Reduced oxygen tension results in reduced human T cell proliferation and increased intracellular oxidative damage and susceptibility to apoptosis upon activation

Cell culture and in vitro models are the basis for much biological research, especially in human immunology. Ex vivo studies of T cell physiology employ conditions attempting to mimic the in vivo situation as closely as possible. Despite improvements in controlling the cellular milieu in vitro, most of what is known about T cell behavior in vitro is derived from experiments on T cells exposed to much higher oxygen levels than are normal in vivo. In this study, we report a reduced proliferative response and increased apoptosis susceptibility after T cell activation at 2% oxygen compared to in air. To explain this observation, we tested the hypothesis of an impaired efficacy of intracellular protective mechanisms including antioxidant levels, oxidized protein repair (methionine sulfoxide reductases), and degradation (proteasome) activities. Indeed, after activation, there was a significant accumulation of intracellular oxidized proteins at more physiological oxygen levels concomitant with a reduced GSH:GSSG ratio. Proteasome and methionine sulfoxide reductase activities were also reduced. These data may explain the increased apoptotic rate observed at more physiological oxygen levels. Altogether, this study highlights the importance of controlling oxygen levels in culture when investigating oxygen-dependent phenomena such as oxidative stress.     

The N-terminal domain of PMTV TGB1 movement protein is required for nucleolar localization, microtubule association, and long-distance movement

The triple-gene-block (TGB)1 protein of Potato mop-top virus (PMTV) was fused to fluorescent proteins and expressed in epidermal cells of Nicotiana benthamiana under the control of the 35S promoter. TGB1 fluorescence was observed in the cytoplasm, nucleus, and nucleolus and occasionally associated with microtubules. When expressed from a modified virus (PMTV.YFP-TGB1) which formed local lesions but was not competent for systemic movement, yellow fluorescent protein (YFP)-TGB1 labeled plasmodesmata in cells at the leading edge of the lesion and plasmodesmata, microtubules, nuclei, and nucleoli in cells immediately behind the leading edge. Deletion of 84 amino acids from the N-terminus of unlabeled TGB1 within the PMTV genome abolished movement of viral RNA to noninoculated leaves. When the same deletion was introduced into PMTV.YFP-TGB1, labeling of microtubules and nucleoli was abolished. The N-terminal 84 amino acids of TGB1 were fused to green fluorescent protein (GFP) and expressed in epidermal cells where GFP localized strongly to the nucleolus (not seen with unfused GFP), indicating that these amino acids contain a nucleolar localization signal; the fusion protein did not label microtubules. This is the first report of nucleolar and microtubule association of a TGB movement protein. The results suggest that PMTV TGB1 requires interaction with nuclear components and, possibly, microtubules for long-distance movement of viral RNA.     

The interaction of zinc with membrane-associated 18.5 kDa myelin basic protein: an attenuated total reflectance-Fourier transform infrared spectroscopic study

Myelin basic protein (MBP) is an essential structural protein required for tight compaction of the myelin sheath of the central nervous system, and belongs to the family of intrinsically disordered proteins. It contains a high proportion of polar and charged amino acids, and has an adaptive conformation depending on its environment and binding surfaces (membranes) or partners (other proteins or small ligands including divalent cations). Zinc is an important stabilizing component of myelin and its concentration is substantially higher than that of any other trace element in the brain. In this study, we investigate the effect of zinc on different variants of 18.5 kDa MBP, including new recombinant forms lacking hexahistidine tags which would interfere with the binding of the cation. Isothermal titration calorimetry showed the dissociation constant to be in the micromolar range for all variants. Circular dichroism spectroscopy showed that there was minimal effect of zinc on the secondary structure on MBP in aqueous solution. When MBP was reconstituted with myelin-mimetic membranes, attenuated total reflectance-Fourier transform infrared spectroscopy revealed that there was a rearrangement of secondary structure components upon addition of zinc that was subtly different for each variant, indicative of a synergistic protein–membrane–cation interaction.     

