Quantitative switch in integrin expression accompanies differentiation of F9 cells treated with retinoic acid

Surface Coatings Modulate the Differences in the Adhesion Forces of Eukaryotic and Prokaryotic Cells as Detected by Single Cell Force Microscopy

Single cell force microscopy was used to investigate the maximum detachment force (MDF) of primary neuronal mouse cells (PNCs), osteoblastic cells (MC3T3), and prokaryotic cells (Staphylococcus capitis subsp. capitis) from different surfaces after contact times of 1 to 5 seconds. Positively charged silicon nitride surfaces were coated with positively charged polyethyleneimine (PEI) or poly-D-lysine. Laminin was used as the second coating. PEI induced MDFs of the order of 5 to 20 nN, slightly higher than silicon nitride did. Lower MDFs (1 to 5 nN) were detected on PEI/laminin with the lowest on PDL/laminin. To abstract from the individual cell properties, such as size, and to obtain cell type-specific MDFs, the MDFs of each cell on the different coatings were normalized to the silicon nitride reference for the longest contact time. The differences in MDF between prokaryotic and eukaryotic cells were generally of similar dimensions, except on PDL/laminin, which discriminated against the prokaryotic cells. We explain the lower MDFs on laminin by the spatial prevention of the electrostatic cell adhesion to the underlying polymers. However, PEI can form long flexible loops protruding from the surface-bound layer that may span the laminin layer and easily bind to cellular surfaces and the small prokaryotic cells. This was reflected in increased MDFs after two-second contact times on silicon nitride, whereas the two-second values were already observed after one second on PEI or PEI/laminin. We assume that the electrostatic charge interaction with the PEI loops is more important for the initial adhesion of the smaller prokaryotic cells than for eukaryotic cells.

αvβ5 integrin mediates the effect of vitronectin on the initial stage of differentiation in mouse cerebellar granule cell precursors

Vitronectin (VN), one of the extracellular matrix proteins, controls the maturation of cerebellar granule cells (CGCs) through the promotion of the initial differentiation stage progress. However, the receptors of VN in the initial differentiation stage of CGC precursors (CGCPs) have not been clarified. In this study, we characterized the receptor candidates for VN in CGCPs. First, we confirmed that αvβ3 and αvβ5 integrins, which are receptor candidates for VN, were co-localized with VN in the developing cerebellum and primary cultured CGCPs. Next, the knockdown (KD) of αv, β3, and β5 integrins with small interference RNA (siRNA) for each integrin reduced the ratio of Tuj1, a final differentiation marker, -positive CGCPs. We further studied whether αvβ3 and αvβ5 integrins control the initial differentiation stage. The KD of αv and β5, but not β3, integrins significantly increased the ratio of transient axonal glycoprotein 1 (TAG1), an initial differentiation marker, -positive CGCPs, whereas the KD of αv and β3 integrins, not β5 integrin, stimulated the proliferation of CGCPs. Overexpression of β5 integrin stimulated the progress of the initial differentiation stage as well. To confirm the interaction between αvβ5 integrin and VN, VN was added to β5 integrin-KD CGCPs. The promotion of the progress of initial differentiation by VN was abrogated by β5 integrin KD using small hairpin RNA (shRNA). Taken together, our results indicated that αvβ5 integrin, as the very receptor of VN, is responsible for the progress of the initial differentiation stage in mouse CGCPs.

A biological breadboard platform for cell adhesion and detachment studies

The dynamic nature of cell adhesion and detachment, which plays a critical role in a variety of physiological and pathological phenomena, still remains unclear. This motivates the pursuit of controllable manipulation of cell adhesion and detachment for a better understanding of cellular dynamics. Here we present an addressable, multifunctional, and reusable platform, termed the biological breadboard (BBB), for spatiotemporal manipulation of cell adhesion and detachment at cellular and subcellular levels. The BBB, composed of multiple gold electrodes patterned on a Pyrex substrate, is surface-modified with arginine-glycine-aspartic acid terminated thiol (RTT) and polyethylene glycol (PEG) to achieve a cell-adhesive surface on the gold electrodes and a cell-resistive surface on the Pyrex substrate, respectively. Cell adhesion is regulated by the steric repulsion of PEG chains, while cell detachment is controlled by the reductive desorption of a gold-thiol self-assembled monolayer (SAM) at an activation potential of -0.90 to -1.65 V. Experimental characterizations using NIH 3T3 fibroblasts are presented to demonstrate the utility of our device.

Quantitative measurement of cell adhesion using centrifugal force

In order to study the biophysical forces involved in cell-substrate (or cell-cell) adhesion, it is necessary to measure the strength of adhesion. Two questions can be addressed using the centrifugal cell adhesion assay provided in this unit: what is the ligand-receptor affinity for cells adhering at 4 degrees C and what is the strength of the ATP-dependent processes that strengthen adhesion at 37 degrees C. In both cases, the strength of adhesion is measured as the resistance to disruption in the presence of a measured centrifugal force.

