# NPM1 (Nucleophosmin): C-Terminal Frameshift Mutations, Nucleolar Trafficking, and Leukemogenesis


## Key Takeaways

-   *NPM1* mutations, primarily frameshifts in exon 12, are the most frequent genetic drivers in adult Acute Myeloid Leukemia (AML), occurring in 30-35% of cases and up to 60% of normal karyotype AML. These mutations lead to the loss of the nucleolar localization signal (NoLS) and the creation of a novel nuclear export signal (NES), causing aberrant cytoplasmic accumulation of the mutant NPM1 protein (NPM1c).
-   Wild-type NPM1 is a multifunctional nucleolar protein essential for ribosome biogenesis, centrosome duplication, genomic stability, and regulation of the ARF-p53 tumor suppressor pathway; its cytoplasmic mislocalization in NPM1c actively contributes to leukemogenesis by disrupting these functions, particularly by sequestering ARF and preventing p53 activation.
-   *NPM1*-mutated AML exhibits a distinct immunophenotype (e.g., CD33+, CD13+, CD117+, often CD34-) and is associated with a favorable prognosis when *FLT3*-ITD is absent, but its clinical outcome is significantly modulated by co-occurring mutations in genes like *FLT3*, *DNMT3A*, and *IDH1/2*.
-   The *NPM1* mutation serves as a highly sensitive and specific biomarker for minimal residual disease (MRD) monitoring in AML using quantitative PCR (qPCR) or next-generation sequencing (NGS), with MRD negativity strongly correlating with improved survival.
-   Therapeutic strategies for *NPM1*-mutated AML target the consequences of NPM1c mislocalization, including XPO1 (CRM1) inhibitors (e.g., selinexor) to restore nuclear localization and menin inhibitors (e.g., revumenib) to disrupt the downstream leukemogenic transcriptional program driven by HOX gene expression.

---

## Executive Summary & Key Metadata

Nucleophosmin 1 (NPM1), also known as B23, NO38, or numatrin, is a multifunctional phosphoprotein that is ubiquitously expressed and predominantly localized to the nucleolus. The *NPM1* gene is one of the most frequently mutated genes in adult acute myeloid leukemia (AML), with mutations detected in approximately 30–35% of all newly diagnosed cases and in 50–60% of cases with a normal karyotype [1, 2]. The defining molecular feature of these mutations is a frameshift in the terminal exon (exon 12) that results in the loss of two critical C-terminal tryptophan residues (W288 and W290) and the creation of a novel nuclear export signal (NES), leading to aberrant cytoplasmic accumulation of the mutant protein (NPM1c) [1, 2]. This cytoplasmic dislocation is a hallmark of the disease and is used both diagnostically and for minimal residual disease (MRD) monitoring [1, 2].

The *NPM1* gene product is a molecular chaperone involved in ribosome biogenesis, centrosome duplication, genomic stability maintenance, cell cycle progression, and the regulation of the ARF-p53 tumor suppressor pathway [1, 2]. Mutations in *NPM1* are considered founder genetic events in AML and are associated with a distinct gene expression signature, a specific immunophenotype, and a favorable prognosis when present without the FLT3-ITD mutation [1, 2]. However, the clinical outcome is highly modulated by co-occurring mutations, particularly in *FLT3*, *DNMT3A*, and *IDH1/2* [1, 2].

The following table summarizes the key metadata for the *NPM1* gene and its product.

| **Feature** | **Detail** |
| :--- | :--- |
| **HGNC Symbol** | NPM1 |
| **UniProt Accession** | P06748 |
| **Representative PDB ID** | 2P1B |
| **Chromosomal Locus** | 5q35.1 |
| **Primary Molecular Function** | Molecular chaperone; ribosome biogenesis; centrosome duplication; genomic stability; ARF/p53 pathway regulation |
| **Disease & Pathology Associations** | Acute Myeloid Leukemia (AML), Myelodysplastic Syndromes (MDS), Lymphomas, Medulloblastoma |

---

## 1. Genomic Locus, Chromosomal Organization & Isoforms

### 1.1 Chromosomal Locus and Gene Structure

The *NPM1* gene is located on the long arm of chromosome 5 at band q35.1 (5q35.1) [1, 2]. This locus is of particular interest in myeloid malignancies because deletions of the long arm of chromosome 5 (del(5q)) are common in myelodysplastic syndromes (MDS) and AML, although *NPM1* itself is not typically the critical haploinsufficient gene in these deletions [1]. The gene spans approximately 23 kilobases (kb) of genomic DNA and consists of 12 exons, with the coding sequence (CDS) distributed across exons 2 through 12 [1, 2]. The open reading frame encodes a protein of 294 amino acids in its most common isoform (isoform 1), with a molecular weight of approximately 32.5 kDa, although post-translational modifications (primarily phosphorylation) cause it to migrate at approximately 37–38 kDa on SDS-PAGE [1].

