Abstract 1507: Disruption of KCNH2 Trafficking May Contribute to Severe Clinical Phenotype of Trafficking Deficient Long-QT Type-1 Mutation KCNQ1-T587M
Background: The trafficking deficient long QT syndrome (LQTS)-associated KCNQ1 mutation T587M has previously been associated with a severe clinical phenotype that was not explained by biophysical characteristics of the mutation per se.
Objective: We have previously shown significant interactions between KCNQ1 and KCNH2 and speculated that T587M-KCNQ1 might affect this interaction. We therefore compared the effects of KCNQ1 and T587M-KCNQ1 on KCNH2 trafficking and function.
Methods/Results: While heterologous co-expression of wildtype (WT) KCNQ1 and KCNH2 in CHO cells increased KCNH2 current (H2+Q1, Fig. A⇓, *P<0.05) in comparison to KCNH2 expressed alone (H2), co-transfection of KCNH2 with T587M-KCNQ1 failed to increase IKCNH2. Immunoblots of specific plasma membrane preparations (Fig. B⇓) and confocal microscopy indicated increased KCNH2 membrane localization in KCNQ1 co-transfected cells, while total KCNH2 expression remained unaffected. These results indicated a chaperone effect as the potential underlying mechanism. Furthermore, effective co-immunoprecipitation of WT channels occurred. T587M-KCNQ1 also co-precipitated with KCNH2, but the LQTS mutant was retained perinuclearly (Fig. C⇓) and additionally failed to increase membrane KCNH2 expression (Fig. B⇓), abolishing the WT KCNQ1 chaperone function.
Conclusions: Trafficking-deficient T587M-KCNQ1 lacks the KCNH2 chaperone function that occurs with WT KCNQ1, limiting KCNH2 membrane localization and potentially explaining the malignant LQTS phenotype. Consideration of KCNQ1-KCNH2 interactions may be important for understanding mutation-specific clinical variability in LQTS presentations.