CD95/Fas ligand mRNA is toxic to cells through more than one mechanism

Analysis of the Contribution of 6-mer Seed Toxicity to HIV-1-Induced Cytopathicity

HIV-1 (HIV) infects CD4+ T cells, the gradual depletion of which can lead to AIDS in the absence of antiretroviral therapy (ART). Some cells, however, survive HIV infection and persist as part of the latently infected reservoir that causes recurrent viremia after ART cessation. Improved understanding of the mechanisms of HIV-mediated cell death could lead to a way to clear the latent reservoir. Death induced by survival gene elimination (DISE), an RNA interference (RNAi)-based mechanism, kills cells through short RNAs (sRNAs) with toxic 6-mer seeds (positions 2 to 7 of sRNA). These toxic seeds target the 3' untranslated region (UTR) of mRNAs, decreasing the expression of hundreds of genes critical for cell survival. In most cells under normal conditions, highly expressed cell-encoded nontoxic microRNAs (miRNAs) block access of toxic sRNAs to the RNA-induced silencing complex (RISC) that mediates RNAi, promoting cell survival. HIV has been shown to inhibit the biogenesis of host miRNAs in multiple ways. We now report that HIV infection of cells deficient in miRNA expression or function results in enhanced RISC loading of an HIV-encoded miRNA HIV-miR-TAR-3p, which can kill cells by DISE through a noncanonical (positions 3 to 8) 6-mer seed. In addition, cellular RISC-bound sRNAs shift to lower seed viability. This also occurs after latent HIV provirus reactivation in J-Lat cells, suggesting independence of permissiveness of cells to viral infection. More precise targeting of the balance between protective and cytotoxic sRNAs could provide new avenues to explore novel cell death mechanisms that could be used to kill latent HIV. IMPORTANCE Several mechanisms by which initial HIV infection is cytotoxic to infected cells have been reported and involve various forms of cell death. Characterizing the mechanisms underlying the long-term survival of certain T cells that become persistent provirus reservoirs is critical to developing a cure. We recently discovered death induced by survival gene elimination (DISE), an RNAi-based mechanism of cell death whereby toxic short RNAs (sRNAs) containing 6-mer seed sequences (exerting 6-mer seed toxicity) targeting essential survival genes are loaded into RNA-induced silencing complex (RISC) complexes, resulting in inescapable cell death. We now report that HIV infection in cells with low miRNA expression causes a shift of mostly cellular RISC-bound sRNAs to more toxic seeds. This could prime cells to DISE and is further enhanced by the viral microRNA (miRNA) HIV-miR-TAR-3p, which carries a toxic noncanonical 6-mer seed. Our data provide multiple new avenues to explore novel cell death mechanisms that could be used to kill latent HIV.