Novel α2β1 integrin inhibitors reveal that integrin binding to collagen under shear stress conditions does not require receptor preactivation

Laminin-derived peptide, IKVAV, modulates macrophage phenotype through integrin mediation

Macrophages are highly plastic immune cells known to exist on a spectrum of phenotypes including pro-inflammatory (M1) or pro-healing (M2). Macrophages interact with extracellular matrix (ECM) ligands, such as fragments of collagen and laminin. Interaction of macrophages with ECM ligands is mediated through integrin receptors. However, the role of ECM ligands in directing macrophage function through integrins is not yet fully understood. Particularly, α2β1 has been implicated in modulating macrophage function, but complexity in mechanisms employed for integrin-ligation especially with laminin-derived peptides makes it challenging to understand macrophage-ECM interactions. We hypothesize that targeting α2β1 through laminin-derived peptide, IKVAV, will modulate macrophage phenotype. In this work we: i) investigated macrophage response to IKVAV in 2D and in a 3D platform, and ii) identified α2β1's role as it pertains to macrophage modulation via IKVAV. Soluble IKVAV treatment significantly reduced M1 markers and increased M2 markers via immunocytochemistry and gene expression. While the 3D ECM-mimicking PEG-IKVAV hydrogels did not have significant effects in modulating macrophage phenotype, we found that macrophage modulation via IKVAV is dependent on the concentration of peptide used and duration of exposure. To investigate integrin-ligand interactions for macrophages, α2β1 signaling was modulated by antagonists and agonists. We observed that blocking α2β1 reduces M1 activation. To understand integrin-ligand interactions and leveraging the therapeutic ability of macrophages in designing immunomodulatory solutions, it is critical to elucidate IKVAV's role in mediating macrophage phenotype.

Gut microbial co-metabolite 2-methylbutyrylcarnitine exacerbates thrombosis via binding to and activating integrin α2β1

Thrombosis represents the leading cause of death and disability upon major adverse cardiovascular events (MACEs). Numerous pathological conditions such as COVID-19 and metabolic disorders can lead to a heightened thrombotic risk; however, the underlying mechanisms remain poorly understood. Our study illustrates that 2-methylbutyrylcarnitine (2MBC), a branched-chain acylcarnitine, is accumulated in patients with COVID-19 and in patients with MACEs. 2MBC enhances platelet hyperreactivity and thrombus formation in mice. Mechanistically, 2MBC binds to integrin α2β1 in platelets, potentiating cytosolic phospholipase A2 (cPLA2) activation and platelet hyperresponsiveness. Genetic depletion or pharmacological inhibition of integrin α2β1 largely reverses the pro-thrombotic effects of 2MBC. Notably, 2MBC can be generated in a gut-microbiota-dependent manner, whereas the accumulation of plasma 2MBC and its thrombosis-aggravating effect are largely ameliorated following antibiotic-induced microbial depletion. Our study implicates 2MBC as a metabolite that links gut microbiota dysbiosis to elevated thrombotic risk, providing mechanistic insight and a potential therapeutic strategy for thrombosis.

Integrin β1 is a key determinant of the expression of angiotensin-converting enzyme 2 (ACE2) in the kidney epithelial cells

The expression of the angiotensin-converting enzyme 2 (ACE2) is altered in multiple chronic kidney diseases like hypertension and renal fibrosis, where the signaling from the basal membrane proteins is critical for the development and progression of the various pathologies. Integrins are heterodimeric cell surface receptors that have important roles in the progression of these chronic kidney diseases by altering various cell signaling pathways in response to changes in the basement membrane proteins. It is unclear whether integrin or integrin-mediated signaling affects the ACE2 expression in the kidney. The current study tests the hypothesis that integrin β1 regulates the expression of ACE2 in kidney epithelial cells. The role of integrin β1 in ACE2 expression in renal epithelial cells was investigated by shRNA-mediated knockdown and pharmacological inhibition. In vivo studies were carried out using epithelial cell-specific deletion of integrin β1 in the kidneys. Deletion of integrin β1 from the mouse renal epithelial cells reduced the expression of ACE2 in the kidney. Furthermore, the downregulation of integrin β1 using shRNA decreased ACE2 expression in human renal epithelial cells. ACE2 expression levels were also decreased in renal epithelial cells and cancer cells when treated with an integrin α2β1 antagonist, BTT 3033. SARS-CoV-2 viral entry to human renal epithelial cells and cancer cells was also inhibited by BTT 3033. This study demonstrates that integrin β1 positively regulates the expression of ACE2, which is required for the entry of SARS-CoV-2 into kidney cells.

