Plectin deficiency on cytoskeletal disorganization and transformation of human liver cells in vitro.

Plectin is a versatile cytoplasmic cross-linking protein that connects intermediate filaments to microfilaments, microtubules, and membrane adhesion sites. The cross-linking functions of plectin help organize the cytoskeleton into a stable meshwork important for maintaining uniformity in cell size and shape. As cells of hepatocellular carcinoma are morphologically different from normal human hepatocytes, we hypothesized that altered plectin expression and cytoskeletal organization underlies this pleomorphic transformation. To test this hypothesis, we analyzed expression levels and organization of all cytoskeletal elements, including intermediate filaments, microfilaments, and microtubules, after plectin knockdown in human Chang liver cells. We found that expression of cytokeratin 18, but not actin or tubulin, was downregulated by suppression of plectin protein. Furthermore, cytokeratin networks were partially collapsed and actin-rich stress fibers were increased. The organization of microtubule networks, by contrast, was unaltered. These findings support our hypothesis that, via effects on cytoskeletal organization, plectin deficiency might play an important role in the transformation of human liver cells.