Abstract
A number of viral proteases are able to cleave translation initiation factors leading to the inhibition of cellular translation. This is the case of human immunodeficiency virus type 1 protease (HIV-1 PR), which hydrolyzes eIF4GI and poly(A)-binding protein (PABP). Here, the effect of HIV-1 PR on cellular and viral protein synthesis has been examined using cell-free systems. HIV-1 PR strongly hampers translation of pre-existing capped luc mRNAs, particularly when these mRNAs contain a poly(A) tail. In fact, HIV-1 PR efficiently blocks cap- and poly(A)-dependent translation initiation in HeLa extracts. Addition of exogenous PABP to HIV-1 PR treated extracts partially restores the translation of polyadenylated luc mRNAs, suggesting that PABP cleavage is directly involved in the inhibition of poly(A)-dependent translation. In contrast to these data, PABP cleavage induced by HIV-1 PR has little impact on the translation of polyadenylated encephalomyocarditis virus internal ribosome entry site (IRES)-containing mRNAs. In this case, the loss of poly(A)-dependent translation is compensated by the IRES transactivation provided by eIF4G cleavage. Finally, translation of capped and polyadenylated HIV-1 genomic mRNA takes place in HeLa extracts when eIF4GI and PABP have been cleaved by HIV-1 PR. Together these results suggest that proteolytic cleavage of eIF4GI and PABP by HIV-1 PR blocks cap- and poly(A)-dependent initiation of translation, leading to the inhibition of cellular protein synthesis. However, HIV-1 genomic mRNA can be translated under these conditions, giving rise to the production of Gag polyprotein.
Highlights
Viruses rely on cellular machinery to synthesize their proteins since this complex process requires numerous components that cannot all be encoded by viral genomes
Pre-treatment with 20 ng of human immunodeficiency virus (HIV)-1 PR did not affect Gag production irrespective of the dose of HIV-1 genomic (HIV-1g) mRNA used (Figure 6D). These results indicate that HIV-1g mRNA can be translated when eIF4GI and poly(A)-binding protein (PABP) are cleaved by HIV-1 PR
Cleavage of translation initiation factors is a mechanism employed by a number of animal viruses to modulate host and viral protein synthesis [3]
Summary
Viruses rely on cellular machinery to synthesize their proteins since this complex process requires numerous components that cannot all be encoded by viral genomes. Viral mRNAs have to compete with host mRNAs for ribosomes and other components of the translation machinery [1]. A number of viral proteases are involved in the proteolysis of translation initiation factors, such as eIF4G and PABP [2,3]. Under these conditions the association of host mRNAs with ribosomes is severely impaired, whereas viral mRNAs can efficiently interact with the translation machinery [1,2]
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