HDAC-mediated control of ERK- and PI3K-dependent TGF-β-induced extracellular matrix-regulating genes

Histone deacetylases (HDACs) regulate the acetylation of histones in the control of gene expression. Many non-histone proteins are also targeted for acetylation, including TGF-β signalling pathway components such as Smad2, Smad3 and Smad7. Our studies in mouse C3H10T1/2 fibroblasts suggested that a number of TGF-β-induced genes that regulate matrix turnover are selectively regulated by HDACs. Blockade of HDAC activity with trichostatin A (TSA) abrogated the induction of a disintegrin and metalloproteinase 12 (Adam12) and tissue inhibitor of metalloproteinases-1 (Timp-1) genes by TGF-β, whereas plasminogen activator inhibitor-1 (Pai-1) expression was unaffected. Analysis of the activation of cell signalling pathways demonstrated that TGF-β induced robust ERK and PI3K activation with delayed kinetics compared to the phosphorylation of Smads. The TGF-β induction of Adam12 and Timp-1 was dependent on such non-Smad signalling pathways and, importantly, HDAC inhibitors completely blocked their activation without affecting Smad signalling. Analysis of TGF-β-induced Adam12 and Timp-1 expression and ERK/PI3K signalling in the presence of semi-selective HDAC inhibitors valproic acid, MS-275 and apicidin implicated a role for class I HDACs. Furthermore, depletion of HDAC3 by RNA interference significantly down-regulated TGF-β-induced Adam12 and Timp-1 expression without modulating Pai-1 expression. Correlating with the effect of HDAC inhibitors, depletion of HDAC3 also blocked the activation of ERK and PI3K by TGF-β. Collectively, these data confirm that HDACs, and in particular HDAC3, are required for activation of the ERK and PI3K signalling pathways by TGF-β and for the subsequent gene induction dependent on these signalling pathways.     

Dynamic accumulation and redistribution of methylmercury in the lens of developing zebrafish embryos and larvae

Neurotoxic methylmercury compounds are widespread in the environment and human exposure worries many communities worldwide. Despite numerous studies addressing methylmercury toxicity, the detailed mechanisms underlying its transport and accumulation, especially during early developmental stages, remain unclear. Zebrafish larvae are increasingly used as a model system for studies of vertebrate development and toxicology. Previously, we have identified the lens epithelium as the primary site for cellular mercury accumulation in developing zebrafish larvae (Korbas et al. in Proc Natl Acad Sci USA 105:12108–12112, 2008). Here we present a study on the dynamics of methylmercury accumulation and redistribution in the lens following embryonic and larval exposure to methylmercury l-cysteineate using synchrotron X-ray fluorescence imaging. We observed highly specific accumulation of mercury in the lens that continues well after removal of fish from treatment solutions, thus significantly increasing the post-exposure loading of mercury in the lens. The results indicate that mercury is redistributed from the original target tissue to the eye lens, identifying the developing lens as a major sink for methylmercury in early embryonic and larval stages.     

Tissue section AFM: In situ ultrastructural imaging of native biomolecules

Conventional approaches for ultrastructural high-resolution imaging of biological specimens induce profound changes in bio-molecular structures. By combining tissue cryo-sectioning with non-destructive atomic force microscopy (AFM) imaging we have developed a methodology that may be applied by the non-specialist to both preserve and visualize bio-molecular structures (in particular extracellular matrix assemblies) in situ. This tissue section AFM technique is capable of: i) resolving nm–µm scale features of intra- and extracellular structures in tissue cryo-sections; ii) imaging the same tissue region before and after experimental interventions; iii) combining ultrastructural imaging with complimentary microscopical and micromechanical methods. Here, we employ this technique to: i) visualize the macro-molecular structures of unstained and unfixed fibrillar collagens (in skin, cartilage and intervertebral disc), elastic fibres (in aorta and lung), desmosomes (in nasal epithelium) and mitochondria (in heart); ii) quantify the ultrastructural effects of sequential collagenase digestion on a single elastic fibre; iii) correlate optical (auto fluorescent) with ultrastructural (AFM) images of aortic elastic lamellae.     

Characterization of starvation‐induced dispersion in Pseudomonas putida biofilms: genetic elements and molecular mechanisms

Pseudomonas putida OUS82 biofilm dispersal was previously shown to be dependent on the gene PP0164 (here designated lapG). Sequence and structural analysis has suggested that the LapG geneproduct belongs to a family of cysteine proteinases that function in the modification of bacterial surface proteins. We provide evidence that LapG is involved in P. putida OUS82 biofilm dispersal through modification of the outer membrane‐associated protein LapA. While the P. putida lapG mutant formed more biofilm than the wild‐type, P. putida lapA and P. putida lapAG mutants displayed decreased surface adhesion and were deficient in subsequent biofilm formation, suggesting that LapG affects LapA, and that the LapA protein functions both as a surface adhesin and as a biofilm matrix component. Lowering of the intracellular c‐di‐GMP level via induction of an EAL domain protein led to dispersal of P. putida wild‐type biofilm but did not disperse P. putida lapG biofilm, indicating that LapG exerts its activity on LapA in response to a decrease in the intracellular c‐di‐GMP level. In addition, evidence is provided that associated to LapA a cellulase‐degradable exopolysaccharide is part of the P. putida biofilm matrix.