LncRNA CASC2 enhances sensitivity of glioma cells to temozolomide by ABCG2

Objective To explore the effect of long noncoding RNA cancer susceptibility 2 (lncRNA CASC2) on the sensitivity of glioma cells to temazolamide (TMZ) and investigate the underling mechanism. Methods Forty glioma tissue samples derived from the 40 patients undergoing surgical treatment in our department from July 2018 to March 2020 were enrolled in this study. The expression of lncRNA CASC2 in the glioma tissues was detected with RT-PCR, and the results were analyzed with pathological grades and compared between the patients with isocitrate dehydrogenase (IDH) 1/2 mutant (n=17) and IDH 1/2 wild type (n=9). Glioma cells U251 were cultured and transfected with plasmid pc-CASC2 to overexpress lncRNA CASC2 and/or interfering RNA of multi-drug resistance protein ABCG2. CCK-8 assay and flow cytometry were used to detect the cell viability and apoptotic rate in above cell groups after 30 μg/mL TMZ treatment. After mouse intracranial glioma model was established, high performance liquid chromatography was adopted to determine the concentration of TMZ. The correlation between lncRNA CASC2 and ABCG2 was detected by immunofluorescence staining and RNA immunoprecipitation. Results LncRNA CASC2 level was decreased in the glioma tissues with IDH 1/2 wild type, and had a negative correlation with pathological grade of glioma. LncRNA CASC2 overexpression resulted in significantly lower IC50 to TMZ (36.7±4.2 μg/mL) than the U251 cells after pc-Null transfection (t=4.41, P < 0.05). Under 30 μg/mL TMZ stimulation, the cell viability was reduced and the proportion of apoptotic cells was increased after lncRNA-CASC2 overexpression. In the mouse intracranial glioma model, the concentration of intracellular TMZ active product was increased after lncRNA-CASC2 overexpression. LncRNA CASC2 and ABCG2 were evenly distributed in the cytoplasm, and RNA immunoprecipitation showed that the content of lncRNA CASC2 in ABCG2 antibody group was higher than that in IgG control group. In addition, down-regulation of intracellular ABCG2 by siRNA decreased the TMZ sensitivity of U251 cells that could enhanced by lncRNA CASC2. Conclusion LncRNA CASC2 improves the sensitivity of glioma U251 cells to TMZ. However, ABCG2 inhibition by siRNA attenuates the above effects of lncRNA CASC2.