Mutational analysis of poliovirus 2Apro -: Distinct inhibitory functions of 2Apro on translation and transcription

Transient expression of poliovirus 2A(pro) in mammalian cells by means of the recombinant vaccinia virus vT7 expression system leads to drastic inhibition of both cellular and vaccinia virus gene expression (Aldabe, R., Feduchi, E., Novoa, I., and Carrasco, L. (1995) FEBS Lett. 377, 1-5; Aldabe, R., Feduchi, E., Novoa, I., and Carrasco, L. (1995) Biochem. Biophys. Res. Commun. 215, 928-936). To obtain further insights into the molecular basis of this inhibition, a number of 2A(pro) variants were generated and expressed in COS-1 cells. The effect of these variants on cellular translation, on vaccinia virus-specific translation, and on transcription of the reporter gene luciferase was analyzed. The ability of the different 2A(pro) variants to block cellular translation depends on their capacities to cleave eIF-4G. The blockade exerted by 2A(pro) on transcription of the luciferase gene reinforces the notion that this protease is a potent inhibitor of RNA polymerase II-mediated transcription. Some of the 2A(pro) variants tested failed to block luciferase transcription, despite the fact that eIF-4G cleavage and inhibition of translation were observed. Two reconstituted polioviruses mutated in 2A(pro) were defective in inhibiting luciferase transcription, yet were still able to cleave eIF-4G and block translation. These findings indicate that 2A(pro) interferes with cellular gene expression at both the transcriptional and translational levels. Moreover, these two effects probably reflect the inactivation of different host proteins by poliovirus 2A(pro).