Search

In animal cultured cells, it has been reported that gravity change affects cell function and cell proliferation. But, the response mechanism of gravity change has not been known yet. A point of mechanism is what is sensor for response of gravity change. It is hypothesized that gravity change is sensed by cytoskeleton and transduced into biochemical signal via integrin, whose cytoplasmic domain is bind to one of cytoskeleton, actin filament. Integrin is major receptor for extracellular matrix molecules and is responsible not only for cell-extracellular matrix adhesion, but also for transducer of mechanical stimulation into biochemical signal as mechanoreceptor. To verify the hypothesis, a correlation between cell spreading activity and hypergravity-dependent increase of DNA synthesis in animal cultured cells was examined using one of extracellular matrix molecule, fibronectin. Baby hamster kidney (BHK) cells in the experiments, and cultured BHK cells on fibronectin-coated dishes were used. In this system, hypergravity condition (75 G, 20 h) increased 10 to 50 percent of DNA synthesis correlated with fibronectin-dependent increase of cell spreading activity using 0 to 100 microgram/ml fibronectin. Since integrin and actin filament play an important role in cell spreading, this result suggested that integrin and actin filament are involved in hypergravity response. To examine mechanism of hypergravity response in more detail, hypergravity response was observed in shorter period (2 h). Hypergravity condition (75 G, 2 h) also increased about 50 percent of DNA synthesis in BHK cells. Cytochalasin B, which inhibits actin polymerization, abolished the increase of DNA synthesis, indicating that actin filament plays a role in hypergravity response. To examine whether signal transduction via integrin is involved in hypergravity response, amount of phosphorylated tyrosin residue, which is responsible for signal transduction via integrin, was observed in BHK cells. This result showed that hypergravity increased the level of phosphorylated tyrosine residue and phosphorylation of src and paxillin. In addition, hypergravity promoted the formation of stress fiber in BHK cells. These results demonstrate that hypergravity response is mediated by a cell-adhesive molecule, integrin and cytoskeleton in BHK cells., 資料番号: AA0045438008