Alain Duperray

Fibrinogen mediates leukocyte adhesion to vascular endothelium through an ICAM-1-dependent pathway

Leukocyte traffic in immune-inflammatory responses requires regulated adhesion of leukocyte subsets to vascular endothelium. We show that fibrinogen or normal human plasma enhances by 2- to 5-fold the adhesion of cells of myeloid and lymphoid lineage to endothelium. This mechanism is mediated by fibrinogen binding to complementary membrane receptors on leukocytes and endothelial cells. Using an affinity chromatography purification strategy, genetically engineered transfectants, and direct binding studies to the isolated recombinant protein, we identified a novel hematopoietic fibrinogen receptor participating in this adhesion pathway as intercellular adhesion molecule 1 (ICAM-1). Accordingly, a new model can be proposed, in which fibrinogen binding to a variety of vascular cell receptors mediates a specific pathway of cell to cell adhesion by bridging together leukocytes and endothelial cells.

Long-Lived Two-Photon Excited Luminescence of Water-Soluble Europium Complex: Applications in Biological Imaging Using Two-Photon Scanning Microscopy

A new europium complex presenting good solubility and stability in water, intense emission in the red (616 nm), long luminescence lifetime, and significant two-photon absorption cross-section in the biological window has been designed and successfully used for two-photon scanning microscopy bioimaging experiments on fixed cancer cells.

Inhibitor of growth 4 suppresses cell spreading and cell migration by interacting with a novel binding partner, liprin alpha1.

Inhibitor of growth 4 (ING4) is a candidate tumor suppressor that plays a major role in gene regulation, cell cycle control, apoptosis, and angiogenesis. ING4 expression is down-regulated in glioblastoma cells and head and neck squamous cell carcinoma. Here, we identified liprin alpha1/PPFIA1, a cytoplasmic protein necessary for focal adhesion formation and axon guidance, as a novel interacting protein with ING4. ING4 and liprin alpha1 colocalized at lamellipodia in the vicinity of vinculin. Overexpressed ING4 suppressed cell spreading and cell migration. In contrast, overexpressed liprin alpha1 enhanced cell spreading and cell migration. Knockdown of endogenous ING4 with RNA interference induced cell motility, whereas knockdown of endogenous liprin alpha1 suppressed cell motility. ING4 also suppressed cell motility that was enhanced by liprin alpha1. However, ING4 did not further suppress cell motility when liprin alpha1 was suppressed with RNA interference, suggesting a functional and mechanistic interdependence between these proteins. In addition to its nuclear functions, cytoplasmic ING4 interacts with liprin alpha1 to regulate cell migration and, with its known antiangiogenic function, may prevent invasion and metastasis.

Analysis of the Roles of ICAM-1 in Neutrophil Transmigration Using a Reconstituted Mammalian Cell Expression Model: Implication of ICAM-1 Cytoplasmic Domain and Rho-Dependent Signaling Pathway

Interaction between ICAM-1 (CD54) and fibrinogen (fg) has been shown to enhance leukocyte adhesion, but its specific role in the process of migration across endothelial cell junctions remains unclear. To overcome the problem of multiple adhesion receptors found on endothelial cells, we have engineered stable Chinese hamster ovary cell lines expressing ICAM-1 (Chinese hamster ovary ICAM-1). The transfection of ICAM-1 alone in these cells is sufficient to recapitulate the entire process of neutrophil adhesion and transmigration. This phenomenon was mediated by fg-ICAM-1 interactions, as depletion of fg, as well as the use of an Ab that specifically inhibits ICAM-1-fg interaction (2D5), completely abolished the effect of ICAM-1 expression on PMN transmigration. In addition, this ICAM-1-mediated transmigration is clearly dependent on the occurrence of fg-ICAM-1 interactions on the monolayer, and not on neutrophils, as the preincubation of the PMN with the mAb was ineffective. Furthermore, PMN transmigration, but not adhesion, is totally abolished when the ICAM-1 cytoplasmic domain is deleted, indicating that signaling inside the cell is required to mediate the fg-ICAM-1 effect on transmigration. Using a specific inhibitor of the small GTP-binding protein Rho, we have obtained evidence that this signaling cascade is involved. Thus, our results clearly show that ICAM-1 plays a key role in the migration of leukocytes across cell junctions, and indicate that this phenomenon is not a direct consequence of the enhanced adhesion mediated by the expression of ICAM-1.

