Photo of Ruth Murrell-Lagnado

Ruth Murrell-Lagnado
Reader in Neuroscience
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T: +44 (0)1273 877049

Research

ION CHANNELS: THEIR CELL BIOLOGY, FUNCTION AND REGULATION.

MECHANISMS REGULATING P2X7 RECEPTOR SIGNALLING

The low affinity, non-desensitizing P2X7 receptor is unique within the P2X family, both with respect to its structure and function. In epithelial, endothelia and immune cells it regulates cell growth and proliferation as well as programmed cell death and the release of inflammatory mediators. It mediates the effects of extracellular ATP as a DAMP signal and is up regulated in many tissues throughout the periphery and CNS in response to damage and inflammation. P2X7 receptor up-regulation contributes to pathologies and we are particularly interested in its role in cancer and neurological diseases. We study its regulation by alternative splicing of the primary transcript (Nicke et al, 2009; Masin et al., 2012, Xu et al., 2012), by its trafficking and targeting within the cell (Boumechache et al. 2009) and by its lipid environment at the plasma membrane (Robinson et al., 2014).

P2X7 receptor signaling is dependent upon the opening of its cation selective pore which is triggered by the binding of extracellular ATP. Receptor activation can undergo profound sensitization and this is regulated by the folowing: 1) Expression of alternatively splice variants. 2) Species variation and Single Nucleotide Polymorphisms (SNPs). 3) Membrane environment, e.g. cholesterol

THE ROLE OF INTRACELLULAR P2X4 RECEPTORS IN LYSOSOME FUNCTION AND DYSFUNCTION

We previously showed that one member of the P2X family, P2X4, is targeted to lysosomes, where it resists degradation and can subsequently be delivered to the cell surface to up-regulate the cellular response to ATP (Bobanovic et al. 2002; Royle et al. 2002; Royle et al. 2005; Qureshi et al. 2007, Boumechache et al., 2009). This targeting to lysosomes suggests that the receptor might also function within these acidic intracellular compartments as well as at the cell surface, similar to P2X-like channels in Dictyostelium. Currents mediated by lysosomal P2X4 receptors were recently shown as part of a collaboration with Xianping Dong (Huang et al., 2014). P2X4 receptors are highly calcium permeable and can promote lysosome fusion (Cao et al., 2015).  They are pH dependent and would normally be inhibited by the acidic environment of the lysosome. Thus, within the lysosome, P2X4 receptors are likely to be gated by changes in luminal pH rather than changes in luminal ATP. We are currently investigating a synergistic interaction between P2X4 and P2X7 receptors and its role in regulating lysosome fusion and function. This include fusion with the plasma membrane and fusion with late endosomes and autophagosomes and the regulation of autophagy. We use fluorescence microscopy, electrophysiology and molecular and biochemical techniques. We are particular interested in how P2X4 and P2X7 interact in the regulation of lysosome exocytosis and secretion in breast cancer cells.

DRUG DISCOVERY TARGETED AT P2X RECEPTORS

 Fragment-Based Dug-Discovery (FBDD) is being utilized to identify novel P2X ligands for treatment of conditions indicated. The initial 96 well plate assay is based upon the use of a voltage-sensitive fluorescent dye and FlexStation. Hits are further characterised using two-electrode voltage clamp and radio ligand binding. P2X1 is targeted for development of antithrombotics, P2X4 for analgesics and for heart failure and P2X7 for treatment of neuropathic and inflammatory pain and cancer. 

REGULATION OF CALCIUM SIGNALLING BY THE SIGMA1 RECEPTOR

The Sigma1 receptor is resident within the endoplasmic reticulum (ER) and acts as a chaperone protein and a regulator of ion channels, both within the ER and at the plasma membrane. It is widely distributed in the brain and in peripheral tissues and is also highly expressed in cancer cells. It binds a wide variety of ligands including neurosteroids, benzomorphans and psychotropic drugs and has been implicated in several diseases that range from cancers to cocaine and alcohol addiction, to neurodegenerative disorders. It also contributes to neuroprotection and synaptic plasticity. Our work in this area is currently focused on elucidating the mechanisms by which Sigma1R controls Calcium Release Activated Calcium (CRAC) channels and luminal ER and mitochondrial calcium concentrations (Srivats et al., 2016). Our main objective is to understand how this underlies the protective action of Sigma1R in neurons within the central nervous system and why mutations in Sigma contribute to neurodegenerative diseases.  The techniques being utilized include [Ca2+] measurements using targeted Ca2+ sensing reporter proteins imaged by confocal microscopy, TIRF microscopy or using a FLIPR assay system.