Abstract
The major virulence determinant of Legionella pneumophila is the type IVB secretion system (T4BSS), which delivers approximately 330 effector proteins into the host cell to modulate various cellular processes. However, the functions of most effector proteins remain unclear. WipA, an effector, was the first phosphotyrosine phosphatase of Legionella with unknown function. In this study, we found that WipA induced relatively strong growth defects in yeast in a phosphatase activity-dependent manner. Phosphoproteomics data showed that WipA was likely involved into endocytosis, FcγR-mediated phagocytosis, tight junction, and regulation of actin cytoskeleton pathways. Western blotting further confirmed WipA dephosphorylates several proteins associated with actin polymerisation, such as p-N-WASP, p-ARP3, p-ACK1, and p-NCK1. Thus, we hypothesised that WipA targets N-WASP/ARP2/3 complex signalling pathway, leading to disturbance of actin polymerisation. Indeed, we demonstrated that WipA inhibits host F-actin polymerisation by reducing the G-actin to F-actin transition during L. penumophila infection. Furthermore, the intracellular proliferation of wipA/legK2 double mutant was significantly impaired at the late stage of infection, although the absence of WipA does not confer any further effect on actin polymerisation to the legK2 mutant. Collectively, this study provides unique insights into the WipA-mediated regulation of host actin polymerisation and assists us to elucidate the pathogenic mechanisms of L. pnuemophila infection.