Introduction
Lung. Cancer Introduction
Extracellular vesicles (EVs) are lipid bilayer-enclosed extracellular structures which can be formed by outward budding of the plasma membrane or by an intracellular endocytic trafficking pathway involving fusion of multivesicular late endocytic compartments with the plasma membrane.
These fusion events result in the extracellular release of the intraluminal vesicles of these compartments, generating a subtype of EVs termed ‘exosomes’ [1].
Information transmission between tumor cells and various cells in the microenvironment plays an important role in tumor metastasis, and exosomes are one of the important mediums of intercell communication [1, 2].
Exosomes are vesicles with a diameter of 30–100 nm secreted by different types of cells [3].
They carry many kinds of substances, such as lipids, nucleic acids, and proteins, and are widely distributed in body fluids, including urine, plasma, lavage fluid, serosal effusion, and cerebrospinal fluid [4].
Exosomes have important roles in multiple physiological and pathological processes, exerting biological functions. On the one hand, they are necessary to maintain normal physiological responses. On the other hand, in the pathological state, especially in the tumor environment, they promote carcinogenesis, proliferation, migration, invasion, immunosuppression, and angiogenesis as well as reshape the microenvironment [5].
In recent years, the study of exosomes in tumor has received enormous interest.
Exosomes contain bio-macromolecules to participate in information exchange between cells [6].
They can increase the invasion ability of tumor cells and promote tumor metastasis, which has become a research hotspot in the field of cancer recently [7, 8].
Different types of tumor cells secrete different exosome contents. Additionally, factors affecting cell homeostasis, such as a hypoxic microenvironment, survival pressure, and chemotherapy drugs, induces tumor cells to secrete exosomes [9, 10].
Therefore, the volume of exosomes secreted by tumors is much higher than that of normal cells. Although the role of most exosomal compounds in cancer is unclear, previous studies have shown that tumor-derived exosomes promote tumor growth and metastasis by inducing epithelial–mesenchymal transformation (EMT) of tumor cells.
They also promote angiogenesis, the transformation of cancer-associated fibroblasts, immunosuppression, and formation of a premetastatic microenvironment by acting on stromal cells in the microenvironment [11–15].
Several studies have shown that differential expression of exosome contents is closely related to lung cancer metastasis, playing an important role in the multilink and multistep process [16, 17].
The multiple mechanisms of tumor-derived exosomes promoting cancer metastasis are mainly summarized in Fig. 1.
The abscission of cancer cells is essentially a manifestation of increased migration and invasion of tumor cells. Compared with those in healthy people, exosomes are more abundant in circulating body fluids of patients with lung cancer.
A number of studies have found that exosomes promote the occurrence and development of lung cancer by promoting the formation of the lung cancer microenvironment,
increasing the ability of tumor cell invasion and metastasis, mediating tumor immunosuppression, and participating in chemo-radiotherapy resistance [18].
The study of the underlying mechanisms of exosomes in tumor genesis and development may provide new ideas for early and effective diagnosis and treatment of lung cancer metastasis. Therefore, in this article, the relevant research status of the role of exosomes in lung cancer migration and invasion, immunosuppression and escape, angiogenesis, and other processes is reviewed.
Fig. 1.
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