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Biomedical subjects

E Ehrenfeld

Publications and source records attributed to E Ehrenfeld.

At least 19 recordsLinked to original sources
PubMed2001

Requirements for assembly of poliovirus replication complexes and negative-strand RNA synthesis.

HeLa cells were transfected with several plasmids that encoded all poliovirus (PV) nonstructural proteins. Viral RNAs were transcribed by T7 RNA polymerase expressed from recombinant vaccinia virus. All plasmids produced similar amounts of viral proteins that were processed identically; however, RNAs were designed either to serve as templates for replication or to contain mutations predicted to prevent RNA replication. The mutations included substitution of the entire PV 5' noncoding region (NCR) with the encephalomyocarditis virus (EMCV) internal ribosomal entry site, thereby deleting the 5'-terminal cloverleaf-like structure, or insertion of three nucleotides in the 3Dpol coding sequence. Production of viral proteins was sufficient to induce the characteristic reorganization of intracellular membranes into heterogeneous-sized vesicles, independent of RNA replication. The vesicles were stably associated with viral RNA only when RNA replication could occur. Nonreplicating RNAs localized to distinct, nonoverlapping regions in the cell, excluded from the viral protein-membrane complexes. The absence of accumulation of positive-strand RNA from both mutated RNAs in transfected cells was documented. In addition, no minus-strand RNA was produced from the EMCV chimeric template RNA in vitro. These data show that the 5'-terminal sequences of PV RNA are essential for initiation of minus-strand RNA synthesis at its 3' end.

Cytoplasmic Vesicles↗
PubMed2000

Formation of the poliovirus replication complex requires coupled viral translation, vesicle production, and viral RNA synthesis.

Poliovirus (PV) infection induces the rearrangement of intracellular membranes into characteristic vesicles which assemble into an RNA replication complex. To investigate this transformation, endoplasmic reticulum (ER) membranes in HeLa cells were modified by the expression of different cellular or viral membrane-binding proteins. The membrane-binding proteins induced two types of membrane alterations, i.e., extended membrane sheets and vesicles similar to those found during a PV infection. Cells expressing membrane-binding proteins were superinfected with PV and then analyzed for virus replication, location of membranes, viral protein, and RNA by immunofluorescence and fluorescent in situ hybridization. Cultures expressing cellular or viral membrane-binding proteins, but not those expressing soluble proteins, showed a markedly reduced ability to support PV replication as a consequence of the modification of ER membranes. The altered membranes, regardless of their morphology, were not used for the formation of viral replication complexes during a subsequent PV infection. Specifically, membrane sheets were not substrates for PV-induced vesicle formation, and, surprisingly, vesicles induced by and carrying one or all of the PV replication proteins did not contribute to replication complexes formed by the superinfecting PV. The formation of replication complexes required active viral RNA replication. The extensive alterations induced by membrane-binding proteins in the ER resulted in reduced viral protein synthesis, thus affecting the number of cells supporting PV multiplication. Our data suggest that a functional replication complex is formed in cis, in a coupled process involving viral translation, membrane modification and vesicle budding, and viral RNA synthesis.

Coated Vesicles↗
PubMed1999

Differential utilization of poly(rC) binding protein 2 in translation directed by picornavirus IRES elements.

The translation of picornavirus genomic RNAs occurs by a cap-independent mechanism that requires the formation of specific ribonucleoprotein complexes involving host cell factors and highly structured regions of picornavirus 5' noncoding regions known as internal ribosome entry sites (IRES). Although a number of cellular proteins have been shown to be involved in picornavirus RNA translation, the precise role of these factors in picornavirus internal ribosome entry is not understood. In this report, we provide evidence for the existence of distinct mechanisms for the internal initiation of translation between type I and type II picornavirus IRES elements. In vitro translation reactions were conducted in HeLa cell cytoplasmic translation extracts that were depleted of the cellular protein, poly(rC) binding protein 2 (PCBP2). Upon depletion of PCBP2, these extracts possessed a significantly diminished capacity to translate reporter RNAs containing the type I IRES elements of poliovirus, coxsackievirus, or human rhinovirus linked to luciferase; however, the addition of recombinant PCBP2 could reconstitute translation. Furthermore, RNA electrophoretic mobility-shift analysis demonstrated specific interactions between PCBP2 and both type I and type II picornavirus IRES elements; however, the translation of reporter RNAs containing the type II IRES elements of encephalomyocarditis virus and foot-and-mouth disease virus was not PCBP2 dependent. These data demonstrate that PCBP2 is essential for the internal initiation of translation on picornavirus type I IRES elements but is dispensable for translation directed by the structurally distinct type II elements.

