The changing integrin expression and a role for integrin β8 in the chondrogenic differentiation of mesenchymal stem cells

Many cartilage tissue engineering approaches aim to differentiate human mesenchymal stem cells (hMSCs) into chondrocytes and develop cartilage in vitro by targeting cell-matrix interactions. We sought to better inform the design of cartilage tissue engineering scaffolds by understanding how integrin expression changes during chondrogenic differentiation. In three models of in vitro chondrogenesis, we studied the temporal change of cartilage phenotype markers and integrin subunits during the differentiation of hMSCs. We found that transcript expression of most subunits was conserved across the chondrogenesis models, but was significantly affected by the time-course of differentiation. In particular, ITGB8 was up-regulated and its importance in chondrogenesis was further established by a knockdown of integrin β8, which resulted in a non-hyaline cartilage phenotype, with no COL2A1 expression detected. In conclusion, we performed a systematic study of the temporal changes of integrin expression during chondrogenic differentiation in multiple chondrogenesis models, and revealed a role for integrin β8 in chondrogenesis. This work enhances our understanding of the changing adhesion requirements of hMSCs during chondrogenic differentiation and underlines the importance of integrins in establishing a cartilage phenotype.

Integrins on eggs: focal adhesion kinase is activated at fertilization, forms a complex with integrins, and is necessary for cortex formation and cell cycle initiation

We investigate the proposal that integrins and focal adhesion kinase (FAK) form a complex that has structural and signaling functions in eggs. FAK protein is present in eggs and is phosphorylated at fertilization. pY(397)FAK localizes to the membrane 30 min after fertilization, which correlates with the expression of βC integrins and egg cortex development. The βC integrin and pY(397)FAK coimmunoprecipitate from egg cortex lysates. PF573 228 and Y11, inhibitors of FAK, interfere with pronuclear fusion and reduce the abundance of pY(397)FAK and cortical actin without affecting microvillar actin. Cyclin E normally accumulates in the nucleus 15 min after fertilization, then returns to background levels. PF573 228- or Y11-treated eggs accumulate cyclin E in the nucleus; however, levels remain high. In addition, PF573 228 interferes with the accumulation of pERK1/2 in the nucleus and in eggs initiating mitosis. Injection of eggs with a fusion protein consisting of the focal adhesion-targeting domain of FAK fused to green fluorescent protein interferes with cortex formation and produces abnormal nuclei. These data indicate that an integrin-FAK adhesion complex forms at the egg surface that functions in formation of actin arrays in the egg cortex and provides signaling inputs for cell cycle initiation.

Blocking of integrins inhibits HIV-1 infection of human cervical mucosa immune cells with free and complement-opsonized virions

The initial interaction between HIV-1 and the host occurs at the mucosa during sexual intercourse. In cervical mucosa, HIV-1 exists both as free and opsonized virions and this might influence initial infection. We used cervical explants to study HIV-1 transmission, the effects of opsonization on infectivity, and how infection can be prevented. Complement opsonization enhanced HIV-1 infection of dendritic cells (DCs) compared with that by free HIV-1, but this increased infection was not observed with CD4(+) T cells. Blockage of the α4-, β7-, and β1-integrins significantly inhibited HIV-1 infection of both DCs and CD4(+) T cells. We found a greater impairment of HIV-1 infection in DCs for complement-opsonized virions compared with that of free virions when αM/β2- and α4-integrins were blocked. Blocking the C-type lectin receptor macrophage mannose receptor (MMR) inhibited infection of emigrating DCs but had no effect on CD4(+) T-cell infection. We show that blocking of integrins decreases the HIV-1 infection of both mucosal DCs and CD4(+) T cells emigrating from the cervical tissues. These findings may provide the basis of novel microbicidal strategies that may help limit or prevent initial infection of the cervical mucosa, thereby reducing or averting systemic HIV-1 infection.

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

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

Gene silencing of porcine MUC13 and ITGB5: candidate genes towards Escherichia coli F4ac adhesion

BACKGROUND

Integrin beta-5 (ITGB5) and mucin 13 (MUC13) genes are highly expressed on the apical surface of intestinal epithelia and are thought to be candidate genes for controlling the expression of the receptor for enterotoxigenic Escherichia coli (ETEC) F4ac. Human MUC13 protein has an expected role in protecting intestinal mucosal surfaces and porcine ITGB5 is a newly identified potential receptor for ETEC F4ac.

