Circ_LDLR promoted the development of papillary thyroid carcinoma via regulating miR-195-5p/LIPH axis.

Background: Emerging studies have demonstrated that circular RNAs (circRNAs) are key regulators for tumorigenesis in cancers, including papillary thyroid carcinoma (PTC). In this study, we aimed to explore the effects of circ_LDLR on PTC.

Methods: Quantitative real-time polymerase chain reaction (qRT-PCR) was performed to determine the levels of circ_LDLR, miR-195-5p and lipase H (LIPH). RNase R digestion assay and Actinomycin D assay were utilized to analyze the characteristics of circ_LDLR. Colony formation assay and 3-(4,5-dimethyl-2-thiazolyl)-2, 5-diphenyl-2--tetrazolium bromide (MTT) assay were conducted to evaluate cell proliferation. Western blot assay was used for the determination of protein levels. Flow cytometry analysis was applied to determine cell apoptosis. Transwell assay was performed to determine cell migration and invasion. Dual-luciferase reporter assay was used to verify the associations among circ_LDLR, miR-195-5p and LIPH. The murine xenograft model was constructed to explore the roles of circ_LDLR in vivo.

Results: Compared to normal tissues and cells, circ_LDLR was upregulated in PTC tissues and cells. Silencing of circ_LDLR suppressed PTC cell colony formation, proliferation, migration and invasion and promoted apoptosis in vitro and hampered tumor growth in vivo. For mechanism investigation, circ_LDLR could regulate LIPH expression via sponging miR-195-5p. Moreover, miR-195-5p inhibition restored the effects of circ_LDLR knockdown on the malignant behaviors of PTC cells. MiR-195-5p overexpression inhibited PTC cell colony formation, proliferation, migration and invasion and facilitated apoptosis by targeting LIPH.

Conclusion: Circ_LDLR knockdown decelerated PTC progression by regulating miR-195-5p/LIPH axis, which might provide a novel therapeutic target for PTC.