Exosome-mediated Circ＿0001492 Regulates The Radiosensitivity Of Non-small Cell Lung Cancer Via The MiR-145-5p/CDC25A Axis

Background and PurposeLung cancer is the leading cause of cancer deaths in the United States and around the world,accounting for one in five of every 35,000 deaths in 2015,according to the World Health Organization.There are two main types of lung cancer:small cell lung cancer and non-small cell lung cancer(NSCLC),among which non-small cell lung cancer accounts for 85% of all lung cancer prevalence rates and is the main pathological type.NSCLC is poor diagnosed at the early stage,with more than 40% of the NSCLC patients diagnosed at the the stage III.More than 50% of NSCLC patients received radiation therapy(radiotherapy alone or in combination with chemotherapy or surgery).However,the inherent radiosensitivity and dose-limiting toxicity of tumors limit the therapeutic potential of radiotherapy.Most non-small cell lung cancer patients show intrinsic or acquired radiotherapy tolerance,leading to radiotherapy failure.Therefore,it is very important to discover and explore the molecular mechanisms that influence the radiotherapy sensitivity of NSCLC in clinical treatment and improve the survival rate of patients with NSCLC.Exosomes are a class of 30-100 nm small vesicles that can originate from a variety of cells,such as astrocytes,epithelial cells,neurons,hematopoietic stem cells,fibroblasts,fat cells,melanocytes,mesothelioma cells,and even tumor cells.Meanwhile exosomes have been successfully purified from many body fluids including semen,breast milk,plasma or serum,urine,nasal secretions,saliva,amniotic fluid,serebrospinal fluid,pleural effusion and ascites.Exosomes carry a range of biologically active substances,including proteins,lipids,and DNA and RNA that are common to or unique to cells.These specific substances play a regulatory role on receptor cells by mediating inter-cell information transfer.Multiple roles of tumor-derived exosomes in tumor development have been reported,and they are involved in tumor growth,formation,metastasis,microenvironmental regulation,immune regulation,and drug resistance generation.In addition,exosomes were abundant with circRNA,which was 2 to 6 times more expressed than parental cells.Circ RNAs is a novel endogenous non-coding RNAs found in eukaryotic cells,which is precursor m RNAs(pre-m RNAs)generated by a special variable splicing method.Because they have been shown to be tissue specific and have signature properties,they can be potentially useful biomarkers for diagnosis,prognosis and detection of a variety of diseases,such as cancer,osteoarthritis,diabetes and neurodegenerative diseases.At the same time,circRNA plays a number of key functions,the most significant of which is the function of micro RNA(miRNA)sponge – it can bind to one or more miRNAs to regulate the expression of its downstream genes.Moreover,tumor cells release exosomes containing tumor-specific circRNA,which regulate the expression of adjacent and distal cells and play an important role in tumor genesis and progression.Recent studies have found that circ＿0001492 is highly expressed in patients with lung adenocarcinoma and may be involved in the occurrence of lung cancer.On this basis,this study will further explore the effect of exosome-mediated circ＿0001492 on the radiosensitivity of NSCLC,so as to reveal the molecular mechanism of drug resistance in NSCLC and provide a new target for the treatment of NSCLC.Materials and MethodsExosomes from A549 cells(A549-exo)were isolated and identified.The expression of circ＿0001492 in NSCLC tissues,A549 cells and A549-exo was analyzed by RT-qPCR,The effects of A549-exo on the radiotherapy sensitivity of NSCLC cells HCC827 and H1299 were analyzed by plate cloning,MTT and flow cytometry.Double luciferase assay verified the relationship between circ＿0001492,miR-145-5p and CDC25 A,and analyzed the effect of overexpression of miR-145-5p or knockdown of CDC25 A on the radiotherapy sensitivity of A549-exo-induced HCC827 and H1299 cells.Resultscirc＿0001492 was highly expressed in non-small cell lung cancer radiotherapy resistant tissues and A549-exo.A549-exo treatment can promote the increase of circ＿0001492 expression in HCC827 and H1299 cells of non-small cell lung cancer,and reduce the sensitivity of HCC827 and H1299 cells to radiotherapy.circ＿0001492,as the endogenous competitive RNA of miR-145-5p,regulates CDC25 A in HCC827 and H1299 cells.Overexpression of miR-145-5p or knockdown of CDC25 A could reverse the reduced sensitivity of A549-exo to HCC827 and H1299 cells to radiotherapy.ConclusionsExosome-mediated circ＿0001492 could negatively regulate the radiotherapy sensitivity of non-small cell lung cancer cells through the miR-145-5p/CDC25A axis.