METHODOLOGY/PRINCIPAL FINDINGS

To test the hypothesis that ITGB5 and MUC13 both play key roles in protection of the intestinal mucosa against pathogenic bacterium, porcine intestinal epithelial cells (IPEC-J2) were transfected with ITGB5-targeting, MUC13-targeting or negative control small interfering RNA (siRNA), respectively. Firstly, we measured mRNA expression levels of mucin genes (MUC4, MUC20), pro-inflammatory genes (IL8, IL1A, IL6, CXCL2), anti-inflammatory mediator SLPI, and PLAU after RNAi treatments with and without ETEC infection. Secondly, we compared the adhesions of ETEC to the pre- and post-knockdown IPEC-J2 cells of ITGB5 and MUC13, respectively. We found that ITGB5 and MUC13 knockdown both had small but significant effects in attenuating the inflammation induced by ETEC infection, and both increased bacterial adhesion in response to F4ac ETEC exposure.

CONCLUSIONS/SIGNIFICANCE

Our current study first reported that ITGB5 and MUC13 are important adhesion molecules of mucosal epithelial signaling in response to Escherichia coli in pigs. These data suggest that both ITGB5 and MUC13 play key roles in defending the attachment and adhesion of ETEC to porcine jejunal cells and in maintaining epithelial barrier and immunity function.

Desmoglein-2-integrin Beta-8 interaction regulates actin assembly in endothelial cells: deregulation in systemic sclerosis

Background

The inability of endothelial cells of patients affected by the diffuse form of Systemic sclerosis (SSc) to perform angiogenesis is a marker of the disease. We previously demonstrated that desmoglein-2 reduction is a major difference between (SSc)-microvascular endothelial cells (MVECs) and normal (N)-MVECs. Here we investigated the role of desmoglein-2 in human N-MVECs and SSc-MVECs angiogenesis.

Methodology/principal findings

Angiogenesis was studied by Matrigel invasion, capillary morphogenesis in vitro and Matrigel plug assay in vivo. Gene profiling was studied by Affymetrix technology and signal transduction by Western blotting. Colocalization was validated by immunoprecipitation and confocal microscopy. SiRNAs were used to validate the roles of specific molecules. We observed that desmoglein-2 co-localizes with integrin-beta8 in N-MVECs. This complex is required to signal through Rac, FAK, SMAD1/5 and MAP-kinases, promoting an angiogenic program. Inhibition of desmoglein-2 by DSG2-siRNA impaired actin stress fibres formation, capillary morphogenesis in vitro and angiogenesis in vivo. Transcriptome profiling after DSG2 inhibition revealed alterations of several genes involved in actin organization. siRNA inhibition of integrin-beta8 and RAC2 also resulted into capillary morphogenesis impairment in N-MVECs, due to reduced expression of the same actin-assembly genes that were down-regulated by DSG2 silencing. SSc-MVECs showed down-regulation of the same genes in DSG2-siRNA treated N-MVECs, suggesting that impairment of desmoglein-2/integrin-beta8 complex contributes to angiogenesis derangement in SSc. Transfection of DSG2 in SSc-MVEC partially restored their angiogenic properties in vitro.

Conclusions/significance

We have shown that impairment of actin assembly as a result of desmoglein-2/integrin-beta8 complex formation is a major factor contributing to angiogenesis deregulation in Systemic sclerosis.

The HCMV gH/gL/UL128-131 complex triggers the specific cellular activation required for efficient viral internalization into target monocytes

We have established that HCMV acts as a specific ligand engaging and activating cellular integrins on monocytes. As a result, integrin signaling via Src activation leads to the functional activation of paxillin required for efficient viral entry and for the biological changes in monocytes needed for viral dissemination. These biological/molecular changes allow HCMV to use monocytes as "vehicles" for systemic spread and the establishment of lifelong persistence. However, it remains unresolved how HCMV specifically induces this observed monocyte activation. It was previously demonstrated that the HCMV gH/gL/UL128-131 glycoprotein complex facilitates viral entry into biologically relevant cell types. Nevertheless, the mechanism by which the gH/gL/UL128-131 complex promotes this process is unknown. We now show that only HCMV virions possessing the gH/gL/UL128-131 complex are capable of activating integrin/Src/paxillin-signaling in monocytes. In fibroblasts, this signaling is reversed, such that virus lacking the gH/gL/UL128-131 complex is the only virus able to induce the paxillin activation cascade. The presence of the gH/gL/UL128-131 complex also may have an inhibitory effect on integrin-mediated signaling pathway in fibroblasts. Furthermore, we demonstrate that the presence of the gH/gL/UL128-131 complex on the viral envelope, through its activation of the integrin/Src/paxillin pathway, is necessary for efficient HCMV internalization into monocytes and that appropriate actin and dynamin regulation is critical for this entry process. Importantly, productive infection in monocyte-derived macrophages was seen only in cells exposed to HCMV expressing the gH/gL/UL128-131 complex. From our data, the HCMV gH/gL/U128-131 complex emerges as the specific ligand driving the activation of the receptor-mediated signaling required for the regulation of the actin cytoskeleton and, consequently, for efficient and productive internalization of HCMV into monocytes. To our knowledge, our studies demonstrate a possible molecular mechanism for why the gH/gL/UL128-131 complex dictates HCMV tropism and why the complex is lost as clinical isolates are passaged in the laboratory.

