The chaperone dynein LL1 mediates cytoplasmic transport of empty and mature hepatitis B virus capsids

BACKGROUND & AIMS

Hepatitis B virus (HBV) has a DNA genome but replicates within the nucleus by reverse transcription of an RNA pregenome, which is converted to DNA in cytoplasmic capsids. Capsids in this compartment are correlated with inflammation and epitopes of the capsid protein core (Cp) are a major target for T cell-mediated immune responses. We investigated the mechanism of cytoplasmic capsid transport, which is important for infection but also for cytosolic capsid removal.

METHODS

We used virion-derived capsids containing mature rcDNA (matC) and empty capsids (empC). RNA-containing capsids (rnaC) were used as a control. The investigations comprised pull-down assays for identification of cellular interaction partners, immune fluorescence microscopy for their colocalization and electron microscopy after microinjection to determine their biological significance.

RESULTS

matC and empC underwent active transport through the cytoplasm towards the nucleus, while rnaC was poorly transported. We identified the dynein light chain LL1 as a functional interaction partner linking capsids to the dynein motor complex and showed that there is no compensatory transport pathway. Using capsid and dynein LL1 mutants we characterized the required domains on the capsid and LL1.

CONCLUSIONS

This is the first investigation on the detailed molecular mechanism of how matC pass the cytoplasm upon infection and how empC can be actively removed from the cytoplasm into the nucleus. Considering that hepatocytes with cytoplasmic capsids are better recognized by the T cells, we hypothesize that targeting capsid DynLL1-interaction will not only block HBV infection but also stimulate elimination of infected cells.

LAY SUMMARY

In this study, we identified the molecular details of HBV translocation through the cytoplasm. Our evidence offers a new drug target which could not only inhibit infection but also stimulate immune clearance of HBV infected cells.

Importin β Can Bind Hepatitis B Virus Core Protein and Empty Core-Like Particles and Induce Structural Changes

Hepatitis B virus (HBV) capsids are found in many forms: immature single-stranded RNA-filled cores, single-stranded DNA-filled replication intermediates, mature cores with relaxed circular double-stranded DNA, and empty capsids. A capsid, the protein shell of the core, is a complex of 240 copies of core protein. Mature cores are transported to the nucleus by a complex that includes both importin α and importin β (Impα and Impβ), which bind to the core protein's C-terminal domains (CTDs). Here we have investigated the interactions of HBV core protein with importins in vitro. Strikingly, empty capsids and free core protein can bind Impβ without Impα. Cryo-EM image reconstructions show that the CTDs, which are located inside the capsid, can extrude through the capsid to be bound by Impβ. Impβ density localized on the capsid exterior near the quasi-sixfold vertices, suggested a maximum of 30 Impβ per capsid. However, examination of complexes using single molecule charge-detection mass spectrometry indicate that some complexes include over 90 Impβ molecules. Cryo-EM of capsids incubated with excess Impβ shows a population of damaged particles and a population of "dark" particles with internal density, suggesting that Impβ is effectively swallowed by the capsids, which implies that the capsids transiently open and close and can be destabilized by Impβ. Though the in vitro complexes with great excess of Impβ are not biological, these results have implications for trafficking of empty capsids and free core protein; activities that affect the basis of chronic HBV infection.

G-quadruplex DNA and ligand interaction in living cells using NMR spectroscopy

Using in-cell NMR spectroscopy to probe ligand binding to a G-quadruplex nucleic acid.

Gathering structural information from biologically relevant molecules inside living cells has always been a challenging task. In this work, we have used multidimensional NMR spectroscopy to probe DNA G-quadruplexes inside living Xenopus laevis oocytes. Some of these structures can be found in key regions of chromosomes. G-quadruplexes are considered potential anticancer therapeutic targets and several lines of evidence indirectly point out roles in key biological processes, such as cell proliferation, genomic instability or replication initiation. However, direct demonstrations of the existence of G-quadruplexes in vivo are scarce. Using SOFAST-HMQC type spectra, we probed a tetramolecular G-quadruplex model made of d(TG₄T)₄ inside living Xenopus laevis oocytes. Our observations lead us to conclude that the quadruplex structure is formed within the cell and that the intracellular environment preferentially selects a conformation that most resembles the one found in vitro under KCl conditions. We also show for the first time that specific ligands targeting G-quadruplexes can be studied using high resolution NMR directly inside living cells, opening new avenues to study ligand binding discrimination under physiologically relevant conditions with atomic detail.

Inhibition of protein kinase C phosphorylation of hepatitis B virus capsids inhibits virion formation and causes intracellular capsid accumulation

Capsids of hepatitis B virus and other hepadnaviruses contain a cellular protein kinase, which phosphorylates the capsid protein. Some phosphorylation sites are shown to be essential for distinct steps of viral replication as pregenome packaging or plus strand DNA synthesis. Although different protein kinases have been reported to phosphorylate the capsid protein, varying experimental approaches do not allow direct comparison. Furthermore, the activity of a specific protein kinase has not yet been correlated to steps in the hepadnaviral life cycle. In this study we show that capsids from various sources encapsidate active protein kinase Calpha, irrespective of hepatitis B virus genotype and host cell. Treatment of a virion expressing cell line with a pseudosubstrate inhibitor showed that inhibition of protein kinase C phosphorylation did not affect genome maturation but resulted in capsid accumulation and inhibited virion release to the medium. Our results imply that different protein kinases have distinct functions within the hepadnaviral life cycle.

