Lack of direct correlation between p220 cleavage and the shut-off of host translation after poliovirus infection

Poliovirus induces a drastic inhibition of host protein synthesis soon after infection of susceptible cells. The correlation between this inhibition and the cleavage of p220, a polypeptide that forms part of protein synthesis initiation factor elF-4F, has been examined in detail. Measurements of protein synthesis at half-hourly intervals after infection with poliovirus show the lack of direct correlation between p220 cleavage and the blockade of cellular translation. Moreover, the use of inhibitors of poliovirus RNA synthesis helped to dissociate those two events more clearly. Thus, in the presence of guanidine or Ro 09-0179 when little shut-off was induced by poliovirus extensive proteolytic degradation of p220 took place. When HeLa cells infected with poliovirus are placed at 28° the inhibition of host protein synthesis is prevented and cellular translation continues for at least 8 hr, albeit at a reduced level compared to cells incubated at 37°. At 28°, cleavage of p220 is observed and about 80% of p220 is degraded after 6 hr of incubation at that temperature. Strikingly, when cells in which more than 50% of p220 is cleaved are shifted to 37°, cellular translation recuperates to 100%, in spite of the fact that no detectable p220 is present. Furthermore, if poliovirus-infected cells are incubated for 2 hr at 37° to permit the cleavage of p220 and then are shifted to 28° in the presence of guanidine, cellular proteins are synthesized at the same level as uninfected HeLa cells incubated at 28°. These results show that translation of cellular mRNAs takes place in cells containing a cleaved p220 and indicate that this cleavage is not directly responsible for the shut-off of host translation induced by poliovirus.