Critical role of nucleostemin in pre-rRNA processing

J Biol Chem. 2009 Feb 20;284(8):4968-77. doi: 10.1074/jbc.M804594200. Epub 2008 Dec 23.

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.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Carrier Proteins / genetics
  • Carrier Proteins / metabolism*
  • Cell Cycle / physiology*
  • DEAD-box RNA Helicases / genetics
  • DEAD-box RNA Helicases / metabolism
  • GTP-Binding Proteins
  • HeLa Cells
  • Humans
  • Multiprotein Complexes / genetics
  • Multiprotein Complexes / metabolism
  • Nuclear Proteins / genetics
  • Nuclear Proteins / metabolism*
  • Proteins / genetics
  • Proteins / metabolism
  • RNA Precursors / genetics
  • RNA Precursors / metabolism*
  • RNA Processing, Post-Transcriptional / physiology*
  • RNA, Ribosomal, 28S / genetics
  • RNA, Ribosomal, 28S / metabolism*
  • Ribosomes / genetics
  • Ribosomes / metabolism*
  • Signal Transduction / physiology
  • Tumor Suppressor Protein p53 / genetics
  • Tumor Suppressor Protein p53 / metabolism

Substances

  • Carrier Proteins
  • EBNA1BP2 protein, human
  • GNL3 protein, human
  • Multiprotein Complexes
  • Nuclear Proteins
  • PES1 protein, human
  • Proteins
  • RNA Precursors
  • RNA, Ribosomal, 28S
  • TP53 protein, human
  • Tumor Suppressor Protein p53
  • DDX21 protein, human
  • GTP-Binding Proteins
  • DEAD-box RNA Helicases