Chemokine CXCL14; a double-edged sword in cancer development.

Cancer is a leading cause of death worldwide and imposes a substantial financial burden. Therefore, it is essential to develop cost-effective approaches to inhibit tumor growth and development. The imbalance of cytokines and chemokines play an important role among different mechanisms involved in cancer development. One of the strongly conserved chemokines that is constitutively expressed in skin epithelia is the chemokine CXCL14. As a member of the CXC subfamily of chemokines, CXCL14 is responsible for the infiltration of immune cells, maturation of dendritic cells, upregulation of major histocompatibility complex (MHC)-I expression, and cell mobilization. Moreover, dysregulation of CXCL14 in several cancers has been identified by several studies. Depending on the type or origin of the tumor and components of the tumor microenvironment, CXCL14 plays a conflicting role in cancer. Although fibroblast-derived CXCL14 has a tumor-supportive role, epithelial-derived CXCL14 mainly inhibits tumor progression. Hence, this review will elucidate what is known on the mechanisms of CXCL14 and its therapeutic approaches in tumor treatment. CXCL14 is a promising approach for cancer immunotherapy.

Smoking-induced CXCL14 expression in the human airway epithelium links chronic obstructive pulmonary disease to lung cancer.

CXCL14, a recently described epithelial cytokine, plays putative multiple roles in inflammation and carcinogenesis. In the context that chronic obstructive pulmonary disease (COPD) and lung cancer are both smoking-related disorders associated with airway epithelial disorder and inflammation, we hypothesized that the airway epithelium responds to cigarette smoking with altered CXCL14 gene expression, contributing to the disease-relevant phenotype. Using genome-wide microarrays with subsequent immunohistochemical analysis, the data demonstrate that the expression of CXCL14 is up-regulated in the airway epithelium of healthy smokers and further increased in COPD smokers, especially within hyperplastic/metaplastic lesions, in association with multiple genes relevant to epithelial structural integrity and cancer. In vitro experiments revealed that the expression of CXCL14 is induced in the differentiated airway epithelium by cigarette smoke extract, and that epidermal growth factor mediates CXCL14 up-regulation in the airway epithelium through its effects on the basal stem/progenitor cell population. Analyses of two independent lung cancer cohorts revealed a dramatic up-regulation of CXCL14 expression in adenocarcinoma and squamous-cell carcinoma. High expression of the COPD-associated CXCL14-correlating cluster of genes was linked in lung adenocarcinoma with poor survival. These data suggest that the smoking-induced expression of CXCL14 in the airway epithelium represents a novel potential molecular link between smoking-associated airway epithelial injury, COPD, and lung cancer.

Antibody-assisted enhancement of biological activities of CXCL14 in human monocytic leukemia-derived THP-1 cells and high fat diet-induced obese mice.

CXCL14 is a CXC-type chemokine acting on tissue macrophages, immature dendritic cells, natural killer cells, and epithelial tumor cells. It also serves as a metabolic regulator in obese mice by blunting insulin activity. In contrast to other CXC chemokines, it remains to be clarified how CXCL14 activates its putative receptors on the cell surface and whether it induces chemokinesis. This is mainly due to the insufficient sensitivity of currently available bioassays for CXCL14. In this study, we found that the anti-CXCL14 monoclonal antibody, MAB730, remarkably enhances the activities of CXCL14 in human monocytic leukemia-derived THP-1 cells and immature dendritic cells. MAB730 augmented CXCL14-mediated chemotaxis and chemokinesis with distinct dose requirement. Chemotaxis inducing activity was retained in the MAB730 F(ab')(2) fraction, but not in the Fab fraction, implying that ligand dimerization is involved in the MAB730-assisted enhancement of CXCL14 activity. In addition, MAB730 was more efficient than heparin at inhibiting CXCL14 binding to low affinity receptors on THP-1 cells. Finally, in vivo administration of MAB730 antibody into high fat diet-induced obese mice increased whole body insulin resistance and glucose intolerance. These unique properties of MAB730 will be useful for elucidating the molecular mechanism of cellular responses elicited by CXCL14.

Increased plasma levels of stromal-derived factor-1 (SDF-1/CXCL12) enhance human thrombopoiesis and mobilize human colony-forming cells (CFC) in NOD/SCID mice.

OBJECTIVE: Stromal-derived factor-1 (SDF-1/CXCL12) is chemotactic for lympho/hematopoietic stem cells. We have previously shown that increasing peripheral blood (PB) levels of SDF-1 with adenovectors expressing human SDF-1 complementary DNA (ad-SDF-1) leads to hematopoietic stem cell mobilization as well as migration of megakaryocytes and thrombocytosis in mice. Herein, we studied the in vivo effects of ad-SDF-1 and of an analogue peptide of SDF-1 (CTCE-0214) on human hematopoiesis in a xenotransplant model. MATERIALS AND METHODS: Sublethally irradiated (300 cGY) NOD/SCID mice transplanted with human cord blood mononuclear cells (CB MNC) were injected with ad-SDF-1 (10(9) plaque forming units, i.v., x 1) or CTCE-0214 (10 mg/kg/dose, i.v. q 24 hours x 7). Effects on megakaryocytopoiesis (CD41+ cells and platelets) as well as stem cell mobilization were monitored. RESULTS: CB MNC in NOD/SCID mice are able to differentiate into CD41+ cells and platelets, peaking at week 9 at a mean of 3.7 x 10(3)/microL. i.v. injection of ad-SDF-1 increased human CD41+ cells by day 4 in PB and was followed by an increase in human platelet production by day 5, with return to baseline by day 30. Human colony-forming cells (CFC) were mobilized from bone marrow to spleen (by day 6-13) and to PB (by day 13). Human CD34+ and CD33+ cells were mobilized by this treatment as well. A novel SDF-1 peptide agonist (CTCE-0214) also mobilized human CFC and enhanced human thrombopoiesis. CONCLUSION: SDF-1 and its analogue may be of clinical value in stimulating platelet recovery after chemo/radiation treatment as well as in stem cell mobilization.

