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

Plectin is a versatile cytoplasmic cross-linking protein that connects intermediate fi laments to microfi laments, 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 fi laments, microfi laments, 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 fi bers were increased. The organization of microtubule networks, by contrast, was unaltered. These fi ndings support our hypothesis that, via effects on cytoskeletal organization, plectin defi ciency might play an important role in the transformation of human liver cells.