The Dual Role of LOXL4 in Pathogenesis and Development of Human Malignant Tumors / 中国生物化学与分子生物学报

ABSTRACT

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 L0XL4 has a dual role of promoting or inhibiting tumors in different types of human malignant tumors. L0XL4 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 L0XL4 can also promote tumor cell proliferation and immune escape by activating the PI3K/Akt signaling pathway. L0XL4 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.