CCR9: A Member of the Chemokine Receptor Family, an Emerging Target for Numerous Tumor Researches!

1. What is CCR9?

1.1 CCR9 Structure

CCR9, a vital protein in the chemokine receptor family, operates as a G protein-coupled receptor with a distinctive seven-transmembrane structure. These receptors, crucial for cell motility and differentiation, exert their effects through interactions with chemokines. Categorized into CC, CXC, CX3C, and C-type subfamilies, CCR9 specifically falls under the CC group (Click here for an introduction to the chemokine receptors family). With two transcripts, A (369 amino acids, 42 kDa) and B (357 amino acids, 40.8 kDa), CCR9 earns its name due to its structural likeness to CCR6 and CCR7. The functional zone of CCR9 lies predominantly within the seven-transmembrane structure, spanning amino acids 65 to 317 (Figure 1) ^[1-3].

Figure 1. The molecular structure of CCR9 ^[1]

1.2 CCR9 Expression and Function

CCR9 is mainly found in immature thymocytes, peripheral blood CD8+ T cells, certain dendritic cells, and small intestinal endothelial cells, playing a key role in maintaining the body's internal balance. Research indicates that CCR9 is involved in various diseases like inflammatory bowel disease, acute hepatitis, and rheumatoid arthritis. Moreover, there's substantial evidence showing abnormal overexpression of CCR9 in various malignant tumors. This elevated expression often links to drug resistance, metastasis, and poor prognosis, suggesting CCR9's potential involvement in diverse biological activities related to tumor progression, including cancers in the colon, melanoma, prostate, and non-small-cell lung ^[1-6].

2. What is the Ligand for CCR9?

CCR9's specific ligand is Thymus Expressed Chemokine (TECK)/CCL25, a member of the CC chemokine family located on chromosome 19 p13.2. Comprising 150 amino acids with signal peptides in the terminal 23, CCL25 is primarily expressed in the thymus and small intestinal epithelial cells, with lesser expression in the testis, brain tissue, liver, and activated proT cells. Ongoing research in tumor molecular biology is gradually uncovering the regulatory roles of CCR9 and CCL25 in tumors ^[7-10].

Research data shows a connection between serum CCL25 and MMP-9, VEGF-D, and AKT, indicating that the CCR9/CCL25 axis may regulate the PI3K/AKT pathway and its downstream effector cytokines (VEGF-D and MMP-9). Moreover, the CCR9/CCL25 signaling pathway inhibits MOLT4 apoptosis induced by cycloheximide (CHX). The binding of CCL25 to CCR9 activates a downstream signaling pathway that involves PI3K and leads to AKT phosphorylation. This AKT activation promotes signaling molecules like Bad and GSK-3β, supporting cell survival. Hence, CCR9 and CCL25 emerge as potential target molecules in cancer research ^[7-10].

3. How's the Mechanism of CCR9/CCL25 in Tumors?

3.1 CCR9/CCL25 and PI3K/AKT Signaling Pathways

The PI3K-Akt signaling pathway is a crucial intracellular route closely tied to the initiation, progression, and malignancy of various human tumors, as established by numerous studies. This pathway is intricately regulated by tumor-related genes, including PTEN, CTMP, and SHLP2. Recent findings reveal that the CCR9/CCL25 axis activates the PI3K/AKT signaling pathway. This activation is implicated in non-small cell lung cancer cell anti-apoptotic processes, the regulation of anti-apoptotic mechanisms in prostate cells, and the inhibition of apoptosis induced by the chemotherapeutic drug Etoposide in prostate cancer cells. Additionally, in breast and ovarian cancer studies, the interaction of CCR9/CCL25 impedes chemotherapeutic drug-induced tumor cell apoptosis. These findings collectively suggest that CCR9/CCL25 may influence tumor cell apoptosis through the PI3K/AKT signaling pathway (Figure 2) ^{[1, 11-13]}.

