Circ_DLG1 facilitates esophageal squamous cell carcinoma progression by mediating miR-338-3p/MAP3K9 axis via activating MAPK/ERK pathway
Esophageal squamous cell carcinoma (ESCC) is an aggressive malignancy with a high incidence and poor prognosis. The document of circular RNAs (circRNAs) is frequently associated with cancer development. This study intended to explore the functional mechanism of circ_DLG1 in ESCC. Methods: The expression of circ_DLG1, miR-338-3p and Mitogen-Activated Protein Kinase Kinase Kinase 9 (MAP3K9) was measured by quantitative real-time polymerase chain reaction (qRT-PCR). Cell cycle, proliferation,
... proliferation, migration and invasion were performed for functional analysis using ow cytometry, 3-(4, 5dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide (MTT) and transwell assay, respectively. The protein levels of MAP3K9, p38, phosphor p38 (p-p38), ERK1/2, phosphor ERK1/2 (p-ERK1/2) were detected by western blot. Bioinformatics tool for target prediction used the online tool starBase. Dualluciferase reporter assay was performed to verify the target relationship. The animal experiments were performed to ascertain the role of circ_DLG1 in vivo. Results: The expression of circ_DLG1 was elevated in ESCC tissues, plasma and cells. Circ_DLG1 knockdown inhibited cell cycle, proliferation, migration and invasion. MAP3K9 was highly expressed in ESCC tissues and cells, and its overexpression rescued the effects of circ_DLG1 knockdown. MiR-338-3p was a link between circ_DLG1 and MAP3K9, and circ_DLG1 regulated the expression of MAP3K9 by targeting miR-338-3p. The MAPK/ERK pathway was involved in the circ_DLG1/miR-338-3p/MAP3K9 regulatory axis. Circ_DLG1 knockdown blocked the tumor growth in vivo by regulating miR-338-3p and MAP3K9. Conclusion: Circ_DLG1 contributed to the malignant progression of ESCC by mediating the miR-338-3p/MAP3K9 axis via activating the MAPK/ERK signaling pathway. This paper provided a novel action mode of circ_DLG1 in ESCC. Background Esophageal cancer (EC) is an aggressive malignancy, leading to a weak overall survival rate (10% ~20%) . EC evolves into the eighth most common cancer and the sixth cause of cancer-related death  . According to the cell types involved, EC can be divided into esophageal adenocarcinoma (EAC) and esophageal squamous cell carcinoma (ESCC)  . ESCC shows greater geographic diversity in morbidity, mortality and sex ratios, especially in Eastern and Asian countries [4, 5] . Risk factors for ESCC are thought to be related to diet, lifestyle and genetic polymorphisms  . However, the complex molecular mechanisms of ESCC initiation and development have not been fully understood. Therefore, there is an absolute need to improve medical treatment by identifying novel therapeutic targets. With the development of high-throughput sequencing technique, a growing number of circular RNAs (circRNAs) closely linked to cancers have been identi ed  . CircRNAs are a new type of non-coding RNAs formed by back-splicing without 5' cap and 3' poly-A tail  , which is different from linear mRNAs. Thousands of circRNAs are abundant, relatively stable and widely expressed in eukaryotic cells [9, 10] .