Na v 1.5, the pore-forming ␣ subunit of the cardiac voltagegated Na ؉ channel complex, is required for the initiation and propagation of the cardiac action potential. Mutations in Na v 1.5 cause cardiac arrhythmias and sudden death. The cardiac Na ؉ channel functions as a protein complex; however, its complete components remain to be fully elucidated. A yeast two-hybrid screen identified a new candidate Na v 1.5-interacting protein, ␣B-crystallin. GST pull-down, co-immunoprecipitation, and immunostaining analyses validated the interaction between Na v 1.5 and ␣B-crystallin. Whole-cell patch clamping showed that overexpression of ␣B-crystallin significantly increased peak sodium current (I Na ) density, and the underlying molecular mechanism is the increased cell surface expression level of Na v 1.5 via reduced internalization of cell surface Na v 1.5 and ubiquitination of Na v 1.5. Knock-out of ␣B-crystallin expression significantly decreased the cell surface expression level of Na v 1.5. Co-immunoprecipitation analysis showed that ␣B-crystallin interacted with Nedd4-2; however, a catalytically inactive Nedd4-2-C801S mutant impaired the interaction and abolished the up-regulation of I Na by ␣B-crystallin. Na v 1.5 mutation V1980A at the interaction site for Nedd4-2 eliminated the effect of ␣B-crystallin on reduction of Na v 1.5 ubiquitination and increases of I Na density. Two disease-causing mutations in ␣B-crystallin, R109H and R151X (nonsense mutation), eliminated the effect of ␣B-crystallin on I Na . This study identifies ␣B-crystallin as a new binding partner for Na v 1.5. ␣B-Crystallin interacts with Na v 1.5 and increases I Na by modulating the expression level and internalization of cell surface Na v 1.5 and ubiquitination of Na v 1.5, which requires the protein-protein interactions between ␣B-crystallin and Na v 1.5 and between ␣B-crystallin and functionally active Nedd4-2.Na v 1.5 is the pore-forming ␣ subunit of the major cardiac voltage-gated Na ϩ channel complex. It generates the sodium current (I Na ) 4 that plays an essential role in the initiation and propagation of the cardiac action potential (1-3). Mutations in the SCN5A gene (encoding Na v 1.5) cause several inherited arrhythmias, including atrial fibrillation, Brugada syndrome, long QT syndrome, progressive cardiac conduction defect disease, sick sinus syndrome, and dilated cardiomyopathy (4). Na v 1.5 exists in vivo in a multiprotein complex, which interacts with the actin cytoskeleton and the extracellular matrix to provide an important functional link between channel complexes, cardiac structure, and electrical functioning (5, 6). Several proteins have been reported to bind to Na v 1.5 (5-7). We have previously reported a small protein, MOG1, with a function in nucleocytoplasmic protein transport that interacts directly with Na v 1.5, promotes trafficking of Na v 1.5 to the cell surface, and increases peak I Na density (4, 6). Specifically, MOG1 facilitates export of Na v 1.5 from the endoplasmic reticulum as well as targeting of Na v 1.5...
The SCN5A gene encodes cardiac sodium channel Nav1.5 and causes lethal ventricular arrhythmias/sudden death and atrial fibrillation (AF) when mutated. MicroRNAs (miRNAs) are important post-transcriptional regulators of gene expression, and involved in the pathogenesis of many diseases. However, little is known about the regulation of SCN5A by miRNAs. Here we reveal a novel post-transcriptional regulatory mechanism for expression and function of SCN5A/Nav1.5 via miR-192-5p. Bioinformatic analysis revealed that the 3′-UTR of human and rhesus SCN5A, but not elephant, pig, rabbit, mouse, and rat SCN5A, contained a target binding site for miR-192-5p and dual luciferase reporter assays showed that the site was critical for down-regulation of human SCN5A. With Western blot assays and electrophysiological studies, we demonstrated that miR-192-5p significantly reduced expression of SCN5A and Nav1.5 as well as peak sodium current density INa generated by Nav1.5. Notably, in situ hybridization, immunohistochemistry and real-time qPCR analyses showed that miR-192-5p was up-regulated in tissue samples from AF patients, which was associated with down-regulation of SCN5A/Nav1.5. These results demonstrate an important post-transcriptional role of miR-192-5p in post-transcriptional regulation of Nav1.5, reveal a novel role of miR-192-5p in cardiac physiology and disease, and provide a new target for novel miRNA-based antiarrhythmic therapy for diseases with reduced INa.
