肝癌细胞内高表达的PEDF通过调控脂肪酸代谢促进肝癌生长的作用及机制研究

Our previous studies revealed that PEDF could inhibit tumor growth and metastasis by suppressing angiogenesis and inducing tumor cell apoptosis. PEDF was down-regulated in most kind of tumors. However, in our recent studies, we found that PEDF expression was up-regulated in hepatocellular carcinoma (HCC) and the main distribution was located in hepatocellular carcinoma cells. The functions and the underling mechanism of high expression PEDF in hepatocellular carcinoma cells without anti-tumor effect need to be further explored. In our preliminary data, the gene sequence encoding PEDF signal peptide has point mutation and its expressed protein could not be secreted to extracellular matrix. There is a positive correlation between the production of fatty acids (FA) and the expression of PEDF in hepatocellular carcinoma. Overexpression of PEDF without signal peptide increased the concentration of FA in hepatocellular carcinoma cells and promoted hepatocellular carcinoma cells proliferation. Thus, our preliminary experiments suggested that PEDF may promote hepatocellular carcinoma cells proliferation by regulating FA metabolism. The details were designed in the research project: 1. How does the mutation of gene coding PEDF signal peptide modify the PEDF protein structure and biological properties, and finally resulting in PEDF secretion inhibition. 2. The possible pathways that PEDF promotes hepatocellular carcinoma cells proliferation by regulating triacylglycerol mobilization, fatty acid de novo synthesis and/or oxidation. 3. Exploring the mechanism of PEDF up-regulation in hepatocellular carcinoma. The purpose of the presenting study is to identify the novel role of PEDF with multifunction in regulating fatty acid metabolism and promoting proliferation in hepatocellular carcinoma cells. The results of the study may facilitate our understanding to hepatocellular carcinoma and provide new strategy for the prevention and treatment of hepatocellular carcinoma.

我们以往研究发现PEDF通过抑制血管新生、诱导肿瘤细胞凋亡抑制肿瘤生长和转移，在大多数肿瘤中PEDF呈低表达。然而我们最近发现，在人肝癌组织中PEDF呈高表达且主要分布于肝癌细胞内，高表达的PEDF不抑制肝癌生长及其可能作用亟待解决。预实验表明源自肝癌组织的PEDF基因信号肽序列发生点突变且其表达的蛋白不能分泌到细胞外，肝癌组织中脂肪酸升高与PEDF成正相关,过表达缺失信号肽的PEDF可增加肝癌细胞内脂肪酸含量并促进肝癌细胞增殖，提示PEDF可能通过调控脂肪酸代谢促进肝癌生长。本项目拟探讨:①PEDF信号肽编码基因突变导致其结构和性质改变使PEDF分泌受阻的机制；②细胞内PEDF是否通过促进脂解、增加从头合成，减少氧化利用增加脂肪酸含量促进肝癌生长；③PEDF在肝癌中升高的机制。旨在阐明具有抑癌功能的PEDF在肝癌细胞中异常升高的作用及机制，为理解PEDF作用的多样性和治疗肝癌提供新思路。

本研究旨在探讨肝癌发展过程中PEDF的表达及不同的活性，以及细胞内PEDF对肝癌脂质病变的作用及其机制。我们发现PEDF在HCC肿瘤组织中高表达，抑制血管生成，但与患者预后无关。动物实验表明，PEDF早期促进肿瘤生长，晚期抑制HCC进展过程中的肿瘤血管生成。然而，促肿瘤活性主要是由细胞内的PEDF产生的，它在体内和体外导致游离脂肪酸(FFA)的积累。在HCC组织中，PEDF的高表达与从头脂肪酸合成中FFA和关键酶FASN的高表达呈正相关，与AMPK和FFA氧化关键酶CPT1a的表达呈负相关。机制上，细胞内PEDF通过抑制AMPK的活化，导致FFA的积累，最终促进HCC细胞的生长，从而通过上调FASN的表达，促进新生脂肪酸合成的增加，通过下调CPT1a，抑制FFA的氧化。本研究将有助于全面了解PEDF在HCC中的多样性作用，为肝癌的预防和治疗提供新的策略。