β5 integrin up-regulation in brain-derived neurotrophic factor promotes cell motility in human chondrosarcoma

Chondrosarcoma is a primary malignant bone cancer, with a potent capacity to invade locally and cause distant metastasis; it has a poor prognosis and shows a predilection for metastasis to the lungs. Brain derived neurotrophic factor (BDNF) is a small-molecule protein from the neurotrophin family of growth factors that is associated with the disease status and outcomes of cancers. However, the effect of BDNF on migration activity in human chondrosarcoma cells is mostly unknown. Here, we found that human chondrosarcoma tissues showed significant expression of BDNF, which was higher than that in normal cartilage and primary chondrocytes. We also found that BDNF increased the migration and expression of β5 integrin in human chondrosarcoma cells. In addition, knockdown of BDNF expression markedly inhibited migratory activity. BDNF-mediated migration and β5 integrin up-regulation were attenuated by antibody, inhibitor, or siRNA against the TrkB receptor. Pretreatment of chondrosarcoma cells with PI3K, Akt, and NF-κB inhibitors or mutants also abolished BDNF-promoted migration and integrin expression. The PI3K, Akt, and NF-κB signaling pathway was activated after BDNF treatment. Taken together, our results indicate that BDNF enhances the migration of chondrosarcoma by increasing β5 integrin expression through a signal transduction pathway that involves the TrkB receptor, PI3K, Akt, and NF-κB. BDNF thus represents a promising new target for treating chondrosarcoma metastasis.

Characterization of 14-3-3-ζ Interactions with integrin tails

Integrins are a family of heterodimeric (α+β) adhesion receptors that play key roles in many cellular processes. Integrins are unusual in that their functions can be modulated from both outside and inside the cell. Inside-out signaling is mediated by binding adaptor proteins to the flexible cytoplasmic tails of the α- and β-integrin subunits. Talin is one well-known intracellular activator, but various other adaptors bind to integrin tails, including 14-3-3-ζ, a member of the 14-3-3 family of dimeric proteins that have a preference for binding phosphorylated sequence motifs. Phosphorylation of a threonine in the β2 integrin tail has been shown to modulate β2/14-3-3-ζ interactions, and recently, the α4 integrin tail was reported to bind to 14-3-3-ζ and associate with paxillin in a ternary complex that is regulated by serine phosphorylation.

Here, we use a range of biophysical techniques to characterize interactions between 14-3-3-ζ and the cytoplasmic tails of α4, β1, β2 and β3 integrins. The X-ray structure of the 14-3-3-ζ/α4 complex indicates a canonical binding mode for the α4 phospho-peptide, but unexpected features are also observed: residues outside the consensus 14-3-3-ζ binding motif are shown to be essential for an efficient interaction; in contrast, a short β2 phospho-peptide is sufficient for high-affinity binding to 14-3-3-ζ. In addition, we report novel 14-3-3-ζ/integrin tail interactions that are independent of phosphorylation. Of the integrin tails studied, the strongest interaction with 14-3-3-ζ is observed for the β1A variant. In summary, new insights about 14-3-3-ζ/integrin tail interactions that have implications for the role of these molecular associations in cells are described.

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Integrin tails are important for bidirectional signaling across the membrane.

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14-3-3-ζ binding to integrin tails has been studied using biophysical techniques.

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Residues outside the 14-3-3 binding motif contribute to affinity in α4 but not in β2.

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Phosphorylation-independent 14-3-3-ζ interactions with integrin tails are reported.

Integrin α1 has a long helix, extending from the transmembrane region to the cytoplasmic tail in detergent micelles

Integrin proteins are very important adhesion receptors that mediate cell-cell and cell-extracellular matrix interactions. They play essential roles in cell signaling and the regulation of cellular shape, motility, and the cell cycle. Here, the transmembrane and cytoplasmic (TMC) domains of integrin α1 and β1 were over-expressed and purified in detergent micelles. The structure and backbone relaxations of α1-TMC in LDAO micelles were determined and analyzed using solution NMR. A long helix, extending from the transmembrane region to the cytoplasmic tail, was observed in α1-TMC. Structural comparisons of α1-TMC with reported αIIb-TMC domains indicated different conformations in the transmembrane regions and cytoplasmic tails. An NMR titration experiment indicated weak interactions between α1-TMC and β1-TMC through several α1-TMC residues located at its N-terminal juxta-transmembrane region and C-terminal extended helix region.

