PROTEOLYSIS OF HUMAN EUKARYOTIC TRANSLATION INITIATION-FACTOR EIF4GII, BUT NOT EIF4GI, COINCIDES WITH THE SHUTOFF OF HOST PROTEIN-SYNTHESISAFTER POLIOVIRUS INFECTION
A. Gradi et al., PROTEOLYSIS OF HUMAN EUKARYOTIC TRANSLATION INITIATION-FACTOR EIF4GII, BUT NOT EIF4GI, COINCIDES WITH THE SHUTOFF OF HOST PROTEIN-SYNTHESISAFTER POLIOVIRUS INFECTION, Proceedings of the National Academy of Sciences of the United Statesof America, 95(19), 1998, pp. 11089-11094
Eukaryotic initiation factor (eIF) 4GI is a component of the cap-bindi
ng protein complex eIF4F, which is required for cap-dependent translat
ion. Infection of cells by poliovirus results in a precipitous decline
of host cell protein synthesis, which is preceded by the cleavage of
eIF4GI, Cleavage of eIF4GI results in the inhibition of cap-dependent
translation. Poliovirus translation is not affected by eIF4GI cleavage
, however, because poliovirus mRNA is translated by a cap-independent
mechanism. Cleavage of eIF4GI alone cannot explain the shutoff of host
protein synthesis, because after infection in the presence of inhibit
ors of virus replication, eIF4GI is cleaved, yet host protein synthesi
s is only partially inhibited. Here we show that eIF4GII, a recently d
iscovered functional homolog of eIF4GI, is more resistant to polioviru
s-mediated cleavage than eIF4GI, and that its proteolysis is concomita
nt with the shutoff of host cell protein synthesis. Moreover, infectio
n with poliovirus in the presence of inhibitors of virus replication r
esulted in efficient cleavage of eIF4GI, but only partial proteolysis
of eIF4GII. Thus, cleavage of both eIF4GI and eIF4GII appears to be re
quired for the shutoff of host protein synthesis after poliovirus infe
ction. These results explain several earlier reports documenting the l
ack of correlation between eIF4GI cleavage and inhibition of cellular
mRNA translation after poliovirus infection.