Inhibition of translation by poliovirus: inactivation of a specific initiation factor.

Abstract

Translation of vesicular stomatitis virus (VSV) mRNA, like host mRNA translation, is inhibited in cells infected with poliovirus. To study the mechanism of poliovirus-induced inhibition of protein synthesis, we prepared extracts from poliovirus-infected and uninfected HeLa cells. Poliovirus mRNA was translated in Iysates from both infected and uninfected cells, while VSV mRNA was translated only in the lysate from uninfected cells. Addition of purified translation initiation factors to the extract frosi infected cells showed that one factor eIF4B, could restore VSV mRNA translation in the infected lysate, but did not increase poliovirus mRNA translation. Further experiments involving translation of VSV mRNA in mixed extracts from poliovirus-infected and uninfected cells showed (j) that there was not an excess of an inhibitor of VSV mRNA translation in the infected 1 sate, but (ii) that an activity that caused a slow inactivation oleIF-4B was present in the infected lysate. Inactivation of eIF4B appears to~e the mechanism by which poliovirus -infection causes a selective inhibition of translation. Inhibition of host protein synthesis occurring after virus infection has been demonstrated in many eukaryotic virus-host systems (1). The best studied case of inhibition of protein synthesis is that caused by picornaviruses such as poliovirus, but the mechanism that allows discrimination between host and viral mRNA translation has not been elucidated. Infection by poliovirus results in extensive inhibition of host protein synthesis at the initiation step (2, 3). During poliovirus infection the host mRNAs are not degraded (2, 3) and their capping, methylation, and polyadenylation are not affected (4). Furthermore, translation of vesicular stomatitis virus (VSV) mRNAs is prevented when VSV-infected cells are superinfected with poliovirus (5, 6). VSV mRNA synthesis continues normally in the superinfected cells and the untranslated VSV mRNA can be translated in vitro after purification from the infected cell (6). Also, the kinetics of poliovirus inhibition of host and VSV protein synthesis are identical, suggesting that they occur by the same mechanism (6).In this study we have used translation of VSV mRNA in extracts derived from poliovirus-infected and uninfected HeLa cells to study the mechanism of translation inhibition by poliovirus. VSV directs the synthesis of five mRNAs that encode the five viral proteins (7,8). These mRNAs, like cellular mRNAs, have capped and methylated 5' termini that are important in ribosome recognition (9). In contrast, poliovirus mRNA has a 5' terminus of pUp (10, 11). The evidence presented here indicates that loss of a single initiation factor activity (eIF-4B) can explain the inhibition of VSV and host mRNA translation by poliovirus. Other work has indicated that this factor interacts with the 5' cap structure on mRNA (12). Thus, poliovirus mRNA may bypass the cap-dependent recognitionThe costs of publication of this article were defrayed in part by the payment of page charges. Th...

Translation of Capped Virus mRNA in Encephalomyocarditis Virus-infected Cells

“…It has been suggested that poliovirus infection leads to the specific inactivation of an initiation factor required for the translation of capped mRNAs (Helentjaris & Ehrenfeld, 1978;Rose et al, 1978;Trachsel et al, 1980). In agreement with this suggestion, poliovirus infection of HeLa cells interferes with the development of herpesvirus and leads to the inhibition of vesicular stomatitis virus (VSV) protein synthesis under some conditions (Doyle & Holland, 1972;Saxton & Stevens, 1972;Ehrenfeld &Lund, 1977).…”

“…On the basis that cell-free systems from poliovirus-infected cells translate uncapped mRNAs but not capped mRNAs (Rose et al, 1978;Trachsel et al, 1980), it was suggested that poliovirus infection inactivates a protein factor necessary for the translation of capped mRNAs, but dispensable for the translation of uncapped mRNAs. In agreement with this idea, infection of cells with poliovirus interferes with the translation of herpesvirus or VSV mRNAs (Doyle & Holland, 1972;Saxton & Stevens, 1972;Ehrenfeld &Lund, 1977).…”

The Regulation of Translation in Reovirus-infected Cells

“…Moreover, not all reovirus proteins behave in the same way, because some of them are more resistant to inhibition than others. This result is difficult to explain if we assume that poliovirus destroys a factor involved in cap recognition, necessary for the translation of capped reovirus m R N A s (Rose et al, 1978). The pattern of translation after EMC virus superinfection was similar, i.e.…”

Protein Synthesis in HeLa Cells Double-infected with Encephalomyocarditis Virus and Poliovirus

“…Poliovirus and EMC virus inhibit host protein synthesis in HeLa cells to different degrees, so that higher multiplicities of EMC virus than poliovirus are required to inhibit protein synthesis in HeLa cells with similar kinetics. Because of this difference in inhibition of host protein synthesis between EMC virus and poliovirus, and because of the different ability of the extracts from EMC virus-and poliovirus-infected cells to translate capped mRNAs (Lawrence & Thach, 1974;Rose et al, 1978), Jen et al (1980) suggested that the mechanisms used by both viruses to block host protein synthesis are different.…”