Different Functions Of DEPTOR In Modulating Sensitivity To Chemotherapy For Esophageal Squamous Cell Carcinoma

Background and aimsDEP domain-containing mTOR-interacting protein(DEPTOR)is an endogenous inhibitor of mammalian target of rapamycin(mTOR).It is usually regarded as a tumor suppressor which has been confirmed in colorectal cancer,multiple myeloma and pancreatic cancer.However,DEPTOR has been reported to be essential for the survival and proliferation of a subset of multiple myelomas。The high expression of DEPTOR inhibits the activity of mTOR pathway,leading to the activation of Akt and the survival of multiple myeloma cells through negative feedback mechanism.At present,two articles have reported the relationship between DEPTOR and the prognosis of esophageal cancer.A study showed that DEPTOR was upregulated in patients with esophageal squamous cell carcinoma and suggested a shorter survival period.Another study showed that DEPTOR expression was downregulated in esophageal squamous cell carcinoma and suggested poor prognosis.The results of these two studies suggest that the expression of DEPTOR in esophageal cancer and its role in predicting the prognosis of esophageal squamous cell carcinoma(ESCC)is not clear.The purpose of this study is to determine the expression of DEPTOR in esophageal cancer,and its impact on the prognosis of esophageal cancer.We also investigate the role of DEPTOR on esophageal cancer cell line chemotherapy response.Methods1.23 cases of esophageal cancer specimens were collected from thoracic surgery in the Nanfang hospital.The specimens were divided into two parts.A part of the tissues were fixed,embedded,sliced and Immunohistochemical staining were usedto observe the expression of DEPTOR protein.2.The tissue microarray was obtained from Shanghai Outdo Biotech Company.Immunohistochemical staining was performed.We evaluated the expression of DEPTOR.Survival probabilities were calculated using the Kaplan-Meier method.3.The expression levels of DEPTOR in TE-1,TE-13,KYSE-510,EC-109 cell line were detected by immunoblotting.ESCC cell lines were classified into relatively high and low DEPTOR-expressing subgroups according to DEPTOR expression in the esophageal squamous epithelial cell line HET-1A.4.Cell proliferation assays were carried out with Cell Counting Kit-8.Cells were plated in 96-well plates at approximately 1×104cells per well.The absorbance(450 nm)was measured using a BioTek Synegry HTX multi-mode reader.5.By using the method of immunoblotting,we explored the molecular mechanism of DEPTOR in affecting the sensitivity of esophageal cancer cells.ResultsHere we show that DEPTOR expression was significantly increased in tumor tissues and predicted good survival in early stage ESCC patients but not in advanced stage patients.In vitro studies showed that ESCC cell lines could be classified into relatively high and low DEPTOR-expressing subgroups according to DEPTOR expression in the esophageal squamous epithelial cell line HET-1A.In our study,different levels of DEPTOR expression absolutely determined the response to chemotherapy.In relatively low-expressing cell lines,DEPTOR increased chemotherapy sensitivity via deactivation of the Akt pathway.In relatively high-expressing cell lines,DEPTOR increased cell survival and chemoresistance by strong feedback activation of the IRS1-PI3K-Akt-survivin pathway that occurred after downregulation of ribosomal protein S6 kinase(S6K).Collectively,our findings highlight the dichotomous nature of DEPTOR functions in modulating chemotherapy sensitivity in different ESCC cells.