Tumor necrosis factor inhibits spread of hepatitis C virus among liver cells, independent from interferons

BACKGROUND & AIMS: Tumor necrosis factor (TNF) an inflammatory cytokine expressed by human fetal liver cells (HFLCs) following infection with cell culture-derived hepatitis C virus. TNF has been reported to increase entry of HCV pseudoparticles into hepatoma cells and inhibit signaling by interferon alpha (IFNA), but have no effect on replication of HCV RNA. We investigated the effects of TNF on HCV infection of and spread among Huh-7 hepatoma cells and primary HFLCs.  METHODS: Human hepatoma (Huh-7 and Huh-7.5) and primary HFLCs were incubated with TNF and/or recombinant IFNΑ2Α, IFNB, IFNL1, and IFNL2 before or during HCV infection. We used 2 fully infectious HCV chimeric viruses of genotype 2A in these studies: J6/JFH (Clone 2) and Jc1(p7-nsGluc2A) (Jc1G), which encodes a secreted luciferase reporter. We measured HCV replication, entry, spread, production, and release in hepatoma cells and HFLCs. RESULTS: TNF inhibited completion of the HCV infectious cycle in hepatoma cells and HFLC in a dose-dependent and time-dependent manner. This inhibition required TNF binding to its receptor. Inhibition was independent of IFNA, IFNB, IFNL1, IFNL2, or JAK signaling via STAT. TNF reduced production of infectious viral particles by Huh-7 and HFLC, and thereby reduced numbers of infected cells and size of foci. TNF had little effect on HCV replicons and increased entry of HCV pseudoparticles. When cells were incubated with TNF before infection, the subsequent anti-viral effects of IFNs were increased. CONCLUSION: In a cell culture system, we found TNF to have antiviral effects independently of, as well as in combination with, IFNs. TNF inhibits HCV infection despite increased HCV envelope glycoprotein-mediated infection of liver cells. These findings contradict those from other studies, which reported that TNF blocks signal transduction in response to IFNs. The destructive inflammatory effects of TNF must be considered along with its antiviral effects

Aldosterone and amiloride alter ENaC abundance in vascular endothelium

The amiloride-sensitive epithelial sodium channel (ENaC) is usually found in the apical membrane of epithelial cells but has also recently been described in vascular endothelium. Because little is known about the regulation and cell surface density of ENaC, we studied the influence of aldosterone, spironolactone, and amiloride on its abundance in the plasma membrane of human endothelial cells. Three different methods were applied, single ENaC molecule detection in the plasma membrane, quantification by Western blotting, and cell surface imaging using atomic force microscopy. We found that aldosterone increases the surface expression of ENaC molecules by 36% and the total cellular amount by 91%. The aldosterone receptor antagonist spironolactone prevents these effects completely. Acute application of amiloride to aldosterone-pretreated cells led to a decline of intracellular ENaC by 84%. We conclude that, in vascular endothelium, aldosterone induces ENaC expression and insertion into the plasma membrane. Upon functional blocking with amiloride, the channel disappears from the cell surface and from intracellular pools, indicating either rapid degradation and/or membrane pinch-off. This opens new perspectives in the regulation of ENaC expressed in the vascular endothelium

Role of the primer activation signal in tRNA annealing onto the HIV-1 genome studied by single-molecule FRET microscopy

HIV-1 reverse transcription is primed by a cellular tRNAlys3 molecule that binds to the primer binding site (PBS) in the genomic RNA. An additional interaction between the tRNA molecule and the primer activation signal (PAS) is thought to regulate the initiation of reverse transcription. The mechanism of tRNA annealing onto the HIV-1 genome was examined using ensemble and single-molecule Förster Resonance Energy Transfer (FRET) assays, in which fluorescent donor and acceptor molecules were covalently attached to an RNA template mimicking the PBS region. The role of the viral nucleocapsid (NC) protein in tRNA annealing was studied. Both heat annealing and NC-mediated annealing of tRNAlys3 were found to change the FRET efficiency, and thus the conformation of the HIV-1 RNA template. The results are consistent with a model for tRNA annealing that involves an interaction between the tRNAlys3 molecule and the PAS sequence in the HIV-1 genome. The NC protein may stimulate the interaction of the tRNA molecule with the PAS, thereby regulating the initiation of reverse transcription. Copyrigh