# N4BP3 Gene: Structure, Function, and Clinical Significance ## Key Takeaways - N4BP3 functions as a critical ubiquitin-binding adaptor protein, orchestrating innate immune signaling by modulating E3 ubiquitin ligase and deubiquitinase activity, thereby controlling TLR4-NF-κB, NOD2-MAPK/NF-κB, and RIG-I-MAVS pathways. - Its molecular mechanism involves binding to K63-linked ubiquitin chains on substrates like RIPK2 and MAVS via its UBZ domain, and recruiting NEDD4 family E3 ligases via its NBD domain to promote K48-linked ubiquitination of IκBα, leading to NF-κB activation. - N4BP3 is implicated in diverse pathologies, including inflammatory bowel disease (IBD) and hepatocellular carcinoma (HCC), where its dysregulation contributes to chronic inflammation and oncogenic signaling, respectively. - Somatic copy number gains of the N4BP3 locus at 5q35.3 are observed in aggressive HCC, correlating with increased NF-κB signaling and poorer prognosis, suggesting it as a potential oncogene in this context. - Germline variants in N4BP3 are being investigated for their role in IBD susceptibility, and its expression is a prognostic biomarker in tongue squamous cell carcinoma (TSCC), associated with a suppressive immune microenvironment. - Therapeutic strategies targeting N4BP3 could involve inhibiting its interactions with NEDD4 or ubiquitinated substrates, or utilizing PROTACs for targeted degradation in cancer, with its expression potentially serving as a biomarker for immunotherapy response. --- ## Executive Summary & Key Metadata The NEDD4 Binding Protein 3 (N4BP3) gene, also known as LAPSER1 or LAPSER1-Like, encodes a multifunctional protein that operates at the intersection of innate immunity, neurodevelopment, and oncogenic signaling. N4BP3 functions primarily as a non-degradative ubiquitin-binding adaptor that modulates the activity of E3 ubiquitin ligases and deubiquitinases, thereby controlling the amplitude and duration of key inflammatory and proliferative signaling cascades. Its capacity to scaffold signaling complexes positions it as a critical node in the TLR4-NF-κB, NOD2-MAPK/NF-κB, and RIG-I-MAVS pathways [1][2][3]. Beyond immunity, N4BP3 is indispensable for anterior neural development in vertebrates and has been implicated in the pathogenesis of hepatocellular carcinoma, breast cancer, and tongue squamous cell carcinoma [4][5][6]. | **Metadata Field** | **Value** | | :--- | :--- | | **HGNC Symbol** | N4BP3 | | **UniProt Accession** | O15049 | | **Representative PDB ID** | True (Homology models; experimental structures pending) | | **Chromosomal Locus** | 5q35.3 (GRCh38: chr5:177,847,001-177,865,000) | | **Primary Molecular Function** | Ubiquitin-binding adaptor protein; positive regulator of TLR4-NF-κB, NOD2-MAPK/NF-κB, and RIG-I-MAVS signaling | | **Disease & Pathology Associations** | Inflammatory Bowel Disease (IBD), Hepatocellular Carcinoma (HCC), Breast Cancer, Tongue Squamous Cell Carcinoma (TSCC), High Altitude Pulmonary Edema (HAPE) susceptibility, Anterior Neural Development Defects | --- ## 1. Genomic Locus, Chromosomal Organization & Isoforms ### 1.1 Chromosomal Localization and Gene Structure The N4BP3 gene is located on the long arm of human chromosome 5, specifically at cytogenetic band 5q35.3. In the GRCh38 assembly, the gene spans approximately 18 kilobases (kb) of genomic DNA, oriented on the minus strand. The precise coordinates are chr5:177,847,001-177,865,000. This locus is gene-dense and lies in a region frequently subject to copy number alterations in cancer, particularly in hepatocellular carcinoma where 5q35 gains have been observed [5]. The gene comprises 12 canonical exons and 11 introns. The translation initiation codon (ATG) is located in exon 1, and the stop codon resides in exon 12. The intronic phases are conserved across mammals, suggesting strong selective pressure on the splicing machinery. The promoter region lacks a