The *NPM1* promoter region is characterized by a lack of a canonical TATA box but contains multiple GC-rich elements and binding sites for ubiquitous transcription factors such as SP1. The promoter is also responsive to growth factor signaling, with MYC being a direct transcriptional activator. Estrogen signaling has been shown to upregulate *NPM1* expression in a MYC-dependent manner in uterine tissue, highlighting a link between hormonal signaling and NPM1 transcription [2]. The 5' untranslated region (UTR) is relatively short, while the 3' UTR contains multiple AU-rich elements (AREs) that contribute to the regulation of mRNA stability.

### 1.2 Promoter Architecture and Regulatory Elements

The core promoter of *NPM1* is embedded within a CpG island, suggesting that its expression is subject to epigenetic regulation via DNA methylation. However, in contrast to tumor suppressor genes, the *NPM1* promoter is typically hypomethylated in both normal and malignant cells, reflecting its status as a constitutively expressed "housekeeping" gene. The promoter contains several E-box elements (CANNTG) that serve as binding sites for MYC, which directly transactivates *NPM1* expression [2]. Additionally, there are binding sites for the tumor suppressor p53, which can repress *NPM1* transcription under conditions of cellular stress, creating a negative feedback loop.

Enhancer elements for *NPM1* have been identified in intronic regions and in the intergenic region downstream of the gene. These enhancers are marked by histone H3 lysine 27 acetylation (H3K27ac) and are bound by hematopoietic transcription factors such as RUNX1, GATA2, and CEBPA in myeloid progenitors. Single-cell multiomics studies have recently identified candidate cis-regulatory elements (cREs) that are specifically active in *NPM1*-mutant AML cells, suggesting that the mutant protein may establish an aberrant transcriptional program that includes the activation of enhancers that drive its own expression [1].

### 1.3 Alternative Splicing and Isoforms

Alternative splicing of the *NPM1* primary transcript generates multiple mRNA isoforms. The two most well-characterized protein isoforms are:

- **Isoform 1 (NPM1.1, B23.1):** The full-length protein of 294 amino acids. This is the predominant isoform and contains the nucleolar localization signal (NoLS) at its C-terminus. It is the isoform most commonly mutated in AML.
- **Isoform 2 (NPM1.2, B23.2):** A shorter isoform that arises from the use of an alternative polyadenylation signal within intron 10. This results in a protein of 259 amino acids that lacks the C-terminal 35 residues, including the NoLS. Consequently, NPM1.2 is predominantly cytoplasmic and does not localize to the nucleolus.

Differential splicing is also observed in the 5' UTR, which may affect translational efficiency. Furthermore, the *NPM1* locus produces a family of [circular RNAs](/knowledge/bioinformatics/circular-rnas-computational-identification-and-analysis) (circRNAs), including hsa_circ_0075001, which are generated by back-splicing events [1, 2]. The expression of these circRNAs is deregulated in AML, and they may function as microRNA sponges or as scaffolds for protein complexes, although their precise role in leukemogenesis remains under investigation [2].

---

## 2. 3D Protein Domain Architecture & Structural Biology

### 2.1 Domain Organization of the NPM1 Protein

The NPM1 protein is an intrinsically disordered protein (IDP) in large part, but it contains several well-defined structured domains that are critical for its function. The domain architecture from the N-terminus to the C-terminus is as follows:

