Mitochondrial potassium channel Kv1.3 mediates Bax-induced apoptosis in lymphocytes

doi:10.1073/pnas.0804236105

Mitochondrial potassium channel Kv1.3 mediates Bax-induced apoptosis in lymphocytes

*Department of Biology and
^¶Consiglio Nazionale della Ricerche Institute of Neuroscience and Department of Biomedical Sciences, University of Padova, Viale G. Colombo 3, 35121 Padua, Italy;
^†Department of Molecular Biology, University of Essen, Hufelandstrasse 55, 45122 Essen, Germany; and
^§Department of Physiology, University of Tuebingen, Gmelinstrasse 5, 72076 Tuebingen, Germany

Communicated by Tullio Pozzan, University of Padua, Padua, Italy, May 13, 2008 (received for review December 14, 2007)

Abstract

The potassium channel Kv1.3 has recently been located to the inner mitochondrial membrane of lymphocytes. Here, we show that mouse and human cells that are genetically deficient in either Kv1.3 or transfected with siRNA to suppress Kv1.3-expression resisted apoptosis induced by several stimuli, including Bax over-expression. Retransfection of either Kv1.3 or a mitochondrial-targeted Kv1.3 restored cell death. Bax interacted with and functionally inhibited mitochondrial Kv1.3. Incubation of isolated Kv1.3-positive mitochondria with recombinant Bax, t-Bid, or toxins that bind to and inhibit Kv1.3 successively triggered hyperpolarization, formation of reactive oxygen species, release of cytochrome c, and marked depolarization. Kv1.3-deficient mitochondria were resistant to Bax, t-Bid, and the toxins. Mutation of Bax at K128, which corresponds to a conserved lysine in Kv1.3-inhibiting toxins, abrogated its effects on both Kv1.3 and mitochondria. These findings suggest that Bax mediates cytochrome c release and mitochondrial depolarization in lymphocytes, at least in part, via its interaction with mitochondrial Kv1.3.

Footnotes

^‖To whom correspondence should be addressed. E-mail: erich.gulbins{at}uni-duisburg-essen.de
Author contributions: I.S., J.B., F.L., M.Z., and E.G. designed research; I.S., J.B., H.G., M.S., B.W., M.Z., and E.G. performed research; I.S., M.Z., and E.G. analyzed data; and I.S., M.Z., and E.G. wrote the paper.
↵^‡Present address: Department of Internal Medicine, University of Regensburg, 93053 Regensburg, Germany.
The authors declare no conflict of interest.
This article contains supporting information online at www.pnas.org/cgi/content/full/0804236105/DCSupplemental.