title: Cardiac glycoside ouabain induces activation of ATF-1 and StAR expression by interacting with the α4 isoform of the sodium pump in Sertoli cells.
abstract: Sertoli cells express α1 and α4 isoforms of the catalytic subunit of Na(+),K(+)-ATPase (sodium pump). Our recent findings demonstrated that interactions of the α4 isoform with cardiotonic steroids (CTS) like ouabain induce signaling cascades that resemble the so-called non-classical testosterone pathway characterized by activation of the c-Src/c-Raf/Erk1/2/CREB signaling cascade. Here we investigate a possible physiological significance of the activated cascade. The results obtained in the current investigation show that the ouabain-induced signaling cascade also leads to the activation of the CREB-related activating transcription factor 1 (ATF-1) in the Sertoli cell line 93RS2 in a concentration- and time-dependent manner, as demonstrated by detection of ATF-1 phosphorylated on Ser63 in western blots. The ouabain-activated ATF-1 protein was found to localize to the cell nuclei. The sodium pump α4 isoform mediates this activation, as it is ablated when cells are incubated with siRNA to the α4 isoform. Ouabain also leads to increased expression of steroidogenic acute regulator (StAR) protein, which has been shown to be a downstream consequence of CREB/ATF-1 activation. Taking into consideration that CTS are most likely produced endogenously, the demonstrated induction of StAR expression by ouabain establishes a link between CTS, the α4 isoform of the sodium pump, and steroidogenesis crucial for male fertility and reproduction.
authors.affiliation: Institut für Veterinär-Physiologie und -Biochemie, Fachbereich Veterinärmedizin, Justus-Liebig-Universität Giessen, Germany.
authors.forename: Raimund
authors.initials: R
authors.lastname: Dietze
authors.forename: Lutz
authors.initials: L
authors.lastname: Konrad
authors.forename: Mazen
authors.initials: M
authors.lastname: Shihan
authors.forename: Ulrike
authors.initials: U
authors.lastname: Kirch
authors.forename: Georgios
authors.initials: G
authors.lastname: Scheiner-Bobis
mesh_terms: D051697:Activating Transcription Factor 1 / Q000235:genetics / Q000378:metabolism*; D000818:Animals; D015153:Blotting, Western; D002316:Cardiotonic Agents / Q000494:pharmacology*; D017362:Cyclic AMP Response Element-Binding Protein / Q000235:genetics / Q000378:metabolism; D007124:Immunoenzyme Techniques; D008297:Male; D010042:Ouabain / Q000494:pharmacology*; D010750:Phosphoproteins / Q000235:genetics / Q000378:metabolism*; D010766:Phosphorylation / Q000187:drug effects; D020033:Protein Isoforms; D012333:RNA, Messenger / Q000235:genetics; D034741:RNA, Small Interfering / Q000235:genetics; D051381:Rats; D060888:Real-Time Polymerase Chain Reaction; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012708:Sertoli Cells / Q000187:drug effects / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects; D000254:Sodium-Potassium-Exchanging ATPase / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D000098682:Steroidogenic Acute Regulatory Protein
chemical_list: D051697:Activating Transcription Factor 1; D002316:Cardiotonic Agents; D017362:Cyclic AMP Response Element-Binding Protein; D010750:Phosphoproteins; D020033:Protein Isoforms; D012333:RNA, Messenger; D034741:RNA, Small Interfering; D000098682:Steroidogenic Acute Regulatory Protein; D010042:Ouabain; C485720:Atp1a4 protein, rat; D000254:Sodium-Potassium-Exchanging ATPase