VGLL3 is a mechanosensitive protein that promotes cardiac fibrosis through liquid-liquid phase separation

Myofibroblasts cause tissue fibrosis by producing extracellular matrix proteins, such as collagens. Humoral factors like TGF-β, and matrix stiffness are important for collagen production by myofibroblasts. However, the molecular mechanisms regulating their ability to produce collagen remain poorly characterised. Here, we show that vestigial-like family member 3 (VGLL3) is specifically expressed in myofibroblasts from mouse and human fibrotic hearts and promotes collagen production. Further, substrate stiffness triggers VGLL3 translocation into the nucleus through the integrin β1-Rho-actin pathway. In the nucleus, VGLL3 undergoes liquid-liquid phase separation via its low-complexity domain and is incorporated into non-paraspeckle NONO condensates containing EWS RNA-binding protein 1 (EWSR1). VGLL3 binds EWSR1 and suppresses miR-29b, which targets collagen mRNA. Consistently, cardiac fibrosis after myocardial infarction is significantly attenuated in Vgll3-deficient mice, with increased miR-29b expression. Overall, our results reveal an unrecognised VGLL3-mediated pathway that controls myofibroblasts' collagen production, representing a novel therapeutic target for tissue fibrosis.

Mechanism of platelet activation and potential therapeutic effects of natural drugs

BACKGROUND

Cardiovascular disease is one of the most concerning chronic diseases in the world. Many studies have shown that platelet overactivation is a very important factor in the occurrence and development of cardiovascular diseases. At present, the widely used antiplatelet drugs have some defects, such as drug resistance and adverse reactions.

PURPOSE

The purpose of this article is to summarize the main mechanisms and pathways of platelet activation, the main targets of antiplatelet aggregation, and the antiplatelet aggregation components of natural drugs and their mechanisms of action to provide new research ideas for the development and application of antiplatelet drugs.

STUDY DESIGN AND METHODS

In this review, we systematically searched the PubMed, Google Scholar, Web of Science, and CNKI databases and selected studies based on predefined eligibility criteria. We then assessed their quality and extracted data.

RESULTS

ADP, AA, THR, AF, collagen, SDF-1α, and Ca²⁺ can induce platelet aggregation and trigger thrombosis. Natural drugs have a good inhibitory effect on platelet activation. More than 50 kinds of natural drugs and over 120 kinds of chemical compounds, including flavonoids, alkaloids, saponins, terpenoids, coumarins, and organic acids, have significantly inhibited platelet activation activity. The MAPK pathway, cGMP-PKG pathway, cAMP-PKA pathway, PI3K-AKT pathway, PTK pathway, PLC pathway, and AA pathway are the main mechanisms and pathways of platelet activation.

CONCLUSION

Natural drugs and their active ingredients have shown good activity and application prospects in anti-platelet aggregation. We hope that this review provides new research ideas for the development and application of antiplatelet drugs.

Perspectives on pediatric congenital aortic valve stenosis: Extracellular matrix proteins, post translational modifications, and proteomic strategies

In heart valve biology, organization of the extracellular matrix structure is directly correlated to valve function. This is especially true in cases of pediatric congenital aortic valve stenosis (pCAVS), in which extracellular matrix (ECM) dysregulation is a hallmark of the disease, eventually leading to left ventricular hypertrophy and heart failure. Therapeutic strategies are limited, especially in pediatric cases in which mechanical and tissue engineered valve replacements may not be a suitable option. By identifying mechanisms of translational and post-translational dysregulation of ECM in CAVS, potential drug targets can be identified, and better bioengineered solutions can be developed. In this review, we summarize current knowledge regarding ECM proteins and their post translational modifications (PTMs) during aortic valve development and disease and contributing factors to ECM dysregulation in CAVS. Additionally, we aim to draw parallels between other fibrotic disease and contributions to ECM post-translational modifications. Finally, we explore the current treatment options in pediatrics and identify how the field of proteomics has advanced in recent years, highlighting novel characterization methods of ECM and PTMs that may be used to identify potential therapeutic strategies relevant to pCAVS.

Anti-GPVI Fab reveals distinct roles for GPVI signaling in the first platelet layer and subsequent layers during microfluidic clotting on collagen with or without tissue factor

The collagen receptor glycoprotein VI (GPVI) drives strong platelet activation, however its role at later stages of clotting remains less clear. Controlled timing of addition of anti-human GPVI Fab (clone E12) with microfluidic venous whole blood flow over collagen (± lipidated tissue factor, TF) produced distinct effects on platelets, fibrin, P-selectin exposure, and phosphatidylserine (PS) exposure. On collagen alone, Fab present initially potently reduced platelet deposition on collagen, while Fab added 90 s after initial platelet deposition, stopped subsequent platelet accumulation (despite the absence of fibrin). With thrombin generation via TF, Fab added at either t = 0 or 90 s had no effect on platelet deposition. However, Fab added initially, but not at 90-s, blocked fibrin formation. Gly-Pro-Arg-Pro ablated fibrin formation without effect on platelet accumulation (regardless of Fab added at t = 0 or 90 s), indicating thrombin signaling can suffice over GPVI signaling. Still, Fab moderately reduced P-selectin exposure with thrombin present and fibrin absent. On collagen/TF, Fab present initially ablated PS exposure, but had no effect when added 30 to 90-s later. The thrombin generated via PS exposure had an important role in driving platelet deposition in the presence of Fab, since inhibition of PS via annexin V binding in the presence of Fab significantly inhibited platelet deposition. We conclude GPVI signaling in the first platelet layer on collagen dictates thrombin and fibrin production, but the role of GPVI at subsequent times after formation of the first monolayer is obscured by thrombin-induced signaling.

