miR-34c regulates the permeability of blood-tumor barrier via MAZ-mediated expression changes of ZO-1, occludin, and claudin-5.

The purposes of this study were to investigate the potential roles of miR-34c in regulating blood-tumor barrier (BTB) functions and its possible molecular mechanisms. The over-expression of miR-34c significantly impaired the integrity and increased the permeability of BTB, which were detected in an in vitro BTB model by transendothelial electric resistance and horseradish peroxidase flux assays, respectively. Meanwhile, real-time quantitative PCR (qRT-PCR), Western blot and immunofluorescence assays successively demonstrated downregulation of ZO-1, occludin, and claudin-5 and miR-34c silencing uncovered the opposite results. Dual-luciferase reporter assays results revealed myc-associated zinc-finger protein (MAZ) is a target gene of miR-34c. Besides, mRNA and protein expressions of MAZ were reversely regulated by miR-34c. The down-expression of MAZ significantly impaired the integrity and increased the permeability of BTB as well as downregulated the expressions of ZO-1, occludin, and claudin-5. And chromatin immunoprecipitation verified that MAZ interacted with "GGGCGGG," "CCCTCCC," and "GGGAGGG" DNA sequence of ZO-1, occludin, and claudin-5 promoter, respectively. The over-expression or silencing of either miR-34c or MAZ was performed simultaneously to further explore their functional relations, and results elucidated that miR-34c and MAZ displayed reverse regulatory effects on the integrity and permeability of BTB as well as the expressions of ZO-1, occludin, and claudin-5. In conclusion, our present study indicated that miR-34c regulated the permeability of BTB via MAZ-mediated expression changes of ZO-1, occludin, and claudin-5.