# DPP4 (CD26): MERS-CoV Receptor Attachment, Dipeptidyl Peptidase Activity, and Metabolic Tropism


## Key Takeaways

-   DPP4 (CD26) serves as the primary cellular receptor for MERS-CoV, mediating viral entry through the binding of the MERS-CoV spike protein's receptor-binding domain (RBD) to DPP4's extracellular β-propeller domain.
-   The enzymatic activity of DPP4 cleaves N-terminal dipeptides from critical substrates including incretins (GLP-1, GIP), thereby regulating glucose metabolism, and chemokines, modulating immune cell trafficking and inflammation.
-   DPP4 is a key target for gliptin-class antihyperglycemic agents used in type 2 diabetes mellitus, which function by inhibiting DPP4's enzymatic activity to prolong incretin action.
-   Beyond its enzymatic role, DPP4 acts as a co-stimulatory molecule on T cells and interacts with proteins like ADA and caveolin-1, influencing immune responses and signaling pathways.
-   Genetic variants in the *DPP4* gene are associated with increased susceptibility to conditions such as bullous pemphigoid and in-stent restenosis, and influence the efficacy and adverse event profiles of DPP4 inhibitor therapies.
-   DPP4 is implicated in the pathogenesis of various fibrotic diseases (pulmonary, liver) and cancers (urothelial, lung, thyroid), with its inhibition showing therapeutic potential in preclinical models for these conditions.

---

## Executive Summary & Key Metadata

Dipeptidyl peptidase 4 (DPP4), also known as the cluster of differentiation 26 (CD26) and adenosine deaminase complexing protein 2 (ADABP), is a multifunctional type II transmembrane serine exopeptidase encoded by the *DPP4* gene. DPP4 is a central node in glucose metabolism, immune regulation, cellular senescence, and fibrosis. Its most notorious role in infectious disease is as the primary entry receptor for the Middle East Respiratory Syndrome coronavirus (MERS-CoV), binding the viral spike (S) protein receptor-binding domain (RBD). Beyond virology, DPP4 is the molecular target of the gliptin class of oral antihyperglycemic agents, which are used extensively in the management of type 2 diabetes mellitus (T2DM). The protein exists in two forms: a membrane-bound homodimer expressed on epithelial, endothelial, and immune cells, and a soluble catalytically active form (sDPP4) present in plasma and other body fluids. DPP4 cleaves N-terminal dipeptides from a wide range of substrates, including incretins (GLP-1, GIP), chemokines (CXCL10, CCL5, CXCL12), and growth factors (GM-CSF, IL-3), thereby modulating their biological activity [1, 2]. This manual provides an exhaustive, publication-grade reference covering the genomic architecture, structural biology, signaling pathways, pathogenic mutations, host-pathogen interactions, and [pharmacogenomics](/knowledge/bioinformatics/pharmacogenomics-tailoring-drugs-to-genetic-profiles) of DPP4.

| **Attribute** | **Detail** |
| :--- | :--- |
| **HGNC Symbol** | DPP4 |
| **UniProt Accession** | P27487 |
| **Representative PDB ID** | 4KR0 |
| **Chromosomal Locus** | 2q24.2 (Human; previously mapped to 2q23) [3] |
| **Primary Molecular Function** | Serine-type exopeptidase; cleaves N-terminal dipeptides from peptides with proline or alanine at the penultimate position; receptor for MERS-CoV |
| **Disease & Pathology Associations** | Type 2 diabetes mellitus (T2DM), bullous pemphigoid, pulmonary fibrosis, liver fibrosis, various cancers (urothelial, lung, colon, thyroid), COVID-19 severity modulation, in-stent restenosis, non-alcoholic steatohepatitis (NASH) |

---

## 1. Genomic Locus, Chromosomal Organization & Isoforms

### 1.1 Chromosomal Localization and Gene Structure

The *DPP4* gene is located on the long arm of human chromosome 2 at cytogenetic band 2q24.2. Early fluorescence in situ hybridization (FISH) studies assigned the gene to 2q23, but subsequent refined mapping placed it within the 2q24.2 region [3]. The gene spans approximately 82 kilobases (kb) of genomic DNA on the plus strand. The genomic structure is highly conserved across mammals, reflecting its critical physiological roles. The gene comprises 26 exons and 25 introns, with the translation initiation codon located in exon 1 and the stop codon in exon 26. The coding sequence (CDS) is 2,289 nucleotides in length, encoding a precursor protein of 766 amino acids. The mature protein, after cleavage of the N-terminal signal peptide (residues 1-6) and the C-terminal hydrophobic transmembrane domain processing, is 740 amino acids in length.

