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RefSeq (mRNA)



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Nucleophosmin (NPM), also known as nucleolar phosphoprotein B23 or numatrin, is a protein that in humans is encoded by the NPM1 gene.[1][2]


NPM1 is associated with nucleolar ribonucleoprotein structures and binds single-stranded and double-stranded nucleic acids, but it binds preferentially G-quadruplex forming nucleic acids. It is involved in the biogenesis of ribosomes and may assist small basic proteins in their transport to the nucleolus. Its regulation through SUMOylation (by SENP3 and SENP5) is another facet of the proteins's regulation and cellular functions.

It is located in the nucleolus, but it can be translocated to the nucleoplasm in case of serum starvation or treatment with anticancer drugs. The protein is phosphorylated.

Nucleophosmin has multiple functions:[3]

  1. Histone chaperones
  2. Ribosome biogenesis and transport
  3. Genomic stability and DNA repair
  4. Endoribonuclease activity
  5. Centrosome duplication during cell cycle
  6. Regulation of ARF-p53 tumor suppressor pathway
  7. RNA helix destabilizing activity
  8. Inhibition of caspase-activated DNase
  9. Prevents apoptosis when located in nucleolus

Clinical significance

NPM1 gene is up-regulated, mutated and chromosomally translocated in many tumor types. Chromosomal aberrations involving NPM1 were found in patients with non-Hodgkin lymphoma, acute promyelocytic leukemia, myelodysplastic syndrome, and acute myelogenous leukemia.[4] Heterozygous mice for NPM1 are vulnerable to tumor development. In solid tumors NPM1 is frequently found overexpressed, and it is thought that NPM1 could promote tumor growth by inactivation of the tumor suppressor p53/ARF pathway; on the contrary, when expressed at low levels, NPM1 could suppress tumor growth by the inhibition of centrosome duplication.

Of high importance is NPM involvement in acute myelogenous leukemia,[5] where a mutated protein lacking a folded C-terminal domain (NPM1c+) has been found in the cytoplasm in patients. This aberrant localization has been linked to the development of the disease. Strategies against this subtype of acute myelogenous leukemia include the refolding of the C-terminal domain using pharmalogical chaperones and the displacement of the protein from nucleolus to nucleoplasm, which has been linked to apoptotic mechanisms.


NPM1 has been shown to interact with

Nucleophosmin has multiple binding partners:[3]

  1. rRNA
  2. HIV Rev and Rex peptide
  3. p53 tumor suppressor
  4. ARF tumor suppressor
  5. MDM2 (mouse double minute 2, ubiquitin ligase)
  6. Ribosome protein S9
  7. Phosphatidylinositol 3,4,5-triphosphate (PIP3)
  8. Exportin-1 (CRM1, chromosome region maintenance)
  9. Nucleolin/C23
  10. Transcription target of myc oncogene


  1. Liu QR, Chan PK (March 1993). "Characterization of seven processed pseudogenes of nucleophosmin/B23 in the human genome". DNA Cell Biol. 12 (2): 149–56. doi:10.1089/dna.1993.12.149. PMID 8471164.
  2. Morris SW, Kirstein MN, Valentine MB, Dittmer KG, Shapiro DN, Saltman DL, Look AT (March 1994). "Fusion of a kinase gene, ALK, to a nucleolar protein gene, NPM, in non-Hodgkin's lymphoma". Science. 263 (5151): 1281–4. doi:10.1126/science.8122112. PMID 8122112.
  3. 3.0 3.1 Lindström MS (2011). "NPM1/B23: A Multifunctional Chaperone in Ribosome Biogenesis and Chromatin Remodeling". Biochem Res Int. 2011: 195209. doi:10.1155/2011/195209. PMC 2989734. PMID 21152184.
  4. Falini B, Nicoletti I, Bolli N, Martelli MP, Liso A, Gorello P, Mandelli F, Mecucci C, Martelli MF (April 2007). "Translocations and mutations involving the nucleophosmin (NPM1) gene in lymphomas and leukemias". Haematologica. 92 (4): 519–32. doi:10.3324/haematol.11007. PMID 17488663.
  5. Meani, Natalia; Alcalay, Myriam (2014). "Role of nucleophosmin in acute myeloid leukemia". Expert Review of Anticancer Therapy. 9 (9): 1283–1294. doi:10.1586/era.09.84. ISSN 1473-7140.
  6. Lee SB, Xuan Nguyen TL, Choi JW, Lee KH, Cho SW, Liu Z, Ye K, Bae SS, Ahn JY (October 2008). "Nuclear Akt interacts with B23/NPM and protects it from proteolytic cleavage, enhancing cell survival". Proc. Natl. Acad. Sci. U.S.A. 105 (43): 16584–9. doi:10.1073/pnas.0807668105. PMC 2569968. PMID 18931307.
  7. 7.0 7.1 Sato K, Hayami R, Wu W, Nishikawa T, Nishikawa H, Okuda Y, Ogata H, Fukuda M, Ohta T (July 2004). "Nucleophosmin/B23 is a candidate substrate for the BRCA1-BARD1 ubiquitin ligase". J. Biol. Chem. 279 (30): 30919–22. doi:10.1074/jbc.C400169200. PMID 15184379.
  8. Li YP, Busch RK, Valdez BC, Busch H (April 1996). "C23 interacts with B23, a putative nucleolar-localization-signal-binding protein". Eur. J. Biochem. 237 (1): 153–8. doi:10.1111/j.1432-1033.1996.0153n.x. PMID 8620867.

Further reading