Hypoxic Tumor-Derived Exosomal Circular RNA SETDB1 Promotes Invasive Growth via the miR-7/SP1 Axis in Lung Adenocarcinoma

Abstract

Background: Hypoxia is a common feature of solid tumors and is associated with aggressiveness and poor prognosis of patients. Exosomes are involved in mediating cellular environment interactions. circRNAs are a class of non-coding RNAs (ncRNAs) broadly expressed in cells and exosomes. However, in lung adenocarcinoma tumor development, functions and regulatory mechanisms of exosomal circ-RNAs induced by hypoxia remain poorly understood. Methods: Through microarray analysis, we explored the expression of exosomal circRNAs from hypoxic stress adenocarcinoma cell line supernatant. Differentially expressed circRNAs were identified between exosomes extracted from hypoxic and normoxic conditions. We concentrated on hsa-circ-0003439, which is situated on chromosome 1 and derived from SETDB1, and thus we named it circSETDB1. Findings: We discovered that exosomes obtained from hypoxic lung adenocarcinoma cells improved the migration, invasion and proliferation capacity of normoxic LUAD cells. Given that exosomes carry circRNAs to change cellular functions. CircSETDB1 was found to be significantly up-regulated in hypoxia-induced exosomes from lung adenocarcinoma cell lines compared with exosomes in the normal condition. Moreover, knockdown of circSETDB1 significantly inhibited cell proliferation, invasion and migration in vitro. Importantly, we proved that circSETDB1 was up-regulated in serum exosomes in LUAD patients, which was closely associated with T stage, and lymph node metastasis in patients. Furthermore, functional experiments in vitro and vivo and analysis of RIP, bioinformatics and luciferase reporter assay confirm the mechanism of circSETDB1/miR-7/ Specificity Protein 1 (SP1) axis in the development of lung adenocarcinoma. Interpretation: From our results, it can be concluded that the hypoxic microenvironment may cause tumor cells to produce circSETDB1-rich exosomes supplied to normoxic cells to promote prometastatic behaviors through a miR-7/SP1 axis. More attention should be paid to the value of exosomes in tumor diagnosis and therapy. Funding Statement: This work was supported by International Exchange Program for Graduate Students, Tongji University. Declaration of Interests: All authors declare that they have no competing interests. Ethics Approval Statement: For donating their samples, all individuals had signed informed permission. The use of tissues for this study has been approved by the ethics committee of Shanghai Pulmonary Hospital of Tongji University and Shanghai Changhai Hospital of The Second Military Medical University.