Unraveling the Role of CCR9 and CCL25 in Immune Regulation

What are CCR9 and CCL25？

Chemokine receptor 9 (CCR9) is a small transmembrane protein comprising seven regions, belonging to the G protein-coupled receptor (GPCR) family. It is predominantly found on the surfaces of immune and intestinal cells and plays a pivotal role in the differentiation of immature T lymphocytes, as well as in certain inflammatory responses.

Chemokine ligand 25 (CCL25), on the other hand, serves as the exclusive ligand for CCR9. It is primarily secreted by thymic epithelial cells and intestinal epithelial cells. CCL25 holds a critical function in orchestrating the directed migration and homing of CCR9-positive cells to specific target tissues.

In recent years, research has unveiled that CCR9 and CCL25 are significantly upregulated in some tumors, thereby contributing to their malignant progression.

The Structure of CCR9 and CCL25

CCR9, found on chromosome 3p21.31, belongs to the β-chemokine receptor family. It has two transcript variants: A (369 amino acids, 42 kDa) and B (357 amino acids, 40.8 kDa). In Fig. 1a, you can observe the molecular structure of CCR9 (amino acids 44 to 241). CCR9 primarily exists in immature T lymphocytes and on the surfaces of intestinal cells, where it plays a crucial role in T lymphocyte development and specific tissue homing, facilitated by its binding to a particular ligand.

CCL25, also known as thymus-expressed chemokine (TECK), is a member of the CC chemokine family and serves as the specific ligand for CCR9. Positioned on chromosome 19p13.2, CCL25 has three isotypes: isotype 1 (150 amino acids, 16.6 kDa), isotype 2 (84 amino acids, 9.5 kDa), and isotype 3 (149 amino acids, 16.5 kDa). Fig. 1b provides an illustration of the molecular structure of CCL25 (amino acids 28 to 93). Additionally, you can see a simulated interaction between CCL25 and CCR9 in Fig. 1c.

Fig.1 The structures of CCR9 and CCL25.

CCL25/CCR9 Induces Tumor Metastasis

CCL25/CCR9 Increases the Expression of MMP2 and MMP9 to Degrade Collagen type IV

The degradation of the extracellular matrix and basal membrane stands as a pivotal step in cancer cell invasion and metastasis. This process primarily involves matrix metalloproteinases (MMPs), a group of proteolytic enzymes closely linked to tumor metastasis. Most MMPs feature functional domains that regulate catalytic activity and substrate recognition, while others possess domains devoid of catalytic activity but contribute to tumor progression. Take MMP-2 and MMP-9, for instance, which contain three fibronectin-like repeats within their catalytic domains, enabling them to interact with and degrade substrates like gelatin, collagen, and laminin, particularly collagen type IV—a major component of the basal membrane.

Studies have revealed that the interaction between CCL25/CCR9 amplifies the expression of MMP-2 and MMP-9. This increase in expression has been associated with tumor metastasis in various cancers, including ovarian cancer, prostate cancer, non-small cell lung cancer, and endometriosis.

CCL25/CCR9 Induces Cancer Cells Polarization and Microvilli Absorption

In our earlier research, we made a noteworthy discovery: CCR9 exhibited robust expression in CD4+ T cells taken from individuals with T-ALL (T-cell acute lymphoblastic leukemia), while its expression in normal T cells was either minimal or non-existent. This finding was pivotal because when CCR9 was internalized within the CD4+ T cells of T-ALL patients, it resulted in the loss of chemotactic and adhesive effects on leukemia cells. This strongly implied that CCR9 plays a significant role in the infiltration and metastasis of leukemia cells.

Subsequent investigations delved deeper, revealing that CCL25/CCR9 prompts polarization and microvilli absorption in MOLT4 cells. This, in turn, actively contributes to the infiltration and trafficking of leukemia cells, with the involvement of the RhoA-ROCK-MLC and ezrin pathway. For a visual representation of this mechanism, please refer to Fig. 2, illustrating how CCR9 mediates tumor metastasis.

Fig.2 Diagram summarizing the reviewed mechanisms by which CCR9 induces different aspects of tumor metastasis.

The Role of CCR9/CCL25 in Inflammatory Diseases

Inflammation serves as a fundamental component of numerous physiological and pathological processes. Notably, chronic inflammation plays a significant role in the pathophysiology of various contemporary diseases. What distinguishes inflammatory diseases is their broad scope, intricate underlying mechanisms, and considerable variation in prognosis. Consequently, our primary emphasis is on exploring the influence of CCR9/CCL25 in the context of inflammatory diseases, and we aim to provide an in-depth examination of their mechanisms of action in these related conditions.

Cardiovascular Disease

Cardiovascular disease, also referred to as circulatory disease, encompasses a range of conditions that affect the circulatory system, including the heart and blood vessels. It has consistently ranked among the leading causes of human mortality. Conditions such as heart failure, cardiac hypertrophy, and atherosclerosis fall under the umbrella of cardiovascular disease (CVD). Importantly, CVD is characterized as a chronic vascular inflammatory disease, carrying a significant burden of morbidity, mortality, and disability, posing a substantial threat to human health.

