Regulation of Cell Signaling Dynamics by the Protein Kinase-Scaffold Ste5

Department of Pharmacology, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA.
Molecular cell (Impact Factor: 14.46). 07/2008; 30(5):649-56. DOI: 10.1016/j.molcel.2008.04.016
Source: PubMed

ABSTRACT Cell differentiation requires the ability to detect and respond appropriately to a variety of extracellular signals. Here we investigate a differentiation switch induced by changes in the concentration of a single stimulus. Yeast cells exposed to high doses of mating pheromone undergo cell division arrest. Cells at intermediate doses become elongated and divide in the direction of a pheromone gradient (chemotropic growth). Either of the pheromone-responsive MAP kinases, Fus3 and Kss1, promotes cell elongation, but only Fus3 promotes chemotropic growth. Whereas Kss1 is activated rapidly and with a graded dose-response profile, Fus3 is activated slowly and exhibits a steeper dose-response relationship (ultrasensitivity). Fus3 activity requires the scaffold protein Ste5; when binding to Ste5 is abrogated, Fus3 behaves like Kss1, and the cells no longer respond to a gradient or mate efficiently with distant partners. We propose that scaffold proteins serve to modulate the temporal and dose-response behavior of the MAP kinase.

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Available from: Henrik G Dohlman, Jul 31, 2015
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    • "Early-to midlog-phase yeast cells containing the polarity marker Bem1-GFP were grown and loaded on to a microfluidics chamber as described earlier. A pheromone gradient was generated as described elsewhere (Hao et al., 2008). The specific dose of pheromone used to generate the gradient varied depending on the pheromone sensitivity of the strain. "
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    ABSTRACT: G proteins and their associated receptors process information from a variety of environmental stimuli to induce appropriate cellular responses. Generally speaking, each cell in a population responds within defined limits, despite large variation in the expression of protein signaling components. Therefore, we postulated that noise suppression is encoded within the signaling system. Using the yeast mating pathway as a model, we evaluated the ability of a regulator of G protein signaling (RGS) protein to suppress noise. We found that the RGS protein Sst2 limits variability in transcription and morphogenesis in response to pheromone stimulation. While signal suppression is a result of both the GAP (GTPase accelerating) and receptor binding functions of Sst2, noise suppression requires only the GAP activity. Taken together, our findings reveal a hitherto overlooked role of RGS proteins as noise suppressors and demonstrate an ability to uncouple signal and noise in a prototypical stimulus-response pathway.
    Molecular Cell 06/2014; 55(1). DOI:10.1016/j.molcel.2014.05.019 · 14.46 Impact Factor
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    • "The direction of the mating projection is influenced by the pheromone spatial gradient, and this gradient-sensing behavior was demonstrated indirectly in mating experiments (Jackson and Hartwell, 1990; Jackson et al., 1991) and more directly by pioneering micropipette studies (Segall, 1993). More recently, we (Moore et al., 2008) and others (Paliwal et al., 2007; Hao et al., 2008) used microfluidics to study gradient-dependent projection formation more quantitatively. We found that yeast cells are excellent at sensing and responding to static gradients, showing good accuracy, slope sensitivity, dynamic range, and amplification (Moore et al., 2008). "
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    ABSTRACT: Yeast cells polarize by projecting up mating pheromone gradients, a classic cell polarity behavior. However, these chemical gradients may shift direction. We examined how yeast cells sense and respond to a 180(o) switch in the direction of microfluidically-generated pheromone gradients. We identified two behaviors: at low concentrations of α-factor, the initial projection grew by bending, whereas at high concentrations, cells formed a second projection toward the new source. Mutations that increased heterotrimeric G-protein activity expanded the bending growth morphology to high concentrations; mutations that increased Cdc42 activity resulted in second projections at low concentrations. Gradient sensing projection bending required interaction between Gβγ and Cdc24, whereas gradient non-sensing projection extension was stimulated by Bem1 and hyper-activated Cdc42. Interestingly, a mutation in Gα affected both bending and extension. Finally, we searched for a genetic perturbation that would exhibit both behaviors; overexpression of the formin Bni1, a component of the polarisome, made both bending growth projections and second projections at low and high α-factor concentrations suggesting a role for Bni1 downstream of the heterotrimeric G-protein and Cdc42 during gradient sensing and response. Thus, we demonstrated that G-proteins modulate in a ligand-dependent manner two fundamental cell polarity behaviors in response to gradient directional change.
    Molecular biology of the cell 12/2012; 24(4). DOI:10.1091/mbc.E12-10-0739 · 5.98 Impact Factor
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    • "The fi rst term on the right - hand side of Eq. 1 represents the phosphorylation of Fus3 by active Ste7 . Our previous work demon - strated the slow phosphorylation rate of Fus3 depends on full cata - lytic activity ( Hao et al . , 2008a ) . That is , a mutant containing a " kinase - dead " version of Fus3 displayed rapid activation kinetics similar to Kss1 . Therefore we allowed the rate constant k 1 ′ for Fus3 activation in the inhibitor pretreated fus3 - as strain to vary from the value k 1 in strains containing wild - type Fus3 . The second term in Eq . 1 models the"
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    ABSTRACT: Different environmental stimuli often use the same set of signaling proteins to achieve very different physiological outcomes. The mating and invasive growth pathways in yeast each employ a mitogen-activated protein (MAP) kinase cascade that includes Ste20, Ste11, and Ste7. Whereas proper mating requires Ste7 activation of the MAP kinase Fus3, invasive growth requires activation of the alternate MAP kinase Kss1. To determine how MAP kinase specificity is achieved, we used a series of mathematical models to quantitatively characterize pheromone-stimulated kinase activation. In accordance with the computational analysis, MAP kinase feedback phosphorylation of Ste7 results in diminished activation of Kss1, but not Fus3. These findings reveal how feedback phosphorylation of a common pathway component can limit the activity of a competing MAP kinase through feedback phosphorylation of a common activator, and thereby promote signal fidelity.
    Molecular biology of the cell 08/2012; 23(19):3899-910. DOI:10.1091/mbc.E12-04-0333 · 5.98 Impact Factor
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