Research Interests and Techniques

My lab focuses on signal transduction research with an emphasis on the use of molecular pharmacological approaches to understand how G protein-coupled receptors (GPCRs) shape short-term and longer-term responses to extracellular signals.  Current projects span interests in molecular neurobiology (using neurons and glial cells) and smooth muscle (vascular, airways and GU tract) physiology and pharmacology.  We are particularly interested in all aspects of muscarinic acetylcholine and metabotropic glutamate receptor physiology and pharmacology.

Confocal images of rat mesenteric arterial smooth muscle cells expressing an eGFP-PKCα construct and loaded with the Ca²⁺-sensitive fluorescent dye Fura-Red (Taken from Nelson et al. (2008) Am J Physiol – see Publications)

Background

A wide variety of G protein-coupled receptors (GPCRs) link to phospholipase C isoenzymes via  G_q/11  proteins to hydrolyze phosphatidylinositol 4,5-bisphosphate (PIP₂) and generate inositol 1,4,5-trisphosphate (IP₃) and sn-1,2-diacylglycerol (DAG).  The latter second messengers regulate intracellular Ca²⁺ concentration and protein kinase C activity, whereas PIP2 has emerged as an important regulator of processes including vesicle trafficking, cytoskeletal remodelling and ion channel modulation.  Research within the group has concentrated on signalling by by G_q/11-coupled GPCRs, including how Ca²⁺ (±PKC) can encode specific signals that regulate plastic changes in cellular responses and longer term decision-making in cells.  We have long-standing interests in muscarinic acetylcholine and metabotropic glutamate (particularly group 1 - mGlu1/mGlu5) receptors, as well as GPCRs for other mediators including lysophosphatidic acid, dopamine, endothelin-1, angiotensin II, histamine, oxytocin and neuromedin U.

A major advance in recent years has been the generation of 'biosensors' that allows signalling events to be visualized within single cells.  An example of such a biosensor is composed of the pleckstrin homology domain of PLCδ1 tagged with enhanced green fluorescent protein (eGFP-PH).  This construct can be introduced into cells by cDNA transfection and visualized within single cells by confocal fluorescence microscopy.  Under basal conditions eGFP-PH associates with PIP₂ which is found predominantly in the inner leaflet of the plasma membrane.  On PLC activation the increase in IP₃ concentration (and the decrease in PIP₂ concentration) causes eGFP-PH to dissociate from the plasma membrane and accumulate in the cytoplasm.  This translocation can be tracked and quantified.  Using a variety of biosensors, as well as conventional Ca²⁺-sensitive fluorescent dyes (e.g. fluo-4), an array of signalling events can be visualized in living cells in real-time.

The signalling consequences of decreasing G_q/11α expression using short hairpin RNAi in HEK cell expressing the human M3 muscarinic acetylcholine receptor (Taken from Atkinson et al. (2006) Mol Pharmacol – see Publications)

Current Research Projects

1.  Involvement of IP3 in encoding different patterns of change in [Ca2+]i.  We are investigating how different GPCRs are able to generate defined patterns of Ca2+ signal in cells.  These studies address (i) how different PLCs are recruited following GPCR activation, (ii) how feedback regulation at the level of the receptor-G protein-PLC, or at the level of the IP₃R can regulate oscillatory Ca2+ patterning, (iii) how the Ca2+ signatures (together with other activated signalling pathways) can regulate longer term changes, for example through the regulation of transcription factors and transcriptional activity.  Some aspects of this work are already being investigated in neurons with a particular emphasis on how metabotropic and ionotropic inputs interact to regulate both IP₃ and Ca²⁺ in the cell bodies and dendrites of hippocampal neurons.

2.  Regulation of GPCR activity by phosphorylation-dependent and -independent mechanisms.  Attenuation of signalling outputs following prolonged or recurrent receptor activation is referred to as desensitization.  Considerable evidence has accumulated to suggest that both G protein-coupled receptor kinases (GRKs) and second messenger-regulated kinases (e.g. PKC and PKA) can phosphorylate GPCRs.  We have studied this desensitization/internalization process for the M3 mACh receptor expressed endogenously in the SH-SY5Y neuroblastoma and have highlighted an important role for GRK6.  The use of the eGFP-PH biosensor for IP3 has also allowed us to study mACh receptor desensitization in single hippocampal neurons.  We are currently working on the relative roles that receptor phosphorylation and phosphorylation-independent mechanisms (for example, mediated by the ability of some GRKs to bind to and sequester Gαq/11 and/or Gβγ subunits) play in receptor regulation.

