Replication of tobacco mosaic virus. II. The in vitro synthesis of high molecular weight virus-specific RNAs

Immunotherapeutic effects of recombinant colorectal cancer antigen produced in tomato fruits

The production of pharmacological vaccines in plants has been an important goal in the field of plant biotechnology. GA733-2, the protein that is also known as colorectal carcinoma (CRC)-associated antigen, is a strong candidate to produce a colorectal cancer vaccine. Tomato is the one of the major targets for production of an edible vaccine, as tomato is a fruit consumed in fresh form. It also contains high content of vitamins that aid activation of immune response. In order to develop an edible colorectal cancer vaccine, the transgene rGA733-Fc that encodes a fusion protein of GA733-2, the fragment crystallizable (Fc) domain, and the ER retention motif (rGA733-Fc) was introduced into tomato plants (Solanumlycopersicum cv. Micro-Tom). The transgenic plants producing rGA733-Fc (rGA733-Fc^OX) protein were screened based on stable integration of transgene expression cassette and expression level of rGA733-Fc protein. Further glycosylation pattern analysis revealed that plant derived rGA733-Fc protein contains an oligomannose glycan structure, which is a typical glycosylation pattern found on ER-processing proteins. The red fruits of rGA733-Fc^OX transgenic tomato plants containing approximately 270 ng/g FW of rGA733-Fc protein were orally administered to C57BL/6 mice. Oral administration of tomato fruits of the rGA733-Fc expressing transgenic plants delayed colorectal cancer growth and stimulated immune responses compared to oral administration of tomato fruits of the h-Fc expressing transgenic plants in the C57BL/6J mice. This is the first study showing the possibility of producing an edible colorectal cancer vaccine using tomato plants. This research would be helpful for development of plant-derived cancer edible vaccines.

Optimization of the human colorectal carcinoma antigen GA733-2 production in tobacco plants

The colorectal carcinoma-associated protein GA733-2 is one of the representative candidate protein for the development of plant-derived colorectal cancer vaccine. Despite of its significant importance for colorectal vaccine development, low efficiency of GA733-2 production limits its wide applications. To improve productivity of GA733-2 in plants, we here tested multiple factors that affect expression of recombinant GA733-2 (rGA733-2) and rGA733 fused to fragment crystallizable (Fc) domain (rGA733-Fc) protein. The rGA733-2 and rGA733-Fc proteins were highly expressed when the pBINPLUS vector system was used for transient expression in tobacco plants. In addition, the length of interval between rGA733-2 and left border of T-DNA affected the expression of rGA733 protein. Transient expression analysis using various combinations of Agrobacterium tumefaciens strains (C58C1, LBA4404, and GV3101) and tobacco species (Nicotiana tabacum cv. Xanthi nc and Nicotiana benthamiana) revealed that higher accumulation of rGA733-2 and rGA733-Fc proteins were obtained by combination of A. tumefaciens LBA4404 and Nicotiana benthamiana. Transgenic plants generated by introduction of the rGA733-2 and rGA733-Fc expression cassettes also significantly accumulated corresponding recombinant proteins. Bioactivity and stability of the plant-derived rGA733 and rGA733-Fc were evaluated by further in vitro assay, western blot and N-glycosylation analysis. Collectively, we here suggest the optimal condition for efficient production of functional rGA733-2 protein in tobacco system.

Effect of cordycepin triphosphate on in vitro RNA synthesis by plant viral replicases

In vitro RNA synthesis by tobacco mosaic virus and cowpea chlorotic mottle virus replicase were inhibited by cordycepin triphosphate. Inhibition could be overcome with higher concentrations of ATP in assay mixtures but not with UTP. Products synthesized in vitro by tobacco mosaic virus RNA replicase in the presence of inhibitor revealed replicative form but not replicative intermediate RNAs. These results suggest that cordycepin triphosphate competes specifically with ATP and results in premature termination of viral RNA synthesis in vitro.