5' Untranslated Regions↗
PubMed1999

Requirements for RNA replication of a poliovirus replicon by coxsackievirus B3 RNA polymerase.

A chimeric poliovirus type 1 (PV1) genome was constructed in which the 3D RNA polymerase (3D(pol)) coding sequences were replaced with those from coxsackievirus B3 (CVB3). No infectious virus was produced from HeLa cells transfected with the chimeric RNA. Processing of the PV1 capsid protein precursor was incomplete, presumably due to inefficient recognition of the P1 protein substrate by the chimeric 3CD proteinase containing CVB3 3D sequences. The ability of the chimeric RNA to replicate in the absence of capsid formation was measured after replacement of the P1 region with a luciferase reporter gene. No RNA synthesis was detected, despite efficient production of enzymatically active 3D(pol) from the 3D portion of the chimeric 3CD. The chimeric 3CD protein was unable to efficiently bind to the cloverleaf-like structure (CL) at the 5' end of PV1 RNA, which has been demonstrated previously to be required for viral RNA synthesis. The CVB3 3CD protein bound the PV1 CL as well as PV1 3CD. An additional chimeric PV1 RNA that contained CVB3 3CD sequences also failed to produce virus after transfection. Since processing of PV1 capsid protein precursors by the CVB3 3CD was again incomplete, a luciferase-containing replicon was also analyzed for RNA replication. The 3CD chimera replicated at 33 degrees C, but not at 37 degrees C. Replacement of the PV1 5'-terminal CL with that of CVB3 did not rescue the temperature-sensitive phenotype. Thus, there is an essential interaction(s) between 3CD and other viral P2 or P3 protein products required for efficient RNA replication which is not fully achieved between proteins from the two different members of the same virus genus.

Blotting, Western↗
PubMed1999

Hepatitis A virus capsid protein VP1 has a heterogeneous C terminus.

Hepatitis A virus (HAV) encodes a single polyprotein which is posttranslationally processed into the functional structural and nonstructural proteins. Only one protease, viral protease 3C, has been implicated in the nine protein scissions. Processing of the capsid protein precursor region generates a unique intermediate, PX (VP1-2A), which accumulates in infected cells and is assumed to serve as precursor to VP1 found in virions, although the details of this reaction have not been determined. Coexpression in transfected cells of a variety of P1 precursor proteins with viral protease 3C demonstrated efficient production of PX, as well as VP0 and VP3; however, no mature VP1 protein was detected. To identify the C-terminal amino acid residue of HAV VP1, we performed peptide sequence analysis by protease-catalyzed [18O]H2O incorporation followed by liquid chromatography ion-trap microspray tandem mass spectrometry of HAV VP1 isolated from purified virions. Two different cell culture-adapted isolates of HAV, strains HM175pE and HM175p35, were used for these analyses. VP1 preparations from both virus isolates contained heterogeneous C termini. The predominant C-terminal amino acid in both virus preparations was VP1-Ser274, which is located N terminal to a methionine residue in VP1-2A. In addition, the analysis of HM175pE recovered smaller amounts of amino acids VP1-Glu273 and VP1-Thr272. In the case of HM175p35, which contains valine at amino acid position VP1-273, VP1-Thr272 was found in addition to VP1-Ser274. The data suggest that HAV 3C is not the protease responsible for generation of the VP1 C terminus. We propose the involvement of host cell protease(s) in the production of HAV VP1.

3C Viral Proteases↗
PubMed1998

Effects of poliovirus 3AB protein on 3D polymerase-catalyzed reaction.

