Nucleophosmin protein expression level, but not threonine 198 phosphorylation, is essential in growth and proliferation
Open Access
- 29 June 2009
- journal article
- research article
- Published by Springer Science and Business Media LLC in Oncogene
- Vol. 28 (36), 3209-3220
- https://doi.org/10.1038/onc.2009.178
Abstract
Nucleophosmin (NPM), an oligomeric phosphoprotein and nucleolar target of the ARF tumor suppressor, contributes to several critical cellular processes. Previous studies have shown that the human NPM's phosphorylation by cyclin E–cyclin-dependent kinase 2 (cdk2) on threonine (Thr) 199 regulates its translocation from the centrosome during cell cycle progression. Given our previous finding that ARF directly binds NPM, impeding its transit to the cytoplasm and arresting cells before S-phase entry, we hypothesized that ARF might also inhibit NPM phosphorylation. However, ARF induction did not impair phosphorylation of the cdk2 target residue in murine NPM, Thr198. Furthermore, phosphorylation of Thr198 occurred throughout the cell cycle and was concomitant with increases in overall NPM expression. To investigate the cell's presumed requirement for NPM-Thr198 phosphorylation in promoting the processes of growth and proliferation, we examined the effects of a non-phosphorylatable NPM mutant, T198A, in a clean cell system in which endogenous NPM had been removed by RNA interference. Here, we show that the T198A mutant is fully capable of executing NPM's described roles in nucleocytoplasmic shuttling, ribosome export and cell cycle progression. Moreover, the proliferative defects observed with stable NPM knockdown were restored by mutant NPM-T198A expression. Thus, we demonstrate that the reduction in NPM protein expression blocks cellular growth and proliferation, whereas phosphorylation of NPM-Thr198 is not essential for NPM's capacity to drive cell cycle progression and proliferation.Keywords
This publication has 41 references indexed in Scilit:
- Nucleophosmin Serves as a Rate-Limiting Nuclear Export Chaperone for the Mammalian RibosomeMolecular and Cellular Biology, 2008
- TSC1 Sets the Rate of Ribosome Export and Protein Synthesis through Nucleophosmin TranslationCancer Research, 2007
- Cell cycle progression and de novo centriole assembly after centrosomal removal in untransformed human cellsThe Journal of cell biology, 2007
- Nucleophosmin Is Essential for Ribosomal Protein L5 Nuclear ExportMolecular and Cellular Biology, 2006
- Phosphorylation regulates nucleophosmin targeting to the centrosome during mitosis as detected by cross-reactive phosphorylation-specific MKK1/MKK2 antibodiesBiochemical Journal, 2004
- Proteomic characterization of the human centrosome by protein correlation profilingNature, 2003
- Specific Phosphorylation of Nucleophosmin on Thr199 by Cyclin- dependent Kinase 2-Cyclin E and Its Role in Centrosome DuplicationPublished by Elsevier BV ,2001
- In vivo interaction of nucleophosmin/B23 and protein C23 during cell cycle progression in HeLa cellsCancer Letters, 1999
- Association of p19ARF with Mdm2 inhibits ubiquitin ligase activity of Mdm2 for tumor suppressor p53The EMBO Journal, 1999
- Identification and characterization of nucleophosmin/B23/numatrin which binds the anti-oncogenic transcription factor IRF-1 and manifests oncogenic activityOncogene, 1997