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

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

Phosphoproteomics identifies potential downstream targets of the integrin α2β1 inhibitor BTT-3033 in prostate stromal cells

Background

Integrin α2β1 inhibitor BTT-3033 (1-(4-fluorophenyl)-N-methyl-N-[4[[(phenylamino)carbonyl]amino]phenyl]-1H-pyrazole-4-sulfonamide) was recently reported to inhibit neurogenic and thromboxane A2-induced human prostate smooth muscle contraction, and thus represents a target with a different inhibition spectrum than that of α1-blockers in benign prostate hyperplasia (BPH) treatments. Clarifying the underlying mechanisms of the inhibition effects will provide insights into the role of integrin α2β1 in prostate contraction and enable new intracellular targets for smooth muscle contraction to be explored.

Methods

ProteomeHD was used to predict and enrich the top co-regulated proteins of integrin α2 (ITGA2). A phosphoproteomic analysis was conducted on human prostate stromal cells (WPMY-1) treated with 1 or 10 µM of BTT-3033 or solvent for controls. A clustering analysis was conducted to identify the intracellular targets that were inhibited in a dose-dependent manner. Gene ontology (GO) and annotation enrichments were conducted to examine any functional alterations and identify possible downstream targets. A Kinase-substrate enrichment analysis (KSEA) was conducted to identify kinases-substrate relationships.

Results

Enrichments of the actin cytoskeleton and guanosine triphosphatases (GTPases) signaling were predicted from the co-regulated proteins with ITGA2. LIM domain kinases, including LIM domain and actin-binding 1 (LIMA1), zyxin (ZYX), and thyroid receptor-interacting protein 6 (TRIP6), which are functionally associated with focal adhesions and the cytoskeleton, were present in the clusters with dose-dependent phosphorylation inhibition pattern. 15 substrates were dose-dependently inhibited according to the KSEA, including polo-like kinase 1 (PLK1), and GTPases signaling proteins, such as disheveled segment polarity protein 2 (DVL2).

Conclusions

In this study, we proposed that the mechanisms underlying the contractile and proliferative effects of integrin α2β1 are the LIM domain kinases, including the ZYX family, and substrates, including PLK1 and DVL2.

Integrin activation is an essential component of SARS-CoV-2 infection

SARS-CoV-2 infection depends on binding its spike (S) protein to angiotensin-converting enzyme 2 (ACE2). The S protein expresses an RGD motif, suggesting that integrins may be co-receptors. Here, we UV-inactivated SARS-CoV-2 and fluorescently labeled the envelope membrane with octadecyl rhodamine B (R18) to explore the role of integrin activation in mediating cell entry and productive infection. We used flow cytometry and confocal microscopy to show that SARS-CoV-2R18 particles engage basal-state integrins. Furthermore, we demonstrate that Mn2+, which induces integrin extension, enhances cell entry of SARS-CoV-2R18. We also show that one class of integrin antagonist, which binds to the αI MIDAS site and stabilizes the inactive, closed conformation, selectively inhibits the engagement of SARS-CoV-2R18 with basal state integrins, but is ineffective against Mn2+-activated integrins. RGD-integrin antagonists inhibited SARS-CoV-2R18 binding regardless of integrin activation status. Integrins transmit signals bidirectionally: 'inside-out' signaling primes the ligand-binding function of integrins via a talin-dependent mechanism, and 'outside-in' signaling occurs downstream of integrin binding to macromolecular ligands. Outside-in signaling is mediated by Gα13. Using cell-permeable peptide inhibitors of talin and Gα13 binding to the cytoplasmic tail of an integrin's β subunit, we demonstrate that talin-mediated signaling is essential for productive infection.

