Abstract
Elevated macrophage infiltration in tumor tissues is associated with breast cancer metastasis. Cancer cell migration/invasion toward angiogenic microvasculature is a key step in metastatic spread. We therefore studied how macrophages stimulated breast cancer cell interactions with endothelial cells. Macrophages produced cytokines, such as interleukin-8 and tumor necrosis factor-α, to stimulate endothelin (ET) and ET receptor (ETR) expression in breast cancer cells and human umbilical vascular endothelial cells (HUVECs). ET-1 was induced to a greater extent from HUVECs than from breast cancer cells, resulting in a density difference that facilitated cancer cell chemotaxis toward HUVECs. Macrophages also stimulated breast cancer cell adhesion to HUVECs and transendothelial migration, which were repressed by ET-1 antibody or ETR inhibitors. The ET axis induced integrins, such as αV and β1, and their counterligands, such as intercellular adhesion molecule-2 and P-selectin, in breast cancer cells and HUVECs, and antibodies against these integrins efficiently suppressed macrophage-stimulated breast cancer cell interactions with HUVECs. ET-1 induced Ets-like kinase-1 (Elk-1), signal transducer and activator of transcription-3 (STAT-3), and nuclear factor-κB (NF-κB) phosphorylation in breast cancer cells. The use of inhibitors to prevent their phosphorylation or ectopic overexpression of dominant-negative IκBα perturbed ET-1-induced integrin αV and integrin β1 expression. The physical associations of these three transcriptional factors with the gene promoters of the two integrins were furthermore evidenced by a chromatin immunoprecipitation assay. Finally, our mouse orthotopic tumor model revealed an ET axis-mediated lung metastasis of macrophage-stimulated breast cancer cells, suggesting that the ET axis was involved in macrophage-enhanced breast cancer cell endothelial interactions.
Highlights
The relation between tumor-infiltrating macrophages and tumor cell migration/invasion toward blood vessels remained unclear
The results revealed that both ET receptor (ETR)-A and ETR-B levels were significantly increased in Macrophage-conditioned medium (MCM)-treated MCF-7 cells; only ETR-B was induced in human umbilical vascular endothelial cells (HUVECs) (Fig. 1A)
The results indicated that in both MCF-7 cells and HUVECs, the induction of ET and ETR expression by MCM was drastically blocked by IL-8RA and sTNFR (Fig. 1D), suggesting that macrophages stimulated ET and ETR expression through the secretion of IL-8 and TNF-␣
Summary
The relation between tumor-infiltrating macrophages and tumor cell migration/invasion toward blood vessels remained unclear. Results: Macrophage induced the endothelin-integrin axis to stimulate breast cancer cell chemotaxis and adhesion toward endothelial cells and transendothelial migration. Our mouse orthotopic tumor model revealed an ET axis-mediated lung metastasis of macrophagestimulated breast cancer cells, suggesting that the ET axis was involved in macrophage-enhanced breast cancer cell endothelial interactions. The malignancy of many human cancers represented by breast cancer is correlated with elevated levels of macrophage infiltration (reviewed in Ref. 2) These tumor-infiltrating macrophages can act as an important promoter of tumor progression, most notably via paracrine interaction with tumor cells, to enhance tumor cell migration/invasion, tumor angiogenesis, and metastasis (3–7). The ET axis is associated with tumor angiogenesis by directly modulating endothelial cell proliferation, migration, invasion, protease production, and tube formation or by indirectly inducing hypoxia-inducible factor-1␣-mediated VEGF production in cancer cells (12–16). Our mouse orthotopic tumor model revealed that the ET axis was involved in MCM-stimulated lung metastasis of breast cancer
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
