Upregulation of molecular motor-encoding genes during hepatocyte growth factor- and epidermal growth factor-induced...

Hepatocyte growth factor (HGF) and epidermal growth factor (EGF) are known to stimulate the locomotion of epithelial cells in culture. However, 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 expression of molecular motor-encoding genes. Primary cultures of hepatocytes were treated with 10 ng/ml of HGF or EGF and observed with phase and fluorescence microscopy at 10, 24, and 48 h after treatment. We found that, over time, treated cells spread and became elongated after 24 h of 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-(beta-actin, alpha-tubulin) and molecular motor-(dynein, kinesin, and myosin 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 I alpha (2.4-fold), 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 show for the first time that a selective upregulation of molecular motor-encoding genes correlates with alterations in cell shape and motility induced by HGF and EGF.