Integrin activation is an essential component of SARS-CoV-2 infection

Cellular entry of coronaviruses depends on binding of the viral spike (S) protein to a specific cellular receptor, the angiotensin-converting enzyme 2 (ACE2). Furthermore, the viral spike protein expresses an RGD motif, suggesting that cell surface integrins may be attachment co-receptors. However, using infectious SARS-CoV-2 requires a biosafety level 3 laboratory (BSL-3), which limits the techniques that can be used to study the mechanism of cell entry. Here, we UV-inactivated SARS-CoV-2 and fluorescently labeled the envelope membrane with octadecyl rhodamine B (R18) to explore the role of integrin activation in mediating both cell entry and productive infection. We used flow cytometry and confocal fluorescence microscopy to show that fluorescently labeled SARS-CoV-2 ^R18 particles engage basal-state integrins. Furthermore, we demonstrate that Mn ²⁺ , which activates integrins and induces integrin extension, enhances cell binding and entry of SARS-CoV-2 ^R18 in proportion to the fraction of integrins activated. We also show that one class of integrin antagonist, which binds to the αI MIDAS site and stabilizes the inactive, closed conformation, selectively inhibits the engagement of SARS-CoV-2 ^R18 with basal state integrins, but is ineffective against Mn ²⁺ -activated integrins. At the same time, RGD-integrin antagonists inhibited SARS-CoV-2 ^R18 binding regardless of integrin activity state. Integrins transmit signals bidirectionally: 'inside-out' signaling primes the ligand binding function of integrins via a talin dependent mechanism and 'outside-in' signaling occurs downstream of integrin binding to macromolecular ligands. Outside-in signaling is mediated by Gα ₁₃ and induces cell spreading, retraction, migration, and proliferation. Using cell-permeable peptide inhibitors of talin, and Gα ₁₃ binding to the cytoplasmic tail of an integrin's β subunit, we further demonstrate that talin-mediated signaling is essential for productive infection by SARS-CoV-2.

α2β1 integrins spatially restrict Cdc42 activity to stabilise adherens junctions

Background

Keratinocytes form the main protective barrier in the skin to separate the underlying tissue from the external environment. In order to maintain this barrier, keratinocytes form robust junctions between neighbouring cells as well as with the underlying extracellular matrix. Cell–cell adhesions are mediated primarily through cadherin receptors, whereas the integrin family of transmembrane receptors is predominantly associated with assembly of matrix adhesions. Integrins have been shown to also localise to cell–cell adhesions, but their role at these sites remains unclear.

Results

Here we show that α2β1 integrins are enriched at mature keratinocyte cell–cell adhesions, where they play a crucial role in organising cytoskeletal networks to stabilize adherens junctions. Loss of α2β1 integrin has significant functional phenotypes associated with cell–cell adhesion destabilisation, including increased proliferation, reduced migration and impaired barrier function. Mechanistically, we show that α2β1 integrins suppress activity of Src and Shp2 at cell–cell adhesions leading to enhanced Cdc42–GDI interactions and stabilisation of junctions between neighbouring epithelial cells.

Conclusion

Our data reveals a new role for α2β1 integrins in controlling integrity of epithelial cell–cell adhesions.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12915-021-01054-9.

Understanding collagen interactions and their targeted regulation by novel drugs

Introduction: Among protein and fibers in the extracellular matrix (ECM), collagen is the most copious and widely employed in cosmetic, food, pharmaceutical, and biomedical industries due to its extensive biocompatible and versatile properties. In the last years, the knowledge about functions of collagens increased and expanded dramatically. Once considered only crucial for the ECM scaffolding and mechanotransduction, additional functional roles have now been ascribed to the collagen superfamily which are defined by other recently discovered domains, supramolecular assembly and receptors.Areas covered: Given the importance of each step in the collagen biosynthesis, folding and signaling, medicinal chemists have explored small molecules, peptides, and monoclonal antibodies to modulate enzymes, receptors and interactions with the physiological ligands of collagen. These compounds were also explored toward diseases and pathological conditions. The authors discuss this providing their expert perspectives on the subject area.Expert opinion: Understanding collagen protein properties and its interactome is beneficial for therapeutic drug design. Nevertheless, compounds targeting collagen-based interactome suffered from the presence of different isoforms for each target and the lack of specific 3D crystal structures able to guide properly drug design.

Flow studies on human GPVI-deficient blood under coagulating and noncoagulating conditions

The role of glycoprotein VI (GPVI) in platelets was investigated in 3 families bearing an insertion within the GP6 gene that introduces a premature stop codon prior to the transmembrane domain, leading to expression of a truncated protein in the cytoplasm devoid of the transmembrane region. Western blotting and flow cytometry of GP6hom (homozygous) platelets confirmed loss of the full protein. The level of the Fc receptor γ-chain, which associates with GPVI in the membrane, was partially reduced, but expression of other receptors and signaling proteins was not altered. Spreading of platelets on collagen and von Willebrand factor (which supports partial spreading) was abolished in GP6hom platelets, and spreading on uncoated glass was reduced. Anticoagulated whole blood flowed over immobilized collagen or a mixture of von Willebrand factor, laminin, and rhodocytin (noncollagen surface) generated stable platelet aggregates that express phosphatidylserine (PS). Both responses were blocked on the 2 surfaces in GP6hom individuals, but adhesion was not altered. Thrombin generation was partially reduced in GP6hom blood. The frequency of the GP6het (heterozygous) variant in a representative sample of the Chilean population (1212 donors) is 2.9%, indicating that there are ∼4000 GP6hom individuals in Chile. These results demonstrate that GPVI supports aggregation and PS exposure under flow on collagen and noncollagen surfaces, but not adhesion. The retention of adhesion may contribute to the mild bleeding diathesis of GP6hom patients and account for why so few of the estimated 4000 GP6hom individuals in Chile have been identified.