Poliovirus RNA replication requires the activities of a viral RNA-dependent RNA polymerase, 3Dpol, in conjunction with several additional viral and likely cellular proteins. The importance of both the 3A and 3B coding regions has been documented previously by genetic tests, and their biochemical activities have been the subject of several recent investigations. In this study, we examined the previously reported stimulation of 3D-catalyzed RNA synthesis by 3AB. We show that 3AB does not stimulate RNA synthesis on templates that are stably base paired to a primer, indicating that 3AB does not stabilize or otherwise activate 3Dpol for chain elongation. Similarly, it does not alter the kinetic parameters or binding affinities of 3D for substrates. In the absence of a primer, or in the presence of a primer that does not form a stable hybrid with the template, 3AB increases the utilization of 3'-hydroxyl termini as sites for chain elongation by 3D, and thereby stimulates RNA synthesis. 3AB may interact with and stabilize these sites and/or may recruit 3Dpol to the site, resulting in stimulation of the initiation of elongation events. We propose that this activity is required for stabilizing weak interactions that occur during nucleotidyl-protein-primed initiation events in the viral RNA replication complex.

Base Sequence↗
PubMed1998

trans-encapsidation of a poliovirus replicon by different picornavirus capsid proteins.

A trans-encapsidation assay was established to study the specificity of picornavirus RNA encapsidation. A poliovirus replicon with the luciferase gene replacing the capsid protein-coding region was coexpressed in transfected HeLa cells with capsid proteins from homologous or heterologous virus. Successful trans-encapsidation resulted in assembly and production of virions whose replication, upon subsequent infection of HeLa cells, was accompanied by expression of luciferase activity. The amount of luciferase activity was proportional to the amount of trans-encapsidated virus produced from the cotransfection. When poliovirus capsid proteins were supplied in trans, >2 x 10(6) infectious particles/ml were produced. When coxsackievirus B3, human rhinovirus 14, mengovirus, or hepatitis A virus (HAV) capsid proteins were supplied in trans, all but HAV showed some encapsidation of the replicon. The overall encapsidation efficiency of the replicon RNA by heterologous capsid proteins was significantly lower than when poliovirus capsid was used. trans-encapsidated particles could be completely neutralized with specific antisera against each of the donor virus capsids. The results indicate that encapsidation is regulated by specific viral nucleic acid and protein sequences.

Capsid↗
PubMed1998

Interaction of poly(rC) binding protein 2 with the 5' noncoding region of hepatitis A virus RNA and its effects on translation.

Utilization of internal ribosome entry segment (IRES) structures in the 5' noncoding region (5'NCR) of picornavirus RNAs for initiation of translation requires a number of host cell factors whose distribution may vary in different cells and whose requirement may vary for different picornaviruses. We have examined the requirement of the cellular protein poly(rC) binding protein 2 (PCBP2) for hepatitis A virus (HAV) RNA translation. PCBP2 has recently been identified as a factor required for translation and replication of poliovirus (PV) RNA. PCBP2 was shown to be present in FRhK-4 cells, which are permissive for growth of HAV, as it is in HeLa cells, which support translation of HAV RNA but which have not been reported to host replication of the virus. Competition RNA mobility shift assays showed that the 5'NCR of HAV RNA competed for binding of PCBP2 with a probe representing stem-loop IV of the PV 5'NCR. The binding site on HAV RNA was mapped to nucleotides 1 to 157, which includes a pyrimidine-rich sequence. HeLa cell extracts that had been depleted of PCBP2 by passage over a PV stem-loop IV RNA affinity column supported only low levels of HAV RNA translation. Translation activity was restored upon addition of recombinant PCBP2 to the depleted extract. Removal of the 5'-terminal 138 nucleotides of the HAV RNA, or removal of the entire IRES, eliminated the dependence of HAV RNA translation on PCBP2.

Binding Sites↗
PubMed1998

Coding sequences enhance internal initiation of translation by hepatitis A virus RNA in vitro.

