Collapse of late endosomal pH elicits a rapid Rab7 response via V-ATPase and RILP

Endosomal-lysosomal trafficking entails progressive acidification of endosomal compartments by the H(+)-V-ATPase to reach low lysosomal pH. Disruption of proper pH affects lysosomal function and the balance of protein synthesis and degradation (proteostasis). Disruption of endosomal pH also impairs endocytic maturation upstream of the lysosome. Using a lysosomal damage model (LLOMe), we identify the late endosomal small GTPase Rab7 as a rapid responder to endosomal/lysosomal pH neutralization. Luminal pH neutralization in LLOMe leads to increased assembly of the V(1)G(1) subunit of the V-ATPase on endosomal membranes and stabilization of Rab7 in the GTP-bound form. Rab7 stabilization is driven by a combination of pump assembly and the Rab7 effector RILP, while contributing to loss of late endosome tubulation and recycling of membrane receptors, like CI-M6PR. Our findings suggest a physiological cascade on late endosomes driven by V-ATPase assembly and Rab7 stabilization to counteract pH neutralization, and a novel model of how late endosomes broadly contribute to cellular stress responses, including LLOMe-mediated damage.