Collagen I Fibrous Substrates Modulate the Proliferation and Secretome of Estrogen Receptor-Positive Breast Tumor Cells in a Hormone-Restricted Microenvironment

The fibril orientation of type I collagen has been shown to contribute to tumor invasion and metabolic changes. Yet, there is limited information about its impact on tumor cells' behavior in a restrictive growth environment. Restrictive growth environments are generated by the inhibition of a proliferation stimulus during therapy or as an inflammatory response to suppress tumor expansion. In this study, the impact of a type I collagen matrix orientation and fibrous architecture on cell proliferation and response to estrogen receptor (ER) therapy were examined using estrogen-dependent breast tumor cells (MCF-7 and T-47D) cultured in a hormone-restricted environment. The use of hormone-free culture media, as well as pharmacological inhibitors of ER, Tamoxifen, and Fulvestrant, were investigated as hormone restrictive conditions. Examination of cultures at 72 h showed that tumor cell proliferation was significantly stimulated (1.8-fold) in the absence of hormones on collagen fibrous substrates, but not on polycaprolactone fibrous substrates of equivalent orientation. ER inhibitors did not suppress cell proliferation on collagen fibrous substrates. The examination of reporter cells for ER signaling showed a lack of activity, thus confirming a shift toward an ER-independent proliferation mechanism. Examination of two selective inhibitors of α2β1 and α1β1 integrins showed that cell proliferation is suppressed in the presence of the α2β1 integrin inhibitor only, thereby indicating that the observed changes in tumor cell behavior are caused by a combination of integrin signaling and/or an intrinsic structural motif that is uniquely present in the collagen fibrils. Adjacent coculture studies on collagen substrates showed that tumor cells on collagen can stimulate the proliferation of cells on tissue culture plastic through soluble factors. The magnitude of this effect correlated with the increased surface anisotropy of the substrate. This sensing in fibril orientation was further supported by a differential expression pattern of secreted proteins that were identified on random and aligned orientation substrates. Overall, this study shows a new role for electrospun collagen I fibrous substrates by supporting a shift toward an ER-independent tumor cell proliferation mechanism in ER+ breast tumor cells.

Investigation of Cancer Cell Migration and Proliferation on Synthetic Extracellular Matrix Peptide Hydrogels

Chemical and mechanical properties of a tumor microenvironment are essential players in cancer progression, and it is important to precisely control the extracellular conditions while designing cancer in vitro models. The study investigates synthetic hydrogel matrices from multi-arm polyethylene glycol (PEG) functionalized with collagen-like peptide (CLP) CG(PKG)₄(POG)₄(DOG)₄ alone and conjugated with either cell adhesion peptide RGD (mimicking fibronectin) or IKVAV (mimicking laminin). Human glioblastoma HROG36, rat C6 glioma cells, and A375 human melanoma cells were grown on the hydrogels and monitored for migration, proliferation, projected cell area, cell shape index, size and number, distribution of focal contacts in individual cells, and focal adhesion number. PEG-CLP-RGD induced migration of both glioma cell lines and also stimulated proliferation (assessed as metabolic activity) of HROG36 cells. Migration of C6 cells were also stimulated by PEG-CLP-IKVAV. These responses strongly correlated with the changes in adhesion and morphology parameters of individual cells – projected cell area, cell shape index, and focal contact number. Melanoma A375 cell proliferation was increased by PEG-CLP-RGD, and this was accompanied by a decrease in cell shape index. However, neither RGD nor IKVAV conjugated to PEG-CLP stimulated migratory capacity of A375 cells. Taken together, the study presents synthetic scaffolds with extracellular matrix (ECM)-mimicking peptides that allow for the exploration of the effect of ECM signaling to cancer cells.

Inhibition of neurogenic and thromboxane A2 -induced human prostate smooth muscle contraction by the integrin α2β1 inhibitor BTT-3033 and the integrin-linked kinase inhibitor Cpd22

INTRODUCTION

Prostate smooth muscle contraction is critical for etiology and treatment of lower urinary tract symptoms in benign prostatic hyperplasia (BPH). Integrins connect the cytoskeleton to membranes and cells to extracellular matrix, what is essential for force generation in smooth muscle contraction. Integrins are composed of different subunits and may cooperate with integrin-linked kinase (ILK). Here, we examined effects of inhibitors for different integrin heterodimers and ILK on contraction of human prostate tissues.

METHODS

Prostate tissues were obtained from radical prostatectomy. Integrins and ILK were detected by Western blot, real-time polymerase chain reaction (RT-PCR), and double fluorescence staining. Smooth muscle contractions of prostate strips were studied in an organ bath. Contractions were compared after application of solvent (controls), the ILK inhibitor Cpd22 (N-methyl-3-(1-(4-(piperazin-1-yl)phenyl)-5-(4'-(trifluoromethyl)-[1,1'-biphenyl]-4-yl)-1H-pyrazol-3-yl)propanamide), the integrin α2β1 inhibitor BTT-3033 (1-(4-fluorophenyl)-N-methyl-N-[4[[(phenylamino)carbonyl]amino]phenyl]-1H-pyrazole-4-sulfonamide), or the integrin α4β1/α9β1 inhibitor BOP (N-(benzenesulfonyl)- l-prolyl- l-O-(1-pyrrolidinylcarbonyl)tyrosine sodium salt).