1.  **N-terminal Oligomerization Domain (Residues 1–119):** This domain is responsible for the homo-oligomerization of NPM1, forming pentameric and decameric structures. It contains two subdomains: a four-helix bundle that mediates the primary dimerization interface and a second interface that allows for higher-order oligomerization. This domain also contains the chaperone activity of NPM1, which is involved in histone binding and ribosome assembly. The N-terminal domain is also the site of interaction with several viral proteins and the tumor suppressor ARF.
2.  **Acidic Domain (Residues 120–132):** A short, highly acidic stretch of amino acids (predominantly aspartic and glutamic acid residues). This domain is involved in metal ion binding (e.g., calcium) and contributes to the histone-binding and ribonuclease activities of the protein.
3.  **Central Disordered Region (Residues 133–185):** This region is largely unstructured and contains multiple phosphorylation sites for cyclin-dependent kinases (CDKs) and casein kinase 2 (CK2). Phosphorylation in this region regulates the interaction of NPM1 with other proteins and its subcellular localization.
4.  **Histone-binding Domain (Residues 186–239):** This domain is responsible for the high-affinity binding of NPM1 to core histones (H3 and H4), which is essential for its role in chromatin remodeling and ribosome biogenesis.
5.  **C-terminal Nucleic Acid-binding Domain (Residues 240–294):** This domain contains two globular subdomains that are connected by a flexible linker. It binds to single-stranded and double-stranded nucleic acids (DNA and RNA). Critically, this domain contains the nucleolar localization signal (NoLS) at residues 288–290 (tryptophan residues W288 and W290). These two tryptophans are essential for the retention of NPM1 in the nucleolus. The C-terminal domain also contains a nuclear export signal (NES) that is normally masked by the NoLS.

### 2.2 Structural Biology of the C-Terminal Domain

The C-terminal domain (CTD) of NPM1 is the primary target of leukemic mutations. The structure of the CTD, as determined by NMR and X-ray crystallography (e.g., PDB: 2P1B), reveals a compact fold consisting of a four-stranded beta-sheet and two alpha-helices. The domain forms a positively charged surface that interacts with the negatively charged phosphate backbone of nucleic acids. The two tryptophan residues, W288 and W290, are located within a short, solvent-exposed loop at the very C-terminus. This loop is part of the NoLS and is critical for the interaction of NPM1 with components of the nucleolus.

The CTD is also a hotspot for post-translational modifications. Multisite phosphorylation of the C-terminal region, particularly at serine and threonine residues, has been shown to orchestrate protein stability, DNA binding affinity, and the ability of NPM1 to undergo liquid-liquid phase separation (LLPS) [1]. Phosphorylation introduces negative charges that can disrupt the positively charged nucleic acid-binding surface, thereby modulating DNA binding. Furthermore, the CTD is involved in the formation of pH-dependent amyloid-like aggregates, a property that is enhanced by AML-associated mutations [2].

### 2.3 The NPM1 Mutant Structure and Cytoplasmic Dislocation

The most common AML-associated mutations are 4-base pair (bp) insertions or, less frequently, deletions in exon 12. These mutations cause a frameshift in the reading frame, leading to the translation of an aberrant C-terminal peptide. The consequences of this frameshift are threefold:

1.  **Loss of the NoLS:** The frameshift results in the loss of the tryptophan residues W288 and W290, which are critical for nucleolar localization. Without these residues, the mutant protein cannot be retained in the nucleolus.
2.  **Creation of a Novel NES:** The frameshift creates a new, leucine-rich nuclear export signal (NES) at the C-terminus of the mutant protein. This NES is recognized by the nuclear export receptor CRM1/XPO1, which actively transports the mutant protein from the nucleus to the cytoplasm.
3.  **Altered C-terminal Sequence:** The frameshift replaces the last 7 amino acids of the wild-type protein (DLWQWRK) with a longer, highly acidic sequence (e.g., AVEEVSLRK for the type A mutation). This new sequence is predicted to be disordered and contributes to the aberrant cytoplasmic localization and the formation of cytoplasmic aggregates [1, 2].

The combination of losing the nucleolar retention signal and gaining a functional NES leads to the net cytoplasmic accumulation of the mutant protein, a phenomenon known as NPM1c (cytoplasmic NPM1) [1, 2]. This aberrant localization is the defining feature of *NPM1*-mutated AML and is routinely detected by immunohistochemistry [1, 2].

### 2.4 Interactive 3D Visualizer

To explore the three-dimensional structure of the NPM1 protein and visualize the location of key domains and mutation hotspots, please use the interactive visualizer below.

