Quantitative analysis of trafficking defects induced by heterozygous expression of hERG voltage sensor domain variants

11.1). Mistrafficking of hERG LOF variants is the dominant cause of LQT2. We recently characterized greatly attenuated cell surface trafficking in eight natural variants in a region of the hERG voltage sensor domain identified using evolutionary analysis. Here we have used quantitative On/In-Cell western assays to characterize trafficking of these variants under heterozygous conditions more relevant to the clinical circumstance. Dominant-negative effects of variant on wild-type (WT) cell surface expression and WT rescue of variant mistrafficking were separately assessed in co-expressions in which only WT or variant carried the HA-tag used to detect cell surface expression. Co-expression of all variants reduced cell surface expression and exhibited dominant-negative effects on trafficking. However, when compared to previous studies that utilized hERG glycosylation status as a measure of trafficking efficiency, the heterozygous effects on trafficking were smaller than expected. An identified relationship between pharmacological rescue of variant trafficking by the hERG blocker E-4031 and by co-expression with WT hERG indicated that inherent "rescuability" of variants might be characterized in advance of efforts to identify non-blocking trafficking rescuers.