title: Na,K-ATPase beta1-subunit increases the translation efficiency of the alpha1-subunit in MSV-MDCK cells.
abstract: The Na,K-ATPase consists of an alpha- and beta-subunit. Moloney sarcoma virus-transformed MDCK cells (MSV-MDCK) express low levels of Na,K-ATPase beta(1)-subunit. Ectopic expression of Na,K-ATPase beta(1)-subunit in these cells increased the protein levels of the alpha(1)-subunit of Na,K-ATPase. This increase was not due to altered transcription of the alpha(1)-subunit gene or half-life of the alpha(1)-subunit protein because both alpha(1)-subunit mRNA levels and half-life of the alpha(1)-subunit protein were comparable in MSV-MDCK and beta(1)-subunit expressing MSV-MDCK cells. However, short pulse labeling revealed that the initial translation rate of the alpha(1)-subunit in beta(1)-subunit expressing MSV-MDCK cells was six- to sevenfold higher compared with MSV-MDCK cells. The increased translation was specific to alpha(1)-subunit because translation rates of occludin and beta-catenin, membrane and cytosolic proteins, respectively, were not altered. In vitro cotranslation/translocation experiments using rabbit reticulocyte lysate and rough microsomes revealed that the alpha(1)-subunit mRNA is more efficiently translated in the presence of beta(1)-subunit. Furthermore, sucrose density gradient analysis revealed significantly more alpha(1)-subunit transcript associated with the polysomal fraction in beta(1)-subunit expressing MSV-MDCK cells compared with MSV-MDCK cells, indicating that in mammalian cells the Na,K-ATPase beta(1)-subunit is involved in facilitating the translation of the alpha(1)-subunit mRNA in the endoplasmic reticulum.
authors.affiliation: Department of Pathology and Laboratory Medicine, David Geffen School of Medicine at the University of California, Los Angeles, Los Angeles, California 90095, USA. arajasekaran@mednet.ucla.edu
authors.forename: Sigrid A
authors.initials: SA
authors.lastname: Rajasekaran
authors.forename: Jegan
authors.initials: J
authors.lastname: Gopal
authors.forename: Dianna
authors.initials: D
authors.lastname: Willis
authors.forename: Cromwell
authors.initials: C
authors.lastname: Espineda
authors.forename: Jeffery L
authors.initials: JL
authors.lastname: Twiss
authors.forename: Ayyappan K
authors.initials: AK
authors.lastname: Rajasekaran
mesh_terms: D000818:Animals; D002457:Cell Extracts / Q000737:chemistry; D002461:Cell Line, Transformed; D002462:Cell Membrane / Q000737:chemistry; D004285:Dogs; D015971:Gene Expression Regulation, Enzymologic; D008980:Moloney murine sarcoma virus / Q000378:metabolism; D011132:Polyribosomes / Q000737:chemistry / Q000378:metabolism; D014176:Protein Biosynthesis; D021122:Protein Subunits / Q000032:analysis / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D012333:RNA, Messenger / Q000032:analysis / Q000378:metabolism; D000254:Sodium-Potassium-Exchanging ATPase / Q000032:analysis / Q000378:metabolism / Q000502:physiology*; D015854:Up-Regulation
chemical_list: D002457:Cell Extracts; D021122:Protein Subunits; D012333:RNA, Messenger; D000254:Sodium-Potassium-Exchanging ATPase