A feed-forward loop coupling extracellular BMP transport and morphogenesis in Drosophila wing

A variety of extracellular factors regulate morphogenesis during development. However, coordination between extracellular signaling and dynamic morphogenesis is largely unexplored. We address the fundamental question by studying posterior crossvein (PCV) development in Drosophila as a model, in which long-range BMP transport from the longitudinal veins plays a critical role during the pupal stages. Here, we show that RhoGAP Crossveinless-C (Cv-C) is induced at the PCV primordial cells by BMP signaling and mediates PCV morphogenesis cell-autonomously by inactivating members of the Rho-type small GTPases. Intriguingly, we find that Cv-C is also required non-cell-autonomously for BMP transport into the PCV region, while a long-range BMP transport is guided toward ectopic wing vein regions by loss of the Rho-type small GTPases. We present evidence that low level of ß-integrin accumulation at the basal side of PCV epithelial cells regulated by Cv-C provides an optimal extracellular environment for guiding BMP transport. These data suggest that BMP transport and PCV morphogenesis are tightly coupled. Our study reveals a feed-forward mechanism that coordinates the spatial distribution of extracellular instructive cues and morphogenesis. The coupling mechanism may be widely utilized to achieve precise morphogenesis during development and homeostasis.

It has been extensively studied how tissue morphogenesis is regulated by a variety of extracellular cues. Given that dynamic morphogenesis coincides with arrival of extracellular factors, there must be also mechanisms that coordinate extracellular signaling and intracellular morphogenesis. However, the coordination is largely unknown, due to the complexity of morphogenesis in vivo. We addressed the fundamental question by studying posterior crossvein (PCV) development in Drosophila as a model, in which a long-range transport of bone morphogenetic protein (BMP) type ligands from adjacent longitudinal veins plays a critical role during the pupal stages. Here, we first showed that RhoGAP Crossveinless-C (Cv-C) is induced at the PCV region by BMP signal and mediates PCV morphogenesis. By modulating wing vein morphogenesis, we then found that PCV morphogenesis is required for BMP transport, while ectopic wing vein morphogenesis sufficiently guides a long-range BMP transport. These data suggest a feed-forward mechanism that coordinates the spatial distribution of extracellular instructive cues and morphogenesis. The coupling mechanism may be widely utilized to achieve precise tissue morphogenesis and tissue homeostasis.

HB-EGF promotes intestinal restitution by affecting integrin-extracellular matrix interactions and intercellular adhesions

Restitution is a critical form of intestinal epithelial cell (IEC) healing. We have previously shown that heparin-binding epidermal-like growth factor (HB-EGF) is necessary for IEC restitution; however, the mechanisms by which HB-EGF promotes restitution remain poorly understood. This study was designed to investigate whether HB-EGF promotes intestinal restitution by affecting integrin-extracellular matrix (ECM) interactions and intercellular adhesions. The effect of HB-EGF administration was examined in a murine necrotizing enterocolitis (NEC) model in vivo and an IEC line scrape-wound healing model in vitro. We evaluated the effect of HB-EGF on the expression of integrins, E-cadherin/β-catenin, and integrin α5β1-dependent cell-ECM interactions. We found that HB-EGF promoted intestinal restitution and the expression of integrin α5β1. HB-EGF promoted integrin α5β1-dependent cell adhesion and spreading. In addition, HB-EGF decreased the expression E-cadherin/β-catenin, via the activation of v-erb-b2 erythroblastic leukemia viral oncogene homolog (ErbB-1). We conclude that HB-EGF promotes intestinal restitution by affecting integrin-ECM interactions and intercellular adhesions.

Phenotypical characteristics of peripheral blood monocytes in normal pregnancy and gestosis

Monocyte migration from the peripheral blood to the uterine decidual tissue is essential for the regulation of placental development. We evaluated the phenotypical changes in the peripheral blood monocytes in pregnant women. The peripheral blood counts of monocytes expressing CD11b, CD47, and integrin β7 were elevated in women with normal gestation in comparison with nonpregnant women; the intensity of CD62P, CD11b, CD11c, CD29, CD31, and CD54 expression was higher in pregnancy. The counts of monocytes expressing adhesion molecules were similar in normal pregnancy and gestosis. Gestosis was characterized by higher counts of monocytes expressing IFN-γ receptor (CD119) and more intense expression of this receptor. Changes in the monocyte phenotype can promote their adhesion to the uterine vascular endothelium and further migration of these cells to the decidual tissue.