3. How does G protein subtype recruitment affect signalling patterns downstream of GPCRs?  We have previously presented evidence consistent with the group 1 mGlu receptors linking to Gi/o proteins as well as Gq/11 (and in the case of mGlu1 receptors Gs) proteins.  This 'promiscuous' coupling can result in a modified regulation of phosphoinositide turnover, and importantly in the case of the mGlu1 receptor a mechanism for linking to the extracellular signal-regulated protein kinase (ERK) MAPK pathway.  We are currently expanding these studies by using a number of approaches (e.g. RNAi) selectively to eliminate one or more Gα protein subtype and/or effector protein.

4. Pharmacological studies of constitutive activity and agonist-selective trafficking of signal at the mACh receptors.  There are at least three distinct objectives/projects in this area:  (i) Using mutant human mACh receptor subtypes we are investigating how increased constitutive activity affects a number of pharmacological properties, including inverse agonism, agonist-dependent and -independent G protein activation, receptor phosphorylation and downstream signalling, and the up-regulation of receptor expression by inverse agonists. (ii) Using either standard second messenger assays or a [35S]-GTPγS/immunoprecipitation approach, we are also investigating whether different mACh receptor agonists can activate different subsets of Gα protein subtypes. (iii) Some mACh receptor antagonists have been reported to display different affinity profiles in different cells/tissues leading to the idea that tissue selectivity may be possible between tissues that appear to express an identical GPCR subtype.  We have confirmed this phenomenon in guinea-pig tissues expressing M₃ mACh receptors and are currently exploring possible mechanistic bases for such selectivity.

5. Explorations of GPCR 'cross-talk' in physiological regulation.  We are interested in how coincident activation of different GPCR subtypes can lead to inhibitory of facilitatory interactions at multiple levels in signal transduction pathways ('cross-talk').  At present this work focuses on cross-talk between G_q/11-coupled and G_i/o-coupled GPCRs (e.g. M₂ and M₃ mACh receptors), and G_q/11-coupled and G_s-coupled GPCRs (e.g. M₃ mACh receptors and β₂-adrenoceptors).

Research Expertise

1. Culturing, genetically manipulating and metabolically labelling mammalian cell-lines, and generating primary cultures e.g.  cerebellar granule cells, hippocampal neurones, astrocytes, smooth muscle cells derived from arterial (aortic/mesenteric), airway or uterine sources.

Immunocytochemical staining of rat cerebrocortical astrocytes grown in G5 supplement for 4-5 days (left panel, anti-mGlu5; middle panel, anti-GFAP, right panel, merge).

2. A wide variety of molecular pharmacological techniques including: radioligand binding; [³⁵S]-GTPγS binding assays and Gα-specific immunoprecipitation/immunocapture; second messenger assays (cAMP, cGMP, IP₃) and all aspects of assessing phosphoinositide turnover (including [³H]-PI/PIP/PIP₂ separation, etc.). PLC/PLA2/PLD assays. Cell growth and proliferation assays (e.g. [³H]-thymidine incorporation). Standard SDS-PAGE/western blot approaches, including experience with a wide array of signalling component antibodies (for receptors, G proteins, effectors, protein kinases and transcription factors). Measurement of ERK/JNK/p38 through phospho-specific antibodies and [³²P]-ATP/kinase activity assays. Immunocytochemistry.

3. Population and single cell imaging approaches: confocal fluorescence microscopy to assess Ca²⁺ and biosensor reporters for second messengers/signaling intermediates using translocating probes (e.g. eGFP-PH) and FRET biosensors.

4. Molecular manipulation of protein activity/function in intact cells through the use of dominant-negative protein expression, antisense and RNAi/siRNA approaches.

