SUMO and Cytoplasmic RNA Viruses: From Enemies to Best Friends.

SUMO is a ubiquitin-like protein that covalently binds to lysine residues of target proteins and regulates many biological processes such as protein subcellular localization or stability, transcription, DNA repair, innate immunity, or antiviral defense. SUMO has a critical role in the signaling pathway governing type I interferon (IFN) production, and among the SUMOylation substrates are many IFN-induced proteins. The overall effect of IFN is increasing global SUMOylation, pointing to SUMO as part of the antiviral stress response. Viral agents have developed different mechanisms to counteract the antiviral activities exerted by SUMO, and some viruses have evolved to exploit the host SUMOylation machinery to modify their own proteins. The exploitation of SUMO has been mainly linked to nuclear replicating viruses due to the predominant nuclear localization of SUMO proteins and enzymes involved in SUMOylation. However, SUMOylation of numerous viral proteins encoded by RNA viruses replicating at the cytoplasm has been lately described. Whether nuclear localization of these viral proteins is required for their SUMOylation is unclear. Here, we summarize the studies on exploitation of SUMOylation by cytoplasmic RNA viruses and discuss about the requirement for nuclear localization of their proteins.