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PubMed1987

Autoregulation of tubulin expression is achieved through specific degradation of polysomal tubulin mRNAs.

We have utilized protein synthesis inhibitors to investigate the autoregulatory mechanism that uses the concentration of unpolymerized tubulin subunits to specify tubulin mRNA content in animal cells. Puromycin and pactamycin, both of which remove RNAs from polysomes, completely unlink tubulin RNA content from the level of free subunits, whereas pretreatment of cells with cycloheximide, which traps mRNAs onto stalled polyribosomes, enhances the specific degradation of tubulin RNAs in response to increases in the subunit content. Moreover, in the absence of protein synthesis inhibitors, the tubulin RNAs that are lost from cells with elevated free tubulin subunit levels are those that are associated with polyribosomes. Further, beta-tubulin mRNAs encoding a truncated translation product of only 26 amino acids (and that cannot be polyribosomal) are not substrates for autoregulation. We conclude that autoregulation of tubulin synthesis is achieved by specifically altering the stability of tubulin RNAs that are bound to polyribosomes.

Animals↗
PubMed2001

Mutations in hepatitis C virus RNAs conferring cell culture adaptation.

As an initial approach to studying the molecular replication mechanisms of hepatitis C virus (HCV), a major causative agent of acute and chronic liver disease, we have recently developed selectable self-replicating RNAs. These replicons lacked the region encoding the structural proteins and instead carried the gene encoding the neomycin phosphotransferase. Although the replication levels of these RNAs within selected cells were high, the number of G418-resistant colonies was reproducibly low. In a search for the reason, we performed a detailed analysis of replicating HCV RNAs and identified several adaptive mutations enhancing the efficiency of colony formation by several orders of magnitude. Adaptive mutations were found in nearly every nonstructural protein but not in the 5' or 3' nontranslated regions. The most drastic effect was found with a single-amino-acid substitution in NS5B, increasing the number of colonies approximately 500-fold. This mutation was conserved with RNAs isolated from one cell line, in contrast to other amino acid substitutions enhancing the efficiency of colony formation to a much lesser extent. Interestingly, some combinations of these nonconserved mutations with the highly adaptive one reduced the efficiency of colony formation drastically, suggesting that some adaptive mutations are not compatible.

3' Untranslated Regions↗
PubMed2006

Germinal vesicle material drives meiotic cell cycle of mouse oocyte through the 3'UTR-dependent control of cyclin B1 synthesis.

We compared the profile of histone H1 kinase activity, reflecting Maturation Promoting Factor (MPF) activity in oocytes bisected at the germinal vesicle (GV) stage and allowed to mature as separate oocyte halves in vitro. Whereas the oocyte halves containing the nucleus exhibited the same profile of increased kinase activity as that typical for intact oocytes, the anuclear halves revealed strong inhibition of the increase in this activity soon after germinal vesicle breakdown (GVBD). In contrast, the profile of MAP kinase activity did not differ significantly between anuclear and nucleus-containing oocyte halves throughout maturation. Of the two MPF components, CDK1 and cyclin B1, the amount of the latter was significantly reduced in anuclear halves, a reduction due to low-level synthesis and not to enhanced degradation. Expression of three reporter luciferase RNAs constructed, respectively, to contain cyclin B1-specific 3'UTR, the globin-specific 3'UTR, or no 3'UTR sequence was enhanced in nuclear halves, with significantly greater enhancement for the construct containing cyclin B1-specific 3'UTR as compared to the two other RNAs. We conclude that the profile of activity of MPF during mouse oocyte maturation is controlled by an unknown GV-associated factor(s) acting via 3'UTR-dependent control of cyclin B1 synthesis. These results require the revision of the hitherto prevailing view that the control of MPF activity during mouse oocyte maturation is independent of GV-derived material.

3' Untranslated Regions↗
PubMed1982

Transient expression of the chicken lysozyme gene after transfer into human cells.

The chicken lysozyme gene was inserted into an SV40-based plasmid vector, and the recombinants were transfected into the human cell lines HeLa and MCF-7. Correct and efficient transient expression directed by the lysozyme promoter was found in both of these cell lines, as determined by S1 nuclease mapping and Northern blot analysis of the RNAs made. SV40 sequences dramatically enhance the expression of the lysozyme gene. This enhancing effect is only acting in cis and is distance/orientation dependent, since clones containing the lysozyme gene in either orientation produce different amounts of correct lysozyme transcripts. The transfected lysozyme gene was not induced by steroid hormone treatment of the cells.

