An RNA-binding protein secreted by Listeria monocytogenes activates RIG-I signaling

RNA binding proteins (RBPs) perform key cellular activities by controlling the function of bound RNAs. The widely held assumption that RBPs are strictly intracellular has been challenged by the discovery of secreted RBPs. While extracellular RBPs have been described in mammals, secreted bacterial RBPs have not been reported. Here, we show that the bacterial pathogen L. monocytogenes secretes a small RBP that we named Zea. We show that Zea binds a subset of L. monocytogenes RNAs causing their accumulation in the extracellular medium. Furthermore, during L. monocytogenes infection, Zea binds RIG-I, the non-self-RNA innate immunity sensor, potentiating interferon beta production. Mouse infection studies revealed that Zea modulates L. monocytogenes virulence. Together, this study uncovered the presence of an extracellular ribonucleoprotein complex from bacteria and its involvement in host-pathogen crosstalk