Abstract
Carcinoembryonic antigen-related cell adhesion molecule 1 (CEACAM1), a cell adhesion molecule expressed on epithelial cells and activated immune cells, is downregulated in many cancers and plays a role in inhibition of inflammation in part by inhibition of granulocyte colony-stimulating factor (G-CSF) production by myeloid cells. As macrophages are associated with a poor prognosis in breast cancer, but play important roles in normal breast, we hypothesized that CEACAM1 downregulation would lead to tumor promotion under inflammatory conditions. Cocultures of proinflammatory M1 macrophages with CEACAM1 negative MCF7 breast cells produced high levels of G-CSF (10 ng/mL) compared to CEACAM1-transfected MCF7/4S cells (1 ng/mL) or anti-inflammatory M2 macrophage cocultures (0.5 or 0.1 ng/mL, MCF7 or MCF7/4S, respectively). The expression of CEACAM1 on M1s was much greater than for M2s and was observed only in cocultures with either MCF7 or MCF7/4S cells. When M1 macrophages were mixed with MCF7 cells and implanted in murine mammary fat pads of nonobese diabetic/severe combined immunodeficient mice, tumor size and blood vessel density were significantly greater than MCF7 or MCF7/4S only tumors which were hardly detected after 8 weeks of growth. In contrast, M1 cells had a much reduced effect on MCF7/4S tumor growth and blood vessel density, indicating that the tumor inhibitory effect of CEACAM1 is most likely related to its anti-inflammatory action on inflammatory macrophages. These results support our previous finding that CEACAM1 inhibits both G-CSF production by myeloid cells and G-CSF-stimulated tumor angiogenesis.