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    Peter M Pryciak PhD

    TitleAssociate Professor
    InstitutionUniversity of Massachusetts Medical School
    DepartmentBiochemistry and Molecular Pharmacology
    AddressUniversity of Massachusetts Medical School
    55 Lake Avenue North
    Worcester MA 01655
    Phone508-856-8756
      Other Positions
      InstitutionUMMS - Graduate School of Biomedical Sciences
      DepartmentInterdisciplinary Graduate Program

      InstitutionUMMS - Graduate School of Biomedical Sciences
      DepartmentMD/PhD Program

      InstitutionUMMS - Graduate School of Biomedical Sciences
      DepartmentMolecular Genetics and Microbiology

      InstitutionUMMS - Programs, Centers and Institutes
      DepartmentProgram in Cell Dynamics

        Overview 
        Narrative

        Academic Background

        B.S., University of California, Los Angeles, 1983.
        Ph.D., University of California, San Francisco 1992.

        Postdoctoral Fellow, University of Washington, Seattle,1992-1996.

        Signal Transduction and Cell Polarity

        Photo: Peter Pryciak Research in my laboratory is aimed at understanding how cellular behavior is dictated by external signals. Our studies stress three general topics: What is the role of subcellular compartmentalization in signal transduction? How do cells judge the location of extracellular cues and mount a directional response? How is signaling specificity ensured?

        To investigate these issues, we use the simple eukaryotic cells of bakers yeast,Saccharomyces cerevisiae. The yeast mating reaction provides examples of signal transduction and cell shape control in a model system that is highly amenable to experimentation using genetics, biochemistry, and cell biology. Here, secreted pheromones stimulate fusion of partner cells in a process involving cell cycle arrest, transcriptional regulation, and cell polarization. These responses are mediated by two signaling modules found in all eukaryotes from yeast to humans: heterotrimeric G proteins and mitogen activated protein (MAP) kinase cascades. We also study two other ubiquitous proteins, the GTPase Cdc42 and a PAK-family kinase (Ste20), which control signaling and cytoskeletal rearrangements.

        Subcellular localization can play a crucial role in signal transduction. Activation of the mating pathway involves plasma membrane recruitment of the MAP kinase cascade “scaffold” protein, Ste5 (Pryciak and Huntress, 1998).(see Figure 1 and Figure 2) This recruitment requires synergistic protein-protein and protein-membrane interactions (Winters et al, 2005). Furthermore, Ste5 localization is regulatedduring the cell cycle by cyclin-dependent kinases (CDKs), which phosphorylate Ste5 near its membrane-binding domain and thus inhibit membrane recruitment and signaling (Strickfaden et al, 2007). This allows cells that are beginning a new division cycleto ignore the antiproliferative and differentiation effects of pheromone, which otherwise wouldcause a catastrophic division arrest.The factor awaiting the MAP kinase cascade at the membrane is the PAK-family kinase Ste20, whose activity and localization are regulated by multiple factors including Cdc42 (Lamson et al, 2002), the SH3 domain protein Bem1 (Winters and Pryciak, 2005),and direct membrane interactions (Takahashi and Pryciak, 2007).(see Figure 3)

        Another project is focused on how cells polarize toward localized signals.(see Figure 4) This behavior, exhibited by many cell types, implies communication between proteins that sense the signal and those that govern cell polarity. Indeed, in addition to its role in activating the MAP kinase cascade, the yeast heterotrimeric G protein has a separate function in orienting cell polarity along gradients of pheromone chemoattractants.This involves the formation of multiprotein complexes between Gbg and polarity-control proteins (Butty et al, 1998). Our recent work suggests that Gbg must be regulated in a spatially-asymmetric manner by the receptor and Ga subunit in order for itto properly guide cell polarization (Strickfaden and Pryciak, 2008).

