The rab7 GTPase controls the maturation of Salmonella typhimurium-containing vacuoles in HeLa cells

Following entry into non-phagocytic HeLa cells, the facultative pathogen Sa lmonella typhimurium survives and replicates within a membrane-bound vacuol e, Preceding the initiation of intracellular replication there is a lag pha se, during which the bacteria modulate their environment, This phase is cha racterized by the rapid recycling of early endosomal proteins present on th e nascent vacuole followed by the acquisition of a subset of lysosomal prot eins. To gain a better understanding of the mechanism of intracellular surv ival, we have followed the biogenesis of the S.typhimurium-containing vacuo le (SCV)in HeLa cells expressing different mutant forms of the small GTPase rab7, We demonstrate that the SCV recruits pre-existing lysosomal glycopro teins (Lgps) in a rab7-dependent manner, without directly interacting with lysosomes, We also show the transient accumulation, in the vicinity of the SCV, of novel rab7- and Lgp-containing vesicles containing very low amounts of cathepsin D, The size of these vesicles is dependent on rab7 activity, suggesting a role for rab7 in their homotypic fusion, Taken together, these results indicate that rab7 regulates SCV biogenesis during the phase chara cterized by the rapid acquisition of lysosomal proteins, We propose that SC V maturation involves its interaction with rab7/Lgp-containing vesicles whi ch are possible intermediate cargo components of the late endocytic pathway .