title: SUMO-Modification of the La Protein Facilitates Binding to mRNA In Vitro and in Cells.
abstract: The RNA-binding protein La is involved in several aspects of RNA metabolism including the translational regulation of mRNAs and processing of pre-tRNAs. Besides its well-described phosphorylation by Casein kinase 2, the La protein is also posttranslationally modified by the Small Ubiquitin-like MOdifier (SUMO), but the functional outcome of this modification has not been defined. The objective of this study was to test whether sumoylation changes the RNA-binding activity of La. Therefore, we established an in vitro sumoylation assay for recombinant human La and analyzed its RNA-binding activity by electrophoretic mobility shift assays. We identified two novel SUMO-acceptor sites within the La protein located between the RNA recognition motif 1 and 2 and we demonstrate for the first time that sumoylation facilitates the RNA-binding of La to small RNA oligonucleotides representing the oligopyrimidine tract (TOP) elements from the 5' untranslated regions (UTR) of mRNAs encoding ribosomal protein L22 and L37 and to a longer RNA element from the 5' UTR of cyclin D1 (CCND1) mRNA in vitro. Furthermore, we show by RNA immunoprecipitation experiments that a La mutant deficient in sumoylation has impaired RNA-binding activity in cells. These data suggest that modulating the RNA-binding activity of La by sumoylation has important consequences on its functionality.
authors.affiliation: Medical University of South Carolina, Department of Biochemistry & Molecular Biology, Charleston, South Carolina, United States of America.
authors.forename: Venkatesh
authors.initials: V
authors.lastname: Kota
authors.affiliation: Medical University of South Carolina, Department of Biochemistry & Molecular Biology, Charleston, South Carolina, United States of America.
authors.forename: Gunhild
authors.initials: G
authors.lastname: Sommer
authors.affiliation: Institute of Research in Immunology and Cancer University de Montreal, Station Centre-ville, Montreal, Canada.
authors.forename: Chantal
authors.initials: C
authors.lastname: Durette
authors.affiliation: Institute of Research in Immunology and Cancer University de Montreal, Station Centre-ville, Montreal, Canada.
authors.forename: Pierre
authors.initials: P
authors.lastname: Thibault
authors.affiliation: Department of Neurosciences-0626, University of California, San Diego, La Jolla, California, United States of America.
authors.forename: Erna A
authors.initials: EA
authors.lastname: van Niekerk
authors.affiliation: Department of Biological Sciences, University of South Carolina, Columbia, South Carolina, United States of America.
authors.forename: Jeffery L
authors.initials: JL
authors.lastname: Twiss
authors.affiliation: Medical University of South Carolina, Department of Biochemistry & Molecular Biology, Charleston, South Carolina, United States of America.
authors.forename: Tilman
authors.identifier: http://orcid.org/0000-0002-3248-3129
authors.initials: T
authors.lastname: Heise
mesh_terms: D020413:3' Untranslated Regions; D001665:Binding Sites; D019938:Cyclin D1 / Q000235:genetics*; D024202:Electrophoretic Mobility Shift Assay; D006801:Humans; D010750:Phosphoproteins / Q000737:chemistry / Q000378:metabolism*; D011485:Protein Binding; D011499:Protein Processing, Post-Translational; D012333:RNA, Messenger / Q000378:metabolism*; D012269:Ribosomal Proteins / Q000235:genetics*; D058207:Sumoylation
chemical_list: D020413:3' Untranslated Regions; C530104:CCND1 protein, human; C574674:La protein, human; D010750:Phosphoproteins; D012333:RNA, Messenger; D012269:Ribosomal Proteins; D019938:Cyclin D1