Complex Interactions between Human Myoblasts and the Surrounding 3D Fibrin-Based Matrix

Anchorage of muscle cells to the extracellular matrix is crucial for a range of fundamental biological processes including migration, survival and differentiation. Three-dimensional (3D) culture has been proposed to provide a more physiological in vitro model of muscle growth and differentiation than routine 2D cultures. However, muscle cell adhesion and cell-matrix interplay of engineered muscle tissue remain to be determined. We have characterized cell-matrix interactions in 3D muscle culture and analyzed their consequences on cell differentiation. Human myoblasts were embedded in a fibrin matrix cast between two posts, cultured until confluence, and then induced to differentiate. Myoblasts in 3D aligned along the longitudinal axis of the gel. They displayed actin stress fibers evenly distributed around the nucleus and a cortical mesh of thin actin filaments. Adhesion sites in 3D were smaller in size than in rigid 2D culture but expression of adhesion site proteins, including α5 integrin and vinculin, was higher in 3D compared with 2D (p<0.05). Myoblasts and myotubes in 3D exhibited thicker and ellipsoid nuclei instead of the thin disk-like shape of the nuclei in 2D (p<0.001). Differentiation kinetics were faster in 3D as demonstrated by higher mRNA concentrations of α-actinin and myosin. More important, the elastic modulus of engineered muscle tissues increased significantly from 3.5±0.8 to 7.4±4.7 kPa during proliferation (p<0.05) and reached 12.2±6.0 kPa during differentiation (p<0.05), thus attesting the increase of matrix stiffness during proliferation and differentiation of the myocytes. In conclusion, we reported modulations of the adhesion complexes, the actin cytoskeleton and nuclear shape in 3D compared with routine 2D muscle culture. These findings point to complex interactions between muscle cells and the surrounding matrix with dynamic regulation of the cell-matrix stiffness.

Millisecond lifetime imaging with a europium complex using a commercial confocal microscope under one or two-photon excitation

The long luminescence lifetime of lanthanide based bioprobes is a great advantage for their specific detection in autofluorescent or labelled cells and tissues. It is also a valuable tool for sensing the physicochemical microenvironment and molecular interactions by Forster resonance energy transfer (FRET). However, standard confocal and multiphoton laser scanning microscopes are not adapted for imaging with such temporal resolution, because the typical pixel dwell time is too short compared to the luminescence lifetime. We show that the rapid sampling rate and laser control of a usual confocal microscope can instead be used for precise measurement of long lifetime decays (μs to ms range). Furthermore, both raster- and line-scanning microscopes can specifically detect long luminescence signals in the time-gated mode by shifting the pinhole or the confocal slit in the lagging direction. We characterized the subcellular localization and accurately measured the millisecond luminescence lifetimes of the benchmark two-photon europium probe [Na]3[EuL1G3], and specifically imaged this label in the presence of short-lived fluorescent species. Fine variations of the luminescence lifetime of this lanthanide complex were revealed and mapped in cells in the presence of a FRET acceptor, allowing quantification of the FRET efficiency independently of donor concentration. These results demonstrate a high and yet unexploited potential of quantitative confocal and multiphoton microscopy for time-gated and lifetime imaging of lanthanide-based biological sensors.

Evidence of a Functional Role for Interaction between ICAM-1 and Nonmuscle α-Actinins in Leukocyte Diapedesis

ICAM-1 is involved in both adhesion and extravasation of leukocytes to endothelium during inflammation. It has been shown that the ICAM-1 cytoplasmic domain is important for transendothelial migration of leukocytes but the precise molecular mechanisms involving the intracytoplasmic portion of ICAM-1 is not known. To characterize precisely the molecular scaffolding associated with ICAM-1, we have used the yeast two-hybrid system, and we have identified six different proteins interacting with the ICAM-1 cytoplasmic domain. In this study, we report that the two forms of nonmuscle α-actinin (i.e., α-actinin 1 and α-actinin 4) associate with ICAM-1, and that these interactions are essential for leukocyte extravasation. These interactions were further confirmed by coimmunoprecipitation and immunofluorescence in endothelial cells and in ICAM-1-transfected Chinese hamster ovary cells. The function of these interactions was analyzed by point mutation of charged amino acids located on ICAM-1 cytoplasmic domain. We have identified three charged amino acids (arginine 480, lysine 481, and arginine 486) which are essential in the binding of α-actinins to the ICAM-1 cytoplasmic tail. Mutation of these amino acids completely inhibited ICAM-1-mediated diapedesis. Experiments with siRNA inhibiting specifically α-actinin 1 or α-actinin 4 on endothelial cells indicated that α-actinin 4 had a major role in this phenomenon. Thus, our data demonstrate that ICAM-1 directly interacts with cytoplasmic α-actinin 1 and 4 and that this interaction is required for leukocyte extravasation.

