title: Inhibitory GEF phosphorylation provides negative feedback in the yeast polarity circuit.
abstract: Cell polarity is critical for the form and function of many cell types. During polarity establishment, cells define a cortical "front" that behaves differently from the rest of the cortex. The front accumulates high levels of the active form of a polarity-determining Rho-family GTPase (Cdc42, Rac, or Rop) that then orients cytoskeletal elements through various effectors to generate the polarized morphology appropriate to the particular cell type [1, 2]. GTPase accumulation is thought to involve positive feedback, such that active GTPase promotes further delivery and/or activation of more GTPase in its vicinity [3]. Recent studies suggest that once a front forms, the concentration of polarity factors at the front can increase and decrease periodically, first clustering the factors at the cortex and then dispersing them back to the cytoplasm [4-7]. Such oscillatory behavior implies the presence of negative feedback in the polarity circuit [8], but the mechanism of negative feedback was not known. Here we show that, in the budding yeast Saccharomyces cerevisiae, the catalytic activity of the Cdc42-directed GEF is inhibited by Cdc42-stimulated effector kinases, thus providing negative feedback. We further show that replacing the GEF with a phosphosite mutant GEF abolishes oscillations and leads to the accumulation of excess GTP-Cdc42 and other polarity factors at the front. These findings reveal a mechanism for negative feedback and suggest that the function of negative feedback via GEF inhibition is to buffer the level of Cdc42 at the polarity site.
authors.affiliation: Department of Pharmacology and Cancer Biology, Duke University Medical Center, Durham, NC 27710, USA.
authors.forename: Chun-Chen
authors.initials: CC
authors.lastname: Kuo
authors.affiliation: Institute of Integrative Biology, University of Liverpool, Liverpool L69 7ZB, UK.
authors.forename: Natasha S
authors.initials: NS
authors.lastname: Savage
authors.affiliation: Department of Pharmacology and Cancer Biology, Duke University Medical Center, Durham, NC 27710, USA.
authors.forename: Hsin
authors.initials: H
authors.lastname: Chen
authors.affiliation: Department of Pharmacology and Cancer Biology, Duke University Medical Center, Durham, NC 27710, USA.
authors.forename: Chi-Fang
authors.initials: CF
authors.lastname: Wu
authors.affiliation: Department of Pharmacology and Cancer Biology, Duke University Medical Center, Durham, NC 27710, USA.
authors.forename: Trevin R
authors.initials: TR
authors.lastname: Zyla
authors.affiliation: Department of Pharmacology and Cancer Biology, Duke University Medical Center, Durham, NC 27710, USA. Electronic address: daniel.lew@duke.edu.
authors.forename: Daniel J
authors.initials: DJ
authors.lastname: Lew
mesh_terms: D016764:Cell Polarity; D003198:Computer Simulation; D025461:Feedback, Physiological; D020662:Guanine Nucleotide Exchange Factors / Q000378:metabolism*; D008954:Models, Biological; D010766:Phosphorylation; D012441:Saccharomyces cerevisiae / Q000166:cytology / Q000378:metabolism*; D015398:Signal Transduction; D020846:cdc42 GTP-Binding Protein, Saccharomyces cerevisiae / Q000378:metabolism
chemical_list: D020662:Guanine Nucleotide Exchange Factors; D020846:cdc42 GTP-Binding Protein, Saccharomyces cerevisiae