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Brain cytokines and the 5-HT system during poly I:C-induced fatigue.

Fatigue is evoked not only by peripheral factors, such as muscle fatigue, but also by the central nervous system (CNS). For example, it is generally known that the feeling of fatigue is greatly influenced by psychological aspects, such as motivation. However, little is known about the central mechanisms of fatigue. The clinical symptoms of chronic fatigue syndrome (CFS) are shown to include disorders in neuroendocrine, autonomic, and immune systems. On the other hand, it has been demonstrated that cytokines produced in the brain play significant roles in neural-immune interactions through their various central actions, including hypothalamo-pituitary and sympathetic activation, as well as immunosuppression. In this article, using the immunologically induced fatigue model, which was achieved by intraperitoneal (i.p.) injection of synthetic double-stranded RNAs, polyriboinosinic: polyribocytidylic acid (poly I:C) in rats, we show an involvement of brain interferon-alpha (IFN-alpha) and serotonin (5-HT) transporter (5-HTT) in the central mechanisms of fatigue. In the poly I:C-induced fatigue rats, expression of IFN-alpha and 5-HTT increased, while extracellular concentration of 5-HT in the medial prefrontal cortex decreased, probably on account of the enhanced expression of 5-HTT. Since the poly I:C-induced reduction of the running wheel activity was attenuated by a 5-HT(1A) receptor agonist, but not by 5-HT(2), 5-HT(3), or dopamine D(3) receptor agonists, it is suggested that the decrease in 5-HT actions on 5-HT(1A) receptors may at least partly contribute to the poly I:C-induced fatigue.

Animals↗

Host heterogeneous ribonucleoprotein K (hnRNP K) as a potential target to suppress hepatitis B virus replication.

BACKGROUND: Hepatitis B virus (HBV) infection results in complications such as cirrhosis and hepatocellular carcinoma. Suppressing viral replication in chronic HBV carriers is an effective approach to controlling disease progression. Although antiviral compounds are available, we aimed to identify host factors that have a significant effect on viral replication efficiency. METHODS AND FINDINGS: We studied a group of hepatitis B carriers by associating serum viral load with their respective HBV genomes, and observed a significant association between high patient serum viral load with a natural sequence variant within the HBV enhancer II (Enh II) regulatory region at position 1752. Using a viral fragment as an affinity binding probe, we isolated a host DNA-binding protein belonging to the class of heterogeneous nuclear ribonucleoproteins--hnRNP K--that binds to and modulates the replicative efficiency of HBV. In cell transfection studies, overexpression of hnRNP K augmented HBV replication, while gene silencing of endogenous hnRNP K carried out by small interfering RNAs resulted in a significant reduction of HBV viral load. CONCLUSION: The evidence presented in this study describes a wider role for hnRNP K beyond maintenance of host cellular functions and may represent a novel target for pharmacologic intervention of HBV replication.

Amino Acid Sequence↗

T-cell malignancies with mature phenotypes: altered cell cycle regulation by HLA class I molecules.

Soluble anti-HLA class I monoclonal antibodies (MoAbs) modulate normal T-lymphocyte proliferation induced via the CD3/Ti and the CD2 pathway, but do not induce proliferation of normal T lymphocytes in the absence of additional mitogenic stimuli. In this report, we show that anti-HLA class I MoAbs induce DNA synthesis in peripheral blood mononuclear cells from a patient with a CD4+CD8+T-prolymphocytic leukemia (T-PLL) and from a patient with a CD4-CD8+ T-chronic lymphocytic leukemia (T-CLL), in the absence of detectable additional mitogenic stimuli. Proliferation of leukemic T cells is induced by both whole Igs and Fab' fragments of anti-HLA class I MoAbs, arguing in favor of their direct interactions with the proliferating cells as the mechanism underlying the mitogenic effect. This interpretation is also supported by the ability of anti-HLA class I MoAbs to induce proliferation of leukemic T-cell preparations, depleted of accessory cells. DNA synthesis in T-CLL and T-PLL cells is preceded by expression of G1-specific messenger RNAs, ie. c-myc, 2F1, Tac, and interferon-gamma, in activated cells. Cell proliferation is inhibited by the protein kinase C inhibitor H7, indicating that activation of this enzyme is required for the mitogenic effect of anti-HLA class I MoAbs. The latter inhibit the proliferation of T-CLL cells as well as that of normal T cells stimulated with anti-CD3 MoAbs and enhance that of both types of cells stimulated with anti-CD2 MoAbs. In addition, anti-HLA class I MoAb Q6/64 in combination with anti-CD2 MoAb 9.6 or MoAb 9-1 induces proliferation of leukemic T cells to a greater extent than the individual MoAbs, but is not mitogenic for normal T cells. Anti-HLA class I MoAbs restore the cytolytic activity of T-CLL cells that is lost after 5 days of incubation of control medium, suggesting that HLA class I antigens may mediate a signal contributing to the activation state. The present results indicate that leukemic T-cell proliferation can be triggered via HLA class I molecules and suggest a potential role for these antigens in the in vivo growth of malignant clones.