TRACTION PATTERNS OF TUMOR CELLS

The traction exerted by a cell on a planar deformable substrate can be indirectly obtained on the basis of the displacement field of the underlying layer. The usual methodology used to address this inverse problem is based on the exploitation of the Green tensor of the linear elasticity problem in a half space (Boussinesq problem), coupled with a minimization algorithm under force penalization. A possible alternative strategy is to exploit an adjoint equation, obtained on the basis of a suitable minimization requirement. The resulting system of coupled elliptic partial differential equations is applied here to determine the force field per unit surface generated by T24 tumor cells on a polyacrylamide substrate. The shear stress obtained by numerical integration provides quantitative insight of the traction field and is a promising tool to investigate the spatial pattern of force per unit surface generated in cell motion, particularly in the case of such cancer cells.

Tumor cell/endothelial cell tight contact upregulates endothelial adhesion molecule expression mediated by NFκB: Differential role of the shear stress

Cancer metastasis is a multistep process involving cell-cell interactions, but little is known about the adhesive interactions and signaling events during extravasation of tumor cells (TCs). In this study, cell adhesion molecule (CAM) expression was investigated using an in vitro assay, in which TCs were seeded onto an endothelial cell (ECs) monolayer and cocultured during 5 h. Flow cytometry, confocal microscopy as well as western blot analysis indicated that endothelial ICAM-1 (Inter Cellular Adhesion Molecule-1), VCAM-1 (Vascular Adhesion Molecule-1) and E-selectin were up-regulated after TC-EC coculture, whereas no change was observed for CAMs expression in tumor cells. This increased CAMs expression required tight contact between TCs and ECs. Incubation of ECs with the pyrrolidine-dithiocarbamate NFkappaB inhibitor prior to coculture, fully prevented coculture-induced expression of endothelial CAMs. Using specific blocking antibodies we showed an implication of ICAM-1 and VCAM-1 for TCs extravasation and VCAM-1 for adhesion. Moreover, fluid flow experiments revealed that high shear stress totally abolished coculture-induced as well as TNFalpha-induced CAMs over-expression. This study suggests that TCs could act as a potent inflammatory stimulus on ECs by inducing CAMs expression via NFkappaB activation, and that this action can be modulated by shear stress.

Time-dependent traction force microscopy for cancer cells as a measure of invasiveness

The migration of tumor cells of different degrees of invasivity is studied, on the basis of the traction forces exerted in time on soft substrates (Young modulus ∼ 10 kPa). It is found that the outliers of the traction stresses can be an effective indicator to distinguish cancer cell lines of different invasiveness. Here, we test two different epithelial bladder cancer cell lines, one invasive (T24), and a less invasive one (RT112). Invasive cancer cells move in a nearly periodic motion, with peaks in velocity corresponding to higher traction forces exerted on the substrate, whereas less invasive cells develop traction stresses almost constant in time. The dynamics of focal adhesions (FAs) as well as cytoskeleton features reveals that different mechanisms are activated to migrate: T24 cells show an interconnected cytoskeleton linked to mature adhesion sites, leading to small traction stresses, whereas less invasive cells (RT112) show a less‐structured cytoskeleton and unmature adhesions corresponding to higher traction stresses. Migration velocities are smaller in the case of less invasive cells. The mean squared displacement shows super‐diffusive motion in both cases with higher exponent for the more invasive cancer cells. Further correlations between traction forces and the actin cytoskeleton reveal an unexpected pattern of a large actin rim at the RT112 cell edge where higher forces are colocalized, whereas a more usual cytoskeleton structure with stress fibers and FAs are found for T24 cancer cells. We conjecture that this kind of analysis can be useful to classify cancer cell invasiveness.