title: Switching of the positive feedback for RAS activation by a concerted function of SOS membrane association domains.
abstract: Son of sevenless (SOS) is a guanine nucleotide exchange factor that regulates cell behavior by activating the small GTPase RAS. Recentin vitrostudies have suggested that an interaction between SOS and the GTP-bound active form of RAS generates a positive feedback loop that propagates RAS activation. However, it remains unclear how the multiple domains of SOS contribute to the regulation of the feedback loop in living cells. Here, we observed single molecules of SOS in living cells to analyze the kinetics and dynamics of SOS behavior. The results indicate that the histone fold and Grb2-binding domains of SOS concertedly produce an intermediate state of SOS on the cell surface. The fraction of the intermediated state was reduced in positive feedback mutants, suggesting that the feedback loop functions during the intermediate state. Translocation of RAF, recognizing the active form of RAS, to the cell surface was almost abolished in the positive feedback mutants. Thus, the concerted functions of multiple membrane-associating domains of SOS governed the positive feedback loop, which is crucial for cell fate decision regulated by RAS.
authors.affiliation: Cellular Informatics Laboratory, RIKEN, Wako, Saitama 351-0198, Japan; Nanobiology Laboratories, Graduate School of Frontier Biosciences, Osaka University, Suita, Osaka 565-0871, Japan.
authors.forename: Yuki
authors.initials: Y
authors.lastname: Nakamura
authors.affiliation: Laboratory for Cell Signaling Dynamics, RIKEN QBiC, Suita, Osaka 565-0874, Japan.
authors.forename: Kayo
authors.initials: K
authors.lastname: Hibino
authors.affiliation: Nanobiology Laboratories, Graduate School of Frontier Biosciences, Osaka University, Suita, Osaka 565-0871, Japan.
authors.forename: Toshio
authors.initials: T
authors.lastname: Yanagida
authors.affiliation: Cellular Informatics Laboratory, RIKEN, Wako, Saitama 351-0198, Japan; Nanobiology Laboratories, Graduate School of Frontier Biosciences, Osaka University, Suita, Osaka 565-0871, Japan.
authors.forename: Yasushi
authors.initials: Y
authors.lastname: Sako
keywords: EGF-RAS-MAPK system; cell signaling; fluorescence microscopy; single-molecule imaging