赖氨酰氧化酶样蛋白4在人类恶性肿瘤发生与发展中的作用

赖氨酰氧化酶样蛋白4(lysyl oxidase like 4, LOXL4)是一种属于赖氨酰氧化酶(lysyl oxidase, LOX)蛋白质家族的分泌型铜依赖性胺氧化酶,参与细胞外基质(extracellular matrix, ECM)的组装和维持。LOXL4蛋白在人类肝癌、胃癌、乳腺癌、宫颈癌、头颈鳞癌、食管癌和结直肠癌中表达上调,而在人类膀胱癌和肺癌中表达下调并抑制肿瘤的生长,表明LOXL4蛋白在不同类型的人类恶性肿瘤中具有促癌或抑癌的双向作用。肿瘤细胞外泌体中的LOXL4蛋白通过催化作用产生过氧化氢,后者直接激活FAK/Src信号通路,并促进细胞基质粘附和细胞迁移。外泌体介导的LOXL4还可以通过激活PI3K/Akt信号通路来促进肿瘤细胞的增殖和免疫逃逸。肿瘤细胞中的 LOXL4可以经外泌体转运至巨噬细胞,进一步通过STAT1和STAT3介导的信号通路激活细胞免疫抑制功能和激活程序性死亡配体 1(programmed death ligand 1, PD-L1)表达,触发巨噬细胞的免疫抑制功能,促进肿瘤细胞的免疫逃逸。此外,LOXL4蛋白还能通过激活p53蛋白和抑制Ras/ERK信号转导通路发挥抑癌功能。本文主要总结了LOXL4蛋白的结构、功能及其在人类恶性肿瘤发生发展的作用机制,进一步探讨LOXL4蛋白在恶性肿瘤研究中的应用前景,为恶性肿瘤的临床诊断、治疗和筛选预后标志物提供理论基础和参考依据。

The Dual Role of LOXL4 in Pathogenesis and Development of Human Malignant Tumors

Lysyl oxidase like 4 (LOXL4) is one member of the LOX protein family and is a secreted copper-dependent amine oxidase involved in the assembly and maintenance of extracellular matrix (ECM). LOXL4 is up-regulated in human liver cancer, gastric cancer, breast cancer, cervical cancer, head and neck squamous cell carcinoma, esophageal carcinoma and colorectal cancer, but down-regulated in human bladder and lung cancer. It also inhibits tumor growth in bladder and lung cancer, suggesting that LOXL4 has a dual role of promoting or inhibiting tumors in different types of human malignant tumors. LOXL4 in tumor cell exosomes promotes cell matrix adhesion and cell migration by activating the FAK/Src pathway, which is dependent on its amine oxidase activity through a hydrogen peroxide-mediated mechanism. Exosome-mediated LOXL4 can also promote tumor cell proliferation and immune escape by activating the PI3K/Akt signaling pathway. LOXL4 can be transported to macrophages via exosomes in tumor cells, where it further activates the immunosuppression function of cells and the expression of programmed death ligand 1 (PD-L1) via STAT1- and STAT3-mediated signaling pathways. It then will trigger the immunosuppressive function of macrophages and promote the immune escape of tumor cells. In addition, LOXL4 can also exert the tumor suppressive function by activating p53 and inhibiting the Ras/ERK pathway. This paper mainly reviews the structure and the function of LOXL4, and the relationship between LOXL4 and the pathogenesis and development of human malignant tumors. We then further explore the application of LOXL4 in the study of malignant tumors, laying a theoretical foundation for its future utilization in the clinical diagnosis and treatment, and screening of prognostic markers of human malignant tumors.