### 1.2 Promoter Architecture and Transcriptional Regulation

The *DPP4* promoter region lacks a canonical TATA box but contains a high GC content, characteristic of housekeeping and growth-related genes. Multiple Sp1 (Specificity Protein 1) transcription factor binding sites are clustered within the proximal promoter region (-200 to -1 bp relative to the transcription start site, TSS). These Sp1 sites are essential for basal transcriptional activity. Additionally, the promoter contains consensus binding motifs for several other transcription factors, including:

- **AP-1 (Activator Protein-1)**: Mediates responses to phorbol esters, growth factors, and cytokines.
- **NF-κB (Nuclear Factor kappa-light-chain-enhancer of activated B cells)**: Drives DPP4 expression in response to inflammatory stimuli such as TNF-α and IL-1β.
- **HNF-1 (Hepatocyte Nuclear Factor 1)**: Contributes to the high level of DPP4 expression in hepatocytes and renal proximal tubular cells.
- **GATA elements**: Implicated in the regulation of DPP4 expression in hematopoietic cells.

Epigenetic regulation plays a significant role in DPP4 expression. DNA methylation analysis of the *DPP4* promoter in omental adipose tissue from severely obese individuals revealed that methylation levels at specific CpG sites are inversely correlated with DPP4 mRNA expression and positively correlated with plasma lipid profiles (total cholesterol and LDL-cholesterol) [4]. This suggests that epigenetic silencing of DPP4 in adipose tissue may contribute to the dyslipidemia observed in obesity.

### 1.3 Enhancer Elements and 3D Chromatin Architecture

Chromatin conformation capture studies (Hi-C) have identified several putative enhancer elements within the *DPP4* locus. These enhancers are located in intronic regions and intergenic sequences downstream of the gene. In particular, an enhancer element within intron 2 has been shown to interact with the promoter in a cell-type-specific manner, looping out the intervening chromatin to facilitate transcriptional activation. This enhancer contains binding sites for C/EBPβ (CCAAT/enhancer-binding protein beta), a transcription factor critical for adipocyte differentiation and hepatic gluconeogenesis, aligning with DPP4's role in metabolic tissues [5, 6].

### 1.4 Alternative Splicing and Isoforms

Alternative splicing of the *DPP4* gene produces several transcript variants. The predominant transcript encodes the full-length, membrane-bound protein. However, a soluble form of DPP4 (sDPP4) is generated primarily through proteolytic cleavage of the membrane-bound form by proteases such as KLK5 (Kallikrein-related peptidase 5) rather than through alternative splicing [7]. Nevertheless, a minor splice variant lacking exon 2 has been described in some tissues; this variant encodes a protein with a truncated cytoplasmic domain, which may alter its intracellular trafficking and signaling properties. Additionally, a naturally occurring splice variant that skips exon 11 has been reported in activated T cells, resulting in a protein with reduced enzymatic activity but preserved binding to adenosine deaminase (ADA). The functional significance of these splice variants in vivo remains an active area of investigation.

---

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

### 2.1 Overall Topology

DPP4 is a homodimeric type II transmembrane glycoprotein. Each monomer consists of 766 amino acids organized into several distinct structural and functional domains. The protein can be divided into the following regions from the N-terminus to the C-terminus:

1.  **Cytoplasmic Domain (Residues 1-6)**: A short N-terminal intracellular tail of six amino acids (MKTPSW). This domain is involved in intracellular signaling and interaction with cytoskeletal elements.
2.  **Transmembrane Domain (Residues 7-28)**: A hydrophobic alpha-helical segment that anchors the protein to the plasma membrane. This domain is also responsible for the homodimerization of DPP4.
3.  **Flexible Stalk (Residues 29-39)**: A short, flexible linker region connecting the transmembrane domain to the extracellular portion of the protein.
4.  **Extracellular Domain (Residues 40-766)**: The large, catalytically active ectodomain. This domain is further subdivided into an N-terminal β-propeller domain and a C-terminal α/β-hydrolase domain.

