RNase L Mediates Transient Control of The Interferon Response Through Modulation of The Double-stranded RNA-Dependent Protein Kinase PKR

The transient control of diverse biological responses that occurs in response to varied forms of stress is often a highly regulated process. During the interferon (IFN) response, translational repression due to phosphorylation of eukaryotic initiation factor 2α, eIF2α, by the double-stranded RNA-dependent protein kinase, PKR, constitutes a means of inhibiting viral replication. Here we show that the transient nature of the IFN response against acute viral infections is regulated, at least in part, by RNase L. During the IFN antiviral response in RNase L-null cells, PKR mRNA stability was enhanced, PKR induction was increased, and the phosphorylated form of eIF2α appeared with extended kinetics compared with similarly treated wild type cells. An enhanced IFN response in RNase L-null cells was also demonstrated by monitoring inhibition of viral protein synthesis. Furthermore, ectopic expression of RNase L from a plasmid vector prevented the IFN induction of PKR. These results suggest a role for RNase L in the transient control of the IFN response and possibly of other cytokine and stress responses

RNase L Mediates Transient Control of The Interferon Response Through Modulation of The Double-stranded RNA-Dependent Protein Kinase PKR

The transient control of diverse biological responses that occurs in response to varied forms of stress is often a highly regulated process. During the interferon (IFN) response, translational repression due to phosphorylation of eukaryotic initiation factor 2α, eIF2α, by the double-stranded RNA-dependent protein kinase, PKR, constitutes a means of inhibiting viral replication. Here we show that the transient nature of the IFN response against acute viral infections is regulated, at least in part, by RNase L. During the IFN antiviral response in RNase L-null cells, PKR mRNA stability was enhanced, PKR induction was increased, and the phosphorylated form of eIF2α appeared with extended kinetics compared with similarly treated wild type cells. An enhanced IFN response in RNase L-null cells was also demonstrated by monitoring inhibition of viral protein synthesis. Furthermore, ectopic expression of RNase L from a plasmid vector prevented the IFN induction of PKR. These results suggest a role for RNase L in the transient control of the IFN response and possibly of other cytokine and stress responses

The Association of Toll-Like Receptor 4 Polymorphism with Hepatitis C Virus Infection in Saudi Arabian Patients

Hepatitis C virus (HCV) is a single stranded RNA virus. It affects millions of people worldwide and is considered as a leading cause of liver diseases including cirrhosis and hepatocellular carcinoma. A recent study reported that TLR4 gene polymorphisms are good prognostic predictors and are associated with protection from liver fibrosis among Caucasians. This study aims to investigate the implication of genetic polymorphisms of TLR4 gene on the HCV infection in Saudi Arabian patients. Two SNPs in the TLR4 gene, rs4986790 (A/G) and rs4986791 (C/T), were genotyped in 450 HCV patients and 600 uninfected controls. The association analysis confirmed that both SNPs showed a significant difference in their distribution between HCV-infected patients and uninfected control subjects ( < 0.0001; OR = 0.404, 95% CI = 0.281-0.581) and ( < 0.0001; OR = 0.298, 95% CI = 0.201-0.443), respectively. More importantly, haplotype analysis revealed that four haplotypes, AC, GT, GC, and AT (rs4986790, rs4986791), were significantly associated with HCV infection when compared with control subjects. One haplotype AC was more prominently found when chronic HCV-infected patients were compared with cirrhosis/HCC patients (frequency = 94.7% and = 0.04). Both TLR4 SNPs under investigation were found to be significantly implicated with HCV-infection among Saudi Arabian population

Transcriptional Control of The Human Plasma Membrane Phospholipid Scramblase 1 gene is Mediated by Interferon-α

