Differential expression and analysis of extrachromosomal circular DNAs as serum biomarkers in lung adenocarcinoma.

ABSTRACT

BACKGROUND: Extrachromosomal circular DNAs (eccDNAs) increase the number of proto-oncogenes by enhancing oncogene expression to promote tumorigenesis. However, there are limited reports on differential eccDNA expression and analysis in lung cancer, especially in lung adenocarcinoma (LAD). METHODS: Three LAD and three corresponding NT tissues samples were used for eccDNA next-generation sequencing analysis, and an additional 20 were used for quantitative PCR (qPCR) evaluations. We further performed qPCR amplification using serum samples from LAD patients and healthy medical examiners. RESULTS: eccDNAs from LAD samples were mainly 200-1000 bp in length. Gene annotation analysis revealed that most eccDNAs were derived from chromosomes 1 and 2. The top-ten increased and top-ten decreased eccDNAs in LAD tissues were CircD-ARPC1B, CircD-ARPC1A, CircD-FAM49B, CircD-SDK1, CircD-KCNG1, CircD-POLR2F, CircD-SS18L1, CircD-SLC16A3, CircD-CSNK1D, CircD-KCTD1, and CircD-TMIGD2, CircD-PDIA5, CircD-VAV2, CircD-GATAD2A, CircD-CAB39L, CircD-KHDC1, CircD-FOXN3, CircD-SULT2B1, CircD-DPP9, and CircD-CSNK1D. qPCR demonstrated that the expression of CircD-DZRN3 was higher in LAD tissues than in normal lung tissues, whereas CircD-LGR6 and CircD-UMODL1 expression levels were lower in LAD than in normal lung tissues. Furthermore, the serum CircD-PDZRN3 level increased, while CircD-LGR6 decreased in LAD. Receiver operating characteristic (ROC) analysis showed that area under curve (AUC) of serum CircD-PDZRN3 (0.991), CircD-LGR6 (0.916) was higher than that of serum carcinoembryonic antigen (CEA) (0.825), CY211 (cytokeratin 19 fragment) (0.842), SCCA(squamous cell carcinoma antigen) (0.857) for the diagnosis of LAD. CONCLUSIONS: Our study first showed that several eccDNAs were aberrantly expressed in LAD, among which CircD-PDZRN3 and CircD-LGR6 clearly distinguished LAD patients from healthy controls, indicating their potential as biomarkers.