Association of surfactant protein D with pulmonary metastases from colon cancer

Surfactant protein D (SP-D) is a member of the collectin family of proteins, which is secreted by airway epithelial cells. SP-D serves an important role in the immune system and in the inflammatory regulation of the lung. SP-D was recently found to suppress lung cancer progression by downregulating epidermal growth factor signaling. However, the relationship between SP-D and pulmonary metastases from colon cancer remains unknown. The present study aimed to determine whether SP-D may suppress the development of the mouse rectal carcinoma cell line, CMT93, in vitro. The present study investigated the effect of SP-D on pulmonary metastases from colon cancer in vivo using SP-D knockout mice. A wound healing assay and cell invasion assay revealed that SP-D suppressed the proliferation, migration and invasion of CMT-93 cells. After injection of CMT-93 cells into the tail vein, SP-D knockout mice were significantly more susceptible to developing pulmonary metastases than C57/BL6 mice (control). Moreover, a novel cell line (CMT-93 pulmonary metastasis; CMT-93 PM) was established from the lesions of pulmonary metastases in C57/BL6 mice following injection of CMT93 into the tail vein. CMT-93 PM exhibited more robust invasion and proliferation compared to CMT93, which was unaffected by exposure to SP-D. A higher incidence of pulmonary metastases was detected following injection of CMT93 PM into the tail vein of C57/BL6 mice compared with CMT-93. Consequently, SP-D may be involved in the pathogenesis of pulmonary metastases from colon cancer.