MMP1, a matrix metalloproteinase that degrades the extracellular matrix, is produced not only by cancer cells but also synthesized in stromal and inflammatory cells during tumorigenesis, invasion and lung metastasis. However, the function of MMP1 expression from host cells, especially tumor-associated macrophages (TAMs), and cells in the lung parenchyma remains to be elucidated. Here we demonstrate that in vitro macrophages co-cultured with tumor cells drastically enhance MMP1 expression, which is further exacerbated upon cigarette smoke exposure. In addition, in vivo, macrophage specific MMP1 was found to have a causative role in primary tumor development and lung metastasis, which was enhanced under smoke exposure as demonstrated in a transgenic mouse model that expressed human MMP1 specifically in macrophages (Mac-MMP1). In contrast, MMP1 from lung cells (Lung-MMP1) reduced colonization to the lung despite the fact that collagen deposition decreased in the Lung-MMP1 mouse tumors. These results demonstrate that the varying cellular source of MMP1 in tumors leads to the complexity observed in the tumor microenvironment. Furthermore, macrophage-specific inhibition of MMP1 secretion may be a potential therapy to aid in the reduction of lung metastasis.
Keywords: MMP1; Macrophages; Metalloproteinase; Metastasis.