Effect Of P21～(WAF1/CIP1) On Prostate Cancer Cell Growth

As one of the male malignant tumor, the mortality of prostate cancer is just at the second place after lung cancer. Presently, morbidity of prostate cancer rise rapidly and became the main factor threaten male health in our country. Its complicate pathogenesis, easy aggravation and metabasis, especially there is no effective therapeutics after it developing to androgen independent prostate cancer made it is urgent to finding the key molecular target or signal pathway and investigating the targeting drug.Many studies have pointed out that quercetin can inhibit many tumor cells growth and the cell DNA synthesis such as leucocythemia, colon carcinoma, pulmonary carcinoma, liver cancer, ovarian cancer, bladder carcinoma, breast cancer, laryngocarcinoma, etc, and it can induce the tumor cells apoptosis. Study has also shown that quercetin can effectively inhibit the expression and function of AR to inhibit the development of androgen dependent prostate cancer. But in the differentiation and development of prostate cancer, in addition to AR, cell cycle also plays a very important role. The mechanism of quercetin involved in cell cycle arrest in prostate cancer cells remains unclear. In our study, we investigated the effects of quercetin on proliferation and cell cycle arrest through several methods.The result of experiment showed quercetin can inhibited growth of prostate cancer cells obviously, and also can raise expression level of p21 to block the cell cycle at G₀/G₁ and G₂/M transition. It contains a canonical androgen response element (ARE) and the binding sites for transcription factor Sp1 in its promoter upstream. To investigate the mechanism of quercetin raise p21 expression, we detect the Sp1 expression level by Western blot. The result is quercetin made the Sp1 express in a higher level, it supposed that quercetin raise the p21 expression through increase the Sp1 expression and enhance the interaction of Sp1 and the binding sites in p21 promoter upstream to regulate cell cycle. This hypothesis will need to be tested in future experiments.We can learn that p21 play an important role in prostate cancer through the sdudy above. As a anti-oncogene, there were so many sdudies confirmed the effects of p21 in development of cancr. The cyclin-dependent kinase inhibitor p21 is induced by both p53-dependent and -independent mechanisms and induction of p21 may cause cell cycle arrest. As a proliferation inhibitor, p21 is poised to play an important role in preventing tumor development.This notion is supported by data indicating that p21-null mice are more prone to spontaneous and induced tumorigenesis, and p21 synergises with other tumor supressors to protect against tumor progression. However, a number of recent studies have pointed out that in addition to being an inhibitor of cell proliferation, p21 acts as an inhibitor of apoptosis in a number of systems. The same as above, there are different report about the factor of influent p21 expression in prostate cancer and its effect on prostate cancer cells. Someone reported that overexpressed androgen receptor linked to p21 silencing may be responsible for androgen independence and resistance to apoptosis of a prostate cancer cell line. And also, there is another report said that androgen can induce p21gene through an ARE and Sp1 binding sites in the p21 proximal promoter. This suggests that p21 may have an antiapoptotic function in prostatic epithelial cells. Therefore, the effect of p21 in prostate cancer cells is still in debate, investigating the effect of p21 in prostate cancer cells is still a hot topic.To observe the role of p21 directly, a eukaryotic expression vector pPSA-TAT-p21 containing of p21^WAF1/CIP1 gene fused to TAT transduction domain under the control of prostate-specific antigen(PSA) promoter was constructed and transient transfection of the vector into the prostate cancer cell to observe the expression of p21 in prostate cancer cells and its effect on cells.The results showed that pPSA-TAT-p21 expressed specilly in prostate cancer cells, and it appeared that TAT-p21 had more inhibitory effect when compared to p21 group.In a word, my research proved that quercetin can inhibit growth of prostate cancer cells and raise p21 expression by increasing Sp1 protein expression level, accordingly, quercetin changes cell cycle to show its anticancer activity. In addition, the vector pPSA-TAT-p21 could target express in prostate cancer cells and showed inhibition on cell proliferation.This study provided a preliminary experiment evidence for the targeting gene therapy of prostate cancer.