Two novel fully functional isoforms of CX3CR1 are potent HIV coreceptors.

We identified two novel isoforms of the human chemokine receptor CX3CR1, produced by alternative splicing and with N-terminal regions extended by 7 and 32 aa. Expression of the messengers coding these isoforms, compared with that of previously described V28 messengers, is lower in monocytes and NK cells, but higher in CD4(+) T lymphocytes. CX3CR1 and its extended isoforms were expressed in HEK-293 cells and compared for expression, ligand binding, and cellular responses. In steady state experiments, all three CX3CR1 isoforms bound CX3CL1 with similar affinity. In kinetic binding studies, however, k(on) and k(off) were significantly greater for the extended CX3CR1 isoforms, thereby suggesting that the N-terminal extensions may alter the functions induced by CX3CL1. In signaling studies, all three CX3CR1 isoforms mediated agonist-dependent calcium mobilization, but the EC(50) was lower for the extended than for the standard isoforms. In addition, chemotactic responses for these extended isoforms shifted left, also indicating a more sensitive response. Finally, the longer variants appeared to be more potent HIV coreceptors when tested in fusion and infection assays. In conclusion, we identified and characterized functionally two novel isoforms of CX3CR1 that respond more sensitively to CX3CL1 and HIV viral envelopes. These data reveal new complexity in CX3CR1 cell activation and confirm the critical role of the N-terminal domain of the chemokine receptors in ligand recognition and cellular response.

Cloning, mRNA distribution, and functional expression of an avian counterpart of the chemokine receptor/HIV coreceptor CXCR4.

The chemokine signaling system, which coordinates the basal and emergency trafficking of leukocytes, presumably coevolved with the hematopoietic system. To study its phylogenetic origins, we used the open reading frame (ORF) of the human chemokine receptor CXCR4 as a genomic probe, since in mammals it is the most highly conserved chemokine receptor known. CXCR4 cross-hybridized to genomic DNA from mouse and chicken, but not zebrafish, Drosophila, or Caenorhabditis elegans. Accordingly, we cloned the corresponding chicken cDNA. The ORF is 359 codons long versus 352 for human CXCR4, and encodes a protein 82% identical to human CXCR4. In a calcium flux assay of receptor function, CHO-K1 cells stably transfected with the chicken cDNA responded specifically to human SDF-1, the specific ligand for CXCR4, but not to a panel of other chemokines tested at 100 nM. SDF-1 activated the cells in a dose-dependent manner (EC50 approximately 5 nM), whereas parental CHO-K1 cells did not respond. The CHO-K1 cell transfectants also bound 125I-SDF-1 specifically. Leukocytes from chicken peripheral blood expressed chCXCR4 mRNA and responded to human SDF-1 in a calcium flux assay with an EC50 similar to that for chCXCR4-transfected CHO cells, suggesting that this response is mediated by native chCXCR4. Analysis of chicken genomic DNA with the chicken cDNA as probe revealed a pattern consistent with a single copy gene, and the absence of any closely related genes. mRNA was detected in brain, bursa, liver, small and large intestine, embryonal fibroblasts, and blood leukocytes, but not in stomach or pancreas. These results, which identify the first functional non-viral, non-mammalian chemokine receptor, suggest that the origins of a functional chemokine system extend at least to birds and suggest that, as in mammals, CXCR4 functions in many avian tissues.

Adenosine diphosphate strongly potentiates the ability of the chemokines MDC, TARC, and SDF-1 to stimulate platelet function.

Platelet activation is normally induced by primary agonists such as adenosine diphosphate (ADP), thrombin, and collagen, whereas other agonists, such as epinephrine, can play important accessory roles. It is now reported that the macrophage-derived chemokine (MDC), thymus activation-regulated chemokine (TARC), and stromal cell-derived factor one (SDF-1) are highly effective activators of platelet function under a variety of conditions, stimulating platelet shape change, aggregation, and adhesion to collagen or fibrinogen. Chemokine-mediated platelet activation was rapid and maximal (less than 5 seconds) under arterial flow conditions and depended strongly on the presence of low levels of primary agonists such as ADP or thrombin. Concentrations of ADP (0.05-0.25 microM) or thrombin (0.005-0.02 U/mL) that induced minimal aggregation caused major aggregation acting in combination with the chemokines. The ability of apyrase to block chemokine-dependent aggregation or adhesion was consistent with an important role for ADP. Chemokine-stimulated aggregation was also insensitive to indomethacin, suggesting that the activation of cyclo-oxygenase is not involved. TARC, MDC, and SDF-1 increased intracellular calcium concentrations [Ca(2+)](i) when combined with low levels of ADP. The MDC and TARC receptor CCR4 was expressed on platelets, and an anti-CCR4 antibody blocked aggregation induced by TARC or MDC. Treatment of platelets with SDF-1 and MDC rapidly exposed P-selectin (CD62P) on the cell surface but did not induce the secretion of serotonin. These findings suggest that the chemokines MDC, TARC, and SDF-1, which may be produced during inflammatory responses, coupled with low levels of ADP or thrombin, can serve as strong stimuli for activating platelet function.