Spatial-temporal reorganization of activated integrins

Characterization and functional analysis of integrin αV in Sebastes schlegelii: Implications for apoptosis, adhesion, and migration in intestinal cells

Integrins, as essential cell adhesion molecules, consist of an α subunit and a β subunit that interact with extracellular matrix proteins and cell surface ligands to mediate cellular adhesion and signaling. The integrin αV subfamily is widely expressed on the cell surface and plays a critical role in regulating cell growth, apoptosis, and various cellular processes. To explore the function of integrin αV in teleosts, we retrieved the integrin αV (SsITGαV) sequences from the Sebastes schlegelii genome and assessed the tissue expression and response to Edwardsiella tarda stimuli of SsITGαV. We evaluated the effects of SsITGαV in the intestinal cell line on apoptosis, migration, and adhesion using flow cytometry, scratch assays, and cell adhesion experiments by overexpressing and RNA interference methods. The results showed that the coding sequence of SsITGαV comprises 1055 amino acids, containing a signal peptide and a transmembrane domain. SsITGαV is expressed in various tissues, with the highest expression observed in the gill. We investigated the expression pattern of SsITGαV in the head kidney post E. tarda stimulation and observed an increase in its expression. Subcellular localization revealed that SsITGαV predominantly resides in the extracellular matrix. SsITGαV facilitated apoptosis, enhanced cell adhesion, and promoted cell migration in the intestinal cell line. According to the qRT-PCR analysis, alterations in the expression levels of apoptosis-related genes caspase-3, caspase-8, and caspase-10, along with inflammatory factors IL-1 β, IL-6, and IL-8, were positively linked to changes in SsITGαV. These findings provide insights into the function of the integrin αV gene in teleosts, establishing a foundation for further investigation into the role of the integrin α subfamily in lower vertebrates.

Introgression of a Danbaekkong high-protein allele across different genetic backgrounds in soybean

Soybean meal is a major component of livestock feed due to its high content and quality of protein. Understanding the genetic control of protein is essential to develop new cultivars with improved meal protein. Previously, a genomic region on chromosome 20 significantly associated with elevated protein content was identified in the cultivar Danbaekkong. The present research aimed to introgress the Danbaekkong high-protein allele into elite lines with different genetic backgrounds by developing and deploying robust DNA markers. A multiparent population consisting of 10 F5-derived populations with a total of 1,115 recombinant inbred lines (RILs) was developed using "Benning HP" as the donor parent of the Danbaekkong high-protein allele. A new functional marker targeting the 321-bp insertion in the gene Glyma.20g085100 was developed and used to track the Danbaekkong high-protein allele across the different populations and enable assessment of its effect and stability. Across all populations, the high-protein allele consistently increased the content, with an increase of 3.3% in seed protein. A total of 103 RILs were selected from the multiparent population for yield testing in five environments to assess the impact of the high-protein allele on yield and to enable the selection of new breeding lines with high protein and high yield. The results indicated that the high-protein allele impacts yield negatively in general; however, it is possible to select high-yielding lines with high protein content. An analysis of inheritance of the Chr 20 high-protein allele in Danbaekkong indicated that it originated from a Glycine soja line (PI 163453) and is the same as other G. soja lines studied. A survey of the distribution of the allele across 79 G. soja accessions and 35 Glycine max ancestors of North American soybean cultivars showed that the high-protein allele is present in all G. soja lines evaluated but not in any of the 35 North American soybean ancestors. These results demonstrate that G. soja accessions are a valuable source of favorable alleles for improvement of protein composition.

Endothelial cell spreading on lipid bilayers with combined integrin and cadherin binding ligands

Endothelial cells play a central role in the vascular system, where their function is tightly regulated by both cell-extracellular matrix (e.g., via integrins) and cell-cell interactions (e.g., via cadherins). In this study, we incorporated cholesterol-modified integrin and N-cadherin peptide binding ligands in fluid supported lipid bilayers. Human umbilical vein endothelial cell adhesion, spreading and vinculin localization in these cells were dependent on ligand density. One composition led to observe a higher extent of cell spreading, where cells exhibited extensive lamellipodia formation and a qualitatively more distinct N-cadherin localization at the cell periphery, which is indicative of N-cadherin clustering and a mimic of cell-cell contact formation. The results can be used to reconstitute the endothelial-pericyte interface on biomedical devices and materials.

