title: FXYD-11 associates with Na+-K+-ATPase in the gill of Atlantic salmon: regulation and localization in relation to changed ion-regulatory status.
abstract: The Na(+)-K(+)-ATPase is the primary electrogenic component driving transepithelial ion transport in the teleost gill; thus regulation of its level of activity is of critical importance for osmotic homeostasis. In the present study, we examined the dynamics of the gill-specific FXYD-11 protein, a putative regulatory subunit of the pump, in Atlantic salmon during seawater (SW) acclimation, smoltification, and treatment with cortisol, growth hormone, and prolactin. Dual-labeling immunohistochemistry showed that branchial FXYD-11 is localized in Na(+)-K(+)-ATPase immunoreactive cells, and coimmunoprecipitation experiments confirmed a direct association between FXYD-11 and the Na(+)-K(+)-ATPase α-subunit. Transfer of freshwater (FW)-acclimated salmon to SW induced a parallel increase in total α-subunit and FXYD-11 protein expression. A similar concurrent increase was seen during smoltification in FW. In FW fish, cortisol induced an increase in both α-subunit and FXYD-11 abundance, and growth hormone further stimulated FXYD-11 levels. In SW fish, prolactin induced a decrease in FXYD-11 and α-subunit protein levels. In vitro cortisol (18 h, 10 μg/ml) stimulated FXYD-11, but not FXYD-9, mRNA levels in gills from FW and SW salmon. The data show that Na(+)-K(+)-ATPase expressed in branchial mitochondrion-rich cells is accompanied by FXYD-11, and that regulation of the two proteins is highly coordinated. The demonstrated association of FXYD-11 and α-subunit strengthens our hypothesis that FXYD-11 has a role in modulating the pump's kinetic properties. The presence of putative phosphorylation sites on the intracellular domain of FXYD-11 suggests the possibility that this protein also may transmit external signals that regulate Na(+)-K(+)-ATPase activity.
authors: Institute of Biology, University of Southern Denmark, Odense, Denmark. tipsmark@uark.edu
authors: Christian K
authors: CK
authors: Tipsmark
authors: Yasser A
authors: YA
authors: Mahmmoud
authors: Russell J
authors: RJ
authors: Borski
authors: Steffen S
authors: SS
authors: Madsen
mesh_terms: D000064:Acclimatization; D000818:Animals; D015153:Blotting, Western; D029941:Fish Proteins / Q000235:genetics / Q000378:metabolism*; D005880:Gills / Q000187:drug effects / Q000201:enzymology*; D013006:Growth Hormone / Q000378:metabolism; D006706:Homeostasis; D006854:Hydrocortisone / Q000494:pharmacology; D007150:Immunohistochemistry; D047468:Immunoprecipitation; D017136:Ion Transport; D007700:Kinetics; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D011388:Prolactin / Q000378:metabolism; D021122:Protein Subunits; D012333:RNA, Messenger / Q000378:metabolism; D054712:Salinity; D020317:Salmo salar / Q000235:genetics / Q000378:metabolism*; D012623:Seawater; D000254:Sodium-Potassium-Exchanging ATPase / Q000235:genetics / Q000378:metabolism*
chemical_list: D029941:Fish Proteins; D008565:Membrane Proteins; D021122:Protein Subunits; D012333:RNA, Messenger; D011388:Prolactin; D013006:Growth Hormone; D000254:Sodium-Potassium-Exchanging ATPase; D006854:Hydrocortisone