| Summary: | 碩士 === 國防醫學院 === 生物及解剖學研究所 === 92 === Bone resorption is primarily carried out by osteoclasts. The osteoclastic bone resorption starts with adhesion to the bone matrix, leading to cytoskeletal reorganization that is important for the migration of these cells to and between the resorption sites and their polarization during the resorption process. It has been well studied that, the calcitonin induced quiescent and retraction effects in osteoclasts which involved PKA and PKC pathways, respectively. However, the detailed mechanism is still unknown. Recently, effects of calcitonin on the turnover of podosome and function of PYK2 had been reported. Therefore, this signaling molecule in podosome could be the potential targets for the calcitonin-induced signaling. Using immunoprecipitation and immunofluoresecent microscopy methods, our previous results showed that decreased tyrosine phosphorylation and redistribution of PYK2 in osteoclasts upon calcitonin stimulation. Though the effects of calcitonin on PYK2 in osteoclasts are clear, it is still difficult to show the PYK2-mediated signaling actually involved in calcitonin-induced podosome reorganization. To address this issue, microinjection of fluorescent G-actin in living osteoclasts was performed. In real time, we observed that calcitonin induced reorganization of the podosomes and disruption of the actin ring. Calcitonin induced redistribution and dephosphorylation of PYK2 in osteoclasts. Calcitonin induced the transient dephosphorylation of PYK2, which correlated with the decreased phosphorylation of Tyr402, the autophosphorylation site of PYK2. We created a model of microinjection in isolated living rabbit osteoclasts in which the mechanism of signal transduction could be studied in more detail.
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