In vitro viral RNA synthesis by a subcellular fraction of TMV-inoculated tobacco protoplasts

A subcellular fraction which can synthesize viral RNA and subgenomic RNA in vitro was prepared from tobacco mosaic virus (TMV)-inoculated tobacco protoplasts. S(1)-Resistant fragment analysis with strand specific TMV cDNA showed that a large amount of plus-stranded and a small amount of minus-stranded, genome-size RNA was synthesized by this subcellular fraction. Plus-stranded subgenomic RNA of coat protein mRNA size was also synthesized. The time course of the appearance of viral RNA synthetic activity was consistent with that of the appearance of TMV infectivity in vivo.

Use of micrococcal nuclease in the purification of highly template dependent RNA-dependent RNA polymerase from brome mosaic virus-infected barley

The template dependence of RNA-dependent RNA polymerase from brome mosaic virus (BMV)-infected barley was greatly increased by micrococcal nuclease digestion of the endogenous RNA. [32P]UMP incorporation by the nuclease-treated enzyme was stimulated 20-fold when BMV RNA was added as template, while incorporation by the untreated enzyme was stimulated only 5-fold by the addition of BMV RNA. Other properties of BMV polymerase were not changed significantly by nuclease digestion. The extract remained highly active and template specific. Analysis of the products of the reaction showed that separated BMV RNA components could be replicated independently to yield full-length replicative-form RNAs. These data provide strong evidence that the extract is capable of initiating RNA synthesis and that it includes the intact viral replicase. This method should be of general use, allowing the study of cell-free replication of any viral nucleic acid without requiring purification or solubilization of the replicase.

TYMV RNA replication in vivo: replicative intermediate is mainly single stranded

We have used an in vitro labeled, membrane-bound ds[3H]RNA (C. Mouches, C. Bove, and J. M. Bove, 1974, Virology 58, 409-423) to develop a technique by which dsRNA can be detected on glycol methacrylate-embedded ultrathin sections by its resistance to RNase digestion at high but not at low ionic strength. The RNase-resistant ds[3H]RNA is detected on the sections by high-resolution autoradiography. The technique requires that prior to RNase digestion the ultrathin sections be first submitted to a Pronase step. This is accomplished by floating the sections on Pronase (1 mg/ml) for 15 min at 30 degrees , washing the sections three times, and digesting with RNase at high ionic strength for 90 min at 30 degrees . When the washing steps and the RNase hydrolysis are carried out at low ionic strength, dsRNA is completely hydrolyzed. We have applied the Pronase-RNase technique to investigate whether TYMV-specific dsRNA exists in situ after in vivo labeling of the RNAs. [3H]Uridine was fed for 1, 3, and 6 hr through the petiole of healthy or TYMV-infected leaves in the presence or absence of actinomycin D. For a given treatment aliquots of the same leaves were used for three parallel experiments: (1) Araldite embedding for autoradiography; (2) glycol methacrylate embedding for enzyme digestion and autoradiography; and (3) RNA extraction and analysis by polyacrylamide gel electrophoresis. These experiments have shown that after a [3H]uridine absorption by TYMV-infected leaves for 1 hr, in the presence of actinomycin D:dsRNA was the main labeled RNA species seen on the gels; Araldite-embedded sections were labeled specifically at the chloroplast periphery, while glycol methacrylate-embedded sections, submitted to the Pronase-RNase technique to detect dsRNA, were found to contain no dsRNA. Thus replicative intermediate RNA in TYMV-infected cells is essentially single stranded in vivo, and dsRNA is an artifact generated during the RNA extraction procedure.

Subcellular localization of tobacco mosaic virus minus strand RNA in infected protoplasts

Radioactive RNA probes were prepared which specifically hybridize with sequences complementary to 5' and 3' regions of tobacco mosaic virus (TMV) RNA. These probes were used in Northern hybridization to locate TMV-RNA minus strands in the subcellular fractions of infected tobacco protoplasts. When the protoplasts were lysed with Triton X-100, full-length minus strands were present in the cytoplasmic but not in the nuclear fraction. With mechanically broken protoplasts, the crude nuclear fraction (250 g pellet) contained small amount of minus strands which appeared to derive from unbroken protoplasts, but most of minus strands were recovered in a fraction sedimented between 250 and 2500 g, little if any being found in lighter fractions. The results indicate that TMV-RNA replicates in association with an extranuclear structure.

