Glucocorticoids regulate MiR-29c levels in vascular smooth muscle cells through transcriptional and epigenetic mechanisms

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Aims:The objective of this study was to determine the underlying mechanism by which glucocorticoids (GCs) induce of miR-29c expression in vascular smooth muscle cells.Main methods:QRT-PCR was used for miR-29c detection. Protein levels were determined by western blotting. Knockdown of SP1, DNMT1 and DNMT3A was achieved through transfection with their specific respective siRNAs. The effect of GCs on SP1 activity was determined by luciferase reporter assay and the methylation status in miR-29c promoter was detected by methylation specific PCR. CHIP assay was used to determine the binding ability of SP1 and glucocorticoid receptor (GR) in miR-29c promoter.Key findings:Treatment of RASMC with SP1 siRNA or SP1 inhibitor, mithramycin A, as well as DNMT1 and DNMT3A siRNAs and an inhibitor of DNMTs, Decitabine, resulted in increased expression of miR-29c (P < 0.05). Treatment RASMC with dexamethasone (DEX, 0.1 μM) for 24 h reduced the expression of SP1 and phosphorylated SP1 at threonine 453 protein levels, repressed SP1 activity, and inhibited the expression of DNMT1 and DNMT3A proteins (P < 0.05). Treatment with mifepristone, a GR antagonist, blocked the inhibitory effect of DEX on DNMT1 and DNMT3A protein expression. DEX also suppressed SP1 binding ability in miR-29c promoter and inhibited methylation of miR-29c promoter (P < 0.05). Treatment of RASMC with DEX (0.1 μM) significantly (P < 0.05) increased the binding of GR to the miR-29c promoter.Significance:The stimulatory effect of GCs on miR-29c expression is mediated by these three mechanisms: transcriptionally regulated by SP1, and epigenetically through a methylation-dependent process and GR.

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