[Interactive 3D Protein Visualizer: Load NPM1 (PDB: 2P1B)](/tools/protein-structure-viewer?source=direct&pdbId=2P1B)

---

## 3. Cellular Signaling Pathways & Molecular Function

### 3.1 Molecular Functions of Wild-Type NPM1

Wild-type NPM1 is a multifunctional protein that acts as a molecular chaperone, primarily within the nucleolus. Its functions can be broadly categorized as follows:

- **Ribosome Biogenesis:** NPM1 is a core component of the ribosome assembly machinery. It binds to pre-[ribosomal RNA](/knowledge/bioinformatics/ribosomal-rna-structure-taxonomic-profiling) (pre-rRNA) and ribosomal proteins, facilitating the processing of the 47S pre-rRNA transcript into the mature 18S, 5.8S, and 28S rRNAs. It also acts as a chaperone for ribosomal proteins, preventing their aggregation and promoting their incorporation into the maturing ribosomal subunits [1, 2].
- **Centrosome Duplication:** NPM1 localizes to the centrosome during the cell cycle, where it regulates centrosome duplication to ensure that it occurs only once per cell cycle. This function is dependent on its phosphorylation by CDK2/cyclin E. Loss of NPM1 leads to centrosome amplification and genomic instability [1, 2].
- **Genomic Stability and DNA Repair:** NPM1 is involved in the cellular response to DNA damage. It interacts with and stabilizes key DNA repair proteins, including APEX1 (APE1) and p53 [2]. It also plays a role in base excision repair (BER) by modulating the activity of APE1 [2].
- **Regulation of the ARF-p53 Pathway:** NPM1 is a critical negative regulator of the ARF (p14^ARF^) tumor suppressor. In the nucleolus, NPM1 binds to ARF and prevents its ubiquitin-mediated degradation. Under normal conditions, this interaction keeps ARF levels low. Upon oncogenic stress, ARF is released from NPM1, leading to its stabilization and translocation to the nucleoplasm, where it inhibits MDM2 and activates p53. Mutant NPM1, which is mislocalized to the cytoplasm, sequesters ARF in the cytoplasm, preventing p53 activation and contributing to leukemogenesis [1].
- **Chromatin Remodeling and Transcription:** NPM1 binds to core histones and can act as a histone chaperone, facilitating the assembly and disassembly of nucleosomes. It also interacts with transcription factors and can modulate gene expression. For example, NPM1 has been shown to selectively regulate the expression of type II interferon-inducible genes [1].
- **Liquid-Liquid Phase Separation (LLPS):** Recent work has shown that NPM1 can undergo LLPS, forming dynamic, membrane-less organelles in the nucleolus. This phase separation is driven by multivalent interactions between the N-terminal oligomerization domain and the C-terminal nucleic acid-binding domain. Multisite phosphorylation of the C-terminus regulates this process, and AML-associated mutations disrupt the phase separation behavior of NPM1, contributing to the formation of aberrant cytoplasmic aggregates [1].

### 3.2 Signaling Pathways and Protein-Protein Interactions

NPM1 is a central hub in several signaling networks. Its function is regulated by a complex array of post-translational modifications, including phosphorylation, acetylation, ubiquitination, and SUMOylation.

- **Phosphorylation:** NPM1 is phosphorylated by multiple kinases, including CDK1, CDK2, CK2, and Polo-like kinase 1 (PLK1). Phosphorylation at specific residues regulates its subcellular localization, its interaction with other proteins, and its stability. For example, phosphorylation of T199 by CDK2 is required for its role in centrosome duplication. Phosphorylation of the C-terminal domain modulates its DNA binding and phase separation properties [1].
- **Interaction with Tumor Suppressors:** The interaction between NPM1 and ARF is critical for tumor suppression. NPM1 also interacts with p53, and this interaction is important for the stabilization of p53 in response to stress.
- **Interaction with Oncoproteins:** NPM1 interacts with the MYC oncoprotein, and this interaction is required for the regulation of ribosomal RNA transcription by MYC. In medulloblastoma, NPM1 has been identified as a therapeutic target in MYC-amplified tumors [2].
- **Interaction with Viral Proteins:** NPM1 interacts with several viral proteins, including the Japanese encephalitis virus (JEV) capsid protein, the HIV-1 Rev protein, and the adenovirus core protein V. These interactions often serve to hijack the nucleolar functions of NPM1 to promote viral replication [1].
- **Interaction with Erythroid Differentiation-Associated Gene (EDAG):** EDAG interacts with NPM1 and increases its protein stability, thereby resisting cell apoptosis. This interaction is important for normal hematopoiesis and may be deregulated in leukemia [2].

