THE SMALL GTP-BINDING PROTEIN RAB7 IS ESSENTIAL FOR CELLULAR VACUOLATION INDUCED BY HELICOBACTER-PYLORI CYTOTOXIN

The VacA cytotoxin, produced by toxigenic strains of Helicobacter pylo ri, induces the formation of large vacuoles highly enriched in the sma ll GTPase rab7. To probe the role of rab7 in vacuolization, HeLa cells were transfected with a series of rab mutants and exposed to VacA. Do minant-negative mutants of rab7 effectively prevented vacuolization, w hereas homologous rab5 and rab9 mutants were only partially inhibitory or ineffective, respectively. Expression of wild-type or GTPase-defic ient rab mutants synergized with VacA in inducing vacuolization. In vi tro fusion of late endosomes was enhanced by active rab7 and inhibited by inactive rab7, consistent with vacuole formation by merging of lat e endosomes in a process that requires functional rab7. Taken together , the effects of overexpressed rab proteins described here indicate th at continuous membrane flow along the endocytic pathway is necessary f or vacuole growth.