title: Multiple controls regulate nucleostemin partitioning between nucleolus and nucleoplasm.
abstract: Nucleostemin plays an essential role in maintaining the continuous proliferation of stem cells and cancer cells. The movement of nucleostemin between the nucleolus and the nucleoplasm provides a dynamic way to partition the nucleostemin protein between these two compartments. Here, we show that nucleostemin contains two nucleolus-targeting regions, the basic and the GTP-binding domains, that exhibit a short and a long nucleolar retention time, respectively. In a GTP-unbound state, the nucleolus-targeting activity of nucleostemin is blocked by a mechanism that traps its intermediate domain in the nucleoplasm. A nucleostemin-interacting protein, RSL1D1, was identified that contains a ribosomal L1-domain. RSL1D1 co-resides with nucleostemin in the same subnucleolar compartment, unlike the B23 and fibrillarin, and displays a longer nucleolar residence time than nucleostemin. It interacts with both the basic and the GTP-binding domains of nucleostemin through a non-nucleolus-targeting region. Overexpression of the nucleolus-targeting domain of RSL1D1 alone disperses nucleolar nucleostemin. Loss of RSL1D1 expression reduces the compartmental size and amount of nucleostemin in the nucleolus. Our work reveals that the partitioning of nucleostemin employs complex mechanisms involving both nucleolar and nucleoplasmic components, and provides insight into the post-translational regulation of its activity.
authors.affiliation: Center for Cancer and Stem Cell Biology, Alkek Institute of Biosciences and Technology, Texas A&M Health Science Center, 2121 W Holcombe Blvd, Houston, TX 77030-3303, USA.
authors.forename: Lingjun
authors.initials: L
authors.lastname: Meng
authors.forename: Hiroaki
authors.initials: H
authors.lastname: Yasumoto
authors.forename: Robert Y L
authors.initials: RY
authors.lastname: Tsai
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D015152:Blotting, Northern; D016466:CHO Cells; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D002460:Cell Line; D045744:Cell Line, Tumor; D002466:Cell Nucleolus / Q000378:metabolism*; D002467:Cell Nucleus / Q000235:genetics / Q000378:metabolism*; D006224:Cricetinae; D003412:Cricetulus; D036681:Fluorescence Recovery After Photobleaching; D006801:Humans; D047468:Immunoprecipitation; D042581:Intranuclear Space / Q000378:metabolism; D008856:Microscopy, Fluorescence; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism*; D021381:Protein Transport; D034622:RNA Interference; D016415:Sequence Alignment; D020798:Two-Hybrid System Techniques
chemical_list: D002352:Carrier Proteins; D009687:Nuclear Proteins