Two Rab7 isotypes, Eh Rab7A and Eh Rab7B, play distinct roles in biogenesis of lysosomes and phagosomes in the enteric protozoan parasite Entamoeba histolytica

Abstract

Rab7 small GTPase plays a crucial role in the regulation of trafficking to late endosomes, lysosomes and phagosomes. While most eukaryotes encode a single Rab7, the parasitic protist Entamoeba histolytica possesses nine Rab7. In this study, to understand the significance of the presence of multiple Rab7 isotypes, a role of two representative Rab7 isotypes, Eh Rab7A and Eh Rab7B, was investigated. Eh Rab7B was exclusively localized to acidic vacuoles containing lysosomal proteins, e.g. amoebapore-A and cysteine protease. This lysosome localization of Eh Rab7B was in good contrast to Eh Rab7A, localized to a non-acidic compartment in steady state, and only partially colocalized with lysosomal proteins. Overexpression of Eh Rab7B resulted in augmentation of late endosome/lysosome acidification, similar to the Eh Rab7A overexpression. Expression of Eh Rab7B-GTP mutant caused dominant-negative phenotypes including decrease in late endosome/ lysosome acidification and missecretion of lysosomal proteins, while Eh Rab7A-GTP enhanced acidification but did not affect either intracellular or secreted cysteine protease activity. Expression of either Eh Rab7B or Eh Rab7B-GTP mutant caused defect in phagocytosis, concomitant with the disturbed formation and disassembly of prephagosomal vacuoles, the compartment previously shown to be linked to efficient ingestion. Altogether, these data indicate that the two Rab7 isotypes play distinct but co-ordinated roles in lysosome and phagosome biogenesis. © 2007 The Authors; Journal compilation © 2007 Blackwell Publishing Ltd.