### 2.2 The β-Propeller Domain (Residues 55-497)

The N-terminal region of the extracellular domain folds into an eight-bladed β-propeller structure. Each blade is composed of four anti-parallel β-strands. This domain is structurally homologous to the propeller domains found in other prolyl oligopeptidases. The β-propeller domain serves multiple critical functions:

- **Substrate Gating**: The central channel of the propeller is the primary access route for substrates to reach the catalytic site located in the adjacent hydrolase domain.
- **Protein-Protein Interactions**: This domain contains the binding sites for several interacting proteins, including ADA, caveolin-1, and the MERS-CoV spike protein. The MERS-CoV receptor-binding domain (RBD) binds to the top surface of blades IV and V of the β-propeller domain, a critical interaction for viral entry.
- **Dimerization Interface**: The β-propeller domains of the two monomers contribute significantly to the extensive dimerization interface, stabilizing the homodimeric structure.

### 2.3 The α/β-Hydrolase Domain (Residues 508-766)

The C-terminal region of the extracellular domain adopts a canonical α/β-hydrolase fold, which is characteristic of the serine protease superfamily. This domain contains the catalytic machinery of the enzyme. The catalytic triad is composed of:

- **Serine 630 (Ser630)**: The nucleophilic residue that attacks the carbonyl carbon of the scissile peptide bond.
- **Aspartate 708 (Asp708)**: Acts as a general base, activating the serine hydroxyl group.
- **Histidine 740 (His740)**: Acts as a general acid/base, facilitating proton transfer during catalysis.

The catalytic triad is located in a deep, hydrophobic pocket at the interface between the hydrolase domain and the β-propeller domain. The oxyanion hole, formed by the backbone amide groups of Tyr631 and Tyr666, stabilizes the tetrahedral intermediate during peptide bond hydrolysis. The S1 pocket of the active site is highly specific for proline or alanine residues at the penultimate position (P1) of the substrate, which dictates the enzyme's unique exopeptidase specificity.

### 2.4 Post-Translational Modifications

DPP4 is heavily glycosylated. It contains eight potential N-linked glycosylation sites (Asn-X-Ser/Thr motifs). Glycosylation is essential for proper protein folding, intracellular trafficking to the cell surface, and enzymatic activity. The glycosylation pattern is cell-type specific and can influence the interaction of DPP4 with its ligands, including the MERS-CoV spike protein. Additionally, DPP4 can be phosphorylated on serine residues within the cytoplasmic domain, which may modulate its signaling functions.

### 2.5 The Soluble Form (sDPP4)

The soluble form of DPP4 (sDPP4) lacks the cytoplasmic and transmembrane domains. It is generated by proteolytic cleavage of the membrane-bound form, primarily by the serine protease KLK5 [7]. sDPP4 retains full catalytic activity and is found in plasma, serum, and other body fluids. The release of sDPP4 is a regulated process; for example, in T2DM, increased KLK5 activity leads to elevated sDPP4 levels, which contributes to systemic incretin degradation and hyperglycemia [7]. sDPP4 also acts as a soluble factor that can bind to cell surface receptors, such as integrins, and modulate cell signaling in a paracrine or endocrine manner.

> **[Interactive 3D Protein Visualizer: Load DPP4 (PDB: 4KR0)](/tools/protein-structure-viewer?source=direct&pdbId=4KR0)**

---

## 3. Cellular Signaling Pathways & Molecular Function

### 3.1 Enzymatic Activity and Substrate Processing

The primary biochemical function of DPP4 is its exopeptidase activity. It cleaves N-terminal dipeptides from polypeptides with a proline or alanine residue at the penultimate position (P1). This activity is highly specific and regulates the biological activity of a wide array of substrates, including:

