Overexpression of miR‐18a negatively regulates myocyte enhancer factor 2D to increase the permeability of the blood–tumor barrier via Krüppel‐like factor 4‐mediated downregulation of zonula occluden‐1, claudin‐5, and occludin

Abstract

miR-18a represses angiogenesis and tumor evasion by weakening vascular endothelial growth factor and transforming growth factor-β signaling to prolong the survival of glioma patients, although it is thought to be an oncogene. This study investigates the potential effects of miR-18a on the permeability of the blood-tumor barrier (BTB) and its possible molecular mechanisms. An in vitro BTB model was successfully established. The endogenous expression of miR-18a in glioma vascular endothelial cells (GECs) was significantly lower than that in normal vascular ECs, and the overexpression of miR-18a significantly increased the permeability of the BTB as well as downregulating the mRNA and protein expressions of tight junction-related proteins zonula occluden-1 (ZO-1), claudin-5, and occludin in GECs. Dual luciferase reporter assays revealed that miR-18a bound to the 3'-untranslated region (3'UTR) of myocyte enhancer factor 2D (MEF2D). The overexpression of both miR-18a and MEF2D with the 3'UTR significantly weakened the effect caused by miR-18a of decreasing the mRNA and protein expressions of ZO-1, claudin-5 and occludin and of increasing the permeability of the BTB. Chromatin immunoprecipitation showed that MEF2D could directly bind to KLF4 promoter. This study shows that miR-18a targets and negatively regulates MEF2D, which further regulates tight junction-related proteins ZO-1, claudin-5, and occludin through transactivation of KLF4 and, finally, changes the permeability of the BTB. MiR-18a should garner growing attention because it might serve as a potential target in opening the BTB and providing a new strategy for the treatment of gliomas.

VCAM-1 induces signals that stimulate ZO-1 serine phosphorylation and reduces ZO-1 localization at lung endothelial cell junctions

“…These studies are the first to report that with allergic inflammation, there is increased N‐cadherin and angiomotin and decreased ZO‐1. ZO‐1 was not contiguous in the endothelial cell junctions, which is consistent with previous reports that ZO‐1 is not contiguous in junctions of endothelial cells . An increase in expression of N‐cadherin in lung endothelial cells has also been reported to increase with neutophilic inflammation induced by administration of endotoxin, but the mechanism was not defined.…”

“…ZO-1 was not contiguous in the endothelial cell junctions, which is consistent with previous reports that ZO-1 is not contiguous in junctions of endothelial cells. 59,60 An increase in expression of N-cadherin in lung endothelial cells has also been reported to increase with neutophilic inflammation induced by administration of endotoxin, 61,62 but the mechanism was not defined. The increase in angiomotin in mouse lungs with allergic inflammation is consistent with studies in humans which demonstrated that angiomotin is expressed by lung endothelial cells in patients with asthma.…”

Downregulation of circulating miR 802‐5p and miR 194‐5p and upregulation of brain MEF2C along breast cancer brain metastasization

“…MEF2C is a member of the MEF2 protein family that was initially associated with the development of heart and muscle and is now known to have close connections with biological features that are characteristic of cancer, like uncontrolled proliferation and enhancement of invasion (Chen et al , ). Accordingly, one of its members, MEF2D, has been related to lung cancer (Zhang et al , ), hepatocellular carcinoma (Ma et al , ), and glioma (Zhao et al , ), with its expression regulated by miR‐1244, miR‐122, and miR‐18a, respectively. Besides miRNAs, signaling pathways such as Ca 2+ signaling pathway, EGFR, MAP kinase, Wnt, and PI3K/Akt signaling pathways can activate MEF2 (Chen et al , ).…”

Mechanism of piR-DQ590027/MIR17HG regulating the permeability of glioma conditioned normal BBB

“…miR-200b regulates RMP-7 to increase the permeability of BTB by negatively modulating the target genes RhoA and ROCKII [ 45 ]. miR-18a overexpression binds to MEF2D and negatively regulates its expression; MEF2D then binds to the promoter region of KLF4, and finally KLF4 decreases the expressions of ZO-1, occludin, and claudin-5 and increases the permeability of BTB [ 46 ]. Overexpressed miR-18a also binds to RUNX1 and then negatively regulates its expression, and then the decrease in RUNX1 leads to inhibition of the transcription and thus the expressions of ZO-1, occludin, and claudin-5, further increasing BTB permeability [ 47 ].…”