Abstract

Introduction Hypoxia and tumor-associated macrophage (TAM) are key regulators in remodeling the microenvironment of esophageal squamous cell carcinoma (ESCC). Hypoxia could stimulate tumor cells to secrete more exosomes and activate TAMs to M2 type. Here, we investigated the function and the underlying mechanism of tumor-derived exosomal hsa-circ-0048117 in TAM polarization in ESCC. Collectively, these data indicate that PC cells generate miR-301a-3p-rich exosomes in a hypoxic microenvironment, which then polarize macrophages to promote malignant behaviors of PC cells. Methods Transmission electron microscopy (TEM) and nanoparticle tracking analysis (NTA) were used to analyze the physical characteristics of exosomes. High-throughput sequencing and bioinformatic analysis were performed to screen the potential exosomal circRNA. FISH, Ago2 RIP, pull-down and dual-luciferase reporter assay were conducted to figure out the correlation among hsa-circ-0048117, miR-140 and toll-like receptor 4 (TLR4). Flow cytometry and Western blot were used to evaluate their joint effect in macrophages polarization. Then, the invasion and migration ability were evaluated by transwell experiment. At last, serum exo-hsa-circ-0048117 in ESCC patients was compared and the correlation between its expression and T stage, N stage and TNM grades was analyzed. Results Hsa-circ-0048117 was significantly upregulated and enriched in exosomes secreted by hypoxia pre-challenged tumor cells and contributed to M2 macrophage polarization. Hsa-circ-0048117 depletion in macrophage led to inhibition of M2 polarization while restoration of hsa-circ-0048117 could rescue the process. Moreover, hsa-circ-0048117 could act as sponge of miR-140 by competing with TLR4 to facilitate the M2 macrophage polarization.