Integrin activation

"Caught in the net": the extracellular matrix of the bone marrow in normal hematopoiesis and leukemia

The influence of the bone marrow microenvironment on normal hematopoiesis, but also leukemia, has largely been accepted. However, the focus has been predominantly on the role of various cell types or cytokines maintaining hematopoietic stem cells or protecting leukemia stem cells from different therapies. A frequently overlooked component of the bone marrow microenvironment is the extracellular matrix, which not only provides a mechanical scaffold, but also serves as a source of growth factors. We discuss here how extracellular matrix proteins directly or indirectly modulate hematopoietic stem cell physiology and influence leukemia progression. It is hoped that existing and future studies on this topic may propel forward the possibility of augmenting normal hematopoiesis and improving therapies for leukemia, for instance, by targeting of the extracellular matrix in the bone marrow.

Precise coordination of cell-ECM adhesion is essential for efficient melanoblast migration during development

Melanoblasts disperse throughout the skin and populate hair follicles through long-range cell migration. During migration, cells undergo cycles of coordinated attachment and detachment from the extracellular matrix (ECM). Embryonic migration processes that require cell-ECM attachment are dependent on the integrin family of adhesion receptors. Precise regulation of integrin-mediated adhesion is important for many developmental migration events. However, the mechanisms that regulate integrin-mediated adhesion in vivo in melanoblasts are not well understood. Here, we show that autoinhibitory regulation of the integrin-associated adapter protein talin coordinates cell-ECM adhesion during melanoblast migration in vivo Specifically, an autoinhibition-defective talin mutant strengthens and stabilizes integrin-based adhesions in melanocytes, which impinges on their ability to migrate. Mice with defective talin autoinhibition exhibit delays in melanoblast migration and pigmentation defects. Our results show that coordinated integrin-mediated cell-ECM attachment is essential for melanoblast migration and that talin autoinhibition is an important mechanism for fine-tuning cell-ECM adhesion during cell migration in development.

Uremic Toxins and Ciprofloxacin Affect Human Tenocytes In Vitro

Tendinopathy is a rare but serious complication of quinolone therapy. Risk factors associated with quinolone-induced tendon disorders include chronic kidney disease accompanied by the accumulation of uremic toxins. Hence, the present study explored the effects of the representative uremic toxins phenylacetic acid (PAA) and quinolinic acid (QA), both alone and in combination with ciprofloxacin (CPX), on human tenocytes in vitro. Tenocytes incubated with uremic toxins +/- CPX were investigated for metabolic activity, vitality, expression of the dominant extracellular tendon matrix (ECM) protein type I collagen, cell-matrix receptor β1-integrin, proinflammatory interleukin (IL)-1β, and the ECM-degrading enzyme matrix metalloproteinase (MMP)-1. CPX, when administered at high concentrations (100 mM), suppressed tenocyte metabolism after 8 h exposure and at therapeutic concentrations after 72 h exposure. PAA reduced tenocyte metabolism only after 72 h exposure to very high doses and when combined with CPX. QA, when administered alone, led to scarcely any cytotoxic effect. Combinations of CPX with PAA or QA did not cause greater cytotoxicity than incubation with CPX alone. Gene expression of the pro-inflammatory cytokine IL-1β was reduced by CPX but up-regulated by PAA and QA. Protein levels of type I collagen decreased in response to high CPX doses, whereas PAA and QA did not affect its synthesis significantly. MMP-1 mRNA levels were increased by CPX. This effect became more pronounced in the form of a synergism following exposure to a combination of CPX and PAA. CPX was more tenotoxic than the uremic toxins PAA and QA, which showed only distinct suppressive effects.

RIAM-VASP Module Relays Integrin Complement Receptors in Outside-In Signaling Driving Particle Engulfment

The phagocytic integrins and complement receptors α_Mβ₂/CR3 and α_Xβ₂/CR4 are classically associated with the phagocytosis of iC3b-opsonized particles. The activation of this receptor is dependent on signals derived from other receptors (inside-out signaling) with the crucial involvement of the Rap1-RIAM-Talin-1 pathway. Here, we analyze the implication of RIAM and its binding partner VASP in the signaling events occurring downstream of β₂ integrins (outside-in) during complement-mediated phagocytosis. To this end, we used HL-60 promyelocytic cell lines deficient in RIAM or VASP or overexpressing EGFP-tagged VASP to determine VASP dynamics at phagocytic cups. Our results indicate that RIAM-deficient HL-60 cells presented impaired particle internalization and altered integrin downstream signaling during complement-dependent phagocytosis. Similarly, VASP deficiency completely blocked phagocytosis, while VASP overexpression increased the random movement of phagocytic particles at the cell surface, with reduced internalization. Moreover, the recruitment of VASP to particle contact sites, amount of pSer157-VASP and formation of actin-rich phagocytic cups were dependent on RIAM expression. Our results suggested that RIAM worked as a relay for integrin complement receptors in outside-in signaling, coordinating integrin activation and cytoskeletal rearrangements via its interaction with VASP.

Rumex acetosa modulates platelet function and inhibits thrombus formation in rats

Background

The Rumex acetosa has been used in medicinal treatment, food technology and phytotherapeutics in Eastern Asia and many other countries. However, its effect on cardiovascular system and antiplatelet activity remained to be known. In this study, we examined the antiplatelet activity of R. acetosa in detailed manner to understand underlying mechanism.

Methods

To study this, whole blood was obtained from male Sprague Dawley (SD) rats and aggregation of washed platelets measured using light transmission aggregometry. Intracellular calcium ion concentration ([Ca²⁺]_i) was measured using Fura-2/AM while ATP release evaluated by luminometer. Activation of integrin α_IIbβ₃ analyzed by flow cytometry and clot retraction. Furthermore, we studied the signaling pathways mediated by R. acetosa extract by western blot analysis.

Results

R. acetosa extract markedly inhibited collagen-induced platelet aggregation and ATP release in a dose-dependent manner. It also suppressed [Ca²⁺]_i mobilization, integrin α_IIbβ₃ activation and clot retraction. The extract significantly attenuated phosphorylation of the MAPK pathway (i.e., ERK1/2, JNK), MKK4, PI3K/Akt, and Src family kinase.

Conclusion

Taken together, this data suggests that R. acetosa extract exhibits anti-platelet activity via modulating MAPK, PI3K/Akt pathways, and integrin α_IIbβ₃-mediated inside-out and outside-in signaling, and it may protect against the development of platelet-related cardiovascular diseases.

Stimulation of Fibronectin Matrix Assembly by Lysine Acetylation

Diabetic nephropathy, a devastating consequence of diabetes mellitus, is characterized by the accumulation of extracellular matrix (ECM) that disrupts the kidney's filtration apparatus. Elevated glucose levels increase the deposition of a fibronectin (FN) matrix by mesangial cells, the primary matrix-producing cells of the kidney, and also increase acetyl-CoA leading to higher levels of lysine acetylation. Here, we investigated the connection between acetylation and the ECM and show that treatment of mesangial cells with deacetylase inhibitors increases both acetylation and FN matrix assembly compared to untreated cells. The matrix effects were linked to lysine 794 (K794) in the β1 integrin cytoplasmic domain based on studies of cells expressing acetylated (K794Q) and non-acetylated (K794R) mimetics. β1(K794Q) cells assembled significantly more FN matrix than wildtype β1 cells, while the non-acetylated β1(K794R) form was inactive. We show that mutation of K794 affects FN assembly by stimulating integrin-FN binding activity and cell contractility. Wildtype and β1(K794Q) cells but not β1(K794R) cells further increased their FN matrix when stimulated with deacetylase inhibitors indicating that increased acetylation on other proteins is required for maximum FN assembly. Thus, lysine acetylation provides a mechanism for glucose-induced fibrosis by up-regulation of FN matrix assembly.

