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(Circulation Research. 2008;103:269.)
© 2008 American Heart Association, Inc.

Cellular Biology

Reactive Oxygen Species-Induced Activation of p90 Ribosomal S6 Kinase Prolongs Cardiac Repolarization Through Inhibiting Outward K⁺ Channel Activity

Zhibo Lu, Jun-ichi Abe, Jack Taunton, Yan Lu, Tetsuro Shishido, Carolyn McClain, Chen Yan, Sheng Ping Xu, Thomas M. Spangenberg, Haodong Xu

From the Department of Pathology and Laboratory Medicine (Z.L., S.P.X., H.X.), University of Rochester Medical Center and Aab Cardiovascular Research Institute (Z.L., J.A., Y.L., T.S., C.M., C.Y., S.P.X., T.M.S., H.X.), University of Rochester School Medicine and Dentistry, Rochester, NY; and the Department of Cellular and Molecular Pharmacology (J.T.), University of California, San Francisco, Calif.

Correspondence to Haodong Xu, MD, PhD, Department of Pathology and Laboratory Medicine, Box 626, University of Rochester Medical Center, 601 Elmwood Avenue, Rochester, NY 14642. E-mail Haodong_Xu{at}urmc.rochester.edu

p90 ribosomal S6 kinase (p90RSK) is activated in cardiomyopathies caused by conditions such as ischemia/reperfusion injury and diabetes mellitus in which prolongation of cardiac repolarization and frequent arrhythmias are common. Molecular mechanisms underlying the electric remodeling in cardiac diseases are largely unknown. In the present study, we determined the role of p90RSK activation in the modulation of voltage-gated K⁺ channel activity determining cardiac repolarization. Mice with increased cardiac p90RSK activity due to transgenic expression of p90RSK (p90RSK-Tg) had prolongation of QT intervals and of ventricular myocyte action potential durations. Fast transient outward K⁺ current (I_to,f), slow delayed outward K⁺ current (I_K,slow), and steady-state K⁺ current (I_SS) were significantly decreased in p90RSK-Tg mouse ventricular myocytes. mRNA levels of Kv4.3, Kv4.2, Kv1.5, Kv2.1, and KChIP2 from ventricles between p90RSK-Tg and nontransgenic littermate control mice were similar, as assessed by quantitative reverse transcriptase–polymerase chain reaction, indicating that p90RSK regulates voltage-gated K⁺ channels through posttranslational modification. Kv4.3- and Kv1.5- rather than Kv4.2- and Kv2.1-encoded channels in HEK 293 cells were inhibited by p90RSK. In vitro phosphorylation analysis showed that Kv4.3 was phosphorylated by p90RSK at 2 conserved sites, Ser516 and Ser550. p90RSK expression significantly inhibited Kv4.3- and Kv4.3 and KChIP2-encoded channel activities in HEK 293 cells, whereas p90RSK’s effects were blocked by amino acid mutation(s) at phosphorylation site(s) in Kv4.3. Hydrogen peroxide, a mediator of induced cardiac p90RSK activation in ischemia/reperfusion injury and diabetes mellitus, had effects similar to those of p90RSK on Kv4.3- or Kv4.3- and KChIP2-encoded channels. Fluoromethylketone, a specific p90RSK inhibitor, abolished hydrogen peroxide effects. These findings indicate that p90RSK activation is critical for reactive oxygen species-mediated inhibition of voltage-gated K⁺ channel activity and leads to prolongation of cardiac repolarization.

Key Words: arrhythmias • cardiac repolarization • hydrogen peroxide • p90RSK • phosphorylation • reactive oxygen species • voltage-gated outward K⁺ currents

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