Vero cells injected with adenovirus type 2 mRNA produce authentic viral polypeptide patterns: early mRNA promotes growth of adenovirus-associated virus

Characterization of the function of Adenovirus L4 gene products and their impact on AAV vector production

Efficient manufacturing of recombinant adenovirus-associated virus (AAV) vectors is critical to the successful development of genomic medicines. We attempted to optimize AAV vector production in a producer cell line platform. In this system, helper functions required for AAV replication and production are provided via infection with a replication-competent wild-type Adenovirus. To evaluate strategies for the reduction of replication and packaging of adenovirus and to understand the interplay of recombinant AAV and the helper virus during AAV vector production, wild-type adenovirus was compared to a mutant (Ad5ts149) containing a temperature-sensitive mutation in the DNA polymerase gene. Infection of a producer cell line with Ad5ts149 at the restrictive temperature reduced recombinant AAV titer and altered the pattern of AAV protein expression. Further investigation revealed that the adenoviral late L4-22K/33K gene products regulated both AAV rep/cap gene transcription and splicing of the rep/cap transcripts. Furthermore, the L4-33K gene products were found to impact AAV production in both the producer cell line and transient transfection platforms. Optimization of Adenovirus L4-22K/33K expression to facilitate efficient expression and splicing of AAV rep/cap transcripts therefore represents a unique opportunity to optimize AAV vector production.

Expression of thermotolerance following microinjection of poly(A)RNA isolated from thermotolerant CHO cells

Poly(A)RNA was isolated from thermotolerant cells and microinjected into recipient non-tolerant Chinese hamster ovary (CHO) cells. The injected cells expressed thermotolerance to a subsequent test heat treatment both in terms of the end-points of colony formation (cell survival) and resumption of protein synthesis after test heating (translational labelling). The magnitude of thermotolerance expression was dependent on the experimental end-point (increase up to 3.8-fold for translational labelling and approximately 2-fold for survival) and on the time between microinjection and the test heat treatment. Control experiments showed that poly(A)RNA from non-tolerant cells did not alter the heat response of microinjected cells. Proteins corresponding to the poly(A)RNA from thermotolerant cells were analysed by in vitro translation and by labelling of microinjected cells, followed by SDS-PAGE. In vitro translations showed high levels of transcripts for classical heat-shock proteins (HSP 70/72, 89, 110) in poly(A)RNA from thermotolerant versus control cells. However, proteins synthesized in intact cells showed no detectable differences when cells were microinjected with poly(A)RNA from thermotolerant versus control cells, or not injected at all. In principle the data show that microinjection of specific poly(A)RNA fractions can be used for defining the contribution of individual gene products to the cellular heat response.

Isolation and characterization of a viable adenovirus mutant defective in nuclear transport of the DNA-binding protein

The isolation and characterization of an adenovirus mutant, Ad5dl802r1, containing two independent deletions in the 72-kilodalton (kDa) DNA-binding protein (DBP) gene is described. The two deletions remove amino acids 23 through 105 of DBP, resulting in the production of a 50-kDa product. Expression of this truncated DBP was delayed 12 to 24 h compared with that of the 72-kDa protein produced by wild-type adenovirus type 5. The DBP was located primarily in the cytoplasm of infected cells, whereas the wild-type product was predominantly nuclear. Therefore, DBP appears to contain a nuclear localization signal within the deleted region. Ad5dl802r1 DNA synthesis, viral late gene expression, and virus production were all delayed 12 to 24 h and were approximately 10-fold lower than with wild-type adenovirus type 5. These phenotypic properties can be accounted for by the delay in synthesis and the inefficient accumulation of the 50-kDa DBP within the nucleus of infected cells. The truncated DBP also lacks the majority of amino acids which are phosphorylated in the normal protein. The loss of these phosphorylation sites does not appear to seriously impair the ability of the protein to carry out its functions.

Functions of purified E1A protein microinjected into mammalian cells

We have purified the human type C adenovirus E1A 13S mRNA gene product, expressed in Escherichia coli, and demonstrate that the protein exhibits genuine viral functions upon microinjection into mammalian cells. We show that the E1A protein activates expression of the adenovirus E2A gene and induces expression from the major late transcription unit of the adenovirus E1A deletion mutant, H5dl312. We use this functional assay to examine the stability of E1A protein microinjected into cells and find that E1A exhibits full function for at least 18 hours after its injection. In addition, the purified E1A protein was used to generate a high-titer monospecific rabbit antiserum. This antiserum was used to detect and localize E1A proteins within adenovirus-infected cells as well as within microinjected cells. The E1A protein is found to rapidly and quantitatively localize to the cell nucleus following microinjection into the cell cytoplasm. Thus, nuclear localization is an intrinsic property of the E1A polypeptide. The ability of the E1A protein to localize to the cell nucleus and to induce expression from the H5dl312 major late transcription unit is shown to be highly heat stable.

