Cellular hnRNPA0 limits HIV-1 production by interference with LTR-activity and programmed ribosomal frame-shifting

Abstract

The interplay between host factors and viral components has a profound impact on the viral replication efficiency and fitness. Heterogeneous nuclear ribonucleoproteins (hnRNPs), in particular members of the subfamily A/B, have been broadly studied as HIV-1 host dependency factors, however, the least related member hnRNPA0 has so far not been functionally studied in its potential role affecting viral replication. In this study, we revealed that hnRNPA0 overexpression in HEK293T cells significantly reduced HIV-1 long terminal repeat (LTR) activity up to 3.5-fold, leading to a significant decrease in total viral mRNA (5.5-fold) and protein levels (3-fold). Conversely, knockdown of hnRNPA0 enhanced LTR activity, suggesting its negative regulatory role in viral gene expression. Moreover, the splicing pattern of HIV-1 remained largely unaffected by altered hnRNPA0 levels indicating changes in viral mRNA expression predominantly occurred at the transcriptional level. Moreover, hnRNPA0 overexpression was found to significantly reduce the programmed ribosomal frameshift efficiency of HIV-1, resulting in a shift in the HIV-1 p55/p15 ratio, compromising viral fitness. Synergistic inhibition of LTR activity and thus reduced viral mRNA transcription and impaired ribosomal frameshifting efficiency, which is important for viral infectivity, were detrimental to HIV-1 replication. Additionally, our study revealed that hnRNPA0 levels were lower in therapy naive HIV-1-infected individuals compared to healthy controls and temporarily repressed after IFN-I treatment in HIV-1 target cells. Our findings highlight the significant role of hnRNPA0 in HIV-1 replication and suggests that its IFN-I regulated expression levels are decisive for viral fitness. ImportanceRNA binding proteins, in particular heterogeneous nuclear ribonucleoproteins (hnRNPs) have been extensively studied as host dependency factors for HIV-1 since they are involved in multiple cellular gene expression processes. However, the functional role of hnRNPA0, the least related member of the hnRNPA/B family, and its potential impact on viral replication remains unclear. For the first time, our findings demonstrate the significance of hnRNPA0 in restricting viral replication efficiency. We demonstrate that hnRNPA0 plays a pleiotropic role in limiting viral replication being a negative regulator of viral transcription and significantly impairing ribosomal frameshifting. Our study also revealed hnRNPA0 as an IFN-regulated host factor that is temporarily repressed after IFN-I treatment in HIV-1 target cells and lower expressed in therapy-naive HIV-1-infected individuals compared to healthy controls. Understanding the mode of action between hnRNPA0 and HIV-1 might help to identify novel therapeutically strategies against HIV-1 and other viruses.