Date Published: December 12, 2018
Publisher: Impact Journals
Author(s): Feng Liu, Jin Zhang, Long Qin, Ziyao Yang, Jianxia Xiong, Yanyan Zhang, Ruihuan Li, Shujing Li, Huifang Wang, Bo Yu, Wenjun Zhao, Weiran Wang, Zhensu Li, Jing Liu.
Anaplastic thyroid carcinoma (ATC) responds for the majority of death of thyroid carcinoma and often causes chemotherapy resistance. We investigated the influence of circEIF6 (Hsa_circ_0060060) on the cisplatin-sensitivity in papillary thyroid carcinoma (PTC) and ATC cells, and explored its regulation to downstream molecules miR-144-3p and Transforming Growth Factor α (TGF-α). Differentially expressed circRNAs in PTC were analyzed using the GSE93522 data downloaded. Expressions of circEIF6, miR-144-3p, TGF-α, autophagy-related proteins and apoptosis-related proteins were determined using qRT-PCR or western blot. RNA pull-down assay and dual luciferase report assay were applied to reveal the target relationships. Autophagy marker LC3 and cell proliferation marker ki67 were evaluated by immunofluorescence and immunohistochemistry. Cell viability was evaluated with MTT assay and cell apoptosis was assessed by flow cytometric analysis. CircEIF6, could promote autophagy induced by cisplatin, thus inhibiting cell apoptosis and enhancing the resistance of PTC and ATC cells to cisplatin. Has-miR-144-3p was the target of circEIF6 and was regulated by circEIF6. Besides, circEIF6 promoted autophagy by regulating miR-144-3p/TGF-α axis, enhancing the cisplatin-resistance in PTC and ATC cells. CircEIF6 promoted tumor growth by regulating miR-144-3p/TGF-α and circEIF6 knock-down enhanced cisplatin sensitivity in vivo. CircEIF6 could provide a target for therapy of cisplatin-resistance in thyroid carcinoma.
Thyroid carcinoma is a common cancer, which can be roughly divided into well-differentiated thyroid carcinoma including papillary and follicular thyroid carcinoma, anaplastic thyroid carcinoma (ATC) and medullary thyroid carcinoma (MTC) . However, ATC is an orphan disease with high fatality rate and the effective treatment is not available at present. Generally, these cancers are treated with surgery, radiotherapy, chemotherapy, target therapy, or multimodal therapy . Recently, multi kinase inhibitors (MKIs) as a new drug, show positive activity against receptors of different growth factors, and thus can inhibit tumor cells growth and proliferation. Moreover, MKIs play a function on differentiated thyroid carcinoma [3,4]. Although patients’ condition had some improvements by using those therapies, some patients did not respond to radioiodine (RAI) therapy  and occurred drug-resistance, especially in patients with ATC. Due to the undifferentiated phenotype and its aggressive nature of ATC, resistance to conventional treatments such as radiotherapy and chemotherapy, was often observed in the patients with ATC , including cisplatin-resistance . Therefore, the patients with ATC have a very poor prognosis.
ATC as a type of thyroid carcinoma, accounts for small percentage in thyroid carcinoma, however, it is responsible for the majority of death in all thyroid malignancies. Traditional therapies for thyroid carcinoma, such as radioiodine and chemotherapy, could induce the drug resistance, thus contributing to the very poor prognosis in ATC . Recently, several new chemotherapy agents have been applied, such as sorafenib, imatinib, and axitinib, with superimposable activity and response rates of 35%-75%, but the chemoresistance was still not improved . Therefore, making the mechanism of drug-resistance clear is very important. In our study, we identified a number of aberrantly expressed circRNAs in PTC tissue and found that circEIF6 could enhance chemoresistance (cisplatin-resistance) to influence the chemotherapy effects. To figure out the further reason of chemoresistance enhanced by circEIF6, circEIF6, its target miR-144-3p, and downstream mRNA TGF-α were all focused on in PTC and ATC.
As a number of abnormally expressed circRNAs in the PTC tissues were identified, we found that circEIF6 was upregulated and negatively correlated with miR-144-3p. Further experiments showed that circEIF6 could enhance cisplatin-resistance by autophagy activation in TPC1 and BHT101 cells. While the circEIF6 was inhibited, the expression of miR-144-3p was increased and cisplatin-resistance was weaken, as well as TGF-α was declined in vivo and in vitro.