Figure 2. CCR9/CCL25 and PI3K/AKT signaling pathways ^[1]

3.2 CCR9/CCL25 and JAK/STAT Signaling Pathways

The JAK/STAT signaling pathway swiftly transmits extracellular-to-nuclear signals, with recent studies emphasizing its impact on cell growth, proliferation, and transformation, particularly through STAT3 activation. While T-cell-mediated immunotherapy is effective against tumors, its weakness in generating in vivo anti-tumor cytotoxic effects limits its efficacy. CCR9 has been identified as mediating this weakened effect via the STAT signaling pathway. Inhibiting CCR9 expression in vivo significantly improves the efficacy of tumor-specific T cell-mediated immunotherapy. Therefore, exploring the connection between CCR9/CCL25 and the JAK/STAT signaling pathway is crucial for advancing tumor immunity research ^{[6, 14-15]}.

4. The Roles of CCR9 in Different Tumors

In malignant tumors, chemokines and their receptors impact every stage of disease development, including lymphocyte recruitment, neoangiogenesis, tumor proliferation, survival, invasion, and metastasis. Numerous studies confirm the high expression of CCR9 and CCL25 in various cancers, emphasizing their crucial roles in tumor invasion, migration, drug resistance, and anti-regulation. This underscores the potential significance of investigating CCR9 and CCL25 for targeted tumor research.

4.1 CCR9 and T-Lymphocyte Leukemia Research

In T-lymphoblastic leukemia, CCR9 is highly expressed in CD4+T cells, both in acute (TALL) and chronic (TCLL) cases, unlike normal CD4+-positive T cells. This heightened expression is associated with cell proliferation, survival, and evasion from regulation. The interaction of CCR9 and CCL25 affects the activation of forkhead transcription factor (FKHR) and glycogen synthase kinase-3β (GSK-3β), inhibiting the apoptotic signaling pathway and suppressing apoptosis in malignant cells ^[16-17].

Furthermore, CCR9-CCL25 has different effects on various T lymphocytes. It promotes development and maintains homeostasis in CD4+CD8+double-positive T lymphocytes, while in TALL CD4+ positive T lymphocytes, it encourages abnormal cell proliferation and inhibits apoptosis^[17]. Additionally, CCR9 may regulate cell development and homeostasis through the Notch1 signaling pathway, influencing the biological mechanisms of leukemia cells. Simultaneously, CCL25, by modulating the apoptosis inhibitory protein Livin, affects the growth and apoptosis of leukemic T lymphocytes ^[18].

4.2 CCR9 and Colorectal Cancer Research

CCL25 is highly expressed in small intestinal and colonic epithelial cells, guiding CCR9-positive T-lymphocytes to specific locations in the digestive system. In colorectal cancer, CCR9 levels are significantly elevated in adenocarcinoma and pre-invasive cells compared to invasive and metastatic stages. Despite incomplete validation of cellular expression, it's established that CCR9 is highly expressed in colorectal cancer. In vitro studies confirm that the CCR9-CCL25 axis significantly enhances the invasive ability of colon cancer cells. These findings highlight the strong association between CCR9/CCL25 expression and the development and invasive progression of colorectal cancer ^{[9, 19]}.

4.3 CCR9 and Prostate Cancer Research

In prostate cancer research, CCR9 expression decreases from prostate lymph node cancer cell lines to prostate cancer cell lines and normal prostate epithelial cells, with the highest expression in lymph node cancer cells. This implies a link between the CCR9/CCL25 axis and prostate cancer lymph node metastasis. The interaction of CCR9/CCL25 regulates anti-apoptotic signaling proteins, leading to a significant inhibition of etoposide-induced apoptosis in the presence of CCL25. Blocking the CCR9/CCL25 pathway with CCR9 antagonists reverses this apoptosis inhibition. Elevated CCR9 expression is connected with increased migration and invasion of prostate tumor cells, and inhibiting the CCR9/CCL25 interaction effectively reduces their migration and invasive potential ^[20-21].

