ShlA toxin of Serratia induces P2Y2- and α5β1-dependent autophagy and bacterial clearance from host cells

Abstract

Serratia marcescens is an opportunistic human pathogen involved in antibiotic-resistanthospital acquired infections. Upon contact with the host epithelial cell and prior to internalization,Serratia induces an early autophagic response that is entirely dependent on the ShlA toxin. OnceSerratia invades the eukaryotic cell and multiples inside an intracellular vacuole, ShlA expressionalso promotes an exocytic event that allows bacterial egress from the host cell withoutcompromising its integrity. Several toxins, including ShlA, were shown to induce ATP efflux fromeukaryotic cells. Here, we demonstrate that ShlA triggered a non-lytic release of ATP from CHOcells. Enzymatic removal of accumulated extracellular ATP (eATP) or pharmacological blockageof the eATP-P2Y2 purinergic receptor inhibited the ShlA-promoted autophagic response in CHOcells. Despite the intrinsic ecto-ATPase activity of CHO cells, the effective concentration andkinetic profile of eATP was consistent with the established affinity of the P2Y2 receptor and the known kinetics of autophagy induction. Moreover, eATP removal or P2Y2 receptor inhibition alsosuppressed the ShlA-induced exocytic expulsion of the bacteria from the host cell. Blocking α5β1integrin highly inhibited ShlA-dependent autophagy, a result consistent with α5β1 transactivationby the P2Y2 receptor. In sum, eATP operates as the key signaling molecule that allows theeukaryotic cell to detect the challenge imposed by the contact with the ShlA toxin. Stimulation ofP2Y2-dependent pathways evokes the activation of a defensive response to counteract cell damage and promotes the non-lytic clearance of the pathogen from the infected cell.