Hepatitis A virus (HAV), unlike other picornaviruses, has a slow-growth phenotype in permissive cell lines and in general does not induce host cell cytopathology. Although there are no published reports of productive infection of HeLa cells by HAV, HAV RNA appears to be readily translated in HeLa cells when transcribed by T7 RNA polymerase provided by a recombinant vaccinia virus. The 5' noncoding region of HAV was fused to poliovirus (PV) coding sequences to determine the effect on translation efficiency in HeLa cell extracts in vitro. Conditions were optimized for utilization of the HAV internal ribosome entry segment (IRES). Transcripts from chimeric constructs fused precisely at the initiation codon were translated very poorly. However, chimeric RNAs which included 114 or more nucleotides from the HAV capsid coding sequences downstream of the initiation codon were translated much more efficiently than those lacking these sequences, making HAV-directed translation efficiency similar to that directed by the PV IRES. Sixty-six nucleotides were insufficient to confer increased translation efficiency. The most 5'-terminal HAV 138 nucleotides, previously determined to be upstream of the IRES, had an inhibitory effect on translation efficiency. Constructs lacking these terminal sequences, or those in which the PV 5'-terminal sequences replaced those from HAV, translated three- to fourfold better than those with the intact HAV 5'-terminal end.

Cell Extracts↗
PubMed1997

Induction of intracellular membrane rearrangements by HAV proteins 2C and 2BC.

Hepatitis A virus (HAV) is distinguished from other picornaviruses by its slow and relatively poor, noncytopathic growth in cultures of mammalian cells. The 2C and 2BC proteins of HAV have been implicated in the determination of virus growth in cultured cells. The homologous proteins from other picornaviruses, such as poliovirus, have been demonstrated to exhibit multiple activities, such as RNA binding, nucleotide binding and NTPase, and membrane binding and reorganization. At least some of these activities are required for viral RNA replication. We report here that HAV 2C and 2BC proteins, like their poliovirus counterparts, can induce rearrangement of intracellular membranes and directly or indirectly interact with membranes. Therefore, the inefficient replication properties of HAV are not consequences of the inherent ability of 2C (2BC) to interact with membranes. The effect of 2C (2BC) protein sequences derived from a cell culture-adapted (cc) strain of HAV was compared with that of corresponding protein sequences from either a wild-type (wt) strain of HAV or a faster replicating cytopathic (cp) strain. The analysis demonstrated that mutations acquired in wt virus during adaptation to cell culture do not change dramatically either the ability of these proteins to associate with membranes and induce membrane alterations or the specific architecture of the induced membrane structures. On the other hand, 2C, but not 2BC, protein from the cp strain of HAV induced different membrane structures.

Gene Expression Regulation↗
PubMed1997

One of two NTP binding sites in poliovirus RNA polymerase required for RNA replication.

The poliovirus RNA-dependent RNA polymerase (3Dpol) has been shown to contain two NTP binding sites by chemical cross-linking of oxidized nucleotide to the intact protein. Only one site (Lys-61) was shown to be essential for RNA chain elongation activity by purified enzyme; however, a full-length viral RNA, coding for an altered lysine residue (K276L) in the second site, generated virus with a minute plaque phenotype that rapidly reverted to a wild-type phenotype with Arg-276 replacing Leu-276 in 3D. Viruses with lysine to leucine substitutions in other positions of the second binding site of their polymerase proteins grew with wild-type phenotype. To test the significance of the second binding site, poliovirus 3Dpol was generated with lysine (wild-type), leucine, or arginine at residue 276 and tested for NTP cross-linking using 32P-oxidized GTP. Analysis of cyanogen bromide peptides of each 3D preparation showed that the second NTP binding site had severely reduced NTP binding in mu276(Leu) but not in the revertant mu276(Arg), despite the reported requirement for lysine in the cross-linking reaction. To eliminate the possibility that 32P-oxidized GTP cross-linked to Arg at residue 276, a model system was designed with unmodified amino acid or acetylated (alpha-amino) amino acid and 32P-oxidized GTP. Cross-linking to lysine, but not leucine or arginine, was observed thus eliminating the possibility that NTP could be cross-linked to residue 276 in 3D. We conclude that NTP binding at the second site in poliovirus 3D is at lysine residues at positions other than 276 (278 or 283), and nucleotide binding at these sites has no bearing on elongation activity or replication of the virus. Nucleotide binding only at the site including Lys-61 is essential for RNA replication.

