| dc.description.abstract | Tumor cells develop owing to overexpression of cyclins or lack of CKIs. These mutations result in the fault of regulatory checkpoints mechanism of cell cycle, whereby cancer cells obtain the abilities to resist apoptosis. Bladder cancer is a common cancer in the human urinary system. As a companion to the surgical treatment, patients can be also treated by the assistant intravesical therapy that utilizes chemotherapy agents such as mytomicin C to kill the remaining cancer cells after the surgery to reduce tumor recurrent. During the treatment of chemotherapy, the pressure influence should be considered as a factor that affects the intravesical condition. Previous research has found that mytomicin C induced apoptosis is enhanced by applying the static pressure, suggesting that pressure treatment has the ability to inhibit cancer cell proliferation. However, the cellular mechanism of this mechanical stress still remains unclear.
In this study we develop and utilize a gas pressure bioreactor system to impose static pressure (40 kPa) on BFTC905 cells, a bladder cancer cell line, and investigate how this mechanical stress affects the bladder cancer cells. Results from MTT assay showed that the cell proliferation was inhibited by the static pressure treatment. Results from flow cytometry indicated that a large portion of cells were arrested in G1 phase after pressure application for 10hours. Western blots analysis showed that the protein expressions of cyclin D (D1, D3), CDK4 and CDK6, which regulate early G1 phase cell cycle, were up-regulated compared with the controlled groups after pressure treatment in BFTC905 cells. We also found that the expressions of cyclin E1 and CDK2, which regulate late G1 phase cell cycle, were down-regulated after pressure treatment. The percentage of cell population gradually decreased in S-phase, G2-phase and M-phase relative to G1-phase over the pressure treatment, probably due to G1-phase arrest caused by static pressure.
Furthermore we found that the cyclin-dependent-kinase inhibitor p27kip1 was up-regulated profoundly after 10hr pressure treatment, and p21Cip1/waf1 was slightly increased. This implied that the role played by p27kip1 may be more important than p21Cip1/waf1 in static pressure treatment. Also, dephosphorylation of Ser608 in Rb after the pressure treatment confirmed that the cell cycle was arrested in G1-phase. According to these findings, we concluded that the static pressure induced cell cycle arrest at G1-phase through escalating the p21 Cip1/waf1 and p27 Cip1/waf1 levels, decreasing the cyclin E1 and CDK2 expressions, and inducing the dephosphorylation of Ser608 in Rb. | en_US |