NPM1

NPM1 Full Name

nucleophosmin (nucleolar phosphoprotein B23, numatrin)

NPM1 Introduction

The NPM1 gene encodes Nucleophosmin (also known as B23 or numatrin), a highly conserved, highly abundant phosphoprotein that resides primarily within the nucleolus. Structurally, NPM1 typically forms a pentameric ring, which facilitates its function as a molecular chaperone. Biologically, NPM1 is a dynamic multitasking protein that constantly shuttles between the nucleolus, the nucleoplasm, and the cytoplasm. Its primary physiological role is to orchestrate ribosome biogenesis by acting as a chaperone for core histones and ribosomal proteins, facilitating their assembly with ribosomal RNA. Beyond the ribosome, NPM1 is deeply involved in regulating the cell cycle and maintaining genomic stability. It controls centrosome duplication to ensure proper chromosome segregation during mitosis and acts as a critical stress sensor. In response to cellular stress, NPM1 interacts with major tumor suppressor pathways, specifically by binding to and stabilizing the ARF protein, which in turn prevents the degradation of p53, thereby inducing cell cycle arrest or apoptosis.

Figure 1. Schematic representation of full-length NPM1 structure. (Source: Di Matteo A, et al. 2016)

The clinical significance of NPM1 is paramount in hematological malignancies, where it serves as one of the most critical diagnostic and prognostic biomarkers. NPM1 is the most frequently mutated gene in Acute Myeloid Leukemia (AML), occurring in approximately 30% of all adult cases, particularly those with a normal karyotype. The hallmark genetic alteration is a frameshift mutation in exon 12. This specific mutation destroys the protein's nucleolar localization signal and creates a novel nuclear export signal, forcing the mutant protein (NPM1c+) to aberrantly accumulate in the cytoplasm. This abnormal cytoplasmic localization disrupts multiple regulatory pathways, directly driving leukemogenesis. Furthermore, the NPM1 gene is highly prone to chromosomal translocations; the most famous being the t(2;5) translocation in Anaplastic Large Cell Lymphoma (ALCL), which creates the oncogenic NPM-ALK fusion protein. In solid tumors, such as gastric and prostate cancers, the wild-type NPM1 protein is frequently overexpressed, fueling the increased demand for protein synthesis in rapidly dividing cancer cells.

Alternate Names for NPM1

NPM1; nucleophosmin (nucleolar phosphoprotein B23, numatrin); B23; NPM; nucleophosmin; nucleolar protein NO38; nucleophosmin/nucleoplasmin family, member 1;

• 1. Falini B, et al. Cytoplasmic nucleophosmin in acute myelogenous leukemia with a normal karyotype. N Engl J Med. 2005 Jan 20;352(3):254-66.
  2. Di Matteo A, et al. Molecules that target nucleophosmin for cancer treatment: an update. Oncotarget. 2016 Jul 12;7(28):44821-44840.