Regulation of HERG potassium channel activation by protein kinase C independent of direct phosphorylation of the channel protein.
OBJECTIVE
Patients with HERG-associated long QT syndrome typically develop tachyarrhythmias during physical or emotional stress. Previous studies have revealed that activation of the beta-adrenergic system and consecutive elevation of the intracellular cAMP concentration regulate HERG channels via protein kinase A-mediated phosphorylation of the channel protein and via direct interaction with the cAMP binding site of HERG. In contrast, the influence of the alpha-adrenergic signal transduction cascade on HERG currents as suggested by recent reports is less well understood. The aim of the present study was to elucidate the biochemical pathways of the protein kinase C (PKC)-dependent regulation of HERG currents.


METHODS
HERG channels were heterologously expressed in Xenopus laevis oocytes, and currents were measured using the two-microelectrode voltage clamp technique.


RESULTS
Application of the phorbol ester PMA, an unspecific protein kinase activator, shifted the voltage dependence of HERG activation towards more positive potentials. This effect could be mimicked by activation of conventional PKC isoforms with thymeleatoxin. Coexpression of HERG with the beta-subunits minK or hMiRP1 did not alter the effect of PMA. Specific inhibition of PKC abolished the PMA-induced activation shift, suggesting that PKC is required within the regulatory mechanism. The PMA-induced effect could still be observed when the PKC-dependent phosphorylation sites in HERG were deleted by mutagenesis. Cytoskeletal proteins such as actin filaments or microtubules did not affect the HERG activation shift.


CONCLUSIONS
In addition to the known effects of PKA and cAMP, HERG channels are also modulated by PKC. The molecular mechanisms of this PKC-dependent process are not completely understood but do not depend on direct PKC-dependent phosphorylation of the channel.
Thomas
Dierk
D
Department of Cardiology, Medical University Hospital Heidelberg, Bergheimerstrasse 58, D-69115 Heidelberg, Germany. dthomas@ix.urz.uni-heidelberg.de
Zhang
Wei
W
Wu
Kezhong
K
Wimmer
Anna-Britt
AB
Gut
Bernd
B
Wendt-Nordahl
Gunnar
G
Kathöfer
Sven
S
Kreye
Volker A W
VA
Katus
Hugo A
HA
Schoels
Wolfgang
W
Kiehn
Johann
J
Karle
Christoph A
CA
D000818:Animals; D001145:Arrhythmias, Cardiac / Q000378:metabolism*; D027682:Cation Transport Proteins; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism / Q000494:pharmacology; D004268:DNA-Binding Proteins; D000072237:ERG1 Potassium Channel; D004789:Enzyme Activation; D051638:Ether-A-Go-Go Potassium Channels; D005260:Female; D006801:Humans; D016297:Mutagenesis, Site-Directed; D009865:Oocytes; D018408:Patch-Clamp Techniques; D010703:Phorbol Esters / Q000494:pharmacology; D010766:Phosphorylation; D015221:Potassium Channels / Q000032:analysis / Q000235:genetics* / Q000378:metabolism; D024642:Potassium Channels, Voltage-Gated; D011493:Protein Kinase C / Q000378:metabolism* / Q000494:pharmacology; D015398:Signal Transduction / Q000187:drug effects; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D015534:Trans-Activators; D000071230:Transcriptional Regulator ERG; D014982:Xenopus laevis
D027682:Cation Transport Proteins; D004268:DNA-Binding Proteins; C072312:ERG protein, human; D000072237:ERG1 Potassium Channel; D051638:Ether-A-Go-Go Potassium Channels; C000606913:KCNH2 protein, human; C092509:KCNH6 protein, human; D010703:Phorbol Esters; D015221:Potassium Channels; D024642:Potassium Channels, Voltage-Gated; D015534:Trans-Activators; D000071230:Transcriptional Regulator ERG; C080287:thymeleatoxin; D017868:Cyclic AMP-Dependent Protein Kinases; D011493:Protein Kinase C; D013755:Tetradecanoylphorbol Acetate