A major risk factor for colon cancer growth and progression is chronic inflammation. We have shown that the MAPK-activated protein kinase 2 (MK2) pathway is critical for colon tumor growth in colitis-associated and spontaneous colon cancer models. This pathway is known to regulate expression of the tumor-promoting cytokines, IL-1, IL-6, and TNF-α. However, little is known about the ability of MK2 to regulate chemokine production. This is the first study to demonstrate this pathway also regulates the chemokines, MCP-1, Mip-1α, and Mip-2α (MMM). We show that these chemokines induce tumor cell growth and invasion and that MK2 inhibition suppresses tumor cell production of chemokines and reverses the resulting pro-tumorigenic effects. Addition of MMM to colon tumors significantly enhances tumor growth in control tumors and restores tumor growth in the presence of MK2 inhibition. We also demonstrate that MK2 signaling is critical for chemokine expression and macrophage influx to the colon tumor microenvironment. MK2 signaling in macrophages was essential for inflammatory cytokine/chemokine production, whereas MK2 macrophages or MK2 inhibition suppressed cytokine expression. We show that addition of bone marrow-derived macrophages to the tumor microenvironment enhances tumor growth in control tumors and restores tumor growth in tumors treated with MK2 inhibitors, while addition of MK2 macrophages had no effect. This is the first study to demonstrate the critical role of the MK2 pathway in chemokine production, macrophage influx, macrophage function, and tumor growth.

Recruitment of immune cells from the vasculature relies on the presentation of glycosaminoglycan-bound chemokines on the luminal side of vascular endothelial cells. However, the current model of chemokine-glycosaminoglycan interactions, and its implications for receptor interactions, remains poorly developed. We propose a refined 'Chemokine Cloud' model, arguing that chemokines are not presented to leukocytes bound to glycosaminoglycans, but rather, in solution while sequestered within the hydrated glycocalyx. We posit that glycosaminoglycans provide an immobilized chemokine depot maintaining a 'cloud' of 'solution-phase' chemokines within the glycocalyx, and that it is this soluble form of any given chemokine that interacts with leukocyte-bound receptors. Our proposition clarifies certain anomalies associated with the current model of chemokine-glycosaminoglycan interactions, with implications for the design of blockers of chemokine function.

Chemokines are small secreted proteins that orchestrate migration and positioning of immune cells within the tissues. Chemokines are essential for the function of the immune system. Accumulating evidence suggest that chemokines play important roles in tumor microenvironment. In this review we discuss an association of chemokine expression and activity within the tumor microenvironment with cancer outcome. We summarize regulation of immune cell recruitment into the tumor by chemokine-chemokine receptor interactions and describe evidence implicating chemokines in promotion of the "inflamed" immune-cell enriched tumor microenvironment. We review both tumor-promoting function of chemokines, such as regulation of tumor metastasis, and beneficial chemokine roles, including stimulation of anti-tumor immunity and response to immunotherapy. Finally, we discuss the therapeutic strategies target tumor-promoting chemokines or induce/deliver beneficial chemokines within the tumor focusing on pre-clinical studies and clinical trials going forward. The goal of this review is to provide insight into comprehensive role of chemokines and their receptors in tumor pathobiology and treatment.

T-cell trafficking at vascular sites has emerged as a key step in antitumour immunity. Chemokines are credited with guiding the multistep recruitment of CD8(+) T cells across tumour vessels. However, the multiplicity of chemokines within tumours has obscured the contributions of individual chemokine receptor/chemokine pairs to this process. Moreover, recent studies have challenged whether T cells require chemokine receptor signalling at effector sites. Here we investigate the hierarchy of chemokine receptor requirements during T-cell trafficking to murine and human melanoma. These studies reveal a non-redundant role for Gαi-coupled CXCR3 in stabilizing intravascular adhesion and extravasation of adoptively transferred CD8(+) effectors that is indispensable for therapeutic efficacy. In contrast, functional CCR2 and CCR5 on CD8(+) effectors fail to support trafficking despite the presence of intratumoral cognate chemokines. Taken together, these studies identify CXCR3-mediated trafficking at the tumour vascular interface as a critical checkpoint to effective T-cell-based cancer immunotherapy.

