Estradiol Binding to Maxi-K Channels Induces Their Down-regulation via Proteasomal Degradation

• Published in: The Journal of biological chemistry 2004-01, Vol.279 (2), p.1217-1223
• Main Authors: Korovkina, Victoria P., Brainard, Adam M., Ismail, Plabon, Schmidt, Thomas J., England, Sarah K.
• Format: Article
• Language: English
• Subjects: Amino Acid Motifs; Cell Line; Cysteine Endopeptidases - metabolism; Dose-Response Relationship, Drug; Down-Regulation; Estradiol - chemistry; Estradiol - metabolism; Humans; Large-Conductance Calcium-Activated Potassium Channels; Leupeptins - pharmacology; Microscopy, Fluorescence; Multicatalytic endopeptidase complex; Multienzyme Complexes - metabolism; Muscle, Smooth, Vascular - cytology; Mutation; Potassium Channels - chemistry; Potassium Channels, Calcium-Activated - chemistry; Potassium Channels, Calcium-Activated - metabolism; Proteasome Endopeptidase Complex; Protein Binding
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M309158200

Estrogens exert their biological action via both genomic and non-genomic mechanisms. Proteins different from classical estradiol receptors are believed to mediate the latter effects. Here we demonstrate that the maxi-K channel functions as an estrogen-binding protein in transfected HEK293 cells. Whole-cell maxi-K channel currents and protein expression were attenuated by exposure to either 17α- or 17β-estradiol. This effect was dose-dependent for 17β-estradiol at concentrations ranging from 10 nm to 1 μm, while 17α-estradiol inhibited channel expression only at 1 μm. These effects were mediated by direct low affinity binding of estradiol to the maxi-K channel but not to its accessory β1-subunit, as revealed by cell membrane estradiol binding assays. However, specific binding of estradiol to the channel was facilitated by the presence of the β1 subunit. Addition of MG-132, a blocker of proteasomal degradation, stabilized channel expression. These data suggest that channel down-regulation is mediated by estrogen-induced proteasomal degradation, similar to the pathway used for estrogen receptor degradation. Membrane expression of endogenous maxi-K channels in cultured vascular smooth muscle cells was also attenuated by prolonged exposure to 17α- and 17β-estradiol. Thus our studies demonstrate that estrogen binds to maxi-K channels and may directly regulate channel expression and function. These results will have important implications in understanding estradiol-induced effects in multiple tissues including vascular smooth muscle.