RIN1 Mediated Rescue of Rab5 Activity: A Novel Insight on Pseudomonas‐Phagosome Interaction

Abstract

The Rab proteins are a family of small GTP-binding proteins that regulate intracellular membrane trafficking of several pathogens. Rab5 was found to be present on phagosomes following phagocytosis of several bacterial pathogens and latex beads. Our earlier findings suggest that heat inactivated Pa is rapidly and efficiently internalized where as live Pa blocks Rab5 activity and subverts macrophage internalization at an early stage of phagocytosis. It was also observed that expression of Rab5-Guanine exchange factor (GEF) Ras interference 1 (Rin1), but not other GEFs (Rabex5 or Rap6) reversed this down regulation of Rab5 activity. In this current study, the molecular mechanism by which Rin1 rescues Rab5 activity has been investigated. To examine the modulation of Rab5 activity by live Pa at the time of internalization, we recorded the activity of endogenous Rab5 in a time dependent study and observed that Rab5 activity was attenuated at a very early time point (2.5 min) of phagocytosis. Interestingly, upon over-expressing Rin1 in macrophage cells, the Rab5 activity sustained for a prolonged time (20 min) reversing the negative effect from Pa. Further investigations revealed Rin1 Vps9 domain together with Rin1 Ras Associated (RA) domain are required for optimal Rab5 activation. Since Rin1 RA domain is essential for Rin1 interaction with Ras as an effector protein, the dynamics of Rin1 and Ras interaction during live Pa phagocytosis was investigated and Ras-Rin1 complex formation was confirmed during the period of early phagocytic processes. These observations highlight a novel mechanism of Rab5 activation as well as Rab5 targeting to phagosome membrane during internalization of live Pa.