Summary: | 碩士 === 國立中央大學 === 生物醫學工程研究所 === 102 === Uncontrolled cell division is the cause of malignant cell development. To date, there are large amount of literatures that investigate the cause of cancer and try to develop applicable strategies for cancer therapy. It has been well addressed that the mutation of tumor suppressor, overexpression of cyclins or loss of CKIs are common in a variety of human cancers. Those mutations, overexpressions or deletions will result in the malfunction of regulatory checkpoints mechanism of the cell, or make the cancer cells obtain abilities to resist apoptosis. At the end, unlimited cell proliferation will eventually lead tumorigenesis.
Bladder cancer is a common cancer in human urinary system. In addition to the primary surgical treatment, patients will be treated by adjuvant intravesical therapy that utilize chemotherapy agents such as mytomicin C to kill the remaining cancer cells after the surgery to prevent tumor recurrence. However not only the cytotoxic stress for cells but also the pressure effect were present in the bladder during the intravesical therapy. It is suggested that hydrostatic pressure stimulation may have the ability to inhibit cancer cell proliferation, because the drugs induced apoptosis will be enhanced by applying the hydrostatic pressure. However, the cellular mechnism of this mechanical stress still remain unclear.
This study applied the hydrostatic pressure bioreactor system to provide the hydrostatic pressure (10 kPa) on BFTC905 cells, a cell line of bladder cancer, and investigated how this mechanical stress effects the bladder cancer cells under physiological conditions. Results from flow cytometry showed most of cells stay in G1 phase, and rare cells go into apoptosis after 5 h hydrostatic pressure application. And we also found undetectable p53 expression after treated hydrostatic pressure by Western blot analysis no matter we applied hydrostatic pressure or not in BFTC905 cells. Our data shown the expression of cyclin D (D1, D3) and CDK4, CDK6 were the same as control cells after treatment, and these would be the results of loss of INK4 proteins in BFTC905 cells. However, under hydrostatic pressure stimulation, we found most of cells stayed in S phase and cells in G2/M were declined, also the phosphorylation state of Cdc2 on Tyr15 was increased within 2.5 h. But after treatment for 5 h, most of cells stayed in G1 phase and cyclin E1 and CDK2 were decreased. Not only that, but the data also shown both of cyclin A2 and cyclin B1 were down-regulated after treatement for 5 h, and Ser10 of histone H3 remained in the hypophosphorylation state. These evidences suggested hydrostatic pressure stimulation might cause cell cycle delay in G2/M transition and induce G1 arrest, simultaneously.
Futhermore, unlike p21, p27 levels were strongly inhibited in BFTC905 cells in the originated status. However, p27 levels were significantly increased by hydrostatic pressure application whether p21 levels just slightly increase. Also Ser807/811 of Rb became hypophosphorylation after treatment within 2.5 h or 5 h. These finding concluded that hydrostatic pressure stimulation induce G1 arrest by elavated p21 and p27 levels in a p53-independent manner, results cyclin E1 and CDK2 degradation, and hypophophorylation of Ser807/811 of Rb.
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