How integrins are activated

Intestinal epithelial CD98 synthesis specifically modulates expression of colonic microRNAs during colitis

The transmembrane glycoprotein CD98 is known to be involved in intestinal inflammation. In the present study, we found that CD98 overexpression in intestinal epithelial cells does not normally affect the expression of colonic (epithelial and immune cell) microRNAs (miRNAs), small noncoding RNAs that posttranscriptionally regulate a wide variety of biological processes. However, upon dextran sulfate sodium (DSS) treatment, the expression of several colonic miRNAs, but not miRNAs from other tissues such as liver and spleen, were differentially regulated in mice overexpressing CD98 in epithelial cells compared with wild-type (WT) animals. For example, the level of colonic miRNA 132 was not affected by DSS treatment in WT animals but was upregulated in mice overexpressing CD98 in intestinal epithelial cells. Other colonic miRNAs, including colonic miRNA 23a and 23b, were downregulated in WT animals after DSS treatment but not in colonic epithelial cell CD98-overexpressing mice. Interestingly, the expression of potential miRNA target genes affected intestinal epithelial cells that overexpress CD98 and cell types that did not overexpress CD98 but were in close proximity to CD98-overexpressing intestinal epithelial cells. Taken together, these observations show that the combination of an inflammatory context and intestinal epithelial cell expression of CD98 affects the regulation of miRNA expression in colonic epithelial and immune cells. This is new evidence that protein expression modulates miRNA expression and suggests the existence of regulatory crosstalk between proteins and miRNAs in diseases such as colitis.

Cell interactions with hierarchically structured nano-patterned adhesive surfaces

The activation of well-defined numbers of integrin molecules in predefined areas by adhesion of tissue cells to biofunctionalized micro-nanopatterned surfaces was used to determine the minimum number of activated integrins necessary to stimulate focal adhesion formation. This was realized by combining micellar and conventional e-beam lithography, which enabled deposition of 6 nm large gold nanoparticles on predefined geometries. Patterns with a lateral spacing of 58 nm and a number of gold nanoparticles, ranging from 6 to 3000 per adhesive patch, were used. For α(v) β(3)-integrin activation, gold nanoparticles were coated with c(-RGDfK-)-thiol peptides, and the remaining glass surface was passivated to prevent non-specific protein adsorption and cell adhesion. Results show that focal adhesion formation is dictated by the underlying hierarchical nanopattern. Adhesive patches with side lengths of 3000 nm and separated by 3000 nm, or with side lengths of 1000 nm and separated by 1000 nm, containing approximately 3007 ± 193 or 335 ± 65 adhesive gold nanoparticles, respectively, induced the formation of actin-associated, paxillin-rich focal adhesions, comparable in size and shape to classical focal adhesions. In contrast, adhesive patches with side lengths of 500, 250 or 100 nm, and separated from adjacent adhesive patches by their respective side lengths, containing 83 ± 11, 30 ± 4, or 6 ± 1 adhesive gold nanoparticles, respectively, showed a significant increase in paxillin domain length, caused by bridging the pattern gap through an actin bundle in order to mechanically, synergistically strengthen each single adhesion site. Neither paxillin accumulation nor adhesion formation was induced if less than 6 c(-RGDfK-)-thiol functionalised gold nanoparticles per adhesion site were presented to cells.

Intestinal epithelial CD98: an oligomeric and multifunctional protein

The intestinal epithelial cell-surface molecule, CD98 is a type II membrane glycoprotein. Molecular orientation studies have demonstrated that the C-terminal tail of human CD98 (hCD98), which contains a PDZ-binding domain, is extracellular. In intestinal epithelial cells, CD98 is covalently linked to an amino-acid transporter with which it forms a heterodimer. This heterodimer associates with beta(1)-integrin and intercellular adhesion molecular 1 (ICAM-1) to form a macromolecular complex in the basolateral membranes of polarized intestinal epithelial cells. This review focuses on the multifunctional roles of CD98, including involvement in extracellular signaling, adhesion/polarity, and amino-acid transporter expression in intestinal epithelia. A role for CD98 in intestinal inflammation, such as Intestinal Bowel Disease (IBD), is also proposed.