Nuclear entry of hepatitis B virus capsids involves disintegration to protein dimers followed by nuclear reassociation to capsids

Assembly and disassembly of viral capsids are essential steps in the viral life cycle. Studies on their kinetics are mostly performed in vitro, allowing application of biochemical, biophysical and visualizing techniques. In vivo kinetics are poorly understood and the transferability of the in vitro models to the cellular environment remains speculative. We analyzed capsid disassembly of the hepatitis B virus in digitonin-permeabilized cells which support nuclear capsid entry and subsequent genome release. Using gradient centrifugation, size exclusion chromatography and immune fluorescence microscopy of digitonin-permeabilized cells, we showed that capsids open and close reversibly. In the absence of RNA, capsid re-assembly slows down; the capsids remain disintegrated and enter the nucleus as protein dimers or irregular polymers. Upon the presence of cellular RNA, capsids re-assemble in the nucleus. We conclude that reversible genome release from hepatitis B virus capsids is a unique strategy different from that of other viruses, which employs irreversible capsid destruction for genome release. The results allowed us to propose a model of HBV genome release in which the unique environment of the nuclear pore favors HBV capsid disassembly reaction, while both cytoplasm and nucleus favor capsid assembly.

Viral capsids facilitate protection of the enclosed viral genome and participate in the intracellular transport of the genome. At the site of replication capsids have to release the genome, but after replication new capsids have to be assembled for encapsidation of the progeny genomes. Detailed data on stability of capsids and kinetics of their formation and dissociation are obtained for several viruses in vitro, allowing biophysical or electron microscopical techniques. These approaches, however, do not consider the impact of cellular interaction partners. Using digitonin-permeabilized cells which support hepadnaviral genome release actively, we analyzed the disassembly kinetic of the hepatitis B virus (HBV) capsid. Using different analytical methods we found that HBV capsids disintegrate to protein dimers which reassemble to capsids inside the nucleus. The study provides a link between in vitro and in vivo data showing that HBV uses a unique strategy. We propose a model in which the unique environment of the nuclear pore favors the disassembly reaction, while both cytoplasm and nucleus favor assembly.

Rupture of mitral chorda tendinea following blunt chest trauma

Acute mitral insufficiency, originated from rupture of mitral chordae tendineae secondary to nonpenetrating thoracic trauma, is an unusual condition. This diagnosis is difficult to establish because physical examination, electrocardiogram, and cardiac enzymes are neither sensitive nor specific. The diagnosis of rupture must be quickly established because this disorder may be fatal. This paper reports the case of a patient with acute mitral insufficiency secondary to a mitral valve chord rupture a week after a nonpenetrating thoracic trauma.

Formation of N-branched oligonucleotides as by-products in solid-phase oligonucleotide synthesis

During the synthesis of oligonucleotides by the standard phosphoramidite method using 2'-deoxycytidine- derivatized solid support, a side reaction was observed that gave rise to the formation of high molecular weight N-branched oligomers having two identical chains linked to the 3'-terminal 2'-deoxycytidine. Postsynthesis treatment with neat triethylamine trihydrofluoride selectively cleaved the phosphoramidate linkage and converted the N-branched oligomers back to the expected oligonucleotides.

In vitro selection procedures for identifying DNA and RNA aptamers targeted to nucleic acids and proteins

In vitro selection or systematic evolution of ligands by exponential enrichment is a combinatorial procedure that allows the identification of oligonucleotides showing properties of interest-so-called aptamers-through iterative selection/amplification rounds. Libraries containing as many as 1014 different sequences can be screened against a wide range of molecules. Ribonucleic acid (RNA), deoxyribonucleic acid (DNA), or chemically modified aptamers generally display high affinity and exquisite specificity of interaction with the target. Aptamers show a promising potential for diagnostic and therapeutic purposes. We describe here methods successfully used in our laboratory for the selection of RNA or DNA aptamers against an RNA structure (the transactivation response element of HIV-1) and a protein (the human ribonuclease H1).