Circulating endothelial progenitor cell and platelet microparticle impact on platelet activation in hypertension associated with hypercholesterolemia

Aim

The purpose of this project was to evaluate the influence of circulating endothelial progenitor cells (EPCs) and platelet microparticles (PMPs) on blood platelet function in experimental hypertension associated with hypercholesterolemia.

Methods

Golden Syrian hamsters were divided in six groups: (i) control, C; (ii) hypertensive-hypercholesterolemic, HH; (iii) ‘prevention’, HHin-EPCs, HH animals fed a HH diet and treated with EPCs; (iv) ‘regression’, HHfin-EPCs, HH treated with EPCs after HH feeding; (v) HH treated with PMPs, HH-PMPs, and (vi) HH treated with EPCs and PMPs, HH-EPCs-PMPs.

Results

Compared to HH group, the platelets from HHin-EPCs and HHfin-EPCs groups showed a reduction of: (i) activation, reflected by decreased integrin 3β, FAK, PI3K, src protein expression; (ii) secreted molecules as: SDF-1, MCP-1, RANTES, VEGF, PF4, PDGF and (iii) expression of pro-inflammatory molecules as: SDF-1, MCP-1, RANTES, IL-6, IL-1β; TFPI secretion was increased. Compared to HH group, platelets of HH-PMPs group showed increased activation, molecules release and proteins expression. Compared to HH-PMPs group the combination EPCs with PMPs treatment induced a decrease of all investigated platelet molecules, however not comparable with that recorded when EPC individual treatment was applied.

Conclusion

EPCs have the ability to reduce platelet activation and to modulate their pro-inflammatory and anti-thrombogenic properties in hypertension associated with hypercholesterolemia. Although, PMPs have several beneficial effects in combination with EPCs, these did not improve the EPC effects. These findings reveal a new biological role of circulating EPCs in platelet function regulation, and may contribute to understand their cross talk, and the mechanisms of atherosclerosis.

Circulating permeability factor suPAR: from concept to discovery to clinic

Kidney filtration functions through a hydrostatically driven multicellular barrier that includes visceral epithelial cells termed podocytes. These cells have delicate foot processes by which they ensure proper generation of urine. Most forms of chronic kidney disease start with disruption of podocytes, allowing for a breakdown of kidney barrier function and loss of plasma proteins from the blood into the urine (proteinuria). A classic podocyte disease is focal segmental glomerulosclerosis (FSGS) which progresses from podocyte injury to chronic kidney disease (CKD) and end-stage renal disease (ESRD) in a well-defined histopathological pattern. FSGS can recur after kidney transplantation in 30% or more cases, affecting both children and adults with rapid disease onset. This scenario has led credence to the concept that FSGS is caused by one or more circulating blood factor (s) that in turn cause podocyte injury. Decades of search for viable circulating permeability factor candidates have sparked research in this area. Recently, soluble urokinase plasminogen activator receptor (suPAR) was identified in a majority of patients with FSGS as a soluble factor that acts through binding to and activating podocyte beta 3 integrin. These observations show promise for novel therapeutic development to eliminate a portion of FSGS cases.

Expression of GALNT2 in human extravillous trophoblasts and its suppressive role in trophoblast invasion

Extravillus trophoblast (EVT) invasion plays a critical role in placental development. Integrins bind to extracellular matrix (ECM) proteins to mediate EVT cell adhesion, migration, and invasion. Changes in O-glycans on β1-integrin have been found to regulate cancer cell behavior. We hypothesize that O-glycosyltransferases can regulate EVT invasion through modulating the glycosylation and function of β1-integrin. Here, we found that the GALNT1 and GALNT2 mRNA were highly expressed in HTR8/SVneo and first trimester EVT cells. Immunohistochemstry and immunofluorescence staining showed that GALNT2 was expressed in subpopulations of EVT cells in deciduas, but not in syncytiotrophoblasts and cytotrophoblasts of placental villi. The percentage of GALNT2-positive EVT cells increased with gestational ages. Overexpression of GALNT2 in HTR8/SVneo cells significantly enhanced cell-collagen IV adhesion, but suppressed cell migration and invasion. Notably, we found that GALNT2 increased the expression of Tn antigen (GalNAc-Ser/Thr) on β1-integrin as revealed by Vicia Villosa agglutinin (VVA) binding. Furthermore, GALNT2 suppressed the phosphorylation of focal adhesion kinase (FAK), a crucial downstream signaling molecule of β1-integrin. Our findings suggest that GALNT2 is a critical initiating enzyme of O-glycosylation for regulating EVT invasion.