The Extracellular Matrix: An Accomplice in Gastric Cancer Development and Progression

The extracellular matrix (ECM) is a dynamic and highly organized tissue structure, providing support and maintaining normal epithelial architecture. In the last decade, increasing evidence has emerged demonstrating that alterations in ECM composition and assembly strongly affect cellular function and behavior. Even though the detailed mechanisms underlying cell-ECM crosstalk are yet to unravel, it is well established that ECM deregulation accompanies the development of many pathological conditions, such as gastric cancer. Notably, gastric cancer remains a worldwide concern, representing the third most frequent cause of cancer-associated deaths. Despite increased surveillance protocols, patients are usually diagnosed at advanced disease stages, urging the identification of novel diagnostic biomarkers and efficient therapeutic strategies. In this review, we provide a comprehensive overview regarding expression patterns of ECM components and cognate receptors described in normal gastric epithelium, pre-malignant lesions, and gastric carcinomas. Important insights are also discussed for the use of ECM-associated molecules as predictive biomarkers of the disease or as potential targets in gastric cancer.

Anti-platelet role of Korean ginseng and ginsenosides in cardiovascular diseases

Cardiovascular diseases prevail among modern societies and underdeveloped countries, and a high mortality rate has also been reported by the World Health Organization affecting millions of people worldwide. Hyperactive platelets are the major culprits in thrombotic disorders. A group of drugs is available to deal with such platelet-related disorders; however, sometimes, side effects and complications caused by these drugs outweigh their benefits. Ginseng and its nutraceuticals have been reported to reduce the impact of thrombotic conditions and improve cardiovascular health by antiplatelet mechanisms. This review provides (1) a comprehensive insight into the available pharmacological options from ginseng and ginsenosides (saponin and nonsaponin fractions) for platelet-originated cardiovascular disorders; (2) a discussion on the impact of specific functional groups on the modulation of platelet functions and how structural modifications among ginsenosides affect platelet activation, which may further provide a basis for drug design, optimization, and the development of ginsenoside scaffolds as pharmacological antiplatelet agents; (3) an insight into the synergistic effects of ginsenosides on platelet functions; and (4) a perspective on future research and the development of ginseng and ginsenosides as super nutraceuticals.

Talin Autoinhibition Regulates Cell-ECM Adhesion Dynamics and Wound Healing In Vivo

Cells in multicellular organisms are arranged in complex three-dimensional patterns. This requires both transient and stable adhesions with the extracellular matrix (ECM). Integrin adhesion receptors bind ECM ligands outside the cell and then, by binding the protein talin inside the cell, assemble an adhesion complex connecting to the cytoskeleton. The activity of talin is controlled by several mechanisms, but these have not been well studied in vivo. By generating mice containing the activating point mutation E1770A in talin (Tln1), which disrupts autoinhibition, we show that talin autoinhibition controls cell-ECM adhesion, cell migration, and wound healing in vivo. In particular, blocking autoinhibition gives rise to more mature, stable focal adhesions that exhibit increased integrin activation. Mutant cells also show stronger attachment to ECM and decreased traction force. Overall, these results demonstrate that modulating talin function via autoinhibition is an important mechanism for regulating multiple aspects of integrin-mediated cell-ECM adhesion in vivo.

Aloe Vera/Collagen Mixture Induces Integrin α1β1 and PECAM-1 Genes Expression in Human Adipose-Derived Stem Cells

Purpose: Natural biomaterials are a key base in tissue engineering, and collagen, as the main content of the extracellular matrix (ECM), is frequently used in tissue engineering. Aloe vera has some therapeutic effects on ulcers, therefore, the use of this natural resource has always been considered for improving collagen function. We aimed to evaluate the effect of Aloe vera/ Collagen blended on cell viability, cell attachment, and angiogenic potential by determining of integrin α1β1 and platelet endothelial cell adhesion molecule (PECAM-1) genes expression in human adipose-derived stem cells (hASCs).

Methods: In this study, hASCs after harvesting of adipose tissues from abdominal subcutaneous adipose tissue and isolation, were cultured in four groups of control, collagen gel, Aloe vera gel, and Aloe vera/collagen blended in vitro environment at 24h and then cell viability was assessed by MTT (3-(4,5-dimethylthiazol 2-yl)-2,5-diphenyltetrazolium) assay. Integrin α1β1 and PECAM-1 genes expression were evaluated by real-time RT-PCR.

Results: The results of MTT showed that the combination of Aloe vera/collagen was retained the cell viability at the normal range and improved it. In real-time RT-PCR results, integrin α1β1 and PECAM-1 gene expression were increased in the Aloe vera/collagen blended group compared to the control group.

Conclusion: For tissue engineering purposes, Aloe vera improves collagen properties in the culture of hASCs by increasing the expression of the integrin α1β1 and PECAM-1 genes.

Dynamins 2 and 3 control the migration of human megakaryocytes by regulating CXCR4 surface expression and ITGB1 activity

Megakaryocyte (MK) migration from the bone marrow periosteal niche toward the vascular niche is a prerequisite for proplatelet extension and release into the circulation. The mechanism for this highly coordinated process is poorly understood. Here we show that dynasore (DNSR), a small-molecule inhibitor of dynamins (DNMs), or short hairpin RNA knockdown of DNM2 and DNM3 impairs directional migration in a human MK cell line or MKs derived from cultured CD34⁺ cells. Because cell migration requires actin cytoskeletal rearrangements, we measured actin polymerization and the activity of cytoskeleton regulator RhoA and found them to be decreased after inhibition of DNM2 and DNM3. Because SDF-1α is important for hematopoiesis, we studied the expression of its receptor CXCR4 in DNSR-treated cells. CXCR4 expression on the cell surface was increased, at least partially because of slower endocytosis and internalization after SDF-1α treatment. Combined inhibition of DNM2 and DNM3 or forced expression of dominant-negative Dnm2-K44A or GTPase-defective DNM3 diminished β1 integrin (ITGB1) activity. DNSR-treated MKs showed an abnormally clustered staining pattern of Rab11, a marker of recycling endosomes. This suggests decreased recruitment of the recycling pathway in DNSR-treated cells. Altogether, we show that the GTPase activity of DNMs, which governs endocytosis and regulates cell receptor trafficking, exerts control on MK migration toward SDF-1α gradients, such as those originating from the vascular niche. DNMs play a critical role in MKs by triggering membrane-cytoskeleton rearrangements downstream of CXCR4 and integrins.

Binding of the protein ICln to α-integrin contributes to the activation of IClswell current

ICl_swell is the chloride current induced by cell swelling, and plays a fundamental role in several biological processes, including the regulatory volume decrease (RVD). ICln is a highly conserved, ubiquitously expressed and multifunctional protein involved in the activation of ICl_swell. In platelets, ICln binds to the intracellular domain of the integrin αIIb chain, however, whether the ICln/integrin interaction plays a role in RVD is not known. Here we show that a direct molecular interaction between ICln and the integrin α-chain is not restricted to platelets and involves highly conserved amino acid motifs. Integrin α recruits ICln to the plasma membrane, thereby facilitating the activation of ICl_swell during hypotonicity. Perturbation of the ICln/integrin interaction prevents the transposition of ICln towards the cell surface and, in parallel, impedes the activation of ICl_swell. We suggest that the ICln/integrin interaction interface may represent a new molecular target enabling specific ICl_swell suppression in pathological conditions when this current is deregulated or plays a detrimental role.