Selective inhibitory DNA aptamers of the human RNase H1

Human RNase H1 binds double-stranded RNA via its N-terminal domain and RNA-DNA hybrid via its C-terminal RNase H domain, the latter being closely related to Escherichia coli RNase HI. Using SELEX, we have generated a set of DNA sequences that can bind efficiently (K(d) values ranging from 10 to 80 nM) to the human RNase H1. None of them could fold into a simple perfect double-stranded DNA hairpin confirming that double-stranded DNA does not constitute a trivial ligand for the enzyme. Only two of the 37 DNA aptamers selected were inhibitors of human RNase H1 activity. The two inhibitory oligomers, V-2 and VI-2, were quite different in structure with V-2 folding into a large, imperfect but stable hairpin loop. The VI-2 structure consists of a central region unimolecular quadruplex formed by stacking of two guanine quartets flanked by the 5' and 3' tails that form a stem of six base pairs. Base pairing between the 5' and 3' tails appears crucial for conferring the inhibitory properties to the aptamer. Finally, the inhibitory aptamers were capable of completely abolishing the action of an antisense oligonucleotide in a rabbit reticulocyte lysate supplemented with human RNase H1, with IC50 ranging from 50 to 100 nM.

Saline spa water or combined water and UV-B for psoriasis vs conventional UV-B: lessons from the Salies de Béarn randomized study

OBJECTIVE

To study the effects of UV-B therapy and saline spa water given alone or in combination for the treatment of psoriasis.

DESIGN

Randomized, controlled, comparative study with blinded observers.

SETTING

Salies de Béarn, saline spa water center located in the southwest of France.

PARTICIPANTS

Seventy-one adult patients with psoriasis with a Psoriasis Area and Severity Index (PASI) score greater than 10.

INTERVENTION

Patients were randomly assigned to 1 of 3 treatments: spa water alone (group A); UV-B 311-nm phototherapy alone (group B); and a combination of the 2 therapies (group C). The 3 groups were treated on a daily basis 5 days a week for a total of 21 days.

MAIN OUTCOME MEASURES

Change in PASI score from baseline as determined by an investigator blinded to randomization; variation in quality of life, adverse effects, and long-term effects (1 year after treatment).

RESULTS

Four patients dropped out because of secondary effects. Efficacy was similar in groups B and C, with changes in PASI of -64% and -55%, respectively at 3 weeks. For group A, change in PASI was -29%, thus showing a minor therapeutic effect of saline spa water alone and poor efficacy compared with groups B and C (P<.001). More adverse effects were reported in groups A and C but did not reach significance. Combined saline spa water and UV-B therapy had no sparing effect on UV-B dosages. One year after treatment, no long-term benefit could be attributed specifically to a given regimen, but the patients had overall significantly better PASI scores than at baseline.

CONCLUSIONS

Saline spa water alone had a minor therapeutic effect in psoriasis, and the beneficial effect of bathing to enhance phototherapy was not demonstrated.

RNA and N3'-->P5' kissing aptamers targeted to the trans-activation responsive (TAR) RNA of the human immunodeficiency virus-1

We used in vitro selection to identify RNA aptamers able to selectively bind to the TAR RNA motif of HIV-1, an unperfect RNA hairpin involved in the transcription of the retroviral genome. We selected aptameric RNA hairpins giving rise to kissing complexes with TAR. The N3'-->P5' phosphoramidate variant of the aptamer bind to TAR with a Kd in the low nanomolar range. However, only the RNA-RNA loop-loop complex is recognized by the Rop protein of E. coli which is specific for kissing complexes.

Eukaryotic ribonucleases HI and HII generate characteristic hydrolytic patterns on DNA-RNA hybrids: further evidence that mitochondrial RNase H is an RNase HII

RNase H activities from HeLa cells (either of cytoplasmic or mitochondrial origin), and from mitochondria of beef heart and Xenopus ovaries, have been tested with RNA-DNA substrates of defined length (20 bp) and sequence. Substrates were either blunt-ended, or presented DNA or RNA overhangs. The hydrolysis profiles obtained at early times of the digestion showed a good correlation between the class of RNase H, either type I or II assigned according to biochemical parameters, whatever the organism. Consequently, the pattern of primary cuts can be considered as a signature of the predominant RNase H activity. For a given sequence, hydrolysis profiles obtained are similar, if not identical, for either blunt-ended substrates or those presenting overhangs. However, profiles showed variations depending on the sequence used. Of the three sequences tested, one appears very discriminatory, class I RNases H generating a unique primary cut 3 nt from the 3' end of the RNA strand, whereas class II RNases H generated two simultaneous primary cuts at 6 and at 8 nt from the 5' end of the RNA strand. Hydrolysis profiles further confirm the assignation of the mitochondrial RNase H activity from HeLa cells, beef heart and Xenopus oocytes to the class II.

