title: Activated K-Ras and H-Ras display different interactions with saturable nonraft sites at the surface of live cells.
abstract: Ras-membrane interactions play important roles in signaling and oncogenesis. H-Ras and K-Ras have nonidentical membrane anchoring moieties that can direct them to different membrane compartments. Ras-lipid raft interactions were reported, but recent studies suggest that activated K-Ras and H-Ras are not raft resident. However, specific interactions of activated Ras proteins with nonraft sites, which may underlie functional differences and phenotypic variation between different Ras isoforms, are unexplored. Here we used lateral mobility studies by FRAP to investigate the membrane interactions of green fluorescent protein-tagged H- and K-Ras in live cells. All Ras isoforms displayed stable membrane association, moving by lateral diffusion and not by exchange with a cytoplasmic pool. The lateral diffusion rates of constitutively active K- and H-Ras increased with their expression levels in a saturable manner, suggesting dynamic association with saturable sites or domains. These sites are distinct from lipid rafts, as the activated Ras mutants are not raft resident. Moreover, they appear to be different for H- and K-Ras. However, wild-type H-Ras, the only isoform preferentially localized in rafts, displayed cholesterol-sensitive interactions with rafts that were independent of its expression level. Our findings provide a mechanism for selective signaling by different Ras isoforms.
authors.affiliation: Department of Neurobiochemistry, George S. Wise Faculty of Life Sciences, Tel Aviv University, 69978, Israel.
authors.forename: Hagit
authors.initials: H
authors.lastname: Niv
authors.forename: Orit
authors.initials: O
authors.lastname: Gutman
authors.forename: Yoel
authors.initials: Y
authors.lastname: Kloog
authors.forename: Yoav I
authors.initials: YI
authors.lastname: Henis
mesh_terms: D000818:Animals; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism*; D002784:Cholesterol / Q000378:metabolism; D015870:Gene Expression / Q000502:physiology; D049452:Green Fluorescent Proteins; D007202:Indicators and Reagents; D007536:Isomerism; D008164:Luminescent Proteins; D021962:Membrane Microdomains / Q000378:metabolism; D016283:Proto-Oncogene Proteins p21(ras) / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D051381:Rats; D015398:Signal Transduction / Q000502:physiology*; D014162:Transfection
chemical_list: D007202:Indicators and Reagents; D008164:Luminescent Proteins; D049452:Green Fluorescent Proteins; D002784:Cholesterol; D016283:Proto-Oncogene Proteins p21(ras)