Evidence for proteasomal degradation of Kv1.5 channel protein.
BACKGROUND
The voltage-gated potassium channel Kv1.5 plays a critical role in the maintenance of the membrane potential. While protein degradation is one of the major mechanisms for the regulation of channel functions, little is known on the degradation mechanism of Kv1.5.


RESULTS
Kv1.5 was expressed in COS cells and its degradation, intracellular localization, and channel activities were assessed by pulse-chase analysis, immunofluorescence, and patch clamp techniques, respectively. Expressed Kv1.5 had a half-life time of approximately 6.7 h, which was prolonged by the proteasome inhibitors of MG132, ALLN, proteasomal inhibitor 1, or lactacystine, but not by a lysosomal inhibitor chloroquine. MG132 increased the protein level of Kv1.5, as well as the level of its ubiquitinated form in a dose-dependent manner. Similar effects of MG132 on endogenous Kv1.5 were seen in cultured rat atrial cells. Within a cell, Kv1.5 was mainly localized in both the endoplasmic reticulum and Golgi apparatus. MG132 increased the immunoreactivity of Kv1.5 in these compartments and also increased Ik(ur) currents through the cell-surface Kv1.5. Pretreatment with either brefeldin A or colchicine abolished MG132-induced increase in Ik(ur) currents.


CONCLUSIONS
Kv1.5 is degraded by the proteasome. The inhibition of the proteasome increased Ik(ur) currents secondary to stabilization of the channel protein in the endoplasmic reticulum/Golgi apparatus.
Kato
Masaru
M
Department of Cardiovascular Medicine, Tottori University Faculty of Medicine, Japan.
Ogura
Kazuyoshi
K
Miake
Junichiro
J
Sasaki
Norihito
N
Taniguchi
Shin-Ichi
S
Igawa
Osamu
O
Yoshida
Akio
A
Hoshikawa
Yoshiko
Y
Murata
Mitsunobu
M
Nanba
Eiji
E
Kurata
Yasutaka
Y
Kawata
Yasushi
Y
Ninomiya
Haruaki
H
Morisaki
Takayuki
T
Kitakaze
Masafumi
M
Hisatome
Ichiro
I
D000818:Animals; D019556:COS Cells; D002478:Cells, Cultured; D002522:Chlorocebus aethiops; D015853:Cysteine Proteinase Inhibitors / Q000494:pharmacology; D004553:Electric Conductivity; D004721:Endoplasmic Reticulum / Q000737:chemistry; D006056:Golgi Apparatus / Q000737:chemistry; D051666:Kv1.5 Potassium Channel; D007976:Leupeptins / Q000494:pharmacology; D032383:Myocytes, Cardiac / Q000187:drug effects / Q000378:metabolism; D009842:Oligopeptides; D018408:Patch-Clamp Techniques; D010455:Peptides / Q000235:genetics; D024642:Potassium Channels, Voltage-Gated / Q000032:analysis / Q000378:metabolism*; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism*; D051381:Rats; D011993:Recombinant Fusion Proteins / Q000032:analysis; D014452:Ubiquitins / Q000378:metabolism
D015853:Cysteine Proteinase Inhibitors; C496983:Kcna5 protein, rat; D051666:Kv1.5 Potassium Channel; D007976:Leupeptins; D009842:Oligopeptides; D010455:Peptides; D024642:Potassium Channels, Voltage-Gated; D011993:Recombinant Fusion Proteins; D014452:Ubiquitins; C085706:FLAG peptide; D046988:Proteasome Endopeptidase Complex; C072553:benzyloxycarbonylleucyl-leucyl-leucine aldehyde