Paxillin: A Hub for Mechano-Transduction from the β3 Integrin-Talin-Kindlin Axis

Focal adhesions are specialized integrin-dependent adhesion complexes, which ensure cell anchoring to the extracellular matrix. Focal adhesions also function as mechano-signaling platforms by perceiving and integrating diverse physical and (bio)chemical cues of their microenvironment, and by transducing them into intracellular signaling for the control of cell behavior. The fundamental biological mechanism of creating intracellular signaling in response to changes in tensional forces appears to be tightly linked to paxillin recruitment and binding to focal adhesions. Interestingly, the tension-dependent nature of the paxillin binding to adhesions, combined with its scaffolding function, suggests a major role of this protein in integrating multiple signals from the microenvironment, and accordingly activating diverse molecular responses. This minireview offers an overview of the molecular bases of the mechano-sensitivity and mechano-signaling capacity of core focal adhesion proteins, and highlights the role of paxillin as a key component of the mechano-transducing machinery based on the interaction of cells to substrates activating the β3 integrin-talin1-kindlin.

Structural and functional analysis of LIM domain-dependent recruitment of paxillin to αvβ3 integrin-positive focal adhesions

The LIM domain-dependent localization of the adapter protein paxillin to β3 integrin-positive focal adhesions (FAs) is not mechanistically understood. Here, by combining molecular biology, photoactivation and FA-isolation experiments, we demonstrate specific contributions of each LIM domain of paxillin and reveal multiple paxillin interactions in adhesion-complexes. Mutation of β3 integrin at a putative paxillin binding site (β3^VE/YA) leads to rapidly inward-sliding FAs, correlating with actin retrograde flow and enhanced paxillin dissociation kinetics. Induced mechanical coupling of paxillin to β3^VE/YA integrin arrests the FA-sliding, thereby disclosing an essential structural function of paxillin for the maturation of β3 integrin/talin clusters. Moreover, bimolecular fluorescence complementation unveils the spatial orientation of the paxillin LIM-array, juxtaposing the positive LIM4 to the plasma membrane and the β3 integrin-tail, while in vitro binding assays point to LIM1 and/or LIM2 interaction with talin-head domain. These data provide structural insights into the molecular organization of β3 integrin-FAs.

Toward redesigning the PEG surface of nanocarriers for tumor targeting: impact of inner functionalities on size, charge, multivalent binding, and biodistribution

Achieving accurate and efficacious tumor targeting with minimal off-target effects is of paramount importance in designing diagnostic and therapeutic agents for cancer. In this respect, nanocarriers have gained enormous popularity because of their attainable multifunctional features, as well as tumor-targeting potential by extravasation. However, once administered into the bloodstream, nanocarriers face various in vivo obstacles that may significantly impair their performance needed for clinical translation. Herein, we demonstrate a strategy to enhance tumor-targeting efficiency by embedding functionalities in the interior region of partially PEGylated nanocarriers (ca. 10 nm in diameter), intended for active or passive targeting. The cooperative impact of these topologically inner functional groups (IFGs) was marked: enhancements of >100-fold in IC50in vitro (e.g., a high-avidity ligand with cationic IFGs) and >2-fold in tumor accumulation at 2 h post-injection in vivo (e.g., a high-avidity ligand with anionic IFGs), both against the fully PEGylated counterpart. Analogous to allosteric modulators, properly employed IFGs may substantially improve the process of effectively directing nanocarriers to tumors, which is otherwise solely dependent on avidity or extravasation.

Guiding hMSC Adhesion and Differentiation on Supported Lipid Bilayers

Mesenchymal stem cells (MSCs) are intensively investigated for regenerative medicine applications due to their ease of isolation and multilineage differentiation capacity. Hence, designing instructive microenvironments to guide MSC behavior is important for the generation of smart interfaces to enhance biomaterial performance in guiding desired tissue formation. Supported lipid bilayers (SLBs) as cell membrane mimetics can be employed as biological interfaces with easily tunable characteristics such as biospecificity, mobility, and density of predesigned ligand molecules. Arg-Gly-Asp (RGD) ligand functionalized SLBs are explored for guiding human MSC (hMSC) adhesion and differentiation by studying the effect of changes in ligand density and mobility. Cellular and molecular analyses show that adhesion occurs through specific interactions with RGD ligands where the extent is positively correlated to changes in ligand density. Furthermore, cell area is significantly regulated by ligand density on ligand-mobile SLBs when compared to ligand-immobile SLBs. Finally, the osteogenic differentiation capacity of hMSCs is positively correlated to ligand density on ligand-mobile SLBs indicating that regulation of cell spreading is linked to cell differentiation capacity. These results demonstrate that hMSC behavior can be directed on SLBs by molecular design and presents SLBs as versatile platforms for future engineering of smart biomaterial coatings.