Research Group and Funding 

Present Group Members

Ex Lab Alumni

Post-doctoral

John Mackrill, Helen Sherriffs, Jonathon Willets, Mark Nash, Kenneth Young, Daniela Billups, Danijela Markovic, Hasib Salah-Uddin, Gavin Morris, Melissa Jordan

Doctoral/Masters

Emma Whitham (PhD, 1991), Anthony Morgan (PhD, 1992), Stephen Jenkinson (PhD, 1993), David Adams (PhD, 1994), Peter Simpson (PhD, 1995), Nageen Hashmi (MRes, 1996), Alan Carruthers (PhD, 1997), Donna Boxall (PhD, 1998), Rick Davis (PhD, 1999), Elizabeth Akam (PhD, 1999), Kirsti Hill (MRes, 1999), Paul Wylie (PhD, 2000), Ruth Saunders (PhD, 2000), David Hornigold (PhD, 2001), Jules Selkirk (PhD, 2001), Drew Burdon (PhD, 2002), Sukhwinder Thandi (PhD, 2004), Carl Nelson (PhD, 2004), Mark Dowling, (PhD, 2004), Helen Warwick (PhD, 2005), Peter Atkinson (PhD, 2005), Paula Bartlett (PhD, 2006), Elizabeth Rosethorne (PhD, 2007), David Pier (PhD, 2007); Rachel Thomas (PhD, 2009); Sophie Bradley (PhD, 2011); George Shehatou (PhD, 2011); Aminah Loonat (MRes, 2011); Khaled Al-Hosaini (PhD, 2011); David Sweeney(PhD, 2011)

Current Funding

British Heart Foundation (Programme Grant)

British Heart Foundation (Project Grant)
UCB Collaborative Grant

Eisai Collaborative Grant

BBSRC and MRC (CASE) Studentship funding

Recent Publications

ORIGINAL RESEARCH PAPERS (2006-present)

Morris, G.E., Nelson, C.P., Brighton, P.J., Standen, N.B., Challiss, R.A.J. and Willets, J.M. (2012) Arrestins differentially regulate ET(A) and P2Y(2) receptor-mediated cell signalling and migration in arterial smooth muscle. Am. J. Physiol. Cell Physiol. in press
Sutcliffe, A., Hollins, F., Gomez, E., Saunders, R., Doe, C., Cooke, M.S., Challiss, R.A.J. and Brightling, C.E. (2012) Increased NOX4 expression mediates intrinsic airway smooth muscle hyper-contractility in asthma. Am. J. Respir. Crit. Care Med. in press
Hu, J., Thor, D., Zhou, Y., Wang, Y., McMillin, S.M. Liu, T., Mistry, R., Challiss, R.A.J., Costanzi, S. and Wess, J. (2012) Structural aspects of M(3) muscarinic acetylcholine receptor dimer formation and activation. FASEB J. in press
Selway, J.L., Moore, C.E., Mistry, R., Challiss, R.A.J. and Herbert, T.P. (2012) Molecular mechanisms of muscarinic acetylcholine receptor-stimulated increase in cytosolic free Ca2+ concentration and ERK1/2 activation in the MIN6 pancreatic β-cell-line. Acta Diabetologica in press
Dupont, G., Loomekandja Lokenye, E.F. and Challiss, R.A.J. (2011) A model for Ca2+ oscillations stimulated by the type 5 metabotropic glutamate receptor: an unusual mechanism based on repetitive, reversible phosphorylation of the receptor. Biochemie 93, 2132-2138
Challiss, R.A.J. and Wess, J. (2011) GPCR-G protein preassembly. Nat. Chem. Biol. 7, 657-658

Nelson, C.P., Rainbow, R.D., Brignell, J.L., Perry, M.D., Willets, J.M.,  Davies, N.W., Standen, N.B. and Challiss, R.A.J. (2011) Principal role of adenylyl cyclase 6 in K+-channel regulation and vasodilator signalling in vascular smooth muscle cells. Cardiovasc. Res. 91,694-702

Bradley, S.J. and Challiss, R.A.J. (2011) Defining protein kinase/phosphatase isoenzymic regulation of mGlu5 receptor-stimulated phospholipase C and Ca2+ responses in astrocytes. Br. J. Pharmacol. 164,755-771