Detection of proteins binding to short RNA.DNA hybrids or short antisense oligonucleotides in Xenopus laevis oocytes and human macrophage cell extracts by photoaffinity radiolabeling

Using a 12 base pair RNA.DNA hybrid, substituted with bromouracil on either the RNA or DNA strand, we have detected by photoaffinity radiolabeling a limited set of proteins able to bind to RNA.DNA hybrids in both Xenopus oocyte extracts and human macrophage extracts. Resulting patterns of crosslinked proteins were highly dependent on the strand (DNA or RNA) that was substituted. With one exception, none of the proteins investigated in competition experiments was found to be absolutely specific for RNA.DNA hybrids, as at least one other nucleic acid, either single-stranded DNA or single-stranded RNA, was found to compete efficiently. None of the proteins detected in this assay correspond to the size expected for RNases H. Using the same methodology, we have detected proteins that bind to short oligodeoxyribonucleotides. Although we have essentially detected in Xenopus oocytes one prominent protein of approximately 75 kDa, corresponding to replication protein A (RPA) whatever the oligonucleotide used, the patterns obtained with extracts of human macrophages were more complex and dependent on the oligonucleotide used. If a protein corresponding to RPA was observed most of the time, other crosslinks of similar or sometimes higher intensity were also detected. Interestingly, among these, one protein of 35 kDa appears paradoxically to bind and crosslink to a dodecamer but not to an octadecamer containing the same sequence placed either at its 3'-end or 5'-end.

Immunometric assay of BN 52080, a heptapeptide C-terminal analogue of sorbin

A novel type of enzyme immunometric assay has been developed for a heptapeptide, BN 52080. This compound is a short C-terminal analogue of sorbin and is under clinical evaluation for treatment of chronic diarrhea. In this solid-phase immobilized epitope immunoassay (SPIE-IA), the peptide is first immunologically bound to polyclonal antibodies adsorbed to a solid phase and then, after covalent immobilization with glutaraldehyde, is released from the antibody paratope by NaOH. The peptide linked to the solid phase is further quantified with a tracer consisting of the same antibodies purified by affinity chromatography and coupled to acetylcholinesterase. This assay has a detection limit of 10 pg/ml and is therefore five times more sensitive than competitive enzyme immunoassay using the same antibodies and BN 52080 coupled to acetylcholinesterase as tracer. The assay is specific and allows direct measurement of peptide in human plasma after subcutaneous or intravenous administration of 200 micrograms of BN 52080 to volunteers.

Purification and characterization of human ribonuclease HII

A ribonuclease H activity from human placenta has been separated by ion exchange chromatography from the major RNase HI enzyme. Additional chromatographic steps allowed further purification, more than 3,000 fold compared to the crude extract in which it represents about 15% of the total RNase H activity. The enzyme requires Mg2+ ions for its activity, is strongly inhibited by the addition of Mn2+ ions or other divalent transition metal ions, and exhibits a pH optimum between 8.5 and 9. It shows a strong sensitivity to the SH-blocking agent N-ethylmaleimide. It has a strict specificity for double-stranded RNA-DNA duplexes and exhibits neither single-stranded nor double-stranded RNase (or DNase) activities. Therefore, this enzyme displays the characteristics of class II RNase H and is now termed RNase HII. Renaturation gel assays and gel filtration experiments proved a monomeric structure for the active enzyme with a native molecular weight of about 33 kDa. The human RNase HII acts as an endonuclease and releases oligoribonucleotides with 3'-OH and 5'-phosphate ends. It is therefore a candidate for the RNase H-mediated effect of antisense oligodeoxynucleotides.

Characterization and subcellular localization of ribonuclease H activities from Xenopus laevis oocytes

Ribonuclease H activities present in fully grown Xenopus oocytes were investigated by using either liquid assays or renaturation gel assays. Whereas the test in solution detected an apparently unique class I ribonuclease H activity, the activity gels did not detect this enzyme but another one with the molecular weight expected for a class II ribonuclease H. The ribonuclease HI was found to be primarily concentrated in the germinal vesicle, but around 5% of this activity was detectged in the cytoplasm and may correspond to the activity involved in antisense oligonucleotide-mediated destruction of messenger RNAs. The concentration of this class I ribonuclease H in oocytes is similar to that in somatic cells. The class II ribonuclease H remained undetectable by the test in solution because its activity was cryptic. On activity gel, a polypeptide with the apparent molecular mass of 32 kDa, expected for a ribonuclease HII, was found to be concentrated in mitochondria although no RNase H activity could be detected by using the liquid assay. Based on sedimentation studies, we hypothesize that the apparent absence of RNase H activity in solution could be the result of the association of this 32-kDa polypeptide with other polypeptides, or possibly nucleic acids, to form a multimer of, until now, unknown function.

Production of double-stranded RNA during synthesis of bromouracil-substituted RNA by transcription with T7 RNA polymerase

Using T7 RNA polymerase we synthesized a short oligoribonucleotide containing bromouracil by in vitro transcription of a synthetic DNA template. Whereas the major transcript obtained had the expected size and was apparently homogeneous on a sequencing gel, additional analysis revealed the presence of double-stranded RNA in this preparation. As this was not observed when the same template was transcribed in the presence of uracil, we hypothesize that bromouracil promoted the apparition of double-stranded 'parasitic' RNA presumably by favouring priming for the RNA-dependent RNA synthesis of the T7 RNA polymerase or by facilitating an end-to-end copy mechanism.