In research conducted on CCR9 knockout (CCR9-/-) mice, where surgical ligation of the left anterior descending coronary artery induced myocardial infarction (MI), it was observed that the expression of CCR9 in the hearts of mice significantly increased following MI. Lowering CCR9 expression led to improved survival rates, reduced left ventricular dysfunction, decreased infarct size, and enhanced cardiac function post-MI. Additionally, the absence of CCR9 in the mouse MI heart markedly increased the expression of Bcl-2 while reducing the expression of Bax and cleaved caspase 3, thus mitigating cardiomyocyte apoptosis. Inflammation is a pivotal pathological response to damage and repair, and CCR9 deficiency was found to lower mRNA levels of pro-inflammatory cytokines (IL-6, IL-1β, and TNF-α) and dampen the inflammatory response post-MI. Furthermore, CCR9 plays a role in structural remodeling primarily by interfering with the NF-κB and MAPK signaling pathways. These findings affirm that CCR9/CCL25 may play a positive role in the context of MI.

Hepatitis

Hepatitis encompasses a range of conditions typically triggered by various pathogenic factors, including parasites, viruses, drugs, bacteria, and autoimmune factors. These factors collectively damage liver cells and their functions, giving rise to a host of discomforting bodily symptoms and abnormal liver function indicators.

It is widely acknowledged that the liver's immune cells are intricately involved in the development of liver diseases. In particular, inflammatory macrophages play a pivotal role in initiating liver injury, which can subsequently lead to liver fibrosis and even cancer. Research has revealed that CCR9+ inflammatory macrophages are instrumental in provoking acute liver injury through their interaction with helper T 1 (Th1) cells within the inflamed liver.

Further investigations uncovered that macrophages expressing CCR9+CD11b+ exacerbate liver damage by producing inflammatory cytokines and promoting the development of Th1 cells during concanavalin A-induced murine acute liver injury and human acute hepatitis. Detailed analysis, including the use of liver-shielded radiation and bone marrow transplantation mouse models, revealed that these CCR9+CD11b+ macrophages originate from bone marrow-derived monocytes rather than liver-resident macrophages. Additionally, when in contact with hepatic stellate cells, these CD11b+ inflammatory macrophages actively contribute to the pathogenesis of experimental liver fibrosis upon the knockout of the CCR9 gene.

These findings were further validated in human samples, conclusively establishing the pathogenic role of the CCR9/CCL25 axis as a potential therapeutic target for a variety of liver diseases.

Fig.3 Schematic diagram illustrating the regulation of molecular mechanisms of CCR9/CCL25 in inflammatory diseases.

Asthma

Asthma, a lung disease, is characterized by reversible airway obstruction, airway inflammation, and heightened airway responsiveness to various triggers. The involvement of chemokine receptors in leukocyte recruitment is well-established and closely tied to the pathology of asthma.

To explore this further, an ovalbumin (OVA)-induced allergic inflammation model was developed in CCR9–/– mice, with a focus on CCR9 and CCL25 expression in eosinophils and T lymphocytes six hours after OVA challenge. Notably, when compared to their wild-type counterparts, CCR9-deficient mice exhibited a significant reduction (nearly 50%) in peribronchial infiltration, as well as a decrease (30%) in the total number of eosinophils recruited in bronchoalveolar fluid (BALF).

Additionally, in CCR9–/– mice, OVA administration led to a decrease in the recruitment of inflammatory cells, which altered the expression of IL-10, CCL11, and CCL25 24 hours after OVA exposure. Interestingly, OVA-stimulated CCR9-deficient mice showed elevated levels of TGF-β and IL-17 compared to WT mice. Conversely, the anti-inflammatory chemokine IL-10 saw a significant reduction (over 60%). Furthermore, CCL25 expression in WT mice increased as early as six hours post-OVA challenge, while it consistently decreased in CCR9–/– mice.

These findings confirm that CCR9 deficiency exerts a positive regulatory influence on eosinophils and lymphocytes during the early stages of inflammation induction, suggesting their potential as targets for the modulation of asthma-related inflammation.

Cancer

Within the microenvironment, a dynamic interplay exists between tumor formation and the immune system, with chemokines serving as critical mediators in this intricate relationship. T cells represent a pivotal component of the anti-cancer immune response. CD4+ T cells wield significant regulatory influence, while CD8+ T cell stem cell-like subgroups possess the ability to self-renew and differentiate into effector cells, capable of generating enduring anti-tumor immune responses and specifically targeting tumor cells.

Studies have shed light on the essential role of CCR9 in modulating T cell function. CD4+ CCR9+ T helper cells exhibit elevated expression of interleukin 21 and stimulate the production of T cell costimulatory factor, transcription factor B cell CLL/lymphoma 6 (Bcl-6), and Maf. These factors are characteristic of autoimmune diseases affecting the accessory organs of the digestive system. Notably, the CCR9 signal during the activation of naive T cells fosters the differentiation of memory CD4+ T cells that produce α 4 β + 7 IFN-γ, thereby enhancing the immune microenvironment within gastrointestinal tissues and influencing effector immunity in infections and cancer.

In a particular study, NP-siCD47/CCL25 significantly enhanced the invasiveness of CCR9+CD8+ T cells, suppressed CD47 expression in tumor cells, and curtailed tumor cell metastasis and growth through T-cell-dependent immunity. Furthermore, research has highlighted CCR9's regulatory role in the STAT signaling pathway in T cells, inhibiting the secretion and cytotoxicity of type 1 cytokines in T lymphocytes. This underscores the potential of inhibiting CCR9 expression as a means to bolster tumor-specific T cell immunotherapy.

In conclusion, targeting the CCR9/CCL25 axis holds promise as a novel approach for cancer treatment, potentially inducing a sustained antitumor response within the autoimmune system of tumor patients.

CCR9 and CLL25 Protein

Recombinant Human C-C Chemokine Receptor Type 9 (CCR9) Protein (GST)

Click here for more CCR9

Recombinant Human CCL25 Protein

Click here for more CLL25

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