title: Translational regulation of Na-K-ATPase subunit mRNAs by glucocorticoids.
abstract: Glucocorticoids (GC) regulate Na-K-ATPase-subunit mRNA transcription. However, GC-induced increases in Na-K-ATPase activity are not always paralleled by changes in subunit mRNA abundance. We therefore examined posttranscriptional mechanisms of subunit gene regulation by GC. cDNA-derived mRNAs encoding alpha 1-, alpha 3-, and beta 1-subunits were tested for stability and translation efficiency in a cell-free lysate, in the presence of hydrocortisone (HC) or dexamethasone (Dex). No effect of HC on subunit mRNA stability was noted. Translation efficiency of alpha1- and alpha 3-mRNAs, but not of beta 1-mRNA, was significantly increased by HC and Dex. Deletion of the 5'untranslated region (5'UT) of alpha 1-mRNA abolished this effect. Translation of a chimeric beta 1-mRNA, constructed by transposing the 5'UT of alpha 1 onto the coding region of beta1, was enhanced by HC. Transposition of a putative steroid-modulatory element conserved in the 5'UT of all alpha isoforms (ACAGGACCC) onto the coding region of beta 1-mRNA rendered it responsive to HC. A synthetic primer containing the ACAGGACCC sequence abolished the effect of HC on alpha 1- and chimeric beta 1-mRNAs. Our results indicate that GC can directly enhance Na-K-ATPase translation in vitro in a subunit-specific manner, via a putative GC-modulatory element situated in a predicted loop structure within the 5'UT of alpha-mRNAs.
authors.affiliation: Pediatric Nephrology, Yale University School of Medicine, New Haven, Connecticut 06520, USA. pdevaraj@aecom.yu.edu
authors.forename: P
authors.initials: P
authors.lastname: Devarajan
authors.forename: E J
authors.initials: EJ
authors.lastname: Benz
mesh_terms: D020121:5' Untranslated Regions / Q000235:genetics; D000818:Animals; D000893:Anti-Inflammatory Agents / Q000494:pharmacology; D002474:Cell-Free System; D003001:Cloning, Molecular; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects*; D005938:Glucocorticoids / Q000494:pharmacology*; D006801:Humans; D006854:Hydrocortisone / Q000494:pharmacology; D014176:Protein Biosynthesis / Q000187:drug effects; D012333:RNA, Messenger / Q000096:biosynthesis*; D051381:Rats; D012156:Reticulocytes / Q000187:drug effects / Q000378:metabolism; D000254:Sodium-Potassium-Exchanging ATPase / Q000096:biosynthesis*; D013045:Species Specificity
chemical_list: D020121:5' Untranslated Regions; D000893:Anti-Inflammatory Agents; D005938:Glucocorticoids; D012333:RNA, Messenger; D000254:Sodium-Potassium-Exchanging ATPase; D006854:Hydrocortisone