Divergent expression of laminin and fibronectin in non-tumorigenic and transformed liver epithelial cells

The immunocytochemical expression of laminin and fibronectin by non-transformed liver epithelial cells and by transformed cells derived from the same cell line, TRL1215, was examined in ethionine-transformed cells (ETC), untreated control cells at the same high passage level (HPC), and untreated, low passage cells (LPC). At confluence, a divergent expression of laminin and fibronectin was observed in the three sublines. In flat areas of polygonal cells, LPC showed abundant laminin staining and sparse fibronectin staining; HPC had intermediate expression of both; and ETC had sparse laminin staining and abundant fibronectin. Specifically, the laminin network was often found at intercellular junctions, outlining individual LPC, outlining groups of HPC, and having a focal expression in ETC. A fine reticulum of laminin was seen in large areas of LPC, in relatively small areas of HPC, and in multilayered areas of ETC. Fibronectin was visible as thick, matted fibrils, which were sparse in LPC, loosely arranged in HPC and dense in ETC. Prior studies had shown that the increased fibronectin expression in the transformed cells was associated with increased expression of actin stress fibres, increased cell spreading and increased numbers of focal contacts between cell and substrate. The divergent expression of laminin and fibronectin shown here indicates that these two matrix proteins need not be expressed in a parallel manner during transformation, and that increased fibronectin, but not laminin, is associated with maximal cell spreading and adhesion.