4.4 CCR9 and Ovarian Cancer Research

The study used tissue microarray and immunohistochemistry to examine CCR9 expression in epithelial ovarian cancer tissues, analyzing its relationship with clinicopathological features. Results indicated higher levels of CCR9 and CCL25 in ovarian cancer compared to normal tissues, associated with positive lymph node metastasis, histologic grading, and clinical stage. Elevated CCR9 expression in ovarian cancer tissues, particularly in specific subtypes, suggests its potential role in cancer progression. In vitro studies further highlighted the significant impact of CCR9-CCL25 interaction in promoting the invasive and migratory behavior of ovarian cancer cells ^[22-23].

4.5 CCR9 and Breast Cancer Research

In breast cancer, CCR9 expression is significantly higher in tumor tissues than in adjacent normal tissues, especially in poorly differentiated tumors. The CCR9/CCL25 axis creates a favorable environment for breast tumor cell growth and imparts resistance to cisplatin in a PI3K/Akt-dependent manner. In vitro experiments indicate that CCR9 expression correlates with tumor invasiveness, being high in highly invasive breast cancer cell lines and significantly lower in less invasive ones. Transwell assays confirm that CCR9-CCL25 promotes invasion and migration of breast cancer cells. Thus, the role of the CCR9/CCL25 axis in breast cancer development and progression parallels its impact in colon and ovarian cancers ^[24-26].

4.6 CCR9 and Pancreatic Cancer Research

Cellular experiments revealed that the interaction between chemokine receptor CCR9 and its ligand CCL25 significantly boosted the proliferation of adenoepithelial endothelial tumors and pancreatic cancer cells. CCR9 was expressed in pancreatic cancer tissues, and cancer cells produced CCL25, leading to increased CCR9 expression and promoting cancer cell invasion. Both CCR9 and CCL25 were present in draining lymph nodes, pancreatic cancer tissues, and benign lesions, with the highest expression in draining lymph nodes. The CCR9-CCL25 interaction in pancreatic cancer strongly correlated with lymph node metastasis, tumor cell differentiation, and TNM stage. Researchers suggest that CCR9 could be a promising focus for comprehensive treatment research in pancreatic cancer ^[27-28].

4.7 CCR9 and Lung Adenocarcinoma Research

High CCR9 and ALDH1A1 expression in lung adenocarcinoma strongly links to distant metastasis and poor prognosis. ALDH1A1 expression and distant metastasis independently pose risks to overall survival. Further investigation reveals a positive correlation between CCR9 and ALDH1A1 expression in lung adenocarcinoma. CCR9 expression notably rises in ALDHhigh cells, and the CCR9/CCL25 signaling pathway significantly promotes migration and invasion of lung adenocarcinoma tumor stem cells (CSCs). This study uncovers a new mechanism for distant metastasis and poor prognosis in lung adenocarcinoma, suggesting CCR9/CCL25 as a potential therapeutic target ^[29-30].

4.8 CCR9 and Non-Small Cell Lung Cancer Research

Examining the expression of CCR9 in non-small cell lung cancer (NSCLC) tissues and adjacent tissues revealed high CCR9 expression in NSCLC tissues, consistent with findings in the NCI-H157 NSCLC cell line. In contrast, normal human bronchial epithelial cells (BEAS-2B) showed no detectable CCR9 expression. In vitro experiments further confirmed the significant role of the CCR9-CCL25 pair in the invasive and migratory capacity of NSCLC cells. This study establishes that CCR9/CCL25 is highly expressed in NSCLC and is associated with NSCLC lymph node metastasis. However, the specific molecules involved in its action remain undisclosed and require further investigation ^[31-34].

