Infect Immun. 2013 Jul;81(7):2426-36.

Regulation of Rab5 function during phagocytosis of live Pseudomonas aeruginosa in macrophages.

Mustafi S, Rivero N, Olson JC, Stahl PD, Barbieri MA.

Department of Biological Sciences, Florida International University, Miami, Florida, USA.

 

ABSTRACT:

Pseudomonas aeruginosa, a Gram-negative opportunistic human pathogen, is a frequent cause of severe hospital-acquired infections. Effectors produced by the type III secretion system disrupt mammalian cell membrane trafficking and signaling and are integral to the establishment of P. aeruginosa infection. One of these effectors, ExoS, ADP-ribosylates several host cell proteins, including Ras and Rab GTPases. In this study, we demonstrated that Rab5 plays a critical role during early stages of P. aeruginosa invasion of J774-Eclone macrophages. We showed that live, but not heat-inactivated, P. aeruginosa inhibited phagocytosis and that this occurred in conjunction with downregulation of Rab5 activity. Inactivation of Rab5 was dependent on ExoS ADP-ribosyltransferase activity, and in J744-Eclone cells, ExoS ADP-ribosyltransferase activity caused a more severe inhibition of phagocytosis than ExoS Rho GTPase activity. Furthermore, we found that expression of Rin1, a Rab5 guanine exchange factor, but not Rabex5 and Rap6, partially reversed the inactivation of Rab5 during invasion of live P. aeruginosa. These studies provide evidence that live P. aeruginosa cells are able to influence their rate of phagocytosis in macrophages by directly regulating activation of Rab5.

PMID: 23630954

paeurginosa_model_2
Fig 1. Pseudomonas aeruginosa uses Type III secretion mechanism and injects effector proteins in host cells. Exoenzyme S (EXOS) is a type III secretion effector protein which ADP-ribosylates small GTPases and modify their activity inside host cells. Rab5, a small GTPase protein is a key regulator of early phagocytosis. Rab5 cycles between GDP- bound inactive form and GTP-bound active form, which are regulated by several Rab5-GAPs (Guanine Activating Proteins) and Rab5-GEFs (Rab5-Guanine Exchange Factors). In this study it was found that live, but not heat inactivated, P. aeruginosa inhibited phagocytosis, and that this occurred in conjunction with down-regulation of Rab5 activity. Inactivation of Rab5 was dependent on EXOS ADP-ribosyltransferase activity and more than one arginine residue in Rab5 are possible target for the ADP-ribosylation modification.

 

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