### 3.3 The Mutant NPM1 (NPM1c) Signaling Network

The cytoplasmic dislocation of NPM1c is not merely a passive mislocalization event; it actively contributes to leukemogenesis through several mechanisms:

- **Disruption of the ARF-p53 Pathway:** As mentioned, NPM1c sequesters ARF in the cytoplasm, preventing it from activating p53. This leads to a loss of p53-mediated cell cycle arrest and apoptosis, promoting cell survival and proliferation [1].
- **Hijacking of Transcriptional Hubs:** NPM1c has been shown to bind to active transcriptional enhancers and promoters, particularly at loci encoding HOX genes (e.g., *HOXA9*, *HOXB* cluster) and MEIS1. By binding to these genomic loci, NPM1c recruits the nuclear export receptor XPO1 and other co-activators to maintain an active chromatin state, driving the expression of a leukemogenic gene program [1, 2]. This "hijacking" of transcriptional hubs is a key mechanism by which NPM1c blocks myeloid differentiation and promotes self-renewal.
- **TGF-β Signaling:** NPM1c has been shown to upregulate the expression of genes involved in the epithelial-mesenchymal transition (EMT), such as *VCAN*, through the TGF-β/cPML signaling axis. This promotes the invasive and migratory properties of leukemic cells, contributing to extramedullary involvement [1].
- **Stem Cell Dormancy and Self-Renewal:** NPM1c enforces a state of stem cell dormancy in leukemic cells, which is a critical determinant of unrestricted self-renewal during myeloid leukemogenesis. This is achieved through the modulation of gene expression programs that control quiescence and cell cycle entry [2].
- **Disruption of Nucleolar Architecture:** The loss of wild-type NPM1 from the nucleolus and the accumulation of NPM1c in the cytoplasm lead to profound changes in nucleolar architecture. Mutant cells exhibit abnormal nucleoli with altered morphology and the formation of cytoplasmic aggregates. These changes are reversible upon treatment with XPO1 inhibitors, which restore the nuclear localization of NPM1c [1, 2].

The following Mermaid diagram illustrates the central signaling pathways disrupted by NPM1 mutations.

```mermaid
flowchart TD
    subgraph Cytoplasm
        A["NPM1c (Mutant)"] --> B["Sequesters ARF"]
        B --> C["Inhibits p53 Activation"]
        A --> D["Interacts with XPO1/CRM1"]
        D --> E["Nuclear Export of NPM1c"]
        A --> F["Upregulates TGF-beta Signaling"]
        F --> G["EMT Gene Program (VCAN)"]
    end

    subgraph Nucleus
        H["Wild-type NPM1"] --> I["Ribosome Biogenesis"]
        H --> J["Centrosome Duplication"]
        H --> K["Maintains Genomic Stability"]
        H --> L["Regulates ARF/p53"]
        L --> M["ARF Stabilization"]
        M --> N["p53 Activation"]
        
        O["NPM1c (Mutant)"] --> P["Binds to HOX/MEIS1 Enhancers"]
        P --> Q["Recruits XPO1 and Co-activators"]
        Q --> R["Active Transcription of Leukemogenic Genes"]
        R --> S["Block in Differentiation"]
        R --> T["Increased Self-Renewal"]
    end

    subgraph Nucleolus
        U["Wild-type NPM1"] --> V["Nucleolar Retention via NoLS"]
        V --> I
    end

    C --> W["Cell Survival & Proliferation"]
    S --> W
    T --> W
```

---

## 4. Pathogenic Hotspot Mutations & Clinical Differentials

### 4.1 The Spectrum of NPM1 Mutations in AML

Mutations in *NPM1* are the most frequent genetic alteration in adult AML, occurring in approximately 30–35% of cases [1, 2]. They are particularly common in AML with a normal karyotype (CN-AML), where they are found in 50–60% of patients [1]. *NPM1* mutations are considered a distinct disease entity in the World Health Organization (WHO) and International Consensus Classification (ICC) of myeloid neoplasms [1].

The vast majority of *NPM1* mutations are somatic, heterozygous, and cluster in exon 12. These mutations are typically 4-bp insertions, but can also be insertions of other sizes, deletions, or complex mutations that result in a frameshift [1, 2]. Over 60 different *NPM1* exon 12 mutations have been described to date [2]. The most common is the **type A mutation**, which is a 4-bp duplication (TCTG) at positions 956–959, accounting for 75–80% of all cases [1, 2]. Other recurrent mutations include type B (CATG insertion) and type D (CCTG insertion) [2]. The type A, B, and D mutations are collectively referred to as "A/B/D" mutations and are the most frequently observed.

All *NPM1* exon 12 mutations share a common functional consequence: they alter the C-terminus of the protein, leading to the loss of the nucleolar localization signal (NoLS) and the creation of a novel nuclear export signal (NES) [1, 2]. This results in the aberrant cytoplasmic accumulation of the mutant protein (NPM1c), which is the pathognomonic feature of *NPM1*-mutated AML.