Breast Neoplasms↗
PubMed1987

The transcription of B2 repeated sequences is regulated during the transition from quiescent to proliferative state in cultured rodent cells.

The RNA polymerase III-dependent transcription of B2 repeated sequences has been monitored during the transition from the quiescent to proliferative state in cultured rodent cells and after polyomavirus-induced transformation. The level of RNAs containing B2 sequences was found to be higher in both the proliferative state of normal cells and in polyomavirus-transformed cells. In both systems, nuclear run-off transcription assays indicated that high levels of B2 RNAs are due to an enhanced transcription rate. These results suggest the presence of a B2-specific RNA pol III transcription factor(s) whose activity is sensitive to cell cycle progression and oncogenic transformation.

Animals↗
PubMed2005

The highly structured encapsidation signal of MuLV RNA is involved in the nuclear export of its unspliced RNA.

The encapsidation signal (Psi) of retroviruses is located in the 5' UTR of the viral genomic unspliced transcript and is highly structured. In the Psi of murine leukaemia virus (MuLV), four stem-loops, called A, B, C and D, promote dimerization and encapsidation of the MuLV unspliced RNA into virions. Through analysis of Psi-deleted transcripts, we found that the AB and CD motifs independently enhanced the cytoplasmic accumulation of RNAs. Furthermore, we showed that over-expression of the Psi sequence in the infected cells led to a competition with the nuclear export of unspliced MuLV transcripts, revealing a new function for these stem-loops in the transport of viral intron-containing RNAs from the nucleus to the cytoplasm.

5' Untranslated Regions↗
PubMed2006

Interaction of viruses with the mammalian RNA interference pathway.

It has been known for some time that plants and insects use RNA interference (RNAi) as nucleic acid-based immunity against viral infections. However, it was unknown whether mammalian cells employ the RNA interference pathway as an antiviral mechanism as well. Over the past years, it has become clear that a variety of viruses, first in plants but recently in insect and mammalian viruses as well, encode suppressors of the RNAi pathway arguing for an antiviral role of this machinery. More recent findings have revealed that certain viruses encode their own microRNAs or microRNA-like RNA molecules, which are processed by the mammalian RNAi machinery. Furthermore, host-encoded microRNAs have been shown to both silence and enhance intracellular levels of viral RNAs. These findings argue that interactions between the RNAi pathway and viral genomes can profoundly affect the outcomes of the viral life cycles and contribute to the pathogenic signatures of the infectious agents.

Animals↗
PubMed1990

Prediction of rho-independent Escherichia coli transcription terminators. A statistical analysis of their RNA stem-loop structures.

Escherichia coli rho-independent transcription terminators are characterized by an RNA structure having a G+C-rich stem-loop followed by a series of uridine residues, but they can be only partially predicted by the stability of this structure or by its primary sequence. A large number of such terminators have been identified or proposed in the literature, and we have constituted a list of them (148 found in 1021 x 10(3) base-pairs of E. coli DNA sequences) in order to analyze statistically the corresponding RNA hairpins. We show that the size of the loops presents a narrow distribution, that their sequences are not random, and that most loops are closed by a C.G base-pair. In particular, 55% of the loops are tetranucleotides and the most abundant loop sequences are UUCG and GAAA. These loops are abundant in prokaryotic and eukaryotic RNAs, and are known to enhance the stability of RNA hairpins. We propose that these tetraloops play an important role in the nucleation of the nascent RNA structures, as does also the presence of a C.G base-pair closing a hairpin loop. This analysis allows us to propose a model of formation of an RNA hairpin during the termination process and to construct an algorithm of prediction of the terminators in a given DNA sequence. For the E. coli sequences, it clearly distinguishes inter- from intracistronic terminator-like structures, and selects 141 of the 148 rho-independent terminators given in the literature, with a very low background. It also predicts with reasonable accuracy the in vitro termination efficiency of known rho-independent terminators, as well as predicting the existence of 35 as yet uncharacterized terminators.

Algorithms↗
PubMed2003

Interferon-gamma induces p11 gene and protein expression in human epithelial cells through interferon-gamma-activated sequences in the p11 promoter.

