Curcumin up‐regulates phosphatase and tensin homologue deleted on chromosome 10 through microRNA‐mediated control of DNA methylation – a novel mechanism suppressing liver fibrosis

Abstract

Phosphatase and tensin homologue deleted on chromosome 10 (PTEN) has been reported to play a role in the suppression of activated hepatic stellate cells (HSCs). Moreover, it has been demonstrated that hypermethylation of the PTEN promoter is responsible for the loss of PTEN expression during HSC activation. Methylation is now established as a fundamental regulator of gene transcription. MicroRNAs (miRNAs), which can control gene expression by binding to their target genes for degradation and/or translational repression, were found to be involved in liver fibrosis. However, the mechanism responsible for miRNA‐mediated epigenetic regulation in liver fibrosis still remained unclear. In the present study, curcumin treatment significantly resulted in the inhibition of cell proliferation and an increase in the apoptosis rate through the up‐regulation of PTEN associated with a decreased DNA methylation level. Only DNA methyltransferase 3b (DNMT3b) was reduced in vivo and in vitro after curcumin treatment. Further studies were performed aiming to confirm that the knockdown of DNMT3b enhanced the loss of PTEN methylation by curcumin. In addition, miR‐29b was involved in the hypomethylation of PTEN by curcumin. MiR‐29b not only was increased by curcumin in activated HSCs, but also was confirmed to target DNMT3b by luciferase activity assays. Curcumin‐mediated PTEN up‐regulation, DNMT3b down‐regulation and PTEN hypomethylation were all attenuated by miR‐29b inhibitor. Collectively, it is demonstrated that curcumin can up‐regulate miR‐29b expression, resulting in DNMT3b down‐regulation in HSCs and epigenetically‐regulated PTEN involved in the suppression of activated HSCs. These results indicate that miRNA‐mediated epigenetic regulation may be a novel mechanism suppressing liver fibrosis.

HOTAIR Epigenetically Modulates PTEN Expression via MicroRNA-29b: A Novel Mechanism in Regulation of Liver Fibrosis

“…10 The miR-29 family consists of miR-29a, miR-29b, and miR-29c, which differ only in two or three bases. 24,25 Recent studies showed that DNMTs may be a target of miR-29 family.…”

“…3 Our previous study found that curcumin upregulates miR-29b expression, leading to the silencing of DNA methyltransferase 3b (DNMT3b) and the loss of phosphatase and tensin homolog deleted on chromosome 10 (PTEN) methylation, which contributes to suppression of activated HSCs. 10 Other ncRNAs, such as long intergenic non-coding RNAs (lincRNAs) and the heterogeneous group of long non-coding RNAs (lncRNAs), have also been reported to be involved in human diseases. [11][12][13] LncRNA is most commonly defined as a non-protein-coding RNA molecule longer than 200 nucleotides.…”

MicroRNA-17-5p activates hepatic stellate cells through targeting of Smad7

“…33 However, our group identified only DNMT3b as a target of miR-29b in rat HSCs. 34 Therefore, the targets of miRNAs may vary in different tissues, and should be determined using confirmatory analyses, such as the dual luciferase reporter experiment. Here, Smad7 was predicted as a target of miR-17-5p, which was confirmed with the dual luciferase reporter experiment.…”

“…Primers for alpha-1 (I) collagen (Col1A1), α-SMA, GAPDH and U6 were designed as described previously. 18 To detect miR-17-5p and miR-238 expression, the RT reaction was performed using the TaqMan MicroRNA Assay (Applied Biosystems, Foster City, CA) according to the manufacturer's instructions. GAPDH and U6 snRNA (Applied Biosystems, Foster City, CA) levels were measured and used to normalize the relative abundance of mRNA and miRNA, respectively.…”

“…11 Previously, we demonstrated that curcumin upregulates miR-29b expression, leading to silencing of DNA methyltransferase 3b (DNMT3b) and loss of phosphatase and tensin homolog deleted on chromosome 10 (PTEN) methylation, which contributes to suppression of activated HSCs. 12 These findings clearly suggest that miRNAs act as HSC regulators and play diverse roles in hepatic fibrosis. miR-17-5p, an important member of the miR-17-92 cluster, plays a crucial role in regulating cell functions, such as proliferation and migration, and is overexpressed in various cancers, including hepatocellular carcinoma (HCC).…”