RESULTS

Western blot analyses of prostate tissues using antibodies raised against integrins α2b, α4, α9, β1, and ILK revealed bands matching the expected sizes of corresponding antigens. Expression of integrins and ILK was confirmed by RT-PCR. Individual variations of expression levels occurred independently from divergent degree of BPH, reflected by different contents of prostate-specific antigen. Double fluorescence staining of prostate sections using antibodies raised against integrins α2 and β1, or against ILK resulted in immunoreactivity colocalizing with calponin, suggesting localization in prostate smooth muscle cells. Electric field stimulation (EFS) induced frequency-dependent contractions, which were inhibited by Cpd22 (3 µM) and BTT-3033 (1 µM) (inhibition around 37% by Cpd22 and 46% by BTT-3033 at 32 Hz). The thromboxane A₂ analog U46619-induced concentration-dependent contractions, which were inhibited by Cpd22 and BTT-3033 (around 67% by Cpd22 and 39% by BTT-3033 at 30 µM U46619). Endothelin-1 induced concentration-dependent contractions, which were not affected by Cpd22 or BTT-3033. Noradrenaline and the α₁ -adrenergic agonists methoxamine and phenylephrine-induced concentration-dependent contractions, which were not or very slightly inhibited by Cpd22 and BTT-3033. BOP did not change EFS- or agonist-induced contraction.

CONCLUSIONS

Integrin α2β1 and ILK inhibitors inhibit neurogenic and thromboxane A₂ -induced prostate smooth muscle contraction in human BPH. A role for these targets for prostate smooth muscle contraction may appear possible.

Mechanochemistry of von Willebrand factor

Von Willebrand factor (VWF), a blood multimeric protein with a very high molecular weight, plays a crucial role in the primary haemostasis, the physiological process characterized by the adhesion of blood platelets to the injured vessel wall. Hydrodynamic forces are responsible for extensive conformational transitions in the VWF multimers that change their structure from a globular form to a stretched linear conformation. This feature makes this protein particularly prone to be investigated by mechanochemistry, the branch of the biophysical chemistry devoted to investigating the effects of shear forces on protein conformation. This review describes the structural elements of the VWF molecule involved in the biochemical response to shear forces. The stretched VWF conformation favors the interaction with the platelet GpIb and at the same time with ADAMTS-13, the zinc-protease that cleaves VWF in the A2 domain, limiting its prothrombotic capacity. The shear-induced conformational transitions favor also a process of self-aggregation, responsible for the formation of a spider-web like network, particularly efficient in the trapping process of flowing platelets. The investigation of the biophysical effects of shear forces on VWF conformation contributes to unraveling the molecular mechanisms of many types of thrombotic and haemorrhagic syndromes.

Extracellular matrix-cell interactions: Focus on therapeutic applications

Extracellular matrix (ECM) macromolecules together with a multitude of different molecules residing in the extracellular space play a vital role in the regulation of cellular phenotype and behavior. This is achieved via constant reciprocal interactions between the molecules of the ECM and the cells. The ECM-cell interactions are mediated via cell surface receptors either directly or indirectly with co-operative molecules. The ECM is also under perpetual remodeling process influencing cell-signaling pathways on its part. The fragmentation of ECM macromolecules provides even further complexity for the intricate environment of the cells. However, as long as the interactions between the ECM and the cells are in balance, the health of the body is retained. Alternatively, any dysregulation in these interactions can lead to pathological processes and finally to various diseases. Thus, therapeutic applications that are based on retaining normal ECM-cell interactions are highly rationale. Moreover, in the light of the current knowledge, also concurrent multi-targeting of the complex ECM-cell interactions is required for potent pharmacotherapies to be developed in the future.

Cell Adhesion by Integrins

Integrins are heterodimeric cell surface receptors ensuring the mechanical connection between cells and the extracellular matrix. In addition to the anchorage of cells to the extracellular matrix, these receptors have critical functions in intracellular signaling, but are also taking center stage in many physiological and pathological conditions. In this review, we provide some historical, structural, and physiological notes so that the diverse functions of these receptors can be appreciated and put into the context of the emerging field of mechanobiology. We propose that the exciting journey of the exploration of these receptors will continue for at least another new generation of researchers.

