Identification and function of circular RNA hsa_circ_0071106: A novel biomarker for differentiation degree of esophageal squamous cell carcinoma.

Background: Esophageal squamous cell carcinoma (ESCC) has a high degree of malignancy, and there is currently no effective treatment. Circular RNA is a novel endogenous noncoding RNA with a stable loop structure. Several theories have been proposed regarding its biogenesis and usefulness as a biomarker in various cancers. Here we explore the predictive value and potential functions of a candidate circRNA (hsa_circ_0071106) in ESCC.

Methods: The altered expression of hsa_circ_0071106 was validated in clinical tissue samples from 64 patients with ESCC. The correlation between the clinical characteristics of these patients and the expression of hsa_circ_0071106 was analyzed by the chi-square test. The receiver operating characteristic (ROC) curves and the area under the ROC curve (AUC) were used to evaluate the diagnostic value of hsa_circ_0071106. The human esophageal carcinoma cell lines ECA109 and ECA9706 and the normal human esophageal epithelial cell line (HET-1A) were applied for functional analysis of hsa_circ_0071106. qRT-PCR, sanger sequencing, agarose gel electrophoresis, RNase R digestion assay, Actinomycin D inhibition assay, nucleoplasm separation assay, and FISH assays were utilized to verify the circular characteristics and subcellular localization of hsa_circ_0071106. SiRNA and circRNA interference lentivirus was constructed to inhibit the expression of hsa_circ_0071106 in the ECA109 and ECA9706 cell lines. We used the EdU assay, Transwell assay, and flow cytometry to detect changes in cell proliferation, invasion, migration, and apoptosis.

Results: We identified that hsa_circ_0071106 showed significantly decreased expression levels in ESCC cells (P < 0.001) and tissue samples (P < 0.001). The correlation analysis of clinicopathological features and gene expression revealed that low expression of hsa_circ_0071106 was related to poor differentiation grade (P < 0.05). ROC curves indicated that hsa_circ_0071106 might have a diagnostic value for ESCC (AUC = 0.826, 95% CI: 0.748-0.904) and a predictive value for a high degree of histological differentiation (AUC = 0.730, 95% CI: 0.607-0.854). Hsa_circ_0071106 has a stable circular structure and was primarily localized in the cytoplasm. A transient knockdown of hsa_circ_0071106 by siRNA promotes proliferation, migration, and invasion and inhibits apoptosis of ESCC cells. A steady knockdown of hsa_circ_0071106 by a lentivirus knockout vector significantly promoted cell migration and invasion in ECA109 and ECA9706 cell lines.

Conclusion: Hsa_circ_0071106 was a downregulated circRNA related to ESCC and promoted ESCC progression by regulating cell migration and invasion. These findings suggest that hsa_circ_0071106 could be a promising diagnostic biomarker and potential therapeutic target and might predict ESCC's histological differentiation degree.