Integrin-Mediated TGFβ Activation Modulates the Tumour Microenvironment

TGFβ (transforming growth factor-beta) is a pleotropic cytokine with contrasting effects in cancer. In normal tissue and early tumours, TGFβ acts as a tumour suppressor, limiting proliferation and inducing apoptosis. However, these effects are eventually abrogated by the loss or inactivation of downstream signalling within the TGFβ pathway, and in established tumours, TGFβ then acts as a tumour promotor through multiple mechanisms including inducing epithelial-to-mesenchymal transition (EMT), promoting formation of cancer-associated fibroblasts (CAFs) and increasing angiogenesis. TGFβ is secrereted as a large latent complex and is embedded in the extracellular matrix or held on the surface of cells and must be activated before mediating its multiple functions. Thus, whilst TGFβ is abundant in the tumour microenvironment (TME), its functionality is regulated by local activation. The αv-integrins are major activators of latent-TGFβ. The potential benefits of manipulating the immune TME have been highlighted by the clinical success of immune-checkpoint inhibitors in a number of solid tumour types. TGFβ is a potent suppressor of T-cell-mediated immune surveillance and a key cause of resistance to checkpoint inhibitors. Therefore, as certain integrins locally activate TGFβ, they are likely to have a role in the immunosuppressive TME, although this remains to be confirmed. In this review, we discussed the role of TGFβ in cancer, the role of integrins in activating TGFβ in the TME, and the potential benefits of targeting integrins to augment immunotherapies.

Sharpin suppresses β1-integrin activation by complexing with the β1 tail and kindlin-1

Background

Previously sharpin has been identified as an endogenous inhibitor of β1-integrin activation by directly binding to a conserved region in the cytoplasmic tails (CTs) of the integrin β1-associated α subunits.

Methods

Here we employed biochemical approaches and cellular analyses to evaluate the function and molecular mechanism of the sharpin-kindlin-1 complex in regulating β1-integrin activation.

Results

In this study, we found that although the inhibition of sharpin on β1-integrin activation could be confirmed, sharpin had no apparent effect on integrin αIIbβ3 activation in CHO cell system. Notably, a direct interaction between sharpin and the integrin β1 CT was detected, while the interaction of sharpin with the integrin αIIb and the β3 CTs were substantially weaker. Importantly, sharpin was able to inhibit the talin head domain binding to the integrin β1 CT, which can mechanistically contribute to inhibiting β1-integrin activation. Interestingly, we also found that sharpin interacted with kindlin-1, and the interaction between sharpin and the integrin β1 CT was significantly enhanced when kindlin-1 was present. Consistently, we observed that instead of acting as an activator, kindlin-1 actually suppressed the talin head domain mediated β1-integrin activation, indicating that kindlin-1 may facilitate recruitment of sharpin to the integrin β1 CT.

Conclusion

Taken together, our findings suggest that sharpin may complex with both kindlin-1 and the integrin β1 CT to restrict the talin head domain binding, thus inhibiting β1-integrin activation.

Distinct Binding Interactions of α5β1-Integrin and Proteoglycans with Fibronectin

Dynamic single-molecule force spectroscopy was performed to monitor the unbinding of fibronectin with the proteoglycans syndecan-4 (SDC4) and decorin and to compare this with the unbinding characteristics of α₅β₁-integrin. A single energy barrier was sufficient to describe the unbinding of both SDC4 and decorin from fibronectin, whereas two barriers were observed for the dissociation of α₅β₁-integrin from fibronectin. The outer (high-affinity) barriers in the interactions of fibronectin with α₅β₁-integrin and SDC4 are characterized by larger barrier heights and widths and slower dissociation rates than those of the inner (low-affinity) barriers in the interactions of fibronectin with α₅β₁-integrin and decorin. These results indicate that SDC4 and (ultimately) α₅β₁-integrin have the ability to withstand deformation in their interactions with fibronectin, whereas the decorin-fibronectin interaction is considerably more brittle.

Proteomics insights into the pathology and prognosis of chronic lymphocytic leukemia

Chronic lymphocytic leukemia (CLL) is an incurable malignant disease of B-lymphocytes characterized by drastically heterogeneous clinical courses. Proteomics is an advanced approach that allows a global profiling of protein expression, providing a valuable chance for the discovery of disease-related proteins. In the last 2 decades, several proteomics studies were conducted on CLL to identify aberrant protein expression underpinning the malignant transformation and progression of the disease. Overall, these studies provided insights into the pathology and prognosis of CLL and reveal protein candidates with the potential to serve as biomarkers and/or therapeutic targets of the tumor. The major findings reported in these studies are discussed here.

Physical Plasma Membrane Perturbation Using Subcellular Optogenetics Drives Integrin-Activated Cell Migration

Cells experience physical deformations to the plasma membrane that can modulate cell behaviors like migration. Understanding the molecular basis for how physical cues affect dynamic cellular responses requires new approaches that can physically perturb the plasma membrane with rapid, reversible, subcellular control. Here we present an optogenetic approach based on light-inducible dimerization that alters plasma membrane properties by recruiting cytosolic proteins at high concentrations to a target site. Surprisingly, this polarized accumulation of proteins in a cell induces directional amoeboid migration in the opposite direction. Consistent with known effects of constraining high concentrations of proteins to a membrane in vitro, there is localized curvature and tension decrease in the plasma membrane. Integrin activity, sensitive to mechanical forces, is activated in this region. Localized mechanical activation of integrin with optogenetics allowed simultaneous imaging of the molecular and cellular response, helping uncover a positive feedback loop comprising SFK- and ERK-dependent RhoA activation, actomyosin contractility, rearward membrane flow, and membrane tension decrease underlying this mode of cell migration.

CD99 Expression in Glioblastoma Molecular Subtypes and Role in Migration and Invasion

Glioblastoma (GBM) is the most aggressive type of brain tumor, with an overall survival of 17 months under the current standard of care therapy. CD99, an over-expressed transmembrane protein in several malignancies, has been considered a potential target for immunotherapy. To further understand this potentiality, we analyzed the differential expression of its two isoforms in human astrocytoma specimens, and the CD99 involved signaling pathways in glioma model U87MG cell line. CD99 was also analyzed in GBM molecular subtypes. Whole transcriptomes by RNA-Seq of CD99-siRNA, and functional in vitro assays in CD99-shRNA, that are found in U87MG cells, were performed. Astrocytoma of different malignant grades and U87MG cells only expressed CD99 isoform 1, which was higher in mesenchymal and classical than in proneural GBM subtypes. Genes related to actin dynamics, predominantly to focal adhesion, and lamellipodia/filopodia formation were down-regulated in the transcriptome analysis, when CD99 was silenced. A decrease in tumor cell migration/invasion, and dysfunction of focal adhesion, were observed in functional assays. In addition, a striking morphological change was detected in CD99-silenced U87MG cells, further corroborating CD99 involvement in actin cytoskeleton rearrangement. Inhibiting the overexpressed CD99 may improve resectability and decrease the recurrence rate of GBM by decreasing tumor cells migration and invasion.