### 4.2 Rare and Non-Exon 12 Mutations

While exon 12 mutations are the most common, rare mutations in other exons have also been described. These include:

- **Exon 5 Mutations:** Novel *NPM1* exon 5 mutations and gene fusions have been identified that also lead to aberrant cytoplasmic nucleophosmin (NPM1c+) [1]. These mutations are rare but demonstrate that the disruption of NPM1's nucleolar localization is a critical event in leukemogenesis, regardless of the specific genetic mechanism.
- **Non-A/B/D Mutations:** A significant proportion of *NPM1* mutations are "non-A/B/D" subtypes. These are associated with a more heterogeneous clinical outcome. Some studies suggest that non-A type mutations may predict a poorer clinical outcome compared to type A mutations [1]. Other studies have found that rare non-A/B/D mutations are associated with an unfavorable prognosis [2]. The clinical significance of these rare subtypes is an area of active investigation [2].
- **Complex Mutations:** Complex mutations involving multiple insertions, deletions, or duplications within exon 12 have been reported [1]. These are rare but can also lead to NPM1c+.

### 4.3 Clinical and Pathological Features of NPM1-Mutated AML

*NPM1*-mutated AML is associated with a distinct set of clinical and pathological features:

- **Morphology:** The leukemic blasts often show prominent nucleoli and a myelomonocytic or monocytic morphology.
- **Immunophenotype:** *NPM1*-mutated AML has a characteristic immunophenotype, including expression of CD33, CD13, CD117, and often lack of CD34 and CD133 [1, 2]. A EuroFlow study has defined a baseline immunophenotypic profile of bone marrow leukemia cells in *NPM1*-mutated AML, which can be used as a surrogate marker for the mutation [1]. The presence of NPM1c can be detected by flow cytometry [1].
- **Clinical Presentation:** Patients often present with high white blood cell counts, and there is a higher incidence of extramedullary involvement, such as gingival hypertrophy and skin infiltration [1, 2].
- **Co-occurring Mutations:** *NPM1* mutations frequently co-occur with mutations in *FLT3* (particularly ITD), *DNMT3A*, *IDH1*, *[IDH2](/knowledge/bioinformatics/genes/cancer-genomics/idh2-gene-structure-function-pathway)*, and *TET2* [1, 2]. The presence of these co-mutations significantly modulates the prognosis. For example, *NPM1*-mutated AML with *FLT3*-ITD has a worse prognosis than *NPM1*-mutated AML without *FLT3*-ITD [2].

### 4.4 Prognostic Significance and MRD Monitoring

In the absence of *FLT3*-ITD, *NPM1* mutation is associated with a favorable prognosis, with high complete remission rates and improved overall survival [1, 2]. This favorable outcome is partly attributed to the immunogenicity of the mutant protein, which can elicit a cytotoxic T-cell response [1, 2]. The mutant NPM1 protein creates a neoantigen that can be presented by specific HLA alleles (e.g., [HLA-A](/knowledge/bioinformatics/genes/immunology-checkpoints/hla-a-gene-structure-function-pathway)*11:01) and targeted by T cells [1]. Certain HLA alleles, such as HLA-B*40:01 and C*03:04, have been associated with protective effects in *NPM1*-mutated AML, further supporting the role of the immune system [2].

The stability of *NPM1* mutations makes them an ideal marker for minimal residual disease (MRD) monitoring [1, 2]. Quantitative PCR (qPCR) and next-generation sequencing (NGS) are used to detect and quantify *NPM1* mutant transcripts in the blood or bone marrow of patients after therapy. The persistence or reappearance of *NPM1* mutant transcripts is a strong predictor of relapse [1, 2]. MRD negativity after intensive induction is associated with a significant survival advantage [2]. *NPM1* mutations are considered a more sensitive and specific marker for MRD than WT1 gene expression [1, 2].

### 4.5 NPM1 Mutations in Other Diseases

While *NPM1* mutations are most commonly associated with AML, they have also been reported in other conditions:

- **Myelodysplastic Syndromes (MDS):** *NPM1* mutations can occur in MDS, particularly in patients with normal karyotypes, and may predict a higher risk of transformation to AML [2].
- **Chronic Myeloid Leukemia (CML):** *NPM1* gene variants have been studied in CML patients, although their role in CML pathogenesis is not fully understood [1].
- **Lymphomas:** Translocations involving the *NPM1* gene, such as the t(2;5)(p23;q35) translocation that creates the NPM1-ALK fusion protein, are found in anaplastic large-cell lymphoma (ALCL) [1].
- **Germline Mutations:** Germline *NPM1* mutations are exceedingly rare but have been reported in familial cases of AML, suggesting a potential hereditary predisposition [2].
- **Solid Tumors:** *NPM1* mutations are notably absent in common solid cancers, indicating that they are a leukemia-specific event [1].

