Nuclear factor kappaB downregulates the transient outward potassium current I(to,f) through control of KChIP2 expression.

RATIONALE: The fast transient outward K(+) current (I(to,f)) plays a critical role in early repolarization of the heart. I(to,f) is consistently downregulated in cardiac disease. Despite its importance, the regulation of I(to,f) in disease remains poorly understood.
OBJECTIVE: Because the transcription factor nuclear factor (NF)-κB is activated in cardiac hypertrophy and disease, we studied the role of NF-κB in mediating I(to,f) reductions induced by hypertrophy. METHODS AND
RESULTS: Culturing neonatal rat ventricular myocytes in the presence of phenylephrine (PE) plus propranolol (Pro), to selectively activate α(1)-adrenergic receptors, caused reductions in I(to,f), as well as KChIP2 and Kv4.3 expression, while increasing Kv4.2 expression. Inhibition of NF-κB, via overexpression of a phosphorylation-deficient mutant of IκBα (IκBαSA) prevented PE/Pro-induced reductions in I(to,f) and KChIP2 mRNA, without affecting Kv4.2 or Kv4.3 expression, suggesting NF-κB mediates the I(to,f) reductions by repressing KChIP2. Indeed, overexpression of the NF-κB activator IκB kinase-β also decreased KChIP2 expression and I(to,f) (despite increasing Kv4.2), whereas IκBαSA overexpression elevated KChIP2 and decreased Kv4.2 levels. In addition, the classic NF-κB activator tumor necrosis factor α also induced NF-κB-dependent reductions of KChIP2 and I(to,f). Finally, inhibition of calcineurin did not prevent PE/Pro-induced reductions in KChIP2.
CONCLUSIONS: NF-κB regulates KChIP2 and Kv4.2 expression. The reductions in I(to,f) observed following α-adrenergic receptor stimulation or tumor necrosis factor α application require NF-κB-dependent decreases in KChIP2 expression.