Transforming Growth Factor-β1 Increases DNA Methyltransferase 1 and 3a Expression through Distinct Post-transcriptional Mechanisms in Lung Fibroblasts

Abstract

DNA methylation is a fundamental epigenetic mark that plays a critical role in differentiation and is mediated by the actions of DNA methyltransferases (DNMTs). TGF-β1 is one of the most potent inducers of fibroblast differentiation, and although many of its actions on fibroblasts are well described, the ability of TGF-β1 to modulate DNA methylation in mesenchymal cells is less clear. Here, we examine the ability of TGF-β1 to modulate the expression of various DNMTs in primary lung fibroblasts (CCL210). TGF-β1 increased the protein expression, but not RNA levels, of both DNMT1 and DNMT3a. The increases in DNMT1 and DNMT3a were dependent on TGF-β1 activation of focal adhesion kinase and PI3K/Akt. Activation of mammalian target of rapamycin complex 1 by Akt resulted in increased protein translation of DNMT3a. In contrast, the increase in DNMT1 by TGF-β1 was not dependent on new protein synthesis and instead was due to decreased protein degradation. TGF-β1 treatment led to the phosphorylation and inactivation of glycogen synthase kinase-3β, which resulted in inhibition of DNMT1 ubiquitination and proteosomal degradation. The phosphorylation and inactivation of glycogen synthase kinase-3β was dependent on mammalian target of rapamycin complex 1. These results demonstrate that TGF-β1 increases expression of DNMT1 and DNMT3a through different post-transcriptional mechanisms. Because DNA methylation is critical to many processes including development and differentiation, for which TGF-β1 is known to be crucial, the ability of TGF-β1 to increase expression of both DNMT1 and DNMT3a demonstrates a novel means by which TGF-β1 may regulate DNA methylation in these cells.

Phosphatidylinositol 3‐Kinase–DNA Methyltransferase 1–miR‐1281–Histone Deacetylase 4 Regulatory Axis Mediates Platelet‐Derived Growth Factor–Induced Proliferation and Migration of Pulmonary Artery Smooth Muscle Cells

“…We found that inhibition of both PI3K and ERK1/2 attenuated PDGFBB‐induced repression of miR‐1281, with PI3K's effect being mediated by upregulation of DNMT1 expression (Figure D and E). These data complement the recent study that identified PI3K–protein kinase B as the key pathway that increased DNMT1 expression by protecting DNMT1 protein from degradation in lung fibroblasts . Our data also reveal that the PI3K–protein kinase B pathway transcriptionally regulates DNMT1 expression in other cell types, such as PASMCs.…”

“…These data complement the recent study that identified PI3K-protein kinase B as the key pathway that increased DNMT1 expression by protecting DNMT1 protein from degradation in lung fibroblasts. 67 Our data also reveal that the PI3K-protein kinase B pathway transcriptionally regulates DNMT1 expression in other cell types, such as PASMCs. PI3K-protein kinase B and MEK1/2-ERK1/2 pathways are known to maintain multiple cross-talk points in a context-dependent way, and their coordinated signaling determines cell fate.…”

Aberrant methylation of EYA4 promotes epithelial‐mesenchymal transition in esophageal squamous cell carcinoma

“…In addition, TGF‐β1 promoted the expression of DNMT1 and DNMT3A, especially DNMT3A, which suggests that TGF‐β1 plays a certain role in the regulation of EYA4 expression in ESCC. In other human malignancies, TGF‐β1 has also been found to affect transcription and expression of downstream target genes via the regulation of DNMT expression . In ovarian cancer cells, TGF‐β1 induced the expression of DNMT and led to extensive genomic hypermethylation, which influenced the transcription of EMT‐related genes and promoted the EMT process .…”

“…In other human malignancies, TGF-b1 has also been found to affect transcription and expression of downstream target genes via the regulation of DNMT expression. [35][36][37] In ovarian cancer cells, TGF-b1 induced the expression of DNMT and led to extensive genomic hypermethylation, which influenced the transcription of EMT-related genes and promoted the EMT process. 38 In hepatocellular carcinoma, TGF-b1 transformed HCC cells into cells with a spindle-shaped morphology, which was accompanied by hypermethylation of CDH1 and the methylation of its promoter.…”

The Mammalian Target of Rapamycin and DNA methyltransferase 1 axis mediates vascular endothelial dysfunction in response to disturbed flow

“…The role of mTOR signaling in modulating DNMT1 expression in cells is controversial. The level of DNMT1 was higher after treatment of the hepatocellular carcinoma cell lines with an mTOR inhibitor, Torin-2, whereas the increase in DNMT1expression by TGF-β treatment was abolished in fibroblasts by FAK, PI3K, and mTOR inhibitors, including rapamycin 37 , 38 . It is possible that the effects of activating mTOR on DNMT1 expression are diverse with respect to the cell types and stimuli.…”