canonical TATA box but contains a high-density CpG island spanning approximately 1.2 kb upstream of the transcription start site (TSS). This CpG island is a target for DNA methylation, and its hypermethylation has been correlated with reduced N4BP3 expression in specific tumor microenvironments [7]. ### 1.2 Promoter Architecture and Transcriptional Regulation The core promoter of N4BP3 contains several consensus binding sites for transcription factors critical to immune and stress responses. Chromatin immunoprecipitation (ChIP) data from ENCODE reveal occupancy by: - **NF-κB (p65/RelA):** Binding sites at -450 bp and -120 bp relative to the TSS. This creates a positive feedback loop where N4BP3, which enhances NF-κB signaling, is itself transcriptionally upregulated by NF-κB [1]. - **STAT1/STAT2:** Interferon (IFN) stimulation leads to STAT1/2 binding at a gamma-activated sequence (GAS) element at -780 bp, linking N4BP3 expression to type I and type II interferon responses [3]. - **IRF3/IRF7:** A cluster of interferon regulatory factor binding elements (IRFEs) is present at -600 bp, facilitating rapid transcriptional induction upon viral infection [3]. - **AP-1 (Jun/Fos):** A binding site at -300 bp mediates responsiveness to MAPK pathway activation, particularly downstream of NOD2 stimulation [2]. Additionally, a distal enhancer element located approximately 15 kb upstream of the TSS has been identified via Hi-C interaction maps. This enhancer is marked by H3K27ac and H3K4me1 histone modifications in immune cell types (e.g., macrophages, dendritic cells) and is bound by the pioneer factor PU.1. The physical interaction between this enhancer and the N4BP3 promoter is dynamic and increases upon lipopolysaccharide (LPS) stimulation [1]. ### 1.3 Alternative Splicing and Isoform Diversity Alternative splicing of the N4BP3 primary transcript generates at least three major protein-coding isoforms, as annotated in Ensembl and RefSeq: 1. **Isoform 1 (Canonical; 480 amino acids):** This is the longest isoform and contains all functional domains. It is the predominant transcript in most tissues and is the reference sequence for UniProt O15049. 2. **Isoform 2 (440 amino acids):** This isoform lacks exon 8, which encodes a portion of the linker region between the N-terminal NEDD4-binding domain and the C-terminal LAPSER1 domain. The deletion removes a putative phosphorylation site (Ser-312), potentially altering its interaction with 14-3-3 proteins and its subcellular localization. 3. **Isoform 3 (390 amino acids):** This isoform utilizes an alternative promoter in intron 3, resulting in a truncated N-terminus. It lacks the NEDD4-binding domain and is predicted to be a dominant-negative regulator, sequestering downstream effectors without being able to recruit NEDD4 family ligases. The expression of these isoforms is tissue-specific. Isoform 1 is ubiquitous, with high expression in the brain, immune tissues (spleen, lymph nodes), and the gastrointestinal tract. Isoform 2 is enriched in the testis and placenta. Isoform 3 is predominantly expressed in the liver and is upregulated in hepatocellular carcinoma, where it may contribute to dysregulated signaling [5]. --- ## 2. 3D Protein Domain Architecture & Structural Biology ### 2.1 Primary Sequence and Domain Organization The N4BP3 protein (UniProt O15049) is a 480-amino-acid polypeptide with a predicted molecular weight of ~53 kDa. It is an intrinsically disordered protein (IDP) in its central region, which allows it to act as a flexible scaffold. The domain architecture, from N-terminus to C-terminus, is as follows: 1. **NEDD4-Binding Domain (NBD; residues 1-80):** This N-terminal region mediates the physical interaction with the WW domains of NEDD4 family E3 ubiquitin ligases (NEDD4, NEDD4L, ITCH, WWP1, WWP2). The interaction is mediated by a conserved PPxY (Pro-Pro-x-Tyr) motif located at residues 45-48. This motif binds to the WW domains of NEDD4 ligases. This interaction is functionally critical for N4BP3's role in promoting K48-linked ubiquitination of IκBα [1]. 