Arginine↗
PubMed1997

Poliovirus 2C protein determinants of membrane binding and rearrangements in mammalian cells.

Poliovirus protein 2C is a 329-amino acid-protein that is essential for viral RNA synthesis and may perform multiple functions. In infected cells, it is associated with virus-specific membrane vesicles. Recombinant 2C protein expressed in transfected cells has been shown to associate with and induce rearrangement of the intracellular membrane network. This study was designed to map the determinants of membrane binding and rearrangement in the 2C protein. Computer-assisted analysis of the protein sequence led to a prediction that the protein folds into a structure composed of three domains. Expression plasmids that encode each or combinations of these predicted domains were used to examine the abilities of the partial protein sequences to associate with intracellular membranes and to induce rearrangement of these membranes in HeLa cells. Biochemical fractionation procedures suggested that the N-terminal region of the protein was required for membrane association. Electron microscopic and immunoelectron microscopic observation showed that both the N- and C-terminal regions, but not the central portion, of 2C protein interact with intracellular membranes and induce major changes in their morphology. The central portion, when fused to the N-terminal region, altered the specific membrane architecture induced by the N-terminal region, giving rise to vesicles resembling those observed during poliovirus infection.

Binding Sites↗
PubMed1997

Requirement of poly(rC) binding protein 2 for translation of poliovirus RNA.

Poly(rC) binding protein 2 (PCBP2) is one of several cellular proteins that interact specifically with a major stem-loop domain in the poliovirus internal ribosome entry site. HeLa cell extracts subjected to stem-loop IV RNA affinity chromatography were depleted of all detectable PCBP2. Such extracts were unable to efficiently translate poliovirus RNA, although extracts recovered from control columns of matrix unlinked to RNA retained full translation activity. Both translation and production of infectious progeny virus were restored in the PCBP2-depleted extracts by addition of recombinant PCBP2, but not by PCBP1, which is a closely related member of the protein family. The data show that PCBP2 is an essential factor, which is required for efficient translation of poliovirus RNA in HeLa cells.

DNA-Binding Proteins↗
PubMed1997

Poly (rC) binding protein 2 forms a ternary complex with the 5'-terminal sequences of poliovirus RNA and the viral 3CD proteinase.

Poly(rC) binding protein 2 (PCBP2) forms a specific ribonucleoprotein (RNP) complex with the 5'-terminal sequences of poliovirus genomic RNA, as determined by electrophoretic mobility shift assay. Mutational analysis showed that binding requires the wild-type nucleotide sequence at positions 20-25. This sequence is predicted to localize to a specific stem-loop within a cloverleaf-like secondary structure element at the 5'-terminus of the viral RNA. Addition of purified poliovirus 3CD to the PCBP2/RNA binding reaction results in the formation of a ternary complex, whose electrophoretic mobility is further retarded. These properties are consistent with those described for the unidentified cellular protein in the RNP complex described by Andino et al. (Andino R, Rieckhof GE, Achacoso PL, Baltimore D, 1993, EMBO J 12:3587-3598). Dicistronic RNAs containing mutations in the 5' cloverleaf-like structure of poliovirus that abate PCBP2 binding show a decrease in RNA replication and translation of gene products directed by the poliovirus 5' noncoding region in vitro, suggesting that the interaction of PCBP2 with these sequences performs a dual role in the virus life cycle by facilitating both viral protein synthesis and initiation of viral RNA synthesis.

3C Viral Proteases↗
PubMed1996

Poly(rC) binding protein 2 binds to stem-loop IV of the poliovirus RNA 5' noncoding region: identification by automated liquid chromatography-tandem mass spectrometry.