Supported Lipid Bilayers for the Generation of Dynamic Cell-Material Interfaces

Supported lipid bilayers (SLB) offer unique possibilities for studying cellular membranes and have been used as a synthetic architecture to interact with cells. Here, the state-of-the-art in SLB-based technology is presented. The fabrication, analysis, characteristics and modification of SLBs are described in great detail. Numerous strategies to form SLBs on different substrates, and the means to patteren them, are described. The use of SLBs as model membranes for the study of membrane organization and membrane processes in vitro is highlighted. In addition, the use of SLBs as a substratum for cell analysis is presented, with discrimination between cell-cell and cell-extracellular matrix (ECM) mimicry. The study is concluded with a discussion of the potential for in vivo applications of SLBs.

Supported Lipid Bilayer Technology for the Study of Cellular Interfaces

Glass-supported lipid bilayers presenting freely diffusing proteins have served as a powerful tool for studying cell-cell interfaces, in particular, T cell-antigen presenting cell (APC) interactions, using optical microscopy. Here we expand upon existing protocols and describe the preparation of liposomes by an extrusion method, and describe how this system can be used to study immune synapse formation by Jurkat cells. We also present a method for forming such lipid bilayers on silica beads for the study of signaling responses by population methods, such as western blotting, flow cytometry, and gene-expression analysis. Finally, we describe how to design and prepare transmembrane-anchored protein-laden liposomes, following expression in suspension CHO (CHOs) cells, a mammalian expression system alternative to insect and bacterial cell lines, which do not produce mammalian glycosylation patterns. Such transmembrane-anchored proteins may have many novel applications in cell biology and immunology.

Nanoclustering as a dominant feature of plasma membrane organization

Early studies have revealed that some mammalian plasma membrane proteins exist in small nanoclusters. The advent of super-resolution microscopy has corroborated and extended this picture, and led to the suggestion that many, if not most, membrane proteins are clustered at the plasma membrane at nanoscale lengths. In this Commentary, we present selected examples of glycosylphosphatidyl-anchored proteins, Ras family members and several immune receptors that provide evidence for nanoclustering. We advocate the view that nanoclustering is an important part of the hierarchical organization of proteins in the plasma membrane. According to this emerging picture, nanoclusters can be organized on the mesoscale to form microdomains that are capable of supporting cell adhesion, pathogen binding and immune cell-cell recognition amongst other functions. Yet, a number of outstanding issues concerning nanoclusters remain open, including the details of their molecular composition, biogenesis, size, stability, function and regulation. Notions about these details are put forth and suggestions are made about nanocluster function and why this general feature of protein nanoclustering appears to be so prevalent.

Patterning of supported lipid bilayers and proteins using material selective nitrodopamine-mPEG

We present a generic patterning process by which biomolecules in a passivated background are patterned directly from physiological buffer to microfabricated surfaces without the need for further processing.

Nanoscale integrin ligand patterns determine melanoma cell behavior

Cells use integrin receptors to adhere onto surfaces by binding to ligands such as the arginine-glycine-aspartic acid (RGD) motif. Cancer cells make use of this adhesion process, which has motivated the development of integrin-directed drugs. However, those drugs may exert paradoxical effects on tumor progression, which raises the question of how integrin function is governed in tumor cells on the nanoscale. We have utilized precisely defined and tunable RGD ligand site densities spanning 1 order of magnitude, i.e., 103 to 1145 ligand sites/μm(2), by using RGD-functionalized gold nanoparticle patterns immobilized on glass by block copolymer (micellar) nanolithography. In an αVβ3 integrin-dependent fashion, human melanoma cells spread, formed focal contacts, and reorganized cytoskeletal fibers on a physiologically relevant RGD density of 349 sites/μm(2). Intriguingly, low doses of solute RGD "shifted" the optimal densities of immobilized ligand along with corresponding melanoma cell integrin clusters and cytoskeletal changes toward those typical for "intermediate" ligand presentation. Consequently, melanoma cells were forced into a "permissive" state, optimizing interactions with suboptimal nanostructured biomimetic surfaces, thus providing an explanation for the seemingly paradoxical effects on tumor progression and a potential clue for individualized antitumoral therapies.