Ubiquitin-specific protease (UBP) family is the largest group of deubiquitinases, which plays important roles in eukaryotic organisms. Comprehensive analysis of UBP genes has not been conducted in the plant pathogenic fungi. In this study, 11 putative UBP genes were identified and characterized in the rice blast fungus Magnaporthe oryzae. Expression profile analysis showed that UBP3, UBP6, UBP12 and UBP14 were highly expressed in different tissues of M. oryzae. In all ubp mutants, especially Δubp3, Δubp12 and previously reported Δubp14, the ubiquitination levels were evidently elevated, which is consistent with their molecular roles in de-ubiquitination. The Δubp1, Δubp3, Δubp4, Δubp8 and Δubp14 mutants were reduced in colony growth. Most of the ubp mutants were severely reduced in conidia production capacity, indicating important roles of the UBPs in conidia formation. Except for Δubp2 and Δubp16, all of the other mutants were decreased in virulence to host plants and defective in invasive growth. These ubp mutants also induced massive ROS accumulation in host cells. We also found that the UBPs may function as both positive and negative regulators in stress response and nutrient utilization of M. oryzae. Collectively, UBPs are important for development, stress response, nutrient utilization and infection of M. oryzae.
The aim of this study was to investigate the effects of simvastatin on insulin secretion in mouse MIN6 cells and the possible mechanism. MIN6 cells were, respectively, treated with 0 μM, 2 μM, 5 μM, and 10 μM simvastatin for 48 h. Radio immunoassay was performed to measure the effect of simvastatin on insulin secretion in MIN6 cells. Luciferase method was used to examine the content of ATP in MIN6 cells. Real-time PCR and western blotting were performed to measure the mRNA and protein levels of inward rectifier potassium channel 6.2 (Kir6.2), voltage-dependent calcium channel 1.2 (Cav1.2), and glucose transporter-2 (GLUT2), respectively. ATP-sensitive potassium current and L-type calcium current were recorded by whole-cell patch-clamp technique. The results showed that high concentrations of simvastatin (5 μM and 10 μM) significantly reduced the synthesis and secretion of insulin compared to control groups in MIN6 cells (P < 0.05). ATP content in simvastatin-treated cells was lower than in control cells (P < 0.05). Compared with control group, the mRNA and protein expression of Kir6.2 increased with treatment of simvastatin (P < 0.05), and mRNA and protein expression of Cav1.2 and GLUT2 decreased in response to simvastatin (P < 0.05). Moreover, simvastatin increased the ATP-sensitive potassium current and reduced the L-type calcium current. These results suggest that simvastatin inhibits the synthesis and secretion of insulin through a reduction in saccharometabolism in MIN6 cells.
Brugada syndrome (BrS) is an inherited arrhythmogenic syndrome leading to sudden cardiac death, partially associated with autosomal dominant mutations in SCN5A, which encodes the cardiac sodium channel alpha-subunit (Nav1.5). To date some SCN5A mutations related with BrS have been identified in voltage sensor of Nav1.5. Here, we describe a dominant missense mutation (R1629Q) localized in the fourth segment of domain IV region (DIV-S4) in a Chinese Han family. The mutation was identified by direct sequencing of SCN5A from the proband’s DNA. Co-expression of Wild-type (WT) or R1629Q Nav1.5 channel and hβ1 subunit were achieved in human embryonic kidney cells by transient transfection. Sodium currents were recorded using whole cell patch-clamp protocols. No significant changes between WT and R1629Q currents were observed in current density or steady-state activation. However, hyperpolarized shift of steady–state inactivation curve was identified in cells expressing R1629Q channel (WT: V1/2 = -81.1 ± 1.3 mV, n = 13; R1629Q: V1/2 = -101.7 ± 1.2 mV, n = 18). Moreover, R1629Q channel showed enhanced intermediate inactivation and prolonged recovery time from inactivation. In summary, this study reveals that R1629Q mutation causes a distinct loss-of-function of the channel due to alter its electrophysiological characteristics, and facilitates our understanding of biophysical mechanisms of BrS.
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