Schizonepeta tenuifolia inhibits collagen stimulated platelet function via suppressing MAPK and Akt signaling

The prevalence of cardiovascular diseases (CVDs) is increasing at a rapid pace in developed countries, and CVDs are the leading cause of morbidity and mortality. Natural products and ethnomedicine have been shown to reduce the risk of CVDs. Schizonepeta (S.) tenuifolia is a medicinal plant widely used in China, Korea, and Japan and is known to exhibit anti-inflammatory, antioxidant, and immunomodulatory activities. We hypothesized that given herbal plant exhibit pharmacological activities against CVDs, we specifically explored its effects on platelet function. Platelet aggregation was evaluated using standard light transmission aggregometry. Intracellular calcium mobilization was assessed using Fura-2/AM, and granule secretion (ATP release) was measured in a luminometer. Fibrinogen binding to integrin αⅡbβ3, was assessed using flow cytometry. Phosphorylation of mitogen-activated protein kinase (MAPK) signaling molecules and activation of the protein kinase B (Akt) was assessed using Western blot assays. S. tenuifolia, extract potently and significantly inhibited platelet aggregation, calcium mobilization, granule secretion, and fibrinogen binding to integrin αⅡbβ3. Moreover, all extracts significantly inhibited MAPK and Akt phosphorylation. S. tenuifolia extract inhibited platelet aggregation and granule secretion, and attenuated collagen mediated GPVI downstream signaling, indicating the potential therapeutic effects of these plant extracts on the cardiovascular system and platelet function. We suggest that S. tenuifolia extract may be a potent candidate to treat platelet-related CVDs and to be used as an antiplatelet and antithrombotic agent.

Pharmacological actions of miltirone in the modulation of platelet function

Salvia miltiorrhiza Bunge contains various active constituents, some of which have been developed as commercially available medicine. Moreover, some other ingredients in Salvia miltiorrhiza play roles in anti-platelet activity. The aim of the present study was to investigate the effects and the underlying mechanism of miltirone, a lipophilic compound of Salvia miltiorrhiza Bunge. The ability of miltirone to modulate platelet function was investigated by a variety of in vitro and in vivo experiments. Platelet aggregation and dense granule secretion induced by various agonists were measured with platelet aggregometer. Clot retraction and spreading were imaged by digital camera and fluorescence microscope. Ferric chloride-induced carotid injury model and pulmonary thromboembolism model were used to check miltirone antithrombotic effect in vivo. To elucidate the mechanisms of anti-platelet activity of miltirone, flow cytometry and western blotting were performed. Miltirone (2, 4, 8 µM) was shown to suppress platelet aggregation, dense granule, and α granule secretion in a dose-dependent manner. Meanwhile, miltirone inhibited the clot retraction and spreading of washed platelets. It reduced the phosphorylation of PLCγ2, PKC, Akt, GSK3β and ERK1/2 in the downstream signal pathway of collagen receptor. It also reduced the phosphorylation of Src and FAK in the integrin αIIbβ3-mediated "outside-in" signaling, while it did not suppress the phosphorylation of β3. In addition, miltirone prolonged the occlusion time and reduced collagen/epinephrine-induced pulmonary thrombi. Miltirone suppresses platelet "inside-out" and "outside-in" signaling by affecting PLCγ₂/PKC/ERK1/2, PI3K/Akt, and Src/FAK signaling. Therefore, miltirone might represent a potential anti-platelet candidate for the prevention of thrombotic disorders.

Regulation and functions of integrin α2 in cell adhesion and disease

Integrins are cell adhesion molecules that are composed of an alpha (α) subunit and a beta (β) subunit with affinity for different extracellular membrane components. The integrin family includes 24 known members that actively regulate cellular growth, differentiation, and apoptosis. Each integrin heterodimer has a particular function in defined contexts as well as some partially overlapping features with other members in the family. As many reviews have covered the general integrin family in molecular and cellular studies in life science, this review will focus on the specific regulation, function, and signaling of integrin α2 subunit (CD49b, VLA-2; encoded by the gene ITGA2) in partnership with β1 (CD29) subunit in normal and cancer cells. Its roles in cell adhesion, cell motility, angiogenesis, stemness, and immune/blood cell regulations are discussed. The pivotal role of integrin α2 in many diseases such as cancer suggests its potential to be used as a novel therapeutic target.

A Calcium Mediated Mechanism Coordinating Vascular Smooth Muscle Cell Adhesion During KCl Activation

Efficient mechanotransduction in vascular smooth muscle cells (VSMCs) is intimately coupled to physical coupling of the cell to extracellular matrix proteins (ECM) by integrins. Integrin adhesion receptors are essential for normal vascular function and defective integrin signaling is associated with cardiovascular disease. However, less is known about the mechanism of integrin activation in VSMCs in relation to vasoregulation. Our laboratory previously demonstrated that the vasoconstrictor Angiotensin II increases VSMC stiffness in concert with enhanced adhesion to fibronectin (FN), indicating an important role for adhesion in contraction. However, the mechanism of this coordination remains to be clarified. In this study, intracellular Ca²⁺ ([Ca²⁺]_i) was hypothesized to link integrin activation through inside-out signaling pathways leading to enhanced adhesion in response to AII. By using atomic force microscopy (AFM) with an anti-α₅ antibody coated AFM probe, we confirmed that cell stiffness was increased by AII, while we observed no change in adhesion to an α₅ integrin antibody. This indicated that increases in cell adhesion to FN induced by AII were occurring through an integrin activation process, as increased membrane integrin expression/receptor density would have been accompanied by increased adhesion to the anti-α₅ antibody. Further studies were performed using either KCl or BAPTA-AM to modulate the level of [Ca²⁺]_i. After KCl, VSMCs showed a rapid transient increase in cell stiffness as well as cell adhesion to FN, and these two events were synchronized with superimposed transient increases in the level of [Ca²⁺]_i, which was measured using the Ca²⁺ indicator, fluo-4. These relationships were unaffected in VSMCs pretreated with the myosin light chain kinase inhibitor, ML-7. In contrast, unstimulated VSMCs incubated with an intracellular calcium chelator, BAPTA-AM, showed reduced cell adhesion to FN as well the expected decrease in [Ca²⁺]_i. These data suggest that in VSMCs, integrin activation is linked to signaling events tied to levels of [Ca²⁺]_i while being less dependent on events at the level of contractile protein activation. These findings provide additional evidence to support a role for adhesion in VSMC contraction and suggest that following cell contractile activation, that adhesion may be regulated in tandem with the contractile event.

Spatio-Temporal Control of Cell Adhesion: Toward Programmable Platforms to Manipulate Cell Functions and Fate

Biophysical and biochemical signals of material surfaces potently regulate cell functions and fate. In particular, micro- and nano-scale patterns of adhesion signals can finely elicit and affect a plethora of signaling pathways ultimately affecting gene expression, in a process known as mechanotransduction. Our fundamental understanding of cell-material signals interaction and reaction is based on static culturing platforms, i.e., substrates exhibiting signals whose configuration is time-invariant. However, cells in-vivo are exposed to arrays of biophysical and biochemical signals that change in time and space and the way cells integrate these might eventually dictate their behavior. Advancements in fabrication technologies and materials engineering, have recently enabled the development of culturing platforms able to display patterns of biochemical and biophysical signals whose features change in time and space in response to external stimuli and according to selected programmes. These dynamic devices proved to be particularly helpful in shedding light on how cells adapt to a dynamic microenvironment or integrate spatio-temporal variations of signals. In this work, we present the most relevant findings in the context of dynamic platforms for controlling cell functions and fate in vitro. We place emphasis on the technological aspects concerning the fabrication of platforms displaying micro- and nano-scale dynamic signals and on the physical-chemical stimuli necessary to actuate the spatio-temporal changes of the signal patterns. In particular, we illustrate strategies to encode material surfaces with dynamic ligands and patterns thereof, topographic relieves and mechanical properties. Additionally, we present the most effective, yet cytocompatible methods to actuate the spatio-temporal changes of the signals. We focus on cell reaction and response to dynamic changes of signal presentation. Finally, potential applications of this new generation of culturing systems for in vitro and in vivo applications, including regenerative medicine and cell conditioning are presented.

