PO-279 Interplay between Indoleamine 2,3-dioxigenase 1 and Notch1 in radiation response of cervical stem cancer cells

Abstract

IntroductionCervical cancer is the fourth common cancer in female around the world. Cancer stem cells (CSCs) are responsible for the initiation, maintenance, drug resistance and metastasis of tumours and are considered as an effective therapeutic target. Indoleamine 2,3-dioxygenase 1 (IDO1) catalyses tryptophan metabolising to kynurenine and plays a role in immunosuppressive microenvironment within cancers. Notch1 expression participates in radioresistance of cancer cells. The purpose of this study is to explore the relationship between Notch1 and IDO1 expression in radiation response of cervical CSCs.Material and methodsCervical CSCs were enriched by tumorsphere cultivation from HeLa or SiHa cervical cancer cell lines. The expression of IDO1 and Notch1 was determined by western blot or real-time RT-PCR. The IDO1 activity in cell lysates was determined by measurement of kynurenine fluorescence converted from tryptophan. Radiation response of cervical cancer cells were determined by clonogenic assay. The binding of Notch intracellular domain (NICD) on IDO1 promoter was determined by chromatin immunoprecipitation (ChIP) assay. shRNA mediated RNA interference was used for knockdown of specific genes.Results and discussionsWe first found that the expression of IDO1, as well as NICD, was increased in cervical tumorspheres by western blot analysis. We also found that the IDO1 activity in total cell lysates was significantly increased in cervical tumorspheres than the parental cells. Using Jurkat T cells as a model, the growth rate of T cells was significantly decreased in conditional medium from tumorsphere cultivation when compared to those from parental adherent culture. In addition, IDO1 expression was suppressed in HeLa or SiHa cervical cancer cells with knockdown of Notch1. The binding of NICD on IDO1 promoter was inhibited by Notch1 inhibitor. The radiosensitivity of cervical cancer cells was increased by the treatment of IDO1 inhibitor but was decreased after treatment of kynurenine. Furthermore, the expression of NICD protein, as well as Notch1 or BMI1 mRNA, was decreased in cervical tumorspheres with IDO1 knockdown. We also observed that Inhibition of AhR or ARNT, the signalling molecules of kynurenine, suppressed CSC activity of cervical cancer cells.ConclusionOur data indicated that there is a reciprocal regulation mechanism of Notch1 and IDO1 expression in cervical CSCs. These results will provide new insights in the development of the combination of immunotherapy and radiotherapy in against cervical cancer.