The effect of interferon (IFN)-gamma on p11 expression was studied in two human epithelial cell lines (BEAS-2B and HeLa). Treatment with IFN-gamma resulted in increased steady-state levels of p11 mRNA and protein expression, with a time-dependent and dose-dependent effect. Transient transfection experiments of a reporter gene construct containing 1498 bp of the 5'-flanking region of the p11 promoter demonstrated that IFN-gamma induced p11 gene expression at the transcriptional level. These effects were inhibited at the promoter and protein levels by a specific JAK-2 kinase inhibitor, AG-490. Functional analysis of the p11 promoter indicates that two gamma-activated sequence elements (GAS) located at positions 1219 and 1090 are important for the induction of the p11 promoter by IFN-gamma. Transfection of mutated reporter constructs demonstrated that the mutation at the GAS-2 site (1090) inhibited the p11 promoter activity, with a reduction of about approximately 73% and mutation at the GAS-3 site (1219) eliminated about 26% of the p11 promoter activity. A STAT1 dominant negative mutant vector at Tyr-701 (JAK kinase phosphorylation site) blocked the effect of IFN-gamma on the p11 promoter activity. IFN-gamma induced a rapid tyrosine phosphorylation and nuclear translocation of STAT1 protein, which is involved in the binding to the GAS-2 site in the p11 promoter by EMSA analysis. These data suggest that IFN-gamma-induced p11 expression is mediated through the binding of STAT1 to GAS sites in the p11 promoter. Inhibition of p11 expression by inhibitory antisense RNAs (iRNA) treatment resulted in enhanced IFN-gamma and calcium ionophore-stimulated arachidonic acid release suggesting that at least in part IFN-gamma-stimulated p11 expression may serve a counterregulatory role.

Annexin A2↗
PubMed1999

Inhibitory mechanism of anti-P30-52 monoclonal antibody against human immunodeficiency virus type 1 (HIV-1) multiplication in infected MT-4 cells.

We have studied the immunological role of human immunodeficiency virus type 1 (HIV-1) p17 because the p17 antibody titer is high in asymptomatic patients and decreases with disease progression. Previously we found that monoclonal antibody (MAb) reactive to the p17-derived peptide 30 to 52 amino acids in length, namely P30-52 MAb, had cross-reactivity to the third variable region of the envelope glycoprotein of HIV-1 (Env V3) and also inhibited the viral multiplication of the supernatant of HIV-1-infected MT-4 cells co-cultured with the MAb. The relation between the cross-reactivity of the P30-52 MAb and the inhibitory mechanism is not clear; however, P30-52 might be useful for the development of therapeutic and vaccination strategies. In the present study, we examined the suppressive mechanism of the P30-52 MAbs, and found that the copy number of HIV-1 RNA in HIV-1-infected MT-4 cells was not reduced by the addition of the P30-52 MAbs, and the expression of RNAs of p17 was slightly enhanced 3 hr after the infection, although that of Env V3 was the same as the control level. In contrast, the expression of cellular p17 DNA and p17 protein was reduced by the addition of the P30-52 MAbs. In conclusion, the P30-52 MAbs did not suppress the HIV-1 mRNA level in the infected cells, but might inhibit DNA synthesis, and consequently bring about a reduction of p17 protein synthesis and a decrease of infectivity of the supernatant. The results demonstrated that the P30-52 MAb could be used as immunotherapeutic substance for HIV-1.

Animals↗
PubMed1990

Translational control in influenza virus-infected cells.

Influenza virus type A has been shown to establish a translational control system such that during infection there is a dramatic inhibition of host cell protein synthesis and viral mRNAs are selectively and efficiently translated. The following review summarizes the complex strategies employed by influenza to accomplish these goals. These include: (i) preventing newly made cellular mRNAs from entering the cytoplasm of infected cells; (ii) inhibiting the initiation and elongation steps of translation of preexisting cellular mRNAs; (iii) possessing RNAs with structural features which enhance translation; (iv) encoding mechanisms to downregulate the interferon induced protein kinase thus allowing overall protein synthesis levels to remain high.

Animals↗
PubMed2003

Whole-genome screening indicates a possible burst of formation of processed pseudogenes and Alu repeats by particular L1 subfamilies in ancestral primates.

BACKGROUND: Abundant pseudogenes are a feature of mammalian genomes. Processed pseudogenes (PPs) are reverse transcribed from mRNAs. Recent molecular biological studies show that mammalian long interspersed element 1 (L1)-encoded proteins may have been involved in PP reverse transcription. Here, we present the first comprehensive analysis of human PPs using all known human genes as queries. RESULTS: The human genome was queried and 3,664 candidate PPs were identified. The most abundant were copies of genes encoding keratin 18, glyceraldehyde-3-phosphate dehydrogenase and ribosomal protein L21. A simple method was developed to estimate the level of nucleotide substitutions (and therefore the age) of PPs. A Poisson-like age distribution was obtained with a mean age close to that of the Alu repeats, the predominant human short interspersed elements. These data suggest a nearly simultaneous burst of PP and Alu formation in the genomes of ancestral primates. The peak period of amplification of these two distinct retrotransposons was estimated to be 40-50 million years ago. Concordant amplification of certain L1 subfamilies with PPs and Alus was observed. CONCLUSIONS: We suggest that a burst of formation of PPs and Alus occurred in the genome of ancestral primates. One possible mechanism is that proteins encoded by members of particular L1 subfamilies acquired an enhanced ability to recognize cytosolic RNAs in trans.

