A phorbol ester‐binding protein is required downstream of Rab5 in endosome fusion

  title={A phorbol ester‐binding protein is required downstream of Rab5 in endosome fusion},
  author={A. Aballay and M. Barbieri and M. Colombo and G. Arenas and P. Stahl and L. Mayorga},
  journal={FEBS Letters},
Previous observations indicate that a zinc and phorbol ester binding factor is necessary for endosome fusion. To further characterize the role of this factor in the process, we used an in vitro endosome fusion assay supplemented with recombinant Rab5 proteins. Both zinc depletion and addition of calphostin C, an inhibitor of protein kinase C, inhibited endosome fusion in the presence of active Rab5. Addition of the phorbol ester PMA (phorbol 12‐myristate 13‐acetate) reversed the inhibition of… Expand
Phorbol ester promotes endocytosis by activating a factor involved in endosome fusion.
It is suggested that PMA stimulates endocytosis by regulating the dynamics of the early endosomes compartment by activating a factor required for endosome fusion. Expand
Transport of mannose-6-phosphate receptors from the trans-Golgi network to endosomes requires Rab31.
It is demonstrated that Rab31 is required for transport of MPRs from TGN to endosomes and for the Golgi/TGN organization. Expand
Calmodulin modulates hepatic membrane polarity by protein kinase C-sensitive steps in the basolateral endocytic pathway.
The results indicate that membrane trafficking at early steps of the basolateral endocytic pathway in HepG2 cells is regulated by an intricate interplay between calmodulin and PKC, which compromises cell polarity by impeding membrane trafficking from early endosomes to the apical membrane. Expand
Subunit organization and Rab interactions of Vps-C protein complexes that control endolysosomal membrane traffic
The Vps-C intersubunit contacts, domain architecture, and interactions with Rab G proteins are systematically dissected using genetic and biochemical approaches. Expand
Roles of the HOPS complex and Sec1/Munc18 proteins in membrane fusion
Roles of the HOPS complex and Sec1/Munc18 proteins in membrane fusion


A factor with a zinc- and phorbol ester-binding domain is necessary for endosome fusion.
Western blot analysis demonstrated the presence of proteins containing PKC-like cysteine-rich regions that are released from endosomal fractions by zinc chelators, indicating that the previously proposed zinc-dependent factor required for endosome fusion could be either a PKC isoform or a protein containing the phorbol ester-binding domain of PKC. Expand
Characterization of Rab5:Q79L-stimulated endosome fusion.
The results indicate that rab5:Q79L promotes fusion by activating factors already present in the membranes and that NSF and phospholipase A2 activities are required downstream of rab5. Expand
Rabaptin-5 is a direct effector of the small GTPase Rab5 in endocytic membrane fusion
Rabies5 recruits rabaptin-5 to purified early endosomes in a GTP-dependent manner, demonstrating functional similarities with other members of the Ras superfamily. Expand
GTPase activity of Rab5 acts as a timer for endocytic membrane fusion
The data reveal that the GTP cycle of Rab proteins differs from that of other GTPases and indicate that GTP hydrolysis acts as a timer that determines the frequency of membrane docking/fusion events. Expand
The small GTPase rab5 functions as a regulatory factor in the early endocytic pathway
It is concluded that rab5 is a rate-limiting component of the machinery regulating the kinetics of membrane traffic in the early endocytic pathway. Expand
Inhibition of rab5 GTPase activity stimulates membrane fusion in endocytosis.
The opposite effects of the rab5 Q79L and S34N mutants suggest that rab5:GTP is required prior to membrane fusion, whereas GTP hydrolysis by rab5 occurs after membrane fusion and functions to inactivate the protein. Expand
Evidence for phosphatidylinositol 3-kinase as a regulator of endocytosis via activation of Rab5.
Wortmannin inhibited constitutive endocytosis of horseradish peroxidase and transferrin in BHK-21 and TRVb-1 cells and indicates that PI 3-kinase plays an important role in regulation of early endosome fusion, probably via activation of Rab5. Expand
Structural features of the GTP-binding defective Rab5 mutants required for their inhibitory activity on endocytosis.
It is believed that Rab5 function requires protein-protein interactions with Rab5-specific regulators and effectors, and some of these interactions are disrupted by Rab5:S34N and Rab4:N133I, which are dominant inhibitors of endocytosis. Expand
EEA1 links PI(3)K function to Rab5 regulation of endosome fusion
The identification of EEA1 as a direct Rab5 effector provides a molecular link between PI(3)K and Rab5, and its restricted distribution to early endosomes indicates that EEA 1 may confer directionality to Rab5-dependent endocytic transport. Expand
Zn2+ depletion blocks endosome fusion.
It is reported that fusion can proceed at very low Ca2+ concentrations, and evidence is presented that Zn2+ depletion blocks endosome fusion, suggesting that this ion is necessary for the function of one or more factors involved in the fusion process. Expand