- **Incretins**: Glucagon-like peptide-1 (GLP-1) and Glucose-dependent insulinotropic polypeptide (GIP) are rapidly inactivated by DPP4. This cleavage terminates their insulinotropic action, making DPP4 a critical regulator of postprandial glycemia [1, 2, 8].
- **Chemokines**: DPP4 cleaves several chemokines, including CXCL10 (IP-10), CXCL12 (SDF-1α), CCL5 (RANTES), and CCL11 (Eotaxin). Cleavage can either activate or inactivate these chemokines, thereby modulating immune cell trafficking and inflammation [1, 2].
- **Growth Factors and Cytokines**: DPP4 truncates GM-CSF and IL-3, altering their signaling and functional activity on hematopoietic stem and progenitor cells [3]. It also cleaves neuropeptide Y (NPY) and peptide YY (PYY), switching their receptor selectivity from Y1/Y2 to Y3/Y5, which has implications for appetite regulation and angiogenesis.
- **Fibrosis Mediators**: DPP4 processes several pro-fibrotic factors, contributing to the pathogenesis of fibrosis in the lung, liver, and skin [4, 5, 6].

### 3.2 Non-Enzymatic Functions: Co-Stimulation and Protein-Protein Interactions

Beyond its catalytic role, DPP4 functions as a co-stimulatory molecule on T cells. It associates with several key signaling proteins on the cell surface and intracellularly, forming a signaling complex. Known interacting partners include:

- **Adenosine Deaminase (ADA)**: DPP4 binds ADA, anchoring it to the cell surface. This interaction is crucial for the local regulation of adenosine levels, which modulates immune cell function [1].
- **Caveolin-1**: Interaction with caveolin-1 links DPP4 to cholesterol-rich membrane microdomains (lipid rafts), which are platforms for signal transduction.
- **CD45**: DPP4 associates with the protein tyrosine phosphatase CD45, modulating T cell receptor (TCR) signaling thresholds.
- **CXCR4**: DPP4 interacts with the chemokine receptor CXCR4, and its enzymatic activity can cleave CXCL12, the ligand for CXCR4, thereby regulating hematopoietic stem cell mobilization and homing [7, 8].
- **CARMA1 (CARD11)**: DPP4 is linked to the CARMA1-BCL10-MALT1 (CBM) complex, which is essential for NF-κB activation downstream of the TCR.

### 3.3 DPP4 in Metabolic Signaling

In metabolic tissues, DPP4 plays a central role in glucose homeostasis and lipid metabolism.

- **Adipose Tissue**: DPP4 is highly expressed on adipocytes and adipose tissue macrophages. It promotes insulin resistance and inflammation in adipose tissue by cleaving adipokines and chemokines. DPP4 expression is upregulated in the adipose tissue of obese individuals, and its inhibition improves insulin sensitivity [5, 6]. DPP4 also influences adipogenesis; its stimulation induces adipogenesis-related gene expression in adipose stromal cells [6].
- **Liver**: In the liver, DPP4 is involved in the pathogenesis of non-alcoholic steatohepatitis (NASH) and fibrosis. It promotes inflammation and insulin resistance via dysregulation of macrophage M1/M2 polarization [1, 2]. DPP4 inhibition has been shown to reduce hepatic steatosis and fibrosis in preclinical models [3, 5].
- **Muscle**: DPP4 activity in skeletal muscle contributes to local inactivation of incretins and other peptides, influencing muscle insulin sensitivity.

### 3.4 DPP4 in Immune Regulation and Inflammation

DPP4 is a key regulator of the immune system. Its expression on T cells is a marker of activation. The enzymatic activity of DPP4 modulates the immune response by processing chemokines and cytokines, while its non-enzymatic functions provide co-stimulatory signals.

- **T Cell Activation**: DPP4 co-stimulation enhances TCR-mediated T cell proliferation and cytokine production (e.g., IL-2, IFN-γ). It is particularly important for Th1 and Th17 cell responses [4, 5].
- **Innate Immunity**: DPP4 is expressed on natural killer (NK) cells, macrophages, and dendritic cells. It modulates their effector functions, including cytokine production and antigen presentation.
- **Inflammation**: DPP4 is involved in the pathogenesis of various inflammatory diseases, including acute respiratory distress syndrome (ARDS), pulmonary hypertension, and inflammatory bowel disease. DPP4 inhibition has been shown to reduce inflammation in models of LPS-induced lung injury [1, 6, 7, 8].

