载脂蛋白APOC2通过STAT3/MAPK-VEGFA通路促进血管生成介导大肠癌转移的机制研究

Tumor metastasis is the main reason for the failure of treatment for colorectal cancer. Angiogenesis and abnormal lipid metabolism are important features of cancer metastasis, but the relationship between them has not been well clarified. We found that the expression of apolipoprotein APOC2 was up-regulated in colorectal cancerous tissues, and was higher in metastatic tumor tissues compared with primary cancer samples. Over-expressing APOC2 in colon cancer cells promotes tumor invasion and angiogenesis, and activates lipoprotein lipase(LPL) and stimulates the level of VEGFA. Additionally, high-throughput data suggest that STAT3/MAPK is a potential downstream target of APOC2. Thus, we speculate that APOC2 may participate in lipid metabolism inducing tumor angiogenesis via activating STAT3/MAPK-VEGFA pathway to promote tumor metastasis. Therefore, this study intends to 1) observe APOC2’s function in colon cancer metastasis by silencing and over-expressing this gene in colon cancer cells; 2) detect the activity of key enzymes of lipid metabolism, and the lipid metabolite using mass spectrometry in APOC2-silenced/over-expressed colon cancer cells; 3) explore APOC2’s effect on tumor angiogenesis by activating STAT3/MAPK pathway by laser confocal microscopy and western blot; 4) verify the mechanism of APOC2’s promoting tumor metastasis by regulating lipid metabolism and angiogenesis through using patient-derived xenograft(PDX) model, combined with public database and large samples of colonic tumor tissues and paired normal tissues, and investigate its clinical value. It is expected to clarify the mechanism of APOC2’s induction of angiogenesis to promote tumor metastasis and provide new insights in the prevention and treatment of colorectal cancer.

肿瘤转移是大肠癌治疗失败的主要原因。血管生成与脂代谢异常是癌转移的重要特征，但两者关系研究较少。我们发现载脂蛋白APOC2在肠癌组织中表达上调，并在转移灶中表达更高；过表达APOC2促进肿瘤侵袭及血管生成，激活脂蛋白脂酶，刺激VEGFA表达。此外高通量数据提示STAT3/MAPK是APOC2潜在的下游靶标。据此，我们推测：APOC2可能参与脂代谢激活STAT3/MAPK-VEGFA信号通路诱导血管生成，促进肿瘤转移。因此，本项目拟①沉默和过表达APOC2观察其在肠癌转移中的作用；②酶活性检测与质谱分析APOC2对脂代谢关键酶及产物的影响；③共聚焦、WB等探讨APOC2通过STAT3/MAPK调控血管生成的途径；④PDX模型验证APOC2促进脂代谢和血管生成诱导转移的机制，结合公共数据库和临床大样本验证其临床价值。本研究可望阐明APOC2诱导血管生成促进肿瘤转移机制，为大肠癌防治提供新思路。

肿瘤转移严重制约大肠癌根治手术疗效与病人预后。我们根据前期工作基础提出假设：载脂蛋白APOC2通过调节脂代谢等途径促进肠癌复发转移。首先，我们利用自建临床样本库和公共数据库扩大验证前期结论，发现APOC2在肠癌肿瘤组织中高表达且与患者预后不良密切相关，且在转移灶中表达量更高，这可能与转录因子MYC和ELF1转录激活APOC2及其启动子区域低甲基化状态有关。通过体内、外功能实验证实稳定过表达APOC2显著增强肠癌细胞增殖和迁移侵袭能力，而干扰APOC2后与之相反。采用质谱和Co-IP技术发现并验证脂代谢关键酶FASN与APOC2直接相互作用，进而下调脂代谢产物二十碳五烯酸（EPA）和二十二碳六烯酸（DHA）增强肠癌细胞增殖能力。最后，APOC2通过增加增加α-酮戊二酸含量激活组蛋白去甲基化酶PHF8活性调控肿瘤细胞增殖及转移相关基因表达。本研究明确了APOC2促进大肠癌转移的分子作用机制，为未来大肠癌防治提供新的理论基础和潜在用药靶点。

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