Research Interests and Techniques

HERG potassium channels. Functional roles in cardiac myocytes, tumour and neuronal cells and structural basis for physiological and pharmacological properties

HERG is the pore forming subunit of channels important for cardiac action potential repolarisation. Reduction of HERG channel function causes long QT syndrome, a disorder of cardiac action potential repolarisation that prolongs the cardiac action potential and predisposes individuals to potentially lethal cardiac arrhythmias and sudden death.

HERG channel gating

HERG channels have unusual gating properties that are important for their physiological function. They exhibit unusually slow activation, but very fast inactivation kinetics - the opposite to most channels. These unusual gating kinetics are important for timing the onset of current during action potential repolarisation. One aim of my research is to determine the structural components of HERG that enable it to function in this manner.

HERG channel pharmacology

At least 70 commonly used drugs have been shown to cause LQTS by blocking HERG channels. The question we have been trying to address is why so many therapeutically and structurally diverse drugs preferentially block HERG channels and not a large number of other channels with a role in action potential repolarisation in the heart. We have been able to identify several unique properties of the HERG channel that make it susceptible to block and have localised the primary drug binding site. Future aims are to identify additional drug binding sites and obtain a more detailed model of the primary binding site, which can be used in the early phases of drug development for detecting compounds with the potential for causing LQTS.

It is becoming clear that HERG channels are modulated by a variety of second messenger pathways. In collaboration with G Willars and A Tobin we are investigating mechanisms of G-protein receptor mediated modulation of HERG channel activity.

Oncogenic potential of HERG

HERG channels are expressed in numerous primary tumour cells and tumour derived cell lines. At present it is not clear if the HERG gene itself is oncogenic or whether HERG channel expression is an adaptation of some cancer cells that provides a selective advantage for cancer cells. We are evaluating the oncogenic potential of HERG and investigating molecular mechanisms of HERG effects on cell proliferation, substrate adhesion, morphology and motility.

Techniques

• Site directed mutagenesis
• Expression of wild type and mutant HERG channels in Xenopus oocytes and mammalian cell lines.
• Two electrode voltage clamp recording and single channel patch clamp recording in oocytes.
• Whole cell and excised macropatch recordings in mammalian cell lines and cardiac myocytes.
• Protein phosphorylation assays and phospho-peptide mapping.
• Cell proliferation, morphology and motility assays.

Research Group and Funding

Present group members

Rachel Caves
Rikesh Patel
Steve Thomson

Current funding

MRC 5 year Career Establishment Award (Feb 2002-2007)
Collaborative partnership with Pfizer Global Research and Development (Dec 2001-2004)
British Heart Foundation project grant (Oct 2001 - 2004)
2 x MRC/Novartis CASE studentships (Oct 2003 – 2006)
BBSRC/GlaxoSmithKline CASE studentship (Oct 2003- 2006)
BBSRC/Pfizer CASE studentship (Oct 2004 – 2007)

Recent Publications

Muskett FW, Thouta S, Thomson SJ, Bowen A, Stansfeld PJ, Mitcheson JS. Mechanistic Insight into Human ether-a-go-go-related Gene (hERG) K+ Channel Deactivation Gating from the Solution Structure of the EAG Domain. J Biol Chem. 2011 Feb 25;286(8):6184-91.

Muskett FW, Mitcheson JS. Resonance assignment and secondary structure prediction of the N-terminal domain of hERG (Kv11.1). Biomol NMR Assign. 2010 Aug 14.

Perry M, Sanguinetti M, Mitcheson J. Revealing the structural basis of action of hERG potassium channel activators and blockers. J Physiol. 2010 Sep 1;588(Pt 17):3157-67.

Stansfeld PJ, Grottesi A, Sands ZA, Sansom MS, Gedeck P, Gosling M, Cox B, Stanfield PR, Mitcheson JS, Sutcliffe MJ. Insight into the mechanism of inactivation and pH sensitivity in potassium channels from molecular dynamics simulations. Biochemistry. 2008 Jul 15;47(28):7414-22.

Mitcheson JS. hERG potassium channels and the structural basis of drug-induced arrhythmias. Chem Res Toxicol. 2008 May;21(5):1005-10.

Hardman RM, Stansfeld PJ, Dalibalta S, Sutcliffe MJ, Mitcheson JS. Activation gating of hERG potassium channels: S6 glycines are not required as gating hinges. J Biol Chem. 2007 Nov 2;282(44):31972-81.

Stansfeld PJ, Gedeck P, Gosling M, Cox B, Mitcheson JS, Sutcliffe MJ. Drug block of the hERG potassium channel: insight from modeling. Proteins. 2007 Aug 1;68(2):568-80.

Cockerill SL, Tobin AB, Torrecilla I, Willars GB, Standen NB, Mitcheson JS. Modulation of hERG potassium currents in HEK-293 cells by protein kinase C. Evidence for direct phosphorylation of pore forming subunits. J Physiol. 2007 Jun 1;581(Pt 2):479-93.

