title: Galectin-1 dimers can scaffold Raf-effectors to increase H-ras nanoclustering.
abstract: Galectin-1 (Gal-1) dimers crosslink carbohydrates on cell surface receptors. Carbohydrate-derived inhibitors have been developed for cancer treatment. Intracellularly, Gal-1 was suggested to interact with the farnesylated C-terminus of Ras thus specifically stabilizing GTP-H-ras nanoscale signalling hubs in the membrane, termed nanoclusters. The latter activity may present an alternative mechanism for how overexpressed Gal-1 stimulates tumourigenesis. Here we revise the current model for the interaction of Gal-1 with H-ras. We show that it indirectly forms a complex with GTP-H-ras via a high-affinity interaction with the Ras binding domain (RBD) of Ras effectors. A computationally generated model of the Gal-1/C-Raf-RBD complex is validated by mutational analysis. Both cellular FRET as well as proximity ligation assay experiments confirm interaction of Gal-1 with Raf proteins in mammalian cells. Consistently, interference with H-rasG12V-effector interactions basically abolishes H-ras nanoclustering. In addition, an intact dimer interface of Gal-1 is required for it to positively regulate H-rasG12V nanoclustering, but negatively K-rasG12V nanoclustering. Our findings suggest stacked dimers of H-ras, Raf and Gal-1 as building blocks of GTP-H-ras-nanocluster at high Gal-1 levels. Based on our results the Gal-1/effector interface represents a potential drug target site in diseases with aberrant Ras signalling.
authors.affiliation: Turku Centre for Biotechnology, Åbo Akademi University, Tykistökatu 6B, 20520 Turku, Finland.
authors.forename: Olga
authors.initials: O
authors.lastname: Blaževitš
authors.affiliation: Turku Centre for Biotechnology, Åbo Akademi University, Tykistökatu 6B, 20520 Turku, Finland.
authors.forename: Yonatan G
authors.initials: YG
authors.lastname: Mideksa
authors.affiliation: Turku Centre for Biotechnology, Åbo Akademi University, Tykistökatu 6B, 20520 Turku, Finland.
authors.forename: Maja
authors.initials: M
authors.lastname: Šolman
authors.affiliation: Turku Centre for Biotechnology, Åbo Akademi University, Tykistökatu 6B, 20520 Turku, Finland.
authors.forename: Alessio
authors.initials: A
authors.lastname: Ligabue
authors.affiliation: Institute for Molecular Bioscience, The University of Queensland, St. Lucia, QLD 4072, Australia.
authors.forename: Nicholas
authors.initials: N
authors.lastname: Ariotti
authors.affiliation: Institute of Biochemistry and Molecular Biology II, Medical Faculty, Heinrich-Heine-University, Düsseldorf, Germany.
authors.forename: Hossein
authors.initials: H
authors.lastname: Nakhaeizadeh
authors.affiliation: Max Planck Institute for Molecular Physiology, 44227 Dortmund, Germany.
authors.forename: Eyad K
authors.initials: EK
authors.lastname: Fansa
authors.affiliation: Turku Centre for Biotechnology, Åbo Akademi University, Tykistökatu 6B, 20520 Turku, Finland.
authors.forename: Anastassios C
authors.initials: AC
authors.lastname: Papageorgiou
authors.affiliation: Max Planck Institute for Molecular Physiology, 44227 Dortmund, Germany.
authors.forename: Alfred
authors.initials: A
authors.lastname: Wittinghofer
authors.affiliation: Institute of Biochemistry and Molecular Biology II, Medical Faculty, Heinrich-Heine-University, Düsseldorf, Germany.
authors.forename: Mohammad R
authors.initials: MR
authors.lastname: Ahmadian
authors.affiliation: Turku Centre for Biotechnology, Åbo Akademi University, Tykistökatu 6B, 20520 Turku, Finland.
authors.forename: Daniel
authors.initials: D
authors.lastname: Abankwa
mesh_terms: D000818:Animals; D002460:Cell Line; D003198:Computer Simulation; D006224:Cricetinae; D019281:Dimerization; D037483:Galectin 1 / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D009154:Mutation; D011485:Protein Binding; D015398:Signal Transduction; D048490:raf Kinases / Q000235:genetics / Q000378:metabolism*; D018631:ras Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*
chemical_list: D037483:Galectin 1; D048490:raf Kinases; D018631:ras Proteins