DNA-methylation-mediated activating of lncRNA SNHG12 promotes temozolomide resistance in glioblastoma

Abstract

Background: Accumulating evidence shows that long noncoding RNAs (lncRNAs) are important regulator molecules involved in diverse biological processes. Acquired drug resistance is a major challenge in the clinical treatment of glioblastoma (GBM), and lncRNAs have been shown to play a role in chemotherapy resistance. However, the underlying mechanisms by which lncRNA mediates TMZ resistance in GBM remain poorly characterized. Methods: Quantitative reverse transcription PCR (qRT-PCR) and fluorescence in situ hybridization assays were used to detect small nucleolar RNA host gene 12 (SNHG12) levels in TMZ-sensitive and TMZ-resistant GBM cells and tissues. The effects of SNHG12 on TMZ resistance were investigated through in vitro assays (western blots, colony formation assays, flow cytometry assays, and TUNEL assays). The mechanism mediating the high expression of SNHG12 in TMZ-resistant cells and its relationships with miR-129-5p, mitogen-activated protein kinase 1 (MAPK1), and E2F transcription factor 7 (E2F7) were determined by bioinformatic analysis, bisulfite amplicon sequencing, methylation-specific PCR, dual luciferase reporter assays, chromatin immunoprecipitation assays, RNA immunoprecipitation assays, immunofluorescence, qRT-PCR, and western blot. For in vivo experiments, an intracranial xenograft tumor mouse model was used to investigate SNHG12 function. Results: SNHG12 was upregulated in TMZ-resistant cells and tissues. Overexpression of SNHG12 led to the development of acquired TMZ resistance, while knockdown of SNHG12 restored TMZ sensitivity. An abnormally low level of DNA methylation was detected within the promoter region of SNHG12, and loss of DNA methylation made this region more accessible to the Sp1 transcription factor (SP1); this indicated that methylation and SP1 work together to regulate SNHG12 expression. In the cytoplasm, SNHG12 served as a sponge for miR-129-5p, leading to upregulation of MAPK1 and E2F7 and endowing the GBM cells with TMZ resistance. Disinhibition of MAPK1 regulated TMZ-induced cell apoptosis and the G1/S cell cycle transition by activating the MAPK/ERK pathway, while E2F7 dysregulation was primarily associated with G1/S cell cycle transition. Clinically, SNHG12 overexpression was associated with poor survival of GBM patients undergoing TMZ treatment. Conclusion: Our results suggest that SNHG12 could serve as a promising therapeutic target to surmount TMZ resistance, thereby improving the clinical efficacy of TMZ chemotherapy.

PGM5-AS1 Inhibits the Malignant Phenotype of Colon Cancer Cells by Regulating PAEP and NME1

“…According to previous studies, abnormally high expression of lncRNA may be induced by transcription activators, stress, DNA methylation, and exosomes [47][48][49][50][51]. For example, the tumor suppressor gene p53 can transcriptionally activate lncRNA Pvt1b [47].…”

“…Stress-induced lncRNA LASTR is up-regulated in hypoxic breast cancer [49]. Upregulation of lncRNA SNHG12, mediated by DNA methylation, thereby activating and increasing temozolomide resistance in glioblastoma [50]. Exosome-mediated lncRNA AFAP1-AS1 activates ERBB2 translation [51].…”

SNHG7 Facilitates Glioblastoma Progression by Functioning as a Molecular Sponge for MicroRNA-449b-5p and Thereby Increasing MYCN Expression

“…Glioblastoma has been identified as a highly infiltrative brain tumor and difficult to cure. 27 Currently, emerging reports have demonstrated the significance of lncRNAs in the tumorigenesis. Using the sequencing technology, a large number of cancer-related lncRNAs have been found.…”

Drug resistance in glioblastoma: are persisters the key to therapy?

“…Belter et al [31] observed a global DNA hypomethylation in the range of therapeutically achieved TMZ concentrations over longer exposure times. Lu et al [38] report that the hypomethylation of promoter region of SNHG12 occurs in TMZ-resistant cells and that this contributed to lnc-RNA-SNHG12 activation resulting in TMZ resistance. Thus, TMZ effect on DNA methylation could be responsible for the increase expression of MGMT in GBM.…”