FTSJ3 is an RNA 2′-O-methyltransferase recruited by HIV to avoid innate immune sensing

In mammals, 2′-O-methylation of RNA is a molecular signature by which the cellular innate immune system distinguishes endogenous from exogenous messenger RNA1–3. However, the molecular functions of RNA 2′-O-methylation are not well understood. Here we have purified TAR RNA-binding protein (TRBP) and its interacting partners and identified a DICER-independent TRBP complex containing FTSJ3, a putative 2′-O-methyltransferase (2′O-MTase). In vitro and ex vivo experiments show that FTSJ3 is a 2′O-MTase that is recruited to HIV RNA through TRBP. Using RiboMethSeq analysis4, we identified predominantly FTSJ3-dependent 2′-O-methylations at specific residues on the viral genome. HIV-1 viruses produced in FTSJ3 knockdown cells show reduced 2′-O-methylation and trigger expression of type 1 interferons (IFNs) in human dendritic cells through the RNA sensor MDA5. This induction of IFN-α and IFN-β leads to a reduction in HIV expression. We have identified an unexpected mechanism used by HIV-1 to evade innate immune recognition: the recruitment of the TRBP–FTSJ3 complex to viral RNA and its 2′-O-methylation.