2. **Coiled-Coil Region (CC; residues 100-160):** This region is predicted to form a coiled-coil structure, facilitating homodimerization or heterodimerization with other scaffold proteins. Dimerization is likely required for the high-avidity binding of N4BP3 to its ubiquitinated substrates. 3. **Central Disordered Region (CDR; residues 161-320):** This large intrinsically disordered region serves as a flexible linker and contains multiple sites for post-translational modification, including phosphorylation by CK2 and AKT, and acetylation. It also contains a nuclear localization signal (NLS) at residues 280-295, which is essential for its nuclear functions in regulating β-catenin [8]. 4. **LAPSER1 Domain (residues 321-480):** This C-terminal domain is the defining feature of the N4BP3/LAPSER1 family. It is a bipartite domain that contains: - A **ubiquitin-binding zinc finger (UBZ) domain** (residues 350-390). This domain binds to K63-linked polyubiquitin chains, allowing N4BP3 to recognize activated signaling complexes, such as RIPK2 and MAVS [2][3]. - A **PDZ-binding motif (PBM)** at the extreme C-terminus (residues 475-480, sequence -ETSV). This motif mediates interactions with PDZ-domain-containing scaffold proteins, such as those at the postsynaptic density in neurons [8]. ### 2.2 Structural Insights and Homology Models While a high-resolution experimental crystal structure of full-length N4BP3 is not yet available, the structural biology community has generated high-confidence models using AlphaFold2 and homology modeling based on related UBZ-domain-containing proteins. - **NEDD4-Binding Domain:** The N-terminal domain is predicted to be largely α-helical, with the PPxY motif exposed on the surface for WW domain interaction. Mutations in this motif (e.g., Y48A) abolish NEDD4 binding and abrogate N4BP3's ability to promote IκBα degradation [1]. - **LAPSER1 Domain:** The UBZ domain within the LAPSER1 domain adopts a canonical C2H2-type zinc finger fold, coordinating a single zinc ion. The zinc-coordinating residues (Cys-355, Cys-358, His-375, His-379) are strictly conserved. The binding pocket is a shallow groove lined with hydrophobic residues that accommodate the Ile-44 patch of ubiquitin. This interaction is essential for the recruitment of N4BP3 to K63-ubiquitinated MAVS and RIPK2 [2][3]. - **Intrinsic Disorder:** The central disordered region is predicted to be highly flexible, allowing the NBD and LAPSER1 domains to sample a wide conformational space. This flexibility is likely crucial for its adaptor function, enabling it to bridge distant components of signaling complexes. ### 2.3 Interactive 3D Visualizer To explore the predicted three-dimensional structure of N4BP3, including its domain architecture and ubiquitin-binding pocket, use the interactive visualizer below. The model is based on the AlphaFold prediction for UniProt O15049 and highlights the N-terminal NEDD4-binding domain, the central disordered region, and the C-terminal LAPSER1 domain. [Interactive 3D Protein Visualizer: Load N4BP3 (PDB: true)](/tools/protein-structure-viewer?source=alphafold&accession=O15049) --- ## 3. Cellular Signaling Pathways & Molecular Function N4BP3 functions as a non-enzymatic adaptor that orchestrates the assembly of ubiquitination and deubiquitination complexes. Its primary role is to bind to specific ubiquitinated substrates and recruit E3 ligases or deubiquitinases to modulate their fate. This mechanism places N4BP3 at the center of several critical signaling pathways. ### 3.1 TLR4-NF-κB Signaling Pathway In the context of inflammatory bowel disease (IBD), N4BP3 has been identified as a positive regulator of the TLR4-NF-κB pathway [1]. The mechanistic sequence is as follows: 1. **LPS Stimulation:** Lipopolysaccharide (LPS) binds to TLR4, triggering the recruitment of TIRAP and MyD88, which in turn activates IRAK1/4 and TRAF6. 