        We are also interested in the fidelity of signaling pathways. In yeast, as in human cells, independent pathways generate different responses to different stimuli. But some proteins can function in multiple pathways, raising the question of how the pathways avoid “crosstalk”.(see Figure 4) Earlier, we showed that pathway-specific binding interactions can route signaling toward specific pathways. We developed a method to force shared signaling proteins to associate with a subset of their possible partners, creating custom signaling molecules that are “steered” toward chosen pathways (Harris et al, 2001). More recently, wefound that membrane recruitment has anenhancing, or "amplifying" effect on signaltransmission, which helps ensure signaling fidelity because it acts only on factors that are included in the recruited signaling complex (Lamson et al, 2006). This effect also alters the input-output signal processing behavior of the MAP kinase cascade, and may help explain why this pathway shows "graded" rather than "switch-like" dose-response behavior (Takahashi and Pryciak, 2008).

        Figures

        Figure 1

        Figure 1. (A) Yeast mating reaction.Mating pheromones (a factor and a factor) cause cells to stop dividing, polarize toward their mating partners, and fuse with each otherto forma diploid zygote. (B) Pheromone response pathway, emphasizing the membrane recruitment of the "scaffold" protein, Ste5, by the heterotrimeric G proteinbg dimer. This allows activation of the MAP kinase cascade.


        Figure 2

        Figure 2. (A)Synergy between two weak interactions contolsSte5 membrane recruitment. (B) The Ste5 PM domain is a putative amphipathic alpha helix that binds acidicphospholipid membranes in vivo and in vitro. (C) Model for CDK inhibition of signaling through thematingMAP kinase pathway. Phosphorylation of multiple sites flanking the PM domain electrostatically interferes with membrane binding, andhence disrupts signaling. The inset at bottom shows cell cycle-dependentfluctuations in the electrophoretic mobility of Ste5, indicative of periodic phosphorylation.


        Figure 3

        Figure 3. Regulation and localizationof Cdc42 targets. (A) The PAK-family kinase Ste20 is localized and activated by the GTPase Cdc42. Our recent results show that this also requires direct membrane interaction by Ste20. (B) Localization of isolated membrane-bindingmotifs calledBR domains (for "basic-rich") from three different Cdc42 targets. (C) Domain structure of yeast Cdc42 targets,illustrating the presence of a membrane-bindingmotif (BR or PH domain)immediately adjacent to the Cdc42-binding motif in each protein.


        Figure 4

        Figure 4. (A) Yeast cell polarization in response to pheromone. A gradient of pheromone normally serves as a spatial cue for the direction of polarization; cells polarize up the chemoattractant gradient in order to find mating partners. However, these cells can polarize in random directions when exposed to a uniform field of chemoattractant, implying the existence of "symmetry breaking" mechanisms that can generate asymmetric responses to symmetric signals, and"directional persistence"mechanismsthat allow for continual reinforcement of the initially chosen direction. (B) Common components are shared among three separate signaling pathways: mating, filamentous growth, and the high osmolarity glycerol (HOG) response. Though individual proteins are shared (e.g., Cdc42, Ste20, Ste50, Ste11), these pathways are insulated from each other so thateach stimulus activates only a single pathway. Pathway-specific scaffold proteins such as Ste5 and Pbs2 are thought to help provide this insulation. (In contrast, no knownscaffold exists for the filamentation pathway.) Membrane-localized assembly can also contribute to signaling fidelity, by limitingphosphorylationevents to those substrates that are co-localized with theactive signaling complex.



        Rotation Projects

        Rotation Projects

        Project #1: Signaling in the MAP kinase cascade. Membranerecruitment ofthe kinase cascade "scaffold" protein, Ste5, initiates signaling. But our recent work suggests that membrane localization alsoboosts signaling efficiency through the kinase cascade, and similar findings have been reported in a mammalian pathway. Yet the mechanism explaining this effect is unknown.This project would use molecular genetic approaches to probe thisphenomenon.

