Fibronectin mediates anchorage-dependent focus formation in cultured human synoviocytes

To determine the effect of extracellular matrix proteins on synoviocyte phenotype, a serum-free, defined-medium culture system was established. Rheumatoid synoviocytes maintained on type I collagen appeared monolayered, whereas cells maintained on fibronectin showed focus formation. Focus formation was abrogated by maintaining cells in the presence of antifibronectin. Focus formation was associated with a fibronectin-rich extracellular matrix, whereas monolayer morphology was associated with matrices containing a greater proportion of collagen. The abundant amount of fibronectin present in the synovial microenvironment may be partially responsible for the transformationlike phenotype displayed by rheumatoid synoviocytes.