Antibodies, Monoclonal↗

Analysis of extracellular West Nile virus particles produced by cell cultures from genetically resistant and susceptible mice indicates enhanced amplification of defective interfering particles by resistant cultures.

[3H]uridine-labeled extracellular West Nile virus (WNV) particles produced by cell cultures obtained from genetically resistant C3H/RV and congenic susceptible C3H/HE mice were compared by sucrose density gradient centrifugation as well as by analysis of the particle RNA. Defective interfering (DI) WNV particles were observed among progeny produced during acute infections in both C3H/RV and C3H/HE cells. Although only a partial separation of standard and DI particles was achieved, the DI particles were found to be more dense than the standard virions. Particles containing several species of small RNAs consistently constituted a major proportion of the total population of virus progeny produced by C3H/RV cells, but a minor proportion of the population produced by C3H/HE cells. Decreasing the multiplicity of infection or extensive plaque purification of the WNV inoculum decreased the proportion of small RNAs found in the progeny virus. The ratio of DI particles to standard virus observed in progeny virus was determined by the cell type used to grow the virus. The ratio could be shifted by passaging virus from one cell type to the other. Homologous interference could be demonstrated with WNV produced by C3H/RV cells but not with virus produced by C3H/HE cells. Continued passage of WNV in C3H/HE cells resulted in a cycling of infectivity. However, passage in C3H/RV cells resulted in the complete loss of infectious virus. Four size classes of small viral RNA, with sedimentation coefficients of about 8, 15, 26, and 34S, were observed in the extracellular particles. A preliminary analysis of these RNAs by oligonucleotide fingerprinting indicated that the smaller RNAs were less complex than the 40S RNA and differed from each other. The data are consistent with the conclusion that WNV DI particles interfere more effectively with standard virus replication and are amplified more efficiently in C3H/RV cells than in congenic C3H/HE cells. The relevance of these findings to the further understanding of genetically controlled resistance to flaviviruses is discussed.

Animals↗

Translation of a nonpolyadenylated viral RNA is enhanced by binding of viral coat protein or polyadenylation of the RNA.

On entering a host cell, positive-strand RNA virus genomes have to serve as messenger for the translation of viral proteins. Efficient translation of cellular messengers requires interactions between initiation factors bound to the 5'-cap structure and the poly(A) binding protein bound to the 3'-poly(A) tail. Initiation of infection with the tripartite RNA genomes of alfalfa mosaic virus (AMV) and viruses from the genus Ilarvirus requires binding of a few molecules of coat protein (CP) to the 3' end of the nonpolyadenylated viral RNAs. Moreover, infection with the genomic RNAs can be initiated by addition of the subgenomic messenger for CP, RNA 4. We report here that extension of the AMV RNAs with a poly(A) tail of 40 to 80 A-residues permitted initiation of infection independently of CP or RNA 4 in the inoculum. Specifically, polyadenylation of RNA 1 relieved an apparent bottleneck in the translation of the viral RNAs. Translation of RNA 4 in plant protoplasts was autocatalytically stimulated by its encoded CP. Mutations that interfered with CP binding to the 3' end of viral RNAs reduced translation of RNA 4 to undetectable levels. Possibly, CP of AMV and ilarviruses stimulates translation of viral RNAs by acting as a functional analogue of poly(A) binding protein or other cellular proteins.