Band 4.1 proteins regulate integrin-dependent cell spreading

Integrins link the extracellular matrix (ECM) to the cytoskeleton to control cell behaviors including adhesion, spreading and migration. Band 4.1 proteins contain 4.1, ezrin, radixin, moesin (FERM) domains that likely mediate signaling events and cytoskeletal reorganization via integrins. However, the mechanisms by which Band 4.1 proteins and integrins are functionally interconnected remain enigmatic. Here we have investigated roles for Band 4.1 proteins in integrin-mediated cell spreading using primary astrocytes as a model system. We demonstrate that Proteins 4.1B and 4.1G show dynamic patterns of sub-cellular localization in astrocytes spreading on fibronectin. During early stages of cell spreading Proteins 4.1B and 4.1G are enriched in ECM adhesion sites but become more diffusely localized at later stages of spreading. Combinatorial inactivation of Protein 4.1B and 4.1G expression leads to impaired astrocyte spreading. Furthermore, in exogenous expression systems we show that the isolated Protein 4.1 FERM domain significantly enhances integrin-mediated cell spreading. Protein 4.1B is dispensable for reactive astrogliosis in experimental models of cortical injury, likely due to functional compensation by related Protein 4.1 family members. Collectively, these findings reveal that Band 4.1 proteins are important intracellular components for integrin-mediated cell spreading.

A novel mutation in β integrin reveals an integrin-mediated interaction between the extracellular matrix and cki-1/p27KIP1

The cell-extracellular matrix (ECM) interaction plays an essential role in maintaining tissue shapes and regulates cell behaviors such as cell adhesion, differentiation and proliferation. The mechanism by which the ECM influences the cell cycle in vivo is poorly understood. Here we demonstrate that the β integrin PAT-3 regulates the localization and expression of CKI-1, a C. elegans homologue of the cyclin dependent kinase inhibitor p27(KIP1). In nematodes expressing wild type PAT-3, CKI-1::GFP localizes primarily to nucleoli in hypodermal cells, whereas in animals expressing mutant pat-3 with a defective splice junction, CKI-1::GFP appears clumped and disorganized in nucleoplasm. RNAi analysis links cell adhesion genes to the regulation of CKI-1. RNAi of unc-52/perlecan, ina-1/α integrin, pat-4/ILK, and unc-97/PINCH resulted in abnormal CKI-1::GFP localization. Additional RNAi experiments revealed that the SCF E3 ubiquitin-ligase complex genes, skpt-1/SKP2, cul-1/CUL1 and lin-23/F-box, are required for the proper localization and expression of CKI-1, suggesting that integrin signaling and SCF E3 ligase work together to regulate the cellular distribution of CKI-1. These data also suggest that integrin plays a major role in maintaining proper CKI-1/p27(KIP1) levels in the cell. Perturbed integrin signaling may lead to the inhibition of SCF ligase activity, mislocalization and elevation of CKI-1/p27(KIP1). These results suggest that adhesion signaling is crucial for cell cycle regulation in vivo.

Spatial coordination of kindlin-2 with talin head domain in interaction with integrin β cytoplasmic tails

Both talin head domain and kindlin-2 interact with integrin β cytoplasmic tails, and they function in concert to induce integrin activation. Binding of talin head domain to β cytoplasmic tails has been characterized extensively, but information on the interaction of kindin-2 with this integrin segment is limited. In this study, we systematically examine the interactions of kindlin-2 with integrin β tails. Kindlin-2 interacted well with β(1) and β(3) tails but poorly with the β(2) cytoplasmic tail. This binding selectivity was determined by the non-conserved residues, primarily the three amino acids at the extreme C terminus of the β(3) tail, and the sequence in β(2) was non-permissive. The region at the C termini of integrin β(1) and β(3) tails recognized by kindlin-2 was a binding core of 12 amino acids. Kindlin-2 and talin head do not interact with one another but can bind simultaneously to the integrin β(3) tail without enhancing or inhibiting the interaction of the other binding partner. Kindlin-2 itself failed to directly unclasp integrin α/β tail complex, indicating that kindlin-2 must cooperate with talin to support the integrin activation mechanism.

The integrin-ligand interaction regulates adhesion and migration through a molecular clutch

