), and α-parvin [PIP] complex proteins, which were all inhibited by the FAK siRNA and Src specific inhibitor (PP2, 10(-7)  M). High glucose also increased F-actin expression, which was inhibited by ILK, PINCH1/2, and α-parvin siRNAs. Finally, high glucose-induced increase of ES cell proliferation was inhibited by TRIO and F-actin binding protein (TRIOBP) siRNA. The results demonstrate that high glucose-induced Cav-1 and IN β1 activation can stimulate ES cell proliferation through the modification of focal adhesion signaling pathways.

Syndecan-1 couples the insulin-like growth factor-1 receptor to inside-out integrin activation

Syndecan-1 (Sdc1) engages and activates the αvβ3 (and/or αvβ5) integrin when clustered in human carcinoma and endothelial cells. Although the engagement is extracellular, the activation mechanism is cytoplasmic. This talin-dependent, inside-out signaling pathway is activated downstream of the insulin-like growth factor-1 receptor (IGF1R), whose kinase activity is triggered by Sdc1 clustering. In vitro binding assays using purified receptors suggest that association of the Sdc1 ectodomain with the integrin provides a 'docking face' for IGF1R. IGF1R docking and activation of the associated integrin is blocked by synstatin (SSTN(92-119)), a peptide derived from the integrin engagement site in Sdc1. IGF1R colocalizes with αvβ3 integrin and Sdc1 in focal contacts, but fails to associate with or activate the integrin in cells either lacking Sdc1 or expressing Sdc1(Δ67-121), a mutant that is unable to form the Sdc1-integrin-IGF1R ternary complex. Integrin activation is also blocked by IGF1R inhibitors or by silencing IGF1R or talin expression with small-interfering RNAs (siRNAs). In both cases, expression of the constitutively active talin F23 head domain rescues integrin activation. We recently reported that SSTN(92-119) blocks angiogenesis and impairs tumor growth in mice, therefore this Sdc1-mediated integrin regulatory mechanism might be a crucial regulator of disease processes known to rely on these integrins, including tumor cell metastasis and tumor-induced angiogenesis.

Comparison of satellite cell-derived myoblasts and C2C12 differentiation in two- and three-dimensional cultures: changes in adhesion protein expression

Changes in the expression of adhesion proteins involved in myoblast differentiation were investigated in monolayer (two-dimensional) and 3D (three-dimensional) cell cultures. The expression of integrin alpha3 subunit, integrin beta1 subunit, ADAM12 (a disintegrin and metalloproteinase 12), tetraspanins CD9 and CD81 and M-cadherin were examined in the murine myoblast cell line C2C12 and in a primary culture of rat satellite cells. Myoblasts in monolayer and 3D cultures showed significant differences in their morphology and cytoskeletal organization. All of the studied proteins participated in myoblast fusion in each culture examined, but differences in their levels of expression were observed. Satellite cell-derived myoblasts exhibited higher expression of adhesion protein mRNAs than C2C12 cells. Also, C2C12 cells from a 3D culture showed slightly higher expression of adhesion protein transcripts than the same cells cultured as a monolayer. Significantly, the levels of adhesion protein mRNAs were found to change in parallel in all cell culture types. Despite this finding, it is important that differences between satellite cell-derived myoblasts and cell line C2C12 grown in monolayer and 3D cultures are taken into account when studying processes of myoblast differentiation in vitro.

Analysis on migration and activation of live macrophages on transparent flat and nanostructured titanium

The immunotoxicity of implanted nanostructured titanium is a paramount issue for vascular, dental and orthopedic applications. However, it has been unclear whether implanted surface nanostructures can inhibit or aggrevate inflammatory responses. Herein, macrophage activation, as evidence of migration, on transparent flat and nanostructured titanium correlated with pro-inflammatory protein synthesis and cytokine release. Through the real-time monitoring of initial cytoskeleton variations, this study identified that macrophage movement was restricted on nanostructured titanium compared to flat titanium surfaces. Furthermore, nanostructured titanium elicited secretion of fewer pro-inflammatory enzyme molecules and cytokines, as well as reduced nitric oxide production. All results collectively indicated that initial macrophage activation can be mitigated by nanoscale surface topography alone, without modification of surface chemistry or stiffness.