Alfalfa mosaic virus↗

Minihelix-containing RNAs mediate exportin-5-dependent nuclear export of the double-stranded RNA-binding protein ILF3.

The karyopherin-related nuclear transport factor exportin-5 preferentially recognizes and transports RNAs containing minihelix motif, a structural cis-acting export element that comprises a double-stranded stem (>14 nucleotides) with a base-paired 5' end and a 3-8-nucleotide protruding 3' end. This structural motif is present in various small cellular and viral polymerase III transcripts such as the adenovirus VA1 RNA (VA1). Here we show that the double-stranded RNA-binding protein, ILF3 (interleukin enhancer binding factor 3) preferentially binds minihelix motif. Gel retardation assays and glutathione S-transferase pull-down experiments revealed that ILF3, exportin-5, RanGTP, and VA1 RNA assembled in a quaternary complex in which the RNA moiety bridges the interaction between ILF3 and exportin-5. Formation of this complex is facilitated by the ability of both exportin-5 and ILF3 to mutually increase their apparent affinity for VA1 RNA. Using microinjection in the nucleus of HeLa cells and transfection experiments, we show here that formation of the cooperative RanGTP-dependent RNA/ILF3/exportin-5 complex promotes the co-transport of VA1 and ILF3 from the nucleus to the cytoplasm. Exportin-5 thus appears as the first example of a nuclear export receptor that mediates RNA export but also promotes transport of proteinaceous cargo through appropriate and specific RNA adaptors.

Active Transport, Cell Nucleus↗

Modulation of ADAR1 editing activity by Z-RNA in vitro.

RNA editing by A-to-I modification has been recognized as an important molecular mechanism for generating RNA and protein diversity. In mammals, it is mediated by a family of adenosine deaminases that act on RNAs (ADARs). The large version of the editing enzyme ADAR1 (ADAR1-L), expressed from an interferon-responsible promoter, has a Z-DNA/Z-RNA binding domain at its N-terminus. We have tested the in vitro ability of the enzyme to act on a 50 bp segment of dsRNA with or without a Z-RNA forming nucleotide sequence. A-to-I editing efficiency is markedly enhanced in presence of the sequence favoring Z-RNA. In addition, an alteration in the pattern of modification along the RNA duplex becomes evident as reaction times decrease. These results suggest that the local conformation of dsRNA molecules might be an important feature for target selectivity by ADAR1 and other proteins with Z-RNA binding domains.

Adenosine Deaminase↗

An RNA chaperone activity of non-specific RNA binding proteins in hammerhead ribozyme catalysis.

We have previously shown that a protein derived from the p7 nucleocapsid (NC) protein of HIV type-1 increases kcat/Km and kcat for cleavage of a cognate substrate by a hammerhead ribozyme. Here we show directly that the increase in kcat/Km arises from catalysis of the annealing of the RNA substrate to the ribozyme and the increase in kcat arises from catalysis of dissociation of the RNA products from the ribozyme. A peptide polymer derived from the consensus sequence of the C-terminal domain of the hnRNP A1 protein (A1 CTD) provides similar enhancements. Although these effects apparently arise from non-specific interactions, not all non-specific binding interactions led to these enhancements. NC and A1 CTD exert their effects by accelerating attainment of the thermodynamically most stable species throughout the ribozyme catalytic cycle. In addition, NC protein is shown to resolve a misfolded ribozyme-RNA complex that is otherwise long lived. These in vitro results suggest that non-specific RNA binding proteins such as NC and hnRNP proteins may have a biological role as RNA chaperones that prevent misfolding of RNAs and resolve RNAs that have misfolded, thereby ensuring that RNA is accessible for its biological functions.

Amino Acid Sequence↗

Genome-wide application of RNAi to the discovery of potential drug targets.

Progress is being made in the development of RNA interference-based (RNAi-based) strategies for the control of gene expression. It has been demonstrated that small interfering RNAs (siRNAs) can silence the expression of target genes in a sequence-specific manner in mammalian cells. Various groups, including our own, have developed systems for vector-mediated specific RNAi. Vector-based siRNA- (or shRNA) expression libraries directed against the entire human genome and siRNA libraries based on chemically synthesized oligonucleotides now allow the rapid identification of functional genes and potential drug targets. Use of such libraries will enhance our understanding of numerous biological phenomena and contribute to the rational design of drugs against heritable, infectious and malignant diseases.

