Pokemon通过调节HIF-1α的稳定性促进肝癌血管生成的功能与机制

Angiogenesis is one of the key factors in the development of hepatocellular carcinoma (HCC). Pokemon is a transcription factor with proto-oncogene activity, play an important role in the process of HCC. However, its function and mechanism during angiogenesis in HCC is not yet explored. Our preliminary data demonstrated that knocked-down of Pokemon significantly inhibits the vascular endothelial cells to form blood vessels in vitro. The vascular density in xenografts tumor which Pokemon knocked-down HCC cells was reduced compared with the control. We found that Pokemon upregulated the protein expression of HIF-1α in HCC cells. However, it did not affect the mRNA expression of HIF-1a , instead of inhibiting the mRNA expression of pVHL which promotes the ubiquitination and degradation of HIF-1a. EMSA, CHIP and Luciferase assay showed that Pokemon bound to the promoter of pVHL and regulated the transcriptional activity of pVHL. Therefore, we speculated that Pokemon inhibits transcription of pVHL, inhibits the degradation of HIF-1a and enhances the angiogenesis in HCC. Thus, in this study, we will further define that Pokemon regulates the transcription of pVHL, inhibits the HIF-1α degradation to promote the angiogenesis in HCC both in vitro and in vivo. To confirm the expression of Pokemon and HIF-1α was positively correlated in HCC tissue and analyze the relationship between its expression and clinical characteristics. We aimed to address the regulation mechanism of Pokemon to promote angiogenesis in HCC development.

血管新生是肝癌发展关键因素之一。Pokemon作为转录抑制因子在肝癌血管新生中的作用及机制尚未明确。本课题前期研究发现，基因沉默Pokemon明显抑制血管内皮细胞成管能力，并显著降低移植瘤血管密度；也发现Pokemon上调肝癌细胞中HIF-1α蛋白水平，但不影响HIF-1α mRNA水平，而是抑制了促进HIF-1α降解的蛋白pVHL mRNA转录。Luciferase、EMSA和CH-IP证实Pokemon抑制pVHL启动子转录活性。由此我们推测，Pokemon通过抑制pVHL转录，影响HIF-1α稳定性，促进肝癌血管生成。因此本课题将：进一步明确Pokemon调控pVHL转录，抑制HIF-1α降解；明确Pokemon通过HIF-1α在体内外促进肝癌血管生成；肝癌标本验证Pokemon与HIF-1α表达呈正相关及与肝癌患者临床特征关系。从而阐明Pokemon促进肝癌血管生成的分子调控机制。

肝癌是一种常见的恶性肿瘤，预后较差。近年来，其发病率和死亡率呈上升趋势。血管生成是肝细胞癌(HCC)发生发展的关键因素之一。Pokemon是一种具有原癌基因活性的转录因子，在肝癌的发生发展过程中发挥着重要作用。然而，其在肝癌血管生成中的作用和机制尚不清楚。在这项研究中，我们发现Pokemon在HCC中显著上调。此外，Pokemon的沉默抑制了HCC的体外毛细管形成和体内血管生成。进一步的实验表明，Pokemon上调肝癌细胞中缺氧诱导因子-1α的蛋白表达。但不影响缺氧诱导因子-1α mRNA的表达，促进缺氧诱导因子-1a的泛素化和降解。EMSA、CHIP和荧光素酶实验证实Pokemon可以直接与pVHL启动子区域结合并抑制其转录。综上所述，这些发现表明，Pokemon通过下调pVHL来稳定缺氧诱导因子-1α，从而加速肝癌的血管生成。可作为肝癌的治疗靶点。