UP-REGULATION OF MOLECULAR MOTOR-ENCODING GENES DURING HEPATOCYTE-GROWTH-FACTOR-INDUCED AND EPIDERMAL-GROWTH-FACTOR-INDUCED CELL MOTILITY

Hepatocyte growth factor (HGF) and epidermal growth factor (EGF) are k nown to stimulate the locomotion of epithelial cells in culture. Howev er, the molecular mechanisms which mediate these important changes are poorly understood. Here we have determined the effects of HGF and EGF on hepatocyte morphology, cytoskeletal organization, and the expressi on of molecular motor-encoding genes. Primary cultures of hepatocytes were treated with 10 ng/ml of HGF or EGF and observed with phase and f luorescence microscopy at 10, 24, and 48 h after treatment. We found t hat, over time, treated cells spread and became elongated after 24 h o f treatment while forming long processes with dramatic alterations in the microtubule and actin cytoskeletons by 48 h. Quantitative Northern blot analysis was performed to measure expression of cytoskeletal-(be ta-actin, alpha-tubulin) and molecular motor-(dynein, kinesin, and myo sin I alpha and II) encoding genes which may contribute to this change in form. We observed the highest increase in levels of expression for myosin II (3.3-fold), kinesin (2.7-fold), myosin I alpha (2.2-fold), and alpha-tubulin (1.9-fold) after only 2 h of treatment with HGF. In contrast, EGF upregulated the expression of myosin 1 alpha (2.4-foId), kinesin (1.5-fold), and dynein (1.5-fold) at 10 h. The expression of the beta-actin gene remained constant in HGF-treated cells, while EGF induced a slight upregulation after 10 h of treatment. These results s how for the first time that a selective upregulation of molecular moto r-encoding genes correlates with alterations in cell shape and motilit y induced by HGF and EGF. (C) 1996 Wiley-Liss, Inc.