PSMA是前列腺癌高特异性瘤标，以往研究表明其与前列腺癌恶性行为密切相关，但具体机制不清。我们前期实验证实沉默PSMA可抑制前列腺癌快速增殖，并与其叶酸水解酶活性及下游分子ERK密切相关，同时伴有钙内流受抑，这提示PSMA的叶酸水解酶活性可介导钙内流激活细胞内Ras/Raf-1/MEK/ERK途径。同时我们检测基因启动子具有AP-1位点的癌干因子SALL4，发现SALL4与磷酸化ERK的表达具有一致性，因此我们推测：PSMA激活ERK通路后,可活化AP-1并使其进入胞核启动SALL4基因的表达,从而促进前列腺癌快速增殖。本项目拟在前期实验的基础上,利用定向诱变的技术使PSMA叶酸水解酶功能失活，检测前列腺癌细胞生物学行为变化；通过检测钙内流、Ras/Raf-1/MEK/ERK通路及其下游重要因子SALL4阐明前列腺癌细胞中PSMA调控SALL4的具体机制，并结合动物实验验证我们的猜测。

PSMA is a high specificity biomarker located in prostate cancer. Previous studies have showed the expression of PSMA is correlated with malignance of prostate cancer. But until now, the concrete mechanism is not clear. Our preliminary work had observed that silencing the PSMA can inhibit the rapid proliferation and metastasis of prostate cancer in vitro. In addition, we also found that the folate hydrolase activity of PSMA and the ERK pathway had involved in this processes. And this process is accompanied with the inhibition of calcium inflow. Sum up all the data and researches, we propose that the folate hydrolase activity of PSMA may activate Ras/Raf-1/MEK/ERK pathway by mediating the inflow of calcium. At the meantime, our team also detected the new transcription factor-SALL4 associated with tumor proliferation and found that the expression of P-ERK was in accordance with SALL4 expression. Together with an AP-1 binding site existed in the SALL4 gene promoter, we further conclude that P-ERK can activate the AP-1 factor in the cytoplasm and then the AP-1 enter into the nucleus, binding to the SALL4 gene promoter and promoting the expression of SALL4. As a result, the tumor can proliferate and metastasize rapidly. Our project is to knock down the folate hydrolase activity of PSMA by technique of mutating the N638A of PSMA on the basis of our previous studies, detect the cell bio-behaviors. In order to explore the mechanism of PSMA up-regulating SALL4, we put emphasis on detecting inflow of calcium, the expression of the Ras/Raf-1/MEK/ERK pathway and the nucleus factor SALL4. Finally, we will testify our hypothesis in vivo.