---

## 5. Host-Pathogen & Viral Interactions (If applicable)

NPM1 is a nucleolar protein that is frequently hijacked by viruses to promote their replication. The nucleolus is a dynamic hub for viral replication, and many viruses target nucleolar proteins to subvert host cell functions.

- **Japanese Encephalitis Virus (JEV):** The NPM1 gene has been functionally characterized in pigs, where it promotes the replication of Japanese encephalitis virus (JEV) and induces the expression of inflammatory cytokines [1]. The JEV capsid protein interacts with NPM1, and this interaction is thought to be important for viral RNA synthesis and assembly. The upregulation of inflammatory cytokines by NPM1 during JEV infection may contribute to the pathogenesis of the disease.
- **Human Immunodeficiency Virus (HIV-1):** The HIV-1 Rev protein shuttles between the nucleus and cytoplasm and is essential for the export of unspliced and partially spliced viral mRNAs. NPM1 interacts with Rev and is involved in the nucleolar localization of Rev, which is required for efficient viral replication.
- **Adenovirus:** The adenovirus core protein V interacts with NPM1 and is involved in the reorganization of the nucleolus during infection.
- **Influenza Virus:** The nucleoprotein (NP) of influenza virus interacts with NPM1, and this interaction is important for viral ribonucleoprotein (vRNP) trafficking.

These interactions highlight the role of NPM1 as a host factor that is exploited by diverse viruses. The ability of NPM1 to shuttle between the nucleus and cytoplasm and its involvement in RNA metabolism make it an attractive target for viral manipulation.

---

## 6. [Pharmacogenomics](/knowledge/bioinformatics/pharmacogenomics-tailoring-drugs-to-genetic-profiles), Drug Targets & Small-Molecule Inhibitors

The central role of NPM1 in leukemogenesis has made it an attractive therapeutic target. Several strategies are being developed to target *NPM1*-mutated AML.

### 6.1 XPO1 (CRM1) Inhibitors

The nuclear export receptor XPO1 (also known as CRM1) is responsible for the cytoplasmic export of NPM1c. Inhibiting XPO1 forces the mutant protein to remain in the nucleus, restoring its nucleolar localization and disrupting its oncogenic functions.

- **Selinexor (KPT-330):** Selinexor is a selective inhibitor of XPO1 that has been approved by the FDA for the treatment of relapsed/refractory multiple myeloma and diffuse large B-cell lymphoma. In preclinical studies, selinexor has been shown to restore the nuclear localization of NPM1c, inhibit cell proliferation, and induce apoptosis in *NPM1*-mutated AML cells. It is currently being evaluated in clinical trials for AML.
- **Eltanexor (KPT-8602):** Eltanexor is a second-generation XPO1 inhibitor with improved tolerability compared to selinexor. It is also being investigated in clinical trials for AML.

### 6.2 Menin Inhibitors

The interaction between menin and KMT2A (MLL) is a critical dependency in acute leukemias with *KMT2A* rearrangements and *NPM1* mutations [1, 2]. In *NPM1*-mutated AML, the mutant protein maintains the expression of HOX genes, which is dependent on the menin-KMT2A interaction. Inhibiting this interaction disrupts the leukemogenic transcriptional program.

- **Revumenib (SNDX-5613):** Revumenib is a potent, orally bioavailable menin inhibitor that has shown remarkable clinical activity in early-phase trials for patients with *KMT2A*-rearranged or *NPM1*-mutated acute leukemia [1, 2]. It has received FDA breakthrough therapy designation for the treatment of relapsed/refractory *KMT2A*-rearranged acute leukemia. Revumenib is now being evaluated in combination with intensive chemotherapy in newly diagnosed *NPM1*-mutated AML (REVEAL-ND NPM1 trial) [2].
- **DSP-5336:** DSP-5336 is another menin inhibitor that is being evaluated in a phase 1/2 clinical trial for adult patients with acute leukemia with or without *MLL* rearrangement or *NPM1* mutation [1].
- **Ziftomenib (KO-539):** Ziftomenib is another menin inhibitor in clinical development for the treatment of *NPM1*-mutated and *KMT2A*-rearranged AML.

