title: Galectin-1 augments Ras activation and diverts Ras signals to Raf-1 at the expense of phosphoinositide 3-kinase.
abstract: Ras proteins activate diverse effector molecules. Depending on the cellular context, Ras activation may have different biological consequences: induction of cell proliferation, senescence, survival, or death. Augmentation and selective activation of particular effector molecules may underlie various Ras actions. In fact, Ras effector-loop mutants interacting with distinctive effectors provide evidence for such selectivity. Interactions of active Ras with escort proteins, such as galectin-1, could also direct Ras selectivity. Here we show that in comparison with Ras transfectants, H-Ras/galectin-1 or K-Ras4B/galectin-1 co-transfectants exhibit enhanced and prolonged epidermal growth factor (EGF)-stimulated increases in Ras-GTP, Raf-1 activity, and active extracellular signal-regulated kinase. Galectin-1 antisense RNA inhibited these EGF responses. Conversely, Ras and galectin-1 co-transfection inhibited the EGF-stimulated increase in phosphoinositide 3-kinase (PI3K) activity. Galectin-1 transfection also inhibited Ras(G12V)-induced PI3K but not Raf-1 activity. Galectin-1 co-immunoprecipitated with Ras(G12V) or with Ras(G12V/T35S) that activate Raf-1 but not with Ras(G12V/Y40C) that activates PI3K. Thus, galectin-1 binds active Ras and diverts its signal to Raf-1 at the expense of PI3K. This demonstrates a novel mechanism controlling the duration and selectivity of the Ras signal. Ras gains selectivity when it is associated with galectin-1, mimicking the selectivity of Ras(T35S), which activates Raf-1 but not PI3K.
authors.affiliation: Department of Neurobiochemistry, The George S. Wise Faculty of Life Sciences, Tel-Aviv University, 69978 Tel-Aviv, Israel.
authors.forename: Galit
authors.initials: G
authors.lastname: Elad-Sfadia
authors.forename: Roni
authors.initials: R
authors.lastname: Haklai
authors.forename: Eyal
authors.initials: E
authors.lastname: Ballan
authors.forename: Hans-Joachim
authors.initials: HJ
authors.lastname: Gabius
authors.forename: Yoel
authors.initials: Y
authors.lastname: Kloog
mesh_terms: D000818:Animals; D015153:Blotting, Western; D019556:COS Cells; D002522:Chlorocebus aethiops; D004815:Epidermal Growth Factor / Q000494:pharmacology; D037483:Galectin 1 / Q000235:genetics / Q000502:physiology*; D049452:Green Fluorescent Proteins; D006801:Humans; D008164:Luminescent Proteins / Q000235:genetics; D019869:Phosphatidylinositol 3-Kinases / Q000235:genetics*; D019908:Proto-Oncogene Proteins c-raf / Q000235:genetics*; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D015398:Signal Transduction; D014162:Transfection; D018631:ras Proteins / Q000378:metabolism*
chemical_list: D004815:Epidermal Growth Factor; D037483:Galectin 1; D049452:Green Fluorescent Proteins; D008164:Luminescent Proteins; D019869:Phosphatidylinositol 3-Kinases; D019908:Proto-Oncogene Proteins c-raf; D011993:Recombinant Fusion Proteins; D018631:ras Proteins