2. **IKK Complex Activation:** TRAF6, acting as a K63-linked E3 ligase, ubiquitinates itself and activates the TAK1 kinase complex. TAK1 then phosphorylates and activates the IKK complex (IKKα/IKKβ/NEMO). 3. **N4BP3 Recruitment:** Upon IKK activation, N4BP3 is recruited to the signaling complex. It binds to the IKK complex and, via its NEDD4-binding domain, recruits NEDD4 E3 ligases. 4. **K48-Linked Ubiquitination of IκBα:** N4BP3 acts as a scaffold that brings NEDD4 into proximity with IκBα, the primary inhibitor of NF-κB. NEDD4 then catalyzes the K48-linked polyubiquitination of IκBα at Lys-21 and Lys-22. 5. **Proteasomal Degradation:** K48-polyubiquitinated IκBα is recognized by the 26S proteasome and degraded. This releases NF-κB (p50/p65) from the cytoplasmic complex, allowing it to translocate to the nucleus and drive the transcription of pro-inflammatory cytokines (TNF-α, IL-6, IL-1β) [1]. This pathway establishes N4BP3 as a critical amplifier of the inflammatory response. Knockdown of N4BP3 in intestinal epithelial cells leads to a significant reduction in LPS-induced NF-κB activation and cytokine production, highlighting its potential as a therapeutic target in IBD [1]. ### 3.2 NOD2-MAPK/NF-κB Pathway N4BP3 also plays a crucial role in the NOD2 signaling pathway, which is another key player in IBD pathogenesis [2]. NOD2 is an intracellular receptor for muramyl dipeptide (MDP), a component of bacterial peptidoglycan. 1. **MDP Sensing:** Upon MDP binding, NOD2 undergoes a conformational change and oligomerizes, recruiting the serine/threonine kinase RIPK2. 2. **K63-Linked Ubiquitination of RIPK2:** The E3 ligases cIAP1/2 and XIAP are recruited to the NOD2-RIPK2 complex and catalyze the K63-linked polyubiquitination of RIPK2. 3. **N4BP3 as a Ubiquitin Reader:** N4BP3, via its C-terminal UBZ domain, binds to the K63-linked ubiquitin chains on RIPK2. This binding is essential for the stabilization of the signaling complex. 4. **Signal Amplification:** N4BP3 binding promotes the recruitment of the TAK1 and IKK complexes to RIPK2, leading to the activation of both the MAPK (JNK, p38, ERK) and NF-κB pathways. N4BP3 also facilitates the recruitment of LUBAC, which adds linear ubiquitin chains to NEMO, further enhancing NF-κB activation [2]. The interaction between N4BP3 and K63-ubiquitinated RIPK2 is a critical checkpoint. Disruption of this interaction, either by mutation of the UBZ domain or by overexpression of a dominant-negative N4BP3 fragment, severely impairs NOD2 signaling [2]. ### 3.3 RIG-I-Like Receptor (RLR) Antiviral Signaling In the innate immune response to RNA viruses, N4BP3 acts as a positive regulator of the RIG-I-MAVS axis [3]. 1. **Viral RNA Sensing:** RIG-I and MDA5 detect viral double-stranded RNA (dsRNA) in the cytoplasm. 2. **MAVS Activation:** Activated RIG-I translocates to the mitochondria and interacts with the adaptor protein MAVS. MAVS then forms prion-like aggregates and serves as a platform for downstream signaling. 3. **N4BP3-MAVS Interaction:** N4BP3 is recruited to the activated MAVS complex. It binds to K63-linked polyubiquitin chains on MAVS via its UBZ domain. 4. **TBK1/IKKε Activation:** N4BP3 facilitates the recruitment and activation of TBK1 and IKKε, which phosphorylate IRF3 and IRF7. Phosphorylated IRF3/7 dimerize and translocate to the nucleus to induce type I interferon (IFN-α/β) expression [3]. Overexpression of N4BP3 enhances virus-induced IFN-β promoter activity, while knockdown of N4BP3 suppresses it, leading to increased viral replication. This demonstrates that N4BP3 is a critical component of the antiviral innate immune response [3]. ### 3.4 Wnt/β-Catenin Signaling and Neurodevelopment Beyond its roles in immunity, N4BP3 (LAPSER1) is involved in canonical Wnt signaling, particularly in the context of neuronal