Gintonin modulates platelet function and inhibits thrombus formation via impaired glycoprotein VI signaling

Panax ginseng (P. ginseng), one of the most valuable medicinal plants, is known for its healing and immunobooster properties and has been widely used in folk medicine against cardiovascular diseases, including stroke and heart attack. In this study, we explored the anti-platelet activity of gintonin (a recently discovered non-saponin fraction of ginseng) against agonist-induced platelet activation. In vitro effects of gintonin on agonist-induced human and rat platelet aggregation, granule secretion, integrin α_IIbβ₃ activation, and intracellular calcium ion ([Ca²⁺]_i) mobilization were examined. Western blot analysis and immunoprecipitation techniques were used to estimate the expression of mitogen-activated protein kinases (MAPKs) and phosphatidylinositol 3-kinase (PI3K)/protein kinase B (Akt) and interaction of glycoprotein VI (GPVI) signaling pathway molecules such as Src family kinases (SFK), tyrosine kinase Syk, and PLCγ2. In vivo effects were studied using acute pulmonary thromboembolism model in mice. Gintonin remarkably inhibited collagen-induced platelet aggregation and suppressed granule secretion, [Ca²⁺]_i mobilization, and fibrinogen binding to integrin α_IIbβ₃ in a dose-dependent manner and clot retraction. Gintonin attenuated the activation of MAPK molecules and PI3K/Akt pathway. It also inhibited SFK, Syk, and PLCγ2 activation and protected mice from thrombosis. Gintonin inhibited agonist-induced platelet activation and thrombus formation through impairment in GPVI signaling molecules, including activation of SFK, Syk, PLCγ2, MAPK, and PI3K/Akt; suggesting its therapeutic potential against platelet related CVD.

Chemokine CC-motif ligand 2 participates in platelet function and arterial thrombosis by regulating PKCα-P38MAPK-HSP27 pathway

BACKGROUND

Studies indicate that chemokine CC-motif ligand 2 (CCL2) is involved in inflammation and atherosclerosis. However, the roles and mechanisms of CCL2 on platelet function and arterial thrombosis are unknown.

METHODS

The expressions of CCL2 or CCR2 in the plasma, platelets and coronary thrombus of ST-elevated myocardial infarction (STEMI) patients were examined by ELISA, Western blot, immunohistochemistry and immunofluorescence. The roles of CCL2 on platelet aggregation, activation and secretion were examined by light transmission aggregometry, flow cytometry and ELISA.

RESULTS

The expressions of CCL2 or CCR2 in the plasma or platelets of STEMI patients with platelet high response were higher than those with platelet normal response; In vitro, exogenous recombinant human CCL2 markedly increased platelet aggregation, activation and granule secretion, which were abolished by CCL2 neutralizing antibody or CCR2 inhibiter. CCL2 increased the phosphorylation levels of PKCα (Thr638), P38MAPK (Thr180/Tyr182) and HSP27 (S78/S82) in human platelets, which were abrogated by PKCα inhibitor (RO 318220) or P38MAPK inhibitor (SB 203580). RO 318220 or SB 203580 diminished CCL2-induced platelet function. In CCL2^-/- mice, platelet aggregation and secretion were attenuated; the phosphorylation of PKCα, P38MAPK and HSP27 were decreased. In a carotid arterial thrombus mouse model, CCL2^-/- mice displayed a significantly extended carotid artery occlusion time compared with wild type.

CONCLUSIONS

CCL2 played important roles in regulating platelet function and arterial thrombosis through the PKCα-P38MAPK-HSP27 pathway, which might provide theoretical basis for searching new antiplatelet drugs and the treatment for cardiovascular diseases.

Cell matrix adhesions in cancer: The proteins that form the glue

The main purposes of Integrin-mediated cell contacts are to interpret bi-directional signals between the extracellular environment and intracellular proteins, as well as, anchor the cell to a matrix. Many cell adhesion molecules have been discovered with a wide spectrum of responsibilities, including recruiting, activating, elongating, and maintaining. This review will perlustrate some of the key incidences that precede focal adhesion formation. Tyrosine phosphorylation is a key signaling initiation event that leads to the recruitment of multiple proteins to focal adhesion sites. Recruitment and concentration of proteins such as Paxillin and Vinculin to Integrin clutches is necessary for focal adhesion development. The assembled networks are responsible for transmitting signals back and forth from the extracellular matrix (ECM) to Actin and its binding proteins. Cancer cells exhibit highly altered focal adhesion dynamics. This review will highlight some key discoveries in cancer cell adhesion, as well as, identify current gaps in knowledge.

On the contributing role of the transmembrane domain for subunit-specific sensitivity of integrin activation

Integrins are α/β heterodimeric transmembrane adhesion receptors. Evidence exists that their transmembrane domain (TMD) separates upon activation. Subunit-specific differences in activation sensitivity of integrins were reported. However, whether sequence variations in the TMD lead to differential TMD association has remained elusive. Here, we show by molecular dynamics simulations and association free energy calculations on TMDs of integrin αIIbβ3, αvβ3, and α5β1 that αIIbβ3 TMD is most stably associated; this difference is related to interaction differences across the TMDs. The order of TMD association stability is paralleled by the basal activity of these integrins, which suggests that TMD differences can have a decisive effect on integrin conformational free energies. We also identified a specific order of clasp disintegration upon TMD dissociation, which suggests that the closed state of integrins may comprise several microstates. Our results provide unprecedented insights into a possibly contributing role of TMD towards subunit-specific sensitivity of integrin activation.

MiR221 promotes precursor B-cell retention in the bone marrow by amplifying the PI3K-signaling pathway in mice

Hematopoietic stem cells and lineage-uncommitted progenitors are able to home to the bone marrow upon transplantation and reconstitute the host with hematopoietic progeny. Expression of miR221 in B-lineage committed preBI-cells induces their capacity to home to the bone marrow. However, the molecular mechanisms underlying miR221-controlled bone marrow homing and retention remain poorly understood. Here, we demonstrate, that miR221 regulates bone marrow retention of such B-cell precursors by targeting PTEN, thus enhancing PI3K signaling in response to the chemokine CXCL12. MiR221-enhanced PI3K signaling leads to increased expression of the anti-apoptotic protein Bcl2 and VLA4 integrin-mediated adhesion to VCAM1 in response to CXCL12 in vitro. Ablation of elevated PI3K activity abolishes the retention of miR221 expressing preBI-cells in the bone marrow. These results suggest that amplification of PI3K signaling by miR221 could be a general mechanism for bone marrow residence, shared by miR221-expressing hematopoietic cells.