The 5' noncoding region of poliovirus RNA contains an internal ribosome entry site (IRES) for cap-independent initiation of translation. Utilization of the IRES requires the participation of one or more cellular proteins that mediate events in the translation initiation reaction, but whose biochemical roles have not been defined. In this report, we identify a cellular RNA binding protein isolated from the ribosomal salt wash of uninfected HeLa cells that specifically binds to stem-loop IV, a domain located in the central part of the poliovirus IRES. The protein was isolated by specific RNA affinity chromatography, and 55% of its sequence was determined by automated liquid chromatography-tandem mass spectrometry. The sequence obtained matched that of poly(rC) binding protein 2 (PCBP2), previously identified as an RNA binding protein from human cells. PCBP2, as well as a related protein, PCBP1, was over-expressed in Escherichia coli after cloning the cDNAs into an expression plasmid to produce a histidine-tagged fusion protein. Specific interaction between recombinant PCBP2 and poliovirus stem-loop IV was demonstrated by RNA mobility shift analysis. The closely related PCBP1 showed no stable interaction with the RNA. Stem-loop IV RNA containing a three nucleotide insertion that abrogates translation activity and virus viability was unable to bind PCBP2.

Amino Acid Sequence↗
PubMed1996

Mutation of lysine residues in the nucleotide binding segments of the poliovirus RNA-dependent RNA polymerase.

The poliovirus 3D RNA-dependent RNA polymerase contains two peptide segments previously shown to cross-link to nucleotide substrates via lysine residues. To determine which lysine residue(s) might be implicated in catalytic function, we engineered mutations to generate proteins with leucine residues substituted individually for each of the lysine residues in the NTP binding regions. These proteins were expressed in Escherichia coli and were examined for their abilities to bind nucleotides and to catalyze RNA chain elongation in vitro. Replacement of each lysine residue in the NTP binding segment located in the central portion of the 3D molecule (Lys-276, -278, or -283) with leucine produced no impairment of GTP binding or polymerase activity. Substitution of leucine for Lys-61 in the N-terminal portion of the protein, however, abolished the binding of protein to GTP-agarose and all detectable polymerase activity. A nearby lysine replacement with leucine at position 66 had no effect on enzyme activity. The three mutations in the central region of 3D were introduced into full-length viral cDNAs, and the infectivities of RNA transcripts were examined in transfected HeLa cells. Growth of virus containing 3D with a mutation at residue 278 (3Dmu278) or 3Dmu283 was indistinguishable from that of the wild type; however, 3Dmu276 generated extremely slow-growing, small-plaque virus. Polyprotein processing by 3CDmu276 was unaffected. Large-plaque variants, in which the Leu-276 codon had mutated again to an arginine codon, emerged at high frequency. The results suggest that a lysine residue at position 61 of 3Dpol is essential for polymerase catalytic function and that a basic (lysine or arginine) residue at position 276 is required for some other function of 3D important for virus growth but not for RNA chain elongation or polyprotein processing.

Chromatography, Agarose↗
PubMed1996

Replication of hepatitis A viruses with chimeric 5' nontranslated regions.

The role of the 5' nontranslated region in the replication of hepatitis A virus (HAV) was studied by analyzing the translation and replication of chimeric RNAs containing the encephalomyocarditis virus (EMCV) internal ribosome entry segment (IRES) and various lengths (237, 151, or 98 nucleotides [nt]) of the 5'-terminal HAV sequence. Translation of all chimeric RNAs, truncated to encode only capsid protein sequences, occurred with equal efficiency in rabbit reticulocyte lysates and was much enhanced over that exhibited by the HAV IRES. Transfection of FRhK-4 cells with the parental HAV RNA and with chimeric RNA generated a viable virus which was stable over continuous passage; however, more than 151 nt from the 5' terminus of HAV were required to support virus replication. Single-step growth curves of the recovered viruses from the parental RNA transfection and from transfection of RNA containing the EMCV IRES downstream of the first 237 nt of HAV demonstrated replication with similar kinetics and similar yields. When FRhK-4 cells infected with recombinant vaccinia virus producing SP6 RNA polymerase to amplify HAV RNA were transfected with plasmids coding for these viral RNAs or with subclones containing only HAV capsid coding sequences downstream of the parental or chimeric 5' nontranslated region, viral capsid antigens were synthesized from the HAV IRES with an efficiency equal to or greater than that achieved with the EMCV IRES. These data suggest that the inherent translation efficiency of the HAV IRES may not be the major limiting determinant of the slow-growth phenotype of HAV.

Animals↗