Animals↗

Characterization of the Hantaan nucleocapsid protein-ribonucleic acid interaction.

The nucleocapsid (N) protein functions in hantavirus replication through its interactions with the viral genomic and antigenomic RNAs. To address the biological functions of the N protein, it was critical to first define this binding interaction. The dissociation constant, K(d), for the interaction of the Hantaan virus (HTNV) N protein and its genomic S segment (vRNA) was measured under several solution conditions. Overall, increasing the NaCl and Mg(2+) in these binding reactions had little impact on the K(d). However, the HTNV N protein showed an enhanced specificity for HTNV vRNA as compared with the S segment open reading frame RNA or a nonviral RNA with increasing ionic strength and the presence of Mg(2+). In contrast, the assembly of Sin Nombre virus N protein-HTNV vRNA complexes was inhibited by the presence of Mg(2+) or an increase in the ionic strength. The K(d) values for HTNV and Sin Nombre virus N proteins were nearly identical for the S segment open reading frame RNA, showing weak affinity over several binding reaction conditions. Our data suggest a model in which specific recognition of the HTNV vRNA by the HTNV N protein resides in the noncoding regions of the HTNV vRNA.

Capsid↗

RNA immunoprecipitation and microarray analysis show a chloroplast Pentatricopeptide repeat protein to be associated with the 5' region of mRNAs whose translation it activates.

Plant nuclear genomes encode hundreds of predicted organellar RNA binding proteins, few of which have been connected with their physiological RNA substrates and functions. In fact, among the largest family of putative RNA binding proteins in plants, the pentatricopeptide repeat (PPR) family, no physiologically relevant RNA ligands have been firmly established. We used the chloroplast-splicing factor CAF1 to demonstrate the fidelity of a microarray-based method for identifying RNAs associated with specific proteins in chloroplast extract. We then used the same method to identify RNAs associated with the maize (Zea mays) PPR protein CRP1. Two mRNAs whose translation is CRP1-dependent were strongly and specifically enriched in CRP1 coimmunoprecipitations. These interactions establish CRP1 as a translational regulator by showing that the translation defects in crp1 mutants are a direct consequence of the absence of CRP1. Additional experiments localized these interactions to the 5' untranslated regions and suggested a possible CRP1 interaction motif. These results enhance understanding of the PPR protein family by showing that a PPR protein influences gene expression through association with specific mRNAs in vivo, suggesting an unusual mode of RNA binding for PPR proteins, and highlighting the possibility that translational regulation may be a particularly common function of PPR proteins. Analogous methods should have broad application for the study of native RNA-protein interactions in both mitochondria and chloroplasts.

5' Untranslated Regions↗

Multiple features contribute to the use of the immunoglobulin M secretion-specific poly(A) signal but are not required for developmental regulation.

The secretory-specific poly(A) signal (mus) of the immunoglobulin mu gene plays a central role in regulating alternative RNA processing to produce RNAs that encode membrane-associated and secreted immunoglobulins. This poly(A) signal is in direct competition with a splice reaction, and regulation requires that these two reaction efficiencies be balanced. The mus poly(A) signal has several unique sequence features that may contribute to its strength and regulation. Site-directed mutations and small internal deletions made in the intact mu gene show that an extensive AU/A-rich sequence surrounding AAUAAA enhances signal use and that, of the two potential downstream GU-rich elements, both of which appear suboptimally located, only the proximal GU-rich sequence contributes substantially to use of this signal. A GU-rich sequence placed at a more standard location did not improve mus poly(A) signal use. All mu genes tested that contained modified mus poly(A) signals were developmentally regulated, indicating that the GU-rich sequences, the sequences between them previously identified as suboptimal U1A binding sites, and an upstream suboptimal U1A site do not contribute to mu mRNA processing regulation. Expression of wild-type and modified mu genes in HeLa cells overexpressing U1A also failed to demonstrate that U1A contributes to mus poly(A) signal regulation.

Animals↗

Foxf1 haploinsufficiency reduces Notch-2 signaling during mouse lung development.