RNA template-directed RNA synthesis by T7 RNA polymerase

In an attempt to synthesize an oligoribonucleotide by run-off transcription by bacteriophage T7 RNA polymerase, a major transcript was produced that was much longer than expected. Analysis of the reaction indicated that the product resulted from initial DNA-directed run-off transcription followed by RNA template-directed RNA synthesis. This reaction occurred because the RNA made from the DNA template displayed self-complementarity at its 3' end and therefore could form an intra- or intermolecular primed template. In reactions containing only an RNA template, the rate of incorporation of NTPs was quite comparable to DNA-dependent transcription. RNA template-directed RNA synthesis has been found to occur with a great number of oligoribonucleotides, even with primed templates that are only marginally stable. In one instance, we observed a multistep extension reaction converting the oligonucleotide into a final product longer than twice its original length. Presumably, such a process could have generated some of the RNAs found to be efficiently replicated by T7 RNA polymerase.

Sensitive detection of low levels of ribonuclease H activity by an improved renaturation gel assay

Renaturation gel assays are good tools to assign enzymatic activities to protein bands. First, proteins are separated by denaturating electrophoresis on substrate-containing gels. Then, following the elimination of the denaturing agent, polypeptides are allowed to renature, thus leading to the degradation of the embedded substrate at positions at which the corresponding activity has moved. Nevertheless, this in situ technique does not only reflect a certain amount of enzyme activity, it also depends upon the ability of an enzyme to renature. Here we present a renaturation gel assay procedure with an improved sensitivity and discuss the detection of E. coli and human ribonuclease H activities as an example.

Characterization of ribonuclease H activities present in two cell-free protein synthesizing systems, the wheat germ extract and the rabbit reticulocyte lysate

Experimental evidence accumulated to date by several research groups indicates that antisense oligodeoxynucleotides targeted against messenger RNA (mRNA) sequences located downstream of the initiation codon fail to inhibit the translation of this mRNA unless the hybrid is cleaved by RNase H. It has previously been shown that exogenous RNase H has to be added to rabbit reticulocyte lysate to obtain translational arrest (unless freshly prepared lysates are used). In contrast there is no need of exogenous RNase H by using wheat germ extract for translation because the level of endogenous RNase H is high enough to ensure cleavage of the hybrid formed between the antisense oligodeoxyribonucleotide and its complementary sequence on the mRNA. Surprisingly, we found that these two cell-free translation systems display similar amounts of RNase H activities when tested under standard conditions (extract diluted 500 times in the RNase H reaction mix). The RNase H activity of the rabbit reticulocyte lysate has a divalent cation requirement and sensitivity to inhibitors similar to class I ribonuclease H, whereas the activity of the wheat germ extract shows similarities to class II ribonuclease H. However, when these activities were assayed under conditions similar to those used for translation experiments, only highly reduced levels of activity were found in comparison to the standard assays. This reduction is due in part to sub-optimal ionic conditions for the endogenous RNase H activities in these extracts, and, for the other part, likely due to interactions with other proteins present in the lysates. In these conditions, however, the remaining activity found in the wheat germ extract was three times higher than the activity found in the rabbit reticulocyte lysate. Whether this difference can by itself explain the indicated differences in the two systems observed in hybrid-arrest of translation experiments remains open to discussion.

Inhibition of translation initiation by antisense oligonucleotides via an RNase-H independent mechanism

We have used alpha-oligomers as antisense oligonucleotides complementary to three different sequences of the rabbit beta-globin mRNA: a region adjacent to the cap site, a region spanning the AUG initiation codon or a sequence in the coding region. These alpha-oligonucleotides were synthesized either with a free 5' OH group or linked to an acridine derivative. The effect of these oligonucleotides on mRNA translation was investigated in cell-free extracts and in Xenopus oocytes. In rabbit reticulocyte lysate and in wheat germ extracts oligomers targeted to the cap site and the initiation codon reduced beta-globin synthesis in a dose-dependent manner, whereas the target mRNA remained intact. The anti-cap alpha-oligomer was even more efficient that its beta-counterpart in rabbit reticulocyte lysate. In contrast, only the alpha-oligomer, linked to the acridine derivative, complementary to the cap region displayed significant antisense properties in Xenopus oocytes. Therefore initiation of translation can be arrested by oligonucleotide/RNA hybrids which are not substrates for RNase-H.

[Antisense oligonucleotides: tools of molecular genetics and therapeutic agents]

The binding of an oligodeoxynucleotide, so-called anti-sense, to the complementary sequence of a messenger RNA can prevent the synthesis of the encoded protein. This approach constitutes a very efficient and specific means to artificially regulate gene expression. Numerous chemical modifications have been introduced into synthetic oligos in order to provide them with properties that unmodified molecules do not display. For instance, oligos built up with methylphosphonate, phosphorothioate and alpha-anomer units lead to molecules that are resistant to DNases. Acridine-linked oligos exhibit an increased affinity for the target sequence due to the intercalation of the dye into the oligo/RNA duplex. Two different mechanisms account for translation inhibition by antisense oligos. Inhibition of the elongation step results only from the induced cleavage of the target RNA by RNase-H. In contrast, oligos targeted upstream of the AUG initiation codon can block the initiation step through an RNase-H independent mechanism. As a consequence, methylphosphonate- and alpha-oligos, which do not elicit RNase-H activity, targeted to the 5' region, are efficient antisense; but they are inactive if targeted to the coding sequence. Experiments performed with antisense oligos in cell-free extracts supported the notion that the mini-exon sequence, acquired by trans-splicing, was present on every message in trypanosomatids and on some of them in nematodes. Furthermore, an acridine-linked oligo complementary to the mini-exon sequence of Trypanosoma brucei induced a lethal effect on cultured procyclics. Therefore these compounds constitute promising tools in molecular genetics and could open new routes to rationally tailor therapeutic agents.

