环状RNA作为一种新型非编码RNA，可以通过竞争性抑制miRNA并调控其靶基因及下游通路，参与多种恶性肿瘤发生发展过程，目前在甲状腺癌中功能不详。我们前期在甲状腺乳头状癌（PTC）及对应癌旁组织中进行高通量测序，发现环状RNA差异表达谱，并在PTC组织及细胞系中验证显示circ_0004458呈高表达。通过功能学研究发现circRNA_0004458可促进PTC细胞增殖和侵袭，生物信息学分析发现其可能结合miR-138并可调控PI3K/AKT通路。基于前期工作，本课题拟通过细胞及动物模型，研究circ_0004458在PTC中的生物学功能，探索circ_0004458结合miR-138调控靶基因PDK1和FAK并作用PI3K/AKT通路的分子机制，同时分析其与患者临床病理学特征及预后关系。本项目将揭示circ_0004458在PTC发生发展的重要作用及机制，为PTC的治疗提供新思路。

Circular RNAs (circRNAs), as a type of novel non-coding RNA, competitive inhibit miRNAs and regulate their downstream target genes and signaling pathways. It is confirmed that circRNAs play an important role in the pathogenesis of various human cancers, though the biological functions of circRNAs in thyroid carcinoma are still unclear. Our preliminary data showed differential circRNA expression profiles between PTC tissues and their corresponding adjacent normal thyroid tissues by high-throughput sequencing. We confirmed that hsa_circ_0004458 is upregulated in PTC tissues as compared with adjacent normal thyroid tissues, also in PTC cell lines by qRT-PCR. We found that hsa_circ_0004458 can promote proliferation and invasion in PTC cell line and in zebrafish model. Furthermore, miR-138 is predicted as a potential target of hsa_circ_0004458 basing on bioinformatics analyses, as well as the PI3K/AKT pathway can be regulated by hsa_circ_0004458 using Western blot tests. Therefore, based on our previous works, this project is to investigate the biological functions of hsa_circ_0004458 in PTC in vivo and in vitro, and to explore the molecular mechanism of hsa_circ_0004458 binding miR-138 and regulating PDK1 and FAK, finagling modulating the PI3K/AKT axis in PTC. In the meantime, we intent to evaluate the correlations between hsa_circ_0004458 and clinicalpathological features and prognosis of PTC. We propose to clarify the functions and molecular mechanisms of hsa_circ_0004458 in PTC, so as to provide a promising therapeutic target for PTC.