Integrins as therapeutic targets in the organ-specific metastasis of human malignant melanoma

Integrins are a large family of adhesion molecules that mediate cell-cell and cell-extracellular matrix interactions. Among the 24 integrin isoforms, many have been found to be associated with tumor angiogenesis, tumor cell migration and proliferation, and metastasis. Integrins, especially αvβ3, αvβ5 and α5β1, participate in mediating tumor angiogenesis by interacting with the vascular endothelial growth factor and angiopoietin-Tie signaling pathways. Melanoma patients have a poor prognosis when the primary tumor has generated distant metastases, and the melanoma metastatic site is an independent predictor of the survival of these patients. Different integrins on the melanoma cell surface preferentially direct circulating melanoma cells to different organs and promote the development of metastases at specific organ sites. For instance, melanoma cells expressing integrin β3 tend to metastasize to the lungs, whereas those expressing integrin β1 preferentially generate lymph node metastases. Moreover, tumor cell-derived exosomes which contain different integrins may prepare a pre-metastatic niche in specific organs and promote organ-specific metastases. Because of the important role that integrins play in tumor angiogenesis and metastasis, they have become promising targets for the treatment of advanced cancer. In this paper, we review the integrin isoforms responsible for angiogenesis and organ-specific metastasis in malignant melanoma and the inhibitors that have been considered for the future treatment of metastatic disease.

Integrin α2β1 in nonactivated conformation can induce focal adhesion kinase signaling

Conformational activation of integrins is generally required for ligand binding and cellular signalling. However, we have previously reported that the nonactivated conformation of α2β1 integrin can also bind to large ligands, such as human echovirus 1. In this study, we show that the interaction between the nonactivated integrin and a ligand resulted in the activation of focal adhesion kinase (FAK) in a protein kinase C dependent manner. A loss-of-function mutation, α2E336A, in the α2-integrin did not prevent the activation of FAK, nor did EDTA-mediated inactivation of the integrin. Full FAK activation was observed, since phosphorylation was not only confirmed in residue Y397, but also in residues Y576/7. Furthermore, initiation of downstream signaling by paxillin phosphorylation in residue Y118 was evident, even though this activation was transient by nature, probably due to the lack of talin involvement in FAK activation and the absence of vinculin in the adhesion complexes formed by the nonactivated integrins. Altogether these results indicate that the nonactivated integrins can induce cellular signaling, but the outcome of the signaling differs from conventional integrin signaling.

Implications of the differing roles of the β1 and β3 transmembrane and cytoplasmic domains for integrin function

Integrins are transmembrane receptors composed of α and β subunits. Although most integrins contain β1, canonical activation mechanisms are based on studies of the platelet integrin, αIIbβ3. Its inactive conformation is characterized by the association of the αIIb transmembrane and cytosolic domain (TM/CT) with a tilted β3 TM/CT that leads to activation when disrupted. We show significant structural differences between β1 and β3 TM/CT in bicelles. Moreover, the 'snorkeling' lysine at the TM/CT interface of β subunits, previously proposed to regulate αIIbβ3 activation by ion pairing with nearby lipids, plays opposite roles in β1 and β3 integrin function and in neither case is responsible for TM tilt. A range of affinities from almost no interaction to the relatively high avidity that characterizes αIIbβ3 is seen between various α subunits and β1 TM/CTs. The αIIbβ3-based canonical model for the roles of the TM/CT in integrin activation and function clearly does not extend to all mammalian integrins.

The integrin-collagen connection--a glue for tissue repair?

The α1β1, α2β1, α10β1 and α11β1 integrins constitute a subset of the integrin family with affinity for GFOGER-like sequences in collagens. Integrins α1β1 and α2β1 were originally identified on a subset of activated T-cells, and have since been found to be expressed on a number of cell types including platelets (α2β1), vascular cells (α1β1, α2β1), epithelial cells (α1β1, α2β1) and fibroblasts (α1β1, α2β1). Integrin α10β1 shows a distribution that is restricted to mesenchymal stem cells and chondrocytes, whereas integrin α11β1 appears restricted to mesenchymal stem cells and subsets of fibroblasts. The bulk of the current literature suggests that collagen-binding integrins only have a limited role in adult connective tissue homeostasis, partly due to a limited availability of cell-binding sites in the mature fibrillar collagen matrices. However, some recent data suggest that, instead, they are more crucial for dynamic connective tissue remodeling events--such as wound healing--where they might act specifically to remodel and restore the tissue architecture. This Commentary discusses the recent development in the field of collagen-binding integrins, their roles in physiological and pathological settings with special emphasis on wound healing, fibrosis and tumor-stroma interactions, and include a discussion of the most recently identified newcomers to this subfamily--integrins α10β1 and α11β1.

Cellular Biomechanics in Drug Screening and Evaluation: Mechanopharmacology

The study of mechanobiology is now widespread. The impact of cell and tissue mechanics on cellular responses is well appreciated. However, knowledge of the impact of cell and tissue mechanics on pharmacological responsiveness, and its application to drug screening and mechanistic investigations, have been very limited in scope. We emphasize the need for a heightened awareness of the important bidirectional influence of drugs and biomechanics in all living systems. We propose that the term 'mechanopharmacology' be applied to approaches that employ in vitro systems, biomechanically appropriate to the relevant (patho)physiology, to identify new drugs and drug targets. This article describes the models and techniques that are being developed to transform drug screening and evaluation, ranging from a 2D environment to the dynamic 3D environment of the target expressed in the disease of interest.

