title: Pharmacologic Approach to Defective Protein Trafficking in the E637K-hERG Mutant with PD-118057 and Thapsigargin.
abstract: Treatment of LQT2 is inadequate. Many drugs which can pharmacologically rescue defective protein trafficking in LQT2 also result in potent blockade of HERG current, negating their therapeutic benefit. It is reported that PD-118057 and thapsigargin can rescue LQT2 without hERG channel blockade, but the precise mechanism of action is unknown. Furthermore, the effect of PD-118057 and thapsigargin on the dominant negative E637K-hERG mutant has not been previously investigated.
  
  
  
  IN THIS STUDY, WE INVESTIGATED: (a) the effect of PD-118057 and thapsigargin on the current amplitudes of WT-hERG and WT/E637K-hERG channels; (b) the effect of PD-118057 and thapsigargin on the biophysical properties of WT-hERG and WT/E637K-hERG channels; (c) whether drug treatment can rescue channel processing and trafficking defects of the WT/E637K-hERG mutant.
  
  
  
  The whole-cell Patch-clamp technique was used to assess the effect of PD-118057 and thapsigargin on the electrophysiological characteristics of the rapidly activating delayed rectifier K(+) current (Ikr) of the hERG protein channel. Western blot was done to investigate pharmacological rescue on hERG protein channel function.
  
  
  
  In our study, PD-118057 was shown to significantly enhance both the maximum current amplitude and tail current amplitude, but did not alter the gating and kinetic properties of the WT-hERG channel, with the exception of accelerating steady-state inactivation. Additionally, thapsigargin shows a similar result as PD-118057 for the WT-hERG channel, but with the exception of attenuating steady-state inactivation. However, for the WT/E637K-hERG channel, PD-118057 had no effect on either the current or on the gating and kinetic properties. Furthermore, thapsigargin treatment did not alter the current or the gating and kinetic properties of the WT/E637K-hERG channel, with the exception of opening at more positive voltages.
  
  
  
  Our findings illustrate that neither PD-118057 nor thapsigargin play a role in correcting the dominant-negative effect of the E637K-hERG mutant.
authors.affiliation: LiHuiLi Hospital, Medical School of NingBo University, NingBo, China.
authors.forename: Haiyan
authors.initials: H
authors.lastname: Mao
authors.forename: Xiaoli
authors.initials: X
authors.lastname: Lu
authors.forename: Justin Michael
authors.initials: JM
authors.lastname: Karush
authors.forename: Xiaoyan
authors.initials: X
authors.lastname: Huang
authors.forename: Xi
authors.initials: X
authors.lastname: Yang
authors.forename: Yanna
authors.initials: Y
authors.lastname: Ba
authors.forename: Ying
authors.initials: Y
authors.lastname: Wang
authors.forename: Ningsheng
authors.initials: N
authors.lastname: Liu
authors.forename: Jianqing
authors.initials: J
authors.lastname: Zhou
authors.forename: Jiangfang
authors.initials: J
authors.lastname: Lian
mesh_terms: D019943:Amino Acid Substitution; D002722:Chlorobenzenes / Q000494:pharmacology*; D000072237:ERG1 Potassium Channel / Q000235:genetics* / Q000378:metabolism*; D059865:Endoplasmic Reticulum Stress / Q000187:drug effects / Q000235:genetics; D018698:Glutamic Acid / Q000235:genetics; D057809:HEK293 Cells; D006801:Humans; D008133:Long QT Syndrome / Q000188:drug therapy / Q000235:genetics* / Q000378:metabolism*; D008239:Lysine / Q000235:genetics; D050505:Mutant Proteins / Q000235:genetics / Q000378:metabolism; D020125:Mutation, Missense; D018408:Patch-Clamp Techniques; D021381:Protein Transport / Q000187:drug effects / Q000235:genetics; D019284:Thapsigargin / Q000494:pharmacology*; D056811:Unfolded Protein Response / Q000187:drug effects / Q000235:genetics; D062367:ortho-Aminobenzoates / Q000494:pharmacology*
chemical_list: C517140:2-(4-(2-(3,4-dichlorophenyl)ethyl)phenylamino)benzoic acid; D002722:Chlorobenzenes; D000072237:ERG1 Potassium Channel; C000606913:KCNH2 protein, human; D050505:Mutant Proteins; D062367:ortho-Aminobenzoates; D018698:Glutamic Acid; D019284:Thapsigargin; D008239:Lysine