4.9 CCR9 and Hepatocellular Carcinoma Research

Using immunohistochemical methods, significantly elevated CCR9 levels were found in hepatocellular carcinoma (HCC) tissues, correlating with patient prognosis. CCR9 expression inversely related to overall survival (OS) in HCC patients, serving as an independent prognostic factor. Further studies revealed that the poor prognosis associated with high CCR9 expression is due to downregulation of cell cycle regulators p21 and p27, coupled with upregulation of cell cycle protein D1, promoting enhanced proliferation and tumorigenicity in HCC. Thus, CCR9 emerges as a novel prognostic marker for HCC. However, the role of CCR9/CCL25 in hepatocellular carcinoma requires further systematic studies ^[35].

4.10 CCR9 and Melanoma Research

CCR9 was highly expressed in melanoma small intestinal metastases, melanoma cells, and derived cell lines, suggesting a crucial role in small intestinal metastasis. Notably, CCR9 expression was specific to melanomas metastasizing to the intestine, indicating a selective process. In vitro, the CCR9/CCL25 axis significantly enhanced melanoma cell invasion and migration, but disrupting this axis with an anti-CCR9 antibody or RNA interference technology markedly reduced its promotion of these abilities ^[36-40].

5. The Prospects for Clinical Drug Research of CCR9

Seven drugs, including SRB1, NR11/1943 (Norgine), OB-003, CCX-025, MLN-3126, Vercirnon Sodium, and CCX-5072, have been investigated as CCR9 antagonists. These drugs block CCR9's interaction with the CCL25 ligand, inhibiting T cell migration and activation. Explored for conditions like inflammatory bowel disease, tumors, and various digestive, immune, ocular, oral, and jaw-related diseases, these drugs are at different developmental stages, with some in clinical trials. Developed by organizations like Sunrock Biopharma SL, Norgine Ltd., and Orion Biotechnology Canada Ltd., most are small molecule compounds and an antibody. Recent research highlights CCR9's significant role in tumorigenesis, making it not just a prognostic indicator but also a potential target for drugs disrupting the CCL25/CCR9 axis. While promising, further studies are crucial for establishing a pharmacological basis for future CCR9 targeting research.

In Conclusion:

CCR9, a chemokine receptor, emerges as a significant player in various cancers. Its high expression signifies unfavorable outcomes, notably in melanoma's small intestinal metastasis. The CCR9/CCL25 axis significantly promotes cancer cell invasion and migration. Seven drugs act as CCR9 antagonists, holding promise for applications in various diseases, including tumors. CCR9 serves as both a prognostic indicator and a potential therapeutic target in cancer research, with ongoing clinical trials for certain drugs. Further studies are essential to establish a robust foundation for CCR9-targeted therapies.

6. CUSABIO CCR9 Recombinant Proteins & Antibodies for Research Use

To fully support researchers and pharmaceutical companies in their research on CCR9 in inflammatory, autoimmune, and tumor diseases, CUSABIO presents CCR9 active proteins & antibodies to support your research on the mechanism of CCR9 or its potential clinical value.

CUSABIO CCR9 Protein

● Recombinant Human C-C chemokine receptor type 9 (CCR9)-VLPs (Active) Code: CSB-MP004848HU

High Purity Validated by SDS-PAGE and SEC-HPLC

CSB-MP004848HU is detected by Mouse anti-6*His monoclonal antibody. The purity of VLPs was greater than 95% as determined by SEC-HPLC.

Excellent Bioactivity Validated by Functional ELISA

Immobilized Human CCR9 at 10μg/mL can bind Anti-CCR9 recombinant antibody (CSB-RA004848MA1HU). The EC₅₀ is 31.67-36.83 ng/mL.The VLPs (The VLPs (CSB-MP3838) is negative control.

● Recombinant Human Atypical chemokine receptor 2 (ACKR2) (Active) Code: CSB-CF004618HU

High Purity Validated by SDS-PAGE

(Tris-Glycine gel) Discontinuous SDS-PAGE (reduced) with 5% enrichment gel and 15% separation gel.

Excellent Bioactivity Validated by Functional ELISA

Immobilized ACKR2 at 1 μg/ml can bind human CCL2. The EC₅₀ of human CCL2 protein is 23.52-30.99 μg/ml.