Fibronectin levels are enhanced in human fibroblasts overexpressing the c-sis protooncogene.

We studied human dermal fibroblasts transfected with a human c-sis cDNA (coding for the platelet-derived growth factor B-chain). Dermal fibroblasts overexpressing c-sis exhibited a stellate morphology with focus formation, enhanced colony formation in methylcellulose-containing growth medium, and increased levels of soluble and extracellular matrix-associated fibronectin. Gene expression of fibronectin was enhanced 10-fold in c-sis-overexpressing fibroblasts relative to controls. Pro-alpha 1 (I) collagen mRNA was not increased in these same c-sis-overexpressing fibroblasts. Transforming growth factor beta 1 treatment of c-sis-transfected cells caused a modest increase (77%) in fibronectin mRNA levels with no increase in soluble fibronectin production after 24 h. In contrast, transforming growth factor beta 1 caused at least a 10-fold increase in fibronectin mRNA and a 2-fold increase in soluble fibronectin from medium conditioned by control fibroblasts. Transforming growth factor beta 1 increased pro-alpha 1 (I) collagen mRNA approximately 3-fold in both control and c-sis-transfected fibroblasts. These studies reveal that a primary biological function of the platelet-derived growth factor B-chain is upregulation of fibronectin gene expression and extracellular matrix formation. The anchorage-independent phenotype of c-sis-overexpressing cells was blocked by the cell adhesion sequence of fibronectin, Arg-Gly-Asp-Ser. Our results demonstrate that interaction of cells with extracellular adhesion receptors is necessary for proliferation in semisolid medium even when cells are overproducing growth factors known to act via autocrine stimulation.