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Hypoxia-induced circPLOD2a/b promote migration and invasion of GBM cells via suppressing XIRP1 through binding to HuR [1]

ABSTRACT: Background. Glioblastoma (GBM) is the most lethal form of brain tumors in human adults, and hypoxia is a common microenvironment in this disease. Circular RNAs (circRNAs) are identified as regulators in cancers including GBM. However, the specific roles of circRNAs in GBM under hypoxic condition remains elusive. Methods. RNA-seq was employed to investigate the expression profile of circRNAs in U87 cells under normoxia and hypoxia. Two circRNAs spliced from the same parental gene, named as circPLOD2a and circPLOD2b, were identified as hypoxia-responsive circRNAs, whose circular structures were verified by, qRT-PCR, RNase R digesting and Sanger sequencing in U87. Knockdown and overexpression of circPLOD2a/b in GBM cells were used to investigate the biological functions of these two circRNAs on tumor progression. Fluorescence in situ hybridization, RNA-pull down, mass spectrometry and RNA immunoprecipitation assays were conducted to explore the interactions between circPLOD2a/b, human antigen R (HuR), xin actin binding repeat containing 1 (XIRP1). Results. CircPLOD2a/b were significantly up-regulated in hypoxic GBM cells and directly induced by HIF1α under hypoxia. Overexpression of circPLOD2a/b enhance GBM cell invasion and migration, which could be inhibited by circPOD2a/b knockdown. Mechanistically, circPLOD2a/b competitively bind to HuR, inhibiting the interaction between HuR and XIRP1, thus promoting the tumor aggressiveness in GBM both in vitro and in vivo through down-regulating XIRP1. Conclusions. Hypoxia-induced circPLOD2a/b were identified as key regulators of migration and invasion in GBM cells, and act as oncogenic circRNAs to attenuate the interaction between HuR and XIRP1, which may be potential therapeutic strategy for GBM treatment.

ORGANISM(S): Homo sapiens

PROVIDER: GSE245634 | GEO | 2023/10/23

REPOSITORIES: GEO

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Project description:Tumor hypoxia is linked to poor outcome for many cancers, but the underlying mechanisms and the environmental factors that initiate tumor hypoxia are poorly understood. Here, we tracked tumor hypoxia in glioblastoma (GBM), a highly malignant brain cancer, in immunocompetent mice with a sensitive fluorescent reporter combined with single cell transcriptomics. We found that hypoxic GBM cells are quiescent and display a mesenchymal transition, both linked to malignant potency. We also captured in vivo hypoxia gene signature, which is more represented in recurrent GBM and predicts worse outcome. Interestingly, hypoxic GBM cells is a diverse population, consisted of four subclusters, and enriched for immune pathways. Concordantly, our reporter highlighted a distinct geographic pattern of immune cells in hypoxic regions, with phagocytic tumor-associated macrophages (TAMs) and CD8+ cytotoxic T cells (CTLs) congregated in hypoxic cores confined by hypoxic GBM cells in pseudopalisading patterns. Mechanistically, this is a dynamic temporospatial process, requiring cytokine CCL8. Remarkably, the sequestered TAMs also experience hypoxia, and they are reprogrammed to an immunotolerant state by factors released from hypoxic GBM cells. Contrary to the conventional viewpoint that hypoxia arises from rapid tumor expansion outstripping vascular supply, we discovered anticancer immunity as an important driving force of tumor hypoxia. Attenuating immune responses by implanting GBM in host mice with immunodeficiency or IL1β deletion significantly decreased GBM hypoxia in well-established tumors. Unexpectedly, radiation therapy (XRT) greatly reduced tumor hypoxia, and when combined with evofosfamide, a prodrug activated by hypoxia, achieved enhanced efficacy in tumor shrinkage and eradication of hypoxic GBM population. Analyses of human patient GBM samples highlighted a connection of mesenchymal subtype, immune response, and tumor hypoxia, all contributing to poor survival. Altogether, our study revealed a reciprocal influence of anti-tumor immunity and tumor hypoxia, which has important ramification for prognosis and immunotherapy for GBM.

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Hypoxia-induced circPLOD2a/b promote migration and invasion of GBM cells via suppressing XIRP1 through binding to HuR [1]

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