Integrin-matrix clusters form podosome-like adhesions in the absence of traction forces

Matrix-activated integrins can form different adhesion structures. We report that nontransformed fibroblasts develop podosome-like adhesions when spread on fluid Arg-Gly-Asp peptide (RGD)-lipid surfaces, whereas they habitually form focal adhesions on rigid RGD glass surfaces. Similar to classic macrophage podosomes, the podosome-like adhesions are protrusive and characterized by doughnut-shaped RGD rings that surround characteristic core components including F-actin, N-WASP, and Arp2/Arp3. Furthermore, there are 18 podosome markers in these adhesions, though they lack matrix metalloproteinases that characterize invadopodia and podosomes of Src-transformed cells. When nontransformed cells develop force on integrin-RGD clusters by pulling RGD lipids to prefabricated rigid barriers (metal lines spaced by 1–2 μm), these podosomes fail to form and instead form focal adhesions. The formation of podosomes on fluid surfaces is mediated by local activation of phosphoinositide 3-kinase (PI3K) and the production of phosphatidylinositol-(3,4,5)-triphosphate (PIP3) in a FAK/PYK2-dependent manner. Enrichment of PIP3 precedes N-WASP activation and the recruitment of RhoA-GAP ARAP3. We propose that adhesion structures can be modulated by traction force development and that production of PIP3 stimulates podosome formation and subsequent RhoA downregulation in the absence of traction force.

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Nontransformed fibroblasts on RGD membranes form podosome-like protrusions

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Nanopatterned RGD membranes enable traction force, suppressing protrusion formation

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Local activation of PI3K transforms prepodosomal-like RGD clusters

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PIP3-bound RhoA GAP ARAP3 is recruited at the protrusion and downregulates RhoA-GTP

Distinct biophysical mechanisms of focal adhesion kinase mechanoactivation by different extracellular matrix proteins

Matrix mechanics controls cell fate by modulating the bonds between integrins and extracellular matrix (ECM) proteins. However, it remains unclear how fibronectin (FN), type 1 collagen, and their receptor integrin subtypes distinctly control force transmission to regulate focal adhesion kinase (FAK) activity, a crucial molecular signal governing cell adhesion/migration. Here we showed, using a genetically encoded FAK biosensor based on fluorescence resonance energy transfer, that FN-mediated FAK activation is dependent on the mechanical tension, which may expose its otherwise hidden FN synergy site to integrin α5. In sharp contrast, the ligation between the constitutively exposed binding motif of type 1 collagen and its receptor integrin α2 was surprisingly tension-independent to induce sufficient FAK activation. Although integrin α subunit determines mechanosensitivity, the ligation between α subunit and the ECM proteins converges at the integrin β1 activation to induce FAK activation. We further discovered that the interaction of the N-terminal protein 4.1/ezrin/redixin/moesin basic patch with phosphatidylinositol 4,5-biphosphate is crucial during cell adhesion to maintain the FAK activation from the inhibitory effect of nearby protein 4.1/ezrin/redixin/moesin acidic sites. Therefore, different ECM proteins either can transmit or can shield from mechanical forces to regulate cellular functions, with the accessibility of ECM binding motifs by their specific integrin α subunits determining the biophysical mechanisms of FAK activation during mechanotransduction.

Enhanced cellular sensitivity from partitioning the integrin receptors into multiple clusters

Integrins are essential receptors for the development and functioning of multicellular organisms because they mediate cell adhesion and migration, and regulate cell proliferation and apoptosis. In response to cues in the extracellular matrix, they are observed to organize into many clusters. The number and size of such clusters are observed to vary according to the concentration of and affinity for the extracellular ligand. The realization of a cluster point pattern is governed by a doubly stochastic process, controlling the number of clusters and the number of points per cluster. We construct entropy measures for the separation of two doubly stochastic processes and demonstrate how the self-organization of integrins in multiple clusters contributes to the accuracy in sensing the extracellular environment.

Tumor microenvironment indoctrination: an emerging hallmark of cancer

Nastiness of cancer does not only reside in the corruption of cancer cells by genetic aberrations that drive their sustained proliferative power--the roots of malignancy--but also in its aptitude to reciprocally sculpt its surrounding environment and cellular stromal ecosystem, in such a way that the corrupted tumor microenvironment becomes a full pro-tumorigenic entity. Such a contribution had been appreciated three decades ago already, with the discovery of tumor angiogenesis and extracellular matrix remodeling. Nevertheless, the recent emergence of the tumor microenvironment as the critical determinant in cancer biology is paralleled by the promising therapeutic potential it carries, opening alternate routes to fight cancer. The study of the tumor microenvironment recruited numerous lead-scientists over the years, with distinct perspectives, and some of them have kindly accepted to contribute to the elaboration of this special issue entitled Tumor microenvironment indoctrination: An emerging hallmark of cancer.