Dynamic interaction between Src and C-terminal Src kinase in integrin alphaIIbbeta3-mediated signaling to the cytoskeleton

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.

Regulation of the prometastatic neuregulin-MMP13 axis by SRC family kinases: therapeutic implications

Metastatic dissemination of tumor cells is responsible for the fatal outcome of breast cancer. Therefore, understanding the mechanisms involved in dissemination is essential for the development of new therapeutic strategies to prevent metastasis. One mechanism involved in metastatic dissemination of breast cancer cells is dependent on control of the production of matrix metalloproteinases by the neuregulins (NRGs). The NRGs are polypeptide factors that act by binding to the ErbB/HER subfamily of receptor tyrosine kinases. NRG‐mediated activation of HER receptors causes an increase in the production of metalloprotease 13 (MMP13, also termed collagenase‐3), which facilitates metastatic dissemination of breast tumors. In this context, we aimed to explore whether the clinically approved tyrosine kinase inhibitor dasatinib was able to neutralize this mechanism of metastatic dissemination. Here, we show that dasatinib restricted NRG‐induced MMP13 upregulation, both in vitro and in vivo, and in vivo metastatic dissemination of breast cancer cells. Chemical proteomics studies showed that the main cellular targets of dasatinib were SRC family kinases (SFKs). Moreover, genetic studies showed that knockdown of SRC or YES strongly inhibited NRG‐induced MMP13 upregulation in vitro. Mechanistically, dasatinib treatment or knockdown of SRC also inhibited ERK1/2 kinases in vitro, which were required for NRG‐induced MMP13 upregulation. These results open the possibility of clinically exploring the antitumoral action of dasatinib in those tumors in which the NRG–MMP13 signaling axis may play a relevant role in the control of tumor cell dissemination.

Expression of typical osteoclast markers by PBMCs after PEG-induced fusion as a model for studying osteoclast differentiation

Bone is a metabolically active organ subjected to continuous remodeling process that involves resorption by osteoclast and subsequent formation by osteoblasts. Osteoclast involvement in this physiological event is regulated by macrophage colony-stimulating factor (M-CSF) and receptor activator of nuclear factor κB ligand (RANKL). Fusion of mono-nuclear pre-osteoclasts is a critical event for osteoclast differentiation and for bone resorption. Here we show that PBMCs can be successfully fused with polyethylenglicol (PEG) in order to generated viable osteoclast-like cells that exhibit tartrate-resistant acid phosphatase (TRAP) and bone resorptive activities. PEG-fused PBMCs expressed additional markers compatible with osteoclastogenic differentiation such as carbonic anhydrase II (CAII), calcitonin receptor (CR), cathepsin K (Cat K), vacuolar ATPase (V-ATPase) subunit C1 (V-ATPase), integrin β3, RANK and cell surface aminopeptidase N/CD13. Actin redistribution in PEG-fused cells was found to be affected by cell cycle synchronization at G0/G1 or G2/M phases. PEG-induced fusion also led to expression of tyrosine kinases c-Src and Syk in their phosphorylated state. Scanning electron microscopy images showed morphological features typical of osteoclast-like cells. The results here shown allow concluding that PEG-induced fusion of PBMCs provides a suitable model system for understanding the mechanisms involved in osteoclastogenesis and for assaying new therapeutic strategies.

Multiphoton microscopy analysis of extracellular collagen I network formation by mesenchymal stem cells

Collagen I is the major fibrous extracellular component of bone responsible for its ultimate tensile strength. In tissue engineering, one of the most important challenges for tissue formation is to get cells interconnected via a strong and functional extracellular matrix (ECM), mimicking as closely as possible the natural ECM geometry. Still missing in tissue engineering are: (a) a versatile, high-resolution and non-invasive approach to evaluate and quantify different aspects of ECM development within engineered biomimetic scaffolds online; and (b) deeper insights into the mechanism whereby cellular matrix production is enhanced in 3D cell-scaffold composites, putatively via enhanced focal adhesion linkage, over the 2D setting. In this study, we developed sensitive morphometric detection methods for collagen I-producing and bone-forming mesenchymal stem cells (MSCs), based on multiphoton second harmonic generation (SHG) microscopy, and used those techniques to compare collagen I production capabilities in 2D- and 3D-arranged cells. We found that stimulating cells with 1% serum in the presence of ascorbic acid is superior to other medium conditions tested, including classical osteogenic medium. In contrast to conventional 2D culture, having MSCs packed closely in a 3D environment presumably stimulates cells to produce strong and complex collagen I networks with defined network structures (visible in SHG images) and improves collagen production. Copyright © 2015 John Wiley & Sons, Ltd.

