title: The small GTPase Rab22 interacts with EEA1 and controls endosomal membrane trafficking.
abstract: Rab22a is a small GTPase that is expressed ubiquitously in mammalian tissues and displays the highest sequence homology to Rab5. In BHK-21 cells, overexpression of the wild-type Rab22a caused formation of abnormally large vacuole-like structures containing the early-endosomal antigen EEA1 but not Rab11, a marker of recycling endosomes or the late-endosomal/lysosomal markers LAMP-1 and lyso-bis-phosphatidic acid. In HeLa cells, overexpressed Rab22a was found on smaller EEA1-positive endosomes, but a portion of the protein was also found in the Golgi complex. Using the yeast two-hybrid system and a biochemical pull-down assay, the GTP-bound form of Rab22a was found to interact with the N-terminus of EEA1. In HeLa cells overexpressing Rab22a or its mutants affected in the GTPase cycle, no significant changes were observed in the uptake of Alexa-transferrin. However, the GTPase-deficient Rab22a Q64L mutant caused a redistribution of transferrin-positive endosomes to the leading edges of cells and a fragmentation of the Golgi complex. In BHK cells, the Q64L mutant caused the accumulation of a fluid phase marker, TRITC-dextran, and a lysosomal hydrolase, aspartylglucosaminidase, in abnormal vacuole-like structures that contained both early and late endosome markers. Both the wild-type Rab22a and the Q64L mutant were found to interfere with the degradation of EGF. These results suggest that Rab22a may regulate the dynamic interactions of endosomal compartments and it may be involved in the communication between the biosynthetic and early endocytic pathways.
authors.affiliation: Department of Molecular Medicine, National Public Health Institute (KTL), Biomedicum, PO Box 104, FIN-00251 Helsinki, Finland.
authors.forename: Maria
authors.initials: M
authors.lastname: Kauppi
authors.forename: Anne
authors.initials: A
authors.lastname: Simonsen
authors.forename: Bjørn
authors.initials: B
authors.lastname: Bremnes
authors.forename: Amandio
authors.initials: A
authors.lastname: Vieira
authors.forename: Judy
authors.initials: J
authors.lastname: Callaghan
authors.forename: Harald
authors.initials: H
authors.lastname: Stenmark
authors.forename: Vesa M
authors.initials: VM
authors.lastname: Olkkonen
mesh_terms: D000818:Animals; D002451:Cell Compartmentation / Q000502:physiology*; D002478:Cells, Cultured; D006224:Cricetinae; D004705:Endocytosis / Q000502:physiology*; D011992:Endosomes / Q000378:metabolism* / Q000648:ultrastructure; D005057:Eukaryotic Cells / Q000166:cytology / Q000201:enzymology*; D006056:Golgi Apparatus / Q000378:metabolism / Q000648:ultrastructure; D006801:Humans; D007425:Intracellular Membranes / Q000378:metabolism*; D008565:Membrane Proteins / Q000378:metabolism*; D009154:Mutation / Q000502:physiology; D011485:Protein Binding / Q000502:physiology; D020033:Protein Isoforms / Q000378:metabolism; D021381:Protein Transport / Q000502:physiology*; D011869:Radioligand Assay; D011993:Recombinant Fusion Proteins; D014168:Transferrin / Q000235:genetics / Q000378:metabolism; D033921:Vesicular Transport Proteins; D020691:rab GTP-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D020696:rab5 GTP-Binding Proteins / Q000235:genetics / Q000378:metabolism
chemical_list: D008565:Membrane Proteins; D020033:Protein Isoforms; C484191:RAB22A protein, human; D011993:Recombinant Fusion Proteins; D014168:Transferrin; D033921:Vesicular Transport Proteins; C093846:early endosome antigen 1; D020691:rab GTP-Binding Proteins; D020696:rab5 GTP-Binding Proteins