Conditional β1-integrin-deficient mice display impaired pancreatic β cell function

β1-Integrin, a critical regulator of β cell survival and function, has been shown to protect against cell death and promote insulin expression and secretion in rat and human islet cells in vitro. The aim of the present study was to examine whether the knockout of β1-integrin in collagen I-producing cells would have physiological and functional implications in pancreatic endocrine cells in vivo. Using adult mice with a conditional knockout of β1-integrin in collagen I-producing cells, the effects of β1-integrin deficiency on glucose metabolism and pancreatic endocrine cells were examined. Male β1-integrin-deficient mice display impaired glucose tolerance, with a significant reduction in pancreatic insulin content (p < 0.01). Morphometric analysis revealed a significant reduction in β cell mass (p < 0.001) in β1-integrin-deficient mice, along with a significant decrease in β cell proliferation, Pdx-1 and Nkx6.1 expression when compared with controls. Interestingly, these physiological and morphometric alterations in female β1-integrin-deficient mice were less significant. Furthermore, β1-integrin-deficient mice displayed decreased FAK (p < 0.05) and ERK1/2 (p < 0.001) phosphorylation, reduced cyclin D1 levels (p < 0.001) and increased caspase 3 cleavage (p < 0.01), while no changes in Akt phosphorylation were observed, indicating that the β1-integrin signals through the FAK-MAPK-ERK pathway in vivo. Our results demonstrate that β1-integrin is involved in the regulation of glucose metabolism and contributes to the maintenance of β cell survival and function in vivo.

Role of hypoxia-induced fibronectin-integrin β1 expression in embryonic stem cell proliferation and migration: Involvement of PI3K/Akt and FAK

Cell migration is largely dependent on integrin (IN) binding to the extracellular matrix, and several signaling pathways involved in these processes have been shown to be modified by hypoxia. Therefore, the aim of this study was to determine the influence of hypoxia on fibronectin (FN) and IN β1 expression in mouse embryonic stem cells (mESCs) and their signaling pathways to modulate proliferation. FN and IN β1 expression were significantly increased in hypoxic mESCs by 24 h. Hypoxia also increased cell attachment, which was accompanied by concomitant increases in the binding level of FN and IN β1. Hypoxia-induced FN expression was mediated by increased phosphatidylinositol 3 kinase (PI3K)/Akt and mammalian target of rapamycin (mTOR) phosphorylation, and hypoxia-inducible factor-1α (HIF-1α) expression. Moreover, under hypoxic conditions, focal adhesion kinase (FAK) and Src phosphorylation were increased in a time-dependent fashion; these increases were blocked by IN β1 antibody. In addition, the hypoxia induced increase of F-actin distribution and cell migration (activation of matrix metalloproteinase-2 and -9) was inhibited by IN β1 antibody. Indeed, hypoxia increased the level of cell-cycle regulatory protein and DNA synthesis. In conclusion, hypoxia increases the proliferation and migration of mESCs via FN-IN β1 production through the PI3K/Akt, mTOR, and HIF-1α pathways, followed by FAK activation.

Defective granulation tissue formation in mice with specific ablation of integrin-linked kinase in fibroblasts - role of TGFβ1 levels and RhoA activity

Wound healing crucially relies on the mechanical activity of fibroblasts responding to TGFβ1 and to forces transmitted across focal adhesions. Integrin-linked kinase (ILK) is a central adapter recruited to integrin β1 tails in focal adhesions mediating the communication between cells and extracellular matrix. Here, we show that fibroblast-restricted inactivation of ILK in mice leads to impaired healing due to a severe reduction in the number of myofibroblasts, whereas inflammatory infiltrate and vascularization of the granulation tissue are unaffected. Primary ILK-deficient fibroblasts exhibit severely reduced levels of extracellular TGFβ1, α-smooth muscle actin (αSMA) production and myofibroblast conversion, which are rescued by exogenous TGFβ1. They are further characterized by elevated RhoA and low Rac1 activities, resulting in abnormal shape and reduced directional migration. Interference with RhoA-ROCK signaling largely restores morphology, migration and TGFβ1 levels. We conclude that, in fibroblasts, ILK is crucial for limiting RhoA activity, thus promoting TGFβ1 production, which is essential for dermal repair following injury.

