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.
Highlights
Nucleostemin (NS)2 is a nucleolar protein preferentially expressed in actively proliferating cells
We showed that NS interacts with three nucleolar proteins involved in pre-rRNA processing and that NS is essential for the nucleolar localization of some of these proteins
Both knockdown and overexpression of NS altered the rate of the processing of 32 S pre-rRNA into 28 S rRNA
Summary
Nucleostemin (NS)2 is a nucleolar protein preferentially expressed in actively proliferating cells. When the NS-positive fractions obtained from the last column, Mono Q, were analyzed by gel filtration, the elution pattern of NS was similar to that observed for HeLa cell extract described above (Fig. 1A, lower panel). SDS-PAGE and silver staining of the Mono Q fractions revealed more than 20 protein bands (Fig. 1C), and this number did not substantially decrease after additional steps of column chromatography (data not shown).
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