Frank, R.A.W., McRae, A.F., Pocklington, A.J., van de Lagemaat, L.N., Navarro, P., Croning, M.D.R., Komiyama, N.H., Bradley, S.J., Challiss, R.A.J., Armstrong, J.D., Finn, R.D., Malloy, M.P., MacLean, A.W., Harris, S.E., Starr, J.M., Bhaskar, S.S., Howard, E.K., Hunt, S.E., Coffey, A.J., Ranganath, V., Deloukas, P., Rogers, J., Muir, W.J., Deary, I.J., Blackwood, D.H., Visscher, P.M. and Grant, S.G.N. (2011) Clustered coding variants in the synaptic receptor complexes of individuals with schizophrenia and bipolar disorder. PLoS-ONE 6, e19011

Chernova, T., Steinert, J.R., Richards, P., Mistry, R., Challiss, R.A.J., Cain, K., Jukes-Jones, R., Smith, A.G. and Forsythe, I.D. (2011) Early failure of N-methyl-D-aspartate receptors and deficient spine formation induced by reduction of regulatory heme in neurons. Mol. Pharmacol. 79, 844-854

Bradley, S.J., Langmead, C.J., Watson, J.M. and Challiss, R.A.J. (2011) Quantitative analysis reveals multiple Mechanisms of allosteric modulation of the mGlu5 receptor in rat astroglia. Mol. Pharmacol. 79, 874-885

Brighton, P.J., Rana, S., Challiss, R.A.J., Konje, J.C. and Willets, J.M. (2011) Arrestins differentially regulate histamine- and oxytocin-evoked phospholipase C and mitogen-activated protein kinase signalling in myometrial cells. Br. J. Pharmacol. 162, 1603-1617

Morris, G.E., Nelson, C.P., Everitt, D., Brighton, P.J., Standen, N.B., Challiss, R.A.J. and Willets, J.M. (2011) G protein-coupled receptor kinase2 and arrestin2 regulate arterial smooth muscle P2Y-purinoceptor signalling. Cardiovasc. Res. 89, 193-203

Morris, G.E., Nelson, C.P., Standen, N.B., Challiss, R.A.J. and Willets, J.M. (2010) Endothelin signalling in arterial smooth muscle is tightly regulated by G protein-coupled receptor kinase 2. Cardiovasc. Res. 85, 424-433

Bradley, S.J., Watson, J.M. and Challiss, R.A.J. (2009) Effects of positive allosteric modulators on single cell oscillatory Ca2+ signaling initiated by the type 5 metabotropic glutamate receptor. Mol. Pharmacol. 76, 1302-1313

Thomas, R.L., Langmead, C.J., Wood, M.D. and Challiss, R.A.J. (2009) Contrasting effects of allosteric and orthosteric agonists on M1 muscarinic acetylcholine receptor internalization and down-regulation. J. Pharmacol. Exp. Ther. 331, 1086-1095

Brighton, P.J., McDonald, J., Taylor, A.H., Challiss, R.A.J., Lambert, D.G., Konje, J.C. and Willets, J.M. (2009) Characterization of anandamide-stimulated cannabinoid receptor signaling in human ULTR myometrial smooth muscle cells. Mol. Endocrinol. 23, 1415-1427

Willets, J.M., Brighton, P.J., Mistry, R., Morris, G.E., Konje, J.C. and Challiss, R.A.J. (2009) Regulation of oxytocin receptor responsiveness by G protein-coupled receptor kinase 6 in human myometrial smooth muscle. Mol. Endocrinol. 23, 1272-1280

Salah-Uddin, H., Scarr, E., Pavey, G., Harris, K., Hagan, J.J., Dean B., Challiss, R.A.J. and Watson J.M. (2009) Altered M1 muscarinic acetylcholine receptor (CHRM1)-Gq/11 coupling in a schizophrenia endophenotype. Neuropsychopharmacology 34, 2156-2166

Nelson, C.P., Willets, J.M., Davies, N.W., Challiss, R.A.J. and Standen, N.B. (2008) Visualizing the temporal effects of vasoconstrictors on PKC translocation and Ca2+ signaling in single resistance arterial smooth muscle cells. Am. J. Physiol. 295, C1590-C1601

Steinert, J.R., Kopp-Scheinpflug, C., Baker, C., Challiss, R.A.J., Mistry, R., Haustein, M., Griffin, S.J., Tong, H., Graham, B.P. and Forsythe, I.D. (2008) Nitric oxide is a volume transmitter regulating postsynaptic excitability at a glutamatergic synapse. Neuron 60, 642-656

