Abstract 17484: MG53 Modulates KChIP2 Expression through Regulation of NF-κB Activity
Background: The fast transient outward K+ current (Ito,f) is an important repolarizing component in heart. Ito,f is formed by specific interaction of the pore-forming Kv4-subunits and obligatory ancillary subunits K+ channel interacting protein 2 (KChIP2). Recent study shows that MG53, a muscle-specific TRIM-family protein is critical for maintaining cardiac electrical stability. In this study, we investigated the possible role of MG53 in regulation of Ito,f activity and the underlying mechanisms.
Methods: Bidirectional manipulations of MG53 expression were performed by adenoviral overexpression of MG53 or knockdown of MG53 with RNA interference in neonatal and adult rat ventricular myocytes. Ito,f was recorded with patch clamp in whole-cell mode 48 h after adenoviral transfection.
Results: Overexpression of MG53 by 100% increased the amplitude of Ito,f by 112%, whereas knockdown of MG53 by 58% decreased it by 38% in neonatal cardiomyocytes. MG53 overexpression slowed the kinetics of inactivation and positively shifted the voltage-dependent inactivation of Ito,f, while knockdown of MG53 contrarily regulated these properties. Consistent with the alterations in Ito,f magnitude, overexpression of MG53 increased the protein levels of KChIP2 by 245%, whereas knockdown of MG53 expression decreased it by 42%. However, neither overexpression nor knockdown of MG53 affected the protein levels of Kv4.2 and Kv4.3. Bidirectional manipulations of MG53 had similar effects in adult cardiomyocytes as those in neonatal cardiomyocytes, except that overexpression of MG53 had less effects on increasing KChIP2 expression and Ito,f magnitude. Biochemical assays showed that overexpression of MG53 decreased nuclear factor (NF)-κB importing into nuclear, whereas knockdown of MG53 increased NF-κB nuclear translocation. Overexpression of NF-κB activator IκB kinase-β inhibited the stimulation effects of MG53 overexpression on the protein expression of KChIP2. Concomitantly, overexpression of NF-κB inhibitor IκBαSA inhibited the suppression effects of MG53 knockdown on KChIP2 expression.
Conclusion: These findings establish MG53 as a novel endogenous regulator of KChIP2 expression and Ito,f activity in heart by modulating NF-κB signaling.
Author Disclosures: W. Liu: None. C. Zhang: None. J. Deng: None. J. liu: None.
- © 2014 by American Heart Association, Inc.