Pro32Pro33 mutations in the integrin β3 PSI domain result in αIIbβ3 priming and enhanced adhesion: reversal of the hypercoagulability phenotype by the Src inhibitor SKI-606

The plasma-membrane integrin αIIbβ3 (CD41/CD61, GPIIbIIIa) is a major functional receptor in platelets during clotting. A common isoform of integrin β3, Leu33Pro is associated with enhanced platelet function and increased risk for coronary thrombosis and stroke, although these findings remain controversial. To better understand the molecular mechanisms by which this sequence variation modifies platelet function, we produced transgenic knockin mice expressing a Pro32Pro33 integrin β3. Consistent with reports utilizing human platelets, we found significantly reduced bleeding and clotting times, as well as increased in vivo thrombosis, in Pro32Pro33 homozygous mice. These alterations paralleled increases in platelet attachment and spreading onto fibrinogen resulting from enhanced integrin αIIbβ3 function. Activation with protease-activated receptor 4- activating peptide, the main thrombin signaling receptor in mice, showed no significant difference in activation of Pro32Pro33 mice as compared with controls, suggesting that inside-out signaling remains intact. However, under unstimulated conditions, the Pro32Pro33 mutation led to elevated Src phosphorylation, facilitated by increased talin interactions with the β3 cytoplasmic domain, indicating that the αIIbβ3 intracellular domains are primed for activation while the ligand-binding domain remains unchanged. Acute dosing of animals with a Src inhibitor was sufficient to rescue the clotting phenotype in knockin mice to wild-type levels. Together, our data establish that the Pro32Pro33 structural alteration modifies the function of integrin αIIbβ3, priming the integrin for outside-in signaling, ultimately leading to hypercoagulability. Furthermore, our data may support a novel approach to antiplatelet therapy by Src inhibition where hemostasis is maintained while reducing risk for cardiovascular disease.

Grace P, Elseberg C, Weber C, Czermak P. Enzymatic detachment of therapeutic mesenchymal stromal cells grown on glass carriers in a bioreactor

Cell therapies require the in vitro expansion of adherent cells such as mesenchymal stromal cells (hMSCs) in bioreactor systems or other culture environments, followed by cell harvest. As hMSCs are strictly adherent cells, cell harvest requires cell detachment. The use of hMSCs for cell therapy requires GMP production in accordance with the guidelines for advanced therapeutic medical products. Therefore, several GMP-conform available proteolytic enzymes were investigated for their ability to promote hMSC detachment. An allogeneic hMSC cell line (hMSC-TERT) that is used in clinical trials in the form of alginate cell capsules was chosen as a model. This study investigated the influence of several factors on the outcome of proteolytic hMSC-TERT detachment. Therefore, hMSC-TERT detachment was analyzed in different cultivation systems (static, dynamic) and in combination with further cell processing including encapsulation. Only two of the commercially available enzymes (AccutaseTM, TrypZeanTM) that fulfill all process requirements (commercial availability, cost, GMP conditions during manufacturing and non-animal origin) are found to be generally suitable for detaching hMSC-TERT. Combining cell detachment with encapsulation demonstrated a high impact of the experimental set up on cell damage. It was preferable to reduce the temperature during detachment and limit the detachment time to a maximum of 20 minutes. Cell detachment in static systems was not comparable with detachment in dynamic systems. Detachment yields in dynamic systems were lower and cell damage was higher for the same experimental conditions. Finally, only TrypZeanTM seemed to be suitable for the detachment of hMSC-TERT from dynamic reactor systems.

Expression and distribution of Src in the nucleus of myocytes in cardiac hypertrophy

The Src kinase is involved in signaling events leading to cardiac hypertrophy. The exact effects of tyrosine phosphorylation and subnuclear distribution on cardiac hypertrophy and failure remain to be investigated. In this study, we examined the intranuclear expression and distribution of c-Src, Src phosphorylated at tyrosine 529 (Src[pY529]), Src phosphorylated at tyrosine 418 (Src[pY418]) and Src phosphorylated at tyrosine 215 (Src[pY215]) in the myocardial nuclei of the left ventricle (LV) from 2-, 6-, 12- and 18-month-old spontaneously hypertensive heart failure (SHHF) rats and age-matched Wistar-Kyoto (WKY) rats as normotensive controls by western blot analysis, immunofluorescent labeling and immunoprecipitation. Cellular Src (c-Src) expression in the myocardial nuclei of the LV of the 2-, 6-, 12- and 18-month-old SHHF rats was not significantly different from that in the myocardial nuclei of the LV of the age-matched WKY rats. Although there were no significant differences observed between the levels of Src[pY529] and Src[pY418] in the myocardial nuclei of the LV of the 2-month-old SHHF and WKY rats, the expression of Src[pY529] significantly decreased, while that of Src[pY418] significantly increased in the myocardial nuclei of the LV of the 6-, 12- and 18-month-old SHHF rats compared to the age-matched WKY controls. Furthermore, as demonstrated by double labeling with antibodies against fibrillarin and Src-associated in mitosis 68 kDa (Sam68), c-Src was co-localized with both Sam68 and fibrillarin in the nuclei; Src[pY529] co-localized with fibrillarin, but Src[pY418] co-localized with Sam68. The results from the present study suggest that the dephosphorylation of Src tyrosine kinase 529, the phosphorylation of tyrosine 418 and their subnuclear redistribution are involved in endonuclear signal transduction in cardiac myocytes, which regulates the development and progression of LV eccentric hypertrophy induced by hypertension.