The forkhead box (Fox) f1 transcription factor is expressed in the mouse splanchnic (visceral) mesoderm, which contributes to development of the liver, gallbladder, lung, and intestinal tract. Pulmonary hemorrhage and peripheral microvascular defects were found in approximately half of the newborn Foxf1(+/-) mice, which expressed low levels of lung Foxf1 mRNA [low-Foxf1(+/-) mice]. Microvascular development was normal in the surviving newborn high-Foxf1(+/-) mice, which compensated for pulmonary Foxf1 haploinsufficiency and expressed wild-type Foxf1 levels. To identify expression of genes regulated by Foxf1, we used Affymetrix microarrays to determine embryonic lung RNAs influenced by Foxf1 haploinsufficiency. Embryonic Foxf1(+/-) lungs exhibited diminished expression of hepatocyte growth factor receptor c-Met, myosin VI, the transcription factors SP-3, BMI-1, ATF-2, and glucocorticoid receptor, and cell cycle inhibitors p53, p21(Cip1), retinoblastoma, and p107. Furthermore, Notch-2 signaling was decreased in embryonic Foxf1(+/-) lungs, as evidenced by significantly reduced levels of the Notch-2 receptor and the Notch-2 downstream target hairy enhancer of split-1. The severity of the Notch-2-signaling defect in 18-day postcoitus Foxf1(+/-) lungs correlated with Foxf1 mRNA levels. Disruption of pulmonary Notch-2 signaling continued in newborn low-Foxf1(+/-) mice, which died of lung hemorrhage and failed to compensate for Foxf1 haploinsufficiency. In contrast, in newborn high-Foxf1(+/-) lungs, Notch-2 signaling was restored to the level found in wild-type mice, which was associated with normal microvascular formation and survival. Foxf1 haploinsufficiency disrupted pulmonary expression of genes in the Notch-2-signaling pathway and resulted in abnormal development of lung microvasculature.

Animals↗

Two gamma interferon-activated site-like elements in the human cytomegalovirus major immediate-early promoter/enhancer are important for viral replication.

Human cytomegalovirus (HCMV) infection directly initiates a signal transduction pathway that leads to activation of a large number of cellular interferon-stimulated genes (ISGs). Our previous studies demonstrated that two interferon response elements, the interferon-stimulated response element and gamma interferon-activated site (GAS), in the ISG promoters serve as HCMV response sites (VRS). Interestingly, two GAS-like VRS elements (VRS1) were also present in the HCMV major immediate-early promoter-enhancer (MIEP/E). In this study, the importance of these VRS elements in viral replication was investigated. We demonstrate that the expression of the major IE genes, IE1 and IE2, is interferon inducible. To understand the biological significance of this signal transduction pathway in HCMV major IE expression, the two VRS1 in the MIEP/E were mutated. Mutant HCMVs in which the VRS elements were deleted or that contained point mutations grew dramatically more slowly than wild-type virus at a low multiplicity of infection (MOI). Insertion of wild-type VRS1 into the mutant viral genome rescued the slow growth phenotype. Furthermore, the expression levels of major IE RNAs and proteins were greatly reduced during infection with the VRS mutants at a low MOI. HCMV microarray analysis indicated that infection of host cells with the VRS mutant virus resulted in a global reduction in the expression of viral genes. Collectively, these data demonstrate that the two VRS elements in the MIEP/E are necessary for efficient viral gene expression and replication. This study suggests that although the HCMV-initiated signal transduction pathway results in induction of cellular antiviral genes, it also functions to stimulate viral major IE gene expression. This might be a new viral strategy in which the pathway is used to regulate gene expression and play a role in reactivation.

Base Sequence↗

The latent-TGFbeta-binding-protein-1 (LTBP-1) is expressed in the organizer and regulates nodal and activin signaling.

The latent TGF-beta binding proteins (LTBP) are believed to control the availability of TGF-beta in the extracellular milieu. To gain insight into the potential roles of LTBP in early development, we isolated the Xenopus LTBP-1 (xLTBP-1) cDNA. The cDNA encodes a protein similar to the mammalian LTBP-1 in both size and domain structure. In addition, we found a novel longer splice isoform of xLTBP. The RNAs for both forms of xLTBP displayed temporal regulation and the shorter transcript is expressed maternally. Both transcripts also display spatial regulation and are found in the dorsal mesoderm of the organizer. In animal cap experiments, LTBP-1 potentiates the activity of activin and nodal. The activity of LTBP-1 did not appear to require covalent association with activin as the addition of medium containing activin and LTBP-1 to animal caps enhanced the activin effect. These results indicate that LTBP-1 may be part of the regulatory system that establishes the threshold of morphogen activity for activins and nodals in the dorsal side of the embryo during gastrulation.

