Factors mediating lipofection potency of a series of cationic phosphonolipids in human cell lines

A series of cationic liposomes known as cationic phosphonolipids (CPs) were evaluated as vehicles for in vitro gene transfer in K562 erythroleukemia cells and 5637 epithelial carcinoma cells. For each CP and target cell type examined, detailed analyses were performed to determine optimal transfection conditions (lipid/ DNA (+/-) charge ratio, amount of complexed episomal DNA, liposomal and lipoplex size, complexation medium and duration of complex-cell exposure time). Lipofection conditions were determined to be both cell- and lipid-type specific. Complexation medium critically affected transfection competence. The initial size of the liposome was not always predictive of lipofection potency. The lipid chemical composition had a strong impact upon lipofection efficiency; DOPE inclusion in the liposome formulations was found to affect the levels of transgene expression in a cell-dependent way. Notably, effective transgene expression was characterized by prominent plasmid nuclear incorporation. Human A gamma- and epsilon-globin transgene nuclear incorporation and expression in 5637 cells post GLB.391-mediated lipofection lends credence to its use as a vehicle of therapeutic transgene delivery.     

The ArcB leucine zipper domain is required for proper ArcB signaling

The Arc two-component system modulates the expression of numerous genes in response to respiratory growth conditions. This system comprises ArcA as the response regulator and ArcB as the sensor kinase. ArcB is a tripartite histidine kinase whose activity is regulated by the oxidation of two cytosol-located redox-active cysteine residues that participate in intermolecular disulfide bond formation. Here, we report that the ArcB protein segment covering residues 70-121, fulfills the molecular characteristics of a leucine zipper containing coiled coil structure. Also, mutational analyses of this segment reveal three different phenotypical effects to be distributed along the coiled coil structure of ArcB, demonstrating that this motif is essential for proper ArcB signaling.     

In the family with ubiquitin

The Cold Spring Harbor meeting on 'The Ubiquitin Family', held in May 2011, brought together scientists from a wide range of fields under the umbrella of ubiquitin and ubiquitin-like protein structure, function and regulation.     

A miniaturized column chromatography method for measuring receptor-mediated inositol phosphate accumulation

Inositol phosphates (IPs), such as 1,4,5-inositol-trisphosphate (IP(3)), comprise a ubiquitous intracellular signaling cascade initiated in response to G protein-coupled receptor-mediated activation of phospholipase C. Classical methods for measuring intracellular accumulation of these molecules include time-consuming high-performance liquid chromatography (HPLC) separation or large-volume, gravity-fed anion-exchange column chromatography. More recent approaches, such as radio-receptor and AlphaScreen assays, offer higher throughput. However, these techniques rely on measurement of IP(3) itself, rather than its accumulation with other downstream IPs, and often suffer from poor signal-to-noise ratios due to the transient nature of IP(3). The authors have developed a miniaturized, anion-exchange chromatography method for measuring inositol phosphate accumulation in cells that takes advantage of signal amplification achieved through measuring IP(3) and downstream IPs. This assay uses centrifugation of 96-well-formatted anion-exchange mini-columns for the isolation of radiolabeled inositol phosphates from cell extracts, followed by low-background dry-scintillation counting. This improved assay method measures receptor-mediated IP accumulation with signal-to-noise and pharmacological values comparable to the classical large-volume, column-based methods. Assay validation data for recombinant muscarinic receptor 1, galanin receptor 2, and rat astrocyte metabotropic glutamate receptor 5 are presented. This miniaturized protocol reduces reagent usage and assay time as compared to large-column methods and is compatible with standard 96-well scintillation counters.     