Translation of adenovirus 2 late mRNAs microinjected into cultured African green monkey kidney cells

Adenovirus 2-infected monkey cells fail to synthesize fiber, a 62,000 Mr virion polypeptide expressed at late times in productively infected cells. Yet these cells contain fiber mRNA that, after isolation, can be translated in vitro. The reason for the failure of monkey cells to translate fiber mRNA has been approached by microinjecting adenovirus mRNA into the cytoplasm of cultured monkey cells. Late adenovirus 2 mRNA, isolated from infected HeLa cells, was efficiently expressed when microinjected into the African green monkey kidney cell line CV-C. Expressed viral proteins identified by immunoprecipitation included the adenovirus fiber polypeptide. This result demonstrates that the monkey cell translational apparatus is capable of recognizing and expressing functional adenovirus fiber mRNA. Microinjection of late virus mRNA into cells previously infected with wild-type adenovirus 2 failed to increase significantly the yield of infectious virus.

Genetics of adeno-associated virus: isolation and preliminary characterization of adeno-associated virus type 2 mutants

We constructed insertion and deletion mutants with mutations within the adeno-associated virus (AAV) sequences of the infectious recombinant plasmid pSM620. Studies of these mutants revealed at least three AAV phenotypes. Mutants with mutations between 11 and 42 map units were partially or completely defective for rescue and replication of the AAV sequences from the recombinant plasmids (rep mutants). The mutants could be complemented by mutants with replication-positive phenotypes. The protein(s) that is affected in rep mutants has not been identified, but the existence of the rep mutants proves that at least one AAV-coded protein is required for viral DNA replication. Also, the fact that one of the rep mutant mutations maps within the AAV intron suggests that the intron sequences code for part of a functional AAV protein. Mutants with mutations between 63 and 91 map units synthesized normal amounts of AAV duplex DNA but could not generate single-stranded virion DNA (cap mutants). The cap phenotype could be complemented by rep mutants and is probably due to a defect in the major AAV capsid protein, VP3. This suggests that a preformed capsid or precursor is required for the accumulation of single-stranded AAV progeny DNA. Mutants with mutations between 48 and 55 map units synthesized normal amounts of AAV single-stranded and duplex DNA but produced substantially lower yields of infectious virus particles than wild-type AAV (lip mutants). The lip phenotype is probably due to a defect in the minor capsid protein, VPI, and suggests the existence of an additional (as yet undiscovered) AAV mRNA. Evidence is also presented for recombination between mutant AAV genomes during lytic growth.

Requirement for either early region 1a or early region 1b adenovirus gene products in the helper effect for adeno-associated virus

Several adenovirus early genes act together to promote growth of the helper-dependent adeno-associated virus (AAV). Data from several laboratories have implicated adenovirus early regions 1a, 1b, 2a, and 4 in the helper effect, as well as the small RNA polymerase III transcript, virus-associated RNA I. Although a subset of these must participate directly in the AAV life cycle, some may play an indirect role by influencing expression of the others. This paper is concerned particularly with the roles of early regions 1a and 1b in the helper effect. We introduced DNA fragments representing the various early regions into AAV-infected or uninfected Vero cells, by the manual microinjection procedure. After labeling the cells with [35S]methionine, we visualized immunoprecipitates of AAV or adenovirus proteins on sodium dodecyl sulfate-polyacrylamide gels. When over 200 copies of each DNA fragment per cell were injected, early regions 2a and 4 were themselves sufficient to provide the helper effect. At 100 copies per cell, however, a third gene became essential, and this could be either early region 1a or 1b. The role of early region 1a is easily explained by its known ability to stimulate transcription of the other early genes. The function of early region 1b is less clear, but it does not simply mimic the action of early region 1a. Instead, there appear to be at least two distinct regulatory pathways which can lead to expression of AAV. To investigate the sequence of regulatory interactions, we microinjected purified adenovirus mRNAs, or combinations of mRNA and DNA, into AAV-infected cells. Our results suggest that adenovirus early products enhance viral gene expression by several mechanisms which can operate independently, but whose effects may be cumulative.

Expression of mRNAs microinjected into somatic cells

The microinjection of macromolecules into living somatic cells has been used to assess the biological activity of a wide variety of macromolecules. This article describes and evaluates the methodology of microinjection with micropipettes and reviews information on the expression of globin mRNAs injected into normal and transformed cultured cells. A brief account is also given of other mRNAs that have been successfully translated in cultured cells.

