RNA extraction and qRT-PCR analysis
Total RNA derived from human OS tissues and cells was isolated using TRIzol reagent (TAKARA, CHN) according to the manufacturer’s instructions. RNA was reverse transcribed into cDNA using a Primer-Script one step RT-PCR kit (TAKARA, CHN). Quantitative real-time PCR experiments were performed using a SYBR Premix Dimmer Eraser kit (TAKARA, CHN) on an ABI 7500 Real-Time PCR System (Applied Biosystems, USA). The fold change in relative expression level was calculated using the 2−ΔΔCt method. Relative circ_0001722 expression was normalized to GAPDH expression, and miR-204-5p expression was normalized to U6 small nuclear RNA (U6 snRNA). The primer sequences used in our study are purchased from Tsingke Biotechnology (Beijing) Co., Ltd and shown in Supplementary Table 2.