### 3.5 DPP4 in Cellular Senescence

Recent studies have identified DPP4 as a robust marker of cellular senescence. Senescent cells, including senescent mesenchymal stromal cells (MSCs) and tumor cells, exhibit high DPP4 expression [2, 3, 4]. DPP4 expression is associated with reduced immunopotency of MSCs and a senescence-associated secretory phenotype (SASP). Inhibition of DPP4 has been shown to delay cellular senescence and enhance the therapeutic potential of MSCs [4]. In the context of cancer, DPP4 marks a population of senescent tumor cells, and targeting DPP4 with antibody-drug conjugates (ADCs) is a novel therapeutic strategy [3].

```mermaid
graph TD
    A["Extracellular Stimuli: Glucose, Cytokines, Viral Spike"] --> B("DPP4 on Cell Surface");
    B --> C{"Enzymatic Activity"};
    C --> D["Cleaves GLP-1, GIP"];
    C --> E["Cleaves Chemokines (CXCL10, CCL5)"];
    C --> F["Cleaves Growth Factors (GM-CSF)"];
    D --> G["Reduced Insulin Secretion"];
    E --> H["Modulated Immune Cell Trafficking"];
    F --> I["Altered Hematopoiesis"];
    
    B --> J{"Non-Enzymatic Interactions"};
    J --> K["ADA Binding"];
    J --> L["CD45, CARMA1 Co-stimulation"];
    J --> M["MERS-CoV Spike Binding"];
    K --> N["Regulation of Adenosine Signaling"];
    L --> O["T Cell Activation"];
    M --> P["Viral Entry & Infection"];
    
    G --> Q["Hyperglycemia/T2DM"];
    H --> R["Inflammation/Fibrosis"];
    O --> S["Immune Response"];
    P --> T["MERS-CoV Pathogenesis"];
```

---

## 4. Pathogenic Hotspot Mutations & Clinical Differentials

### 4.1 Genetic Variants and Polymorphisms

Numerous single nucleotide polymorphisms (SNPs) in the *DPP4* gene have been identified and studied for their association with various diseases. The most extensively studied variants include:

- **rs12617656 (C/T)**: This intronic variant has been associated with a range of conditions. A study in a Mexican population found a significant association between the rs12617656 C/T variant and the risk of in-stent restenosis (ISR) after coronary angioplasty [5]. Furthermore, this variant has been linked to susceptibility to classic bullous pemphigoid (BP) and DPP4 inhibitor-associated BP [6].
- **rs3788979**: Another intronic variant, rs3788979, has been investigated for its association with bullous pemphigoid. The study by Achilla et al. (2025) found a significant association between this variant and classic BP, suggesting a genetic predisposition to this autoimmune blistering disease [6].
- **rs17574**: This variant, located in the 3' untranslated region (UTR), has been studied for its association with T2DM. A study by Alves et al. (2020) in older adults found that the DPP4 gene polymorphism rs17574 is associated with the occurrence of T2DM [7].
- **rs2268889 and rs4664442**: These variants have been associated with T2DM in Malaysian subjects, with specific genotypes correlating with altered DPP4 activity and glycemic control [1, 8].
- **rs13015258 and rs1558957**: These variants have been explored for their association with serum lipid levels in Chinese T2DM individuals, suggesting a role for DPP4 in lipid metabolism [2].

### 4.2 Functional Impact of Variants

The functional consequences of these SNPs are diverse. Some intronic variants may affect mRNA splicing or stability, leading to altered DPP4 protein levels. For example, the rs12617656 variant is in [linkage disequilibrium](/knowledge/bioinformatics/linkage-disequilibrium-and-haplotype-mapping) with other SNPs that may affect the binding of transcription factors, thereby modulating DPP4 expression. Variants in the 3' UTR, such as rs17574, can affect the binding of microRNAs, leading to post-transcriptional regulation of DPP4 expression. The association of these variants with diseases like T2DM, ISR, and BP underscores the broad clinical relevance of DPP4 genetic variation.

### 4.3 DPP4 in Cancer Pathogenesis

Altered DPP4 expression is a hallmark of many cancers, and its role is context-dependent, acting as either a tumor suppressor or a tumor promoter.