Delta crystallins and their nucleic acids

delta-Crystallin is a major structural protein of avian and reptilian lenses that is absent from the lenses of fish, amphibia and mammals. It appears to be a tetrameric protein with a native molecular weight near 200 000 (200K) and polypeptide molecular weight near 50K and 48K) (see Note added in proof). The alpha-crystallin polypeptides are extremely similar, associate in various combinations of four and are held together by hydrophobic interactions. Although principally cytoplasmic, delta-crystallin may associate with the cell membrane. delta-Crystallin differs from other lens crystallins in its alpha-helical content, native and subunit molecular weights, antigenicity, low wavelength of maximum fluorescence emission (315 nm) after excitation at 280 nm and amino acid composition (high in leucine; low in aromatic residues en no cysteine). Analyses of peptides, native and subunit molecular weights, and circular dichroism spectra indicate that the primary, secondary, tertiary and subunit structures of delta-crystallin have been generally conserved during evolution. There are at least two tandemly arranged delta-crystallin containing 13-15 introns in the chicken; a similar structure exists for a cloned delta-crystallin gene in the duck. Experiments with chicken show that delta-crystallin synthesis occurs principally in the embryo, especially during lens fiber cell differentiation. delta-Crystallin synthesis also takes place during lens fiber cell differentiation in culture. There is evidence for both transcriptional and post-transcriptional regulation of delta-crystallin synthesis. Current studies on the crystallographic and primary structures of delta-crystallin, on the structure, evolution and expression of the delta-crystallin genes, and on the translation of delta-crystallin mRNAs make this specialized lens protein an active area of investigation.

Microinjected simian virus 40 cRNA is spliced, as evidenced by electron microscopy

Simian virus 40 cRNA was transcribed in vitro from the early viral DNA strand. The RNA was injected through glass capillaries into the nuclei of monkey cells. After a 2-h incubation, the RNAs were extracted and hybridized to single-stranded simian virus 40 DNA sequences contained in a bacteriophage M13 vector. Electron microscopy revealed processed cRNAs with splice loops in the region of the intron of large T antigen.

Adeno-associated virus helper activity of adenovirus DNA binding protein

The requirement for the adenovirus (Ad) single-stranded DNA binding protein (DBP) in the expression of adeno-associated virus (AAV) proteins was studied by specific immunofluorescent staining of infected cells and in vitro translation of RNA from infected cells. The Ad5 mutant ts125, which carries a mutation in the DBP gene, helped AAV as efficiently as the Ad5 wild type (WT) did at both the permissive (32 degrees C) and nonpermissive (40.5 degrees C) temperatures in HeLa and KB cells. Furthermore, at 40.5 degrees C ts125 was as efficient as Ad5WT was in inducing the expression of AAV proteins in a line of Detroit 6 cells which is latently infected with AAV. However, little if any AAV protein was synthesized when coinfections were carried out with Ad5WT in CV-C cells, a monkey cell line that is highly restrictive for human Ad replication unless the cells are also infected with simian virus 40. On the other hand, AAV protein was efficiently produced in CV-C cells in coinfections with the Ad5 mutant hr404, whose growth is unrestricted in CV-C cells and whose mutation also maps in the DBP gene. Finally, preparations of cytoplasmic RNA extracted from CV-C cells infected with AAV and Ad5WT or from CV-C cells infected with AAV, Ad5WT, and simian virus 40 were each capable of directing the in vitro synthesis of abundant amounts of AAV proteins in a rabbit reticulocyte lysate system. These results indicate that the abnormal DBP of ts125 still retains its helper function for AAV replication, but that the molecular feature of the DBP which relates to the monkey cell host range restriction of Ad's may also account for the observed block to AAV protein translation in CV-C cells.

Effect of deletions in adenovirus early region 1 genes upon replication of adeno-associated virus

The growth of adeno-associated virus (AAV) is dependent upon helper functions provided by adenovirus. We investigated the role of adenovirus early gene region 1 in the AAV helper function by using six adenovirus type 5 (Ad5) host range mutants having deletions in early region 1. These mutants do not grow in human KB cells but are complemented by and grow in a line of adenovirus-transformed human embryonic kidney cells (293 cells); 293 cells contain and express the Ad5 early region 1 genes. Mutants having extensive deletions of adenovirus early region 1a (dl312) or regions 1a and 1b (dl313) helped AAV as efficiently as wild-type adenovirus in 293 cells, but neither mutant helped in KB cells. No AAV DNA, RNA, or protein synthesis was detected in KB cells in the presence of the mutant adenoviruses. Quantitative blotting experiments showed that at 20 h after infection with AAV and either dl312 or dl313 there was less than one AAV genome per cell. In KB cells infected with AAV alone, the unreplicated AAV genomes were detected readily. Apparently, infection with adenovirus mutant dl312 or dl313 results in degradation of most of the infecting AAV genomes. We suggest that at least an adenovirus region 1b product (and perhaps a region 1a product also) is required for AAV DNA replication. This putative region 1b function appears to protect AAV DNA from degradation by an adenovirus-induced DNase. We also tested additional Ad5 mutants (dl311, dl314, sub315, and sub316). All of these mutants were inefficient helpers, and they showed varying degrees of multiplicity leakiness. dl312 and dl313 complemented each other for the AAV helper function, and each was complemented by Ad5ts125 at the nonpermissive temperature. The defect in region 1 mutants for AAV helper function acts at a different stage of the AAV growth cycle than the defect in the region 2 mutant ts125.

