The present study aimed to detect the mutation characteristics of mitochondrial DNA (mtDNA) in Eca109 of Ec9706 cells, and to investigate their association with the nuclear genome (nDNA), thus providing a basis for gene targeting therapies for esophageal squamous cell carcinoma (ESCC). In vitro-cultured Ec9706 and Eca109 cells were analyzed the changes of single-nucleotide polymorphisms (SNPs), insertions/deletions (INDELs), copy number variation, and structure variation (SV) of their genome by high-throughput sequencing. The loci with SV on chromosome 1–12 of the two ESCC cell lines were ≥5% of the mtDNA, but SV on chromosome 13–22, X and Y was ≤3%; >40% of loci exhibited gain or loss; intergenic loci with INDEL changes and SNP features accounted for the majority of mutations. The affected genes encoded proteins including nDNA-encoding intra-mitochondrial-transporting proteins, ATP energy generation-associated proteins and mitochondrial electron respiratory chain proteins, and these proteins were all nucleus-encoded mitochondrial proteins. The transcription, duplication, and translation of the abnormally expressed mtDNA in Ec9706 and Eca109 cells were closely associated with disorders of nuclear DNA products.

Circular RNA (circRNA) regulates malignant tumors, including ovarian cancer (OC). The present research study aimed to reveal the biological mechanism of circRNA mitofusin 2 (circMFN2) in OC. Cell biological behaviors were investigated using clonogenicity assay, EdU assay, transwell assay, and flow cytometry analysis. Quantitative reverse transcription polymerase chain reaction (qRT‐PCR) and western blot analysis were implemented to detect the levels of circMFN2, miR‐198, Cullin 4B (CUL4B), and apoptosis‐related proteins. Glycolysis was assessed by glucose assay kit, lactate assay kit, and ATP level detection kit. The relationships among miR‐198, circMFN2, and CUL4B were verified by dual‐luciferase reporter assay and RNA immunoprecipitation assay. The xenograft mice model was used to analyze tumor growth in vivo. The expression of circMFN2 and CUL4B was increased, while miR‐330‐5p was decreased in OC tissues or cells. The absence of CircMFN2 hindered cell proliferation, migration, invasion, and glycolysis and promoted apoptosis in OC cells. We found that circMFN2 promoted CUL4B expression via sponging miR‐198. MiR‐198 depletion reversed circMFN2 knockdown‐induced effects in OC cells. Furthermore, CUL4B overexpression overturned the inhibitory effect of miR‐198 in OC cells. And the absence of circMFN2 inhibited tumor growth in vivo. CircMFN2 repressed OC progression by regulating the miR‐198/CUL4B axis.