Cellular chemomechanics at interfaces: sensing, integration and response

Living cells are complex entities whose remarkable, emergent capacity to sense, integrate, and respond to environmental cues relies on an intricate series of interactions among the cell's macromolecular components. Defects in mechanosensing, transduction,or responses underlie many diseases such as cancers, immune disorders, cardiac hypertrophy, genetic malformations, and neuropathies. Here, we highlight micro- and nanotechnology-based tools that have been used to study how chemical and mechanical cues modulate the responses of single cells in contact with the extracellular environment. Understanding the physical aspects of these complex processes at the micro- and nanometer scale could produce profound and fundamental new insights into how the processes of cell migration, metastasis, immune function and other areas which are regulated by mechanical forces.

Characterization of the human intestinal CD98 promoter and its regulation by interferon-gamma

Growing evidence that epithelial CD98 plays an important role in intestinal inflammation focused our interest to investigate the transcriptional regulation of CD98. Our mouse-based in vivo and in vitro experiments revealed that epithelial colonic CD98 mRNA expression was transcriptionally increased in intestinal inflammation. We then isolated and characterized a 5'-flanking fragment containing the promoter region required for CD98 gene transcription. Primer extension and rapid amplification of 5'-cDNA ends were used to map a transcriptional initiation site 129 bp upstream from the translational start codon (ATG). Direct sequencing of the 5'-flanking region revealed the presence of four GC-rich stimulating protein (Sp)1 binding domains, one NF-kappaB binding domain, and no TATA box. Binding of Sp1 [Sp1(-874), SP1(-386), Sp1(-187), and Sp1(-177)] and NF-kappaB [NF-kappaB(-213)] to the promoter was confirmed by EMSA and supershift assays. Furthermore, chromatin immunoprecipitation experiments showed the in vivo DNA-Sp1 and DNA-NF-kappaB interactions under basal and IFN-gamma-stimulated conditions. Reporter genes driven by serially truncated and site-mutated CD98 promoters were used to examine basal and IFN-gamma-responsive transcription in transiently transfected Caco2-BBE cells. Our results revealed that Sp1(-187), Sp1(-177), and the NF-kappaB binding site were essential for basal and IFN-gamma-stimulated CD98 promoter activities, whereas Sp1(-874) and Sp1(-386) were not. The results from additional site-mutated CD98 promoters suggested that Sp1(-187), Sp1(-177), and the NF-kappaB site may cooperate in mediating basal and IFN-gamma-stimulated CD98 promoter activities. Finally, we demonstrated that a reduction of Sp1 or NF-kappaB expression reduced CD98 protein expression in unstimulated and IFN-gamma-stimulated Caco2-BBE cells. Collectively, these findings indicate that the Sp1 and NF-kappaB transcription factors are likely to play a significant role in IFN-gamma-mediated transcriptional regulation of CD98 in the intestinal epithelium, providing new insights into the regulation of CD98 expression in intestinal inflammation.

Molecular Engineering of Cellular Environments: Cell Adhesion to Nano‐Digital Surfaces

Engineering of the cellular microenvironment has become a valuable means to guide cellular activities such as spreading, motility, differentiation, proliferation, or apoptosis. This chapter summarizes recent approaches to surface patterning such as topography and chemical patterning from the micrometer to the nanometer scale, and illustrates their application to cellular studies. Particular attention is devoted to nanolithography with self-assembled diblock copolymer micelles that are biofunctionalized with peptide ligands-a method that offers unsurpassed spatial resolution for the positioning of signaling molecules over extended surface areas. Such interfaces are defined here as "nano-digital surfaces," since they enable the counting of individual signaling complexes separated by a biologically inert background. The approach enables the testing of cellular responses to individual signaling molecules as well as their spatial ordering. Detailed consideration is also given to the fact that protein clusters such as those found at focal adhesion sites represent, to a large extent, hierarchically organized cooperativity among various proteins.