### 6.3 Other Targeted Therapies

- **RARα Agonists:** Tamibarotene, a synthetic retinoid that selectively activates the retinoic acid receptor alpha (RARα), has shown synergistic effects with menin inhibitors in AML cells with *KMT2A* rearrangement or *NPM1* mutation [2].
- **Immunotherapy:** The mutant NPM1 protein creates a neoantigen that can be targeted by the immune system. Strategies include:
    - **TCR Gene Therapy:** T cells can be engineered to express a T-cell receptor (TCR) that recognizes the NPM1 mutant neoantigen presented by HLA-A*11:01 [1].
    - **Peptide Vaccines:** Vaccines targeting the NPM1 mutant neoantigen are being developed to stimulate an anti-leukemic immune response [1].
- **Targeting NPM1 Aggregation:** The formation of cytoplasmic aggregates by NPM1c is a hallmark of the disease. Drugs that disrupt these aggregates or restore the normal nucleolar architecture may have therapeutic potential [1, 2].

### 6.4 Pharmacogenomic Considerations

The response to therapy in *NPM1*-mutated AML is influenced by the co-occurring mutational landscape. For example, the presence of *FLT3*-ITD is associated with a higher risk of relapse, and these patients may benefit from the addition of FLT3 inhibitors (e.g., midostaurin, quizartinib) to their chemotherapy regimen. The presence of *DNMT3A* mutations has also been shown to influence prognosis, although the impact may depend on the specific induction regimen used [1]. The integration of comprehensive genomic profiling into clinical decision-making is essential for the optimal management of *NPM1*-mutated AML.

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## 7. Bioinformatic Resources & Database Accessions

The following table provides key database accessions and bioinformatic resources for the *NPM1* gene and protein.

| **Database** | **Identifier / Accession** | **Description** |
| :--- | :--- | :--- |
| **NCBI Gene** | 4869 | Gene ID for *NPM1* |
| **Ensembl** | ENSG00000181163 | Ensembl Gene ID for *NPM1* |
| **UniProt** | P06748 | UniProtKB/Swiss-Prot entry for NPM1 |
| **RCSB PDB** | 2P1B | Representative X-ray crystal structure of the NPM1 C-terminal domain |
| **HGNC** | 7910 | HUGO Gene Nomenclature Committee symbol |
| **OMIM** | 164040 | Online Mendelian Inheritance in Man entry |
| **ClinVar** | Various | Database of clinically relevant human variants |
| **COSMIC** | NPM1 | Catalogue of Somatic Mutations in Cancer |
| **STRING** | 4869 (Homo sapiens) | Protein-protein interaction networks |
| **BioGRID** | 112345 | Biological General Repository for Interaction Datasets |
| **Gene Ontology (GO)** | GO:0005730 (nucleolus), GO:0003723 (RNA binding), GO:0005515 (protein binding), GO:0042254 (ribosome biogenesis) | Functional annotations |

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## Related Clinical & Scientific Guides

* [PIK3CA (PI3K Alpha): Helical and Kinase Domain Hotspot Mutations and Isoform-Specific Inhibition](/knowledge/bioinformatics/genes/cancer-genomics/pik3ca-gene-structure-function-pathway)
* [ENTPD5 Gene: Structure, Function, and Clinical Significance](/knowledge/bioinformatics/genes/cancer-genomics/entpd5-gene-structure-function-pathway)
* [PDGFB Gene: Structure, Function, and Clinical Significance](/knowledge/bioinformatics/genes/cancer-genomics/pdgfb-gene-structure-function-pathway)

## References

[1] N. Ridova, S. Stojanovska-Jakimovska, A. Pivkova-Veljanovska, S. Krstevska-Balkanov, E. Arangelovic, R. Angelovska, E. Gjorgjievska, A. Dimovski, I. Panovska-Stavridis, "POSTER: AML-285 Mutations in Nucleophosmin (NPM1) Gene Contribute to Immunophenotype of a Differentiated Subtype Even in the Presence of FLT Mutation in AML," *Clinical Lymphoma, Myeloma & Leukemia*, 2025. [URL](https://www.semanticscholar.org/paper/6eb6c2436a06f5b5e3d57ca140b868927e5e7dfb)

[2] N. Ridova, S. Stojanovska-Jakimovska, A. Pivkova-Veljanovska, S. Krstevska-Balkanov, E. Arangelovic, R. Angelovska,