Hancox JC, Mitcheson JS. Combined hERG channel inhibition and disruption of trafficking in drug-induced long QT syndrome by fluoxetine: a case-study in cardiac safety pharmacology. Br J Pharmacol. 2006 Nov;149(5):457-9.

Stansfeld PJ, Sutcliffe MJ, Mitcheson JS. Molecular mechanisms for drug interactions with hERG that cause long QT syndrome. Expert Opin Drug Metab Toxicol. 2006 Feb;2(1):81-94. Review.

Kamiya K, Niwa R, Mitcheson JS, Sanguinetti MC. Molecular determinants of HERG channel block. Mol Pharmacol. 2006 May;69(5):1709-16.

Perry M, Stansfeld PJ, Leaney J, Wood C, de Groot MJ, Leishman D, Sutcliffe MJ, Mitcheson JS. Drug binding interactions in the inner cavity of HERG channels: molecular insights from structure-activity relationships of clofilium and ibutilide analogs. Mol Pharmacol. 2006 Feb;69(2):509-19.

Cockerill SL, Mitcheson JS. Direct block of human ether-a-go-go-related gene potassium channels by caffeine. J Pharmacol Exp Ther. 2006 Feb;316(2):860-8.

Sanguinetti MC, Chen J, Fernandez D, Kamiya K, Mitcheson J, Sanchez-Chapula JA. Physicochemical basis for binding and voltage-dependent block of hERG channels by structurally diverse drugs. Novartis Found Symp. 2005;266:159-66; discussion 166-70. Review.

Mitcheson J, Perry M, Stansfeld P, Sanguinetti MC, Witchel H, Hancox J. Structural determinants for high-affinity block of hERG potassium channels. Novartis Found Symp. 2005;266:136-50; discussion 150-8. Review.

Sanguinetti MC, Mitcheson JS. Predicting drug-hERG channel interactions that cause acquired long QT syndrome. Trends Pharmacol Sci. 2005 Mar;26(3):119-24. Review.

Davie C, Pierre-Valentin J, Pollard C, Standen N, Mitcheson J, Alexander P, Thong B. Comparative pharmacology of guinea pig cardiac myocyte and cloned hERG (I(Kr)) channel. J Cardiovasc Electrophysiol. 2004 Nov;15(11):1302-9.

Witchel HJ, Dempsey CE, Sessions RB, Perry M, Milnes JT, Hancox JC, Mitcheson JS. The low-potency, voltage-dependent HERG blocker propafenone—molecular determinants and drug trapping. Mol Pharmacol. 2004 Nov;66(5):1201-12.

Perry M, de Groot MJ, Helliwell R, Leishman D, Tristani-Firouzi M, Sanguinetti MC, Mitcheson J. Structural determinants of HERG channel block by clofilium and ibutilide. Mol Pharmacol. 2004 Aug;66(2):240-9.

Mitcheson JS, Perry MD. Molecular determinants of high-affinity drug binding to HERG channels. Curr Opin Drug Discov Devel. 2003 Sep;6(5):667-74. Review.

Witchel HJ, Milnes JT, Mitcheson JS, Hancox JC. Troubleshooting problems with in vitro screening of drugs for QT interval prolongation using HERG K+ channels expressed in mammalian cell lines and Xenopus oocytes. J Pharmacol Toxicol Methods. 2002 Sep-Oct;48(2):65-80. Review.

Mitcheson JS. Drug binding to HERG channels: evidence for a 'non-aromatic' binding site for fluvoxamine. Br J Pharmacol. 2003 Jul;139(5):883-4. Review.

Chen J, Mitcheson JS, Tristani-Firouzi M, Lin M, Sanguinetti MC. The S4-S5 linker couples voltage sensing and activation of pacemaker channels. Proc Natl Acad Sci U S A. 2001 Sep 25;98(20):11277-82. Epub 2001 Sep 11.

Kamiya K, Mitcheson JS, Yasui K, Kodama I, Sanguinetti MC. Open channel block of HERG K(+) channels by vesnarinone. Mol Pharmacol. 2001 Aug;60(2):244-53.

Tristani-Firouzi M, Chen J, Mitcheson JS, Sanguinetti MC. Molecular biology of K(+) channels and their role in cardiac arrhythmias. Am J Med. 2001 Jan;110(1):50-9. Review.

Mitcheson JS, Chen J, Lin M, Culberson C, Sanguinetti MC. A structural basis for drug-induced long QT syndrome. Proc Natl Acad Sci U S A. 2000 Oct 24;97(22):12329-33.

Chen J, Mitcheson JS, Lin M, Sanguinetti MC. Functional roles of charged residues in the putative voltage sensor of the HCN2 pacemaker channel. J Biol Chem. 2000 Nov 17;275(46):36465-71.

Mitcheson JS, Chen J, Sanguinetti MC. Trapping of a methanesulfonanilide by closure of the HERG potassium channel activation gate. J Gen Physiol. 2000 Mar;115(3):229-40.