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Molecular function of PI(35)P2 and Svp3p in stress signaling

Reference	BB/D522197/1
Principal Investigator / Supervisor	Dr Stephen Dove
Co-Investigators / Co-Supervisors	Professor R H Michell
Institution	University of Birmingham
Department	Sch of Biosciences
Funding type	Research
Value (£)	217,811
Status	Completed
Type	Research Grant
Start date	01/12/2005
End date	31/08/2009
Duration	45 months

Abstract

Phosphoinositides are seven related regulatory phospholipids molecules that influence many cellular processes, including signalling from cell surface receptors, cytoskeletal activity, and endo/exocytosis. Phosphoinositides mainly function by specifically binding to and activating regulatory proteins termed effectors. We discovered phosphatidylinositol 3.5-biphosphate (Ptdins(3.5)P2) and are defining its functions using yeast as a model system. Ptdins(3.5)P2 is present in all eukaryotes, but the genetics of yeast facilitate the identification of new proteins in the pathways in which it is implicated. Fab1p is the kinase that makes Ptdins(3.5)P2: the defects caused by Fab1p inactivation have given numerous insights into the cellular roles of Ptdins(3.5)P2. A relatively unexplored, but important, Ptdins(3.5)P2 function is in stress signalling. Cells that lack Fab1p, and so cannot make Ptdins(3.5)P2, become hyper-sensitive to some types of stress. Moreover, hyper-osmotic, heat or oxidative stresses greatly stimulate Ptdins(3.5)P2 synthesis in yeast. The speed of this increased response suggests that Ptdins(3.5)P2 is a very early signal in stress response pathways. We recently identified an adaptin-like protein with no previously defined functions, which we named Svp3p, that seems to function in a Ptdins(3.5)P2-dependent stress response pathway. Inactivation of Svp3p, which has close homologues only in other fungi, causes some of the same defects in stress signalling as when Fab1p function is compromised. Ptdins(3.5)P2 synthesis also becomes deregulated when cells lack Svp3p, suggesting that Ptdins(3.5)P2 (possibly in complex with Ptdins(3.5)P2 may feedback-inhibit Fab1p. GFP-Syp3p is distributed between cytoplasm and nucleus in unstressed cells. It changes location rapidly when cells are stressed (hyper-osmotic or heat), becoming associated with unidentified cytoplasmic granules. This translocation persists in cells that lack Fab1p, indicating that at least one other stress response pathway influences Svp3p function. The other major pathway mediating responses to hyper-osmotic and heat stresses in eukaryotic cells is the Hog1p MAP kinase pathway, which is not needed for Fab1p activation. We propose to determine whether there is some previously unrecognised link between the Hog1p and Fab1p/ Ptdins(3.5)P2 pathways. Might Fab1p itself, which includes a unique chaperone-like domain that may allow it to detect unfolded proteins and so sense cellular stresses directly ¿ be an uncharacterised Hog1p activator? The aim of this project is to characterise the function of Svp3p in detail, so as to determine whether it is a Ptdins(3.5)P2 effector and/or a regulator of the Fab1p pathway. We also propose to isolate the cytoplasmic granules or proteins that Svp3p associates with during stress to identify novel players in this pathways by a combination of yeast genetics and proteomics.

Summary

Living in the modern world can be a stressful business. However, for the cells that make up our bodies this has always been the case. Change is what causes most stress, in people and in cells. If the environment changes then our cells must rapidly adapt and change their internal workings or they will die. Cells monitor their environment all the time and then transform this information into chemical messages that the rest of the cell can understand and respond to. Defects in this process are associated with human diseases like cancer. Greater knowledge of the way that cells respond to stress is also valuable for industries like brewing, where cell stress causes problems in the fermentation process. The same is true of plants and their crop yields. The tiny machinery that cells use to transform environmental information into chemicals is the subject of our work; some years ago we stumbled across a signal that had never been seen before. The signal is made when cells are stressed and is called PIP2. We want to understand how PIP2 is made and what part of the cell understands (or translates) this signal. The PIP2 signal binds to these translator proteins and then they tell the cell what to do next. We recently isolated a translator for PIP2 called Svp3p. Svp3p is needed for fungal cells to adapt to growing at high temperatures. Fungi are related to mushrooms but yeast, that make bread and beer are also fungi. If fungi do not have Svp3p or if no PIP2 is made, then the fungal cells burst. We want to understand this process by understanding how PIP2 and Svp3p work inside cells by finding out what other parts of the cell they talk to. This might be useful as Svp3p is not found in our bodies or in plants. If we made a drug that attacked Svp3p then we might be able to kill fungi that cause diseases on animals and plants but would be harmless to us.

Committee	Closed Committee - Plant & Microbial Sciences (PMS)
Research Topics	Microbiology
Research Priority	X – Research Priority information not available
Research Initiative	X - not in an Initiative
Funding Scheme	X – not Funded via a specific Funding Scheme

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