c-myc expression is down-regulated by cell-cell and cell-extracellular matrix contacts in normal hepatocytes, but not in hepatoma cells. |
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Authors: | N Shimbara M Takashina C Sato M Iizuka S Kobayashi K Tanaka A Ichihara |
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Affiliation: | Biomaterial Research Institute, Yokohama, Japan. |
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Abstract: | Primary culture of adult rat hepatocytes resulted in marked increase of c-myc expression within a few hours. The high level of c-myc mRNA was maintained throughout culture on collagen-coated dishes, but decreased greatly with time during culture on collagen-gel or matrigel. Expression of c-myc was also down-regulated at high cell density. The decrease in its expression appeared closely related to inhibitions of DNA synthesis and cell spreading. In contrast, hepatoma H4TG cells showed a high level of c-myc expression which was not affected by culture on any extracellular matrices examined or by the cell density. These results suggest that up-regulation of expression of the c-myc gene is linked to G0 to G1 transition during cell cycle progression, which in normal hepatocytes is strictly regulated by cell-cell and cell-extracellular matrix interactions, but that this control mechanism is defective in malignant hepatic tumor cells. |
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