The expression of extracellular matrix and cytoskeleton in fused cells

In the present paper results from our studies on the expression and regulation of the differentiated normal and transformed epithelial and fibroblastic phenotypes are reviewed. The expression of the extracellular matrix- and basement membrane-associated proteins, fibronectin and laminin, and different intermediate filament proteins were studied in different fused cells. Heterokaryons and cytoplasmic hybrids (cybrids) were formed by fusing normal or malignant epithelial cells with normal fibroblasts or malignant glial cells. No differences were observed in the expression of these phenotypic markers between unfused parental cells and the corresponding homokaryons. Thus, the fusion process itself does not cause changes in the expression of these phenotypic markers. In heterokaryons formed after fusion of normal or malignant epithelial cells with normal fibroblasts or malignant glial cells, two or even three different types of intermediate filaments could be co-expressed. Thus, no suppression of the expression of the various intermediate filaments is caused by the non-homologous parental cell. Expression of the extracellular matrix proteins, fibronectin and laminin, on the other hand, could be extinguished by cells and cytoplasts not expressing fibronectin matrix, such as transformed fibroblasts and HeLa cells. These results support the role of transacting regulatory factors controlling the expression of the different extracellular matrix proteins. Alternatively, the results can be explained by changes in the distribution and concentration of the extracellular matrix receptor proteins in the fused cells.