Numerous studies have shown that non–cell-autonomous regulation of cancer cells is an important aspect of tumorigenesis. Cancer cells need to communicate with stromal cells by humoral factors such as VEGF, FGFs, and Wnt in order to survive. Recently, extracellular vesicles (EVs) have also been shown to be involved in cell-cell communication between cancer cells and the surrounding microenvironment and to be important for the development of cancer. In addition, these EVs contain small noncoding RNAs, including microRNAs (miRNAs), which contribute to the malignancy of cancer cells. Here, we provide an overview of current research on EVs, especially miRNAs in EVs. We also propose strategies to treat cancers by targeting EVs around cancer cells.

Programmed cell death ligand-1 (PD-L1) has recently gained considerable attention for its role in tumor immune escape. Here, we identify a miR-197/CKS1B/STAT3-mediated PD-L1 network in chemoresistant non-small-cell lung cancer (NSCLC), independent of immunoinhibitory signals. miR-197 is downregulated in platinum-resistant NSCLC specimens, resulting in the promotion of chemoresistance, tumorigenicity, and pulmonary metastasis in vitro and in vivo. Mechanistic investigations reveal that a miR-197-mediated CKS1B/STAT3 axis exerts tumor progression regulated by various oncogenic genes (Bcl-2, c-Myc, and cyclin D1), and PD-L1 is a putative biomarker of this axis. Furthermore, we demonstrate that a miR-197 mimic sensitizes PD-L1^high drug-resistant cells to chemotherapy. These results indicate that the biological interaction between PD-L1 and chemoresistance occurs through the microRNA regulatory cascade. More importantly, expression levels of miR-197 are inversely correlated with PD-L1 expression (n = 177; P = 0.026) and are associated with worse overall survival (P = 0.015). Our discoveries suggest that the miR-197/CKS1B/STAT3-mediated network can drive tumor PD-L1 expression as a biomarker of this cascade, and miR-197 replacement therapy may be a potential treatment strategy for chemoresistant NSCLC.

Extracellular vesicles (EVs), such as exosomes and microvesicles, encapsulate proteins and microRNAs (miRNAs) as new modulators of both intercellular crosstalk and disease pathogenesis. The composition of EVs is modified by various triggers to maintain physiological homeostasis. In response to cigarette smoke exposure, the lungs develop emphysema, myofibroblast accumulation and airway remodelling, which contribute to chronic obstructive pulmonary disease (COPD). However, the lung disease pathogenesis through modified EVs in stress physiology is not understood. Here, we investigated an EV‐mediated intercellular communication mechanism between primary human bronchial epithelial cells (HBECs) and lung fibroblasts (LFs) and discovered that cigarette smoke extract (CSE)‐induced HBEC‐derived EVs promote myofibroblast differentiation in LFs. Thorough evaluations of the modified EVs and COPD lung samples showed that cigarette smoke induced relative upregulation of cellular and EV miR‐210 expression of bronchial epithelial cells. Using co‐culture assays, we showed that HBEC‐derived EV miR‐210 promotes myofibroblast differentiation in LFs. Surprisingly, we found that miR‐210 directly regulates autophagy processes via targeting ATG7, and expression levels of miR‐210 are inversely correlated with ATG7 expression in LFs. Importantly, autophagy induction was significantly decreased in LFs from COPD patients, and silencing ATG7 in LFs led to myofibroblast differentiation. These findings demonstrate that CSE triggers the modification of EV components and identify bronchial epithelial cell‐derived miR‐210 as a paracrine autophagy mediator of myofibroblast differentiation that has potential as a therapeutic target for COPD. Our findings show that stressor exposure changes EV compositions as emerging factors, potentially controlling pathological disorders such as airway remodelling in COPD.

Accumulation of profibrotic myofibroblasts in fibroblastic foci (FF) is a crucial process for development of fibrosis during idiopathic pulmonary fibrosis (IPF) pathogenesis, and transforming growth factor (TGF)-β plays a key regulatory role in myofibroblast differentiation. Reactive oxygen species (ROS) has been proposed to be involved in the mechanism for TGF-β-induced myofibroblast differentiation. Metformin is a biguanide antidiabetic medication and its pharmacological action is mediated through the activation of AMP-activated protein kinase (AMPK), which regulates not only energy homeostasis but also stress responses, including ROS. Therefore, we sought to investigate the inhibitory role of metformin in lung fibrosis development via modulating TGF-β signaling. TGF-β-induced myofibroblast differentiation in lung fibroblasts (LF) was used for in vitro models. The anti-fibrotic role of metfromin was examined in a bleomycin (BLM)-induced lung fibrosis model. We found that TGF-β-induced myofibroblast differentiation was clearly inhibited by metformin treatment in LF. Metformin-mediated activation of AMPK was responsible for inhibiting TGF-β-induced NOX4 expression. NOX4 knockdown and N-acetylcysteine (NAC) treatment illustrated that NOX4-derived ROS generation was critical for TGF-β-induced SMAD phosphorylation and myofibroblast differentiation. BLM treatment induced development of lung fibrosis with concomitantly enhanced NOX4 expression and SMAD phosphorylation, which was efficiently inhibited by metformin. Increased NOX4 expression levels were also observed in FF of IPF lungs and LF isolated from IPF patients. These findings suggest that metformin can be a promising anti-fibrotic modality of treatment for IPF affected by TGF-β.

Extracellular vesicles (EV), known as exosomes and microvesicles, serve as versatile intercellular communication vehicles. Increasing evidence has shown that cancer cell‐derived EV carry pathogenic components, such as proteins, messenger RNA (mRNA), microRNA (miRNA), DNA, lipids and transcriptional factors, that can mediate paracrine signaling in the tumor microenvironment. These data suggest that EV transfer of cancer pathogenic components enable long‐distance crosstalk between cancer cells and distant organs, resulting in the promotion of the initial steps for pre‐metastatic niche formation. Understanding the metastatic mechanisms through EV transfer may open up a new avenue for cancer therapeutic strategies. Furthermore, the circulating EV have also been of interest as a source for liquid biopsies. EV in body fluids provide a reliable source of miRNA and proteins for cancer biomarkers. The tumor‐specific components in EV effectively provide various messages on the physiological and pathological status of cancer patients. Although many researchers are searching for EV biomarkers using miRNA microarrays and proteome analyses, the detection technology for circulating EV in body fluids has not yet reached the point of clinical application. In this review, we summarize recent findings regarding EV function, specifically in metastasis through the transfer of cancer pathogenic components. Furthermore, we highlight the potential of using circulating EV for cancer diagnosis.