Bacterial ubiquitin ligases hijack the host deubiquitinase OTUB1 to inhibit MTORC1 signaling and promote autophagy

Many bacterial pathogens have evolved effective strategies to interfere with the ubiquitination network to evade clearance by the innate immune system. Here, we report that OTUB1, one of the most abundant deubiquitinases (DUBs) in mammalian cells, is subjected to both canonical and noncanonical ubiquitination during Legionella pneumophila infection. The effectors SidC and SdcA catalyze OTUB1 ubiquitination at multiple lysine residues, resulting in its association with a Legionella-containing vacuole. Lysine ubiquitination by SidC and SdcA promotes interactions between OTUB1 and DEPTOR, an inhibitor of the MTORC1 pathway, thus suppressing MTORC1 signaling. The inhibition of MTORC1 leads to suppression of host protein synthesis and promotion of host macroautophagy/autophagy during L. pneumophila infection. In addition, members of the SidE family effectors (SidEs) induce phosphoribosyl (PR)-linked ubiquitination of OTUB1 at Ser16 and Ser18 and block its DUB activity. The levels of the lysine and serine ubiquitination of OTUB1 are further regulated by effectors that function to antagonize the activities of SidC, SdcA and SidEs, including Lem27, DupA, DupB, SidJ and SdjA. Our study reveals an effectors-mediated complicated mechanism in regulating the activity of a host DUB.