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MBC in Press, published online ahead of print April 30, 2008
Mol. Biol. Cell 10.1091/mbc.E08-02-0128

A more recent version of this article appeared on July 1, 2008
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Submitted on February 7, 2008
Revised on March 19, 2008
Accepted on April 23, 2008

Nucleophosmin Is a Binding Partner of Nucleostemin in Human Osteosarcoma Cells

Hanhui Ma and Thoru Pederson

Program in Cell Dynamics, Department of Biochemistry and Molecular Pharmacology, University of Massachusetts Medical School, Worcester, MA 01605

Monitoring Editor: Wendy Bickmore

Nucleostemin (NS) is expressed in the nucleoli of adult and embryonic stem cells as well as in many tumors and tumor-derived cell lines. In coimmunoprecipitation experiments nucleostemin is recovered with the tumor suppressor p53 and more recently we have demonstrated that nucleostemin exerts its role in cell cycle progression via a p53-dependent pathway. Here we report that in human osteosarcoma cells, nucleostemin interacts with nucleophosmin, a nucleolar protein believed to possess oncogenic potential. Nucleostemin (NS) and nucleophosmin (NPM) displayed an extremely high degree of colocalization in the granular component of the nucleolus during interphase and both proteins associated with pre-nucleolar bodies in late mitosis before the reformation of nucleoli. Coimmunoprecipitation experiments revealed that NS and NPM coreside in complexes and yeast two-hybrid experiments confirmed that they are interactive proteins, revealing the NPM-interactive region to be the 46 amino acid N-terminal domain of NS. In bimolecular fluorescence complementation (BiFC) studies bright nucleolar signals were observed, indicating that these two proteins directly interact in the nucleolus in vivo. These results support the notion that cell cycle regulatory proteins congress and interact in the nucleolus, adding to the emerging concept that this nuclear domain has functions beyond ribosome production.

Address correspondence to: Thoru Pederson (thoru.pederson{at}umassmed.edu)






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