Distinct requirements for C-C chemokine and IL-2 production by naive, previously activated, and anergic T cells

Ag presented by activated APCs promote immunogenic responses whereas Ag presented by resting APCs leads to tolerance. In such a model, the regulation of cytokine release by the presence or absence of costimulation might potentially play a critical role in dictating the ultimate outcome of Ag recognition. C-C chemokines are a structurally defined family of chemoattractants that have diverse effects on inflammation. We were interested in determining the activation requirements for chemokine production by CD4+ T cells. Our data demonstrate for T cell clones and previously activated T cells from TCR-transgenic mice that stimulation with anti-TCR alone results in the production of copious amounts of macrophage-inflammatory protein-1alpha (MIP-1alpha) and other C-C chemokines, and that addition of anti-CD28 gives very little augmentation. Furthermore, MIP-1alpha production is nearly equivalent from both anergic and nonanergic cells. For naive T cells, anti-CD3 stimulation alone led to as much MIP-1alpha production as Ag + APC stimulation. The addition of costimulation gave a 3-10-fold enhancement, but this was 70-fold less than the effect of costimulation on IL-2 production. Thus, although C-C chemokines play a broad role in influencing inflammation, their production by signal 1 alone makes them unlikely to play a critical role in the decision between a tolerogenic and an immunogenic response. Furthermore, the production of MIP-1alpha by anergic T cells, as well as following signal 1 alone, raises the possibility that in vivo this chemokine serves to recruit activated T cells to become tolerant.     

New technologies in scanning probe microscopy for studying molecular interactions in cells

Atomic force microscopy (AFM) is a specialised form of scanning probe microscopy, which was invented by Binnig and colleagues in 1986. Since then, AFM has been increasingly used to study biomedical problems. Because of its high resolution, AFM has been used to examine the topography or shape of surfaces, such as during the molecular imaging of proteins. This, combined with the ability to operate under known force regimes, makes AFM technology particularly useful for measuring intermolecular bond forces and assessing the mechanical properties of biological materials. Many of the constraints (e.g. complex instrumentation, slow acquisition speeds and poor vertical range) that previously limited the use of AFM in cell biology are now beginning to be resolved. Technological advances will enable AFM to challenge both confocal laser scanning microscopy and scanning electron microscopy as a method for carrying out three-dimensional imaging. Its use as both a precise micro-manipulator and a measurement tool will probably result in many novel and exciting applications in the future. In this article, we have reviewed some of the current biological applications of AFM, and illustrated these applications using studies of the cell biology of bone and integrin-mediated adhesion.     

Allosteric regulation of the light-harvesting system of photosystem II

Non-photochemical quenching of chlorophyll fluorescence (NPQ) is symptomatic of the regulation of energy dissipation by the light-harvesting antenna of photosystem II (PS II). The kinetics of NPQ in both leaves and isolated chloroplasts are determined by the transthylakoid delta pH and the de-epoxidation state of the xanthophyll cycle. In order to understand the mechanism and regulation of NPQ we have adopted the approaches commonly used in the study of enzyme-catalysed reactions. Steady-state measurements suggest allosteric regulation of NPQ, involving control by the xanthophyll cycle carotenoids of a protonation-dependent conformational change that transforms the PS II antenna from an unquenched to a quenched state. The features of this model were confirmed using isolated light-harvesting proteins. Analysis of the rate of induction of quenching both in vitro and in vivo indicated a bimolecular second-order reaction; it is suggested that quenching arises from the reaction between two fluorescent domains, possibly within a single protein subunit. A universal model for this transition is presented based on simple thermodynamic principles governing reaction kinetics.     

Cu, Pt, and Pd complexes of the 3-deoxy-1,2-bis(thiosemicarbazone) derived from D-glucose

3-Deoxy-D-erythro-hexos-2-ulose bis(thiosemicarbazone) (1) acts as a tetradentate ligand of the N2S2 type which forms stable coordination complexes with metal(II) cations. The Cu(II), Pt(II), and Pd(II) chelates (2, 4, and 6, respectively) of 1 were synthesized and characterized by elemental analysis and NMR spectroscopy. The NMR spectra of the Pt complex (4) showed the coupling of H-1 and C-1, C-2 of the bis(thiosemicarbazone) with 195Pt (33.7% naturally occurring), which supports the structure proposed for the chelate. The complexes 2, 4, and 6 were acetylated to give the corresponding tri-O-acetyl derivatives 3, 5, and 7. Elimination of Cu(II) from 3 with hydrogen sulfide afforded 8, the tri-O-acetyl derivative of 1. Preliminary studies have shown antiviral activity of chelates 2, 4, and 6 against poliovirus type 1.     

