Lattices of type I collagen select invasive variants of K-ras oncogene-transfected NIH3T3 with less cellular fibronectin.

A clone of NIH3T3 transformant (H3) can yield subcutaneous tumors and experimental pulmonary metastasis in nude mice. Compared to H3 in culture, the cells after in vivo tumor growth (H3-N) acquired enhanced tumorigenicity and metastatic ability. Also, indirect immunofluorescence revealed that cellular fibronectin (c-FN) of H3-N was decreased remarkably. We have studied the interactions between H3 and extracellular matrices to elucidate these phenomena. In the present study, we observed the effect of NIH3T3, H3, and H3-N cultured in type I collagen gel. Morphologically in the collagen gel, NIH3T3 assumed an extensive elongated fiber-like shape, H3 assumed a moderately elongated shape, and H3-N assumed a round or spindle shape with short pseudopodia. Compared to conventional cultures on dishes, cell proliferation of all three types was suppressed in collagen gel, but the degree of the suppression was least in H3-N. As a result, H3-N grew fastest in collagen gel. The variants which acquired growth advantage in the subcutaneum of mice also kept it in collagen gel. H3 cells were cultured in type I collagen gel for 4 weeks, a period comparable to that of tumor formation in nude mice. The cells after this long-term culture (H3-C) acquired enhanced tumorigenicity and metastatic ability nearly equal to that of H3-N. FACS analysis revealed that the c-FN of H3-C had decreased to a value comparable to that of H3-N. This means that type I collagen gel as well as subcutaneous tissues could select variants of H3 with less c-FN through proliferation. Moreover, it is suspected that lattices of type I collagen regulate cell proliferation of fibroblast via c-FN.