OBJECTIVE:Our previous studies have identified CXCL8 as the crucial chemokine responsible for gastric cancer metastasis mediated by loss of RACK1. However, the regulatory effect of CXCL8 on immune surveillance in gastric cancer remains obscure. DESIGN:Flow cytometry analyses were performed to examine major source of CXCL8 and phenotypes of immune cells in fresh tumour tissues from 76 patients with gastric cancer. Real-time PCR was performed to analyse CXCL8 mRNA level in gastric cancer tissues. For immunohistochemical analyses, a total of 420 patients with gastric cancer undergoing curative resection were enrolled. In vitro culture of fresh tumour tissue was performed to evaluate the potential therapeutic effect of blocking CXCL8 pathway in gastric cancer. RESULTS:Increased level of CXCL8 indicates poor clinical outcome and tumour progression in patients with gastric cancer. In gastric cancer tissues, CXCL8 is predominantly secreted by macrophages and colony stimulating factor 2 (CSF-2) facilitates macrophage-derived CXCL8 secretion. High level of CXCL8 is associated with decreased CD8 T cells infiltration and Ki67 CD8 T cells proportion. Moreover, CXCL8 also inhibits CD8 T cells function by inducing the expression of PD-L1 on macrophages. Finally, we show that a small-molecule CXCR2 inhibitor, reparixin, drives the decreased programmed death-ligand 1 (PD-L1) macrophages and promotes antitumour immunity. Accordingly, high levels of CXCL8 macrophages are positively correlated with poor prognosis in patients with gastric cancer. CONCLUSIONS:CXCL8 is predominantly secreted by macrophages and contributes to the immunosuppressive microenvironment by inducing PD-L1 macrophages in gastric cancer. CXCL8 inhibitors may drive antitumour response, providing potential therapeutic effects for patients with gastric cancer.

We investigated the role of chemokines in regulating T cell accumulation in solid tumors. CCL5 and CXCL9 overexpression was associated with CD8 T cell infiltration in solid tumors. T cell infiltration required tumor cell-derived CCL5 and was amplified by IFN-γ-inducible, myeloid cell-secreted CXCL9. CCL5 and CXCL9 coexpression revealed immunoreactive tumors with prolonged survival and response to checkpoint blockade. Loss of CCL5 expression in human tumors was associated with epigenetic silencing through DNA methylation. Reduction of CCL5 expression caused tumor-infiltrating lymphocyte (TIL) desertification, whereas forced CCL5 expression prevented Cxcl9 expression and TILs loss, and attenuated tumor growth in mice through IFN-γ. The cooperation between tumor-derived CCL5 and IFN-γ-inducible CXCR3 ligands secreted by myeloid cells is key for orchestrating T cell infiltration in immunoreactive and immunoresponsive tumors.

As main drivers of leukocyte recruitment during inflammatory reactions, chemokines act as mediatrs of alarmins in priming host defense responses after tissue exposure to toxic or infectious agents, immunomediated damage, and in inflammation-driven tumors. Chemokines can therefore be considered alarm signals generated by tissues in a broad number of conditions, and mechanisms controlling chemokines biological activities are therefore key to regulate tissue reactions induced by alarmins. By transporting, presenting or scavenging different sets of chemokines, atypical chemokine receptors represent an emerign subfamily of chemokine receptors which operates in tissues as chemokine gatekeepers in order to establish and shape their gradients and coordinate leukocyte recruitment.

Chemokines are chemotactic cytokines that direct the traffic of leukocytes and other cells in the body. Chemokines bind to G protein-coupled receptors expressed on target cells to initiate signaling cascades and induce chemotaxis. Although the cognate receptors of most chemokines have been identified, the receptor for the mucosal chemokine CXCL17 is undefined. In this article, we show that GPR35 is the receptor of CXCL17. GPR35 is expressed in mucosal tissues, in CXCL17-responsive monocytes, and in the THP-1 monocytoid cell line. Transfection of GPR35 into Ba/F3 cells rendered them responsive to CXCL17, as measured by calcium-mobilization assays. Furthermore, GPR35 expression is downregulated in the lungs of Cxcl17(-/-) mice, which exhibit defects in macrophage recruitment to the lungs. We conclude that GPR35 is a novel chemokine receptor and suggest that it should be named CXCR8.