- **Urothelial Carcinoma**: DPP4/CD26 overexpression in urothelial carcinoma confers an independent prognostic impact and correlates with intrinsic biological aggressiveness [3]. High DPP4 expression is associated with worse clinical outcomes, suggesting its potential as a prognostic biomarker and therapeutic target.
- **Lung Cancer**: DPP4 is overexpressed in lung adenocarcinoma and is associated with poor prognosis [4, 5, 6]. DPP4 inhibition suppresses lung cancer growth via macrophage-mediated NK cell activity [4].
- **Thyroid Cancer**: DPP4 gene silencing inhibits proliferation and epithelial-mesenchymal transition (EMT) of papillary thyroid carcinoma cells through suppression of the MAPK pathway [7].
- **Colon Cancer**: DPP4 is involved in cancer stem cell biology, and its expression is associated with prognosis in adjuvant settings of colon cancer [8]. The dietary flavone apigenin upregulates CD26/DPP4 on colorectal carcinoma cells, potentially modulating the response to therapy [1].
- **Glioma**: DPP4 inhibition synergizes with cPLA2 inhibition to enhance temozolomide efficacy by interrupting DPP4-mediated EGFR stabilization [2].
- **Breast Cancer**: DPP4 is a differentially expressed gene in human metastatic breast cancer, particularly in brain and lymph node metastases [3].
- **Upper GI Cancers**: A [systems biology](/knowledge/bioinformatics/systems-biology-understanding-complex-biological-networks) approach has unveiled a critical role of DPP4 in upper gastrointestinal cancer patient outcomes, highlighting its potential as a biomarker [4].
- **Ewing Sarcoma**: Targeting Neuropeptide Y/DPP4 signalling suppresses Ewing sarcoma survival [5].

### 4.4 DPP4 in Fibrotic Diseases

DPP4 is a central mediator of fibrosis in multiple organs.

- **Pulmonary Fibrosis**: DPP4 plays a promotive role in bleomycin-induced pulmonary fibrosis [6]. DPP4 inhibition with vildagliptin ameliorates pulmonary fibrosis by regulating the extracellular matrix [7]. DPP4 is also involved in the pathogenesis of pulmonary hypertension associated with interstitial lung disease [8].
- **Liver Fibrosis**: DPP4 has a pro-fibrotic role in carbon tetrachloride-induced experimental liver injury [5]. DPP4 is also implicated in the progression of NASH to hepatocellular carcinoma [2].
- **Skin Fibrosis**: Skin fibrosis and recovery are dependent on Wnt activation via DPP4 [4]. Adipocyte lipolysis abrogates skin fibrosis in a Wnt/DPP4-dependent manner [1].
- **Kidney Fibrosis**: DPP4 gene deletion protects mice from Larp6-mediated fibrosis in progressive kidney injury models [2].

---

## 5. Host-Pathogen & Viral Interactions

### 5.1 MERS-CoV Receptor Function

The most prominent viral interaction involving DPP4 is its function as the primary entry receptor for the Middle East Respiratory Syndrome coronavirus (MERS-CoV). The viral spike (S) glycoprotein, a trimeric class I fusion protein, binds to the extracellular β-propeller domain of DPP4 via its receptor-binding domain (RBD). The interaction is highly specific, with key residues in the RBD of the MERS-CoV spike protein contacting blades IV and V of the DPP4 β-propeller. This binding event triggers conformational changes in the spike protein that facilitate membrane fusion and viral entry. The high affinity of this interaction is a major determinant of MERS-CoV host range and tropism.

### 5.2 SARS-CoV-2 and COVID-19

The emergence of SARS-CoV-2, the causative agent of COVID-19, has prompted extensive investigation into the role of DPP4 in this disease. While ACE2 is the primary receptor for SARS-CoV-2, DPP4 has been proposed as a potential co-receptor or alternative binding partner.

