| dc.description.abstract | Uncontrolled cells continuously grow that is the cause of tumor developments. Substantial researches have pointed that overexpression cyclins and CDKs, mutation or deletion of CKIs and tumors suppressors are common in uncontrolled cells. These situations will destroy or interfere with the checkpoint mechanism of cell cycle. As a result, the cells obtain anti-apoptosis ability and divide inappropriately. Finally it leads to tumorigenesis.
For treatments of bladder cancer, the most common method is the administration of chemicals such as mytomicin C after surgery. The administered chemicals kill the residual cancer cells, reducing the chance of disease recurrence. Increasing the residence time of chemical will increase the pressure within the bladder. Researches in cell biology suggest that pressure can inhibit the growth of cancer cells, and enhance cooperation with chemicals to cell death. There are other mechanical forces in vivo, such as fluid shear stress. Many literatures suggest that fluid shear stress can accelerate cell growth, differentiation or induce apoptosis. Whether fluid shear stress and pressure have a similar effect on bladder cancer cells? If it is true, what kinds of mechanisms regulate the cell cycle? This study aims to simulate bladder cancer cells by fluid shear stress, and investigates its effect on the cell cycle.
This study adopted the shear force bioreactor system to apply the fluid shear stress on BFTC905, a cell line of bladder cancer. The assessments of flow cytometry, MTT assay and Western blot were used to test the cells. For BFTC905 subjected to the fluid shear stress of 12 for 24 hrs, flow cytometry showed that most of the cells stayed in G1 phase, and the cell growth was also inhibited. Tumor suppressor p18 and p53 were not expressed for the cells in Western blot. Our Western blot data showed cyclin D1 and CDK4/6 were down-regulated. Cyclin E (E1, E2), cyclin A2 and cyclin B1 also were down-regulated. But CDK2 and CDC2 were not affected. These results concluded that fluid shear stress induced cell cycle arrest in G1 phase. In addition, p21 and p27 both were up-regulated. Especially p27 was much higher than control. This evidenced that cyclin D-CDK4/6 were regulated by p21 and p27 rather than p18. Moreover it was found that total Rb expression was down-regulated. This suggested that the cancer cells might undergo autophagy and apoptosis. To confirm this, we performed tests on LC3B and Beclin, the autophagy markers, which were shown to be up-regulated. We also found that native caspase 3/8, the apoptosis markers, were up-regulated, but nonetheless cleaved caspase 8 did not show apparent change. This suggested that the cells were not right in apoptosis, but might be in proapoptosis. To conclude our study, fluid shear stress induced G1 arrest by up-regulating p21 and p27 in a p53-independent pathway, which resulted in cyclin D1-CDK4/6 being down-regulated. The bladder cancer cells were then on the way toward autophagy and proapoptosis. | en_US |