Production of fibronectin by normal and malignant human mammary epithelial cells

The production and retention of fibronectin by primary cultures of cells derived from the human breast has been analyzed. Two examples of each of the following cell types were examined: (a) normal epithelium from milk; (b) metastatic breast cancer cells in pleural effusions; (c) fibroblasts; (d) tissue macrophages of milk. Cell-associated fibronectin could be detected by indirect immunofluorescent staining on normal and malignant mammary epithelium and on mammary fibroblasts, but not on milk macrophages. Immune precipitation followed by gel electrophoresis of 35S-labeled cell lysates and conditioned medium confirmed that fibronectin was indeed synthesized by both types of epithelial cells and by fibroblasts, but not by macrophages, and that much of the protein was released into the medium. Quantitative analysis with radioimmune assay of the fibronectin on cells and in media showed that both normal and malignant epithelial cells synthesized levels of protein comparable to that produced by fibroblasts, but only a small fraction (less than 10%) of the material synthesized was retained by the cells. Growth on collagen-coated plastic increased the percentage of fibronectin retained by normal and malignant epithelium but did not affect retention by fibroblasts.