title: Cholesterol down-regulates BK channels stably expressed in HEK 293 cells.
abstract: Cholesterol is one of the major lipid components of the plasma membrane in mammalian cells and is involved in the regulation of a number of ion channels. The present study investigates how large conductance Ca(2+)-activated K(+) (BK) channels are regulated by membrane cholesterol in BK-HEK 293 cells expressing both the α-subunit hKCa1.1 and the auxiliary β1-subunit or in hKCa1.1-HEK 293 cells expressing only the α-subunit hKCa1.1 using approaches of electrophysiology, molecular biology, and immunocytochemistry. Membrane cholesterol was depleted in these cells with methyl-β-cyclodextrin (MβCD), and enriched with cholesterol-saturated MβCD (MβCD-cholesterol) or low-density lipoprotein (LDL). We found that BK current density was decreased by cholesterol enrichment in BK-HEK 293 cells, with a reduced expression of KCa1.1 protein, but not the β1-subunit protein. This effect was fully countered by the proteasome inhibitor lactacystin or the lysosome function inhibitor bafilomycin A1. Interestingly, in hKCa1.1-HEK 293 cells, the current density was not affected by cholesterol enrichment, but directly decreased by MβCD, suggesting that the down-regulation of BK channels by cholesterol depends on the auxiliary β1-subunit. The reduced KCa1.1 channel protein expression was also observed in cultured human coronary artery smooth muscle cells with cholesterol enrichment using MβCD-cholesterol or LDL. These results demonstrate the novel information that cholesterol down-regulates BK channels by reducing KCa1.1 protein expression via increasing the channel protein degradation, and the effect is dependent on the auxiliary β1-subunit.
authors.affiliation: Department of Medicine, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Pokfulam, Hong Kong, China.
authors.forename: Wei
authors.initials: W
authors.lastname: Wu
authors.forename: Yan
authors.initials: Y
authors.lastname: Wang
authors.forename: Xiu-Ling
authors.initials: XL
authors.lastname: Deng
authors.forename: Hai-Ying
authors.initials: HY
authors.lastname: Sun
authors.forename: Gui-Rong
authors.initials: GR
authors.lastname: Li
mesh_terms: D002460:Cell Line; D002462:Cell Membrane / Q000187:drug effects / Q000235:genetics / Q000378:metabolism; D002784:Cholesterol / Q000378:metabolism*; D003331:Coronary Vessels / Q000187:drug effects / Q000378:metabolism; D015536:Down-Regulation / Q000187:drug effects / Q000235:genetics*; D057809:HEK293 Cells; D006801:Humans; D051037:Large-Conductance Calcium-Activated Potassium Channel alpha Subunits / Q000235:genetics* / Q000378:metabolism*; D008077:Lipoproteins, LDL / Q000235:genetics / Q000378:metabolism; D009131:Muscle, Smooth, Vascular / Q000187:drug effects / Q000378:metabolism; D032389:Myocytes, Smooth Muscle / Q000187:drug effects / Q000378:metabolism; D046988:Proteasome Endopeptidase Complex / Q000235:genetics / Q000378:metabolism; D021122:Protein Subunits / Q000235:genetics / Q000378:metabolism; D059748:Proteolysis / Q000187:drug effects; D047392:beta-Cyclodextrins / Q000494:pharmacology
chemical_list: C494841:KCNMA1 protein, human; D051037:Large-Conductance Calcium-Activated Potassium Channel alpha Subunits; D008077:Lipoproteins, LDL; D021122:Protein Subunits; D047392:beta-Cyclodextrins; C108732:methyl-beta-cyclodextrin; D002784:Cholesterol; D046988:Proteasome Endopeptidase Complex