Loss of pericellular fibronectin matrix from heterokaryons of normal human fibroblasts and epithelial cells

The expression of fibronectin in heterokaryons of normal human fibroblasts and normal or malignant epithelial cells was studied by indirect immunofluorescence microscopy. Fibroblasts and their homokaryons showed a characteristic pericellular fibronectin matrix, whereas both normal (MDCK) and malignant (HeLa) epithelial cells, and their homokaryons, lacked such a matrix. The fibroblast homokaryons also showed a typical strong, perinuclear cytoplasmic, fibronectin-specific fluorescence. This was much weaker or absent in the MDCK and HeLa cells and their homokaryons. When human fibroblasts were fused with either normal or malignant epithelial cells, no pericellular matrix-like, fibronectin-specific fluorescence could be seen in the heterokaryons. Interestingly, however, a distinct intracellular fluorescence was seen in the heterokaryons, indicating continued production of fibronectin. The results of the present study indicate that both malignant and normal epithelial cells, which do not deposit fibronectin matrix, can cause its loss in heterokaryons with fibroblasts. Thus, discontinued fibronectin matrix formation does not point exclusively to malignancy, but may also reflect the state of differentiation of the parental cells.