Hypoxic Cancer-Secreted Exosomal miR-182-5p Promotes Glioblastoma Angiogenesis by Targeting Kruppel-like Factor 2 and 4

Abstract

Glioblastoma (GBM) is the most lethal primary brain tumor and has a complex molecular profile. Hypoxia plays a critical role during tumor progression and in the tumor microenvironment (TME). Exosomes released by tumor cells contain informative nucleic acids, proteins, and lipids involved in the interaction between cancer and stromal cells, thus leading to TME remodeling. Accumulating evidence indicates that exosomes play a pivotal role in cell-to-cell communication. However, the mechanism by which hypoxia affects tumor angiogenesis via exosomes derived from tumor cells remains largely unknown. In our study, we found that, compared with the parental cells under normoxic conditions, the GBM cells produced more exosomes, and miR-182-5p was significantly upregulated in the exosomes from GBM cells under hypoxic conditions. Exosomal miR-182-5p directly suppressed its targets Kruppel-like factor 2 and 4, leading to the accumulation of VEGFR, thus promoting tumor angiogenesis. Furthermore, exosome-mediated miR-182-5p also inhibited tight junction-related proteins (such as ZO-1, occludin, and claudin-5), thus enhancing vascular permeability and tumor transendothelial migration. Knockdown of miR-182-5p reduced angiogenesis and tumor proliferation. Interestingly, we found elevated levels circulating miR-182-5p in patient blood serum and cerebrospinal fluid samples, and its expression level was inversely related to the prognosis. Implications: Overall, our data clarify the diagnostic and prognostic value of tumor-derived exosome-mediated miR-182-5p and reveal the distinctive cross-talk between tumor cells and human umbilical vein endothelial cells mediated by tumorderived exosomes that modulate tumor vasculature.

Blood-Based Biomarkers for Glioma in the Context of Gliomagenesis: A Systematic Review

“…Diagnostic sensitivities and specificities of the miRNAs in glioma patients ranged from 47% to perfect accuracy (136,139,141,148,149). miR-21 (136,139), miR-182 (146,147) and miR-222 (139) were also correlated with tumor grade and an AUC of 0.8 was reported for miR-21 (139). Furthermore, miR-21 (143) and miR-222 ( 139) might also have use as a marker to differentiate between glial tumors and other intracranial tumors.…”

“…However, it has been noted that miRNAs may not be good biomarkers as the brain has little influence on miRNA concentrations in blood as compared to other organs (132) and because differences in blood cell counts may more prominently influence variation in circulating miRNA profiles (133,134). Despite that, miR-21 (135)(136)(137)(138)(139)(140)(141)(142)(143), miR-182 (144)(145)(146)(147)(148) and miR-222 (139,149,150) were all found to be increased in the blood of glioma patients as compared to healthy individuals. However, miR-21 (151,152) and miR-222 (136) were also found to not have significantly different results in patients compared to controls.…”

Roles of Non-coding RNAs and Angiogenesis in Glioblastoma

“…The content of miR-182-5p in the exosomes from the GBM cells under hypoxic conditions was higher, compared to parental cells under normoxic conditions. Moreover, exosomal miR-182 5p inhibited its targets KLF2 and KLF4, resulting in higher VEGFR production, thereby increasing tumor angiogenesis (Li et al, 2020). Additionally, the exosomal miR-182-5p also decreased tight junction-related proteins (occludin, ZO-1, and claudin-5), hence, increasing trans endothelial tumor cell migration and vascular permeability.…”

“…MiR-182-5p knock-down decreased tumor proliferation and angiogenesis. It has been reported that the expression level of miR-182-5p in cerebrospinal fluid samples and serum from GBM patients was increased and its expression levels were inversely correlated with patient prognosis (Li et al, 2020).…”

Extracellular MicroRNAs as Intercellular Mediators and Noninvasive Biomarkers of Cancer

“…Several studies on exosomal miRNAs that promote tumor angiogenesis have been recently published. For example, regarding brain tumors, in 2020 Li et al [190] reported that exosomal miR-182-5p derived from glioblastoma cancer cells under hypoxic conditions promotes angiogenesis and inhibits tight-junction-related proteins in recipient vascular endothelial cells. The authors showed that the exosomes derived from the hypoxic glioma cell lines U-251MG and U-87MG facilitate the migration and tube formation of human umbilical vascular endothelial cells (HUVEC) and enhance the endothelial permeability and transendothelial migration of tumor cells.…”