title: Differential translational efficiency of ENaC subunits during lung development.
abstract: The amiloride-sensitive epithelial Na(+) channel (ENaC), the rate-limiting step in epithelial Na(+) transport, consists of three subunits: alpha, beta, and gamma. The abundance of mRNA encoding the alpha-subunit far surpasses the amount for other subunits, and considerably exceeds the predicted subunit protein stoichiometry. We evaluated 5'-untranslated region (UTR) expression and found that fetal rat lung uses alternative 5'UTRs for alpha-ENaC during development. Sucrose density gradient analysis of postnuclear supernatants from fetal rat lung homogenates demonstrated that all three ENaC subunits were associated with high molecular weight polysomes, indicating active translation of the mRNAs, but translational efficiency was much lower for the alpha-subunit. Sucrose density gradient distributions were comparable for the endogenously expressed alpha-ENaC 5'UTRs in rat lung at Fetal Day 20 or Postnatal Day 1 using Northern analysis. Although birth resulted in a global decrease in lung mRNA translation, the loading of ribosomes on ENaC subunit mRNAs was largely unaffected. Evaluation of cytokeratin 18 and vimentin mRNAs in these gradients suggested a cell-specific effect. We conclude that there are different translational efficiencies for ENaC subunits and that perinatal processes globally modulate lung mRNA translation.
authors.affiliation: CIHR Group in Lung Development, Research Institute of the Hospital for Sick Children, Programme in Lung Biology Research, 555 University Avenue, Toronto, ON, M5G 1X8 Canada. gail.otulakowski@sickkids.ca
authors.forename: Gail
authors.initials: G
authors.lastname: Otulakowski
authors.forename: Bijan
authors.initials: B
authors.lastname: Rafii
authors.forename: Hugh
authors.initials: H
authors.lastname: O'Brodovich
mesh_terms: D020121:5' Untranslated Regions; D000818:Animals; D000831:Animals, Newborn; D053503:Epithelial Sodium Channels; D005260:Female; D005333:Fetus / Q000033:anatomy & histology / Q000502:physiology; D005786:Gene Expression Regulation; D005865:Gestational Age; D008168:Lung / Q000196:embryology* / Q000378:metabolism; D008970:Molecular Weight; D011132:Polyribosomes / Q000737:chemistry / Q000378:metabolism; D011247:Pregnancy; D014176:Protein Biosynthesis; D021122:Protein Subunits / Q000235:genetics / Q000378:metabolism*; D012333:RNA, Messenger / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar; D015222:Sodium Channels / Q000235:genetics* / Q000378:metabolism*
chemical_list: D020121:5' Untranslated Regions; D053503:Epithelial Sodium Channels; D021122:Protein Subunits; D012333:RNA, Messenger; D015222:Sodium Channels