title: Oestrogen promotes KCNQ1 potassium channel endocytosis and postendocytic trafficking in colonic epithelium.
abstract: The cAMP-regulated potassium channel KCNQ1:KCNE3 plays an essential role in transepithelial Cl(-) secretion. Recycling of K(+) across the basolateral membrane provides the driving force necessary to maintain apical Cl(-) secretion. The steroid hormone oestrogen (17β-oestradiol; E2), produces a female-specific antisecretory response in rat distal colon through the inhibition of the KCNQ1:KCNE3 channel. It has previously been shown that rapid inhibition of the channel conductance results from E2-induced uncoupling of the KCNE3 regulatory subunit from the KCNQ1 channel pore complex. The purpose of this study was to determine the mechanism required for sustained inhibition of the channel function. We found that E2 plays a role in regulation of KCNQ1 cell membrane abundance by endocytosis. Ussing chamber experiments have shown that E2 inhibits both Cl(-) secretion and KCNQ1 current in a colonic cell line, HT29cl.19A, when cultured as a confluent epithelium. Following E2 treatment, KCNQ1 was retrieved from the plasma membrane by a clathrin-mediated endocytosis, which involved the association between KCNQ1 and the clathrin adaptor, AP-2. Following endocytosis, KCNQ1 was accumulated in early endosomes. Following E2-induced endocytosis, rather than being degraded, KCNQ1 was recycled by a biphasic mechanism involving Rab4 and Rab11. Protein kinase Cδ and AMP-dependent kinase were rapidly phosphorylated in response to E2 on their activating phosphorylation sites, Ser643 and Thr172, respectively (as previously shown). Both kinases are necessary for the E2-induced endocytosis, because E2 failed to induce KCNQ1 internalization following pretreatment with specific inhibitors of both protein kinase Cδ and AMP-dependent kinase. The ubiquitin ligase Nedd4.2 binds KCNQ1 in response to E2 to induce channel internalization. This study has provided the first demonstration of hormonal regulation of KCNQ1 trafficking. In conclusion, we propose that internalization of KCNQ1 is a key event in the sustained antisecretory response to oestrogen.
authors.affiliation: Department of Molecular Medicine, RCSI-ERC, Beaumont Hospital, PO Box 9063, Dublin 9, Ireland.
authors.forename: Raphael
authors.initials: R
authors.lastname: Rapetti-Mauss
authors.forename: Fiona
authors.initials: F
authors.lastname: O'Mahony
authors.forename: Francisco V
authors.initials: FV
authors.lastname: Sepulveda
authors.forename: Valerie
authors.initials: V
authors.lastname: Urbach
authors.forename: Brian J
authors.initials: BJ
authors.lastname: Harvey
mesh_terms: D055372:AMP-Activated Protein Kinases / Q000378:metabolism; D000200:Action Potentials; D033962:Adaptor Protein Complex 2 / Q000378:metabolism; D000818:Animals; D003106:Colon / Q000166:cytology / Q000378:metabolism* / Q000502:physiology; D004705:Endocytosis / Q000187:drug effects*; D056827:Endosomal Sorting Complexes Required for Transport / Q000378:metabolism; D004958:Estradiol / Q000494:pharmacology*; D005260:Female; D019073:HT29 Cells; D006801:Humans; D007413:Intestinal Mucosa / Q000378:metabolism* / Q000502:physiology; D051657:KCNQ1 Potassium Channel / Q000378:metabolism*; D000075702:Nedd4 Ubiquitin Protein Ligases; D011485:Protein Binding; D051745:Protein Kinase C-delta / Q000378:metabolism; D021381:Protein Transport / Q000187:drug effects; D051381:Rats; D017207:Rats, Sprague-Dawley; D044767:Ubiquitin-Protein Ligases / Q000378:metabolism; D020691:rab GTP-Binding Proteins / Q000378:metabolism; D020695:rab4 GTP-Binding Proteins / Q000378:metabolism; D000099193:rab11 GTP-Binding Proteins
chemical_list: D055372:AMP-Activated Protein Kinases; D033962:Adaptor Protein Complex 2; D056827:Endosomal Sorting Complexes Required for Transport; D004958:Estradiol; D051657:KCNQ1 Potassium Channel; D000075702:Nedd4 Ubiquitin Protein Ligases; D051745:Protein Kinase C-delta; D044767:Ubiquitin-Protein Ligases; D020691:rab GTP-Binding Proteins; D020695:rab4 GTP-Binding Proteins; D000099193:rab11 GTP-Binding Proteins; C000618479:NEDD4L protein, rat; C000618483:Nedd4 protein, human; C000618484:Nedd4 protein, rat; C000618485:Nedd4L protein, human