Efficiency of Translation of Viral and Cellular mRNA’s in Extracts from Cells Infected with Encephalomyocarditis Virus

Abstract

The relative efficiency of translation of host cell mRNA and encephalomyocarditis (EMC) virus RNA has been investigated in cell-free preparations from un-infected and EMC virus-infected Krebs-II cells. The ability of cell-free extracts from infected cells to translate exogenously-added EMC virus RNA and total Krebs-II cell mRNA was markedly diminished, but no evidence for the selective inhibition of translation of host cell mRNA in these systems was obtained.

Activation of the translational suppressor 4E-BP1 following infection with encephalomyocarditis virus and poliovirus.

“…To address this apparent discrepancy, we analyzed and translates in a cap-independent fashion, driven by the EMCV internal ribosome entry site) have been used in this study. In accordance with previous studies (22,25,26), all mRNAs tested, regardless of their dependency on the cap for translation, were translated less efficiently in extracts from EMCV-infected than in mock-infected cells. The capdependent globin mRNA translation decreased 2.5-and 8-fold in EMCV R-and EMCV K-2-infected Krebs II ascites translation extracts, respectively, as compared with translation in extracts from mock-infected cells ( Fig.…”

“…Because eIF4E is necessary for cap-dependent but not for cap-independent translation, its sequestration by 4E-BP1 would be expected to specifically inhibit cap-dependent translation in an in vitro translation extract prepared from EMCVinfected cells. However, numerous earlier studies reported that extracts prepared from EMCV-infected cells did not exhibit any selectivity in cap-independent versus cap-dependent translation (15,22,25,26). These findings are in apparent contradiction with the in vivo data that point to a role for 4E-BP1 in the mediation of the shutoff of host protein synthesis exerted by EMCV.…”

“…Also, in sharp contrast to poliovirus, no cleavage of eIF4G occurs in EMCV-infected cells (23). In vitro translation studies showed a general decrease in the ability of EMCV-infected cell extracts to translate both viral and cellular exogenous mRNAs, rather than a specific inhibition of cellular mRNA translation, such as that observed in extracts from poliovirus-infected cells (22,(24)(25)(26). This is in contrast to the in vivo studies showing a selective shutoff of host protein synthesis.…”

Translational elongation rate changes in encephalomyocarditis virus-infected and interferon-treated cells

“…In the case of poliovirus infection of HeLa cells a loss of initiation factor activity postulated to be specific for capped mRNA's has been demonstrated (19,36). In contrast, results on encephalomyocarditis (EMC) virus infection of HeLa and other cells have shown that a comparable factor inactivation does not occur (23,27,31,39). Thus, it is clear that the findings from poliovirus-infected cells are not necessarily applicable to other picornavirus infections.…”