title: Differential membrane localization of ERas and Rheb, two Ras-related proteins involved in the phosphatidylinositol 3-kinase/mTOR pathway.
abstract: Two Ras-related proteins, ERas and Rheb, which are involved in the phosphatidylinositol 3-kinase pathway, display high GTP affinity and have atypical CAAX motifs. The factors governing the intracellular localization of ERas and Rheb are incompletely understood. In the current study, we show by confocal microscopy that ERas is localized to the plasma membrane, whereas Rheb is confined to the endomembranes. Membrane localization of the two proteins was abolished by mutation of the cysteine of the CAAX motif. Membrane targeting was also abolished by a farnesyltransferase inhibitor but not by a geranylgeranyltransferase inhibitor. In mouse fibroblasts deficient in either Rce1 (Ras converting enzyme 1) or Icmt (isoprenylcysteine carboxyl methyltransferase), ERas was mislocalized mainly to the Golgi apparatus, whereas Rheb showed diffuse localization. Mutation of cysteines in the hypervariable region of ERas prevented the plasma membrane localization of ERas, very strongly suggesting that palmitoylation of the cysteines is essential for membrane targeting. The hypervariable region of Rheb does not contain cysteines or polybasic residues, and when it was replaced with the hypervariable region of H-Ras, Rheb displayed plasma membrane localization. These data indicate that ERas shares the same posttranslational modifications with H-Ras and N-Ras and is localized at the plasma membrane. Rheb also shares the same membrane-targeting pathway but because of the absence of palmitoylation is located on endomembranes.
authors.affiliation: Department of Stem Cell Biology, Institute for Frontier Medical Sciences, Kyoto University and CREST, Japan Science and Technology Agency, Kyoto 606-8507, Japan.
authors.forename: Kazutoshi
authors.initials: K
authors.lastname: Takahashi
authors.forename: Masato
authors.initials: M
authors.lastname: Nakagawa
authors.forename: Stephen G
authors.initials: SG
authors.lastname: Young
authors.forename: Shinya
authors.initials: S
authors.lastname: Yamanaka
mesh_terms: D019883:Alkyl and Aryl Transferases / Q000037:antagonists & inhibitors; D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D000818:Animals; D002462:Cell Membrane / Q000378:metabolism*; D002478:Cells, Cultured; D003545:Cysteine / Q000737:chemistry; D010450:Endopeptidases / Q000235:genetics; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005347:Fibroblasts / Q000378:metabolism; D006056:Golgi Apparatus / Q000378:metabolism; D006153:Guanosine Diphosphate / Q000737:chemistry; D006160:Guanosine Triphosphate / Q000737:chemistry; D051379:Mice; D018613:Microscopy, Confocal; D008856:Microscopy, Fluorescence; D008969:Molecular Sequence Data; D020559:Monomeric GTP-Binding Proteins / Q000096:biosynthesis*; D009154:Mutation; D009479:Neuropeptides / Q000096:biosynthesis*; D015689:Oncogene Protein p21(ras) / Q000096:biosynthesis*; D010169:Palmitic Acids / Q000737:chemistry / Q000378:metabolism; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D010957:Plasmids / Q000378:metabolism; D011494:Protein Kinases / Q000378:metabolism*; D011499:Protein Processing, Post-Translational; D000076205:Ras Homolog Enriched in Brain Protein; D017386:Sequence Homology, Amino Acid; D013347:Subcellular Fractions / Q000378:metabolism; D058570:TOR Serine-Threonine Kinases; D018631:ras Proteins / Q000737:chemistry*
chemical_list: D019883:Alkyl and Aryl Transferases; D003545:Cysteine; D010450:Endopeptidases; D004791:Enzyme Inhibitors; D006153:Guanosine Diphosphate; D006160:Guanosine Triphosphate; D020559:Monomeric GTP-Binding Proteins; D009479:Neuropeptides; D015689:Oncogene Protein p21(ras); D010169:Palmitic Acids; D019869:Phosphatidylinositol 3-Kinases; D011494:Protein Kinases; D000076205:Ras Homolog Enriched in Brain Protein; D058570:TOR Serine-Threonine Kinases; D018631:ras Proteins; C474773:ERas protein, mouse; C490213:Rheb protein, mouse; C083291:geranylgeranyltransferase type-I; C546843:mTOR protein, mouse; C491324:Rce1 protein, mouse