Screening For MiRNAs Targeting XIAP And Their Apoptotic Roles In Ovarian Cancer

Background and Objective:The 5-year survival rate of patients with epithelial ovarian cancer remains low due to the chemotherapy resistance.The apoptosis of the cancer cells is depressed.X-linked inhibitor of apoptosis protein(XIAP)has been considered to be the most strong endogenous anti-apoptosis protein until now.It was reported that XIAP expressed dramaticly in many tumor tissues.But the dysrugulation mechanism of XIAP in ovarian cancer tissue is still unclear.MicroRNAs are a large group of small none-coding RNAs which are highly conservative.The deregulation of miRNAs has been associated with tumorgenesis,apoptosis and chemotherapy resistance.It’s very important to screening of miRNAs interaction with XIAP and setting forth the mechanism of apoptosis regulation.It will not only reveal a new regulation net of hereditary information but also aford the important molecular evidence for early diagnosis,classification,staging,therapeutic evaluation and prognosis of tumor.It maybe afford new potential targets for the treatment of ovarian cancer.Methods:First immunohistochemistry was employed to test the expression of XIAP in ovarian cancer tissues.Second a panel of miRNAs were chosen that were predicted to interact with the XIAP 3’UTR using bioimformatics.Using literature analysis the candidate miRNAs were determined whose expression in the ovarian cancer tissue decreased.The interaction was further proved by cellular co-transfection of a dual-luciferase reporter assay and miRNA expression vector in 293T cells.At last Mir-155 and Mir-137 were chosen for further expriments because of their obviously strong interaction with XIAP.Using target site mutation,quantitative reverse transcription-PCR,Weston-Blot and apoptosis functional experiments explicited the effect and probable mechanism on cisplatin-induced apoptosis in ovarian cancer cells.Results:The high expression level of XIAP was observed in ovrian cancer tissue.On the contrary the expression level was very low in the normal ovarian tissue.Overexpressed XIAP inhibited cisplatin-induced apoptosis in ovarian cancer cell SKOV3 while the apoptosis was promoted by decreasing the expression of XIAP.22 candidated miRNAs was chosen whose exprssion decreased in ovarian cancer cells interacting with XIAP 3’UTR.There are 9 miRNAs proved by fure expriments.Among of them miR-137,miR-155,miR-142 and miR-146a showed strong ability in interacting with XIAP 3’UTR.MiR-155 and miR-137 were chosed for furhter experiments due to the strong ablility.We found the two miRNAs could to reduce cisplatin IC50 in SKOV3 and A2780 and promote apoptosis in ovarian cancer cells including primary culture cells.Our research showed the two miRNAs regulated the apoptosis by binding with XIAP 3’UTR directly and dereasing XIAP protein level.It’s different from miR-155 that there are two target sites in miR-137.In addition the expression of miR-137 in ovarian cancer tissues lowered observably and the that of XIAP increased dramaticly compared with normal ovarian tissue.Conclusions:The high expression level of XIAP and the inhibition with the cisplatin-induced apoptosis could be the one of the most important resons in the chemotherapy resistance in ovarian cancer cells.The downregulation of miRNAs played very important roles in the dysregulatin of XIAP in ovarian cancer.They participated in the regulation of ovarian cancer cell apoptosis and the mechanism of the chemotherapy resistance by adjusting the expression of XIAP.The dysrugulation of miRNAs could play a key role in the chemotherapy resistance in ovarian cancer cells.These miRNA could be new potential targets for developing new drugs.