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PERK Branch of the ER Stress Regulates FoxO to Mediate Homocysteine‐induced BK Ca Channel Dysfunction
Author(s) -
Sun WenTao,
Wang XiangChong,
Mak ShiuKwong,
Yu CheukMan,
Yang Qin
Publication year - 2016
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.30.1_supplement.1177.13
Subject(s) - bk channel , endoplasmic reticulum , chemistry , vascular smooth muscle , downregulation and upregulation , endocrinology , medicine , unfolded protein response , homocysteine , potassium channel , biology , biochemistry , smooth muscle , gene
Large‐conductance Ca 2+ ‐activated K + (BK Ca ) channels play an important role in vascular tone regulation. The atherosclerotic risk factor homocysteine inhibits vascular smooth muscle BK Ca channels whereas the mechanisms remain poorly understood. We studied the role of endoplasmic reticulum (ER) stress in homocysteine‐induced BK Ca channel inhibition with further understanding of the molecular determinants. Vasorelaxant response to the BK Ca channel opener NS1619 was studied in endothelium‐denuded porcine small coronary arteries in a myograph. Primary cultured porcine coronary arterial smooth muscle cells (PCASMCs) were used for mRNA and protein analysis of BK Ca channels, as well as patch‐clamp recording of the BK Ca channel current. NS1619‐induced vasorelaxation was significantly inhibited by homocysteine, which was restored by ER stress inhibitors either TUDCA or 4‐PBA. GSK2606414, a selective inhibitor of PKR‐like endoplasmic reticulum kinase (PERK) showed potent protective effect against homocysteine on the NS1619‐induced relaxation and the whole‐cell BK Ca channel current. Homocysteine lowered the protein level of β1 but not α subunit of the BK Ca channel. Exposure to homocysteine did not alter the mRNA expression of both subunits. Downregulation of BK Ca β1 was attenuated by TUDCA, 4‐PBA, and GSK2606414. Pharmacological inhibition of PERK suppressed the nucleic translocation of forkhead box O transcription factor 3a (FoxO3a) in homocysteine‐exposed PCASMCs, associated with a decrease of atrogin‐1 protein and an increase of BK Ca β1 protein. In PCASMCs transfected with FoxO3a siRNA, downregulation of atrogin‐1 protein expression and restoration of BK Ca β1 protein level was observed after homocysteine exposure. This study suggests that ER stress mediates homocysteine‐induced BK Ca channel inhibition in coronary arteries and activation of FoxO3a by PERK underlies ER stress‐mediated BK Ca channel inhibition through a mechanism involving ubiquitin ligase‐enhanced degradation of the channel β1 subunit. Support or Funding Information Supported by RGC/GRF CUHK4774/12M & CUHK14118414; Lui Che Woo Institute of Innovative Medicine ‐ CARE theme 8303303, and CUHK Direct Grant 4054182.