rab7b controls trafficking from endosomes to the tgn

Rab7b is a recently identified member of the Rab GTPase protein family and has high similarity to Rab7. It has been reported that Rab7b is lysosome associated, that it is involved in monocytic differentiation and that it promotes lysosomal degradation of TLR4 and TLR9. Here we investigated further the localization and function of this GTPase. We found that wild-type Rab7b is lysosome associated whereas an activated, GTP-bound form of Rab7b localizes to the Golgi apparatus. In contrast to Rab7, Rab7b is not involved in EGF and EGFR degradation. Depletion of Rab7b or expression of Rab7b T22N, a Rab7b dominant-negative mutant, impairs cathepsin-D maturation and causes increased secretion of hexosaminidase. Moreover, expression of Rab7b T22N or depletion of Rab7b alters TGN46 distribution, cation-independent mannose-6-phosphate receptor (CI-MPR) trafficking, and causes an increase in the levels of the late endosomal markers CI-MPR and cathepsin D. Vesicular stomatitis virus G protein (VSV-G) trafficking, by contrast, is normal in Rab7b-depleted or Rab7b-T22N-expressing cells. In addition, depletion of Rab7b prevents cholera toxin B-subunit from reaching the Golgi. Altogether, these data indicate that Rab7b is required for normal lysosome function, and, in particular, that it is an essential factor for retrograde transport from endosomes to the trans-Golgi network (TGN)

RILP regulates vacuolar ATPase through interaction with the V1G1 subunit

Rab-interacting lysosomal protein (RILP) is a downstream effector of the Rab7 GTPase. GTP-bound Rab7 recruits RILP to endosomal membranes and, together, they control late endocytic traffic, phagosome and autophagosome maturation and are responsible for signaling receptor degradation. We have identified, using different approaches, the V1G1 (officially known as ATP6V1G1) subunit of the vacuolar ATPase (V-ATPase) as a RILP-interacting protein. V1G1 is a component of the peripheral stalk and is fundamental for correct V-ATPase assembly. We show here that RILP regulates the recruitment of V1G1 to late endosomal and lysosomal membranes but also controls V1G1 stability. Indeed, we demonstrate that V1G1 can be ubiquitylated and that RILP is responsible for proteasomal degradation of V1G1. Furthermore, we demonstrate that alterations in V1G1 expression levels impair V-ATPase activity. Thus, our data demonstrate for the first time that RILP regulates the activity of the V-ATPase through its interaction with V1G1. Given the importance of V-ATPase in several cellular processes and human diseases, these data suggest that modulation of RILP activity could be used to control V-ATPase function

The Rab-interacting lysosomal protein (RILP) regulates vacuolar ATPase acting on the V1G1 subunit

RILP is a downstream effector of the Rab7 GTPase. GTP-bound Rab7 recruits RILP on endosomal membranes and, together, they control late endocytic traffic, phagosome and autophagosome maturation and are responsible for signaling receptor degradation. We have identified, using different approaches, the V1G1 subunit of the vacuolar ATPase (V-ATPase) as a RILP interacting protein. V1G1 is a component of the peripheral stalk and it is fundamental for correct V-ATPase assembly. We established that RILP regulates the recruitment of V1G1 subunit to late endosomal/lysosomal membranes but also controls V1G1 stability. Indeed, we demonstrated that V1G1 is ubiquitinated and that RILP is responsible for proteasomal degradation of V1G1. Furthermore, we demonstrated that alterations of V1G1 expression levels impair V-ATPase activity. Thus, our data demonstrate for the first time that RILP regulates the activity of the V-ATPase through the interaction with V1G1. Given the importance of V-ATPase in several cellular processes and human diseases, these data suggest that modulation of RILP activity could be used to control V-ATPase function

RILP regulates vacuolar ATPase through interaction with the V1G1 subunit

Erratum for RILP regulates vacuolar ATPase through interaction with the V1G1 subunit. [J Cell Sci. 2014

Rab7b and receptors trafficking

Rab proteins are key-regulators of intracellular membrane trafficking. Rab7b is a recently identified Rab protein that may downregulate TLR4 and TLR9-mediated inflammatory responses. Rab7b, believed to have similar function as Rab7, controls however vesicular trafficking from endosomes to the TGN. It is localized to late endosomes/lysosomes as well as the TGN. Rab7b interferes with enzymes delivery to lysosomes and with the retrograde Shiga toxin transport to the Golgi. Furthermore, Rab7b depletion alters CI-MPR and TGN46 trafficking. In conclusion, Rab7b, by regulating the transport from late endosomes to the TGN, is fundamental for trafficking of several receptors, opening for a revised scenario for its influence on signaling of Toll-like Receptors (TLRs) and other receptors

Vimentin phosphorylation and assembly are regulated by the small GTPase Rab7a

Intermediate filaments are cytoskeletal elements important for cell architecture. Recently it has been discovered that intermediate filaments are highly dynamic and that they are fundamental for organelle positioning, transport and function thus being an important regulatory component of membrane traffic. We have identified, using the yeast two-hybrid system, vimentin, a class III intermediate filament protein, as a Rab7a interacting protein. Rab7a is a member of the Rab family of small GTPases and it controls vesicular membrane traffic to late endosomes and lysosomes. In addition, Rab7a is important for maturation of phagosomes and autophagic vacuoles. We confirmed the interaction in HeLa cells by co-immunoprecipitation and pull-down experiments, and established that the interaction is direct using bacterially expressed recombinant proteins. Immunofluorescence analysis on HeLa cells indicate that Rab7a-positive vesicles sometimes overlap with vimentin filaments. Overexpression of Rab7a causes an increase in vimentin phosphorylation at different sites and causes redistribution of vimentin in the soluble fraction. Consistently, Rab7a silencing causes an increase of vimentin present in the insoluble fraction (assembled). Also, expression of Charcot-Marie-Tooth 2B-causing Rab7a mutant proteins induces vimentin phosphorylation and increases the amount of vimentin in the soluble fraction. Thus, modulation of expression levels of Rab7a wt or expression of Rab7a mutant proteins changes the assembly of vimentin and its phosphorylation state indicating that Rab7a is important for the regulation of vimentin function

Meningococcal two partner secretion (TPS) proteins promote vacuole escaping and intercellular spreading

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