Characterization of a temperature-sensitive defect of enterovirus type 70

Caspase-3 and -7 mediate apoptosis of human Chang's conjunctival cells induced by enterovirus 70

Enterovirus 70 (EV70) is the major etiological agent of acute hemorrhagic conjunctivitis (AHC). EV70 m.o.i.- (multiplicity of infection) and time-dependently induced apoptosis in human Chang's conjunctival (HCC) cells. UV- or heat-inactivated EV70 did not induce apoptosis. EV70-induced apoptosis was inhibited by cycloheximide and methoxysuccinyl-Ala-Ala-Pro-Val-chloromethylketone (MPCMK), but not actinomycin D and guanidine.HCl (although guanidine.HCl inhibited the apoptosis induced by EV70 infection at 0.5 PFU/cell for 18 h). EV70 infection induced activation of caspase-3 and -7 and degradation of the constitutively activated caspase-6. EV70-induced apoptotic DNA ladders and activated caspase-3 and -7, correlated with virus release. Caspase inhibitor IX (Z-VD-FMK) inhibited EV70-induced apoptosis and virus release, but not intracellular viral production. The results suggest that infectious virus and the syntheses of viral proteins especially EV70 proteases, but not viral genome RNA, are required for caspase-3 and -7-mediated EV70-induced apoptosis, and that apoptosis through cell lysis promotes EV70 release from HCC cells.

A temperature-sensitive defect of enterovirus 70 is located at the uridylylation of the genome-linked protein VPg in vitro

The temperature-sensitive phenotype of enterovirus 70 (EV70) was examined by use of an in-vitro RNA replication system derived from a membrane fraction (crude replication complex, CRC) of EV70-infected HeLa cells. This system was capable of synthesizing the nucleotidyl proteins VPg-pU and VPg-pUpU. Formation of these nucleotidyl proteins was completely abolished when the in-vitro reaction was performed at the nonpermissive temperature for virus replication. Considering our previous observation that the defective stage of the temperature-sensitive growth of EV70 resides in the initiation step of RNA transcription in vivo, it is most likely that the lack of uridylylation of VPg at the restricted temperature in vitro is directly involved in the temperature-sensitive defect of virus growth in vivo.

Characterization of a temperature-sensitive defect of enterovirus 70: effect of elevated temperature on in vitro transcription

A crude replication complex prepared from enterovirus 70-infected cells was used to study the temperature-sensitive characteristic of the virus. The complex showed a temperature sensitivity in the in vitro incorporation of radiolabeled ribonucleoside triphosphate. The endonuclease itself did not account for the restricted RNA synthesis at the nonpermissive temperature. Analyses of the in vitro products by both gel electrophoresis and sucrose density gradient centrifugation showed that the complex synthesized three types of viral RNA only when incubated for a short period of time at the nonpermissive temperature. When the replication complex was treated with a detergent (deoxycholic acid), incorporation of ribonucleoside triphosphate into RNA at the permissive temperature was reduced to the level of that at the nonpermissive temperature. In addition, the in vitro RNA synthesis by the enterovirus 70 replication complex at the permissive temperature required a higher concentration of ATP than of other ribonucleoside triphosphates, whereas such a preference for ATP was not found in the reaction at the nonpermissive temperature. The results indicate that the initiation step of RNA synthesis by the complex is blocked at the nonpermissive temperature. The possible implications of these findings are discussed.

Evolution of enterovirus type 70: oligonucleotide mapping analysis of RNA genome

Different isolates of enterovirus type 70 (EV70) taken between 1971 and 1981 were studied by molecular biological methods to elucidate their evolutional change. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis showed that only a few isolates had a slight alteration in mobility in some viral proteins. On the contrary, oligonucleotide mapping of virion RNA could clearly delineate the molecular changes among isolates. The number of base changes of isolates became greater as the years elapsed. In addition, the number of base changes among recent isolates from different areas of the world was much greater than those among early isolates. Thus, when the isolates were arranged three-dimensionally according to the number of base changes between each other, the constellation of the strains gave rise to a conical shape. The central axis of the figure was the time of isolation of the strains. The early isolates clustered near the top of the conical figure and the recent isolates tended to disperse divergently at the bottom. The figure indicated that all EV70 strains were derived from a common ancestor, and its top would be the time of emergence of the original strain. It was estimated to be around 1966, 3 years prior to the first epidemic in Accra, Ghana. From the results, it was presumed that EV70 would have emerged at a single focus in Africa as a novel human virus. After having circulated there for a few years, the virus spread to the other parts of the world. Based on the difference in the oligonucleotide spots between the recent isolates and early isolates, the base changes of EV70 that occurred during 10 years was estimated to be 320, about 4% (0.4% a year on the average) of the bases of the total RNA genome.