Platelet response to a small molecule inhibitor of α2β1 integrin is associated with ITGA2 C807T dimorphism

High expression of the collagen receptor, α2β1 integrin, on platelets of ITGA2 807T-allele carriers has been identified as a risk factor for thromboembolic conditions, and α2β1 inhibitors are considered to be potential therapeutic agents. In 59 genotyped individuals, we measured α2 expression levels on platelets and analyzed platelet adhesion to collagen under flow conditions. A sulfonamide-type small-molecule inhibitor of α2β1 integrin decreased average platelet adhesion in individuals with the C/T807T genotype but not in those harboring C807C. Thus, genotype can be used to select a human subpopulation that has the highest probability of showing a positive response to α2β1 inhibitors.

TNF-α-stimulated fibroblasts secrete lumican to promote fibrocyte differentiation

In healing wounds and fibrotic lesions, fibroblasts and monocyte-derived fibroblast-like cells called fibrocytes help to form scar tissue. Although fibrocytes promote collagen production by fibroblasts, little is known about signaling from fibroblasts to fibrocytes. In this report, we show that fibroblasts stimulated with the fibrocyte-secreted inflammatory signal tumor necrosis factor-α secrete the small leucine-rich proteoglycan lumican, and that lumican, but not the related proteoglycan decorin, promotes human fibrocyte differentiation. Lumican competes with the serum fibrocyte differentiation inhibitor serum amyloid P, but dominates over the fibroblast-secreted fibrocyte inhibitor Slit2. Lumican acts directly on monocytes, and unlike other factors that affect fibrocyte differentiation, lumican has no detectable effect on macrophage differentiation or polarization. α2β1, αMβ2, and αXβ2 integrins are needed for lumican-induced fibrocyte differentiation. In lung tissue from pulmonary fibrosis patients with relatively normal lung function, lumican is present at low levels throughout the tissue, whereas patients with advanced disease have pronounced lumican expression in the fibrotic lesions. These data may explain why fibrocytes are increased in fibrotic tissues, suggest that the levels of lumican in tissues may have a significant effect on the decision of monocytes to differentiate into fibrocytes, and indicate that modulating lumican signaling may be useful as a therapeutic for fibrosis.

Sulfonamide inhibitors of α2β1 integrin reveal the essential role of collagen receptors in in vivo models of inflammation

Small molecule inhibitors of α2β1 integrin, a major cellular collagen receptor, have been reported to inhibit platelet function, kidney injury, and angiogenesis. Since α2β1 integrin is abundantly expressed on various inflammation-associated cells, we tested whether recently developed α2β1 blocking sulfonamides have anti-inflammatory properties. Integrin α2β1 inhibitors were shown to reduce the signs of inflammation in arachidonic acid-induced ear edema, PAF stimulated air pouch, ovalbumin-induced skin hypersensitivity, adjuvant arthritis, and collagen-induced arthritis. Thus, these sulfonamides are potential drugs for acute and allergic inflammation, hypersensitivity, and arthritis. One sulfonamide with potent anti-inflammatory activity has previously been reported to be selective for activated integrins, but not to inhibit platelet function. Thus, the experiments also revealed fundamental differences in the action of nonactivated and activated α2β1 integrins in inflammation when compared to thrombosis.

Cellular signaling by collagen-binding integrins

The four collagen-binding αI domain integrins form their own subgroup among cell adhesion receptors. The signaling functions of α1β1 and α2β1 integrins have been analyzed in many experimental models, whereas less studies are available about the more recently found α10β1 and α11β1 heterodimers. Interestingly, collagen binding by α1β1 and α2β1 often generates opposite cellular responses. For example α1β1 has often been reported to promote cell proliferation and to suppress collagen synthesis, whereas α2β1 can in many model systems inhibit growth and promote collagen synthesis. There are obviously cell type dependent factors modifying the signaling. Additionally the structure and the organization of collagenous matrix play a critic role. Many recent studies have also stressed the importance of the crosstalk between the integrins and other cell surface receptors.

The therapeutic potential of I-domain integrins

Due to their role in processes central to cancer and autoimmune disease I-domain integrins are an attractive drug target. Both antibodies and small molecule antagonists have been discovered and tested in the clinic. Much of the effort has focused on αLβ2 antagonists. Maybe the most successful was the monoclonal antibody efalizumab, which was approved for the treatment of psoriasis but subsequently withdrawn from the market due to the occurrence of a serious adverse effect (progressive multifocal leukoencephalopathy). Other monoclonal antibodies were tested for the treatment of reperfusion injury, post-myocardial infarction, but failed to progress due to lack of efficacy. New potent small molecule inhibitors of αv integrins are promising reagents for treating fibrotic disease. Small molecule inhibitors targeting collagen-binding integrins have been discovered and future work will focus on identifying molecules selectively targeting each of the collagen receptors and identifying appropriate target diseases for future clinical studies.