Knockdown lncRNA CRNDE enhances temozolomide chemosensitivity through autophagy inhibition by activating PI3K/Akt/mTOR pathway in glioblastoma

Abstract Background Long non-coding RNA (lncRNA) CRNDE is highly expressed in glioma acting as an oncogene in gliomas. However, the regulatory roles of CRNDE in Temozolomide (TMZ) chemoresistance to glioblastoma multiforme (GBM) still are poorly understood. Therefore, we intended to explore the role and possible mechanism of CRNDE in TMZ-induced chemoresistance in GBM. Methods Firstly, we tested the expression level of CRNDE in glioma cell lines and in 30 cases of normal brain tissues and 58 cases of glioma tissue specimens by qRT-PCR. Meanwhile, the correlation between CRNDE level and the clinicopathological characteristics and survival time of patients were analyzed. Then, the CRNDE expression in various glioma cell lines was detected, and CRNDE knockdown cell models were constructed. Subsequently, to explore the effect of CRNDE on chemosensitivity to TMZ, cell viability was detected by the CCK-8 assay and IC50 values, and cell proliferation was detected by cell clone assay and EdU assay, as well as cell survival was detected by apoptosis with flow cytometry under TMZ treatment. Further, the expression of drug-resistance protein ABCG2, autophagic related proteins and PI3K/AKT pathway related proteins were determined by western blot or qRT-PCR in TMZ-treated glioma cells. Finally, the tumor volume and weight were measured and ABCG2 expression was detected by immunohistochemistry assay in mouse tumor xenograft model. Results Our integrated approach demonstrated lncRNA CRNDE was a poor prognosis factor for GBM patient, which was up-regulated in patients who are resistant to TMZ, and closely associated with chemotherapeutic response status to TMZ treatment. Further, functional assays revealed that knockdown of CRNDE could notably reduce glioma cell viability and proliferation, and elevate apoptosis to enhance the chemosensitivity to TMZ in vitro and in vivo. Mechanistically, the depression of CRNDE down-regulated LC3 II/I, Beclin1 and Atg5 expression levels and increased expression of p62 to inhibit autophagy due to the activation of PI3K/Akt/mTOR pathway as well as highly correlated with ABCG2 expression. Conclusions Overall, the study provided a preclinical basis in developing LncRNA CRNDE as a reliable clinical predictor of outcome and prognosis of GBM patient, a potential biomarker for predicting TMZ treatment response and a new therapeutic target for enhancing TMZ sensitivity in GBM by modulating the autophagy through PI3K/Akt/mTOR pathway.