The immune system is a critical element of the host defense against invasion by infectious organisms. Although the role of this system in cancer has yet to be fully defined, there has been considerable progress in understanding how cancer cells escape from """"""""immune surveillance"""""""" or """"""""the immune system"""""""" and also how this system can be amplified to treat cancer patients. The main focus of our research is to dissect the molecular mechanisms regulating the transition from innate to adaptive immunity and identify a new means to control this complex system.Chemokines are small molecular weight, secreted proteins that regulate the trafficking of leukocytes in both physiological and pathological conditions. Recent studies have indicated that metastasis of some cancer cells is also regulated by the chemokine/chemokine receptor system, reinforcing the relevance of studies defining this complex system to cancer. We previously purified and cloned the human chemokine monocyte chemoattractant protein-1 (MCP-1), also known as CCL2, as a molecule potentially responsible for the recruitment of monocytes to sites of delayed-type hypersensitivity (DTH) reaction, an adaptive immune response, and also to tumors in which macrophage infiltration is commonly observed. Studies of MCP-1-deficient mice performed by others defined this molecule as a major monocyte chemoattractant in vivo. In addition, MCP-1 is reported to attract T cells, NK cells and dendritic cells (DCs), and to play a role in the replication of human immunodeficiency virus-1. Thus, MCP-1 is involved in the pathogenesis chronic inflammatory diseases and cancer.MCP-1 is produced by multiple cell types, including macrophages, endothelial cells, epithelial cells and neutrophils. Acute neutrophil-mediated innate immune responses precede subsequent mononuclear cell-dependent chronic inflammation and adaptive immune responses. We, therefore, hypothesized that neutrophil-derived MCP-1 may contribute to the transition from innate to adaptive immunity by attracting monocytes and lymphocytes to sites of injury. To test the hypothesis, we initiated the construction of conditional MCP-1 knockout mice in which the MCP-1 gene is specifically deleted in neutrophils using the Cre/loxP system. We recently succeeded in generating MCP-1-floxed mice, allowing us to generate mice in which the MCP-1 gene is disrupted in myeloid cells (neutrophils and macrophages) or endothelial cells by intercrossing them with existing Cre-expressing mice, such as LysMcre or tie1-cre mice. Macrophages, including foam cells seen in atherosclerosis, and endothelial cells are well known sources of MCP-1, and MCP-1 produced by these cell types is postulated to play a role in monocyte recruitment. Thus, the generation of the MCP-1 floxed mice will enable us to investigate the contribution of MCP-1 produced by distinct cell types, such as myeloid cells or endothelial cells, in the development of innate and adaptive immune responses and to provide cellular targets to intervene in MCP-1 production.In the course of our previous analysis of the mechanisms regulating the expression of MCP-1 in neutrophils, we obtained evidence suggesting that activation with cytokines could induce further maturation of neutrophils and the maturation step was critical for their ability to express MCP-1. To evaluate whether such activated neutrophils develop the capacity to express a repertoire of additional gene products involved in immunity, we performed cDNA arrays, and sequential analysis of gene expression. These studies led us to discover several novel neutrophil gene products involved in immunity, including discoidin domain receptor 1 (DDR1) and chemokine (CC-motif) receptor-like 2 (CCRL2).DDR1, a receptor tyrosine kinase, is highly expressed on malignant tumors of epithelial cell origin, and implicated in tumor invasion. We subsequently detected the induction of DDR1 not only in neutrophils but also in monocytes and lymphocytes, important participants in adaptive immunity. Since DDR1 is activated by binding to collagen, the most abundant protein in the extracellular matrix, we hypothesized that the interaction of DDR1 with collagen could influence the migratory behavior and maturation/differentiation of leukocytes in a tissue microenvironment. In fact, we determined that overexpression of the DDR1a isoform in the human leukemic cell line, THP-1, promoted their migration in three-dimensional collagen lattices. In contrast, interaction of the DDR1b isoform with collagen promoted the differentiation/maturation of macrophages and DCs and up-regulated the production of chemokines in macrophages. We showed, for the first time, that the DDR1b signaling targets two biologically important signaling molecules, p38 mitogen-activated protein kinase (MAPK) and NF-?B. Our future studies will be focused to define the contribution of DDR1 to the development of immune responses in vivo and to identify signaling events that lead to the activation of p38 MAPK and NF-?B.The human Ccrl2 gene codes for an orphan G-protein coupled receptor and is located on the chromosome 3 in close proximity to other known chemokine receptors including CCR5, CCR2, CX3CR1, CCR3 and CCR8. Since all these chemokine receptors are G protein-coupled receptors, we hypothesized that CCRL2 is a functional chemokine receptor. We recently studied the expression and functional significance of this receptor. CCRL2 is highly expressed by neutrophils infiltrating the joints of rheumatoid arthritis (RA) patients. In vitro, CCRL2 expression can be up-regulated in neutrophils by lipopolysaccharide or tumor necrosis factor-a, and CCRL2-transduced HEK293 cells migrated in response to RA joint fluids, indicating that CCRL2 is a functional receptor, potentially responding to chemokine(s) in the fluids. We currently focus on identifing the ligands for this receptor.
Showing the most recent 10 out of 18 publications