Arterial distensibility: acute changes following dynamic exercise in normal subjects

The time course of acute changes in large artery distensibility immediately and for 60 min following maximum treadmill exercise in normal subjects was characterized by simultaneously measuring upper and lower limb pulse wave velocity (PWV). A new oscillometric technique was used, which has proven to be sensitive to changes in distensibility induced by acute changes in vascular tone independently of blood pressure. The observed changes in PWV are attributable to changes in vascular tone corresponding to recovery from a systemic net constrictor response and a local net dilator response to exercise with persisting postexercise vasodilatation. They are inadequately explained by associated changes in blood pressure and cannot be attributed to changes in heart rate or viscosity. Modeled as a system of n coupled linear differential equations, the minimum (and adequate) order required to reproduce these patterns was n = 1 for the upper and n = 2 for the exercising lower limb. The economy of the solution suggests entrainment among the multiple interactive mechanisms governing vasomotor control.     

Potential signalling pathways underlying corticotrophin-releasing hormone-mediated neuroprotection from excitotoxicity in rat hippocampus

In several neurological disorders including cerebral ischaemia, glutamate has been implicated as a neurotoxic agent in the mechanisms leading to neuronal cell death. The role of corticotrophin-releasing hormone (CRH), the 41-amino acid peptide, which activates the HPA axis in response to stressful stimuli, remains controversial. In this study, we report that CRH in low physiological concentrations (2 pM), prevented glutamate-induced neurotoxicity via receptor-mediated mechanisms when administered to organotypic hippocampal cultures both during and after the glutamate-induced insult. Detailed investigations on the mechanisms mediating this neuroprotective effect showed that activation of the adenylate cyclase pathway and induction of MAP kinase phosphorylation mediate the CRH action. In addition we showed that CRH can inhibit the phosphorylation of JNK/SAPK by glutamate. Most importantly, we showed that CRH can afford neuroprotection against neurotoxicity up to 12 h following the insult, suggesting that CRH is acting at a late stage in the neuronal death cycle, and this might be important in the development of novel neuroprotective agents in order to improve neuronal survival following the insult.     

A novel sensor of NADH/NAD+ redox poise in Streptomyces coelicolor A3(2)

We describe the identification of Rex, a novel redox-sensing repressor that appears to be widespread among Gram-positive bacteria. In Streptomyces coelicolor Rex binds to operator (ROP) sites located upstream of several respiratory genes, including the cydABCD and rex-hemACD operons. The DNA-binding activity of Rex appears to be controlled by the redox poise of the NADH/NAD+ pool. Using electromobility shift and surface plasmon resonance assays we show that NADH, but not NAD+, inhibits the DNA-binding activity of Rex. However, NAD+ competes with NADH for Rex binding, allowing Rex to sense redox poise over a range of NAD(H) concentrations. Rex is predicted to include a pyridine nucleotide-binding domain (Rossmann fold), and residues that might play key structural and nucleotide binding roles are highly conserved. In support of this, the central glycine in the signature motif (GlyXGlyXXGly) is shown to be essential for redox sensing. Rex homologues exist in most Gram-positive bacteria, including human pathogens such as Staphylococcus aureus, Listeria monocytogenes and Streptococcus pneumoniae.     

Variable window binding for mutually exclusive alternative splicing

Background

Genes of advanced organisms undergo alternative splicing, which can be mutually exclusive, in the sense that only one exon is included in the mature mRNA out of a cluster of alternative choices, often arranged in a tandem array. In many cases, however, the details of the underlying biologic mechanisms are unknown.

Results

We describe 'variable window binding' - a mechanism used for mutually exclusive alternative splicing by which a segment ('window') of a conserved nucleotide 'anchor' sequence upstream of the exon 6 cluster in the pre-mRNA of the fruitfly Dscam gene binds to one of the introns, thereby activating selection of the exon directly downstream from the binding site. This mechanism is supported by the fact that the anchor sequence can be inferred solely from a comparison of the intron sequences using a genetic algorithm. Because the window location varies for each exon choice, regulation can be achieved by obstructing part of that sequence. We also describe a related mechanism based on competing pre-mRNA stem-loop structures that could explain the mutually exclusive choice of exon 17 of the Dscam gene.

Conclusion

On the basis of comparative sequence analysis, we propose efficient biologic mechanisms of alternative splicing of the Drosophila Dscam gene that rely on the inherent structure of the pre-mRNA. Related mechanisms employing 'locus control regions' could be involved on other occasions of mutually exclusive choices of exons or genes.