Distribution of fibronectin on clonal cell lines of a rat mammary adenocarcinoma growing in vitro and in vivo at primary and metastatic sites.

With the use of a rat 13762 mammary adenocarcinoma tumor, we have examined the relationship between cellular fibronectin (FN) expression and ability to metastasize spontaneously to regional lymphatic and distant blood-borne sites. This model is based on the isolation and establishment of cell clones from primary parental tumor and from spontaneous metastases that show differing metastatic potentials when implanted s.c. into the mammary fat pads of syngeneic female Fischer 344/CRBL rats. Cellular FN expression was determined in tissue culture as well as primary and secondary tumor sites, utilizing: (a) indirect immunofluorescence microscopy with a specific anti-rat FN antibody (in vitro and in vivo grown cells); (b) competition radioimmunoassay for cell-released FN (in vitro grown cells); and (c) surface labeling by radioiodination-sodium dodecyl sulfate-polyacrylamide gel electrophoresis-autoradiography for cell surface-bound FN (in vitro grown cells). Tissue culture-grown parental tumor clones displayed FN at their cell surfaces. At confluency, they expressed higher quantities of FN at their peripheries and in fibrillar structures between adjacent cells and released greater amounts of this glycoprotein. Lung metastases-derived tumor clones released negligible amounts of FN by radioimmunoassay and failed to express detectable amounts of FN by indirect immunofluorescence and cell surface-labeling techniques. However, when parental tumor- and metastasis-derived clones of widely different metastatic potentials were carefully examined for FN expression and release, there was no obvious relationship between metastasis and FN expression or release in culture or display in tumors at primary or secondary sites. The results suggest that expression or release of FN per se is not a determinant of metastasis, although it may be a factor in certain steps of the metastatic sequence.