Algorithms↗
PubMed2001

Selective delivery of estradiol to bone by aspartic acid oligopeptide and its effects on ovariectomized mice.

We have developed a novel osteotropic prodrug of estradiol (E(2)) conjugated with L-Asp-hexapeptide (E(2).3D(6)), which has very low affinity for estrogen receptors, and in this study, we examined its pharmacokinetic behavior and pharmacological potential. After a single iv injection of E(2) x 3D(6) to mice, the half-time for elimination from plasma was about 100 min; however, E(2) was selectively delivered to the bone and eliminated very slowly, declining to the endogenous level at about 7 days. After a single iv injection of E(2), the half-time in plasma was about 70 min, whereas E(2) was highly distributed to the uterus, and the bone concentration of E(2) was only slightly increased at 6 h. When E(2) (0.37 micromol/kg, sc, every third day) or E(2) x 3D(6) (0.11 to 1.1 micromol/kg, sc, every seventh day) was administered to OVX mice for 4 weeks, E(2) increased the bone mineral density (BMD) together with weights of liver and uterus, whereas E(2) x 3D(6) increased only the BMD, in a dose-dependent manner. E(2) x 3D(6) enhanced the expression of messenger RNAs of bone matrix proteins (osteopontin, bone sialoprotein, type I collagen alpha) of OVX mice at 4 h after administration, but E(2) did very slightly. These results indicate that the E(2) prodrug was delivered to the bone, where it gradually released E(2), thereby ameliorating bone loss. This acidic oligopeptide appears to be a good candidate for selective drug delivery to bone.

Animals↗
PubMed1992

Interaction of two cis sites with the RNA replicase of the yeast L-A virus.

L-A is a 4.6-kilobase double-stranded RNA virus of Saccharomyces cerevisiae. The in vitro L-A replication reaction ((-)-strand synthesis) requires an internal site 400 bases from the 3' end in addition to the 3'-terminal 30 nucleotides of the L-A (+)-single-stranded RNA. Elimination of the internal site reduces the template activity 5-10-fold. Here we investigate how the internal site can stimulate the replication reaction which starts at the 3' end of the template. When these two sites are split into two distinct RNA molecules, the internal site can no longer stimulate replication (no trans-activation). However, establishment of an intermolecular hydrogen bonding between these RNAs restored the replication-enhancing activity of the internal site. This result is consistent with a model wherein L-A's RNA polymerase interacts first with the internal site and then with the 3' end site by either looping or by a local dissociation-reassociation mechanism. These results, however, clearly eliminate anchored tracking and sliding models which require continuity of the RNA molecule between these two cis sites.

Autoradiography↗
PubMedDate not supplied

[Mechanism for suppression mRNA translation with antisense oligonucleotides].

Experimental studies of the effects of antisense oligonucleotides on translation of mRNAs in cell-free systems are reviewed. Oligonucleotides complementary to the leader sequences or to the sequence overlapping the initiating codon region of mRNAs inhibit translation of the messengers. In the presence of ribonuclease H, oligodeoxyribonucleotides and their phosphorothioate analogs complementary either to the mentioned mRNA regions or to the mRNA coding sequence suppress the translation due to the RNAs cleavage. This inhibition-enhancing mechanism does not operate in the case of the oligonucleotide analogs--oligonucleoside methylphosphonates and oligonucleotides built of the alpha-nucleosides, since the complexes formed by RNA and these analogs are not substrates of the ribonuclease H. The translation inhibition efficiency is determined by the oligonucleotides lengths and by the availability of the complementary sequence in the mRNA structure. The oligonucleotides inhibitory power can be improved by the coupling to the oligonucleotides of the intercalating groups and the reactive groups.

Cell-Free System↗
PubMed1993

Production of fibrogenic cytokines by interleukin-2-treated peripheral blood leukocytes: expression of transforming growth factor-beta and platelet-derived growth factor B chain genes.