Integrin αM activation and upregulation on esophageal eosinophils and periostin-mediated eosinophil survival in eosinophilic esophagitis

Eosinophilic esophagitis (EoE) is an increasingly recognized allergic disease associated with dysphagia and esophageal fibrosis. We aimed to determine expression patterns of specific eosinophil integrins that promote eosinophilic infiltration of the esophageal epithelium, and to determine how key EoE-related cytokines influence eosinophil activation and survival. Esophageal and peripheral eosinophils were isolated from 20 adult subjects with EoE for immunophenotyping and integrin profiling using multicolor flow cytometry and immunohistochemistry. Expression signatures of eosinophil integrins were further assessed by immunohistochemistry using serial sections of esophageal biopsy specimens. Purified eosinophils were used to assess the effect of EoE-relevant cytokines and recombinant periostin on expression of known eosinophil integrins and eosinophil survival and activation. We found that resting eosinophils express high levels of the β2-pairing integrins αL and αM, and lower levels of α4, α6 and α4β7. The migration of peripheral eosinophils to the esophagus is characterized by the specific induction of αM, and a significant increase in the proportion of αM in high-activity conformation. Periostin, a secreted extracellular matrix protein that is significantly overexpressed in EoE, enhances eosinophil survival, and this effect is mediated by αM interaction. Integrin αM is a specific marker of activated tissue eosinophils in EoE, and promotes eosinophil survival through interactions with periostin. The ability of αMβ2 to mediate eosinophil tissue residency via periostin represents a key mechanism for disease development and a potential therapeutic target in EoE.

Ndr2 Kinase Controls Neurite Outgrowth and Dendritic Branching Through α1 Integrin Expression

The serine/threonine kinase Ndr2 has been shown to control the inside-out activation of the β₁subunit of integrins and the formation of neurites in both primary neurons and neurally differentiated pheochromacytoma (PC12) cells. In this study, we demonstrate that Ndr2 kinase furthermore determines the substrate specificity of neurite extension in PC12 cells via expression of α₁β₁ integrins. We show that stable overexpression of Ndr2 in PC12 cells increases neurite growth and extension on poly-D-lysine substrate, likely involving an increased expression of active β₁ integrin in the growth tips of these cells. By contrast, the Ndr2 overexpressing cells do not show the α₁β₁ integrin-mediated enhancement of neurite growth on collagen IV substrate that can be seen in control cells. Moreover, they entirely fail to increase in response to activation of α₁β₁ integrins via a soluble KTS ligand and show a diminished accumulation of α₁ integrin in neurite tips, although the expression of this subunit is induced during differentiation to comparable levels as in control cells. Finally, we demonstrate that Ndr2 overexpression similarly inhibits the α₁β₁ integrin-dependent dendritic growth of primary hippocampal neurons on laminin 111 substrate. By contrast, lack of Ndr2 impairs the dendritic growth regardless of the substrate. Together, these results suggest that Ndr2 regulates α₁ integrin trafficking in addition to β₁ integrin subunit activation and thereby controls the neurite growth on different extracellular matrix (ECM) substrates.

Eisenia bicyclis (brown alga) modulates platelet function and inhibits thrombus formation via impaired P2Y12 receptor signaling pathway

BACKGROUND AND PURPOSE

Sea weeds have been used since ancient times in Asian countries, especially in Korea, Japan, and China, as both edible sea vegetables and traditional medicinal tonics due to their health benefits. Eisenia bicyclis has been studied for anti-allergic and anti-cancer effects; however, its effects on the cardiovascular system, especially on platelet function, are yet to be explored. Therefore, we examined the effect of E. bicyclis on platelet function.

STUDY DESIGN AND METHODS

E. bicyclis extract (EBE) was prepared and in vitro effects on ADP-induced platelet aggregation, granule secretion, intracellular calcium ion ([Ca2+]i) mobilization, fibrinogen binding to integrin αIIbβ3 and clot retraction were evaluated. Phosphorylation levels of MAPK signaling molecules and P2Y12 receptor downstream signaling pathway components were studied. In vivo effects were studied using an arteriovenous (AV) shunt model.

RESULTS

EBE markedly inhibited in vitro ADP-induced platelet aggregation, granule secretion (ATP release and P-selectin expression), [Ca2+]i mobilization, fibrinogen binding to integrin αIIbβ3, and clot retraction; attenuated MAPK pathway activation; and inhibited phosphorylation of PI3K/Akt, PLCγ2, and Src. The extract significantly inhibited in vivo thrombus weight in an AV shunt model.

CONCLUSION

E. bicyclis inhibits agonist-induced platelet activation and thrombus formation through modulation of the P2Y12 receptor downstream signaling pathway, suggesting its therapeutic potential in ethnomedicinal applications as an anti-platelet and anti-thrombotic compound to prevent cardiovascular diseases.

TGF-β family co-receptor function and signaling

Transforming growth factor-β (TGF-β) family members, which include TGF-βs, activins and bone morphogenetic proteins, are pleiotropic cytokines that elicit cell type-specific effects in a highly context-dependent manner in many different tissues. These secreted protein ligands signal via single-transmembrane Type I and Type II serine/threonine kinase receptors and intracellular SMAD transcription factors. Deregulation in signaling has been implicated in a broad array of diseases, and implicate the need for intricate fine tuning in cellular signaling responses. One important emerging mechanism by which TGF-β family receptor signaling intensity, duration, specificity and diversity are regulated and/or mediated is through cell surface co-receptors. Here, we provide an overview of the co-receptors that have been identified for TGF-β family members. While some appear to be specific to TGF-β family members, others are shared with other pathways and provide possible ways for signal integration. This review focuses on novel functions of TGF-β family co-receptors, which continue to be discovered.

The Changes of Cytoskeletal Proteins Induced by the Fast Effect of Estrogen in Mouse Blastocysts and Its Roles in Implantation

It is necessary for estrogen to activate mouse blastocysts, so that they can attach to endometrial epithelium in implantation and in our previous research, we have proved estrogen can induce a fast increase in intracellular calcium of mouse blastocysts through acting on G protein-coupled receptor 30 (GPR30), which further promotes their implantation. Moreover, there has been evidence that cytoskeletal proteins are involved in integrin-mediated adhesion of many kinds of cells, which also plays an important role in implantation. To prove estrogen induces rapidly the changes of cytoskeletal proteins in mouse blastocysts and its roles in implantation, we first used immunofluorescence staining and laser confocal microscopy to investigate the fast effect of estrogen on the expression and localization of cytoskeletal proteins in mouse blastocysts. Second, we used electroporation associated with RNA interference to knock down one of the important cytoskeletal proteins, talin, in the mouse blastocyst cells to investigate the fast effect of estrogen on the localization of integrins and the binding activity of integrins with their ligand fibronectin (FN). At last, mouse blastocysts with different treatments were cultured with FN or uterine epithelial cell line Ishikawa in vitro, respectively, and transferred into the bilateral uterine horns of recipient mice, to study the role of the fast effect of estrogen on cytoskeletal proteins in blastocysts adhesion and implantation. Our results indicated that estradiol (E2), E2 conjugated with bovine serum album (E2-BSA) and G-1 (a GPR30-specific agonist) could induce cytoskeletal protein talin, vinculin, and actin to cluster in the mouse blastocysts, while G15 (a GPR30-specific antagonist) and BAPTA (a calcium chelator) may block this effect induced by E2-BSA. Furthermore, E2-BSA could induce the clustering and relocalization of integrin β1 and β3 and increase the FN-binding activity of integrins in blastocyst cells, while E2-BSA could not induce these effects in the blastocysts pretreated with talin-small interfering RNA (siRNA). Meanwhile, the adhesion rate and implantation rate of blastocysts pretreated with talin-siRNA were significantly lower than those pretreated with control-siRNA. We provided the first evidence that the fast effect of estrogen might cause the clustering of the cytoskeletal proteins in mouse blastocyst cells and further induce the changes of localization and functional activity of integrins in the blastocyst cells, which play important roles in blastocyst implantation.