Role of altered sialylation of the I-like domain of beta1 integrin in the binding of fibronectin to beta1 integrin: thermodynamics and conformational analyses

N-glycosylation of the I-like domain of beta1 integrin plays an essential role in integrin structure and function, and the altered sialylation of beta1 integrin regulates beta1 integrin binding to fibronectin. However, the structural basis underlying the effect of altered sialylation of the beta1 I-like domain on beta1 integrin binding to fibronectin remains largely unknown. In this study, we used a combination of molecular dynamics simulations and binding free energy analyses to investigate changes in binding thermodynamics and in conformation of the glycosylated beta1 I-like domain-FN-III(9-10) complex caused by altered sialylation of the beta1 I-like domain. Binding free energy analyses showed that desialylation of beta1 I-like domain increased beta1 integrin binding to fibronectin, consistent with experimental results. Interaction analyses showed that altered sialylation of the beta1 I-like domain resulted in significant changes in the interaction of the N-glycans of the I-like domain with both the I-like domain and fibronectin, and these changes could directly affect the allosteric regulation of the interaction between the I-like domain and fibronectin. Altered sialylation of the beta1 I-like domain caused significant conformational changes in key functional sites of both the beta1 I-like domain and fibronectin. In addition, altered sialylation of the beta1 I-like domain resulted in changes in the degree of correlated motions between residues in the I-like domain and residues in fibronectin, and in the degree of motion changes in fibronectin, which could affect beta1 integrin binding to fibronectin. We believe results from this study provide thermodynamic and structural evidence for a role of altered sialylation of beta1 integrin in regulating beta1 integrin binding to fibronectin and it's induced cellular activities.

A small fibronectin-mimicking protein from bacteria induces cell spreading and focal adhesion formation

Fibronectin, a 250-kDa eukaryotic extracellular matrix protein containing an RGD motif plays crucial roles in cell-cell communication, development, tissue homeostasis, and disease development. The highly complex fibrillar fibronectin meshwork orchestrates the functions of other extracellular matrix proteins, promoting cell adhesion, migration, and intracellular signaling. Here, we demonstrate that CagL, a 26-kDa protein of the gastric pathogen and type I carcinogen Helicobacter pylori, mimics fibronectin in various cellular functions. Like fibronectin, CagL contains a RGD motif and is located on the surface of the bacterial type IV secretion pili as previously shown. CagL binds to the integrin receptor alpha(5)beta(1) and mediates the injection of virulence factors into host target cells. We show that purified CagL alone can directly trigger intracellular signaling pathways upon contact with mammalian cells and can complement the spreading defect of fibronectin(-/-) knock-out cells in vitro. During interaction with various human and mouse cell lines, CagL mimics fibronectin in triggering cell spreading, focal adhesion formation, and activation of several tyrosine kinases in an RGD-dependent manner. Among the activated factors are the nonreceptor tyrosine kinases focal adhesion kinase and Src but also the epidermal growth factor receptor and epidermal growth factor receptor family member Her3/ErbB3. Interestingly, fibronectin activates a similar range of tyrosine kinases but not Her3/ErbB3. These findings suggest that the bacterial protein CagL not only exhibits functional mimicry with fibronectin but is also capable of activating fibronectin-independent signaling events. We thus postulate that CagL may contribute directly to H. pylori pathogenesis by promoting aberrant signaling cross-talk within host cells.

Targeted molecular dynamics reveals overall common conformational changes upon hybrid domain swing-out in beta3 integrins

The beta3 integrin family members alphaIIbeta3 and alphaVbeta3 signal bidirectionally through long-range allosteric changes, including a transition from a bent unliganded-closed low-affinity state to an extended liganded-open high-affinity state. To obtain an atomic-level description of this transition in an explicit solvent, we carried out targeted molecular dynamics simulations of the headpieces of alphaIIbeta3 and alphaVbeta3 integrins. Although minor differences were observed between these receptors, our results suggest a common transition pathway in which the hybrid domain swing-out is accompanied by conformational changes within the beta3 betaA (I-like) domain that propagate through the alpha7 helix C-terminus, and are followed by the alpha7 helix downward motion and the opening of the beta6-alpha7 loop. Breaking of contact interactions between the beta6-alpha7 loop and the alpha1 helix N-terminus results in helix straightening, internal rearrangements of the specificity determining loop (SDL), movement of the beta1-alpha1 loop toward the metal ion dependent adhesion site (MIDAS), and final changes at the interfaces between the beta3 betaA (I-like) domain and either the hybrid or the alpha beta-propeller domains. Taken together, our results suggest novel testable hypotheses of intradomain and interdomain interactions responsible for beta3 integrin activation.