title: RIN3: a novel Rab5 GEF interacting with amphiphysin II involved in the early endocytic pathway.
abstract: The small GTPase Rab5, which cycles between active (GTP-bound) and inactive (GDP-bound) states, plays essential roles in membrane budding and trafficking in the early endocytic pathway. However, the molecular mechanisms underlying the Rab5-regulated processes are not fully understood other than the targeting event to early endosomes. Here, we report a novel Rab5-binding protein, RIN3, that contains many functional domains shared with other RIN members and additional Pro-rich domains. RIN3 displays the same biochemical properties as RIN2, the stimulator and stabilizer of GTP-Rab5. In addition, RIN3 exhibits its unique intracellular localization. RIN3 expressed in HeLa cells localized to cytoplasmic vesicles and the RIN3-positive vesicles contained Rab5 but not the early endosomal marker EEA1. Transferrin appeared to be transported partly through the RIN3-positive vesicles to early endosomes. RIN3 was also capable of interacting via its Pro-rich domain with amphiphysin II, which contains SH3 domain and participates in receptor-mediated endocytosis. Interestingly, cytoplasmic amphiphysin II was translocated into the RIN3- and Rab5-positive vesicles when co-expressed with RIN3. These results indicate that RIN3 biochemically characterized as the stimulator and stabilizer for GTP-Rab5 plays an important role in the transport pathway from plasma membrane to early endosomes.
authors.affiliation: Department of Physiological Chemistry, Graduate School of Pharmaceutical Sciences, University of Tokyo, Tokyo 113-0033, Japan.
authors.forename: Hiroaki
authors.initials: H
authors.lastname: Kajiho
authors.forename: Kota
authors.initials: K
authors.lastname: Saito
authors.forename: Kyoko
authors.initials: K
authors.lastname: Tsujita
authors.forename: Kenji
authors.initials: K
authors.lastname: Kontani
authors.forename: Yasuhiro
authors.initials: Y
authors.lastname: Araki
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Kurosu
authors.forename: Toshiaki
authors.initials: T
authors.lastname: Katada
mesh_terms: D000818:Animals; D001692:Biological Transport; D019556:COS Cells; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism; D002478:Cells, Cultured; D002522:Chlorocebus aethiops; D003001:Cloning, Molecular; D022162:Cytoplasmic Vesicles / Q000378:metabolism; D004705:Endocytosis; D011992:Endosomes / Q000378:metabolism*; D020662:Guanine Nucleotide Exchange Factors / Q000235:genetics / Q000378:metabolism; D006367:HeLa Cells; D006801:Humans; D008561:Membrane Fusion / Q000502:physiology; D008565:Membrane Proteins / Q000378:metabolism; D018613:Microscopy, Confocal; D009419:Nerve Tissue Proteins / Q000378:metabolism*; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D020798:Two-Hybrid System Techniques; D033921:Vesicular Transport Proteins; D020696:rab5 GTP-Binding Proteins / Q000378:metabolism*
chemical_list: D002352:Carrier Proteins; D020662:Guanine Nucleotide Exchange Factors; D008565:Membrane Proteins; D009419:Nerve Tissue Proteins; C447829:RIN2 protein, human; C487967:RIN3 protein, human; D033921:Vesicular Transport Proteins; C093846:early endosome antigen 1; C075637:amphiphysin; D020696:rab5 GTP-Binding Proteins