Phosphoroselenoate oligodeoxynucleotides: synthesis, physico-chemical characterization, anti-sense inhibitory properties and anti-HIV activity

Oligodeoxynucleotides with a phosphorus atom in which one of the non-bridging oxygen atoms is substituted by selenium were prepared and investigated with respect to their antisense properties. A general synthesis of phosphoroselenoate analogs of oligonucleotides is described using potassium selenocyanate as the selenium donor. The compounds, characterized by 31P NMR, were shown to decompose to phosphate with a half-life of ca. 30 days. Melting temperatures of duplexes between poly(rA) or poly(rI) with oligo(dT) and oligo(dC), respectively, indicate diminished hybridization capability of phosphoroselenoate oligomers relative to both the unmodified phosphodiester oligomers and the phosphorothioate congeners. A phosphoroselenoate 17-mer is a sequence specific inhibitor of rabbit beta-globin synthesis in wheat germ extract and in injected Xenopus oocytes. In contrast phosphoroselenoate analogs are potent non-sequence specific inhibitors in rabbit reticulocyte lysate. In vitro HIV assays were carried out on a phosphoroselenoate sequence and compared with a phosphorothioate analogue that has previously been shown to exhibit anti-HIV activity (Matsukura et al., Proc. Natl. Acad. Sci. (1987) 84, 7706-7710). The phosphoroselenoate was somewhat less active, and was much more toxic to the cells.

Comparative inhibition of rabbit globin mRNA translation by modified antisense oligodeoxynucleotides

We have studied the translation of rabbit globin mRNA in cell free systems (reticulocyte lysate and wheat germ extract) and in microinjected Xenopus oocytes in the presence of anti-sense oligodeoxynucleotides. Results obtained with the unmodified all-oxygen compounds were compared with those obtained when phosphorothioate or alpha-DNA was used. In the wheat germ system a 17-mer sequence targeted to the coding region of beta-globin mRNA was specifically inhibitory when either the unmodified phosphodiester oligonucleotide or its phosphorothioate analogue were used. In contrast no effect was observed with the alpha-oligomer. These results were ascribed to the fact that phosphorothioate oligomers elicit an RNase-H activity comparable to the all-oxygen congeners, while alpha-DNA/mRNA hybrids were a poor substrate. Microinjected Xenopus oocytes followed a similar pattern. The phosphorothioate oligomer was more efficient to prevent translation than the unmodified 17-mer. Inhibition of beta-globin synthesis was observed in the nanomolar concentration range. This result can be ascribed to the nuclease resistance of phosphorothioates as compared to natural phosphodiester linkages, alpha-oligomers were devoid of any inhibitory effect up to 30 microM. Phosphorothioate oligodeoxyribonucleotides were shown to be non-specific inhibitors of protein translation, at concentrations in the micromolar range, in both cell-free systems and oocytes. Non-specific inhibition of translation was dependent on the length of the phosphorothioate oligomer. These non-specific effects were not observed with the unmodified or the alpha-oligonucleotides.

Specific inhibition of endogenous beta-tubulin synthesis in Xenopus oocytes by anti-messenger oligodeoxynucleotides

An oligodeoxynucleotide containing 27 nucleotides, complementary to a highly conserved sequence of beta-tubulin mRNAs, led to a nearly complete inhibition of beta-tubulin synthesis in Xenopus oocytes after microinjection. Inhibition persisted 24 hours post-injection and was specific for beta-tubulin as the synthesis of alpha-tubulin as well as that of other proteins from the oocyte was not affected. Complete inhibition of beta-tubulin synthesis did not prevent progesterone-induced meiotic maturation and formation of the chromosome spindle. This result indicates that the pool of endogenous tubulin already present in fully-grown oocytes is sufficient to allow normal meiotic maturation. This finding correlates with previous experiments showing that the turn-over of tubulin is very slow in the oocyte.