An analysis of tobacco mosaic virus replicative structures synthesized in vitro

The RNA structures synthesized in vitro by a crude enzyme complex from tobacco mosaic virus (TMV)-infected leaves have been analyzed; the major viral-specific products were similar to TMV-replicative form (RF) and-replicative intermediate (RI) in electrophoretic behavior and ribonuclease sensitivity. Synthesis of these RF-like and RI-like structures neither required nor responded to added viral RNA, but did require all four ribonucleotide triphosphates. Enriched radiolabeled RF-like and RI-like RNA fractions were isolated from non-denaturing agarose gels by electroelution and hybridized to a collection of TMV sequences cloned into bacteriophage M13. Enriched RF-RNA hybridized to sequences of both plus and minus polarity, while enriched RI-RNA hybridized only to inserts of minus polarity, indicating only plus strand synthesis in this fraction. Most of the label incorporated into the plus strand of the enriched RF-RNA was found near the 3'-end of this strand, while most of the label incorporated into enriched RI-RNA was found several hundred bases from the 5'-end of the plus strand.

Hepatitis A virus: growth characteristics of in vivo and in vitro propagated wild and attenuated virus strains

Serial passage of the MS-1 strain hepatitis A virus (HAV) in marmosets was shown to increase the yield of virus and to shorten the incubation period from approximately 55 days in the first passage to 3-7 days in the ninth and higher passages. Intravenous inoculation of susceptible chimpanzees with MS-1 HAV was found to result in a typical course of disease in two animals who had received eighth marmoset-passage virus, including the occurrence of elevated ALT activity, presence of HAV antigen in liver and stool, and seroconversion to anti-HAV. Two chimpanzees inoculated with 20th passage MS-1 HAV (M001 liver homogenate) exhibited normal or nearly normal ALT activity and had no demonstrable or significant HAV in weekly liver biopsy specimens or in serial stool suspensions obtained during 64 days of observation. However, both animals seroconverted to anti-HAV within 2 weeks after inoculation, as did the animals who had received eighth passage MS-1 HAV. These findings suggest that subpassage of the MS-1 strain of HAV in marmosets resulted in the generation of an attenuated virus strain that was still capable of inducing a vigorous antibody response in intravenously infected chimpanzees. Serial propagation of wild and attenuated strains of HAV (HAS-15 and MS-1/M001, respectively) in FRhK-4 cells was associated with a significant decrease in the growth period for both viruses. Our studies have also shown that HAS-15 HAV can be recovered in maximum yield in later passages as early as 2 to 3 days after inoculation.

In vitro replication of tobacco mosaic virus RNA in tobacco callus cultures: solubilization of membrane-bound replicase and partial purification

A fraction containing membrane-bound tobacco mosaic virus RNA replicase was isolated form tobacco mosaic virus-infected tobacco callus cultures. The replicase activity reached a maximum 60 h after inoculation and then declined. The enzyme activity was insensitive to actinomycin D and DNase. The corresponding fraction from healthy callus contained essentially no activity. The viral RNA synthesis in vitro proceeded linearly for 30 min and required the four nucleotide triphosphates and Mg2+ ions. Mn2+ was a poor substitute for Mg2+. During RNA synthesis the product was at least 70% resistant to RNase in 2X SSC (0.15 M NaCl plus 0.015 M sodium citrate), but completely digested by RNase in 0.1X SSC. Analysis of the product by polns) that appeared to be replicative form and a partially RNase-resistant structure similar to replicative intermediate form. Washing the membrane-bound replicase with Mg2+-deficient buffer solubilized enzyme. The solubulized enzyme was further purified by DEAE-Sephadex column chromatography. The DEAE-purified enzyme was nearly completely dependent upon tobacco mosaic virus RNA for activity. Analysis of the product on a sucrose gradient revealed a double-stranded RNA with sedimentation of 16S and smaller heterogeneous RNase-sensitive products.