Study On The Molecular Mechanism Of Radiosensitivity In Esophageal Carcinoma

Esophageal carcinoma is one of the most prevalent malignant tumors in the world,and esophageal squamous cell carcinoma is the most important histological type.Radiotherapy is an important means of treatment of esophageal carcinoma.However,the sensitivity of esophageal carcinoma to radiotherapy is not satisfactory,and radiation resistance will lead to treatment failure.Therefore,there is an urgent need to improve the radiosensitivity in clinical application to understand the mechanism of radiation resistance in esophageal carcinoma[1].High expression of EGFR is common in esophageal carcinoma,and is associated with poor prognosis in esophageal carcinoma.Previous results from our laboratory have shown that irradiation directly inhibits the EGFR signaling pathway in esophageal squamous cell carcinoma cells and induces EGFR translocation into the nucleus.In this study,we focused on the antagonistic mechanism of EGFR signaling inhibition by radiation treatment using esophageal squamous cell carcinoma cell lines as a background.Our findings suggest that inhibition of the EGFR signaling pathway by radiation leads to feedback activation of STAT3,and mechanistic studies suggest that induction of EGFR nuclear entry by radiation enhances the interaction between nuclear EGFR and STAT3 protein,regulates the transcriptional activity of STAT3,activates STAT3 and then enhances the transcription of the IL6 gene,ultimately increasing the expression and secretion of IL6 cytokines.After autocrine to the extracellular space,IL6 can further activate STAT3 by binding to the interleukin 6 receptor(IL6R)on the membrane,forming an IL6R-STAT3-IL6 positive feedback activation loop that promotes cell survival and enhances radioresistance in esophageal squamous cell carcinoma cells.Combined targeting of IL6R-STAT3-IL6 feedback loop can reduce the radioresistance of esophageal squamous cell carcinoma cells and improve the radiosensitivity of esophageal squamous cell carcinoma.In addition,our findings suggest that EGFR can also induce elevated expression of miR-195-5p in esophageal squamous cell carcinoma cells,and after radiation exposure,miR-195-5p expression was decreased and survivin protein expression was increased.Esophageal squamous cell carcinoma cells transfected with miR-195-5p mimic had decreased survival rate,decreased EdU positive cells rate and clonal survival rate,significantly increased apoptosis rate,and decreased survivin mRNA and protein expression levels in cells compared with the negative control group after irradiation.However,KESE510 cells transfected with miR-195-5p antagonist had increased EdU positive cells rate and clonal survival rate,and increased survivin mRNA and protein expression levels in cells compared with the negative control group.To further validate that survivin is a functional target of miR-195-5p,we predicted 95-101 nt of the human BIRC5 3’UTR as a putative binding site for miR-195-5p by the TargetScan Human website,and in the TCGA database,the mRNA levels of miR-195-5p and BIRC5 were negatively correlated in esophageal carcinoma.The results of the dual-luciferase reporter assay showed that overexpression of miR-195-5p in KYSE150 cells was able to inhibit the luciferase activity of the BIRC5 3’UTR reporter.In summary,we investigated the mechanism by which radiation induces feedback activation of the STAT3 signaling pathway downstream of EGFR as well as downregulation of the expression of miR-195-5p,which in turn affects the radiosensitivity of esophageal squamous cell carcinoma cells at the cellular and molecular levels.Our study demonstrates that radiation exposure can regulate STAT3 transcriptional activity by inducing EGFR nuclear translocation and form an IL6R-STAT3-IL6 positive feedback activation loop,which in turn enhances radioresistance in esophageal squamous cell carcinoma cells,and combined targeting of the IL6R-STAT3-IL6 feedback loop can enhance radiotherapy efficacy in esophageal squamous cell carcinoma.In addition,EGFR can also induce increased expression of miR-195-5p in esophageal squamous cell carcinoma cells,and radiation can induce decreased miR-195-5p expression and increased survivin expression in esophageal squamous cell carcinoma cells.Overexpression of miR195-5p can enhance the radiosensitivity of esophageal squamous cell carcinoma cells by negatively regulating the expression of survivin,inhibiting the cell growth and inducing apoptosis.