Activins↗

Regulation of retinoic acid receptor expression in dermal fibroblasts.

Retinoic acid (RA) is known to exert profound effects on growth and differentiation in a variety of cell types in the skin. In vitro studies have also shown that RA modulates gene expression in both fibroblasts and keratinocytes. Recently, three nuclear receptors specific for retinoic acid (RAR alpha, RAR beta, and RAR gamma) have been cloned and all are members of a large multigene family of ligand-inducible transcription enhancer factors. As a first step in defining the role of each receptor in the retinoid response of the skin, we examined the regulation of RAR alpha, RAR beta, and RAR gamma gene expression in human dermal fibroblasts by all-trans-retinoic acid. We demonstrate that human dermal fibroblasts express modest basal levels of RAR alpha and RAR gamma, but not RAR beta. When treated with 1 microM RA, the messenger RNAs for both RAR beta and RAR gamma are induced. In contrast, RAR alpha remains unchanged. The induction of RAR gamma is attenuated by the protein synthesis inhibitor, cycloheximide, while the induction of RAR beta increases slightly. Studies with actinomycin D and cycloheximide show that all three receptors have different half-lives, with RAR gamma having the longest half-life at 8 h. Gel shift analysis of known retinoic acid response elements (RAREs) in the RAR beta and RAR gamma genes demonstrates that the upregulation of these by genes by RA involves increased binding of complexes to the individual RAREs. In summary, these data demonstrate that fibroblasts express all three receptor types. Moreover, striking differences exist in the regulation of RAR gene expression in skin-derived fibroblasts and suggest that each receptor may well have a separate and discrete function in the retinoid response of the skin.

Base Sequence↗

RNAi living-cell microarrays for loss-of-function screens in Drosophila melanogaster cells.

RNA interference (RNAi)-mediated loss-of-function screening in Drosophila melanogaster tissue culture cells is a powerful method for identifying the genes underlying cell biological functions and for annotating the fly genome. Here we describe the development of living-cell microarrays for screening large collections of RNAi-inducing double-stranded RNAs (dsRNAs) in Drosophila cells. The features of the microarrays consist of clusters of cells 200 mum in diameter, each with an RNAi-mediated depletion of a specific gene product. Because of the small size of the features, thousands of distinct dsRNAs can be screened on a single chip. The microarrays are suitable for quantitative and high-content cellular phenotyping and, in combination screens, for the identification of genetic suppressors, enhancers and synthetic lethal interactions. We used a prototype cell microarray with 384 different dsRNAs to identify previously unknown genes that affect cell proliferation and morphology, and, in a combination screen, that regulate dAkt/dPKB phosphorylation in the absence of dPTEN expression.

Animals↗

Stimulatory effect of an indirectly attached RNA helicase-recruiting sequence on the suppression of gene expression by antisense oligonucleotides.

Antisense oligonucleotides (ODNs) are powerful tools with which to determine the consequences of the reduced expression of a selected target gene, and they may have important therapeutic applications. Methods for predicting optimum antisense sites are not always effective because various factors, such as RNA-binding proteins, influence the secondary and tertiary structures of RNAs in vivo. To overcome this obstacle, we have attempted to engineer an antisense system that can unravel secondary and tertiary RNA structures. To create such an antisense system, we connected the constitutive transport element (CTE), an RNA motif that has the ability to interact with intracellular RNA helicases, to an antisense sequence so that helicase-binding hybrid antisense ODN would be produced in cells. We postulated that this modification would enhance antisense activity in vivo, with more frequent hybridization of the antisense ODN with its targeting site. Western blotting analysis demonstrated that a hybrid antisense ODN targeted to the bcl-2 gene suppressed the expression of this gene more effectively than did the antisense ODN alone. Our results suggest that the effects of antisense ODNs can be enhanced when their actions are combined with those of RNA helicases.

Gene Expression Regulation↗