The Small GTPase Rab-35 Facilitates the Initiation of Phagosome Maturation and Acts as a Robustness Factor for Apoptotic Cell Clearance

Authors

Ryan Haley
Zheng Zhou

Publication Date

5-1-2021

Journal

Small GTPases

DOI

10.1080/21541248.2019.1680066

PMID

31607221

PMCID

PMC7939568

PubMedCentral® Posted Date

10-24-2019

PubMedCentral® Full Text Version

Post-print

Published Open-Access

yes

Keywords

Animals, Apoptosis, Caenorhabditis elegans, Caenorhabditis elegans Proteins, Endosomes, Lysosomes, Phagosomes, Phosphatidylinositols, rab GTP-Binding Proteins, Apoptosis, phagocytosis, robustness, synthetic lethality, RAB-35, RAB-5, RAB-7, TBC-10, CED-1, PI(4, 5)P2, PI(3)P

Abstract

We recently identified the novel function of the small GTPase RAB-35 in apoptotic cell clearance in Caenorhabditis elegans, a process in which dying cells are engulfed and degraded inside phagosomes. We have found that RAB-35 functions in two separate steps of cell corpse clearance, cell corpse recognition and the initiation of phagosome maturation. During the latter process, RAB-35 facilitates the removal of phosphatidylinositol-4,5-bisphosphate (PI(4,5)P2) from the membranes of nascent phagosomes and the simultaneous production of phosphatidylinositol-3-P (PI(3)P) on these same membranes, a process that we have coined the PI(4,5)P2 to PI(3)P shift. RAB-35 also promotes the recruitment of the small GTPase RAB-5 to the phagosomal surface. During these processes, the activity of RAB-35 is controlled by the candidate GTPase-activating protein (GAP) TBC-10 and the candidate guanine nucleotide exchange factor (GEF) FLCN-1. Overall, RAB-35 leads a third pathway during cell corpse clearance that functions in parallel to the two known pathways, one led by the phagocytic receptor CED-1 and the other led by the CED-10/Rac1 GTPase. Here, we further report that RAB-35 acts as a robustness factor that maintains the clearance activity and embryonic viability under conditions of heat stress. Moreover, we obtained additional evidence suggesting that RAB-35 acts upstream of RAB-5 and RAB-7. To establish a precise temporal pattern for its own dissociation from phagosomal surfaces, RAB-35 controls the removal of its own GAP. We propose that RAB-35 defines a largely unexplored initial phase of phagosome maturation.