Exploring the Role of RGD-Recognizing Integrins in Cancer

Integrins are key regulators of communication between cells and with their microenvironment. Eight members of the integrin superfamily recognize the tripeptide motif Arg-Gly-Asp (RGD) within extracelluar matrix (ECM) proteins. These integrins constitute an important subfamily and play a major role in cancer progression and metastasis via their tumor biological functions. Such transmembrane adhesion and signaling receptors are thus recognized as promising and well accessible targets for novel diagnostic and therapeutic applications for directly attacking cancer cells and their fatal microenvironment. Recently, specific small peptidic and peptidomimetic ligands as well as antibodies binding to distinct integrin subtypes have been developed and synthesized as new drug candidates for cancer treatment. Understanding the distinct functions and interplay of integrin subtypes is a prerequisite for selective intervention in integrin-mediated diseases. Integrin subtype-specific ligands labelled with radioisotopes or fluorescent molecules allows the characterization of the integrin patterns in vivo and later the medical intervention via subtype specific drugs. The coating of nanoparticles, larger proteins, or encapsulating agents by integrin ligands are being explored to guide cytotoxic reagents directly to the cancer cell surface. These ligands are currently under investigation in clinical studies for their efficacy in interference with tumor cell adhesion, migration/invasion, proliferation, signaling, and survival, opening new treatment approaches in personalized medicine.

Low-affinity binding in cis to P2Y2R mediates force-dependent integrin activation during hantavirus infection

Atomic force microscopy is used to establish that low-affinity integrins bind in cis to P2Y₂R. Integrin activation is initiated by a membrane-normal switchblade motion triggered by integrin priming after the virus binds to the integrin PSI domain. Tensile force between the P2Y₂R and unbending integrin stimulates outside-in signaling.

Pathogenic hantaviruses bind to the plexin-semaphorin-integrin (PSI) domain of inactive, β₃ integrins. Previous studies have implicated a cognate cis interaction between the bent conformation β₅/β₃ integrins and an arginine-glycine-aspartic acid (RGD) sequence in the first extracellular loop of P2Y₂R. With single-molecule atomic force microscopy, we show a specific interaction between an atomic force microscopy tip decorated with recombinant α_IIbβ₃ integrins and (RGD)P2Y₂R expressed on cell membranes. Mutation of the RGD sequence to RGE in the P2Y₂R removes this interaction. Binding of inactivated and fluorescently labeled Sin Nombre virus (SNV) to the integrin PSI domain stimulates higher affinity for (RGD)P2Y₂R on cells, as measured by an increase in the unbinding force. In CHO cells, stably expressing α_IIbβ₃ integrins, virus engagement at the integrin PSI domain, recapitulates physiologic activation of the integrin as indicated by staining with the activation-specific mAB PAC1. The data also show that blocking of the Gα₁₃ protein from binding to the cytoplasmic domain of the β₃ integrin prevents outside-in signaling and infection. We propose that the cis interaction with P2Y₂R provides allosteric resistance to the membrane-normal motion associated with the switchblade model of integrin activation, where the development of tensile force yields physiological integrin activation.

Connecting Protein Conformation and Dynamics with Ligand-Receptor Binding Using Three-Color Förster Resonance Energy Transfer Tracking

Specific binding between biomolecules, i.e., molecular recognition, controls virtually all biological processes including the interactions between cells and biointerfaces, both natural and synthetic. Such binding often relies on the conformation of biomacromolecules, which can be highly heterogeneous and sensitive to environmental perturbations, and therefore difficult to characterize and control. An approach is demonstrated here that directly connects the binding kinetics and stability of the protein receptor integrin α_vβ₃ to the conformation of the ligand fibronectin (FN), which are believed to control cellular mechanosensing. Specifically, we investigated the influence of surface-adsorbed FN structure and dynamics on α_vβ₃ binding using high-throughput single-molecule three-color Förster resonance energy transfer (FRET) tracking methods. By controlling FN structure and dynamics through tuning surface chemistry, we found that as the conformational and translational dynamics of FN increased, the rate of binding, particularly to folded FN, and stability of the bound FN-α_vβ₃ complex decreased significantly. These findings highlight the importance of the conformational plasticity and accessibility of the arginine-glycine-aspartic acid (RGD) binding site in FN, which, in turn, mediates cell signaling in physiological and synthetic environments.

c-Myc promotes renal fibrosis by inducing integrin αv-mediated transforming growth factor-β signaling

Fibrogenesis involves the activation of renal fibroblasts upon kidney injury. However, the mechanisms underlying renal fibroblast activation are poorly characterized. c-Myc is a predominant oncogene encoding a pleiotropic transcription factor that participates in the regulation of various genes, including genes vital for regulating the cell cycle, cell proliferation, and apoptosis. Here we tested whether renal fibrosis in unilateral ureteral obstruction and folic acid-induced renal fibrosis mouse models are associated with the overexpression of c-Myc. Transforming growth factor-β (TGF-β) has been identified as a key mediator of renal fibrosis, and it is secreted in an inactive form as a complex with latency-associated peptide and latent TGF-β-binding proteins. Five αv-containing integrins with different β -subunits can activate TGF-β, and consistent with this we found that c-Myc bound directly to the promoter of integrin αv in renal fibroblasts activating its transcription. This, in turn, induced activation of TGF-β signaling. Pharmacological blockade of c-Myc attenuated renal fibrosis in vivo in the ureteral obstruction and folic acid-treated mouse models and inhibited the proliferation and activation of renal fibroblasts in vitro. Thus, c-Myc overexpression stimulated proliferation and activation of renal fibroblasts by inducing integrin αv -mediated TGF-β signaling. Hence, targeting c-Myc may have clinical utility in the treatment of renal fibrosis.

Synergistic effect of peptide inhibitors derived from the extracellular and intracellular domain of αIIb subunit of integrin αIIbβ3 on platelet activation and aggregation

α_IIbβ₃, the major platelet integrin, plays a central role in hemostasis and thrombosis. Upon platelet activation, conformation of α_IIbβ₃ changes and allows fibrinogen binding and, subsequently, platelet aggregation. It was previously shown that a lipid-modified platelet permeable peptide, which corresponds to the intracellular acidic membrane distal sequence ¹⁰⁰⁰LEEDDEEGE¹⁰⁰⁸ of α_IIb (pal-K-LEEDDEEGE or pal-K-1000-1008), inhibits thrombin-induced human platelet aggregation, by inhibiting talin association with the integrin. YMESRADR, a peptide corresponding to the extracellular sequence 313-320 of α_IIb, is also a potent platelet aggregation inhibitor by mimicking the effect of a clasp between the head domains of α_IIb and β₃. The aim of the present study was to investigate the synergistic effect of the intra- and extracellular- peptide inhibitors on platelet aggregation, as well as on the phosphorylation of two signaling proteins, focal adhesion kinase (FAK) and extracellular signal-regulated kinase (ERK). Platelet preincubation with Pal-K-LEEDDEGE followed by YMESRADR showed a synergistic inhibitory activity on platelet aggregation. Platelet incubation with threshold inhibitory concentrations of both peptides provoked almost the total inhibition of aggregation, PAC-1 binding, and fibrinogen binding, but not P-selectin exposure on activated platelets' surface. Like RGDS peptide, this mixture inhibits FAK phosphorylation whose phosphorylation is well known to be consecutive to the aggregation (postoccupancy events). However, in contrast to RGDS peptide that enhances ERK phosphorylation and activation, the mixture of threshold inhibitory concentrations of Pal-K-LEEDDEEGE and YMESRADR inhibits ERK phosphorylation. We suggest that the use of the intracellular in combination with the extracellular peptide inhibitor, acting with a non-RGD-like mechanism, may provide an alternative way to antagonize integrin α_IIbβ₃ activation.

