Mutant caveolin-3 induces persistent late sodium current and is associated with long-QT syndrome.
BACKGROUND
Congenital long-QT syndrome (LQTS) is a primary arrhythmogenic syndrome stemming from perturbed cardiac repolarization. LQTS, which affects approximately 1 in 3000 persons, is 1 of the most common causes of autopsy-negative sudden death in the young. Since the sentinel discovery of cardiac channel gene mutations in LQTS in 1995, hundreds of mutations in 8 LQTS susceptibility genes have been identified. All 8 LQTS genotypes represent primary cardiac channel defects (ie, ion channelopathy) except LQT4, which is a functional channelopathy because of mutations in ankyrin-B. Approximately 25% of LQTS remains unexplained pathogenetically. We have pursued a "final common pathway" hypothesis to elicit novel LQTS-susceptibility genes. With the recent observation that the LQT3-associated, SCN5A-encoded cardiac sodium channel localizes in caveolae, which are known membrane microdomains whose major component in the striated muscle is caveolin-3, we hypothesized that mutations in caveolin-3 may represent a novel pathogenetic mechanism for LQTS.


RESULTS
Using polymerase chain reaction, denaturing high-performance liquid chromatography, and direct DNA sequencing, we performed open reading frame/splice site mutational analysis on CAV3 in 905 unrelated patients referred for LQTS genetic testing. CAV3 mutations were engineered by site-directed mutagenesis and the molecular phenotype determined by transient heterologous expression into cell lines that stably express the cardiac sodium channel hNa(v)1.5. We identified 4 novel mutations in CAV3-encoded caveolin-3 that were absent in >1000 control alleles. Electrophysiological analysis of sodium current in HEK293 cells stably expressing hNa(v)1.5 and transiently transfected with wild-type and mutant caveolin-3 demonstrated that mutant caveolin-3 results in a 2- to 3-fold increase in late sodium current compared with wild-type caveolin-3. Our observations are similar to the increased late sodium current associated with LQT3-associated SCN5A mutations.


CONCLUSIONS
The present study reports the first CAV3 mutations in subjects with LQTS, and we provide functional data demonstrating a gain-of-function increase in late sodium current.
Vatta
Matteo
M
Department of Pediatrics (Cardiology), Baylor College of Medicine, Texas Children's Hospital, Houston, TX 77030, USA. mvatta@bcm.tmc.edu
Ackerman
Michael J
MJ
Ye
Bin
B
Makielski
Jonathan C
JC
Ughanze
Enoh E
EE
Taylor
Erica W
EW
Tester
David J
DJ
Balijepalli
Ravi C
RC
Foell
Jason D
JD
Li
Zhaohui
Z
Kamp
Timothy J
TJ
Towbin
Jeffrey A
JA
D000595:Amino Acid Sequence; D051244:Caveolin 3 / Q000235:genetics*; D002460:Cell Line; D004252:DNA Mutational Analysis; D004553:Electric Conductivity; D004562:Electrocardiography; D004594:Electrophysiology; D005260:Female; D006801:Humans; D047468:Immunoprecipitation; D008133:Long QT Syndrome / Q000175:diagnosis / Q000235:genetics / Q000378:metabolism / Q000503:physiopathology*; D008297:Male; D008969:Molecular Sequence Data; D009124:Muscle Proteins / Q000378:metabolism; D009154:Mutation; D009206:Myocardium / Q000378:metabolism; D062554:NAV1.5 Voltage-Gated Sodium Channel; D015222:Sodium Channels / Q000378:metabolism*; D013997:Time Factors; D014162:Transfection
D051244:Caveolin 3; D009124:Muscle Proteins; D062554:NAV1.5 Voltage-Gated Sodium Channel; C568320:SCN5A protein, human; D015222:Sodium Channels