Regulation of Ras-MAPK pathway mitogenic activity by restricting nuclear entry of activated MAPK in endoderm differentiation of embryonic carcinoma and stem cells

In response to retinoic acid, embryonic stem and carcinoma cells undergo differentiation to embryonic primitive endoderm cells, accompanied by a reduction in cell proliferation. Differentiation does not reduce the activation of cellular MAPK/Erk, but does uncouple mitogen-activated protein kinase (MAPK) activation from phosphorylation/activation of Elk-1 and results in inhibition of c-Fos expression, whereas phosphorylation of the cytoplasmic substrate p90RSK remains unaltered. Cell fractionation and confocal immunofluorescence microscopy demonstrated that activated MAPK is restricted to the cytoplasmic compartment after differentiation. An intact actin and microtubule cytoskeleton appears to be required for the restriction of MAPK nuclear entry induced by retinoic acid treatment because the cytoskeletal disrupting agents nocodazole, colchicine, and cytochalasin D are able to revert the suppression of c-Fos expression. Thus, suppression of cell proliferation after retinoic acid–induced endoderm differentiation of embryonic stem and carcinoma cells is achieved by restricting nuclear entry of activated MAPK, and an intact cytoskeleton is required for the restraint.

Stabilization of neurites in cerebellar granule cells by transglutaminase activity: identification of midkine and galectin-3 as substrates

The formation of covalent isopeptide cross-links between cell surface protein molecules by the enzyme transglutaminase C influences cell adhesion and morphology. Retinoid-inducible cross-linking activity associated with this enzyme is present in the developing rat cerebellar cortex [Perry M. J. M. et al. (1995) Neuroscience 65, 1063-1076]. A monoclonal antibody was used to localize transglutaminase C to granule neurons in the developing cerebellar cortex. The enzyme was inducible by retinoic acid both in granule neurons cultured from postnatal rat cerebellar cortex and in cells of the embryonic dorsal rhombic lip, which contain granule neuron precursors. A possible biological function for transglutaminase activity was investigated in living granule neurons, cultured on a biomatrix substratum, studied by time-lapse cinematographic analysis using the transglutaminase inactivator RS-48373-007. Inhibition of cross-linking activity did not influence the number of neurites formed by granule neurons, but caused the destabilization of neurites during the initial outgrowth period, seen as an increase in the number of growth cone retractions and the onset of premature axon collateral formation (bifurcation). Inactivation of cross-linking activity prevented the formation of fascicles between neurites only when cells were cultured on a biomatrix surface. Two glial proteins involved in cell-extracellular matrix interactions, midkine and galectin-3, were identified as putative substrates for granule neuron transglutaminase. The results suggest that covalent cross-link formation by transglutaminase C or a related enzyme generates multimeric molecular forms of glial-derived proteins, and plays a role in stabilizing newly formed neurites. A possible non-pathological role for transglutaminase in the control of axon collateral branching by developing granule neurons in the cerebellar cortex is discussed.

Localization and expression of integrin subunits in the embryoid bodies of F9 teratocarcinoma cells

F9 embryonal carcinoma cells can differentiate in vitro into either parietal (PE) or visceral (VE) endoderm, depending upon specific retinoic acid (RA) treatment and growth conditions. In differentiated aggregates of F9 cells (EB), the VE is a polarized monolayer surrounding a core of undifferentiated cells. Within 7 days of treatment the cells organize their cytoskeleton and synthesize large amounts of extracellular matrix proteins to form a basal lamina under the newly formed epithelium. All these changes are likely to involve integrin expression and organization. In this study we have analyzed the spatio-temporal changes in the pattern and level of expression of beta1, beta4, alpha5, alpha6A, and alpha6B integrin subunits. We found that the organization of the VE monolayer in F9 aggregates involves both qualitative and quantitative changes in integrin expression. beta1 is downregulated and accumulates in the forming epithelium. The same occurs for alpha5, although its location on the surface of the aggregate appears to be transient as in fully differentiated EB its distribution is uniform. beta4 and alpha6A are also mainly localized in the VE but they are undetectable in undifferentiated aggregates and their expression is induced by RA treatment. An important exception is represented by alpha6B whose distribution and expression remain almost unchanged throughout treatment.

Modulation of alpha 6/beta 1 integrin expression during differentiation of F9 murine embryonal carcinoma cells to parietal endoderm

In vitro differentiation of the murine embryonal carcinoma (EC) cell line F9 parallels that of the early blastocyst, where visceral (VE) and parietal endoderm (PE) diverge from a common precursor, the primitive endoderm. This differentiation pathway is induced by retinoic acid (RA) and dibutyryl cyclicAMP (dcAMP) and is accompanied by progressive and dramatic changes in cell morphology and functions. Within 7 days of treatment the cells organize their cytoskeleton and synthesize large amounts of extracellular matrix proteins, becoming fully differentiated migratory cells; all these changes are likely to involve integrins expression and organization. We have investigated the changes in beta 1 integrin expression, its maturation, and organization on the cell surface in association with alpha 6, during the transition from undifferentiated F9 stem cells to migrating PE cells. By Western blotting and immunoprecipitation we showed a gradual decrease in the amount of the beta 1 subunit on the cell surface and a parallel progressive accumulation of immature protein, indicating that the control of beta 1 expression during F9 cells differentiation occurs first at post-translational level and then at the level of transcription. Moreover, the induction of differentiation produces a marked decrease of alpha 6B and its association to a high molecular weight protein, while alpha 6A level increases. By immunofluorescence we found that upon differentiation there is a relocation of the beta 1 and alpha 6B integrin subunits from cell-cell contacts to focal contacts where they colocalize with vinculin. On the contrary alpha 6A, weakly present in F9 stem cells, is present in the focal contacts of PE cells and along the stress fibers. We suggest different roles for the two alpha 6 isoforms.