Systems biology analysis of GPCR signalling in yeast - GPCR C-terminal tail directed spatial regulation of RGS.

Wayne Croft, John Davey, Graham Ladds. University of Warwick, Warwick Medical School, Coventry, CV47AL, UK

The ability of cells to perceive and respond correctly to their microenvironment is an essential prerequisite of life. Cells integrate signals from their environment, and neighbours in order to generate appropriate responses that influence critical processes. Errors in cellular signalling are responsible for diseases such as cancer, and diabetes. By understanding cellular transduction networks, we may devise specific and selective treatments to these diseases. Many external signals are detected through the use of G protein-coupled receptor (GPCR) signalling pathways. GPCRs initiate signalling by promoting exchange of GDP, on the Gα subunit of heterotrimeric G-proteins, for GTP, thereby initiating a cellular signalling cascade. Signalling is terminated by hydrolysis of GTP to GDP through the intrinsic GTPase activity of the Gα subunit. Hydrolysis is accelerated by the regulator of G-protein signalling (RGS) proteins.

To overcome the problem of complexity in higher eukaryotic GPCR signalling, the mating-response in fission yeast Schizosaccharomyces pombe is used here to study GPCR signalling in isolation. In vivo data from quantitative assays of transcriptional reporter strains and live-cell fluorescence microscopy informs the development of an ordinary differential equation model of the signalling pathway,

The RGS protein (Rgs1) regulates signalling by catalysing GTP hydrolysis on the Gα subunit (Gpa1). This work presents an additional layer of regulation through controlling the subcellular localisation of Rgs1. Interaction between Rgs1 and the C-terminal tail of the GPCR (Mam2) is demonstrated to be required for tethering Rgs1 to the plasma membrane in close proximity to Gpa1 to facilitate Rgs1 function. A novel, predictive mathematical model describing the plasma membrane trafficking of RGS is developed.

Model output is consistent with in vivo data and the predictions provide conceptual advancement in our understanding of GPCR signaling in Sz. Pombe that can be transferred to more complicated systems in higher eukaryotes.