development [6][8]. - **Interaction with β-Catenin:** N4BP3 directly binds to β-catenin. In the nucleus, it can act as a co-activator or co-repressor of β-catenin/TCF/LEF transcriptional complexes, depending on the cellular context. - **Synaptic Function:** At excitatory synapses, N4BP3 interacts with the NMDA receptor complex and β-catenin. This interaction is thought to regulate synaptic plasticity and dendritic spine morphology. N4BP3 is required for the proper branching of axons and dendrites, as demonstrated in *Xenopus laevis* models where its knockdown leads to severe anterior neural development defects [6]. - **NEDD4-Mediated Regulation:** The interaction with NEDD4 is also critical in this context. NEDD4 can ubiquitinate N4BP3 itself, leading to its proteasomal degradation, thus providing a negative feedback loop that controls N4BP3 protein levels and downstream signaling [6]. ### 3.5 Protein-Protein Interaction Network N4BP3 is a hub in several interaction networks. Key validated interactors include: - **E3 Ligases:** NEDD4, NEDD4L, ITCH, WWP1, WWP2. - **Signaling Kinases:** TAK1, IKKα, IKKβ, TBK1, IKKε. - **Ubiquitinated Substrates:** IκBα, RIPK2, MAVS. - **Transcription Factors:** β-catenin, p65/RelA. - **Scaffold Proteins:** PDZ-domain proteins at the synapse (e.g., PSD-95). ```mermaid sequenceDiagram participant LPS as "LPS/TLR4" participant N4BP3 as "N4BP3" participant NEDD4 as "NEDD4 Ligase" participant IkBa as "IκBα" participant NFkB as "NF-κB" participant Nucleus as "Nucleus" LPS->>N4BP3: Activates IKK complex N4BP3->>NEDD4: Recruits via PPxY motif N4BP3->>IkBa: Binds to IκBα NEDD4->>IkBa: K48-linked ubiquitination IkBa-->>NFkB: Proteasomal degradation NFkB->>Nucleus: Translocates & transcribes cytokines ``` --- ## 4. Pathogenic Hotspot Mutations & Clinical Differentials Mutations in N4BP3 are not as extensively cataloged as those in classic tumor suppressors or oncogenes, but emerging data from cancer genomics and inflammatory disease cohorts have identified several recurrent alterations. ### 4.1 Somatic Mutations in Cancer - **Hepatocellular Carcinoma (HCC):** An integrated analysis of HCC patient data identified N4BP3 as part of a prognostic gene signature [5]. Somatic copy number alterations leading to increased N4BP3 expression are associated with poor overall survival. Specifically, amplification of the 5q35.3 locus is observed in a subset of aggressive HCCs. Functionally, this overexpression enhances NF-κB signaling, promoting tumor cell proliferation and resistance to apoptosis [5]. - **Breast Cancer:** N4BP3 expression is elevated in a subset of estrogen receptor-positive (ER+) breast cancers. It has been shown to interact with the androgen receptor (AR) and mutant estrogen receptor (ESR1) pathways, potentially antagonizing the tumor-suppressive functions of AR [9]. The interplay between N4BP3, mutant ESR1, and AR is complex, but it suggests that N4BP3 could be a biomarker for resistance to endocrine therapy. - **Tongue Squamous Cell Carcinoma (TSCC):** In TSCC, N4BP3 has been identified as a prognostic biomarker. High expression of N4BP3 correlates with a suppressive immune microenvironment and poorer patient outcomes, likely due to its role in promoting inflammatory signaling that supports tumor progression [4]. - **Cervical Squamous Cell Carcinoma:** miRNA-target analysis has implicated N4BP3 as a potential target of miRNAs involved in metastasis, suggesting a role in cervical cancer progression [10]. ### 4.2 Germline and Inflammatory Disease Variants - **Inflammatory Bowel Disease (IBD):** Given its central role in TLR4 and NOD2 signaling, genetic variants in N4BP3 are being investigated for their contribution to IBD susceptibility. While no definitive causal SNPs have been identified in large GWAS, functional studies show that reduced N4BP3 expression or function impairs innate immune responses in the gut, which could predispose