OBJECTIVE: To assess the production of fibrogenic cytokines by interleukin-2 (IL-2)-stimulated peripheral blood leukocytes and to examine their ability to stimulate the production of connective tissue. METHODS: Culture medium from human peripheral blood leukocytes incubated with or without IL-2 was tested for induction of fibroblast proliferation, collagen synthesis, and expression of cytokine genes. RESULTS: Supernatants from IL-2-treated peripheral blood leukocytes induced six times more fibroblast proliferation than medium from leukocytes cultured without IL-2. The expression of type I procollagen and fibronectin messenger RNAs was increased in human fibroblasts in response to leukocyte supernatants. Unstimulated leukocytes expressed minimal levels of transforming growth factor-beta or platelet-derived growth factor B chain messenger RNAs, but could be greatly enhanced by IL-2 treatment. CONCLUSION: Mediators that induce connective tissue production are secreted by IL-2-treated peripheral blood leukocytes. These cytokines may be responsible, in part, for the stimulation of abdominal adhesions in patients receiving intraperitoneal immunotherapy.

Animals↗
PubMed2006

[Double sites short hairpin RNAs targeting epidermal growth factor receptor to promote colon cancer cells apoptosis and enhance 5-fluorouracil chemotherapy effect].

OBJECTIVE: To investigate the differences about RNA interference (RNAi) technique which focuses on single or multiple sites to suppress colon cancer LoVo cell line's epidermal growth factor receptor (EGFR) mRNA and protein expression, induce cell apoptosis and enhance 5-fluorouracil (5-FU) sensitivity. METHODS: The human colon cancer LoVo cells were transfected by liposome with pU6-EGFR-shRNA-1 and pU6-EGFR-shRNA-2 expressive vectors which were established by p Genesil-1 plasmid and EGFR short hairpin RNA (shRNA) synthesized in vitro, then were selected for 4 weeks by using G418. Five groups were selected for the study: Group 1: the normal cultured LoVo cells; Group 2: the negative control plasmid HK; Group 3: pU6-EGFR-shRNA-1 plasmid vector; Group 4: pU6-EGFR-shRNA-2 plasmid vector; Group 5: pU6-EGFR-shRNA-1 and pU6-EGFR-shRNA-2, half for each. The mRNA and protein expression were assessed using Real Time PCR and Western blot, the cell apoptosis was determined via flow cytometry, and the suppressive rate and IC(50) to LoVo cells by 5-FU of different concentrations and time points were carried out by using Cell Counting Kit-8 (CCK-8). RESULTS: Expression plasmids encoding shRNA were successfully established and transfected into the LoVo cells. In group 3, 4 and 5, the mRNA expression was decreased by (80.2 +/- 3.4)%, (81.3 +/- 2.8)% and (90.6 +/- 2.8)%, respectively, and protein expression was decreased by (74.1 +/- 4.0)%, (73.4 +/- 2.3)% and (90.4 +/- 3.3)%, respectively; meanwhile, cell apoptosis increased by (10.4 +/- 0.5)%, (10.1 +/- 0.4)% and (14.2 +/- 0.5)%, respectively. The IC(50) of 5-FU and cell suppressive rate analysis demonstrated that there were significant differences among group 5, groups 3 and 4, and groups 1 and 2, but there were no significant difference between group 1 and group 2, as well as group 3 and group 4. CONCLUSIONS: Both pU6-EGFR-shRNA-1 and pU6-EGFR-shRNA-2 were capable of suppressing EGFR expression of LoVo cells, and therefore promoting apoptosis and increasing the cell toxicity of 5-FU. The targeting double combined sites RNAi technique was significantly better than single site interference. The new therapeutic modalities in the treatment of human colon cancer are suggested by this study.

Apoptosis↗
PubMed1997

Use of differential display analysis to assess the effect of human cytomegalovirus infection on the accumulation of cellular RNAs: induction of interferon-responsive RNAs.

We used differential display analysis to identify mRNAs that accumulate to enhanced levels in human cytomegalovirus-infected cells as compared with mock-infected cells. RNAs were compared at 8 hr after infection of primary human fibroblasts. Fifty-seven partial cDNA clones were isolated, representing about 26 differentially expressed mRNAs. Eleven of the mRNAs were virus-coded, and 15 were of cellular origin. Six of the partial cDNA sequences have not been reported previously. All of the cellular mRNAs identified in the screen are induced by interferon alpha. The induction in virus-infected cells, however, does not involve the action of interferon or other small signaling molecules. Neutralizing antibodies that block virus infection also block the induction. These RNAs accumulate after infection with virus that has been inactivated by treatment with UV light, indicating that the inducer is present in virions. We conclude that human cytomegalovirus induces interferon-responsive mRNAs.

Cells, Cultured↗