title: Silencing of RNA helicase II/Gualpha inhibits mammalian ribosomal RNA production.
abstract: The intricate production of ribosomal RNA is well defined in yeast, but its complexity in higher organisms is barely understood. We recently showed that down-regulation of nucleolar protein RNA helicase II/Gualpha (RH-II/Gualpha or DDX21) in Xenopus oocytes inhibited processing of 20 S rRNA to 18 S and contributed to degradation of 28 S rRNA (Yang, H., Zhou, J., Ochs, R. L., Henning, D., Jin, R., and Valdez, B. C. (2003) J. Biol. Chem. 278, 38847-38859). Since no nucleolar RNA helicase has been functionally characterized in mammalian cells, we used short interfering RNA to search for functions for RH-II/Gualpha and its paralogue RH-II/Gubeta in rRNA production. Silencing of RH-II/Gualpha by more than 80% in HeLa cells resulted in an almost 80% inhibition of 18 and 28 S rRNA production. This inhibition could be reversed by exogenous expression of wild type RH-II/Gualpha. A helicase-deficient mutant form having ATPase activity was able to rescue the production of 28 S but not 18 S rRNA. A phenotype exhibiting inhibition of 18 S and 28 S rRNA production was also observed when the paralogue RH-II/Gubeta was overexpressed. Both down-regulation of RH-II/Gualpha and overexpression of RH-II/Gubeta slowed cell proliferation. The opposite effects of the two paralogues suggest antagonistic functions.
authors.affiliation: Department of Pharmacology, Baylor College of Medicine, Houston, Texas 77030, USA.
authors.forename: Dale
authors.initials: D
authors.lastname: Henning
authors.forename: Rolando B
authors.initials: RB
authors.lastname: So
authors.forename: Runyan
authors.initials: R
authors.lastname: Jin
authors.forename: Lester F
authors.initials: LF
authors.lastname: Lau
authors.forename: Benigno C
authors.initials: BC
authors.lastname: Valdez
mesh_terms: D000251:Adenosine Triphosphatases / Q000378:metabolism; D000818:Animals; D015153:Blotting, Western; D002455:Cell Division; D002460:Cell Line; D002466:Cell Nucleolus / Q000378:metabolism; D053487:DEAD-box RNA Helicases; D004305:Dose-Response Relationship, Drug; D015536:Down-Regulation; D005434:Flow Cytometry; D020868:Gene Silencing; D005822:Genetic Vectors; D006367:HeLa Cells; D006801:Humans; D007700:Kinetics; D051379:Mice; D009154:Mutation; D009865:Oocytes / Q000378:metabolism; D010641:Phenotype; D012313:RNA / Q000378:metabolism*; D020365:RNA Helicases / Q000235:genetics* / Q000502:physiology*; D012335:RNA, Ribosomal / Q000378:metabolism; D034741:RNA, Small Interfering / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012270:Ribosomes / Q000378:metabolism*; D013997:Time Factors; D014162:Transfection; D014981:Xenopus
chemical_list: D012335:RNA, Ribosomal; D034741:RNA, Small Interfering; D012313:RNA; D000251:Adenosine Triphosphatases; C501726:DDX21 protein, human; C410330:DDX56 protein, human; D053487:DEAD-box RNA Helicases; D020365:RNA Helicases