The Dominant Negative LQT2 Mutation A561V Reduces Wild-type HERG Expression

• Published in: The Journal of biological chemistry Vol. 275; no. 15; pp. 11241 - 11248
• Main Authors: Kagan, Anna, Yu, Zhihui, Fishman, Glenn I., McDonald, Thomas V.
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 14.04.2000; American Society for Biochemistry and Molecular Biology
• Subjects: Animals; Cation Transport Proteins; CHO Cells; COS Cells; Cricetinae; DNA-Binding Proteins; ERG1 Potassium Channel; Ether-A-Go-Go Potassium Channels; HERG protein; Humans; Immunoblotting; long QT syndrome; Long QT Syndrome - genetics; Mutation; Potassium Channels - biosynthesis; Potassium Channels - genetics; Potassium Channels, Voltage-Gated; Trans-Activators; Transcriptional Regulator ERG
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.275.15.11241

HERG1 K+ channel mutations are responsible for one form of dominantly inherited long QT syndrome (LQT). Some LQT mutations exert a dominant negative effect on wild-type current expression. To investigate mechanisms of dominant-negative behavior, we co-expressed wild-type HERG with the A561V mutant in mammalian cells. Transfection with various cDNA ratios produced HERG K+ current densities that approached a predicted binomial distribution where mutant and wild-type subunits co-assemble in a tetramer with nearly complete dominance. Using C terminus myc-tagged wild-type HERG we specifically followed the mutant's effect on full-length wild-type HERG protein expression. Co-expression with A561V reduced the abundance of full-length wild-type HERG protein comparable to the current reduction. Reduction of wild-type protein was due to decreased synthesis and increased turnover. Conditions facilitating protein folding (growth at 30 °C, or in 10% glycerol) resulted in partial rescue from the dominant effect, as did the 26 S proteosome inhibitor ALLN. Thus, for A561V, dominant negative effects result from assembly of wild-type subunits with mutant very early in production leading to rapid recognition of mutant channels and targeting for proteolysis. These results establish protein misfolding, cellular proofreading, and bystander involvement as contributing mechanisms for dominant effects in LQT2.