Biochemical and biophysical research communications
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Biochem. Biophys. Res. Commun. · Apr 2011
Independent and joint modulation of rat Nav1.6 voltage-gated sodium channels by coexpression with the auxiliary β1 and β2 subunits.
The Na(v)1.6 voltage-gated sodium channel α subunit isoform is the most abundant isoform in the brain and is implicated in the transmission of high frequency action potentials. Purification and immunocytochemical studies imply that Na(v)1.6 exist predominantly as Na(v)1.6+β1+β2 heterotrimeric complexes. We assessed the independent and joint effects of the rat β1 and β2 subunits on the gating and kinetic properties of rat Na(v)1.6 channels by recording whole-cell currents in the two-electrode voltage clamp configuration following transient expression in Xenopus oocytes. ⋯ The β2 subunit selectively retarded the fast phase of fast inactivation and shifted the voltage dependence of activation towards depolarization without affecting other gating properties and had no effect on the decline of currents following repeated depolarization. The β1 and β2 subunits expressed together accelerated both kinetic phases of fast inactivation, shifted the voltage dependence of activation towards hyperpolarization, and gave currents with a persistent component typical of those recorded from neurons expressing Na(v)1.6 sodium channels. These results identify unique effects of the β1 and β2 subunits and demonstrate that joint modulation by both auxiliary subunits gives channel properties that are not predicted by the effects of individual subunits.
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Biochem. Biophys. Res. Commun. · Apr 2011
Augmented oxygen-mediated transcriptional activation of cytochrome P450 (CYP)1A expression and increased susceptibilities to hyperoxic lung injury in transgenic mice carrying the human CYP1A1 or mouse 1A2 promoter in vivo.
Supplemental oxygen administration is frequently administered to pre-term and term infants having pulmonary insufficiency. However, hyperoxia contributes to the development of bronchopulmonary dysplasia (BPD) in premature infants. Cytochrome P450 (CYP)A enzymes have been implicated in hyperoxic lung injury. ⋯ Also, these mice showed decreased levels of endogenous CYP1A1 and 1A2 expression after prolonged hyperoxia, and were also more susceptible to lung injury than similarly exposed WT mice, with CYP1A2-luc mice showing the greatest injury. Our results support the hypothesis that hyperoxia induces CYP1A enzymes by transcriptional activation of its corresponding promoters, and that decreased endogenous expression of these enzymes contribute to the increased susceptibilities to hyperoxic lung injury in the transgenic animals. In summary, this is the first report providing direct evidence of hyperoxia-mediated induction of CYP1A1 and CYP1A2 expression in vivo by mechanisms entailing transcriptional activation of the corresponding promoters, a phenomenon that has implications for hyperoxic lung injury, as well as other pathologies caused by oxidative stress.
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Biochem. Biophys. Res. Commun. · Mar 2011
Decreased histone deacetylase 2 impairs Nrf2 activation by oxidative stress.
Nuclear factor erythroid 2-related factor 2 (Nrf2) plays a crucial role in cellular defence against oxidative stress by inducing the expression of multiple anti-oxidant genes. However, where high levels of oxidative stress are observed, such as chronic obstructive pulmonary disease (COPD), Nrf2 activity is reduced, although the molecular mechanism for this defect is uncertain. Here, we show that down-regulation of histone deacetylase (HDAC) 2 causes Nrf2 instability, resulting in reduced anti-oxidant gene expression and increase sensitivity to oxidative stress. ⋯ HDAC2 knock-down by RNA interference resulted in reduced H(2)O(2)-induced Nrf2 protein stability and activity in BEAS2B cells, whereas HDAC1 knockdown had no effect. Furthermore, monocyte-derived macrophages obtained from healthy volunteers (non-smokers and smokers) and COPD patients showed a significant correlation between HDAC2 expression and Nrf2 expression (r=0.92, p<0.0001). Thus, reduced HDAC2 activity in COPD may account for increased Nrf2 acetylation, reduced Nrf2 stability and impaired anti oxidant defences.
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Biochem. Biophys. Res. Commun. · Feb 2011
Neuronal targeting, internalization, and biological activity of a recombinant atoxic derivative of botulinum neurotoxin A.
Non-toxic derivatives of botulinum neurotoxin A (BoNT/A) have potential use as neuron-targeting delivery vehicles, and as reagents to study intracellular trafficking. We have designed and expressed an atoxic derivative of BoNT/A (BoNT/A ad) as a full-length 150 kDa molecule consisting of a 50 kDa light chain (LC) and a 100 kDa heavy chain (HC) joined by a disulfide bond and rendered atoxic through the introduction of metalloprotease-inactivating point mutations in the light chain. ⋯ Immunoprecipitation studies indicate that the LC of BoNT/A ad forms a complex with SNAP25 present in the neuronal cytosolic fraction, demonstrating that the atoxic LC retains the SNAP25 binding capability of the wt toxin. Toxicity of BoNT/A ad was found to be reduced approximately 100,000-fold relative to wt BoNT/A.
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Biochem. Biophys. Res. Commun. · Feb 2011
Intraperitoneal AAV9-shRNA inhibits target expression in neonatal skeletal and cardiac muscles.
Systemic injections of AAV vectors generally transduce to the liver more effectively than to cardiac and skeletal muscles. The short hairpin RNA (shRNA)-expressing AAV9 (shRNA-AAV9) can also reduce target gene expression in the liver, but not enough in cardiac or skeletal muscles. Higher doses of shRNA-AAV9 required for inhibiting target genes in cardiac and skeletal muscles often results in shRNA-related toxicity including microRNA oversaturation that can induce fetal liver failure. ⋯ This is because AAV is most likely diluted or degraded in the liver than in cardiac or skeletal muscle during cell division after birth. We report that this systemically injected shRNA-AAV method does not induce any major side effects, such as liver dysfunction, and the dose of shRNA-AAV is sufficient for gene silencing in skeletal and cardiac muscle tissues. This novel method may be useful for generating gene knockdown in skeletal and cardiac mouse tissues, thus providing mouse models useful for analyzing diseases caused by loss-of-function of target genes.