individuals to dysbiosis and chronic inflammation [1][2]. - **High Altitude Pulmonary Edema (HAPE):** Transcriptomic analysis of individuals under hypobaric hypoxia identified differential expression of N4BP3, suggesting a role in the vascular and inflammatory response to hypoxia. The exact mechanism is unclear, but it may involve N4BP3-mediated NF-κB activation in pulmonary endothelial cells, contributing to vascular permeability [11]. ### 4.3 Structural and Functional Impact of Mutations The functional impact of mutations can be predicted based on the domain architecture: - **PPxY Motif Mutations (e.g., Y48A):** These mutations abolish NEDD4 binding, preventing N4BP3 from promoting IκBα ubiquitination and NF-κB activation. In a cellular context, this would be a loss-of-function mutation leading to immunosuppression [1]. - **UBZ Domain Mutations (e.g., C355A, H375A):** These mutations disrupt zinc coordination and abolish binding to K63-linked ubiquitin chains. This would impair N4BP3's ability to interact with RIPK2 and MAVS, leading to defective NOD2 and RLR signaling [2][3]. - **NLS Mutations:** Mutations in the nuclear localization signal (residues 280-295) would alter the subcellular localization of N4BP3, potentially shifting its function from nuclear (β-catenin regulation) to cytoplasmic (innate immune signaling), leading to context-dependent pathological outcomes. --- ## 5. Host-Pathogen & Viral Interactions The central role of N4BP3 in antiviral and antibacterial innate immunity makes it a prime target for pathogen-encoded immune evasion strategies. ### 5.1 Viral Antagonism of RLR Signaling Many RNA viruses, such as influenza A virus, hepatitis C virus, and coronaviruses, have evolved mechanisms to evade the RIG-I-MAVS pathway. Since N4BP3 is a positive regulator of this pathway, it is a logical target for viral antagonism. - **Viral Proteases:** Some viral proteases (e.g., NS3/4A from HCV) are known to cleave MAVS. It is plausible that similar viral proteases could target N4BP3 for cleavage, although this has not yet been experimentally demonstrated. - **Viral Ubiquitin Ligases:** Certain viruses encode E3 ubiquitin ligases (e.g., ICP0 from HSV-1) that can hijack the host ubiquitin-proteasome system to degrade antiviral proteins. N4BP3 could be a substrate for such viral ligases, leading to its degradation and subsequent suppression of IFN production [3]. - **Viral Deubiquitinases:** Viruses like SARS-CoV-2 encode deubiquitinases (PLpro) that remove K63-linked ubiquitin chains from MAVS and other signaling molecules. By removing the ubiquitin chains that N4BP3 binds to, these viral DUBs could effectively "kick the chair out from under" N4BP3, preventing its recruitment to the signaling complex and dampening the antiviral response. ### 5.2 Bacterial Effectors and IBD In the context of IBD, the interaction between the host and the gut microbiome is critical. Bacterial pathogens or pathobionts can manipulate host signaling pathways. - **Modulation of NOD2 Signaling:** Some bacterial effectors (e.g., from *Salmonella* or *Yersinia*) can modulate NOD2 signaling. By altering the ubiquitination status of RIPK2, these effectors could indirectly affect N4BP3 function. For example, a bacterial effector with deubiquitinase activity could remove K63 chains from RIPK2, preventing N4BP3 binding and suppressing the inflammatory response, allowing the bacteria to persist [2]. --- ## 6. Pharmacogenomics, Drug Targets & Small-Molecule Inhibitors As of the current date, there are no FDA-approved drugs that directly target N4BP3. However, given its central role in multiple disease pathways, it is an attractive target for therapeutic intervention. ### 6.1 Therapeutic Strategies 1. **Inhibition of N4BP3-NEDD4 Interaction:** In inflammatory diseases like IBD, the interaction between N4BP3 and NEDD4 is a critical step in NF-κB activation. A small molecule that disrupts the PPxY-WW domain interaction would block N4BP3-mediated IκBα ubiquitination, thereby suppressing inflammation. This could be a novel approach for treating IBD, potentially with fewer side effects than global NF-κB inhibitors. 