title: Estradiol binding to maxi-K channels induces their down-regulation via proteasomal degradation.
abstract: 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 17alpha- or 17beta-estradiol. This effect was dose-dependent for 17beta-estradiol at concentrations ranging from 10 nm to 1 microm, while 17alpha-estradiol inhibited channel expression only at 1 microm. These effects were mediated by direct low affinity binding of estradiol to the maxi-K channel but not to its accessory beta1-subunit, as revealed by cell membrane estradiol binding assays. However, specific binding of estradiol to the channel was facilitated by the presence of the beta1 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 17alpha- and 17beta-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.
authors.affiliation: Department of Physiology and Biophysics, Carver College of Medicine, University of Iowa, Iowa City, Iowa 52242, USA.
authors.forename: Victoria P
authors.initials: VP
authors.lastname: Korovkina
authors.forename: Adam M
authors.initials: AM
authors.lastname: Brainard
authors.forename: Plabon
authors.initials: P
authors.lastname: Ismail
authors.forename: Thomas J
authors.initials: TJ
authors.lastname: Schmidt
authors.forename: Sarah K
authors.initials: SK
authors.lastname: England
mesh_terms: D020816:Amino Acid Motifs; D002460:Cell Line; D003546:Cysteine Endopeptidases / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D015536:Down-Regulation; D004958:Estradiol / Q000737:chemistry / Q000378:metabolism*; D006801:Humans; D051036:Large-Conductance Calcium-Activated Potassium Channels; D007976:Leupeptins / Q000494:pharmacology; D008856:Microscopy, Fluorescence; D009097:Multienzyme Complexes / Q000378:metabolism*; D009131:Muscle, Smooth, Vascular / Q000166:cytology; D009154:Mutation; D015221:Potassium Channels / Q000737:chemistry*; D024681:Potassium Channels, Calcium-Activated / Q000737:chemistry* / Q000378:metabolism*; D046988:Proteasome Endopeptidase Complex; D011485:Protein Binding
chemical_list: D051036:Large-Conductance Calcium-Activated Potassium Channels; D007976:Leupeptins; D009097:Multienzyme Complexes; D015221:Potassium Channels; D024681:Potassium Channels, Calcium-Activated; D004958:Estradiol; D003546:Cysteine Endopeptidases; D046988:Proteasome Endopeptidase Complex; C072553:benzyloxycarbonylleucyl-leucyl-leucine aldehyde