Nanostructured niobium oxide coatings influence osteoblast adhesion

The interaction of osteoblasts was correlated to the roughness of nanosized surface structures of Nb(2)O(5) coatings on polished CP titanium grade 2. Nb(2)O(5) sol-gel coatings were selected as a model surface to study the interaction of osteoblasts with nanosized surface structures. The surface roughness was quantified by determination of the average surface finish (Ra number) by means of atomic force microscopy. Surface topographies with Ra = 7, 15, and 40 nm were adjusted by means of the annealing process parameters (time and temperature) within a sol-gel coating procedure. The observed osteoblast migration was fastest on smooth surfaces with Ra = 7 nm. The adhesion strength, spreading area, and collagen-I synthesis showed the best results on an intermediate roughness of Ra = 15 nm. The surface roughness of Ra = 40 nm was rather peaked and reduced the speed of cell reactions belonging to the adhesion process.

Alpha6 integrin subunit mediates laminin enhancement of cisplatin-induced apoptosis in testicular tumor germ cells

Our study demonstrates that laminin potentiates cisplatin-induced apoptosis in NCCIT, a testicular tumor germ cell line. When cultured on laminin, NCCIT cells displayed a significantly higher susceptibility to cisplatin-induced apoptosis than on plastic or on other ECM components including fibronectin, Type IV collagen and vitronectin. This high cisplatin sensitivity observed on NCCIT cell cultured on laminin was mediated by the alpha6-integrin signaling. The knockdown of the alpha6-integrin subunit by small interfering RNAs suppressed the higher cisplatin-sensitivity supporting the existence of a crosstalk between laminin-alpha6-integrin signaling and cisplatin-induced apoptosis. Our findings indicate that in cisplatin-treated NCCIT cells, the laminin-alpha6-integrin signaling induces the activation of executioner procaspase-3 and -6 as well as apoptosis-inducing factor (AIF) transcription and expression. The ability of integrin-mediated specific stroma-tumor cell interactions to modulate the chemosensitive phenotype of a tumor cell might provide new insights to overcome cisplatin resistance of tumor cells.

Cynaropicrin, a sesquiterpene lactone, as a new strong regulator of CD29 and CD98 functions

Cynaropicrin is a sesquiterpene lactone displaying immunomodulatory effects on the production of cytokine and nitric oxide from macrophages/monocytes. In this study we have examined inhibitory effect of cynaropicrin on activation of major adhesion molecules [CD29 (beta1 integrins), CD43, and CD98] on the cells assessed by U937 (promonocytic cells) homotypic aggregation. Cynaropicrin potently blocked CD29 (beta1 integrins)- and CD98-induced homotypic aggregation with IC(50) values of 3.46 and 2.98 microM, respectively, without displaying cytotoxicity. Similarly, flow cytometric analysis exhibited that cynaropicrin down-regulated strikingly surface level of CD29 and CD147, a functional regulator of CD98, but not CD43. More importantly, cynaropicrin inhibition was linked to blockade of extracellular signal-related kinase (ERK) activation and distinct from other enzyme inhibitors including rottlerin, propranolol, forskolin, and chloroquine, but not cytochalasin B. Therefore, our finding is the first demonstration that cynaropicrin may be a potent functional regulator of CD29 and CD98 via interrupting ERK activation which may be linked to cytoskeleton rearrangement, suggesting further application to CD29- and CD98-mediated diseases such as virus-induced chronic inflammation, and invasion, migration, and metastasis of leukocyte cancer cells.

Attenuation of very late antigen-5-mediated adhesion of bone marrow-derived mast cells to fibronectin by peptides with inverted hydropathy to EF-hands