Adhesive and migratory behavior can be cell type, integrin, and substrate dependent. We have compared integrin and substrate differences using three integrin receptors: α5β1, α6β1, and αLβ2 expressed in a common cell type, CHO.B2 cells, which lack integrin α subunits, as well as in different cell types that express one or more of these integrins. We find that CHO.B2 cells expressing either α6β1 or αLβ2 integrins migrate and protrude faster and are more directionally persistent on laminin or ICAM-1, respectively, than CHO.B2 cells expressing α5β1 on fibronectin. Despite rapid adhesion maturation and the presence of large adhesions in both the α6β1- and αLβ2-expressing cells, they display robust tyrosine phosphorylation. In addition, whereas myosin II regulates adhesion maturation and turnover, protrusion rates, and polarity in cells migrating on fibronectin, surprisingly, it does not have comparable effects in cells expressing α6β1 or αLβ2. This apparent difference in the integration of myosin II activity, adhesion, and migration arises from alterations in the ligand-integrin-actin linkage (molecular clutch). The elongated adhesions in the protrusions of the α6β1-expressing cells on laminin or the αLβ2-expressing cells on ICAM-1 display a novel, rapid retrograde flux of integrin; this was largely absent in the large adhesions in protrusions of α5β1-expressing cells on fibronectin. Furthermore, the force these adhesions exert on the substrate in protrusive regions is reduced compared to similar regions in α5-expressing cells, and the adhesion strength is reduced. This suggests that intracellular forces are not efficiently transferred from actomyosin to the substratum due to altered adhesion strength, that is, avidity, affinity, or the ligand-integrin-actin interaction. Finally, we show that the migration of fast migrating leukocytes on fibronectin or ICAM-1 is also largely independent of myosin II; however, their adhesions are small and do not show retrograde fluxing suggesting other intrinsic factors determine their migration differences.

Anti-proliferation and anti-invasion effects of diosgenin on gastric cancer BGC-823 cells with HIF-1α shRNAs

Drug resistance is a major factor for the limited efficacy of chemotherapy in gastric cancer treatment. Hypoxia-inducible factor-1α (HIF-1α), a central transcriptional factor in hypoxia, is suggested to participate in the resistance. Here, we identified a hypoxia-mimic (cobalt chloride) sensitive gastric cell line BGC-823 to explore whether diosgenin, an aglycone of steroidal saponins, can inhibit cancer cell invasion and survival of solid tumor in a hypoxic mimic microenvironment. We have shown that diosgenin is a potent candidate for decreasing the ability of invasion and survival in cobalt chloride treated BGC-823 cells. In addition, when combined with HIF-1α specific short hairpin RNA (shRNA), diosgenin can inhibit BGC-823 cells more effectively. The anti-invasion role of diosgenin may be related to E-cadherin, integrinα5 and integrin β6. These results suggest that diosgenin may be a useful compound in controlling gastric cancer cells in hypoxia condition, especially when combined with down-regulated HIF-1α.

Mechanical strain regulates osteoblast proliferation through integrin-mediated ERK activation

Mechanical strain plays a critical role in the proliferation, differentiation and maturation of bone cells. As mechanical receptor cells, osteoblasts perceive and respond to stress force, such as those associated with compression, strain and shear stress. However, the underlying molecular mechanisms of this process remain unclear. Using a four-point bending device, mouse MC3T3-E1 cells was exposed to mechanical tensile strain. Cell proliferation was determined to be most efficient when stimulated once a day by mechanical strain at a frequency of 0.5 Hz and intensities of 2500 µε with once a day, and a periodicity of 1 h/day for 3 days. The applied mechanical strain resulted in the altered expression of 1992 genes, 41 of which are involved in the mitogen-activated protein kinase (MAPK) signaling pathway. Activation of ERK by mechanical strain promoted cell proliferation and inactivation of ERK by PD98059 suppressed proliferation, confirming that ERK plays an important role in the response to mechanical strain. Furthermore, the membrane-associated receptors integrin β1 and integrin β5 were determined to regulate ERK activity and the proliferation of mechanical strain-treated MC3T3-E1 cells in opposite ways. The knockdown of integrin β1 led to the inhibition of ERK activity and cell proliferation, whereas the knockdown of integrin β5 led to the enhancement of both processes. This study proposes a novel mechanism by which mechanical strain regulates bone growth and remodeling.

The immune cell composition in Barrett's metaplastic tissue resembles that in normal duodenal tissue

Background and Objective

Barrett's esophagus (BE) is characterized by the transition of squamous epithelium into columnar epithelium with intestinal metaplasia. The increased number and types of immune cells in BE have been indicated to be due to a Th2-type inflammatory process. We tested the alternative hypothesis that the abundance of T-cells in BE is caused by a homing mechanism that is found in the duodenum.

Patients and Methods

Biopsies from BE and duodenal tissue from 30 BE patients and duodenal tissue from 18 controls were characterized by immmunohistochemistry for the presence of T-cells and eosinophils(eos). Ex vivo expanded T-cells were further phenotyped by multicolor analysis using flowcytometry.

