Fig. 3.

Surface expressions of the WT and mutant KCNQ4 subunits in cells mimicking the heterozygous condition of DFNA2 patients Each HA-tagged mutant channel was co-expressed with the Myc-tagged WT KCNQ4 channel in HEK293T cells at ratio 1:1 (0.2 μg each). The HA-tagged WT-KCNQ4 and vector were also co-expressed with the WT myc-KCNQ4 channel as controls. Surface KCNQ4 were affinity-purified and assessed by Western blot. (A) Representative Western blot. Surface expression of all mutant HA-KCNQ4 was improved, although to various degrees, by co-expression of the WT Myc-KCNQ4 channel (Top panel, IP:HA, IB:HA). In contrast, surface expression of the WT Myc-KCNQ4 channel was dramatically decreased in all cases (IP:Myc, IB:Myc), showing that not only the WT KCNQ4 cannot rescue cell surface expression of DFNA2 mutants in these cells but also mutations have dominant-negative effects on the WT KCNQ4 channel. (B) Summary data. Surface expression of the WT and mutant KCNQ4 subunits in cells mimicking the heterozygous condition of DFNA2 patients, relative to the WT value (WT HA-KCNQ4 plus WT myc-KCNQ4 at ratio of 1:1). (C) Summary data. Surface expression of mutant subunits (HA-tagged) with or without co-expression of the WT KCNQ4 subunit (Myc-tagged), relative to the WT value (see B). Each data point in the bar graphs represents the mean ± SD of three experiments (*P ≤ 0.05, **P ≤ 0.01).