载脂蛋白L4在肝细胞癌中的异常表达、 临床意义及分子生物机制探究

Investigation of the Abnormal Expression, Clinical Significance, and Molecular Biological Mechanisms of Apolipoprotein L4 in Hepatocellular Carcinoma

摘要: 目的：探讨载脂蛋白L4 (Apolipoprotein L4, APOL4)基因在肝细胞癌(Hepatocellular Carcinoma, HCC)中的表达及分子机制。方法：基于The Human Protein Atlas (THPA)数据库分析APOL4蛋白在HCC组织及正常肝组织中的表达差异。利用GEPIA平台整合TCGA与GTEx数据，比较APOL4 mRNA在HCC与正常组织中的表达水平，并通过Kaplan-Meier生存曲线评估其与患者总体生存期的关系。进一步开展泛癌分析，评估APOL4表达与肿瘤突变负荷(Tumor Mutational Burden, TMB)及微卫星不稳定性(Microsatellite Instability, MSI)的相关性。通过STRING数据库构建蛋白质–蛋白质互作(Protein-Protein Interaction, PPI)网络，筛选关键互作蛋白。采用DAVID数据库进行GO功能及KEGG通路富集分析，并运用CIBERSORT算法评估APOL4表达与肿瘤免疫细胞浸润的关系。结果：APOL4蛋白在HCC组织中呈中度阳性表达，而正常肝组织中未见表达(P < 0.05)。HCC组织中APOL4 mRNA表达水平显著高于正常对照组，高表达组患者总体生存率显著降低(HR = 1.4, P < 0.05)。泛癌分析显示，APOL4在多种癌症类型中表达上调，其高表达与肝癌、胰腺癌等的不良预后显著相关。突变谱分析提示TP53为最高频突变基因，APOL4表达水平与部分癌种的TMB及MSI评分存在显著相关性。PPI网络分析筛选出PRODH、CHRM4、B4GALNT2、FANCM等10个与APOL4密切互作的蛋白。GO/KEGG富集分析表明，APOL4相关基因显著富集于白细胞介导免疫、趋化性、细胞外基质组织、免疫受体活性及细胞因子–细胞因子受体相互作用、PI3K-Akt信号通路等。免疫浸润分析显示，APOL4高表达组中激活的记忆CD4⁺ T细胞及γδT细胞比例升高。结论：APOL4在HCC组织中表达显著上调，其高表达与患者不良预后密切相关。APOL4可能通过调控免疫细胞浸润、细胞外基质重塑及PI3K-Akt等信号通路参与HCC的发生发展，有望成为HCC潜在的预后生物标志物及治疗靶点。

Abstract: Objective: To investigate the expression and molecular mechanisms of the Apolipoprotein L4 (APOL4) gene in Hepatocellular Carcinoma (HCC). Methods: The difference in APOL4 protein expression between HCC tissues and normal liver tissues was analyzed using The Human Protein Atlas (THPA) database. The GEPIA platform was employed to integrate TCGA and GTEx data to compare APOL4 mRNA expression levels between HCC and normal tissues, and Kaplan-Meier survival curves were used to assess the association between APOL4 expression and overall survival of patients. Pan-cancer analysis was further performed to evaluate the correlation between APOL4 expression and Tumor Mutational Burden (TMB) as well as Microsatellite Instability (MSI). A Protein-Protein Interaction (PPI) network was constructed using the STRING database to identify key interacting proteins. GO function and KEGG pathway enrichment analyses were conducted using the DAVID database, and the CIBERSORT algorithm was applied to evaluate the relationship between APOL4 expression and tumor immune cell infiltration. Results: APOL4 protein showed moderate positive expression in HCC tissues, while no expression was detected in normal liver tissues (P < 0.05). APOL4 mRNA expression levels in HCC tissues were significantly higher than those in the normal control group, and patients in the high-expression group had significantly lower overall survival rates (HR = 1.4, P < 0.05). Pan-cancer analysis revealed that APOL4 expression was upregulated in multiple cancer types, and its high expression was significantly associated with poor prognosis in liver cancer, pancreatic cancer, and others. Mutation profile analysis indicated that TP53 was the most frequently mutated gene, and APOL4 expression levels were significantly correlated with TMB and MSI scores in certain cancer types. PPI network analysis identified 10 proteins, including PRODH, CHRM4, B4GALNT2, and FANCM, that closely interact with APOL4. GO/KEGG enrichment analysis showed that APOL4-related genes were significantly enriched in leukocyte-mediated immunity, chemotaxis, extracellular matrix organization, immune receptor activity, cytokine-cytokine receptor interaction, and the PI3K-Akt signaling pathway. Immune infiltration analysis revealed increased proportions of activated memory CD4⁺ T cells and gamma delta T cells in the APOL4 high-expression group. Conclusion: APOL4 expression is significantly upregulated in HCC tissues, and its high expression is closely associated with poor patient prognosis. APOL4 may participate in the development and progression of HCC by regulating immune cell infiltration, extracellular matrix remodeling, and signaling pathways such as PI3K-Akt, making it a potential prognostic biomarker and therapeutic target for HCC.