Results

The high percentage of CD4⁺-T cells (69±3% (mean±SEM/n = 17, by flowcytometry)), measured by flowcytometry and immunohistochemistry, and the presence of non-activated eosinophils found in BE by immunohistochemical staining, were not different from that found in duodenal tissue. Expanded lymphocytes from these tissues had a similar phenotype, characterized by a comparable but low percentage of αE(CD103) positive CD4⁺cells (44±5% in BE, 43±4% in duodenum of BE and 34±7% in duodenum of controls) and a similar percentage of granzyme-B⁺CD8⁺ cells(44±5% in BE, 33±6% in duodenum of BE and 36±7% in duodenum of controls). In addition, a similar percentage of α4β7⁺ T-lymphocytes (63±5% in BE, 58±5% in duodenum of BE and 62±8% in duodenum of controls) was found. Finally, mRNA expression of the ligand for α4β7, MAdCAM-1, was also similar in BE and duodenal tissue. No evidence for a Th2-response was found as almost no IL-4⁺-T-cells were seen.

Conclusion

The immune cell composition (lymphocytes and eosinophils) and expression of intestinal adhesion molecule MAdCAM-1 is similar in BE and duodenum. This supports the hypothesis that homing of lymphocytes to BE tissue is mainly caused by intestinal homing signals rather than to an active inflammatory response.

Eight paths of ERK1/2 signalling pathway regulating hepatocyte proliferation in rat liver regeneration

Although it is known that hormones, growth factors and integrin promote hepatocyte proliferation in liver regeneration (LR) through ERK1/2 signalling pathway, reports about regulating processes of its intracellular paths in hepatocytes of LR are limited. This study aims at exploring which paths of ERK1/2 signalling pathway participate in the regulation of rat LR, especially in hepatocyte proliferation, and how they do so. In all, 14 paths and 165 genes are known to be involved in ERK1/2 signalling pathway. Of them, 161 genes are included in Rat Genome 230 2.0 Array. This array was used to detect expression changes of genes related to ERK1/2 signalling pathway in isolated hepatocytes of rat LR, showing that 60 genes were related to hepatocytes of LR. In addition, bioinformatics and systems biology methods were used to analyse the roles of 14 above paths in regenerating hepatocytes. We found that three paths, RTK→SHC→GRB2/SOS→RAS→RAF, IntegrinΒ→FAK→RAC→PAK→RAF and GΒγ→PI3KΒγ→RAC→PAK→RAF, promoted the G1 phase progression of hepatocytes by activating ERK1/2. A further four paths, Gq→PLCΒ→PKC→SRC/PYK2→GRB2/SOS→RAS→RAF, RTK→PLCγ→PKC→SRC/PYK2→GRB2/SOS→RAS→RAF, IntegrinΒ→FAK/SRC→GRB2/SOS→RAS→RAF and IntegrinΒ→FAK→RAC→PAK→RAF, advanced the cell progression of S phase and G(2)/M checkpoint by activating ERK1/2, and so did PP1/2→Mek1/2 by decreasing the negative influence on ERK1/2. At the late phase of LR, Gαs→AC→EPAC→Rap1→Raf blocked hepatocyte proliferation by decreasing the activity of ERK1/2 and so did PP1/2→Mek1/2. In summary, 60 genes and 8 paths of ERK1/2 signalling pathway regulated hepatocyte proliferation in rat LR.

Early growth response factor-1 limits biliary fibrosis in a model of xenobiotic-induced cholestasis in mice

Hepatic expression of the transcription factor early growth response-1 (Egr-1) is increased in livers of patients with cholestatic liver disease. Bile acid induction of inflammatory genes in hepatocytes is Egr-1 dependent, and Egr-1 expression is increased in livers of mice after bile duct ligation. Of importance, Egr-1 deficiency reduces liver inflammation and injury in that model. However, it is not known whether Egr-1 promotes inflammation in other models of cholestasis. We tested the hypothesis that Egr-1 contributes to liver inflammation in mice exposed chronically to the bile duct epithelial cell (BDEC) toxicant alpha-naphthylisothiocyanate (ANIT). Egr-1-knockout (Egr-1(-/-)) mice and wild-type mice were fed a diet containing 0.025% ANIT for 2 weeks. Expression of Egr-1 mRNA and protein was significantly increased in livers of mice fed ANIT diet. Egr-1 deficiency did not significantly affect ANIT diet-induced hepatocellular injury, inflammatory gene induction, BDEC hyperplasia, or hepatic neutrophil accumulation. In contrast, the deposition of Type 1 collagen was significantly increased in livers of Egr-1(-/-) mice fed ANIT diet compared with wild-type mice fed ANIT diet. Interestingly, this increase in liver fibrosis occurred in association with elevated expression of the β6 integrin (Itgb6) gene, suggesting the potential for increased local activation of transforming growth factor beta. Taken together, the results indicate that Egr-1 does not contribute to liver injury or inflammation in mice fed a diet containing ANIT. Rather, these studies indicate that Egr-1 deficiency worsens liver fibrosis in conjunction with enhanced expression of the profibrogenic Itgb6 gene.