Transient expression of recombinant ACKR4 (CCRL1) gene, an atypical chemokine receptor in human embryonic kidney (HEK 293) cells

ACKR4 also called CCX-CKR, CCRL1 as a member of atypical chemokine receptors, regulates the biological responses by clearance or transporting homeostatic chemokines such as CCL19, CCL21, CCL25, and CXCL13. Since these chemokines are involved in cancer development and metastasis, ACKR4 could have inhibition roles in cancer cell proliferation and invasion. Forming complexes with chemokine receptors by ACKR4 as in the case of hCXCR3 which lead to chemotaxis prevention is the other function of this protein is. However, as an atypical chemokine receptor, ACKR4 is less well-characterized compared to other members. Here, as the first step in understanding the molecular mechanisms of ACKR4 action, transfectants in HEK293T cell, was generated. In this study, ACKR4 coding sequence was cloned and human embryonic kidney 293T cells were used for recombinant production of ACKR4 protein. The liposome-mediated transfection with ACKR4 CDs, were detected in ACKR4 positive cells as early as 48 h post-transfection. The production of ACKR4 protein was confirmed using RT-PCR, dot blot, western blot, and flow cytometry. ACKR4 may represent a novel molecular target in cancer therapy, which might provide a chance for new therapeutic strategy. Therefore, the first step in the understanding of the molecular mechanisms of ACKR4 action is generation ACKR4-HEK293T recombinant cells.

Naive Treg-like CCR7(+) mononuclear cells indicate unfavorable prognosis in hepatocellular carcinoma

Chemokine receptor-like 1 (CCRL1) has the potential in creating a low level of CCL19 and CCL21 to hinder CCR7(+) cell tracking to tumor tissue. Previously, we found a tumor suppressive role of CCRL1 by impairing CCR7-related chemotaxis of tumor cells in human hepatocellular carcinoma (HCC). Here, we reported a contribution of CCR7(+) mononuclear cells in the tumor microenvironment to the progression of disease. Immunohistochemistry was used to investigate the distribution and clinical significance of CCR7(+) cells in a cohort of 240 HCC patients. Furthermore, the phenotype, composition, and functional status of CCR7(+) cells were determined by flow cytometry, immunofluorescence, and in vitro co-culture assays. We found that CCR7(+) mononuclear cells were dispersed around tumor tissue and negatively related to tumoral expression of CCRL1 (P < 0.001, r = 0.391). High density of CCR7(+) mononuclear cells positively correlated with the absence of tumor capsule, vascular invasion, and poor differentiation (P < 0.05). Survival analyses revealed that increased number of CCR7(+) mononuclear cells was significantly associated with worse survival and increased recurrence. We found that CCR7(+) mononuclear cells featured a naive Treg-like phenotype (CD45RA(+)CD25(+)FOXP3(+)) and possessed tumor-promoting potential by producing TGF-β1. Moreover, CCR7(+) cells were also composed of several immunocytes, a third of which were CD8(+) T cells. CCR7(+) Treg-like cells facilitate tumor growth and indicate unfavorable prognosis in HCC patients, but fortunately, their tracking to tumor tissue is under the control of CCRL1.

Endogenous expression of the atypical chemokine receptor CCX-CKR (CCRL1) gene in human embryonic kidney (HEK 293) cells

CCX-CKR (CCRL1) as one of the chemokine receptor-like proteins is a scavenger of CCL19, CCL21, CCL25, and CXCL13 chemokines. Human CCX-CKR is expressed in various tissues. Since HEK 293 cells are used for both transient and stable expression of CCX-CKR gene, it is important to determine endogenous expression of CCX-CKR gene. Therefore, in the current study endogenous expression of CCX-CKR gene was evaluated in HEK 293 cells. To test the expression of CCX-CKR gene in HEK 293 cells, total RNA was isolated from HEK 293 cells and RT-PCR reaction was primed with the gene-specific primers. Protein expression is then evaluated by Western blot analysis and flow cytometry. Results of this study show that HEK 293 cells express an endogenous CCRL1 gene only at mRNA level. These data therefore represent the important implications for the use of HEK 293 cells as a host cell system for the study of CCX-CKR.

CCRL1/ACKR4 is expressed in key thymic microenvironments but is dispensable for T lymphopoiesis at steady state in adult mice

Thymus colonisation and thymocyte positioning are regulated by interactions between CCR7 and CCR9, and their respective ligands, CCL19/CCL21 and CCL25. The ligands of CCR7 and CCR9 also interact with the atypical receptor CCRL1 (also known as ACKR4), which is expressed in the thymus and has recently been reported to play an important role in normal αβT-cell development. Here, we show that CCRL1 is expressed within the thymic cortex, predominantly by MHC-II(low) CD40(-) cortical thymic epithelial cells and at the subcapsular zone by a population of podoplanin(+) thymic epithelial cells in mice. Interestingly, CCRL1 is also expressed by stromal cells which surround the pericytes of vessels at the corticomedullary junction, the site for progenitor cell entry and mature thymocyte egress from the thymus. We show that CCRL1 suppresses thymocyte progenitor entry into the thymus, however, the thymus size and cellularity are the same in adult WT and CCRL1(-/-) mice. Moreover, CCRL1(-/-) mice have no major perturbations in T-cell populations at different stages of thymic differentiation and development, and have a similar rate of thymocyte migration into the blood. Collectively, our findings argue against a major role for CCRL1 in normal thymus development and function.

CCRL1 marks heterogeneity in cortical and medullary thymic epithelial cells

Cortical thymic epithelial cells (cTECs) and medullary thymic epithelial cells (mTECs), which play essential roles in the establishment of a functionally competent and self-tolerant repertoire of T cells, are derived from common thymic epithelial progenitor cells (pTECs). Recent findings indicate that mTECs are derived from cells that express molecules that are abundant in cTECs rather than mTECs, and provide fresh insight into the characteristics of pTECs and their diversification pathways into TEC subpopulations. In this issue of the European Journal of Immunology, Ribeiro et al. [Eur. J. Immunol. 2014. 44: 2918-2924] focus on CCRL1, an atypical chemokine receptor that is highly expressed by cTECs rather than mTECs, and show that CCRL1-expressing embryonic TECs can give rise to mTECs. Interestingly, Ribeiro et al. further report that a fraction of postnatal mTECs express CCRL1 at a low level, suggesting novel complexity in mTECs.

Comparative modeling of CCRL1, a key protein in masked immune diseases and virtual screening for finding inhibitor of this protein

Human CCRL1 belongs to the family of silent chemokine receptors. This transmembrane protein plays a role in blunting function of chemokines through binding to them. This will attenuate immune responses. Interaction between CCRL1 and CCL21 determines this immune extinction. Thus inhibiting the action of this atypical chemokine seems to stimulate immune responses especially in the case of suppressed and immune deficient conditions. In this study we predicted 3D structure of CCRL1 using comparative modeling and Hiddebn Markov Model algorithm. Final predicted model optimized by Modeller v9.8 and minimized regarding energy level using UCSF chimera candidate version1.5.3. ClasPro webserver was used to find interacting residues between CCRL1 and CCL21. Interacting residues were used as target for chemical inhibitors by simulated docking study. For finding potential inhibitors, library of KEGG compounds screened and 97 obtained chemicals docked against interacting residues between CCRL1- CCL21 and MolDock was used as docking scoring function. Results indicated that Hexadecanal is a potential inhibitor of CCRL1- CCL21 interaction. Inhibition of this interaction will increase intercellular level of CCl21 and interaction between CCL21 and CCR7 causes immune potentiaiton.