Cobalt hexammine inhibition of the hammerhead ribozyme

The effects of Co(NH(3))(6)(3+) on the hammerhead ribozyme are analyzed using several techniques, including activity measurements, electron paramagnetic resonance (EPR), and circular dichroism (CD) spectroscopies and thermal denaturation studies. Co(NH(3))(6)(3+) efficiently displaces Mn(2+) bound to the ribozyme with an apparent dissociation constant of K(d app) = 22 +/- 4.2 microM in 500 microM Mn(2+) (0.1 M NaCl). Displacement of Mn(2+) coincides with Co(NH(3))(6)(3+) inhibition of hammerhead activity in 500 microM Mn(2+), reducing the activity of the WT hammerhead by approximately 15-fold with an inhibition constant of K(i) = 30.9 +/- 2.3 microM. A residual 'slow' activity is observed in the presence of Co(NH(3))(6)(3+) and low concentrations of Mn(2+). Under these conditions, a single Mn(2+) ion remains bound and has a low-temperature EPR spectrum identical to that observed previously for the highest affinity Mn(2+) site in the hammerhead ribozyme in 1 M NaCl, tentatively attributed to the A9/G10.1 site [Morrissey, S. R. , Horton, T. E., and DeRose, V. J. (2000) J. Am. Chem. Soc. 122, 3473-3481]. Circular dichroism and thermal denaturation experiments also reveal structural effects that accompany the observed inhibition of cleavage and Mn(2+) displacement induced by addition of Co(NH(3))(6)(3+). Taken together, the data indicate that a high-affinity Co(NH(3))(6)(3+) site is responsible for significant inhibition accompanied by structural changes in the hammerhead ribozyme. In addition, the results support a model in which at least two types of metal sites, one of which requires inner-sphere coordination, support hammerhead activity.     

Metal interactions with a GAAA RNA tetraloop characterized by (31)P NMR and phosphorothioate substitutions

A metal site in a 5'-GAAA-3' tetraloop, a stabilizing and phylogenetically conserved RNA motif, is explored using (31)P NMR spectroscopy and phosphorothioate modifications. Similar to previous reports [Legault, P., and Pardi, A. (1994) J. Magn. Reson., Ser. B 103, 82-86], the (31)P NMR spectrum of a 12-nucleotide stem-loop sequence 5'-GGCCGAAAGGCC-3' exhibits resolved features from each of the phosphodiester linkages. Titration with Mg(2+) results in distinct shifts of a subset of these (31)P features, which are assigned to phosphodiesters 5' to A6, A7, and G5. Titration with Co(NH(3))(6)(3+) causes only a slight upfield shift in the A6 feature, suggesting that changes caused by Mg(2+) are due to inner-sphere metal-phosphate coordination. R(p)-Phosphorothioate substitutions introduced enzymatically 5' to each of the three A residues of the tetraloop provide well-resolved (31)P NMR features that are observed to shift in the presence of Cd(2+) but not Mg(2+), again consistent with a metal-phosphate site. Analysis of (31)P NMR spectra using the sequence 5'-GGGCGAAAGUCC-3' with single phosphorothioate substitutions in the loop region, separated into R(p) and S(p) diastereomers, provides evidence for an inner-sphere interaction with the phosphate 5' to A7 but outer-sphere or structural effects that cause perturbations 5' to A6. Introduction of an R(p)-phosphorothioate 5' to A7 results in a distinct (31)P NMR spectrum, consistent with thermodynamic studies reported in the accompanying paper that indicate a unique structure caused by this substitution. On the basis of these results and existing structural information, a metal site in the 5'-GAAA-3' tetraloop is modeled using restrained molecular dynamics simulations.     

Cytokine inducible matrix metalloproteinase expression in immortalized rat chondrocytes is independent of nitric oxide stimulation

Summary The objective of this study was to determine if an immortalized mammalian chondrocyte cell line had a profile of matrix metalloproteinase (MMP) expression that was consistent with what has been reported for primary chondrocytes in vitro and in vivo. A combination of zymography, Western, and Northern analysis was used to examine the expression of MMPs that are relevant to cartilage degradation. Both interleukin-1β and tumor necrosis factor α induced a 4- to 9-fold increase in the level of MMP-9 expression in conditioned media, and a 17- to 24-fold increase in MMP-3 mRNA. Other compounds such as basic fibroblast growth factor and staurosporine each increased MMP-9 expression individually and potentiated the effects of the two cytokines. Transforming growth factor β had no positive or inhibitory effects. N-methyl arginine blocked the increase in nitric oxide observed following treatment with the cytokines but did not prevent the increased expression of MMPs. The pattern of metalloproteinase expression observed in IRC cells and the response to cytokines is very similar to what has been reported during the pathogenesis of osteoarthritis. The IRC cells should be useful as a model system to study basic mechanisms controlling chondrocyte MMP expression and to identify pharmacological modulators of this process.