KvLQT1 modulates the distribution and biophysical properties of HERG. A novel alpha-subunit interaction between delayed rectifier currents.
Cardiac repolarization is under joint control of the slow (IKs) and rapid (IKr) delayed rectifier currents. Experimental and clinical evidence indicates important functional interactions between these components. We hypothesized that there might be more direct interactions between the KvLQT1 and HERG alpha-subunits of IKs and IKr and tested this notion with a combination of biophysical and biochemical techniques. Co-expression of KvLQT1 with HERG in a mammalian expression system significantly accelerated HERG current deactivation at physiologically relevant potentials by increasing the contribution of the fast component (e.g. upon repolarization from +20 mV to -50 mV: from 20 +/- 3 to 32 +/- 5%, p < 0.05), making HERG current more like native IKr. In addition, HERG current density was approximately doubled (e.g. tail current after a step to +10 mV: 18 +/- 3 versus 39 +/- 7 pA/picofarad, p < 0.01) by co-expression with KvLQT1. KvLQT1 co-expression also increased the membrane immunolocalization of HERG by approximately 2-fold (p < 0.05). HERG and KvLQT1 co-immunolocalized in canine ventricular myocytes and co-immunoprecipitated in cultured Chinese hamster ovary cells as well as in native cardiac tissue, indicating physical interactions between HERG and KvLQT1 proteins in vitro and in vivo. Protein interaction assays also demonstrated binding of KvLQT1 (but not another K+ channel alpha-subunit, Kv3.4) to a C-terminal HERG glutathione S-transferase fusion protein. Co-expression with HERG did not affect the membrane localization or ionic current properties of KvLQT1. This study shows that the alpha-subunit of IKs can interact with and modify the localization and current-carrying properties of the alpha-subunit of IKr, providing potentially novel insights into the molecular function of the delayed rectifier current system.
Montreal Heart Institute, Department of Medicine, McGill University, Montreal, Quebec H1T 1C8, Canada.
Joachim R
JR
Ehrlich
Marc
M
Pourrier
Manjula
M
Weerapura
Nathalie
N
Ethier
Aida M
AM
Marmabachi
Terence E
TE
Hébert
Stanley
S
Nattel
D000818:Animals; D016466:CHO Cells; D027682:Cation Transport Proteins; D002462:Cell Membrane / Q000378:metabolism; D006224:Cricetinae; D004268:DNA-Binding Proteins; D004285:Dogs; D004305:Dose-Response Relationship, Drug; D000072237:ERG1 Potassium Channel; D004594:Electrophysiology; D051638:Ether-A-Go-Go Potassium Channels; D005982:Glutathione Transferase / Q000378:metabolism; D007477:Ions; D051656:KCNQ Potassium Channels; D051657:KCNQ1 Potassium Channel; D018613:Microscopy, Confocal; D008856:Microscopy, Fluorescence; D009206:Myocardium / Q000166:cytology; D015221:Potassium Channels / Q000737:chemistry / Q000378:metabolism* / Q000502:physiology*; D024642:Potassium Channels, Voltage-Gated; D011233:Precipitin Tests; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D051670:Shaw Potassium Channels; D015534:Trans-Activators; D014162:Transfection
D027682:Cation Transport Proteins; D004268:DNA-Binding Proteins; D000072237:ERG1 Potassium Channel; D051638:Ether-A-Go-Go Potassium Channels; D007477:Ions; C492015:KCNC4 protein, human; C000606913:KCNH2 protein, human; C092509:KCNH6 protein, human; D051656:KCNQ Potassium Channels; D051657:KCNQ1 Potassium Channel; D015221:Potassium Channels; D024642:Potassium Channels, Voltage-Gated; D011993:Recombinant Fusion Proteins; D051670:Shaw Potassium Channels; D015534:Trans-Activators; D005982:Glutathione Transferase