Clinicopathological significance of microRNA‐21 in extracellular vesicles of pleural lavage fluid of lung adenocarcinoma and its functions inducing the mesothelial to mesenchymal transition

Abstract

Background: Pre-resection pleural lavage cytology is useful to predict tumor recurrence and the prognosis of lung cancer patients. Recently, extracellular vesicles (EVs) isolated from effusion specimens have come under the spotlight, and several studies showed that microRNA in EVs is associated with prognosis. MicroRNA-21 (miR-21) is a representative onco-microRNA, and miR-21 in EVs (EV-miR-21) promotes cancer dissemination by inducing mesothelial to mesenchymal transition (MMT) in the peritoneal cavity. In this study, we isolated EVs from pleural lavage fluid and focused on EV-miR-21 as a diagnostic factor with a relationship to pleural dissemination. Methods: The Cancer Genome Atlas dataset comprising of 448 cases of lung adenocarcinoma, tissue microarray of 144 cases of lung adenocarcinoma, and pleural lavage fluid of 41 cases was used to examine miR-21 expression levels. The function of EV-miR-21 was investigated in vitro. Results: The miR-21 expression level in primary sites was associated with a poor prognosis and correlated with pleural invasion of adenocarcinoma. EV-miR-21 levels in pleural lavage fluid were associated with positive cytology and pleural invasion in the primary sites, even in cytology-negative cases. In vitro studies demonstrated that EV-miR-21 induces the MMT. Mesothelial cells in the MMT showed functions similar to cancer-associated fibroblasts, which are an important stromal component in primary sites and disseminated pleural lesions. Conclusions: EV-miR-21 in pleural lavage fluid is important as a diagnostic and prognostic factor. Moreover, EV-miR-21 induces the MMT, which can form premetastatic niches of dissemination in the pleural cavity. K E Y W O R D S dissemination, exosome, extracellular vesicles, mesothelial to mesenchymal transition, microRNA-21, pleural lavage fluid 2880 | WATABE ET Al.

A signature of estimate-stromal-immune score-based genes associated with the prognosis of lung adenocarcinoma

“…Along with the tumor growth, immune cells also play important roles (10). Stromal and immune cells constitute the major components of the tumor microenvironment of LUAD (11,12). Therefore, the prognostic stratification of LUAD patients can be improved by comprehensive evaluation that includes metrics for stromal and immune cells to support personalize prognostication over the TNM staging system.…”

Exosomal MicroRNAs Mediating Crosstalk Between Cancer Cells With Cancer-Associated Fibroblasts and Tumor-Associated Macrophages in the Tumor Microenvironment

“…Mesothelial-to-mesenchymal transition (MMT) ( 71 , 72 ) and epithelial-to-mesenchymal transition (EMT) ( 73 ) might be involved in this process. For example, exosomal miR-21 induces MMT in the peritoneal cavity to promote cancer dissemination in lung cancer ( 74 ) Mesothelial cells were identified as a source of CAFs in peritoneal carcinomatosis ( 72 ). Li et al found that GC-derived exosomal miR-21-5p could lead to MMT of peritoneal mesothelial cells (PMCs) and activation of CAFs through TGF-β/Smad pathway by targeting SMAD7 in vivo ( 64 ).…”

Circulating MicroRNAs in Blood and Other Body Fluids as Biomarkers for Diagnosis, Prognosis, and Therapy Response in Lung Cancer

“…This distinctive expression pattern may suggest that miRNAs present a specific biological function associated with the surrounding tissues under normal physiological conditions [ 10 , 60 , 61 ]. Under pathological conditions, altered levels of miRNAs in body fluids have been associated with the diagnosis of several cancers, including bladder [ 62 ], renal [ 63 ], gastric [ 64 ], pancreatic [ 65 ], brain [ 66 ], and lung cancers [ 67 , 68 ].…”

“…Pleural lavage cytology (PLC) is a technique for detecting subclinical dissemination of malignant cells in the pleural cavity; it is performed by injecting normal saline into the pleural space and aspirating at the time of thoracoscopy. In 2020, Watabe et al [ 68 ] analyzed the clinicopathological significance of the expression levels of only one miRNA (miR-21) in extracellular vesicles (EVs) extracted from the pleural lavage fluid of 41 lung adenocarcinoma patients using digital PCR. They found that EV miR-21 levels in pleural lavage fluid are associated with positive cytology and pleural invasion in the primary sites, even in cytology-negative cases.…”