title: Critical role of nucleostemin in pre-rRNA processing.
abstract: Nucleostemin is a nucleolar protein widely expressed in proliferating cells. Nucleostemin is involved in the regulation of cell proliferation, and both depletion and overexpression of nucleostemin induce cell cycle arrest through the p53 signaling pathway. Although the presence of p53-independent functions of nucleostemin has been previously suggested, the identities of these additional functions remained to be investigated. Here, we show that nucleostemin has a novel role as an integrated component of ribosome biogenesis, particularly pre-rRNA processing. Nucleostemin forms a large protein complex (>700 kDa) that co-fractionates with the pre-60 S ribosomal subunit in a sucrose gradient. This complex contains proteins related to pre-rRNA processing, such as Pes1, DDX21, and EBP2, in addition to several ribosomal proteins. We show that the nucleolar retention of DDX21 and EBP2 is dependent on the presence of nucleostemin in the nucleolus. Furthermore, the knockdown of nucleostemin delays the processing of 32 S pre-rRNA into 28 S rRNA. This is accompanied by a substantial decrease of protein synthesis as well as the levels of rRNAs and some mRNAs. In addition, overexpressed nucleostemin significantly promotes the processing of 32 S pre-rRNA. Collectively, these biochemical and functional studies demonstrate a novel role of nucleostemin in ribosome biogenesis. This is a key aspect of the role of nucleostemin in regulating cell proliferation.
authors.affiliation: Stem Cell Institute, Division of Hematology, Oncology and Transplantation, Department of Medicine, University of Minnesota, Minneapolis, Minnesota 55455, USA.
authors.forename: Liudmila
authors.initials: L
authors.lastname: Romanova
authors.forename: Anthony
authors.initials: A
authors.lastname: Grand
authors.forename: Liying
authors.initials: L
authors.lastname: Zhang
authors.forename: Samuel
authors.initials: S
authors.lastname: Rayner
authors.forename: Nobuko
authors.initials: N
authors.lastname: Katoku-Kikyo
authors.forename: Steven
authors.initials: S
authors.lastname: Kellner
authors.forename: Nobuaki
authors.initials: N
authors.lastname: Kikyo
mesh_terms: D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D002453:Cell Cycle / Q000502:physiology*; D053487:DEAD-box RNA Helicases / Q000235:genetics / Q000378:metabolism; D019204:GTP-Binding Proteins; D006367:HeLa Cells; D006801:Humans; D046912:Multiprotein Complexes / Q000235:genetics / Q000378:metabolism; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism*; D011506:Proteins / Q000235:genetics / Q000378:metabolism; D012322:RNA Precursors / Q000235:genetics / Q000378:metabolism*; D012323:RNA Processing, Post-Transcriptional / Q000502:physiology*; D012339:RNA, Ribosomal, 28S / Q000235:genetics / Q000378:metabolism*; D016601:RNA-Binding Proteins; D012270:Ribosomes / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction / Q000502:physiology; D016159:Tumor Suppressor Protein p53 / Q000235:genetics / Q000378:metabolism
chemical_list: D002352:Carrier Proteins; C432687:EBNA1BP2 protein, human; C469949:GNL3 protein, human; D046912:Multiprotein Complexes; D009687:Nuclear Proteins; C484463:PES1 protein, human; D011506:Proteins; D012322:RNA Precursors; D012339:RNA, Ribosomal, 28S; D016601:RNA-Binding Proteins; C495901:TP53 protein, human; D016159:Tumor Suppressor Protein p53; C501726:DDX21 protein, human; D019204:GTP-Binding Proteins; D053487:DEAD-box RNA Helicases