Abstract
Translation initiation from the human immunodeficiency virus type-1 (HIV-1) mRNA can occur through a cap or an IRES dependent mechanism. Cap-dependent translation initiation of the HIV-1 mRNA can be inhibited by the instability element (INS)-1, a cis-acting regulatory element present within the gag open reading frame (ORF). In this study we evaluated the impact of the INS-1 on HIV-1 IRES-mediated translation initiation. Using heterologous bicistronic mRNAs, we show that the INS-1 negatively impact on HIV-1 IRES-driven translation in in vitro and in cell-based experiments. Additionally, our results show that the inhibitory effect of the INS-1 is not general to all IRESes since it does not hinder translation driven by the HCV IRES. The inhibition by the INS-1 was partially rescued in cells by the overexpression of the viral Rev protein or hnRNPA1.
Highlights
In eukaryotes, the expression of proteins is frequently subject to regulation at the level of the initiation of mRNA translation [1,2]
Following the same experimental approach that was used to establish that instability element (INS)-1 inhibits cap-dependent translation initiation, the INS-1 was placed after the stop codon of the second cistron in the context of the dl human immunodeficiency virus type 1 (HIV-1) internal ribosome entry site (IRES) bicistronic mRNA, that harbors the HIV-1 59UTR within the intercistronic space [6]
Results were expressed as relative luciferase activity (RLA), with the mean luciferase activity of the Renilla luciferase gene (RLuc) and firefly luciferase gene (FLuc) reporters expressed from the dl HIV-1 IRES RNA arbitrarily set to 100% (+/2 SEM)
Summary
The expression of proteins is frequently subject to regulation at the level of the initiation of mRNA translation [1,2]. The unspliced HIV-1 mRNA harbors two IRESes, the first of which is in the 59UTR (here referred to as the HIV-1 IRES) [6,7], and the second of which is within the gag open reading frame (the HIV-1 gag IRES) [8]. This observed redundancy in the possible mechanisms used to initiate translation of the unspliced HIV-1 mRNA, cap- or IRES-dependent, is conserved among primate lentiviruses suggesting that translation initiation of the unspliced mRNA is a key step during the viral life cycle [4]
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