Rate of degradation of [alpha]- and [beta]-oligodeoxynucleotides in Xenopus oocytes. Implications for anti-messenger strategies

End-labelled oligodeoxynucleotides were injected into Xenopus laevis oocytes and their degradation products were analysed by high-performance ion-exchange liquid chromatography after various times of incubation. The oligonucleotides were synthesised with either the natural [beta] anomers or the synthetic [alpha] anomers of deoxynucleotide units. Oligo-[beta] deoxynucleotides are short-lived inside oocytes (half-life approximately equal to 10 min). Covalent attachment of an intercalating agent to the 3'-phosphate and of a methylthiophosphate group at the 5'-end protects oligodeoxynucleotides against 3'- and 5'-exonucleases, respectively. The half-life of such substituted oligodeoxynucleotides is increased to 40 minutes. Oligo-[alpha]-deoxynucleotides are quite resistant to both endo and exonucleases inside Xenopus oocytes. After 8 hours only 40% of a 16-mer oligo-[alpha]-deoxynucleotide were hydrolysed. The rapid degradation of oligo-[beta]-deoxynucleotides suggests that efficient inhibition of translation in Xenopus oocytes involves an RNase H-induced hydrolysis of mRNAs hybridized to oligo-[beta]-deoxynucleotides.

Enzymatic amplification of translation inhibition of rabbit beta-globin mRNA mediated by anti-messenger oligodeoxynucleotides covalently linked to intercalating agents

The effects of anti-messenger oligodeoxynucleotides, covalently linked to an intercalating agent, on translation of rabbit beta-globin mRNA, were investigated both in wheat germ extract and in microinjected Xenopus oocytes. A specific inhibition of beta-globin synthesis was observed in both expression systems with a modified 11-mer covalently linked to an acridine derivative. In injected oocytes a more efficient block was observed with this modified oligonucleotide than with its unsubstituted homolog. This was ascribed to stacking interactions of the intercalating agent with base pairs which provide an additional stabilization of the [mRNA/DNA] hybrid. We demonstrated that in wheat germ extract, the modified and unmodified oligonucleotides behaved similarly due to the presence of a high RNaseH activity. RNaseH was also present, although to a lesser extent, in the oocyte cytoplasm. This anti-messenger DNA-induced degradation of target mRNA resulted in amplified efficiency of hybrid-arrested translation. This additional mechanism might provide anti-sense DNAs with an advantage over anti-sense RNAs.

Kinetic studies of recA protein binding to a fluorescent single-stranded polynucleotide

Fluorescence spectroscopy was used to investigate the binding of Escherichia coli recA protein to a single-stranded polynucleotide. Poly(deoxy-1,N6-ethenoadenylic acid) was prepared by reaction of chloroacetaldehyde with poly(deoxyadenylic acid). The fluorescence of poly(deoxy-1,N6-ethenoadenylic acid) was enhanced upon recA protein binding. The kinetics of the binding process were studied as a function of several parameters: ionic concentration (KCl and MgCl2), pH, nature of the nucleoside triphosphate [adenosine 5'-triphosphate or adenosine 5'-O-(gamma-thiotriphosphate)], protein and polynucleotide concentrations, polynucleotide chain length, and order of sequential additions. The observed kinetic curves exhibited a lag phase followed by a slow binding process characteristic of a nucleation-elongation mechanism with an additional slow step governing the rate of the association process. The lag phase reflecting the nucleation step was not observed when the protein was first bound to the polynucleotide before addition of adenosine 5'-triphosphate. Adenosine 5'-triphosphate induced a dissociation of the recA protein, which was immediately followed by binding of the recA-adenosine 5'-triphosphate-Mg2+ ternary complex. The origin of this "mnemonic effect" and of the different kinetic steps is discussed with respect to protein conformational changes and aggregation phenomena.

The empty delta sign: frequency and significance in 76 cases of dural sinus thrombosis

The presence of the empty delta sign on contrast material-enhanced computed tomographic (CT) scans of the brain is considered pathognomonic of sagittal sinus thrombosis (SST); however, a valid explanation for its appearance is lacking, despite several hypotheses. To determine the frequency of the sign and its prognostic significance, 76 reported cases (112 CT manifestations) of SST and SST-related intracranial sinovenous occlusive disease were reviewed. Ten CT signs related to both disease processes were reported; the empty delta sign was the most frequently reported sign (28.6%) of SST. Patients with hemorrhagic infarction and/or the empty delta sign on CT scans had the poorest prognosis. A case illustrative of the empty delta sign is described in which there was engorgement of endothelial- and nonendothelial-lined spaces in the dura mater with hemorrhagic rupture into the dural leaf. The empty delta sign can probably be explained on the basis of the rich dural venous collateral circulation, consisting primarily of lateral lacunae, a vascular mesh (dural cavernous spaces), and meningeal venous tributaries.

Reactive gliosis simulating butterfly glioma: a neuroradiological case study

Reactive gliosis was found in a 40-year-old man who presented with intractable seizures thought to be due to a malignant neoplasm. Although two separate lesions located bilaterally in the frontal lobes were evident on the computed tomographic scan, a connection between these lesions along the fibers of the corpus callosum was clearly demonstrated on T2-weighted magnetic resonance images. The unusual radiological appearance of this gliosis, which simulated a malignant butterfly glioma on magnetic resonance imaging (MRI), is reported. Because MRI is still a new modality, its images should be interpreted with judicious caution.

