| Summary: | 碩士 === 高雄醫學大學 === 生物科技學系碩士班 === 98 === Lon is an ATP-dependent protease and a stress protein which level will increase when cell is suffered from stresses, such as reactive oxygen species (ROS) or serum starvation. It had been reported that Lon is overexpressed during tumorigenesis, and the decrease of Lon induces a caspase-3-dependent cell death pathway. This thesis further studied the relationship between the level of Lon and tumorigenesis. We used lung cancer as our study model. We observed that Lon is overexpressed in lung cancer cell lines compared to normal lung cells. We hypothesized that overexpression of Lon in cancer cells can prevent cells from apoptosis under stresses. We overexpressed Lon in the cells and treat with H2O2 or UVC. The western blot showed that cells overexpressing Lon have higher resistance to stress-induced apoptosis than control cells. Then we used shRNA to knock down Lon in H1299 lung cancer cells. The H1299 cells became more sensitive and easily underwent apoptosis. According to the result, we concluded that Lon only overexpresses in cancer cells and downregulation of Lon protease in cancer cells can induce their apoptosis. We thought that Lon protein could be a new target for the cancer therapy. Then we used recombinant Lon protein to screen inhibitors from many chemicals extracted from nature herb. We identified Obtusilactone A (OA) is a Lon protease inhibitor in vitro and in vivo. IC50 of OA is 34.1 uM against the enzyme, and OA can induce cell death of tumor cells. In this thesis, we showed that overexpressing Lon can induce tumorigenesis and down-regulating Lon can induce apoptosis. The inhibitor of Lon may be beneficial to cancer therapy. We will study the mechanism of how Lon protease regulates tumorigenesis and induces apoptosis in the future.
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