        Project #2: Membrane targeting domains. Our recent work identified a small membrane-binding domain that guides Ste5 to the plasma membrane, but it does so only acting in conjunction with protein-protein interactions. Relatedly, we have recently found similar domains, and their cooperative relationship with protein-protein interactions, in several other plasma membrane-localized signaling proteins. We suspect this may be a very common arrangement, and that multiple weak interactions are advantageous to ensuring dynamic localization that constantly probes the availability of membrane-localized binding partners. This project would involve conducting a small-scale survey of polarized proteins in yeast, searching for small membrane-binding domains that are critical for their normal localization and function.



        Bibliographic 
        selected publications
        List All   |   Timeline
        1. Pope PA, Bhaduri S, Pryciak PM. Regulation of cyclin-substrate docking by a g1 arrest signaling pathway and the cdk inhibitor far1. Curr Biol. 2014 Jun 16; 24(12):1390-6.
          View in: PubMed
        2. Pope PA, Pryciak PM. Functional overlap among distinct G1/S inhibitory pathways allows robust G1 arrest by yeast mating pheromones. Mol Biol Cell. 2013 Dec; 24(23):3675-88.
          View in: PubMed
        3. Bhaduri S, Pryciak PM. Cyclin-specific docking motifs promote phosphorylation of yeast signaling proteins by G1/S Cdk complexes. Curr Biol. 2011 Oct 11; 21(19):1615-23.
          View in: PubMed
        4. Pryciak PM. Designing new cellular signaling pathways. Chem Biol. 2009 Mar 27; 16(3):249-54.
          View in: PubMed
        5. Takahashi S, Pryciak PM. Membrane localization of scaffold proteins promotes graded signaling in the yeast MAP kinase cascade. Curr Biol. 2008 Aug 26; 18(16):1184-91.
          View in: PubMed
        6. Pryciak PM. Systems biology. Customized signaling circuits. Science. 2008 Mar 14; 319(5869):1489-90.
          View in: PubMed
        7. Strickfaden SC, Pryciak PM. Distinct roles for two Galpha-Gbeta interfaces in cell polarity control by a yeast heterotrimeric G protein. Mol Biol Cell. 2008 Jan; 19(1):181-97.
          View in: PubMed
        8. Takahashi S, Pryciak PM. Identification of novel membrane-binding domains in multiple yeast Cdc42 effectors. Mol Biol Cell. 2007 Dec; 18(12):4945-56.
          View in: PubMed
        9. Strickfaden SC, Winters MJ, Ben-Ari G, Lamson RE, Tyers M, Pryciak PM. A mechanism for cell-cycle regulation of MAP kinase signaling in a yeast differentiation pathway. Cell. 2007 Feb 9; 128(3):519-31.
          View in: PubMed
        10. Lamson RE, Takahashi S, Winters MJ, Pryciak PM. Dual role for membrane localization in yeast MAP kinase cascade activation and its contribution to signaling fidelity. Curr Biol. 2006 Mar 21; 16(6):618-23.
          View in: PubMed
        11. Winters MJ, Lamson RE, Nakanishi H, Neiman AM, Pryciak PM. A membrane binding domain in the ste5 scaffold synergizes with gbetagamma binding to control localization and signaling in pheromone response. Mol Cell. 2005 Oct 7; 20(1):21-32.
          View in: PubMed
        12. Winters MJ, Pryciak PM. Interaction with the SH3 domain protein Bem1 regulates signaling by the Saccharomyces cerevisiae p21-activated kinase Ste20. Mol Cell Biol. 2005 Mar; 25(6):2177-90.
          View in: PubMed
        13. Lamson RE, Winters MJ, Pryciak PM. Cdc42 regulation of kinase activity and signaling by the yeast p21-activated kinase Ste20. Mol Cell Biol. 2002 May; 22(9):2939-51.
          View in: PubMed
        14. Dorer R, Pryciak P, Schrick K, Hartwell LH. The induction of cell polarity by pheromone in Saccharomyces cerevisiae. Harvey Lect. 1994-1995; 90:95-104.
          View in: PubMed
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