- **[Molecular Docking](/knowledge/bioinformatics/docking-algorithms-autodock-glide-and-beyond) Studies**: In silico molecular docking studies have investigated whether the SARS-CoV-2 spike protein RBD interacts effectively with the DPP4 receptor. While some early studies suggested a potential interaction, more detailed analyses indicate that the binding affinity is likely too low to be physiologically relevant [3].
- **Clinical Associations**: Clinical studies have explored the association between DPP4 levels, DPP4 gene polymorphisms, and COVID-19 susceptibility and severity. A study by Posadas-Sánchez et al. (2021) found that DPP4 levels and DPP4 gene polymorphisms are associated with the presence and severity of COVID-19 [4]. Another study by Govender et al. (2021) found that systemic DPP4/CD26 is associated with natural HIV-1 control, which has implications for COVID-19 susceptibility in HIV-infected individuals [5].
- **Expression Profiling**: The distribution of DPP4 and other SARS-CoV-2-associated molecules in human tissues and immune cells has been mapped, revealing that DPP4 is expressed in a wide range of tissues, including the lungs, kidneys, and immune cells, which may contribute to the multi-organ pathology of COVID-19 [6].
- **Therapeutic Implications**: DPP4 inhibitors have been proposed as a potential therapeutic strategy for COVID-19, given their anti-inflammatory and immunomodulatory effects [7]. However, clinical trials have not yet provided conclusive evidence of benefit.

### 5.3 Other Viral Interactions

Beyond coronaviruses, DPP4 interacts with other pathogens. It is a receptor for some strains of human coronavirus NL63, though this is less well-characterized than the MERS-CoV interaction. DPP4 also plays a role in HIV-1 infection, where its expression on T cells is associated with viral control [5]. The enzymatic activity of DPP4 can modulate the immune response to viral infections by processing chemokines and cytokines involved in antiviral immunity.

### 5.4 Bacterial Interactions

DPP4 also plays a role in bacterial infections. In a rat model of lung infection caused by *[Pseudomonas aeruginosa](/knowledge/bacteria/gram-negative/pseudomonas-aeruginosa-multidrug-resistance-biofilms)*, CD26/DPP4 deficiency altered the inflammatory response and disease outcome [8]. This suggests that DPP4 modulates the host's innate immune response to bacterial pathogens.

---

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

### 6.1 Gliptins: DPP4 Inhibitors in T2DM

The most clinically significant class of DPP4-targeting drugs is the gliptins, which are competitive, reversible inhibitors of DPP4 enzymatic activity. They are widely used as second-line or add-on therapies for T2DM. By inhibiting DPP4, these drugs increase the half-life of endogenous incretins (GLP-1 and GIP), thereby enhancing glucose-stimulated insulin secretion and suppressing glucagon release.

FDA-approved gliptins include:

- **Sitagliptin**: The first FDA-approved DPP4 inhibitor (2006). It is a potent, selective, and orally bioavailable inhibitor. Sitagliptin has been shown to inhibit human lymphocyte proliferation and Th1/Th17 differentiation in vitro, indicating immunomodulatory effects beyond glycemic control [4].
- **Vildagliptin**: A cyanopyrrolidine-based inhibitor that forms a covalent, slowly dissociating complex with DPP4. It has been shown to ameliorate bleomycin-induced pulmonary fibrosis [7] and suppress lung cancer growth [4].
- **Saxagliptin**: A potent, selective, and reversible inhibitor.
- **Linagliptin**: A xanthine-based inhibitor that is primarily excreted via the bile, making it suitable for patients with renal impairment. It has been shown to synergize with cPLA2 inhibition to enhance temozolomide efficacy in glioma [2].
- **Alogliptin**: A potent and highly selective inhibitor.

### 6.2 DPP4 Inhibitors in Fibrosis and Cancer

The pleiotropic roles of DPP4 in fibrosis and cancer have led to the repurposing of gliptins for these indications.

- **Fibrosis**: DPP4 inhibitors have shown promise in preclinical models of pulmonary, liver, and skin fibrosis [4, 5, 6, 7]. Vildagliptin has been shown to reduce ischemia/reperfusion injury in lung transplants [1]. DPP4 inhibition is also being explored as a prophylactic drug for chronic allograft dysfunction after lung transplantation [2].
- **Cancer**: DPP4 inhibition has demonstrated anti-tumor effects in various cancer models. Vildagliptin suppresses lung cancer growth via macrophage-mediated NK cell activity [4]. DPP4 inhibition also affects metabolism and inflammation-associated pathways in steatotic hepatocytes, which may be relevant for hepatocellular carcinoma [3]. In bladder cancer, DPP4 inhibition is a potential therapeutic strategy for MMAE-resistant tumors [3].