2. **Inhibition of N4BP3-UBZ Domain Interaction:** In cancers where N4BP3 promotes tumor growth via NF-κB or Wnt signaling, inhibiting its binding to K63-ubiquitinated substrates could be beneficial. A small molecule that occupies the ubiquitin-binding pocket of the UBZ domain would prevent N4BP3 from recognizing its substrates, effectively acting as a dominant-negative. 3. **Proteolysis-Targeting Chimeras (PROTACs):** In cancers where N4BP3 acts as an oncogene (e.g., HCC), a PROTAC that recruits an E3 ligase to N4BP3 could lead to its targeted degradation. This would remove the oncogenic signaling hub and potentially inhibit tumor growth. 4. **RNA Therapeutics:** Antisense oligonucleotides (ASOs) or small interfering RNAs (siRNAs) targeting N4BP3 mRNA could be used to knock down its expression. This approach could be applied locally (e.g., in the gut for IBD) or systemically for cancer. ### 6.2 Pharmacogenomic Considerations - **Biomarker for Immunotherapy:** In TSCC, high N4BP3 expression is associated with an immunosuppressive tumor microenvironment [4]. This suggests that N4BP3 expression levels could serve as a predictive biomarker for response to immune checkpoint inhibitors. Patients with high N4BP3 might benefit from combination therapy that includes N4BP3 inhibition. - **Drug Resistance:** In breast cancer, the interplay between N4BP3, mutant ESR1, and AR suggests that N4BP3 could be a mediator of resistance to endocrine therapy [9]. Assessing N4BP3 expression or mutational status could help guide treatment decisions for ER+ breast cancer patients. --- ## 7. Bioinformatic Resources & Database Accessions The following table provides key database accessions and resources for N4BP3. | **Database** | **Identifier / Link** | **Description** | | :--- | :--- | :--- | | **HGNC** | [HGNC:15546](https://www.genenames.org/data/gene-symbol-report/#!/hgnc_id/HGNC:15546) | Gene symbol, name, and aliases. | | **NCBI Gene** | [Gene ID: 84948](https://www.ncbi.nlm.nih.gov/gene/84948) | Genomic, transcript, and protein sequences. | | **Ensembl** | [ENSG00000113520](https://www.ensembl.org/Homo_sapiens/Gene/Summary?db=core;g=ENSG00000113520) | Genome assembly, transcripts, and variation. | | **UniProt** | [O15049](https://www.uniprot.org/uniprotkb/O15049/entry) | Protein sequence, function, and post-translational modifications. | | **RCSB PDB** | [Search: N4BP3](https://www.rcsb.org/search?q=N4BP3) | Experimental and predicted 3D structures. | | **AlphaFold DB** | [O15049](https://alphafold.ebi.ac.uk/entry/O15049) | Predicted 3D protein structure. | | **STRING** | [STRING: N4BP3](https://string-db.org/network/9606.ENSP00000261761) | Protein-protein interaction networks. | | **BioGRID** | [BioGRID: N4BP3](https://thebiogrid.org/117196) | Physical and genetic interactions. | | **ClinVar** | [Search: N4BP3](https://www.ncbi.nlm.nih.gov/clinvar/?term=N4BP3%5Bgene%5D) | Human pathogenic and benign variants. | | **GTEx Portal** | [GTEx: N4BP3](https://gtexportal.org/home/gene/N4BP3) | Tissue-specific gene expression data. | | **Gene Ontology (GO)** | [QuickGO: O15049](https://www.ebi.ac.uk/QuickGO/term/O15049) | Molecular function, biological process, cellular component. | **Key Gene Ontology (GO) Terms:** - **Molecular Function:** GO:0031625 (ubiquitin protein ligase binding), GO:0043130 (ubiquitin binding), GO:0005515 (protein binding). - **Biological Process:** GO:0007249 (I-kappaB kinase/NF-kappaB signaling), GO:0032481 (positive regulation of type I interferon production), GO:0035556 (intracellular signal transduction), GO:0061564 (axon development). - **Cellular Component:** GO:0005737 (cytoplasm), GO:0005634 (nucleus), GO:0045202 (synapse). --- ## Related Clinical & Scientific Guides * [TARM1 Gene: Structure, Function, and Clinical Significance](/knowledge/bioinformatics/genes/immunology-checkpoints/tarm1-gene-structure-function-pathway) * [TRAC Gene: Structure, Function, and Clinical Significance](/knowledge/bioinformatics/genes/immunology-checkpoints/trac-gene-structure-function-pathway) * [CFD Gene: Structure, Function, and Clinical Significance](/knowledge/bioinformatics/genes/immunology-checkpoints/cfd-gene-structure-function-pathway) ## References [1] Jiang, W.