Release of allergic mediators from mast cells is enhanced by very late Ag (VLA)-5-mediated interaction of these cells with fibronectin. In this report, we show that VLA-5-mediated adhesion of bone marrow-derived mast cells to fibronectin can be induced by two different pathways: first, FcepsilonRI clustering, which depends on calmodulin activation and extracellular Ca(2+), and, second, by Mn(2+) stimulation, which is independent of calmodulin activation and antagonized by Ca(2+). Previous studies have shown the presence of several cation-binding domains in VLA-5 that are homologous to the calcium-binding EF-hands of calmodulin. To show a role for EF-hands of different proteins in VLA-5-mediated adhesion, we used calcium-like peptides (CALP), CALP1 and CALP2, designed to bind to EF-hands based on inverted hydropathy. CALP1 and, more potently, CALP2 inhibited FcepsilonRI-induced adhesion to fibronectin via different mechanisms. The target for the effects of CALP1 and 2 on FcepsilonRI-induced adhesion and degranulation was intracellular and likely involved calmodulin. Interestingly only CALP2 was able to inhibit Mn(2+)-induced calmodulin-independent adhesion by interfering with an extracellular target, which is probably VLA-5. We conclude that CALP1 and 2 can inhibit VLA-5-mediated adhesion of mast cells to fibronectin through binding to EF-hands of multiple proteins, and that these peptides can be used as lead compounds for the development of future therapy against allergy.

Adherence of adoptively transferred alloreactive Th1 cells in lung: partial dependence on LFA-1 and ICAM-1

T helper type 1 (Th1) cells are important effectors in a number of immune-mediated lung diseases. We recently described a murine model of lung injury induced by adoptive transfer of cloned alloreactive Th1 cells. To investigate mechanisms that result in injury to the lung, we studied the in vivo distribution of (51)Cr-labeled Th1 cells. One hour after intravenous administration, >85% of injected radioactivity was left in the lung, and at 24 h, 40% of radioactivity was left in the lung. Adherence of Th1 cells in the lung was significantly inhibited by neutralizing antibody to lymphocyte function-associated antigen-1. Th1 cell adherence also was decreased in lungs of mice deficient in intercellular adhesion molecule-1 (ICAM-1). Th1 cell transfer further induced expression of ICAM-1 and vascular cell adhesion molecule-1 in the lung. Vascular cell adhesion molecule-1-immunoreactive protein was markedly induced in lung endothelium by alloreactive Th1 cells. These findings indicate that Th1 cells localize in normal lung by a mechanism involving lymphocyte function-associated antigen-1 and ICAM-1. Alloreactive cells further induce endothelial adhesion molecules that may facilitate recruitment of inflammatory cells to the lung and amplify Th1 cell-induced lung injury.

Beta3 integrin activation improves alphavbeta3-mediated retraction of fibrin matrices

BACKGROUND

Integrins are heterodimeric transmembrane glycoproteins that mediate cell interactions with the extracellular matrix. In vivo, integrin affinity can be modulated by intracellular signaling events. This can be simulated by a point mutation (D723R) in the cytoplasmic tail of the beta3 integrin subunit which results in constitutive activation. The effects of beta3 integrin activation on the function of alphavbeta3, an integrin which is important to the adhesive events of multiple cell types, were addressed using Chinese hamster ovary cells expressing either the wild-type alphavbeta3 integrin or the mutant alphavbeta3(D723R). The interactions of these cell lines with fibrin matrices were compared.

METHODS

Receptor expression levels were confirmed by FACS analyses using a monoclonal anti-alphavbeta3 antibody. Cell attachment to fibrin-coated dishes was determined after 1 h by fixation and crystal violet staining followed by elution of the dye and OD measurement. Fibrin clot retraction was measured by culturing cells in fibrin clots for 24 h. The clots were detached from the dish and the surface area was calculated at individual time points.

RESULTS

CHO alphavbeta3(D723R) cells displayed a greater than twofold increase in attachment to fibrinogen or to fibrin matrices when compared to wild-type transfectants. Further, CHO alphavbeta3(D723R) cell retraction of fibrin matrices was significantly greater at nearly all time points.

CONCLUSION

Activation of the beta3 integrin subunit significantly improves the interaction of alphavbeta3 with fibrin and may play a role in the integrin-mediated signaling events which occur following vascular injury.

