A Dominant Negative Isoform of the Long QT Syndrome 1 Gene Product

doi:10.1074/jbc.273.12.6837

A Dominant Negative Isoform of the Long QT Syndrome 1 Gene Product*

From the Laboratoire de Physiopathologie et de Pharmacologie Cellulaires et Moléculaires, INSERM CJF96-01, Hôpital Hôtel-Dieu, Nantes, France, the Institut de Pharmacologie Moléculaire et Cellulaire, UPR CNRS 411, Sophia-Antipolis, France, and the Academic Medical Center, University of Amsterdam, Amsterdam, The Netherlands

Abstract

Mutations in the KvLQT1 gene are the cause of the long QT syndrome 1. KvLQT1 gene product is associated with the regulator protein IsK to produce a component of the delayed rectifier K⁺ current in cardiac myocytes. We identified an N-terminal truncated isoform of the KvLQT1gene product, referred to as isoform 2. In RNase protection assays, isoform 2 represented 28.1 ± 0.6% of the totalKvLQT1 expression in the human adult ventricle. COS-7 cells injected intranuclearly with KvLQT1 isoform 1 cDNA exhibited a fast-activating K⁺ current, whereas those injected with a KvLQT1 isoform 1 plus IsK cDNA showed a slow-activating K⁺ current. Cells injected with KvLQT1 isoform 2 plasmid showed no detectable K⁺ current. Those injected with a 1/1 isoform 2/isoform 1 ratio showed no detectable K⁺ current. Those injected with 1/5 and 2/5 ratios showed a K⁺ current with markedly reduced amplitude. Coexpression of the IsK regulator consistently reduced the dominant negative effects of isoform 2. Our results indicate that KvLQT1 isoform 2 exerts a pronounced negative dominance on isoform 1 channels and that the cardiac KvLQT1 K⁺ channel complex is composed of at least three different proteins as follows: isoform 1, isoform 2, and IsK.

Footnotes

↵* This work was supported by INSERM.The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
↵‡ To whom correspondence should be addressed: Laboratoire de Physiopathologie et de Pharmacologie Cellulaires et Moléculaires, INSERM CJF 96.01, Bât HBN, Hôpital Hotel-Dieu, BP 1005, 44093 Nantes, France. Tel.: 33-240-08-75-18; Fax: 33-240-08-75-23; E-mail: denis.escande{at}sante.univ-nantes.fr.
↵1 The abbreviations used are: RACE, rapid amplification of cDNA ends; bp, base pair(s); RT-PCR, reverse transcriptase-polymerase chain reactions; HA, hemagglutinin; PBS, phosphate-buffered saline.
↵2 P. Guicheney, personal communication.
- Received July 15, 1997.
- Revision received December 29, 1997.
The American Society for Biochemistry and Molecular Biology, Inc.