Thomas, R.L., Mistry, R., Langmead, C.J., Wood, M.D. and Challiss, R.A.J. (2008) G protein coupling and signaling pathway activation by M1 muscarinic acetylcholine receptor orthosteric and allosteric agonists. J. Pharmacol. Exp. Ther. 327, 365-374

Nelson, C.P., Nahorski, S.R. and Challiss, R.A.J. (2008) Temporal profiling of changes in phosphatidylinositol 4,5-bisphosphate, inositol 1,4,5-trisphosphate and diacylglycerol allows comprehensive analysis of phospholipase C-initiated signaling in single neurons. J. Neurochem. 107, 802-615

Willets, J.M., Taylor, A.H., Shaw, H., Konje, J.C. and Challiss, R.A.J. (2008) Selective regulation of H1 histamine receptor signaling by G protein-coupled receptor kinase 2 in uterine smooth muscle. Mol. Endocrinol. 22, 1893-1907

Salah-Uddin, H., Thomas, D.R., Davies, C.H., Hagan, J.J., Wood, M.D., Watson, J.M. and Challiss, R.A.J. (2008) Pharmacological assessment of M1 muscarinic acetylcholine receptor-Gq/11 protein coupling in membranes prepared from post mortem human brain tissue. J. Pharmacol. Exp. Ther. 325, 869-874

Rosethorne, E.M., Nahorski, S.R. and Challiss, R.A.J. (2008) Distinct signaling pathways link M3 muscarinic and B2 bradykinin receptors to the regulation of cyclic AMP response-element binding-protein in SH-SY5Y human neuroblastoma cells. Biochem. Pharmacol. 75, 942-955

Willets, J.M., Nelson, C.P., Nahorski, S.R., and Challiss, R.A.J. (2007) The regulation of M1 muscarinic acetylcholine receptor desensitization by synaptic activity in cultured hippocampal neurons. J. Neurochem. 103, 2268-2280

Billups, D., Billups, B. Challiss, R.A.J. and Nahorski, S.R. (2006) Modulation of Gq-protein-coupled inositol trisphosphate and Ca2+ signaling by the membrane potential. J. Neurosci. 26, 9983-9995

Dowling, M.R., Willets, J.M., Budd, D.C., Charlton, S.J., Nahorski, S.R. and Challiss R.A.J. (2006) A single point mutation (N514Y) in the human M3 muscarinic acetylcholine receptor reveals differences in the properties of antagonists: evidence for differential inverse agonism. J. Pharmacol. Exp. Ther. 317, 1134-1142

Atkinson, P.J., Young, K.W., Ennion, S.J., Kew, J.N.C., Nahorski, S.R. and Challiss, R.A.J. (2006) Altered expression of Gαq/11 protein shapes mGlu1 and mGlu5 receptor-mediated single cell inositol 1,4,5-trisphosphate and Ca2+ signaling. Mol. Pharmacol. 69, 174-184

Nelson, C.P., Nahorski, S.R. and Challiss, R.A.J. (2006) Constitutive activity and inverse agonism at the M2 muscarinic acetylcholine receptor. J. Pharmacol. Exp. Ther. 316, 279-288

RECENT REVIEWS

Markovic, D.M. and Challiss, R.A.J. (2009) Alternative splicing of G protein-coupled receptors: physiology and pathophysiology. Cell. Mol. Life Sci. 66, 3337-3352

Nelson, C.P. and Challiss, R.A.J. (2007) “Phenotypic” pharmacology: the influence of cellular environment on G protein-coupled receptor antagonist and inverse agonist pharmacology. Biochem. Pharmacol. 73, 737-751

Willets, J.M., Challiss, R.A.J. and Nahorski, S.R. (2003) Non-visual GRKs: Are we seeing the whole picture? Trends Pharmacol. Sci. 24, 626-633

Hermans, E. and Challiss, R.A.J. (2001) Structural, signalling and regulatory properties of group I metabotropic glutamate receptors: Prototypic family C G protein-coupled receptors. Biochem. J. 359, 465-484

BOOK

Willars, G.B. and Challiss, R.A.J., Editors “Receptor Signal Transduction Protocols” 3rd Edition (2011) Methods in Molecular Biology vol. 746, pp. 1-479; Humana Press Inc., Totowa, USA