Eukaryotic translational control: adeno-associated virus protein synthesis is affected by a mutation in the adenovirus DNA-binding protein

Growth of adeno-associated virus (AAV) requires expression of certain adenovirus (Ad) genes in the same cell. AAV particles contain three proteins, VP1 (Mr 85,700), VP2 (Mr 72,000), and VP3 (Mr 61,500). These proteins have overlapping peptide maps. We recently reported that AAV RNAs make up a 3'-coterminal family of overlapping molecules. We report here that the most abundant AAV mRNA, a 2.3-kilobase spliced RNA, codes for all three proteins--VP1, VP2, and VP3--when translated in an in vitro reticulocyte lysate. This shows that the AAV capsid proteins are coded by the genome sequence between map positions 48.0 and 96.0 (1 map unit is 1% of the genome or 47 base pairs). When AAV was grown in human KB cells with the Ad temperature-sensitive mutant Ad5ts125 at the nonpermissive temperature (40 degrees C), the accumulation in vivo of AAV capsid proteins VP1, VP2, and VP3 was decreased to less than 1/50th. However, normal amounts of the 2.3-kilobase mRNA were accumulated, and this RNA could be efficiently translated in an in vitro reticulocyte lysate system to yield VP1, VP2, and VP3. These experiments suggest that in infected cells control is exerted upon the AAV 2.3-kilobase mRNA at the translational level and that this control can be influenced by mutations in Ad. These Ad mutations map in the region 2 early gene for the Ad DNA-binding protein. The temperature-sensitive system that we have studied may be useful for analysis of translational control of a eukaryotic mRNA.

Locations of adenovirus genes required for the replication of adenovirus-associated virus

We have used DNA transfection to identify several regions of the adenovirus genome needed to induce replication of the defective parvovirus, adenovirus-associated virus (AAV). Previous studies have indicated that only early adenovirus functions are needed to aid the replication of AAV. In this report, we demonstrate that three restriction endonuclease fragments of adenovirus DNA are necessary for production of infectious AAV in 293-31 cells (an adenovirus type 5-transformed human embryonic kidney cell line). These fragments map from 28.5 to 29.4, 59.5 to 75.9, and 89.7 to 100 map units on the adenovirus type 2 genome and correspond to the locations of the VAI RNA gene, early region 2, and early region 4, respectively. The 293-31 cell line, which has been found to express early region 1A and 1B proteins, alone is incapable of supporting AAV replication or even AAV DNA synthesis. Additional experiments with adenovirus type 5 host range mutants (group I, hr1 and group II, hr7) indicate, however, that early region 1A provides an essential function(s) for AAV replication, whereas early region 1B probably does not.

Adenovirus helper function for growth of adeno-associated virus: effect of temperature-sensitive mutations in adenovirus early gene region 2

Adeno-associated virus (AAV) grows efficiently only in cells that are also infected with an adenovirus (Ad). We employed Ad mutants to determine which genes may be required for the AAV helper function. Two mutants of Ad type 5 (Ad5), Ad5ts125 and Ad5ts107, with temperature-sensitive lesions in the E72 DNA-binding protein coded by the Ad early region 2, were deficient for AAV helper functions at the nonpermissive temperature (40 degrees C). In contrast, Ad5ts149, with a temperature-sensitive lesion in the Ad early region 5, was an efficient helper of AAV at the nonpermissive temperature. In KB cells, with the Ad5ts125 or Ad5ts107 mutant as the helper, the accumulation of AAV capsid proteins and AAV particles was decreased by about two logs, whereas AAV DNA synthesis was decreased only severalfold. Cytoplasmic, polyadenylic acid-containing AAV RNA is composed of a set of overlapping, spliced RNAs having different 5' start points. With the ts125 helper at 40 degrees C there was a decreased accumulation of some but not all of these AAV RNAs. The Ad5 E72 protein may have an effect on transcription or more likely posttranscriptional processing of AAV RNA. These observations suggest additional pleiotropic effects of the multifunctional E72 protein and suggest further similarities in the actions of E72 and the simian virus 40 T-antigen.