lncRNA CASC2 downregulation participates in rheumatoid arthritis, and CASC2 overexpression promotes the apoptosis of fibroblast‑like synoviocytes by downregulating IL‑17.

lncRNA cancer susceptibility candidate 2 (CASC2) is a recently identified oncogenic lncRNA in different types of cancers. Our preliminary microarray data showed that lncRNA CASC2 was downregulated in the plasma of patients with rheumatoid arthritis (RA), indicating the involvement of this lncRNA in RA. In the present study, lncRNA CASC2 and IL‑17 in plasma were detected by reverse transcription‑-quantitative PCR and ELISA, respectively. Diagnostic analyses were performed using receiver operating characteristic curves. Flow cytometry was performed to evaluate cell apoptosis. The effects of lncRNA CASC2 on IL‑17 expression were determined via western blotting. lncRNA CASC2 was found to be downregulated, while IL‑17 was upregulated in the plasma of RA patients when compared with these levels in the plasma of healthy controls. Plasma levels of lncRNA CASC2 and IL‑17 were significantly and inversely correlated in both RA patients and healthy controls. Altered plasma levels of lncRNA CASC2 and IL‑17 were able to differentiate RA patients from healthy controls. Overexpression of lncRNA CASC2 promoted, while treatment with IL‑17 inhibited the apoptosis of human fibroblast‑like synoviocytes (HFLSs) isolated from RA patients. Overexpression of lncRNA CASC2 inhibited IL‑17 expression in HFLS, while treatment with IL‑17 did not significantly affect the expression of lncRNA CASC2. Therefore, downregulation of lncRNA CASC2 is involved in RA and lncRNA CASC2 overexpression may promote the apoptosis of HFLS by downregulating IL‑17.