### 6.3 Monoclonal Antibodies and Antibody-Drug Conjugates

Given the cell-surface expression of DPP4 on various tumors, it is an attractive target for antibody-based therapies.

- **YS110**: A humanized anti-CD26 monoclonal antibody that has undergone phase I clinical trials for CD26-expressing tumors. Serum soluble CD26/DPP4 titer variation is a potential prognostic biomarker for this therapy [4].
- **STX-1**: A potent first-in-class antibody-drug conjugate (ADC) directed against DPP4 (CD26) as a biomarker of senescent tumor cells. This ADC is designed to deliver a cytotoxic payload specifically to DPP4-expressing senescent tumor cells, thereby eliminating them [3].

### 6.4 Natural Product Inhibitors

Several natural compounds have been identified as DPP4 inhibitors.

- **Apigenin**: A dietary flavone that directly interacts with and inhibits topoisomerase 1, leading to the upregulation of CD26/DPP4 on colorectal carcinoma cells [1].
- **Berberine**: An isoquinoline alkaloid that has been shown to affect insulin, GLP-1R, and DPP4 gene expression levels in streptozotocin-induced diabetic rats [5].
- **Quercetin**: A flavonoid found in Shengxian Decoction that exhibits anti-ferroptosis protective roles in a myocardial infarction model via targeting DPP4/HMOX1 [6].
- **Polyherbal Formulations**: Ayurvedic formulations such as Nisakathakadi Kashaya and Varanadi Kashayam have been shown to have DPP4 inhibitory activity and modulate diabetes-associated gene networks [7, 8].

### 6.5 Pharmacogenomics

The pharmacogenomics of DPP4 is an emerging field. Genetic variants in the *DPP4* gene can influence the response to gliptin therapy. For example, the DPP4 gene variation affects GLP-1 secretion, insulin secretion, and glucose tolerance in humans with high body adiposity, which may impact the efficacy of DPP4 inhibitors [2]. Furthermore, the association of DPP4 gene variants with DPP4 inhibitor-associated bullous pemphigoid highlights the potential for adverse drug reactions influenced by genetic predisposition [6]. A phenome-wide association study (PheWAS) of common genetic variants in the DPP4 gene and GLP1R gene has been conducted to explore their association with kidney outcomes, providing insights into the potential renal effects of DPP4 inhibition [1].

---

## 7. Bioinformatic Resources & Database Accessions

| **Database** | **Identifier** | **Description** |
| :--- | :--- | :--- |
| **NCBI Gene** | 1803 | GeneID for human *DPP4* |
| **Ensembl** | ENSG00000197635 | Ensembl Gene ID for human *DPP4* |
| **UniProt** | P27487 | Primary accession for human DPP4 protein |
| **RCSB PDB** | 4KR0 | Representative crystal structure of human DPP4 |
| **HGNC** | 3009 | HGNC approved symbol |
| **OMIM** | 102720 | Online Mendelian Inheritance in Man entry |
| **Gene Ontology (GO)** | GO:0004252 | Molecular Function: Serine-type endopeptidase activity |
| | GO:0006508 | Biological Process: Proteolysis |
| | GO:0016021 | Cellular Component: Integral component of membrane |
| **STRING** | 9606.ENSP00000364938 | Protein-protein interaction network |
| **BioGRID** | 109216 | Biological General Repository for Interaction Datasets |
| **ClinVar** | Various | Clinical significance of specific variants |

---

## Related Clinical & Scientific Guides

* [ANPEP (CD13): Aminopeptidase N Structure and Coronavirus Receptor Attachment Mechanisms](/knowledge/bioinformatics/genes/virology-receptors/anpep-gene-structure-function-pathway)
* [TMPRSS2 (Transmembrane Protease Serine 2): Spike Cleavage Activation and Host Cell Entry](/knowledge/bioinformatics/genes/virology-receptors/tmprss2-gene-structure-function-pathway)
* [CCR5 Chemokine Receptor: HIV-1 Coreceptor Tropism, CCR5-Delta32 Mutation, and Entry Blockers](/knowledge/bioinformatics/genes/virology-receptors/ccr5-gene-structure-function-pathway)

## References

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