E3 ubiquitin ligase rififylin has yin and yang effects on rabbit cardiac transient outward potassium currents (I_to) and corresponding channel proteins

Genome-wide association studies have reported a correlation between a SNP of the RING finger E3 ubiquitin protein ligase rififylin (RFFL) and QT interval variability in humans (Newton-Cheh et al., 2009). Previously, we have shown that RFFL downregulates expression and function of the human-like ether-a-go-go-related gene potassium channel and corresponding rapidly activating delayed rectifier potassium current (I_Kr) in adult rabbit ventricular cardiomyocytes. Here, we report that RFFL also affects the transient outward current (I_to), but in a peculiar way. RFFL overexpression in adult rabbit ventricular cardiomyocytes significantly decreases the contribution of its fast component (I_to,f) from 35% to 21% and increases the contribution of its slow component (I_to,s) from 65% to 79%. Since I_to,f in rabbits is mainly conducted by Kv4.3, we investigated the effect of RFFL on Kv4.3 expressed in HEK293A cells. We found that RFFL overexpression reduced Kv4.3 expression and corresponding I_to,f in a RING domain–dependent manner in the presence or absence of its accessory subunit Kv channel-interacting protein 2. On the other hand, RFFL overexpression in Kv1.4-expressing HEK cells leads to an increase in both Kv1.4 expression level and I_to,s, similarly in a RING domain–dependent manner. Our physiologically detailed rabbit ventricular myocyte computational model shows that these yin and yang effects of RFFL overexpression on I_to,f, and I_to,s affect phase 1 of the action potential waveform and slightly decrease its duration in addition to suppressing I_Kr. Thus, RFFL modifies cardiac repolarization reserve via ubiquitination of multiple proteins that differently affect various potassium channels and cardiac action potential duration.