Different effects of the TAR structure on HIV-1 and HIV-2 genomic RNA translation

Abstract

The 5′-untranslated region (5′-UTR) of the genomic RNA of human immunodeficiency viruses type-1 (HIV-1) and type-2 (HIV-2) is composed of highly structured RNA motifs essential for viral replication that are expected to interfere with Gag and Gag-Pol translation. Here, we have analyzed and compared the properties by which the viral 5′-UTR drives translation from the genomic RNA of both human immunodeficiency viruses. Our results showed that translation from the HIV-2 gRNA was very poor compared to that of HIV-1. This was rather due to the intrinsic structural motifs in their respective 5′-UTR without involvement of any viral protein. Further investigation pointed to a different role of TAR RNA, which was much inhibitory for HIV-2 translation. Altogether, these data highlight important structural and functional differences between these two human pathogens.

Translation initiation of the HIV-1 mRNA

“…40 However, translational inhibition imposed by TAR was less pronounced in cells and this was confirmed by the rescue of translational inhibition in the RRL upon addition of cytoplasmic HeLa cell extracts. 34,41 This observation is consistent with the fact that several cellular proteins are known to bind the HIV-1 TAR structure promoting translational activation of HIV-1 mRNA. 42 Studies have shown that the HIV-1 5 0 UTR can adopt 2 spatial conformations which are the branched multiple hairpins (BMH) and the long distance interaction (LDI) structures.…”

“…51 Initiation from the capped end also gave an explanation to the fact that the folding and length of the TAR structure (which is different between HIV type 1 and type 2) had such a great influence on the overall efficiency of translation. 34 This ribosomal scanning hypothesis also fits well with the fact that most natural HIV-1 isolates do not tolerate uAUGs within their 5 0 UTR despite its great length. 8 However, the mechanism by which the 43S preinitiation complex can deal with these stable RNA structures that are known to impair both initial ribosome binding and scanning remains unclear.…”

“…30 In fact, the TAR stem loop structure occludes the cap moiety raising the question of its accessibility for eIF4E during the assembly of the translation initiation complex over the viral mRNA. 34,35 As it was previously demonstrated that the presence of a stem-loop of weaker stability (DG D ¡13.6kcal/mol) at the 5 0 end of a synthetic mRNA is enough to inhibit ribosome recruitment at the 5 0 end, 36 it did not come as a surprise that the presence of TAR alone, or in the context of the HIV-1 5 0 -UTR, is inhibitory to cap-dependent translation in the RRL and in Xenopus oocytes. 34,35,37,38 Addition of the trans-dominant negative eIF4A R362Q mutant 39 Figure).…”

“…34,35 As it was previously demonstrated that the presence of a stem-loop of weaker stability (DG D ¡13.6kcal/mol) at the 5 0 end of a synthetic mRNA is enough to inhibit ribosome recruitment at the 5 0 end, 36 it did not come as a surprise that the presence of TAR alone, or in the context of the HIV-1 5 0 -UTR, is inhibitory to cap-dependent translation in the RRL and in Xenopus oocytes. 34,35,37,38 Addition of the trans-dominant negative eIF4A R362Q mutant 39 Figure). Ribosomal entry at the 5 0 end occurs by the recruitment of a trimeric complex composed of DDX3, PABP and eIF4G whereas internal entry takes place by direct binding of the 43S preinitiation complex to the IRES elements.…”

Thymic HIV-2 Infection Uncovers Posttranscriptional Control of Viral Replication in Human Thymocytes

“…HIV-2 and HIV-1 have been reported to differ significantly in their mechanisms of translation initiation (47). For instance, HIV-2 was described to have a lower translational efficiency than HIV-1 due to differences in the 5= untranslated region (5= UTR) of viral genomic RNA (48,49). In agreement with our observations, in the presence of equivalent T-cell-associated viral gag mRNA levels, the levels of Gag protein production were reported to be lower in T-cell lines and macrophages infected with HIV-2 than those infected with HIV-1 (49).…”