Pro-adhesive and chemotactic activities of thrombospondin-1 for breast carcinoma cells are mediated by alpha3beta1 integrin and regulated by insulin-like growth factor-1 and CD98

Thrombospondin-1 (TSP1) is a matricellular protein that displays both pro- and anti-adhesive activities. Binding to sulfated glycoconjugates mediates most high affinity binding of soluble TSP1 to MDA-MB-435 cells, but attachment and spreading of these cells on immobilized TSP1 is primarily beta1 integrin-dependent. The integrin alpha3beta1 is the major mediator of breast carcinoma cell adhesion and chemotaxis to TSP1. This integrin is partially active in MDA-MB-435 cells but is mostly inactive in MDA-MB-231 and MCF-7 cells, which require beta1 integrin activation to induce spreading on TSP1. Integrin-mediated cell spreading on TSP1 is accompanied by extension of filopodia containing beta1 integrins. TSP1 binding activity of the alpha3beta1 integrin is not stimulated by CD47-binding peptides from TSP1 or by protein kinase C activation, which activate alphavbeta3 integrin function in the same cells. In MDA-MB-231 but not MDA-MB-435 cells, this integrin is activated by pertussis toxin, whereas serum, insulin, insulin-like growth factor-1, and ligation of CD98 increase activity of this integrin in both cell lines. Serum stimulation is accompanied by increased surface expression of CD98, whereas insulin-like growth factor-1 does not increase CD98 expression. Thus, the pro-adhesive activity of TSP1 for breast carcinoma cells is controlled by several signals that regulate activity of the alpha3beta1 integrin.

Numerical analysis of the deformation of an adherent drop under shear flow

The adhesion of leukocytes to substrates is an important biomedical problem and has drawn extensive research. In this study, employing both single and compound drop models, we investigate how hydrodynamics interacts with an adherent liquid drop in a shear flow. These liquid drop models have recently been used to describe the rheological behavior of leukocytes. Numerical simulation confirms that the drop becomes more elongated when either capillary number or initial contact angle increases. Our results show that there exists a thin region between the drop and the wall as the drop undergoes large stretching, which allows high pressure to build up and provides a lift force. In the literature, existing models regard the leukocyte as a rigid body to calculate the force and torque acting on the drop in order to characterize the binding between cell receptors and endothelial ligands. The present study indicates that such a rigid body model is inadequate and the force magnitude obtained from it is less than half of that obtained using the deformable drop models. Furthermore, because of its much higher viscosity, the cell nucleus introduces a hydrodynamic time scale orders of magnitude slower than the cytoplasm. Hence the single and compound drops experience different dynamics during stretching, but exhibit very comparable steady-state shapes. The present work offers a framework to facilitate the development of a comprehensive dynamic model for blood cells.

Growth factor-dependent activation of alphavbeta3 integrin in normal epithelial cells: implications for tumor invasion

Integrin activation is a multifaceted phenomenon leading to increased affinity and avidity for matrix ligands. To investigate whether cytokines produced during stromal infiltration of carcinoma cells activate nonfunctional epithelial integrins, a cellular system of human thyroid clones derived from normal glands (HTU-5) and papillary carcinomas (HTU-34) was employed. In HTU-5 cells, alphavbeta3 integrin was diffused all over the membrane, disconnected from the cytoskeleton, and unable to mediate adhesion. Conversely, in HTU-34 cells, alphavbeta3 was clustered at focal contacts (FCs) and mediated firm attachment and spreading. alphavbeta3 recruitment at FCs and ligand-binding activity, essentially identical to those of HTU-34, occurred in HTU-5 cells upon treatment with hepatocyte growth factor/scatter factor (HGF/SF). The HTU-34 clone secreted HGF/SF and its receptor was constitutively tyrosine phosphorylated suggesting an autocrine loop responsible for alphavbeta3 activated state. Antibody-mediated inhibition of HGF/SF function in HTU-34 cells disrupted alphavbeta3 enrichment at FCs and impaired adhesion. Accordingly, activation of alphavbeta3 in normal cells was produced by HTU-34 conditioned medium on the basis of its content of HGF/SF. These results provide the first example of a growth factor-driven integrin activation mechanism in normal epithelial cells and uncover the importance of cytokine-based autocrine loops for the physiological control of integrin activation.