Interferons (IFNs) mediate their diverse biologic activities through induction of the expression of multiple genes. Whereas the mode of action of certain of these IFN-regulated genes has been well characterized, most of the molecular and cellular events underlying the constellation of biologic responses to the IFNs remain unresolved. This study showed that the newly identified PLSCR1 gene for phospholipid scramblase, previously implicated in remodeling of plasma membrane phospholipids, is regulated at the transcriptional level by IFN-α. Analysis of 5\u27 flanking genomic sequence In reporter constructs showed that transcriptional control of PLSCR1 was entirely regulated by a single IFN-stimulated response element located in the first exon. A similar induction of PLSCR1 by IFN-α2a was also observed in a variety of other human tumor cell lines as well as in human umbilical vein endothelial cells. In these cell lines, the marked IFN-α2a-induced increase in PLSCR1 protein expression, ranging as high as 10-fold above basal levels, was not accompanied by increased cell surface exposure of phosphatidylserine, suggesting that remodeling of the cell surface requires both exposure to IFN and a second yet-to-be identified event to stimulate plasma membrane phospholipid scramblase activity and to mobilize phosphatidyl-serine to the cell surface

Transcriptional Control of The Human Plasma Membrane Phospholipid Scramblase 1 gene is Mediated by Interferon-α

Interferons (IFNs) mediate their diverse biologic activities through induction of the expression of multiple genes. Whereas the mode of action of certain of these IFN-regulated genes has been well characterized, most of the molecular and cellular events underlying the constellation of biologic responses to the IFNs remain unresolved. This study showed that the newly identified PLSCR1 gene for phospholipid scramblase, previously implicated in remodeling of plasma membrane phospholipids, is regulated at the transcriptional level by IFN-α. Analysis of 5\u27 flanking genomic sequence In reporter constructs showed that transcriptional control of PLSCR1 was entirely regulated by a single IFN-stimulated response element located in the first exon. A similar induction of PLSCR1 by IFN-α2a was also observed in a variety of other human tumor cell lines as well as in human umbilical vein endothelial cells. In these cell lines, the marked IFN-α2a-induced increase in PLSCR1 protein expression, ranging as high as 10-fold above basal levels, was not accompanied by increased cell surface exposure of phosphatidylserine, suggesting that remodeling of the cell surface requires both exposure to IFN and a second yet-to-be identified event to stimulate plasma membrane phospholipid scramblase activity and to mobilize phosphatidyl-serine to the cell surface

Suppression of Ovarian Carcinoma Cell Growth in Vivo by The Interferon-Inducible Plasma Membrane Protein, Phospholipid Scramblase 1

Phospholipid scramblase 1 (PLSCR1) is an IFN-inducible, endofacial plasma membrane protein that has been proposed to mediate accelerated transbilayer movement of plasma membrane phospholipids in cells exposed to elevated cytoplasmic [Ca 2+]. The marked transcriptional up-regulation of this gene by IFN in a wide variety of cell types suggested that PLSCR1 might also contribute to biological effects associated with IFN. To study the potential contribution of cellular PLSCR1 to the antiproliferative and tumor-suppressive activities of IFN, PLSCR1 cDNA was stably expressed in the human ovarian cancer cell line HEY1B, and the growth of these cells was compared with matched vector transfected controls both in vitro and in vivo. Whereas we detected no difference in either growth rate or morphology between PLSCR1-transfected cells and vector controls during in vitro culture in serum, when these cells were implanted s.c. into athymic nude mice, we observed a marked suppression of tumor development from cells transfected to express elevated levels of PLSCR1. Tumors from the PLSCR1-transfected cells were greatly reduced in size, showed increased infiltration of leukocytes and macrophages, and appeared to undergo differentiation to a more uniform and spindle-shaped morphology that markedly contrasted the highly undifferentiated and pleiomorphic cell shape normally observed for HEY1B cells in vitro or for vector-transfected control HEY1B cells both in vitro and in vivo. These data suggest that the up-regulation of PLSCR1 expression in tumor cells exposed to IFN may contribute to the observed tumor-suppressive action of this cytokine