Article

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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    • "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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    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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    • "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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