Distinct ErbB2 receptor populations differentially interact with beta1 integrin in breast cancer cell models

ErbB2 is a member of the ErbB family of tyrosine kinase receptors that plays a major role in breast cancer progression. Located at the plasma membrane, ErbB2 forms large clusters in spite of the presence of growth factors. Beta1 integrin, membrane receptor of extracellular matrix proteins, regulates adhesion, migration and invasiveness of breast cancer cells. Physical interaction between beta1 integrin and ErbB2 has been suggested although published data are contradictory. The aim of the present work was to study the interaction between ErbB2 and beta1 integrin in different scenarios of expression and activation. We determined that beta1 integrin and ErbB2 colocalization is dependent on the expression level of both receptors exclusively in adherent cells. In suspension cells, lack of focal adhesions leave integrins free to diffuse on the plasma membrane and interact with ErbB2 even at low expression levels of both receptors. In adherent cells, high expression of beta1 integrin leaves unbound receptors outside focal complexes that diffuse within the plasma membrane and interact with ErbB2 membrane domains. Superresolution imaging showed the existence of two distinct populations of ErbB2: a major population located in large clusters and a minor population outside these structures. Upon ErbB2 overexpression, receptors outside large clusters can freely diffuse at the membrane and interact with integrins. These results reveal how expression levels of beta1 integrin and ErbB2 determine their frequency of colocalization and show that extracellular matrix proteins shape membrane clusters distribution, regulating ErbB2 and beta1 integrin activity in breast cancer cells.

Binding of ZO-1 to α5β1 integrins regulates the mechanical properties of α5β1-fibronectin links

Fundamental processes in cell adhesion, motility, and rigidity adaptation are regulated by integrin-mediated adhesion to the extracellular matrix (ECM). The link between the ECM component fibronectin (fn) and integrin α5β1 forms a complex with ZO-1 in cells at the edge of migrating monolayers, regulating cell migration. However, how this complex affects the α5β1-fn link is unknown. Here we show that the α5β1/ZO-1 complex decreases the resistance to force of α5β1-fn adhesions located at the edge of migrating cell monolayers while also increasing α5β1 recruitment. Consistently with a molecular clutch model of adhesion, this effect of ZO-1 leads to a decrease in the density and intensity of adhesions in cells at the edge of migrating monolayers. Taken together, our results unveil a new mode of integrin regulation through modification of the mechanical properties of integrin-ECM links, which may be harnessed by cells to control adhesion and migration.

Focal adhesion stabilization by enhanced integrin-cRGD binding affinity

In this study we investigate the impact of ligand presentation by various molecular spacers on integrin-based focal adhesion formation. Gold nanoparticles (AuNPs) arranged in hexagonal patterns were biofunctionalized with the same ligand head group, cyclic Arg-Gly-Asp [

Effect of talin1 on apoptosis in hepatoma carcinoma cells via the PI3K/Akt/NF-κB signaling pathway

Talin1 is implicated in many cellular processes, which has been studied in various diseases using molecular biological technology.

Differential response and withdrawal profile of glucocorticoid-treated human trabecular meshwork cells

The goal of the study was to examine secreted protein response and withdrawal profiles from cultured human trabecular meshwork (HTM) cells following short- and long-term glucocorticoid treatment. Primary cultures of five human HTM cell strains isolated from 5 different individual donor eyes were tested. Confluent HTM cells were differentiated in culture media containing 1% FBS for at least one week, and then treated with Dexamethasone (Dex, 100 nM) 3 times/week for 1 or 4 weeks. Cell culture supernatants were collected 3 times per week for 8 weeks. Secretion profiles of myocilin (MYOC), matrix metalloproteinase-2 (MMP2) and fibronectin (FN) were determined by Western blot analysis and MMP2 activity by zymography. Dex treatment reduced MMP2 expression and activity, returning to normal levels shortly after Dex withdrawal in 5 HTM cell strains. All five cell strains significantly upregulated MYOC in response to Dex treatment by an average of 17-fold, but recovery to basal levels after Dex withdrawal took vastly different periods of time depending on cell strain and treatment duration. Dex treatment significantly increased FN secretion in all strains but one, which decreased FN secretion in the presence of Dex. Interestingly, secretion of FN and MYOC negatively correlated during a 4 week recovery period following 4 weeks of Dex treatment. Taken together, the time course and magnitude of response and recovery for three different secreted, extracellular matrix-associated proteins varied greatly between HTM cell strains, which may underlie susceptibility to glucocorticoid-induced ocular hypertension.

Farnesoid X Receptor and Its Ligands Inhibit the Function of Platelets

OBJECTIVE

Although initially seemingly paradoxical because of the lack of nucleus, platelets possess many transcription factors that regulate their function through DNA-independent mechanisms. These include the farnesoid X receptor (FXR), a member of the superfamily of ligand-activated transcription factors, that has been identified as a bile acid receptor. In this study, we show that FXR is present in human platelets and FXR ligands, GW4064 and 6α-ethyl-chenodeoxycholic acid, modulate platelet activation nongenomically.

APPROACH AND RESULTS

FXR ligands inhibited the activation of platelets in response to stimulation of collagen or thrombin receptors, resulting in diminished intracellular calcium mobilization, secretion, fibrinogen binding, and aggregation. Exposure to FXR ligands also reduced integrin α_IIbβ₃ outside-in signaling and thereby reduced the ability of platelets to spread and to stimulate clot retraction. FXR function in platelets was found to be associated with the modulation of cyclic guanosine monophosphate levels in platelets and associated downstream inhibitory signaling. Platelets from FXR-deficient mice were refractory to the actions of FXR agonists on platelet function and cyclic nucleotide signaling, firmly linking the nongenomic actions of these ligands to the FXR.

CONCLUSIONS

This study provides support for the ability of FXR ligands to modulate platelet activation. The atheroprotective effects of GW4064, with its novel antiplatelet effects, indicate FXR as a potential target for the prevention of atherothrombotic disease.

The extracellular matrix niche microenvironment of neural and cancer stem cells in the brain

Numerous studies demonstrated that neural stem cells and cancer stem cells (NSCs/CSCs) share several overlapping characteristics such as self-renewal, multipotency and a comparable molecular repertoire. In addition to the intrinsic cellular properties, NSCs/CSCs favor a similar environment to acquire and maintain their characteristics. In the present review, we highlight the shared properties of NSCs and CSCs in regard to their extracellular microenvironment called the NSC/CSC niche. Moreover, we point out that extracellular matrix (ECM) molecules and their complementary receptors influence the behavior of NSCs/CSCs as well as brain tumor progression. Here, we focus on the expression profile and functional importance of the ECM glycoprotein tenascin-C, the chondroitin sulfate proteoglycan DSD-1-PG/phosphacan but also on other important glycoprotein/proteoglycan constituents. Within this review, we specifically concentrate on glioblastoma multiforme (GBM). GBM is the most common malignant brain tumor in adults and is associated with poor prognosis despite intense and aggressive surgical and therapeutic treatment. Recent studies indicate that GBM onset is driven by a subpopulation of CSCs that display self-renewal and recapitulate tumor heterogeneity. Based on the CSC hypothesis the cancer arises just from a small subpopulation of self-sustaining cancer cells with the exclusive ability to self-renew and maintain the tumor. Besides the fundamental stem cell properties of self-renewal and multipotency, GBM stem cells share further molecular characteristics with NSCs, which we would like to review in this article.