| Budget Amount *help |
¥2,100,000 (Direct Cost: ¥2,100,000)
Fiscal Year 2002: ¥700,000 (Direct Cost: ¥700,000)
Fiscal Year 2001: ¥1,400,000 (Direct Cost: ¥1,400,000)
|
|---|
| Research Abstract |
It is well documented that mechanical stimuli are essential to maintain homeostasis of bone, and osteoblasts can sense the mechanical stimuli. However, the mechanism to transduce the mechanical stimuli to the intracellular signals have not been elucidated yet. We have found that in a culture system of osteoblast-like cells ERK1/2, She and other proteins are tyrosine-phosphorylated by medium flow and egr-1 mRNA increases. Furthermore, these responses were not induced without serum and recovered by the addition of EGF. These findings suggested that EGF signaling is involved in the responses to mechanical stimuli. Moreover, as there were also reports from other researchers that growth factor receptors were activated by mechanical stimuli, we examined whether activation of EGF receptor is also induced in our system. Although the examination of tyrosine-phosphorylation of the EGF receptor did not lead to significant results, during the experiments we noticed that EGF receptor protein increased after medium flow. This increase was induced within 2 minutes of the stimuli. This rapid response suggested that this increase is induced by rather a decrease in the degradation than an increase in the synthesis. Therefore, we examined the effects to the increase by the several inhibitors for the pathways involved in the proteolysis of EGF receptor. The results showed that the protease inhibitor, leupeptin, blocked the increase. Furthermore, the leupeptin sensitive protease might be cathepsin B was deduced. Cathepsin B is reported to degrade EGF receptor in early endosomes and EGF receptor in early endosome is occupied by EGF. This co-localization of the EGF-occupied EGF receptor and the protease might be the reason for our finding that the increase in EGF receptor by medium flow did not occur without EGF in culture media.
|
