Crucial Involvement of Tumor-Associated Neutrophils in the Regulation of Chronic Colitis-Associated Carcinogenesis in Mice

Abstract

Ulcerative colitis (UC) is a major form of chronic inflammation that can frequently progress to colon cancer. Several studies have demonstrated massive infiltration of neutrophils and macrophages into the lamina propria and submucosa in the progression of UC-associated colon carcinogenesis. Macrophages contribute to the development of colitis-associated colon cancer (CAC). However, the role of neutrophils is not well understood. To better understand the involvement of tumor-associated neutrophils (TANs) in the regulation of CAC, we used a mouse CAC model produced by administering azoxymethane (AOM), followed by repeated dextran sulfate sodium (DSS) ingestion. This causes severe colonic inflammation and subsequent development of multiple tumors in mice colon. We observed that colorectal mucosal inflammation became increasingly severe with AOM and DSS treatment. Macrophages infiltrated the lamina propria and submucosa, together with a marked increase in neutrophil infiltration. The chemokine CXCL2 increased in the lamina propria and submucosal regions of the colons of the treated mice, together with the infiltration of neutrophils expressing CXCR2, a specific receptor for CXCL2. This process was followed by neoplastic transformation. After AOM and DSS treatment, the mice showed enhanced production of metalloproteinase (MMP)-9 and neutrophil elastase (NE), accompanied by excessive vessel generation and cell proliferation. Moreover, CXCL2 promoted neutrophil recruitment and induced neutrophils to express MMP-9 and NE in vitro. Furthermore, administration of neutrophil-neutralizing antibodies after the last DSS cycle markedly reduced the number and size of tumors and decreased the expression of CXCR2, CXCL2, MMP-9, and NE. These observations indicate a crucial role for TANs in the initiation and progression of CAC and suggest that the CXCL2–CXCR2 axis might be useful in reducing the risk of UC-associated colon cancer.

The Multifaceted Roles Neutrophils Play in the Tumor Microenvironment

“…Under certain circumstances, administration of neutrophilneutralizing antibodies reduced the number and size of tumors [261,264,265]. The tumorigenic effect of MMP-9, predominantly provided by neutrophils and mast cells, was also reported in a mouse model of skin cancer where MMP-9 knockout mice showed decreased incidence of invasive tumors [266].…”

“…Neutrophil-induced genotoxicity has been related to induction of oxidative DNA damage through release of ROS and myeloperoxidase-related metabolites [258][259][260]. In addition, neutrophils were shown to promote experimental chronic colitis-associated carcinogenesis in mice [261]. Neutrophil recruitment to the inflamed submucosa was mediated by the chemokine CXCL2 through the neutrophil receptor CXCR2, resulting in increased neutrophil secretion of MMP-9 and neutrophil elastase, and consequent excessive angiogenesis and cell proliferation [261].…”

“…In addition, neutrophils were shown to promote experimental chronic colitis-associated carcinogenesis in mice [261]. Neutrophil recruitment to the inflamed submucosa was mediated by the chemokine CXCL2 through the neutrophil receptor CXCR2, resulting in increased neutrophil secretion of MMP-9 and neutrophil elastase, and consequent excessive angiogenesis and cell proliferation [261]. Elastase degrades barrier-forming proteins on epithelial cells [262] and neutrophil-derived elastase was found to degrade the adhesion molecule E-Cadherin on pancreatic ductal adenocarcinoma, leading to tumor cell dyshesion and increased migratory capacity [206].…”

Neutrophils in cancer: neutral no more

“…Inflammation plays an essential role in initiating tumorigenesis by damaging specific tissues 100 (Figure 3). In these models, neutrophils are attracted to tumor-prone tissues via the CXCR2 ligands, CXCL1, CXCL2 and CXCL5 [101][102][103][104] . Application of these carcinogens to CXCR2-deficient mice, which show impaired neutrophil trafficking, prevents papilloma or adenoma formation 102,104 .…”

“…However, it should be noted that CXCR2 expression is not exclusive to neutrophils. Depletion of the entire neutrophil population using anti-Ly6G antibodies phenocopies CXCR2 deficiency and hinders tumorigenesis in both chemically induced 101,102 and spontaneous tumor models 102 . In a zebrafish model of Hras G12V -driven melanoma, wounding-induced inflammation increases the formation of tumors in a neutrophil-dependent manner 105 .…”