Anti-messenger oligodeoxynucleotides: specific inhibition of rabbit beta-globin synthesis in wheat germ extracts and Xenopus oocytes

Oligodeoxyribonucleotides complementary to the initiation region of rabbit beta-globin messenger RNA were used to selectively inhibit translation in a wheat germ extract and in injected Xenopus oocytes. The oligonucleotides interacted specifically with their RNA target as shown by thermal denaturation studies of hybrids on nitrocellulose filters. The longest oligonucleotide used (17-mer) efficiently blocked translation both in vitro and in vivo. In contrast the shortest one (8-mer) exhibited only a limited effect. The translation block was specific. The synthesis of endogenous proteins in oocytes and that of alpha-globin in the in vitro system were not affected by anti-beta-globin oligonucleotides. A non-complementary oligonucleotide had no inhibitory effect.

Binding of recA protein from E. coli to double-stranded DNA: influence of the degree of superhelicity

The binding of the recA protein from E. coli to supercoiled double-stranded DNA is strongly dependent upon the superhelical density of the DNA molecule. A threshold of superhelical density is required for strong binding in the presence of ATP. This finding is consistent with a model in which recA protein first binds to unpaired regions and then polymerises on the contiguous double-stranded lattice.

Absorption and fluorescence studies of the binding of the recA gene product from E. coli to single-stranded and double-stranded DNA. Ionic strength dependence

The binding of the recA gene product from E. coli to double-stranded and single-stranded nucleic acids has been investigated by following the change in melting temperature of duplex DNA and the fluorescence of single-stranded DNA or poly(dA) modified by reaction with chloroacetaldehyde. At low ionic strength, in the absence of Mg2+ ions, RecA protein binds preferentially to duplex DNA or poly(dA-dT). This leads to an increase of the DNA melting temperature. Stabilization of duplex DNA decreases when ionic strength or pH increases. In the presence of Mg2+ ions, preferential binding to single-stranded polynucleotides is observed. Precipitation occurs when duplex DNA begins to melt in the presence of RecA protein. From competition experiments, different single-stranded and double-stranded polydeoxynucleotides can be ranked according to their ability to bind RecA protein. Structural changes induced in nucleic acids upon RecA binding are discussed together with conformational changes induced in RecA protein upon magnesium binding.

Binding of RecA protein to single-stranded nucleic acids: spectroscopic studies using fluorescent polynucleotides

Binding of the recA gene product from Escherichia coli to single-stranded polynucleotides has been investigated using poly(dA) that have been modified by chloroacetaldehyde to yield fluorescent 1,N6-ethenoadenine (epsilon A) bases. A strong enhancement of the fluorescent quantum yield of poly(d epsilon A) is induced upon RecA protein binding. A 4-fold increase is observed in the absence of ATP or ATP gamma S and a 7-fold increase in the presence of either nucleoside triphosphate. RecA protein can bind to poly(d epsilon A) in the absence of both Mg2+ ions and ATP (or ATP gamma S) but Mg2+ ions are required to observe RecA protein binding in the presence of ATP (or ATP gamma S) at pH 7.5. ATP binding to the RecA-poly(d epsilon A) complex induces a dissociation of RecA from the polynucleotide followed by re-binding of [RecA-ATP-Mg2+] ternary complex. Whereas ATP-induced dissociation of RecA-poly(d epsilon A) complexes is a fast process, the subsequent binding reaction of [RecA-ATP-Mg2+] is slow. A model is proposed whereby [RecA-ATP-Mg2+] binding to poly(d epsilon A) involves slow nucleation and elongation processes along the polynucleotide backbone. The nucleation reaction is shown to involve at least a trimer or a tetramer. Polymerization of the [RecA-ATP-Mg2+] ternary complex stops when the polynucleotide is entirely covered with 6 +/- 1 nucleotides per RecA monomer. ATP hydrolysis then induces a release of RecA-ADP complexes from the polynucleotide template.

[Multiple biotin-dependent carboxylase deficiencies (author's transl)]

Two patients presented in early childhood with: 1) alopecia, skin rashs, and candida dermatitis; 2) severe hypotonia, ataxia and motor retardation; 3) frequent episodes of ketoacidosis with hyperlactacidemia. Propionic and methylcrotonic aciduria only appeared on hyperprotidic diet. Mitochondrial biotin-dependent carboxylase activities were decreased in the liver and leukocytes, but were paradoxically normal in cultured fibroblasts whatever the biotin content of the medium. These disorders responded to biotin administration, pointing to multiple biotin-dependent carboxylase deficiencies (MCD). Our report stresses the polymorphism of MCD: major discrepancies concern predominance of carboxylase deficiency, expression of MCD in cultured fibroblasts, and possible involvement of a cytoplasmic biotin enzyme, acetyl CoA carboxylase (ACC). Finally, we suggest that MCD could be of two types: impaired biotin metabolism (absorption, transport, activation) might result in generalization MCD involving ACC. Defective holocarboxylase synthetase might lead to a pure mitochondrial MCD with fibroblastic deficiency and presumably skin integrity.