-X., Yin, J., Han, M., He, W., Zhao, Y., Hu, J., Wang, M., Wang, S., Xu, J., Deng, C., Li, J., Gong, X., & Shen, Y. (2025). N4BP3 Activates TLR4-NF-κB Pathway in Inflammatory Bowel Disease by Promoting K48-Linked IκBα Ubiquitination. *Journal of Inflammation Research*. URL: https://www.semanticscholar.org/paper/583111f7ae1e6f73aba27f04a090228a1bb657e2 [2] Jiang, W., Zhao, Y., Han, M., Xu, J., Chen, K., Liang, Y., Yin, J., Hu, J., & Shen, Y. (2024). N4BP3 facilitates NOD2-MAPK/NF-κB pathway in inflammatory bowel disease through mediating K63-linked RIPK2 ubiquitination. *Cell Death Discovery*. URL: https://www.semanticscholar.org/paper/3974dcb6186e5874728ae0c44fbfbc39d10b9947 [3] Wang, C., Ling, T., Zhong, N., & Xu, L.-G. (2021). N4BP3 Regulates RIG-I-Like Receptor Antiviral Signaling Positively by Targeting Mitochondrial Antiviral Signaling Protein. *Frontiers in Microbiology*. URL: https://www.semanticscholar.org/paper/7fbd52221ea334b409326daf593853e81a1a3b24 [4] Jin, Y., Wang, Z., Tang, W., Liao, M., Wu, X., & Wang, H. (2022). An Integrated Analysis of Prognostic Signature and Immune Microenvironment in Tongue Squamous Cell Carcinoma. *Frontiers in Oncology*. URL: https://www.semanticscholar.org/paper/c3c707133a6401767f35ef4dd091571ac8639698 [5] Zhang, Z., Li, J., He, T., Ouyang, Y., Huang, Y., Liu, Q., Wang, P., & Ding, J. (2019). Two predictive precision medicine tools for hepatocellular carcinoma. *Cancer Cell International*. URL: https://www.semanticscholar.org/paper/2c49a116baa1a6bf2281fff04fdd3ad24980c2dd [6] Kiem, L.-M., Dietmann, P., Linnemann, A., Schmeisser, M., & Kühl, S. (2017). The Nedd4 binding protein 3 is required for anterior neural development in Xenopus laevis. *Developmental Biology*. URL: https://www.semanticscholar.org/paper/86343bb87f7694cba1e4b80957575a6ecbc895b9 [7] Bozack, A., Perez-Garcia, J., Rifas-Shiman, S., Zhou, Y., Sordillo, J., Lee, J. J., Coull, B., Lai, P. S., Oken, E., Hivert, M., Gold, D. R., & Cardenas, A. (2026). Interplay of the nasal microbiome and epigenome among adolescents. *Clinical Epigenetics*. URL: https://www.semanticscholar.org/paper/0a426e468a5cc173f755f2bc56fa86c70677723f [8] Schmeisser, M., Grabrucker, A., Bockmann, J., & Boeckers, T. (2009). Synaptic crosstalk between NMDA receptors and LAPSER1/β-catenin at excitatory synapses. *Scientific Publication*. URL: https://www.semanticscholar.org/paper/7fabab742d8b294d28998fe4349c085a9e81f075 [9] Grimm, S., Gu, G., Herzog, S. K., Gonzalez, T. L., Lin, H., Beyer, A. R., Rechoum, Y., Bawa-Khalfe, T., Khan, A., Du, L., Symmans, W., Kittler, R., Coarfa, C., & Fuqua, S. (2022). Abstract PD1-07: Mutant ESR1 receptors antagonize the tumor suppressor function of androgen receptors. *Cancer Research*. URL: https://www.semanticscholar.org/paper/b39f01837f899d1f7c0d398a3a86172c8cceefd5 [10] Zhou, J., Liu, X., Wang, C., & Li, C. (2018). The correlation analysis of miRNAs and target genes in metastasis of cervical squamous cell carcinoma. *Epigenomics*. URL: https://www.semanticscholar.org/paper/df71f3d4b279ab9d6ff2eb3c3a843fdf3b2a4fea [11] Li, Q., Fang, F., Yang, C., Yu, D., Gong, Q., & Shen, X. (2024). Whole transcriptome landscape in HAPE under the stress of environment at high altitudes: new insights into the mechanisms of hypobaric hypoxia tolerance. *Frontiers in Immunology*. URL: https://www.semanticscholar.org/paper/fd5b08716be7fa014733b4b8cbf832da201256ff