The IKr drug response is modulated by KCR1 in transfected cardiac and noncardiac cell lines.

The cardiac potassium channel encoded by the human ether-à-go-go related gene (HERG) is blocked by a diverse array of common therapeutic compounds. Even transient exposure to such agents may provoke the life-threatening cardiac arrhythmia torsades de pointes in some, but not all, individuals. Although the molecular and genetic factors predicting such wide variability in drug response remain unclear, known sequence variations within the coding region of HERG do not explain the adverse drug response in many cases. Although other proteins can modulate HERG function, no studies have identified protein partners capable of limiting the pharmacological sensitivity of HERG. Here we show that KCR1, a protein identified previously in rat cerebellum, is a plasma membrane-associated protein expressed at the RNA level in the human heart and can be immunoprecipitated with HERG. Functionally, KCR1 reduces the sensitivity of HERG to classic proarrhythmic HERG blockers (sotalol, quinidine, dofetilide) in both cardiac and noncardiac cell lines. We propose that KCR1, when coupled to HERG, may limit the sensitivity of HERG to proarrhythmic drug blockade and may be a rational target for modifying the proarrhythmic effects of otherwise clinically useful compounds.

Cardiac-enriched LIM domain protein fhl2 is required to generate I(Ks) in a heterologous system.

OBJECTIVE: Co-expression of the KvLQT1 and minK potassium channel subunits is required to recapitulate I(Ks), the slow component of the cardiac delayed rectifier current, and mutations in either gene cause the congenital Long QT syndrome. It is becoming increasingly well-recognized that multiprotein channel complexes containing proteins capable of modulating channel function assemble at the plasma membrane. Thus, the aim of our study was to identify proteins involved in I(Ks) modulation. METHODS AND RESULTS: Using a yeast-two-hybrid screen with the intracytoplasmic C-terminus of minK as bait, we identified the cardiac-enriched four-and-a-half LIM domain-containing protein (fhl2) as a potential minK partner. We show interaction between the two proteins in GST pulldown assays and demonstrate overlapping subcellular localization using immunocytochemistry of transfected cells supporting a potential interaction. At the functional level, expression of KvLQT1and minK in HEK cells, which lack endogenous fhl2 protein, generated I(Ks) only when fhl2 was co-expressed. By contrast, in CHO-K1 cells, which express fhl2 endogenously, I(Ks) was suppressed by anti-fhl2 antisense which did not affect the currents generated by KvLQT1alone. CONCLUSION: These data indicate that at least in heterologous cells, the generation of I(Ks) requires fhl2 as an additional protein component.