Circ_0002111/miR-134-5p/FSTL1 signal axis regulates tumor progression and glycolytic metabolism in papillary thyroid carcinoma cells

Background: Circular RNAs (circRNAs) have essential roles in the malignant progression of papillary thyroid carcinoma (PTC). Circ_0002111 was reported to facilitate cell proliferation and invasion abilities in PTC. This study was performed to explore the regulatory mechanism of circ_0002111 in PTC progression. Methods: Reverse transcription-quantitative polymerase chain reaction (RT-qPCR) was used for the level detection of circ_0002111, microRNA-134-5p (miR-134-5p) and Follistatin Like 1 (FSTL1). Cell proliferation was assessed by 3-(4, 5-dimethylthiazol-2-y1)-2, 5-diphenyl tetrazolium bromide (MTT) assay, EdU assay and colony formation assay. Cell migration ability was determined by transwell assay. Glycolysis was analyzed by extracellular acidification rate (ECAR), oxygen consumption rate (OCR), glucose consumption and lactate production. The protein quantification was performed through western blot. Xenograft tumor assay was used for the functional analysis of circ_0002111 in vivo. The target interaction was confirmed by dual-luciferase reporter assay and RNA pull-down assay. Results: The significant upregulation of circ_0002111 was detected in PTC samples and cells. PTC cell proliferation, migration and glycolytic metabolism were suppressed after circ_0002111 downregulation. PTC tumorigenesis in vivo was also inhibited by circ_0002111 knockdown. In addition, circ_0002111 could target miR-134-5p and si-circ_0002111#1-induced inhibition of PTC progression was relieved by miR-134-5p expression downregulation. Furthermore, FSTL1 was a target gene for miR-134-5p and miR-134-5p served as a tumor repressor in PTC by targeting FSTL1. Moreover, circ_0002111 could increase the FSTL1 level via sponging miR-134-5p. Conclusion: All results indicated that circ_0002111 promoted the malignant behaviors of PTC cells partly by regulating the miR-134-5p/FSTL1 molecular network.