Rin1 restores host phagocytic activity during invasion byPseudomonas aeruginosa

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Pseudomonas aeruginosa uses a type III secretion system to deliver toxic effector proteins directly into host cells and alter host protein functions. Exoenzyme S (ExoS), a type III effector protein, ADP-ribosylates Rab5 GTPase and impairs early phagocytic events in macrophage cells. In this study, we tested the hypothesis that Rin1, a Ras effector protein and Rab5 guanine nucleotide exchange factor, generates an intrinsic Rab5 activity cycle during phagocytosis of live P. aeruginosa; thus, allowing proper phagocytic killing. We found that Rab5 activity was attenuated at a very early time point (2.5 min) of the phagocytic process of live but not of heat-inactivated P. aeruginosa. However, upon overexpressing Rin1 in macrophages, the Rab5 activity sustained for a prolonged time (∼20 min) counteracting the negative effects during phagocytosis of live P. aeruginosa. Ras, also a substrate of the ADP-ribosyltransferase activity of ExoS, remained active during the early events of phagocytosis of live as well as heat-inactivated P. aeruginosa. Further examinations revealed that the Rin1 : Vps9 domain (the Rab5 nucleotide catalytic domain) and the Rin1 : RA domain (the Ras association domain of Rin1) are both required for optimal Rin1 function. Finally, the time-based analysis of the ADP-ribosylation status of Rab5 and Ras obtained from this study was consistent in the context of the regulation of (i) Rab5 activity by Rin1 : Vps9 domain and (ii) Ras interaction with Rin1 via the Rin1 : RA domain. These observations highlight a novel crosstalk between Rin1–Rab5 and Rin1–Ras complexes that offsets the anti-phagocytic effects of ExoS in macrophages.

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