N-cadherin expression level modulates integrin-mediated polarity and strongly impacts on the speed and directionality of glial cell migration

Perturbation of cell polarity is a hallmark of cancer cells. In carcinomas, loss of epithelial E-cadherin contributes to the loss of cell polarity and promotes epithelial-mesenchymal transition and carcinoma infiltration. However, the contribution of classical cadherins to the development of non-epithelial tumours is less well documented. We investigated the impact of the level of N-cadherin expression on the polarity and migration of normal and tumour glial cells. Low levels of N-cadherin were frequently observed in human glioma samples and purified glioma cells. Using a wound-healing assay, we show that a decreased level of N-cadherin promotes a faster and less-directed migration both in normal and tumour cells. N-cadherin-mediated contacts control cell velocity and polarity through the regulation of focal adhesions. In cells expressing low levels of N-cadherin, small focal adhesions are present at the entire cell periphery of confluent cells and are not affected by wounding of the cell monolayer. Under these conditions, wound-induced integrin-mediated recruitment of the small GTPase Cdc42, activation of the Cdc42-mediated polarity pathway and centrosome reorientation do not occur. Re-expression of N-cadherin in gliomas restores cell polarity and strongly reduces cell velocity, suggesting that loss of N-cadherin could contribute to the invasive capacity of tumour astrocytes.

Overview: imaging in the study of integrins

Integrins play critical adhesion and signaling roles during development, wound healing, immunity, and cancer. Central to their function is a unique ability to dynamically modulate their adhesiveness and signaling properties through changes in conformation, both homo- and heterotypic protein-protein interactions and cellular distribution. Genetic, biochemical and structural studies have been instrumental in uncovering overall functions, describing ligand and regulatory protein interactions and elucidating the molecular architecture of integrins. However, such approaches alone are inadequate to describe how dynamic integrin behaviors are orchestrated in intact cells. To fill this void, a wide array of distinct light microscopy (largely fluorescence-based) imaging approaches have been developed and employed. Various microscopy technologies, including wide-field, optical sectioning (laser-scanning confocal, spinning-disk confocal, and multiphoton), TIRF and range of novel "Super-Resolution" techniques have been used in combination with diverse imaging modalities (such as IRM, FRET, FRAP, CALI, and fluorescence speckle imaging) to address distinct aspects of integrin function and regulation. This chapter provides an overview of these imaging approaches and how they have advanced our understanding of integrins.

An integrin-contactin complex regulates CNS myelination by differential Fyn phosphorylation

The understanding of how adhesion molecules mediate the axon-glial interactions in the CNS that ensure target-dependent survival of oligodendrocytes and initiate myelination remains incomplete. Here, we investigate how signals from adhesion molecules can be integrated to regulate these initial steps of myelination. We first demonstrate that the Ig superfamily molecule contactin is associated in oligodendrocytes with integrins, extracellular matrix receptors that regulate target-dependent survival by amplification of growth factor signaling. This amplification is inhibited by small interfering RNA-mediated knockdown of contactin in oligodendrocytes. In contrast, the presence of L1-Fc, the extracellular portion of a contactin ligand expressed on axons, enhanced survival and additionally promoted myelination in cocultures of neurons and oligodendrocytes. We further demonstrate that the signals from contactin and integrin are integrated by differential phosphorylation of the Src family kinase Fyn. Integrin induced dephosphorylation of the inhibitory Tyr-531, whereas contactin increased phosphorylation of both Tyr-531 and the activating Tyr-420. The combined effect is an enhanced activity of Fyn and also a dynamic regulation of the phosphorylation/dephosphorylation balance of Fyn, as required for normal cell adhesion and spreading. We conclude, therefore, that a novel integrin/contactin complex coordinates signals from extracellular matrix and the axonal surface to regulate both oligodendrocyte survival and myelination by controlling Fyn activity.

Csk-binding protein can regulate Lyn signals controlling cell morphology

The Src family kinase Lyn is involved in differentiation signals emanating from activated erythropoietin (Epo) receptors, it interacts with COOH-terminal Src kinase-binding protein (Cbp), an adaptor protein that recruits negative regulators COOH-terminal Src kinase (Csk) and suppressor of cytokine signaling-1 (SOCS1). Lyn phosphorylates Cbp on several tyrosine residues, including Tyr314, which recruits Csk/SOCS1, as well as Tyr381 and Tyr409 that bind Lyns own SH2 domain. We show that Cbp alters not only the ability of erythroid cells to differentiate but also their colony morphology. Consequently, we detailed the ability of Cbp to interact with and influence Lyns ability to initiate changes in cellular architecture, which affect cell-cell and cell-substratum interactions. Over-expression of active Lyn promotes filopodia formation while inactive Lyn promotes lamellipodia formation. Conversely, Cbp over-expression, which inhibits Lyn activity, promotes lamellipodia formation, while Cbp mutants preventing its interaction/signaling consequently allow Lyn to promote filopodia formation. Thus, the Lyn-Cbp pathway and subsequent regulation of Lyn signaling and cell morphology involves a dynamic and complex series of interactions.