miR-652-5p promoter hypermethylation enhances glioblastoma malignancy through the SDC1/TGFβ2/pERBB4 complex via HIF2α-mediated regulation under hypoxia.

BACKGROUND: Glioblastoma multiforme (GBM) is highly malignant, and hypoxia often exacerbates its aggressiveness. The aim of this study was to explore the molecular mechanism by which miR-652-5p promoter hypermethylation augments the malignancy of glioblastoma under hypoxic conditions. METHODS: This study combined data from public glioma databases, clinical tissue analysis, and cellular assays. Techniques such as RT‒qPCR, western blotting, miRNA sequencing, and ELISA were used to assess the impact of miR-652-5p under hypoxic conditions. A BALB/c-nu mouse model injected with GBM cells was used for in vivo evaluation. RESULTS: miR-652-5p was markedly upregulated in HIF2α-knockout cells, with promoter hypermethylation linked to reduced methylation post-knockout. Inhibition of miR-652-5p upregulated SDC1, SDC1-Intra, and TGFβ2 expression. Live-cell imaging and fluorescence staining revealed the role of SDC1 in exosome-mediated TGFβ2 secretion. SDC1 knockdown reduced exosome release and TGFβ2 secretion and confirmed the binding of TGFβ2 to SDC1/sSDC1 via HS chains and to ERBB4 on recipient cells. Downregulation of SDC1 and TGFβ2 expression decreased the levels of PI3K, PDK1, p-PDK1, AKT, p-AKT, and mTOR, weakened tumorigenic properties, and extended OS. In vivo results from a nude mouse model supported these findings. CONCLUSIONS: Under hypoxic conditions, miR-652-5p promoter hypermethylation promotes GBM malignancy via the SDC1/TGFβ2/pERBB4 axis in a HIF2α-dependent manner. Understanding this mechanism may lead to the development of epigenetic treatments and personalized medical approaches to improve patient outcomes.